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IEEE Transactions on Antennas and Propagation
Journal Prestige (SJR): 1.309
Citation Impact (citeScore): 5
Number of Followers: 82  
 
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ISSN (Print) 0018-926X
Published by IEEE Homepage  [228 journals]
  • IEEE Antennas and Propagation Society Information

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      Abstract: Presents a listing of the editorial board, board of governors, current staff, committee members, and/or society editors for this issue of the publication.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • IEEE Transactions on Antennas and Propagation Publication Information

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      Abstract: Presents a listing of the editorial board, board of governors, current staff, committee members, and/or society editors for this issue of the publication.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Institutional Listings

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      Abstract: Reports on APS society institutional listings for this issue of the publication.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Message From the Editor-in-Chief

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      Authors: Danilo Erricolo;
      Pages: 6130 - 6130
      Abstract: This August issue contains two sets of articles: the Special Issue on Artificial Intelligence: New Frontiers in Real-Time Inverse Scattering and Electromagnetic Imaging and Regular Papers. This Special Issue is motivated by the fact that, in recent years, it has become evident that artificial intelligence provides new innovative solutions for complex problems. Therefore, the Editorial Board of the IEEE Transactions on Antennas and Propagation invited applications for special issues related to how artificial intelligence, machine learning, and deep learning can assist with challenges in the field of antennas and propagation. Three special issues were accepted and this one focuses on a unified vision for the application of artificial intelligence in inverse scattering and electromagnetic imaging.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Guest Editorial Artificial Intelligence: New Frontiers in Real-Time
           Inverse Scattering and Electromagnetic Imaging

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      Authors: Manuel Arrebola;Maokun Li;Marco Salucci;
      Pages: 6131 - 6134
      Abstract: Understanding and solving complex problems in the physical world has been an intelligent endeavor of humankind. Moreover, the study of artificial intelligence (AI) embodies the dream of designing machines like humans. Research in deep-learning (DL) techniques has attracted much attention in many application areas. With the help of big data technology, massive parallel computing, and fast optimization algorithms, DL has greatly improved the performance of many problems in speech and image processing, power transportation networks, and bio-electromagnetics, among others.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Physics Embedded Deep Neural Network for Solving Volume Integral Equation:
           2-D Case

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      Authors: Rui Guo;Tao Shan;Xiaoqian Song;Maokun Li;Fan Yang;Shenheng Xu;Aria Abubakar;
      Pages: 6135 - 6147
      Abstract: The volume integral equation (VIE) that describes the forward scattering problem is generally solved by iterative methods, such as the conjugate gradient (CG) method. In this work, we unfold the CG method into an iterative deep neural network to accelerate solving the VIE. After the dielectric scatterer’s relative permittivity and the incident field are input into the network, the total field is trained to converge to the ground truth iteratively. In the neural network, Green’s function is taken as an explicit operator to describe wave physics, and the fast Fourier transform (FFT) is applied to accelerate the computation of volume integrations. The global influence of all points in the space is compressed into a layer by the volume integration. In numerical tests, we validate the accuracy, efficiency, and generalization ability of the proposed neural network, and investigate the feasibility of changing the input size and the frequency in the prediction. Results show that the network is scale-independent and adaptable to predict fields in a narrow frequency band. This work provides us a new perspective of incorporating both learned parameters and physics into numerical algorithms for fast computation, and has the potential of being applied in deep-learning-based inverse scattering problems.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Physics Embedded Deep Neural Network for Solving Full-Wave Inverse
           Scattering Problems

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      Authors: Rui Guo;Zhichao Lin;Tao Shan;Xiaoqian Song;Maokun Li;Fan Yang;Shenheng Xu;Aria Abubakar;
      Pages: 6148 - 6159
      Abstract: In this work, we design an iterative deep neural network to solve full-wave inverse scattering problems (ISPs) in the 2-D case. Forward modeling neural networks that predict the scattered field are embedded in an inversion neural network. In an iterative manner, the inversion network predicts the model update from the residual between the simulated data and the observed data. The proposed inversion network can achieve super-resolution reconstruction meanwhile keeping the simulated data of reconstructed models well consistent with the observed data. We validate this method with both synthetic and experimental data inversion. Results show that the inversion network can predict models with high accuracy, efficiency, and good generalization ability. By combining deep learning and physical simulation together, the proposed method provides a way for real-time imaging with high reliability and accuracy.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Cascaded Complex U-Net Model to Solve Inverse Scattering Problems With
           Phaseless-Data in the Complex Domain

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      Authors: Feixiang Luo;Jun Wang;Jie Zeng;Lu Zhang;Boyu Zhang;Kuiwen Xu;Xiling Luo;
      Pages: 6160 - 6170
      Abstract: The phaseless-data inverse scattering problems (PD-ISPs) are non-trivial due to their serious nonlinearity and ill-posed nature. The conventional methods for PD-ISPs can be categorized into single-step methods and two-step methods, where the first ones directly reconstruct the image and the second ones retrieve the phase and amplitude of scattered fields, and then reconstruct the image as the traditional FD-ISPs. However, the single-step methods correspond to solve higher nonlinear optimization problems and the two-step methods highly depend on the quality of the retrieved phase and amplitude information. To solve the above issues, we propose a two-step method with a cascaded complex U-net (CCU-net) model to solve the PD-ISPs in the complex domain. The CCU-net consists of two parts, that is, Phase Retrieval Net (PRNet) and Image Reconstruction Net (IRNet), where the PRNet recovers the phase and amplitude of the scattered field from the measured modulus of the total field and the IRNet takes the recovered scattered field as input to reconstruct the image. These two parts can be independently controlled and achieve joint optimization. Thanks to the strong nonlinear representation ability of complex neural networks, the physical relationship between the scattered fields and the images can be reserved and constructed. Several representative tests including both the synthetic and experimental examples verify that the proposed CCU-net in the complex domain has good robustness, generalization ability, and strong inversion capability when tackling high contrast scatterers and can also fulfill one-step implementation in real time.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Machine Learning Target Count Prediction in Electromagnetics Using Neural
           Networks

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      Authors: Mohsen Sabbaghi;Jun Zhang;George W. Hanson;
      Pages: 6171 - 6183
      Abstract: In this article, we showcase an application of neural networks (NNs) to solve an inverse problem in electromagnetics (EMs). Wires are randomly distributed into an area of known dimensions. The wires are then illuminated with a monochromatic plane wave (PW) at a certain angle of incidence, and the EM field measured at a finite number of uniformly spaced points along the perimeter of the area is then fed into a convolutional neural network (CNN) designed to predict the number of wires. Counting the wires is posed as a supervised classification problem with a known upper limit to the number of wires, and accuracy of 96% has been achieved for the case where the number of the wires is known to be ten or less. A number of approaches have been taken to improve the network performance including frequency variation analysis and illuminating the wire distributions with additional PW angles of incidence. We conclude with an analysis of the network capability to resolve objects based on its performance on known wire distributions, which suggests the existence of a characteristic resolution limit corresponding to the CNN topology.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Physics-Assisted Deep Learning Microwave Imaging Framework for Real-Time
           Shape Reconstruction of Unknown Targets

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      Authors: Álvaro Yago Ruiz;Marta Cavagnaro;Lorenzo Crocco;
      Pages: 6184 - 6194
      Abstract: In this article, an innovative approach to microwave imaging, which combines a qualitative imaging technique and deep learning (DL), is presented. The goal is to develop a tool for reliable and user-independent retrieval of the shape of unknown targets from the knowledge of the scattered fields. Qualitative imaging methods are powerful inverse scattering tools, as they provide morphological information in real time. However, their outcome is a continuous map, which has to be hard-thresholded to clearly identify the targets. This thresholding unavoidably results in case-dependent, often user-biased, results. To deal with this issue, a DL approach, based on a physics-assisted deep neural network, is proposed to automatically classify image pixels, i.e., to generate binary masks, separating the targets (foreground) from the background. In particular, the proposed network binarizes the output of a qualitative imaging inversion technique known as the orthogonality sampling method. For the sake of comparison, a DL method is also exploited, which generates the binary masks directly from the scattered fields without any qualitative imaging aid. A quantitative assessment of the performances of both methods and a test on experimental data are provided.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Enhanced Supervised Descent Learning Technique for Electromagnetic Inverse
           Scattering Problems by the Deep Convolutional Neural Networks

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      Authors: He Ming Yao;Rui Guo;Maokun Li;Lijun Jiang;Michael Kwok Po Ng;
      Pages: 6195 - 6206
      Abstract: This work proposes a novel deep learning (DL) framework to solve the electromagnetic inverse scattering (EMIS) problems. The proposed framework integrates the complex-valued deep convolutional neural network (DConvNet) into the supervised descent method (SDM) to realize both off-line training and on-line “imaging” prediction for EMIS. The offline training consists of two parts: 1) DConvNet training: the training dataset is created, and the proposed DConvNet is trained to realize the EM forward process and 2) SDM training: the trained DConvNet is integrated into the SDM framework, and the average descent directions between the initial prediction and the true label of SDM iterative schemes are learned based on the same dataset in part 1). In the online step, the contrasts (permittivities) reconstruction of scatterers is realized by the SDM iteration process based on learned descent directions, while its forward process is achieved by the trained complex-valued DConvNet. Ultimately, this framework provides a new perspective to integrate the prior information into the EMIS solving process with the maintained accuracy. Unlike the conventional SDM, the novel proposed framework can significantly shorten the computation and realize the real-time imaging. Various numerical examples and discussions are provided to demonstrate the efficiency and accuracy of the proposed novel framework.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Tailored Semiphysics-Driven Artificial Neural Network for
           Electromagnetic Full-Wave Inversion

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      Authors: Yanjin Chen;Miao Zhong;Zhen Guan;Feng Han;
      Pages: 6207 - 6217
      Abstract: This article presents a tailored artificial neural network (ANN) that is designed for electromagnetic (EM) full-wave inversion (FWI). The ANN includes two subnets. The first subnet is a physics-driven fully connected neural network in which the known sensitivity matrix of EM FWI is assigned to the network model parameters. The second subnet is the traditional data-driven convolutional neural network (CNN) U-Net. The role of the first subnet is to convert the scattered EM fields recorded at the receiver array into the preliminary dielectric images of the scatterers with the aid of the fast calculation of the graphics processing unit. Then, the second subnet is used to further refine the scatterer dielectric parameters. In the off-line training, the network parameters in the first subnet are frozen, and only the parameters in the second subnet are optimized. In the online prediction, the whole ANN is used to directly invert the dielectric parameters of the scatterers. The proposed semiphysics-driven ANN is compared with the purely data-driven ANN for the inversion accuracy, training cost, generalization ability, antinoise ability, and so on.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Learning-Based Inversion Method for Solving Electromagnetic Inverse
           Scattering With Mixed Boundary Conditions

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      Authors: Rencheng Song;Youyou Huang;Xiuzhu Ye;Kuiwen Xu;Chang Li;Xun Chen;
      Pages: 6218 - 6228
      Abstract: In this article, a unified learning-based approach is introduced to solve inverse scattering problems (ISPs) with mixed boundary conditions (BCs). The scattering behavior of hybrid dielectric and perfect electric conductors (PEC) scatterers is modeled by the T-matrix method. A rough image of the zero-order T-matrix coefficients for unknown scatterers is first reconstructed by the backpropagation (BP) method, which is then refined by an attention-assisted pix2pix generative adversarial network (GAN). The spatial attention mechanism is utilized to enforce the generator network to learn salient features of the unknown scatterers instead of the background. The adversarial training of the generator and the discriminator further enables the reconstructed image to be constrained by high-level features of reference scatterers. Numerical tests on both synthetic and experimental data verify the superior performance of the proposed method for ISP reconstructions with hybrid scatterers. It effectively expands the application scope of learning-based ISP methods to reconstruct scatterers without knowing the BCs of scatterers in advance.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Fast 3-D Electromagnetic Full-Wave Inversion of Dielectric Anisotropic
           Objects Based on ResU-Net Enhanced by Variational Born Iterative Method

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      Authors: Junjie Fei;Yanjin Chen;Miao Zhong;Feng Han;
      Pages: 6229 - 6239
      Abstract: In this article, a novel artificial neural network named residual U-Net (ResU-Net) is proposed to directly reconstruct 3-D dielectric anisotropic objects from scattered electromagnetic field data recorded at the receiver array. ResU-Net has the same framework as that of U-Net but the convolution kernels are replaced with residual kernels. Meanwhile, the squeeze-and-excitation (SE) operation is added to enable information interaction among different channels and further improve prediction accuracy. ResU-Net is trained by thousands of 3-D homogeneous dielectric anisotropic handwritten digits and the corresponding synthesized scattered field data. In the online prediction, ResU-Net can invert multiple anisotropic model parameters of homogeneous 3-D objects instantaneously. For an inhomogeneous object or multiple homogeneous objects, ResU-Net provides good initial profiles which are fed into the following variational Born iterative method (VBIM) full-wave inversion solver. In addition, the VBIM is implemented in a restricted domain instead of the whole 3-D inversion domain to save computational cost. Numerical experiments show that compared with the traditional iterative solver, such as VBIM, the proposed ResU-Net or the hybrid method can not only achieve higher reconstruction accuracy but also accomplish the multiparametric 3-D inversion in a much faster way.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Learned Global Optimization for Inverse Scattering Problems: Matching
           Global Search With Computational Efficiency

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      Authors: Marco Salucci;Lorenzo Poli;Paolo Rocca;Andrea Massa;
      Pages: 6240 - 6255
      Abstract: The computationally efficient solution of fully nonlinear microwave inverse scattering problems (ISPs) is addressed. An innovative system-by-design (SbD)-based method is proposed to enable, for the first time to the best of the authors’ knowledge, an effective, robust, and time-efficient exploitation of an evolutionary algorithm (EA) to perform the global minimization of the data-mismatch cost function. According to the SbD paradigm as suitably applied to ISPs, the proposed approach is found on: 1) a smart reformulation of the ISP based on the a priori information on the imaged targets for defining a minimum dimensionality and representative set of degrees of freedom (DoFs) and 2) the artificial intelligence (AI)-driven integration of a customized global search technique with a digital twin (DT) predictor based on the Gaussian process (GP) theory. Representative numerical and experimental results are provided to assess the effectiveness and the efficiency of the proposed approach also in comparison with competitive state-of-the-art inversion techniques.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Dielectric Breast Phantoms by Generative Adversarial Network

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      Authors: Wenyi Shao;Beibei Zhou;
      Pages: 6256 - 6264
      Abstract: In order to conduct the research of machine learning (ML)-based microwave breast imaging (MBI), a large number of digital dielectric breast phantoms that can be used as training data (ground truth) are required but are difficult to be achieved from practice. Although a few dielectric breast phantoms have been developed for research purpose, the number and the diversity are limited and are far inadequate to develop a robust ML algorithm for MBI. This article presents a neural network method to generate 2-D virtual breast phantoms that are similar to the real ones, which can be used to develop ML-based MBI in the future. The generated phantoms are similar but are different from those used in training. Each phantom consists of several images with each representing the distribution of a dielectric parameter in the breast map. A statistical analysis was performed over 10 000 generated phantoms to investigate the performance of the generative network. With the generative network, one may generate an unlimited number of breast images with more variations, so the ML-based MBI will be more ready to deploy.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Breast Imaging by Convolutional Neural Networks From Joint Microwave and
           Ultrasonic Data

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      Authors: Yingying Qin;Peipei Ran;Thomas Rodet;Dominique Lesselier;
      Pages: 6265 - 6276
      Abstract: Convolutional neural networks to achieve joint inversion of microwave and ultrasonic data for breast imaging are investigated. Source and field quantities, obtained via backpropagation, are used as inputs. A multistream structure is employed to benefit from data of different modalities. The network outputs the distribution maps of electric and acoustic parameters directly to achieve real-time imaging. Apart from the regression task, a multitask learning strategy is used with a classifier that associates each pixel to a tissue type to yield a segmentation image. Weighted loss is used to assign a higher penalty to pixels in tumors when wrongly classified. Comparisons are carried out between different network structures with the same datasets. The prediction results of the networks are evaluated by Intersection over Union for segmentation results and relative error of retrievals. The simulations on breast phantoms extracted from a dedicated repository show that, with both microwave and ultrasonic data, the network can provide a proper estimate of the breast structure and detection of small tumors. Meanwhile, multitask learning improves the regression results, and multistream input helps to exploit data from different modalities.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Hybrid Neural Network Electromagnetic Inversion Scheme (HNNEMIS) for
           Super-Resolution 3-D Microwave Human Brain Imaging

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      Authors: Li-Ye Xiao;Ronghan Hong;Le-Yi Zhao;Hao-Jie Hu;Qing Huo Liu;
      Pages: 6277 - 6286
      Abstract: Super-resolution three-dimensional (3-D) electromagnetic (EM) inversion for microwave human brain imaging is a typical high contrast EM inverse problem and requires huge computational costs. This work proposes a hybrid neural network electromagnetic inversion scheme (HNNEMIS) which contains shallow and deep neural networks to alleviate the required huge computational costs and solve this high contrast inverse problem. In the proposed scheme, semi-join back propagation neural network (SJ-BPNN) is employed to nonlinearly map the measured scattered electric field to two output channels, namely the permittivity and conductivity of scatterers, respectively. Such a semi-join strategy decreases the computational burden in training and testing processes. Then, a deep learning technique, termed U-Net, is employed to further enhance the imaging quality of the output from SJ-BPNN. To decrease the training cost and make neural networks fast convergent for human brain inversion, a novel training dataset construction strategy which contains the characteristics of human brain is also proposed. Noise-free and noisy numerical examples demonstrate that HNNEMIS has superior super-resolution inversion capabilities for human brain imaging.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Learning Approach to FMCW Radar Target Classification With Feature
           Extraction From Wave Physics

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      Authors: Kai Tan;Tiantian Yin;Hongning Ruan;Siegfred Balon;Xudong Chen;
      Pages: 6287 - 6299
      Abstract: Target classification is of great value when the number of transceivers in a sensing system is relatively small. This article proposes a high-accuracy and efficient classification method with machine learning techniques on frequency-modulated-continuous-wave (FMCW) radar. We first establish the novel mapping relationship from physical space to range-Doppler (PS-RD) image based on wave propagation theory, by which four physical features that effectively capture the kinematic and geometrical characteristics of targets, including speed, total reflectivity (ToRe), area, and incidence angle, are extracted from range-Doppler (R-D) image. Then, a multilayer perceptron (MLP) with a single hidden layer is employed to realize the classification. Since the above-mentioned four physical features, derived from wave physics, are chosen as the input of the neural network, our classifier does not work in a black-box way. The computational complexity of the whole classifier is the same as that of a 2-D fast Fourier transform (FFT), which guarantees a real-time operation. As an example, the proposed classifier is applied to the automotive radar system, where road targets are to be classified into five categories, including pedestrian, bike, sedan, truck/bus, and other static objects. Real-world data obtained from 77 GHz FMCW radars are provided for validation, where the proposed physics-assisted classifier turns out to outperform the state of the art in automotive radar application. The overall accuracy of the real data is about 99% even with complex multiple-target cases.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Artificial Intelligence-Based Low-Terahertz Imaging for Archaeological
           Shards’ Classification

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      Authors: Flora Zidane;Vanna Lisa Coli;Jérôme Lanteri;Julien Marot;Laurent Brochier;Didier Binder;Claire Migliaccio;
      Pages: 6300 - 6312
      Abstract: In order to map the migration and introduction of farming into Europe during the seventh and sixth millennia Before Common Era, archeologists have made a connection between the study of pottery and farming migration. We are interested here in the classification of pottery into coiling and spiral types based on their manufacturing techniques. To distinguish between these two techniques, we look for the lines formed by air bubbles embedded in the pottery samples. Current methods make use of bulky systems, such as computerized tomography scanners or synchrotrons. Microwave acquisition and processing offer an interesting alternative, due to the possibility to have compact and portable systems. In this article, we investigate the classification of pottery based on low-terahertz measurements in the D-band. We process the measurements with 3-D fast Fourier transform. The resulting matrix is classified with an artificial neural network, multilayer perceptron, which is optimized with the gray wolf optimizer, a bioinspired algorithm. The first results show that the accuracy reaches up to 99% using all the acquired spatial and frequency measurements. Then, we optimize the millimeter-wave (mm-Wave) measurement system with a critical criterion on accuracy in two different scenarios. In the first scenario, we reduce the spatial acquisition but maintain the wideband operation and the results show that the accuracy is between 85% and 96%. In the second one, we reduce the spatial acquisition and use a single frequency. For this second scenario, we achieve a classification accuracy, which is between 77% and 100%.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • DMRF-UNet: A Two-Stage Deep Learning Scheme for GPR Data Inversion Under
           Heterogeneous Soil Conditions

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      Authors: Qiqi Dai;Yee Hui Lee;Hai-Han Sun;Genevieve Ow;Mohamed Lokman Mohd Yusof;Abdulkadir C. Yucel;
      Pages: 6313 - 6328
      Abstract: Traditional ground-penetrating radar (GPR) data inversion leverages iterative algorithms that suffer from high computation costs and low accuracy when applied to complex subsurface scenarios. Existing deep learning-based methods focus on the ideal homogeneous subsurface environments and ignore the interference due to clutters and noise in real-world heterogeneous environments. To address these issues, a two-stage deep neural network (DNN), called DMRF-UNet, is proposed to reconstruct the permittivity distributions of subsurface objects from GPR B-scans under heterogeneous soil conditions. In the first stage, a U-shape DNN with first multi-receptive-field convolution (MRF-UNet1) is built to remove the clutters due to inhomogeneity of the heterogeneous soil. Then, the denoised B-scan from MRF-UNet1 is combined with the noisy B-scan to be inputted to the DNN in the second multi-receptive-field convolution (MRF-UNet2). MRF-UNet2 learns the inverse mapping relationship and reconstructs the permittivity distribution of subsurface objects. To avoid information loss, an end-to-end training method combining the loss functions of two stages is introduced. A wide range of subsurface heterogeneous scenarios and B-scans are generated to evaluate the inversion performance. The test results in the numerical experiment and the real measurement show that the proposed network reconstructs the permittivities, shapes, sizes, and locations of subsurface objects with high accuracy. The comparison with existing methods demonstrates the superiority of the proposed methodology for the inversion under heterogeneous soil conditions.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Deep Complex Convolutional Neural Networks for Subwavelength
           Microstructure Imaging

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      Authors: Teng-Fei Wei;Xiao-Hua Wang;Cheng-Hui Qu;
      Pages: 6329 - 6335
      Abstract: To take the advantages of a convolutional neural network (CNN), U-net, and a complex-valued CNN (complex-CNN), a new complex-valued U-net (CU-net) is proposed for deep learning (DL)-based methods to solve inverse scattering problem (ISP). With the proposed CU-net, the complex scattered data carrying rich information of object can be directly used for inversion without any preprocessing, which is very helpful for the accuracy improvement of the final result. To validate the performance of proposed method, a microstructure, consisting of a finite periodic set of circular cylindrical dielectric rods, is considered and detected for textural abnormalities, which contains the missing, flaw, and displacement of the rods. The distances between rods and diameters of rods are both subwavelength, well beyond the Rayleigh criterion, which causes this ISP extremely ill-posed. For comparison, both the conventional iterative method and DL-based method are used to solve this nonlinear problem. Numerical simulations demonstrate that the well-trained DL-based methods can successfully produce excellent results almost in real time and can greatly outperform the conventional iterative methods in terms of quality and efficiency.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Deep-Learning-Enabled Microwave-Induced Thermoacoustic Tomography Based on
           Sparse Data for Breast Cancer Detection

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      Authors: Jiale Zhang;Chenzhe Li;Weichao Jiang;Zhicheng Wang;Lejia Zhang;Xiong Wang;
      Pages: 6336 - 6348
      Abstract: As a rapidly developing novel electromagnetic imaging technique, microwave-induced thermoacoustic tomography (MITAT) has found many applications and attracted tremendous research interest. Using sparse data to reconstruct images is very challenging for MITAT. This work proposes a novel deep-learning-enabled MITAT (DL-MITAT) modality to address the sparse data reconstruction problem and applies it in breast cancer detection. The applied network is a domain transform network called feature projection network (FPNet) + ResU-Net. Detailed structure and implementation method of the network is described. We conduct both simulation and ex vivo experiments with breast phantoms to test the validity of the DL-MITAT approach. The obtained images given by the trained network exhibit much better quality and have much less artifacts than those obtained by a traditional imaging algorithm. We show that only 15 measurements can still reliably recover an image of the breast tumor for both full-view and limited-view configurations in ex vivo experiments. We also provide detailed discussions on the capability and limitations of the proposed scheme. This work presents a new paradigm for MITAT based on sparse data and can be applied in all related applications of MITAT, including biomedical imaging, nondestructive testing, and therapy guidance.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Artificial Intelligence: New Frontiers in Real-Time Inverse Scattering and
           Electromagnetic Imaging

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      Authors: Marco Salucci;Manuel Arrebola;Tao Shan;Maokun Li;
      Pages: 6349 - 6364
      Abstract: In recent years, artificial intelligence (AI) techniques have been developed rapidly. With the help of big data, massive parallel computing, and optimization algorithms, machine learning (ML) and (more recently) deep learning (DL) strategies have been equipped with enhanced learning and generalization capabilities. Besides becoming an essential framework in image and speech signal processing, AI has also been widely applied to solve several electromagnetic (EM) problems with unprecedented computational efficiency, including inverse scattering (IS) and EM imaging. In this article, a review of the most recent progresses in the application of ML and DL for such problems is given. We humbly hope a brief summary could help us better understand the pros and cons of this research topic and foster future research in using AI to address paramount challenges in the field of EM vision.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Theory and Analysis on Radiation Characteristics of Differential
           Rectangular Laminated Resonator Antenna

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      Authors: Yaowei Hou;Yueping Zhang;Zijian Shao;Yulin Fang;Junfa Mao;
      Pages: 6365 - 6376
      Abstract: This article studies differential rectangular laminated resonator antenna (LRA) theoretically and experimentally. A theoretical model is proposed to analyze the radiation characteristics of the differential rectangular LRA based on the waveguide excitation theory. Analytical expressions for the inner fields, modal coefficients, radiation fields, directivity, radiation efficiency, and gain are derived. For verification, a prototype of rectangular LRA differentially fed by L-probes is simulated, fabricated, and measured. Acceptable agreements among the calculated, simulated, and measured results are achieved. The theoretical analysis demonstrates that the differential operation can suppress the adjacent high-order modes near the dominant mode and results in low cross-polarization level and a more symmetric radiation pattern. The proposed theoretical model provides physical insight into the operating principle of rectangular LRA and facilitates the design of rectangular LRAs.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Systematic Generation of Arbitrary Antenna Geometries

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      Authors: Ekrem Altinozen;Ian Harrison;Ana Vukovic;Phillip Sewell;
      Pages: 6377 - 6387
      Abstract: Applications for conformal, wearable antennas are growing for consumer electronics. Hence, it is important to assess to what degree antenna performance can be tolerant to in situ deformations that can take the form of bending, crumpling, and twisting and combinations of these effects. However, generating geometries of arbitrary antenna deformations such as bending, crumpling, and twisting, which can be processed by standard electromagnetic (EM) software, is a major challenge that significantly complicates full assessment of in situ antenna performance. Constructive solid geometry methods of generating geometries is difficult to robustly apply to nonconformal antennas and more flexible techniques required to progress the antenna studies further. To address this challenge, this article investigates the utility of the green coordinate (GC) method for spatial manipulation of 3-D objects. First, calibration of a straightforward application of the GC method against a reference case of a patch antenna bent over a cylindrical surface, which can also be generated exactly, is undertaken. This article shows that systemic scaling distortions are introduced by the GC method and introduces a compensation method that can overcome these distortions. Subsequently, the compensated method is used to obtain new predictions of the EM performance of patch antennas with deformations.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Embroidery Electro-Textile Patch Antenna Modeling and Optimization
           Strategies With Improved Accuracy and Efficiency

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      Authors: Lingnan Song;Botian Zhang;Daisong Zhang;Yahya Rahmat-Samii;
      Pages: 6388 - 6400
      Abstract: In this article, we present systematic modeling and optimization strategies for embroidery electrotextile patch antennas, including material characterization, detailed modeling, stitch density study, and surrogate-based optimization. A detailed full-wave model that accounts for the complex embroidery features is proposed, with the effects of stitch density analyzed and validated through measurements for both rectangular and E-shaped patch antennas. A textile tailored surrogate optimization technique is then implemented to accelerate the computationally expensive full-wave evaluation for the detailed full-wave model, saving almost an order of magnitude of the computation time compared with canonical optimization. The methodologies presented in this article provide a pathway for both improved accuracy and efficiency in designing embroidery electrotextile patch antennas.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Multigap Loop Antenna With Phased Excitation in a Magnetoplasma

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      Authors: Alexander V. Kudrin;Tatyana M. Zaboronkova;Anna S. Zaitseva;Eva V. Bazhilova;
      Pages: 6401 - 6413
      Abstract: Electrodynamic characteristics of a multigap loop antenna immersed in a homogeneous magnetoplasma are studied using the integral equation method. The antenna has the form of a perfectly conducting, infinitesimally thin, narrow strip coiled into a ring with its axis parallel to an external static magnetic field. The antenna current is excited by appropriately phased external voltages applied across the gaps of the strip. A closed-form solution for the current distribution of the antenna is obtained, and the elements of its input admittance matrix are found. Based on this solution, conditions are determined under which such an antenna with phased excitation is capable of selectively exciting waves with given azimuthal indices in the surrounding magnetoplasma.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Impulse Radiating Antenna With Six Feeding Arms and a Tapered Balun

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      Authors: Milivoje F. Miletić;Dragan I. Olćan;
      Pages: 6414 - 6422
      Abstract: We present a design of reflector impulse radiating antenna (IRA) with six feeding arms and a printed tapered balun that also provides broadband matching to a $50 ~Omega $ system. The design is obtained by thorough numerical analysis and optimization. Six feeding arms provide a lower input impedance while maintaining the same boresight gain in comparison to an IRA with four arms. By placing the balun in the antisymmetry plane of the antenna, boresight gain is practically intact and the resulting antenna construction is rigid. In order to increase the power handling for continuous-wave excitations, the resistors between the arms and the reflector are omitted yielding an antenna that can handle at least hundreds of watts. The compromises that arise when omitting the resistors are discussed. The results are verified by comparing the measurements of the fabricated prototype to the results obtained by the numerical analysis.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Circularly Polarized Miniaturized Implantable Antenna for Leadless
           Pacemaker Devices

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      Authors: Abdenasser Lamkaddem;Ahmed El Yousfi;Kerlos Atia Abdalmalak;Vicente González Posadas;Daniel Segovia-Vargas;
      Pages: 6423 - 6432
      Abstract: A compact circularly polarized (CP) implantable antenna working at 915 MHz, at the industrial, scientific, and medical (ISM) band, is developed in this article. The proposed radiator is based on a fully planar and low-profile patch antenna with a ground plane and different slots but without any via holes, which makes the structure a good candidate for implantable devices. The circular polarization is achieved by means of introducing a surrounding and asymmetrical U-shaped structure. A meander line has been included in the inside of the U-shaped structure to increase the electrical length of the antenna without increasing its mechanical dimensions. An impedance bandwidth of 18.9% from 810 to 980 MHz and an axial ratio of 17.2% from 850 to 1010 MHz have been achieved. The proposed antenna has a compact size of $5.2times 5.6times0.25$ mm3, which seems to be the smallest antenna over the recently reported implantable antennas. In addition, the proposed antenna achieves a relatively high gain value of −23 dBi.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Motion-Induced Noise Modeling of Towed Magnetic Antenna

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      Authors: Zhi Huang;Yuzhong Jiang;
      Pages: 6433 - 6443
      Abstract: Motion-induced noise is the main noise that restricts the communication of deeply submerged submarines at extremely low frequencies (ELFs). In this article, a model for analyzing motion-induced noise is established in the context of a long cylindrical antenna towed by a submarine. The model proposed assumes that the antenna vibration caused by vortex obeys Poisson distribution in time and space. The factors involved in the noise generation, such as the speed of the submarine, the length of the towed cable, the transverse motion of the antenna, the pressure of the boundary layer, and the variation of pressure fluctuations with time and space, are further considered in the model. Finally, the derived noise power spectrum from our model shows agreement with the measured data, and has advantages than the result derived from previous work.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Dielectric Decoupler for Compact MIMO Antenna Systems

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      Authors: Chen Yang;Kai Lu;Kwok Wa Leung;
      Pages: 6444 - 6454
      Abstract: A novel decoupling method based on the superposition principle is proposed for compact multi-input–multi-output (MIMO) antenna systems in this work. A dielectric block is introduced to encompass all radiators in a compact MIMO system and works as a decoupler when the block is appropriately designed. Owing to the presence of dielectric–air boundary (DAB) introduced by the dielectric block, scattered paths show up for electromagnetic (EM) waves inside the block. For any two encompassed primary radiators, mutual couplings via the direct and scattered paths are superposed one on another. Because the scatted wave paths can be controlled by changing the shape and dimension of the DAB, mutual coupling between two encompassed primary radiators can be minimized with a properly designed DAB. To illustrate this decoupling principle, the electric field distribution of a basic Hertzian dipole wrapped in a dielectric decoupler is first studied. Results show that this method can generate several field valleys inside the dielectric block and can lead to good isolation when a second radiator is placed at a valley. A dual-port antenna wrapped in a dielectric decoupler is then proposed for demonstration. By optimizing the DAB shape, this antenna can realize a measured 20 dB isolation bandwidth of 12.6%, covering the whole 3.3–3.7 GHz 5G frequency range 1 (FR1) band. Furthermore, a quad-port decoupled antenna is studied to show the generality of the proposed decoupling method. Using a hollow rectangular dielectric block, isolations among four ports of more than 21.5 dB can be obtained in the 3.3–3.7 GHz band with a 20-dB isolation bandwidth of 18%. The envelope correlation coefficients (ECCs) and calculated ergodic channel capacity (CC) results show that the proposed compact dual-port and quad-port antennas are competitive for MIMO applications.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Bandwidth-Enhanced Tunable Decoupling Method for Compact Mobile Terminal
           Antennas

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      Authors: Yi Chen;Changzhou Hua;Yunlong Lu;Jifu Huang;
      Pages: 6455 - 6468
      Abstract: This article presents a tunable decoupling method for closely spaced multielement antenna systems, which is able to enhance the decoupling bandwidth of each tuning state. The decoupling method utilizes parasitic scatterers and tunable circuit components, and its design approach is systematically studied. The decoupling method is evaluated by performing a simulation in which the decoupling bandwidth in a tuned state for a three-element antenna system is examined. In that case, only the circuit components are optimized. As another example of this procedure, the frequency reconfigurable decoupling bandwidth for a two-element antenna system is shown to increase by optimizing the parasitic scatterer and the circuit components in the lossless and realistic cases. This study is concluded by presenting a realistic evaluation for the decoupling of a two-element antenna in different tuned states.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Deionized Water-Infilled Dual-Layer Insulator-Applied Brain-Implanted
           UWB Antenna for Wireless Biotelemetry Applications

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      Authors: Geonyeong Shin;Wonkyo Kim;Min Cheol Kim;Jusung Kim;Jae-Young Chung;Junghyo Nah;Ick-Jae Yoon;
      Pages: 6469 - 6478
      Abstract: We propose a novel double-layered insulator configuration for a human-brain-implanted impulse radio ultra-wideband (IR-UWB) antenna. The dimension of the antenna is $10.0times 11.0times0.954$ mm3, including the dual-layer insulator. The insulator provides a dielectric loading effect of $varepsilon _{r}~approx ~50$ (lossless) for obtaining an improved radiating power and the broadband-impedance-matching characteristic in brain tissues. The outer layer is made of biocompatible 3-D printing material, and the inner insulator is filled with deionized water with $varepsilon _{r}~approx ~80$ and loss tangent (tan $delta$ ) $approx ~0.25$ at 4 GHz. A slotted UWB antenna with the proposed insulator is located between the emulated dura and CSF tissues inside the skull for brain signal detection. The design uses a multilayer phantom, mimicking the seven tissue layers of the brain. The impedance and radiation performance of the proposed antenna configuration are also discussed using the commercial high-precision human phantom model. The designed IR-UWB antenna shows a boresight radiation characteristic toward the top of the head with a proper high gain in the target frequency of 3–5 GHz. The computed expectations are verified experimentally. Furthermore, it is demonstrated that the UWB spectrum generated from a UWB radio-frequency (RF) transmitter can be transmitted stably using the proposed antenna as a transmitting antenna. In addition, the link budget of the system setup is analyzed. The improved gain characteristic of the antenna from the proposed dual-layer insulator can be util-zed to retain the link margins while satisfying the UWB communication regulation and average specific absorption rate (SAR) limitation.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Broadband Low-Profile Monopulse Comparator for Dual-Circularly Polarized
           Feeder

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      Authors: Haojun Yuan;Zewei Wu;Muyao Zhang;Zhen Zhao;Wenqiang Qi;Ran Zhang;Minxing Wang;Shuai Huang;Youlei Pu;Jianxun Wang;Yong Luo;
      Pages: 6479 - 6489
      Abstract: This article proposes a scheme to design a broadband low-profile monopulse comparator for the dual-circularly polarized feeder. For obtaining a compact and easily integrated structure, a monopulse comparator with a ring-shaped symmetrical planner topology is proposed by using the 3 dB coupler and the phase shifter based on the groove gap waveguide (GGW). Then, in order to achieve the equal-amplitude distribution in a broad bandwidth, the asymmetrical coupling structure and the novel dispersion-matched transition are proposed to improve the directivity of a 3 dB coupler. Moreover, a ridge waveguide with periodic grooves featuring stable dispersion change is adopted to design the phase shifter, which contributes to obtain an accurate phase control in the broad frequency band. To validate experimentally the broadband performance, a dual-circularly polarized four-horn feeder with two identical monopulse comparators is designed and fabricated. The results show that the symmetrical radiation patterns with 32 dB null-depth can be obtained from 27 to 31 GHz. The monopulse comparator characterizes broad bandwidth, low loss, and a compact size, which provides a monopulse comparator with accurate amplitude/phase control for the research of the monopulse antenna.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Highly Pattern-Reconfigurable Planar Antenna With 360° Single-
           and Multi-Beam Steering

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      Authors: Yujie Zhang;Zixiang Han;Shiwen Tang;Shanpu Shen;Chi-Yuk Chiu;Ross Murch;
      Pages: 6490 - 6504
      Abstract: A novel single-fed horizontally polarized pattern-reconfigurable antenna is proposed with the key feature that is highly pattern-reconfigurable. The antenna is able to generate a large variety of radiation patterns, including omnidirectional, single-directive, and multi-beam patterns without using phase shifters. The antenna is based on a planar geometry, which consists of an Alford loop and four compact parasitic pixel rings with 60 integrated controlling units utilizing p-i-n diodes. Experimental and simulation results are provided for the proposed antenna design operating at 5 GHz. The results show that the single-beam steering with 7.3 dBi gain through 360° in the azimuth plane is achieved. Moreover, flexible dual-beam steering with one beam fixed and the other beam scanning independently among 360° in the azimuth plane is also demonstrated where each beam has 5 dBi gain. Other radiation modes, such as the omnidirectional mode, the tri-beam-steering mode, and the elevation plane steering mode, are also verified. The features of high pattern reconfigurability, 360° single-beam- and multi-beam-steering ability, full 3-D space scanning, planar geometry, and compatibility with a digital controller make it useful in various sub-6 GHz wireless applications, such as wireless power transfer, RF sensing, and analog precoding.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Design of a Printed Dipole Antenna by Using the Substrate-Integrated
           Double Line Technology

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      Authors: Wei W. Wang;Bing Liu;Yue Zhou;Dong M. Xu;Peng Liu;
      Pages: 6505 - 6513
      Abstract: In this article, a novel printed dipole antenna is proposed with gain enhancement by using the newly emerging substrate-integrated double line (SIDL) technology for potential 5G millimeter-wave (mm-wave) applications. As a three-wire transmission line, the SIDL incorporates two parallel inner strips and one grounded outer conductor. The inner strip pair protrudes and is bent bilaterally to form the dipole’s arms. The outer conductor is stretched out and splits into four strips in a fourfold symmetry along the longitudinal axis to boost the gain. A bilateral slotline technology is used to couple the energy from the feed to the SIDL structure, providing a broadband transition. The shaped SIDL and the transition contribute to the proposed dipole element and then are expanded to a $1times 2$ array, both of which are designed and fabricated by using the standard printed circuit board (PCB) process. The measurement discloses that the element has an actual −10 dB impedance bandwidth from 33.5 to 47.4 GHz (34.4%@40.4 GHz) with a practical peak gain of 7.00 dBi, which for the array are 32.0–45.1 GHz (34.0%@38.6 GHz) and 8.88 dBi, respectively. Good agreement between the simulated and experimental results demonstrates the feasibility of SIDL’s utilization in designing the printed dipole antenna for high-gain and wideband mm-wave applications.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Dual-Band Closed-Slot MIMO Antenna for Terminal Wireless Applications

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      Authors: Chao Wang;Hanyang Wang;Pengfei Wu;Meng Hou;
      Pages: 6514 - 6525
      Abstract: This article presents a dual-band closed-slot multiple-input multiple-output (MIMO) antenna for terminal wireless applications. By simply inserting additional slots between the closely spaced parallel-arranged radiation slots, the signal impedances of common mode (CM) and differential mode (DM) can achieve similar status, and the strong mutual coupling effect is then eliminated. The proposed slot antenna pair shows good isolation of better than 20 dB across the desired Wi-Fi bands. In addition to the one-wavelength slot antenna, flexible extension to a more compact half-wavelength slot pair is given for future industrial design (ID), which provides further validation of the method. We fabricate the $4times4$ MIMO antenna system constituted by two sets of one-wavelength closed-slot pairs. The experimental results show that the proposed MIMO antenna can offer isolation of better than 18 dB, an envelope correlation coefficient (ECC) of lower than 0.1 between all ports, and a wide −3 dB efficiency bandwidths across the desired bands. The results confirm that the proposed antenna is a viable candidate for Wi-Fi communications inside routers.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Transmissive Metasurface With Independent Amplitude/Phase Control and Its
           Application to Low-Side-Lobe Metalens Antenna

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      Authors: Lin-Xiao Wu;Na Zhang;Kai Qu;Ke Chen;Tian Jiang;Junming Zhao;Yijun Feng;
      Pages: 6526 - 6536
      Abstract: In this article, a single-sheet metasurface (MS) for independently manipulating the transmissive phase and amplitude of linearly polarized electromagnetic (EM) wave is proposed. The amplitude modulation is achieved via imposing a rotation angle to flexibly control the ratio of polarization conversion, while the phase modulation is realized by tuning the physical parameters of the unit cell to change its resonance. By integrating the proposed single-sheet MS, a low-profile metalens antenna operating around 12.2 GHz is designed, fabricated, and experimentally validated. In particular, spatially varying amplitude on the MS aperture is designed to meet the Taylor distribution, thus reducing the sidelobe level (SLL) of the metalens antenna. In addition, special MS elements rotation strategy is performed to maintain good polarization isolation-level (PIL) performance. The measured results show that the proposed metalens antenna achieves the peak gain of 25.3 dBi at 12.6 GHz with 3 dB gain bandwidth of 16.4% (11.2–13.2 GHz). Within the 3 dB gain bandwidth, this metalens antenna achieves SLL lower than −20.5 dB with an average value of −23 dB and PIL lower than −22.2 dB with an average value of −26.5 dB. Compared with metalens antenna with phase-only modulations, the proposed metalens antenna realizes a 5.7 dB average SLL suppression. The proposed metalens antenna is a promising candidate in point-to-point communications for wireless and satellite system applications.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Conformal Folded Inverted-F Antenna With Quasi-Isotropic Radiation Pattern
           for Robust Communication in Capsule Endoscopy Applications

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      Authors: Yanyang Wang;Sen Yan;Binke Huang;
      Pages: 6537 - 6550
      Abstract: In this article, an antenna with quasi-isotropic radiation pattern is proposed in a 915 MHz industrial, scientific, and medical (ISM) band for robust communication with external devices. The overall structure of the proposed antenna is a folded inverted-F antenna (FIFA). In the simulation, the proposed antenna is integrated with dummy electronics to form a fully encapsulated capsule endoscope architecture. These dummy electronics are encapsulated in a copper cylindrical bucket used as the antenna ground to avoid electromagnetic (EM) interference between these dummy electronics and the antenna. The spherical phantom model is used in the initial design of the proposed antenna. Subsequently, an anatomical realistic phantom was used to evaluate the performance of the proposed antenna in a more realistic human environment. The simulated gain variation (GV) of the proposed antenna in the regular spherical phantom is about 8 dB, and the reflection and other factors caused by the irregular shape of the realistic human tissue environment lead to the GV of the antenna in the anatomically realistic phantom that is about 4 dB. The measurement of reflection coefficient and radiation pattern is carried out in a semisolid muscle-mimicking phantom using a fabricated prototype of the proposed antenna. The measured GV value is about 10.5 dB. Finally, the specific absorption ratio (SAR) was calculated to meet the human safety regulations and the communication link budget was calculated to evaluate the wireless biological telemetry performance of the proposed antenna.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Textile Via-Loaded Bandwidth-Enhanced Half-Mode Substrate-Integrated
           Cavity Antenna for WLAN Communications

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      Authors: Jie Cui;Feng-Xue Liu;Hongsheng Yin;Lei Zhao;
      Pages: 6551 - 6559
      Abstract: A textile via-loaded bandwidth-enhanced half-mode substrate-integrated cavity (HMSIC) antenna is presented in this article for wireless local area network (WLAN) communications. A strategy for adding shorting vias within the cavity is proposed based on the simulated ${E}$ -field distributions of different modes of the HMSIC antenna. More specifically, the number and positions of vias are studied for maximum shift of lower resonance ( $rm TM_{1,1,0}^{HM}$ mode) so that it merges with higher resonance (rotated $rm TM_{2,2,0}^{HM}$ mode) to achieve a wide 10 dB return loss impedance band. Two prototypes of the designed structure are realized using textile manufacture techniques. A first realization uses embroidered sidewalls to create the cavity and metallic rivets for the shorting vias, and a second prototype uses embroidered vias and a stripline feed. The proposed antenna can operate from 5.09 to 5.9 GHz with a fractional bandwidth of 14.7% according to measurements. The simulated radiation efficiency is above 95% in free space and 82% when worn on the human body in the 5 GHz WLAN band (5.15–5.825 GHz).
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Dual-Frequency Microstrip Leaky-Wave Antenna for High-Gain Broadside
           Radiation

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      Authors: Hui-Dong Li;Lei Zhu;
      Pages: 6560 - 6570
      Abstract: This article presents a resonator-fed dual-frequency dual-mode bidirectional leaky-wave antenna to provide attractive high-gain broadside radiation at dual desired frequencies. First, by analyzing the dispersion diagrams of the first (EH1) and third (EH3) higher order modes of a microstrip line, it is theoretically verified that these two modes can both be suitably employed for bidirectional leaky-wave antenna design. In addition, it is also determined that the ratio between these two operation frequencies can be handily controlled by appropriately loading periodical shorting pins along the nodal lines of the EH3 modal field. As such, the dual-frequency operation principle is thoroughly investigated and determined. Afterward, to effectively excite the desired modes and suppress any unwanted modes of the microstrip line, a dual-frequency resonant-fed strategy is adopted. More specifically, the introduced feeding resonator is first fed by a pair of differential probes, and then, the microstrip EH1 and EH3 modes are excited through the coupling gap. In this way, the desired pure EH1 and EH3 modes are successfully excited. As an example, a dual-frequency bidirectional microstrip leaky-wave antenna is designed to work at 3.6 and 4.9 GHz, and its prototype is simulated, fabricated, and tested. The obtained far-field radiation patterns from simulations and measurements show a reasonable agreement, and the concerned high-gain radiation at the broadside is well achieved at both frequencies.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Millimeter-Wave Fully Integrated Dielectric Resonator Antenna and Its
           Multi-Beam Application

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      Authors: Chaojun Ma;Shao Yong Zheng;Yong Mei Pan;Zhe Chen;
      Pages: 6571 - 6580
      Abstract: To address the issues of the inconvenient fabrication and integration for millimeter-wave (MMW) dielectric resonator antennas (DRAs), a new configuration is proposed. First, a dielectric resonator with artificial electromagnetic boundaries is implemented by introducing the electromagnetic band-gap structure along the four side-wall boundaries of a certain dielectric region on a printed circuit board. The electromagnetic bandgap (EBG) structure is constructed using a printed array of periodic upside-down mushroom-type unit cells. The resonant-mode analysis reveals that the proposed DR can support conventional dielectric resonator modes and dense dielectric patch (DDP) cavity modes simultaneously. To excite the DR, a substrate-integrated gap waveguide transmission line is embedded in the proposed structure for implementing a fully integrated DRA. For demonstration, a fully integrated dielectric resonator antenna (FIDRA) operating at 31 GHz is designed. Simulated results show that the antenna offers an 11.5% −10 dB impedance bandwidth (29.6 to 33.2 GHz), in which a peak gain of 7.85 dBi is obtained. As an extension, a multi-beam antenna array composed of a $1 times 4$ FIDRA antenna array and a SIGW $4 times 4$ Butler matrix is designed and fabricated. The experimental results verified the effectiveness of the proposed configuration in integrating the DRA and feeding network.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Pattern Reconfigurable, Low-Profile, Vertically Polarized, ZOR-Metasurface
           Antenna for 5G Application

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      Authors: Zhan Wang;Shengnan Zhao;Yuandan Dong;
      Pages: 6581 - 6591
      Abstract: A novel miniaturized, aperture-shared, vertically polarized (VP), zeroth-order resonance (ZOR)-based, metasurface antenna with pattern reconfigurability is proposed for sub-6 GHz fifth-generation (5G) application in this article. By exploring an aperture-shared ZOR metasurface with only four p-i-n diodes, the proposed pattern reconfigurable metasurface radiator can be operated at nine radiation states (one omnidirectional beam and eight scanning beams with 45° step). This novel reconfigurable ZOR metasurface is analyzed by equivalent circuit, array theory, and field distribution. To validate the proposed working principles and design guidelines, this VP metasurface-based pattern reconfigurable antenna with a low profile of $0.05lambda _{0}$ is fabricated and measured. It exhibits an 11.5% overlapped −10 dB impedance bandwidth (3.40–3.8 GHz, well covering B42/B43 LTE bands) and a 4.5 dBi peak gain in different radiation states. With the advantages of a miniaturized size (low profile), broadband, flexible pattern switching capacity, good radiation performance, and simple design, it is well poised for space-limited sub-6 GHz microcell applications.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Novel Compact UWB Vivaldi Nonuniform Slot Antenna With Enhanced Bandwidth

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      Authors: Sahar Saleh;Widad Ismail;Intan Sorfina Zainal Abidin;Moh’d Haizal Jamaluddin;Mohammed H. Bataineh;Asem S. Al-Zoubi;
      Pages: 6592 - 6603
      Abstract: A new theory called Vivaldi nonuniform slot profile antenna (VNSPA) is developed based on the nonuniform transmission lines (NTLs) theory and applied to reduce the size of the predesigned compact ultrawide band (UWB) Vivaldi-tapered slot antenna (VTSA) without affecting its performance in terms of matching and bandwidth. Using this theory, 33% of the taper slot length is reduced, resulting in a novel compact UWB Vivaldi nonuniform slot antenna (VNSA). Furthermore, compactness is achieved by performing parametric studies on VNSA with a final 51.94% size reduction. MATLAB optimization codes, CST simulation, and prototype manufacturing and measurement are used to validate the new theory. The proposed antenna provides a measured S11 < −10.89 dB through 2.9–13.55 GHz with 2.91% and 5.8% bandwidth and maximum realized gain enhancement, respectively, as compared with VTSA’s results. The effectiveness of VNSPA theory is proven by comparing the simulated and measured findings of VNSA and VTSA.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Millimeter-Wave Slot-Based Cavity Antennas With Flexibly-Chosen Linear
           Polarization

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      Authors: Shu-Lin Chen;Geng-Bo Wu;Hang Wong;Bao-Jie Chen;Chi Hou Chan;Y. Jay Guo;
      Pages: 6604 - 6616
      Abstract: Slot-based cavity antennas are hailed as promising candidates for millimeter-wave applications. Nevertheless, the linear-polarization (LP) angle of their broadside main beam is limited by the slots etched on the cavity’s top surface. In this work, an innovative technique is developed to significantly improve the selection flexibility of their LP inclination angle. It is attained by an integration of a single-layer, closely spaced C-shaped patch surface. A TE710-mode slot-based cavity antenna is employed as the base configuration, which radiates a broadside beam with its LP along $phi = 90^{circ }$ . To effectively predict and monitor the polarization conversion of the surface-integrated TE710-mode cavity antenna, an analysis method using a unit cavity extracted from its original cavity antenna is presented. A subsequent surface-integrated system with the specified 45° LP was then simulated, fabricated, and measured. The measured results validate that a 45° LP state is achieved with an operating bandwidth from 33.3 to 36.5 GHz. Further investigation is conducted to flexibly choose the LP direction from $phi = 15^{circ }$ to 165°. Two more examples with the fabricated antenna prototypes successfully radiate the specified $phi = 15^{circ }$ and 75° LP beams, respectively. This near-field polarization conversion surface can be generalized to cavities with different resonant modes.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Sparse Array Synthesis Including Mutual Coupling for MU-MIMO Average
           Capacity Maximization

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      Authors: Navid Amani;Amirashkan Farsaei;Sina Rezaei Aghdam;Thomas Eriksson;Marianna V. Ivashina;Rob Maaskant;
      Pages: 6617 - 6626
      Abstract: A hybrid optimization algorithm, including mutual coupling (MC), is proposed to synthesize an irregular sparse array (ISA) for average capacity maximization in a multiuser multiple-input–multiple-output (MU-MIMO) system. The hybrid approach is composed of two phases to suboptimally determine the location of a fixed number of omnidirectional thin dipole antennas in an arbitrary sparse aperture via a diagonal antenna selection matrix. In Phase I, the problem is relaxed to a convex optimization by ignoring the MC and weakening the constraints. The output of Phase I is accounted as a reliable initial guess for the genetic algorithm (GA) in Phase II, which incorporates the MC effects through the coupling matrix and avoids the convex relaxation technique. The proposed approach outperforms the conventional GA with a random initial population, while it avoids trying several starting positions. Meanwhile, the undesirable appearance of grating lobes, due to the undersampling, and the degrading MC effects are suppressed by aperiodicity. It is observed that doubling the conventional interelement spacing (half-wavelength) and finding the location of eight dipoles in a sparse aperture by the proposed method improve the average capacity by 3.27%–11.9% when the number of users varies from two to eight, and the signal-to-noise ratio (SNR) is 30 dB.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Proactive Conformal Waveguide Slot Array Antenna to Synthesize Cosecant
           Squared Pattern Based on 3-D Printing Manufacturing Process

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      Authors: Ya Fei Wu;Hong Rui Zhang;Yu Jian Cheng;Yong Fan;
      Pages: 6627 - 6634
      Abstract: It is difficult for a standing-wave waveguide slot array antenna to generate a complex beam shape in H-plane, such as the cosecant squared pattern. The reason is that a conventional standing-wave waveguide slot array antenna cannot flexibly and independently adjust the amplitude and phase of radiating elements. In this article, a proactive conformal waveguide slot array antenna is designed with the cosecant squared pattern in its H-plane. It is able to control the element phase by proactively curving the array shape. That means the antenna shape is employed as a new parameter to break the limitation in the phase control. Based on this, the proactive conformal waveguide slot array antenna can modulate the element amplitude and phase independently to form the desired complex far-field pattern. The commercial selective laser melting (SLM) technology is applied to print the curved antenna after carefully considering the printing direction and slot shape. A 35 GHz prototype antenna is fabricated and measured. Good performance can be observed in the measured results.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Hollow-Waveguide Tri-Band Shared-Aperture Full-Corporate-Feed Continuous
           Transverse Stub Antenna

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      Authors: Qingchun You;Yunlong Lu;Yi Wang;Jun Xu;Jifu Huang;Wei Hong;
      Pages: 6635 - 6645
      Abstract: This article presents a tri-band shared-aperture full-corporate-feed continuous transverse stub (CTS) antenna based on hollow-waveguide. The multiband operation is enabled by a broadband CTS radiator and a novel six-port parallel-plate waveguide (PPW) multiplexer. The CTS radiation slot is fed by a broadband vertical PPW power divider. The six-port multiplexer is composed of three diplexers, which defines the three frequency bands—Ku, K, and Ka. The quasi-TEM mode in the PPW structure is generated by single-layer linear source generators (LSGs). Four such LSGs operating at three different bands are used to feed into the multiplexer. The amplitude and phase precompensation method is applied in the LSG to overcome the imbalance and spurious reflection caused by the metal walls at the terminal ends of the PPW. This has resulted in improved radiation performance in all three bands. A prototype antenna is designed, fabricated, and measured. Good agreement between simulation and measurement has been shown. The peak gains of the antenna over the frequency range of 11.25–15 GHz, 17.7–22 GHz, and 27.5–32 GHz are better than 24.7, 28.2, and 32.1 dBi, respectively. Over 80% antenna efficiency has been achieved in all three frequency bands.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Low-Profile, Risley-Prism-Based, Beam-Steerable Antenna Employing a
           Single Flat Prism

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      Authors: Zongtang Zhang;Yi Chen Zhong;Hung Luyen;John H. Booske;Nader Behdad;
      Pages: 6646 - 6658
      Abstract: We present a low-profile, mechanically beam-steerable antenna that implements the Risley prism beam-steering concept using only a single flat prism. The proposed antenna achieves 2-D beam steering and consists of two parts: a holographic leaky-wave antenna and a phase-shifting surface (PSS) that acts as a flat prism. The lower holographic leaky-wave antenna acts as the feed for the prism and provides a phase-shifting gradient over its output aperture. When paired with the flat prism, the system can provide 2-D beam steering by mechanically rotating the two layers against each other. Unlike conventional Risley-prism-based beam-steerable antennas, the proposed approach results in a very low-profile antenna and does not need spatial illumination of a two-prism system with a separate feed antenna. The flat prism is implemented using a PSS consisting of low-pass, hexagonal-shaped, spatial phase shifters. A prototype antenna with an overall thickness of only $1.1lambda _{0}$ at 10 GHz was designed, fabricated, and experimentally characterized. Measurement results agree well with theoretical predictions and both show wide-angle beam scanning ranging from 0° to 57° in the elevation plane and 0° to 360° in the azimuth plane. The proposed antenna system has an equivalent aperture diameter of $7.1lambda _{0}$ and a measured peak gain of 22.3 dBc at 10 GHz corresponding to an aperture efficiency of 34.5%. The proposed concept is expected to be useful in designing low-profile, beam-steerable antennas in which the scanning speed can be traded off to reduce system complexity.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Noise Shaping for Phased Array Beamforming

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      Authors: Shahin Sheikh;Ahmed A. Kishk;
      Pages: 6659 - 6670
      Abstract: Quantization of phase and/or amplitude has far-reaching effects on the radiation characteristics of the phased array (PA), including gain, minor lobe level, and point deviation. Traditionally, one common method to address such a nonlinear distortion is using random-phasing to interrupt the error periodicity. Here, we show that the distortion due to the quantization can be better remediated by spectrally shaping the error compared to the random-phasing (dithering) approaches. We adapted the method for phase-only and amplitude-phase synthesis of planar array designed based on analog beamforming (ABF). To do that, for the first time, 2-D real- and complex-coefficient minimum-phase digital finite impulse response (FIR) filters are designed based on the discrete Hilbert transform (DHT) method. In particular, the digital filter design for phase-only synthesis is comprehensively investigated, respecting the error spectra in the beamspace domain. It is shown that by pushing the error out of the so-called visible region, the decrease of antenna directivity due to the quantization can be compensated to some extent, which provides a quite advantage over the uniform distribution of error. For some cases, pushing the error out of the visible region might be impossible. For such cases, we proposed using the spaced-notches filter. It is also shown that the method is on maximum efficacy when both phase and amplitude of the excitation signal are controllable. Thus, complex-valued noise shaping (CV-NS) can be exploited for the phase-amplitude synthesis of the PA, showing quite promising performance.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Automobile Laminated Glass Window Embedded Transmitarray and Ray Tracing
           Validation for Enhanced 5G Connectivity

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      Authors: Seokyeon Hong;Yongwan Kim;Jungsuek Oh;
      Pages: 6671 - 6682
      Abstract: This article presents a 38.5 GHz transmitarray, for the first time, embedded into laminated car glass, and indoor 5G connectivity enhanced by this transmitarray laminated glass has also been validated using a ray-tracing simulator. The transmitarray structure reduces the penetration loss and realizes a desired beam shaping function. Metallic layers of the transmitarray structure adopt the Jerusalem cross shape that minimizes opacity. A ray-tracing simulator was used to analyze electromagnetic fields in a massive space, such as the interior of a car. The proposed transmitarray laminated glass was applied to the passenger side window in the simulation, and the variation in the communication performance with and without the transmitarray was compared. This comparison confirmed that field intensity increases of up to approximately 5 dB are realized at the target area, where communication is mainly performed. In addition, the proposed transmitarray laminated glass increases the field intensity by more than 3 dB, from approximately 36 to 40 GHz. The transmitarray laminated glass has also been fabricated. The maximum field intensity increase of approximately 5 dB, which is similar to the simulation results, was successfully measured at the target area.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Dual-Mode Substrate Wave Cancellation in a 120 GHz 2 × 2 On-Chip
           Dipole Array

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      Authors: Vincent Lammert;Michael Leyrer;Mohamed Hamouda;Robert Weigel;Vadim Issakov;
      Pages: 6683 - 6691
      Abstract: In this article we present the design of a 120 GHz 2 $times $ 2 dipole array in a 130 nm SiGe technology, which employs dual mode substrate wave cancellation to improve radiation efficiency and to avoid uncontrolled radiation from the chip edges. We show a systematic analysis of the involved dielectric slab modes TM0 and TE1 and their effects on the radiation pattern and efficiency. Based on this, the position and orientation of the array elements are derived for optimal cancellation of substrate waves and different feeding techniques are compared. The dipole array shows a measured realized gain of 1 dBi [including ground signal ground (GSG)-pad, Balun, and matching-capacitor, all on-chip], an $S_{11}$ -bandwidth of 18 GHz, and a realized gain bandwidth of 16 GHz. Very good correlation between simulations and measurements is achieved through careful modeling of the probe effects. The presented results provide useful insight on the design of on-chip dipole arrays for future millimeter-wave applications in standard SiGe or CMOS technologies.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Ultralow Scattering Design of Wideband Conformal Arrays Based on Optimally
           Loaded Resistors

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      Authors: Zhechen Zhang;Shiwen Yang;Feng Yang;Yikai Chen;Shi-Wei Qu;Jun Hu;
      Pages: 6692 - 6702
      Abstract: A novel approach based on the use of a resistor-loaded meta-surface (RL-MS) with optimized resistor values is proposed for scattering control in wideband conformal phased arrays. Specifically, the resistance of the loaded resistor in each RL-MS element is varied. As a result, the proposed RL-MS structure not only absorbs incident EM waves but also scatters the remainders away from threatening directions. To accelerate the design process, the scattering matrix approach is used to calculate the scattering patterns efficiently. Proper resistor element distribution can be achieved by optimizing the scattering characteristics. The RL-MS structure is used as the cover layer of a wideband conformal array. By loading the optimized resistors, scattering in the proposed array is reduced to a relatively low level with little degradation of radiation performances. The final designed array achieves 3:1 impedance bandwidth with scanning up to $pm 60^{circ }/pm 45^{circ }$ in the E-/H-plane. Remarkably, a monostatic scattering reduction of approximately 30 dB is observed throughout the X-band in the simulated results of the optimized array. To demonstrate the effectiveness of this design, prototype arrays are fabricated and measured. The measured results are in reasonable agreement with the simulated results.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • K-Band Circularly Polarized Beam Steerable Reflectarray Enabling Internet
           of Space: Conceptualization and Validation

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      Authors: Junbo Wang;Vignesh Manohar;Yahya Rahmat-Samii;
      Pages: 6703 - 6717
      Abstract: Low-cost and lightweight CubeSats have opened new possibilities to realize Internet of Space (IoS), a vision that aims to provide global network access, particularly for remote areas. A key challenge for IoS realization is the development of an antenna that can meet the gain, bandwidth, and polarization requirements for IoS while complying with the small form factor of CubeSats. The challenge is further magnified by the need to dynamically reconfigure the antenna’s beam location to maintain connectivity as the satellite orbits. This work addresses these challenges by proposing a beam steerable reflectarray antenna that can potentially be integrated with CubeSats to enable IoS. A novel reflectarray unit cell containing multiple Archimedean spiral arms is designed to support broadband circularly polarized (CP) operation, and its operational principle is discussed in depth. The unit cell provides four states of phase shift that are electronically switchable, allowing the reflectarray to achieve the required aperture phase for the desired beam scan. Representative reflectarray prototypes are designed, fabricated, and measured. CP beam scan up to 60° in the plane of offset across the targeted frequency band of 17.8–20.2 GHz is achieved.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Novel Low-Profile Phased Antenna With Dual-Port and Its Application in
           1-D Linear Array to 2-D Scanning

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      Authors: Kun Wang;Junping Geng;Han Zhou;Silei Yang;Rui Zhao;Jie Chen;Jingzheng Lu;Xudong Tang;Jing Zhang;Ronghong Jin;
      Pages: 6718 - 6731
      Abstract: A novel low-profile phased antenna with dual-port and its two types of 1-D linear array to 2-D space wide-angle beam scanning are proposed. The antenna unit is composed of fishbone structure and rhombus parasitic patch, which is folded into n-shaped to low profile $0.08lambda $ . By adjusting the phase difference ( $Delta varphi$ ) from 0° to 180°, the antenna working mode is changed from even mode to hybrid mode and to odd mode eventually. Therefore, the proposed antenna unit realizes wide-angle scanning characteristics and continuous switching state from broadside lobe to endfire lobe. Furthermore, the proposed phased antenna element is extended to two kinds of 1-D linear phased array (Array#1 and Array#2) based on the generalized principle of the pattern multiplication. The fabricated Array#1 can realize beam scanning range $- 116^{circ }< theta _{mathrm {m}} < 0^{circ }$ (xo z plane), $0^{circ }< theta _{mathrm {m}} < 63^{circ }$ (yo z plane), and $90^{circ }< Phi _{mathrm {m}} < 169^{circ }$ (xoy plane) and the fabricated Array#2 can achieve $0^{circ }< theta _{mathrm {m}} < 60^{circ }$ (xo z plane), $0^{circ }< theta _{mathrm {m}} < 65^{circ-}$ ( $text{y}{o}text{z}$ plane), and $90^{circ }< Phi _{mathrm {m}} < 152^{circ }$ (xoy plane). The proposed phased antenna unit and its 1-D array can realize 2-D space wide-angle scanning, improving scanning performance and expanding scanning dimensional space in phased array.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Compact Dual Linearly-Polarized Single-Plane Monopulse Antenna Array
           Based on SIW and Strip-Line Feed

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      Authors: Zhichao Sun;Shaobin Liu;Zhiyong Hu;Wenhui He;Xinyuan Zheng;Yuning Yang;
      Pages: 6732 - 6739
      Abstract: A compact dual linearly polarized monopulse antenna array is proposed in this article. The size of the antenna array is $3.13lambda _{0} times 4.38lambda _{0}$ , and it consists of two comparators, multilayer coupling slots, and a group of $4times $ 4 square patches. By using high-order-mode cavities and integrating the feeding network with the radiating part, the size of the antenna is considerably reduced. A prototype of the proposed antenna is fabricated and evaluated to the feasibility of the design. The measured total impedance bandwidth for four ports is 1.6% (18.65–18.95 GHz). The peak gains of the sum pattern with vertical and horizontal polarization are greater than 16.02 and 14.92 dBi, respectively. The null depths of the difference pattern at 18.8 GHz are less than −32 dB. The measurement results are in good agreement with the simulation results.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Radar Cross Section Reduction of Wideband Vivaldi Antenna Arrays With
           Array-Level Scattering Cancellation

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      Authors: Yuewen Gou;Yikai Chen;Shiwen Yang;
      Pages: 6740 - 6750
      Abstract: Wideband phased antenna arrays always contribute large radar cross section (RCS) to low-observed platforms. Low-scattering wideband phased antenna arrays are thus highly demanded. This article proposes to reduce the RCS of wideband phased antenna arrays through array-level scattering cancellation. Two types of Vivaldi antenna elements that exhibit almost the same scanning performance and operating bandwidth are developed. However, the tapered curves are intentionally designed to be different to achieve a 180° reflection phase difference. With these two types of Vivaldi antenna elements, a low-scattering Vivaldi antenna array ( $16times16$ ) is developed by array-level scattering cancellation. A reference Vivaldi antenna array with a single type of antenna element is also developed. Simulation and measurement results of the reference and the proposed antenna array are compared to illustrate the effectiveness of the proposed RCS reduction technique. Both antenna arrays operate over the 8–12 GHz frequency band and scan up to ±60° in the E-/H-planes. However, the proposed Vivaldi antenna array achieves an average of 10 dB monostatic RCS reduction over 6–18 GHz. It indicates that the array-level scattering cancellation technique is promising for developing low-scattering wideband phased antenna arrays.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Hilbert-Ordering Based Clustering of Complex-Excitations Linear Arrays

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      Authors: Arianna Benoni;Paolo Rocca;Nicola Anselmi;Andrea Massa;
      Pages: 6751 - 6762
      Abstract: The clustering of linear phased arrays (PAs) with complex weights is discussed. By exploiting the locality-preservation property of the Hilbert curve, the dimensionality of the problem at hand has been first reduced, and then, a simple clustering algorithm has been applied to maximize the matching of the radiated pattern with a reference one. Both contiguous and noncontiguous partitions of the Hilbert-ordered list of complex excitations have been evaluated to effectively sample the solution space of clustered solutions. A set of representative results, including reference PAs affording steered pencil and shaped beams, are reported for validation purposes as well as to point out the effectiveness of the proposed approach in comparison with state-of-the-art k-means algorithms as well.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Conversion Matrix Method of Moments for Time-Varying Electromagnetic
           Analysis

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      Authors: Stephen F. Bass;Ashley M. Palmer;Kurt R. Schab;K. C. Kerby-Patel;Jessica E. Ruyle;
      Pages: 6763 - 6774
      Abstract: A conversion matrix approach to solving network problems involving time-varying circuit components is applied to the method of moments for electromagnetic scattering analysis. Detailed formulations of this technique’s application to the scattering analysis of structures loaded with time-varying circuit networks or constructed from general time-varying media are presented. The computational cost of the method is discussed, along with an analysis of compression techniques capable of significantly reducing the computational cost for partially loaded systems. Several numerical examples demonstrate the capabilities of the technique and validate it against conventional methods of modeling time-varying electromagnetic systems, such as finite difference time domain and transient circuit co-simulation.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Machine Learning-Based Fast Integer and Fractional Vortex Modes
           Recognition of Partially Occluded Vortex Beams

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      Authors: Jia-Jing Sun;Sheng Sun;Ling-Jun Yang;
      Pages: 6775 - 6784
      Abstract: In this work, a machine learning method is proposed to precisely classify partially occluded integer and fractional vortex modes for the first time in radio frequency (RF). Consequently, we introduce three training schemes, i.e., the direct recognition scheme with the phase data or the amplitude data (PD-DRS and AD-DRS), the phase data or amplitude data interpolated by nearest-neighbor interpolation algorithm (PD-NNI and AD-NNI), and the full data (FD) of the electric field with the NNI algorithm (FD-NNI), to recognize the topological charges. Based on the designed deep convolutional neural network (DCNN) models, the relationship between the test accuracy and the number of sampling points of the three schemes is presented. It is shown that $3times3$ sampling points are enough for FD-NNI to achieve the classification accuracy of 98.2%. To validate the robustness of the proposed models, we evaluate them on the sample carrying up to 50% Gaussian noise, separately. Besides, the effects of propagation distance and the occlusion angle are also investigated. The numerical results present that the interpolated data performs better in terms of accuracy compared with the pure sampled data, among which FD-NNI possesses better generalization ability, suggesting great potential in the practical application of radio vorticity communication.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Remote Water Salinity Sensor Using Metamaterial Perfect Absorber

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      Authors: Majid Amiri;Mehran Abolhasan;Negin Shariati;Justin Lipman;
      Pages: 6785 - 6794
      Abstract: Controlling water salinity plays a key role in farming efficiency. Current sensors are mostly expensive and need regular maintenance. In addition, they require electrical connections or extra power supply that leads to difficult and costly implementation in remote-sensing scenarios. In this article, an accurate and low-profile sensor is developed using a metamaterial perfect absorber (MPA) structure. The proposed sensor works based on the level and frequency of the absorbed signals. Hence, there is no need for electrical connections, which enables remote-sensing applications. Square-shaped channels have been created in a regular FR-4 substrate to facilitate sensing of water salinity levels. A $7 times 7$ array with a total size of $140 ,,text {mm} times 160 ,,text {mm}$ has been fabricated that shows a resolution of 10 MHz per percentage of water salinity. The absorption frequency shifts from $f=3.12$ to 3.59 GHz for salinity level from 0% to 50%. A strong correlation between measurement and simulation results validates the design procedure.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Reconfigurable Vector Vortex Beams Using Spoof Surface Plasmon Ring
           Resonators

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      Authors: Zhen Liao;Yanziyi Che;Leilei Liu;Bai Cao Pan;Ben Geng Cai;Jia Nan Zhou;Guo Qing Luo;Yongmin Liu;
      Pages: 6795 - 6803
      Abstract: In this article, a spoof surface plasmon (SSP) ring resonator to generate dynamically reconfigurable vortex beams is proposed. According to the phase constant control of the SSP and the harmonic radiation principle, the tunable cylindrical vector vortex beams (VVBs) with different topological charges can be obtained. The tunable system that operates by electronic control would utilize varactors to change the wavenumber of SPP on the ring resonator and realize the reconfigurable VVBs modes at a fixed frequency. All VVBs have excellent orbital angular momentum (OAM) purity (above 90%). Interestingly, the antenna also simultaneously radiates the scalar vortex beams with tunable OAM modes. Both numerical simulations and experimental characterizations confirm the theoretical predictions. Because the designed antenna has the advantages of simple feeding network, easy bias circuit, as well as miniaturization and integration compatibility, we anticipate that the antenna will enable a wide range of applications for future wireless communication and imaging technologies.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Frequency-Tunable and Magnitude-Tunable Microwave Metasurface Absorbers
           Enabled by Shape Memory Polymers

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      Authors: Jianjia Yi;Mengyuan Wei;Menglan Lin;Xin Zhao;Lina Zhu;Xiaoming Chen;Zhi Hao Jiang;
      Pages: 6804 - 6812
      Abstract: In this article, we demonstrate a new strategy for achieving a kind of shape-controlled tunable microwave absorbers based on shape memory polymers (SMPs). Using the heat-driven shape memory effect of SMPs, a frequency-tunable absorber and a magnitude-tunable absorber are designed. Both of the designs consist of a periodic metallic array printed on both sides of the FR4 substrate, SMPs’ substrate (VeroWhitePlus) in the middle layer, and a metallic ground at the bottom. The equivalent circuit models are introduced to analyze the operational principles of the two absorbers. Furthermore, the functionalities of the designed shape-controlled tunable absorbers are investigated by full-wave simulations. For the frequency-tunable absorber design, the simulated results indicate that the resonant frequency can be tuned from 11.3 to 13.5 GHz with a frequency shift of 2.2 GHz. For the other design, the simulated results show that the reflection coefficient can be tuned from −17.00 to −1.34 dB. The proposed frequency shift responses and magnitude modulation responses are experimentally demonstrated by fabricating two prototypes containing 33 $times33$ units. The above designs overcome the limitation of the traditional electrically adjustable wave absorber requiring an external power supply, providing a new paradigm for the design of tunable devices.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • An Ultrathin Frequency Selective Rasorber Based on Electromagnetic
           Composite Absorption

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      Authors: Meiling Li;Qihao Yang;Qi Zheng;Xue-Xia Yang;Zixuan Yi;
      Pages: 6813 - 6824
      Abstract: In this article, an ultrathin frequency selective rasorber (FSR) based on electromagnetic composite absorption is proposed. At first, a subwavelength unit (SLU) for electromagnetic composite absorption is designed and its mechanism is discussed under the excitation of electric field ( $E$ -field) and magnetic field ( $H$ -field) of incident electromagnetic waves separately. Next, a single layer ultrathin frequency selective absorber (UFSA) is constructed by eight SLUs, which are arranged by mirror symmetry and 90° rotation symmetry. Then, two UFSAs are designed, which work at different frequencies. The proposed ultrathin FSR, which is constructed by simply stacking two UFSAs, has a transmission band (2.09–2.69 GHz) and two absorption bands (two absorptive peaks above 90% at 2.05 and 2.78 GHz) on both sides of the transmission band. Importantly, compared to the traditional FSR, the profile of the FSR is low and $0.039lambda _{c}$ . Finally, to verify the design and analysis, the proposed FSR was fabricated and measured. A good agreement between the results of the experiment and simulation can be obtained accordingly.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Stable GSTC Formulation for Maxwell’s Equations

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      Authors: Nicolas Lebbe;Kim Pham;Agnès Maurel;
      Pages: 6825 - 6840
      Abstract: We revisit the classical zero-thickness generalized sheet transition conditions (GSTCs) that are a key tool for efficiently designing metafilms able to control the flow of light in the desired way. It is shown that it is more convenient to use an enlarged formulation of the GSTC in which the original metafilm is replaced by GSTCs that exclude the layer from the physical or computational domain. These new “layer” transition conditions have the same form as their “sheet” analogs; hence, they do not necessitate additional complications in their use, and their advantage is that they provide a well-posed problem and, hence, guarantee the stability of numerical schemes in the time domain. These assessments are demonstrated for an all-dielectric structure; the effective susceptibility tensors are derived due to asymptotic analysis combined with homogenization technique, and bounds for the susceptibilities entering the balance of energy are provided. While negative constant susceptibilities appear in the classical zero-thickness GSTCs, their values in the enlarged formulation are always positive, which ensures the stability of the effective problem. The validation of the effective model is provided by means of comparison with direct numerics in two and three dimensions.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Broadband Multilayer Absorber With Switchable Function of Radiation

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      Authors: Jiwen Sun;Qunsheng Cao;Minghai Pan;Lin Zhu;
      Pages: 6841 - 6849
      Abstract: This article presents a novel dual-functional reconfigurable integrated structure in which p-i-n diodes switch the two operating states. The proposed structure consists of a periodic arrangement of square loops printed on dielectric substrates separated by an air spacer. The lumped resistors and switchable p-i-n diodes are soldered at the center of each of the four arms of the squares on the top and bottom layers, respectively. When p-i-ns are on, the designed structure is considered a high-gain antenna array operating within the absorption band. A wideband absorber covering C- and X-bands is constructed using a multistacked circuit analog (CA) absorption structure when p-i-ns are resistors. Besides, the ray-tracing method and the equivalent circuit model are utilized to analyze the operating principle of the states of radiation and absorption, respectively. Finally, a sample of $4 times 4$ integrated units is fabricated and measured. Both simulated and experimental results demonstrate the excellent performance of the proposed structure with a peak measured gain of 13.1 dBi at 8.2 GHz and the reflectivity below −10 dB in the frequency range between 4.02 and 13.82 GHz (fractional bandwidth of 109.8%) under normal incidence.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Single-Layer Ultra-Wideband Multifunctional Transmissive Metasurface

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      Authors: Taoming Lu;Jiong Wu;Zhaoyang Shen;Youcheng Wang;Houyuan Cheng;Yujun Li;Yuejie Yang;Helin Yang;
      Pages: 6850 - 6857
      Abstract: The metasurface is a functional film device based on a subwavelength structure, which has a strong light field control ability and has the advantages of ultrathin, low loss, and easy manufacturing. However, realizing a multifunctional metasurface, yet simple enough to design, manufacture, and thin is still a challenge. In this article, we propose a novel metasurface with negligible thickness as a beam splitter, which can achieve half transmission and half reflection of the incident wave at the same frequency. It also controls the polarization of circularly polarized electromagnetic (EM) waves in the transmission mode. A broadband operation can be achieved based on the geometric phase theory, and the phase control can be achieved by azimuth rotation of the structure. The numerical results of the metasurface are in good agreement with the experimental results in the measured frequency range. The ultrathin multifunctional metasurface realized by the geometric phase principle provides an important stepping stone for simple optical devices and can be extended to a higher frequency range.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Decoupled Potential Integral Equation for Electromagnetic Scattering From
           Arbitrarily Shaped Dielectric Objects

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      Authors: Luke Baumann;H. M. Aktulga;Charles A. Macon;B. Shanker;
      Pages: 6858 - 6871
      Abstract: Recently, integral equation formulations that use potentials as opposed to fields as unknown quantities have been developed for scattering from dielectric objects. It has been shown that these formulations can be construed so that they are well-conditioned across a broad frequency spectrum, a result that has been theoretically proven for spherical systems. Unfortunately, to date, this formulation has not been implemented on practical discretizations of objects. This is the goal of this article. Specifically, we present a well-conditioned and well-tested decoupled potential integral equation (DPIE) formulation and all the necessary implementation details for electromagnetic scattering from homogeneous, dielectric, arbitrarily shaped objects. The resulting decoupled systems do not suffer from low-frequency breakdown. Results that demonstrate these properties are presented for a number of different dielectric targets. Furthermore, in order to fully validate each of the two integral equations for the potentials, we develop analytical solutions for spherical systems.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Switched Huygens Subgridding for the FDTD Method

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      Authors: John Hartley;Antonios Giannopoulos;Nigel Davidson;
      Pages: 6872 - 6882
      Abstract: The solution to finely detailed finite-difference time-domain (FDTD) models is often intractable due to the Courant–Friedrichs–Lewy (CFL) condition. Subgridding offers an attractive solution to this problem. In particular, the Huygens subgridding (HSG) exhibits great performance characteristics. It features high subgridding ratios and relatively small interfacing errors. However, late time instability reduces its utility. This article presents the switched Huygens subgridding (SHSG), a fundamental modification to the HSG that improves its stability. It is shown that the SHSG is at least $143 times $ more stable than the HSG for a 3-D subgridded half-wave dipole problem and at least $10 times $ more stable for a 1-D resonant subgridding problem. The SHSG runs $1.9 times $ faster per iteration (in the dipole experiment) since it does not require a PML in the subgrid to enhance stability. The accuracy of the SHSG is shown to be comparable with the HSG. Also, the fields in all overlapping regions are computed equal to the single space solution at all time steps simplifying the extraction of information in these regions. This new SHSG method is more straightforward to implement and optimize due to the simplicity of its proposed stabilization mechanism.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Analysis of Electromagnetic Scattering From Homogeneous Penetrable Objects
           by a Strong Skeletonization-Based Fast Direct Solver

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      Authors: Ming Jiang;Zhi Rong;Xiong Yang;Lin Lei;Pei Li;Yongpin Chen;Jun Hu;
      Pages: 6883 - 6892
      Abstract: This article presents a fast direct solver based on surface integral equation (SIE) to solve electromagnetic (EM) scattering from homogeneous penetrable objects. The proposed method relies on a strong admissibility skeletonization factorization (SASF) algorithm and Poggio–Miller–Chang–Harrington–Wu–Tsai (PMCHWT) formulation. In the SASF scheme, only well-separated groups that satisfy the strong admissibility condition are considered to be compressed and thus relatively fewer skeleton basis functions are selected. It is an effective way to compress the matrix with small ranks. An independent compression technique is developed for dielectric problems involving electric and magnetic currents, in which skeleton basis functions representing electric and magnetic currents are obtained separately. Moreover, a novel strategy based on matrix normalization is proposed to treat the arising “fill-in” blocks when far-field interactions are compressed. Ultimately, the impedance matrix can be cast into products of a series of block unit triangular matrices and a block diagonal matrix. Several numerical results show that the proposed approach is effective and stable as well as provides an accurate solution for scattering problems of homogeneous penetrable objects.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Iso-Geometric Integral Equation Solvers and Their Compression via Manifold
           Harmonics

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      Authors: A. M. A. Alsnayyan;B. Shanker;
      Pages: 6893 - 6904
      Abstract: The state of the art of electromagnetic integral equations has seen significant growth over the past few decades, overcoming some of the fundamental bottlenecks: computational complexity, low-frequency breakdown, dense-discretization breakdown, preconditioning, and so on. Likewise, the community has seen extensive investment in the development of methods for higher order analysis, in both geometry and physics. Unfortunately, these standard geometric descriptors are continuous, but their normals are discontinuous at the boundary between triangular tessellations of control nodes, or patches, with a few exceptions; as a result, one needs to define additional mathematical infrastructure to define physical basis sets for vector problems. In stark contrast, the geometric representation used for design is second order differentiable almost everywhere on the surfaces. Using these descriptions for analysis opens the door to several possibilities, and is the area we explore in this article. Our focus is on loop subdivision-based isogeometric methods. In this article, our goals are twofold: 1) development of computational infrastructure for isogeometric analysis of electrically large simply connected objects, and 2) introduction of the notion of manifold harmonic transforms and its utility in computational electromagnetics. Several results highlighting the efficacy of these two methods are presented.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Modeling of Metasurfaces Using Discontinuous Galerkin Time-Domain Method
           Based on Generalized Sheet Transition Conditions

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      Authors: Shaowen Tian;Kaiming Wu;Qiang Ren;
      Pages: 6905 - 6917
      Abstract: A new discontinuous Galerkin time-domain (DGTD) method based on generalized sheet transition conditions (GSTCs) for analyzing the transient response of electromagnetic metasurfaces is presented. The discontinuities in electromagnetic fields around the vicinity of the metasurface are modeled by placing virtual edges on both sides of the metasurface. The GSTCs are incorporated in the updating equations of the standard DGTD algorithm by integrating the time-domain GSTCs formula with Galerkin’ s-weighted residual method. The DGTD-GSTC formulation can also simulate a bf piecewise linear approximation of a curved metasurfaces due to the unstructured mesh. This is the first time that DGTD is applied to the simulation of GSTCs. The implementation of this new method is verified by numerical cases.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Method of Moment Analysis of Carbon Nanotubes Embedded in a Lossy
           Dielectric Slab Using a Multilayer Dyadic Green’s Function

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      Authors: Sumitra Dey;Deb Chatterjee;Edward J. Garboczi;Ahmed M. Hassan;
      Pages: 6918 - 6933
      Abstract: Modeling the electromagnetic response of carbon nanotube (CNT) reinforced composites is inherently a 3-D multiscale problem that is challenging to solve in real time for nondestructive evaluation (NDE) applications. This article presents a fast and accurate full-wave electromagnetic solver based on a multilayer dyadic Green’s function approach. In this approach, we account for the effects of the dielectric slab, where the CNTs are embedded, without explicitly discretizing its interfaces. Due to their large aspect ratios, the CNTs are modeled as arbitrary thin wires (ATWs), and the method-of-moment (MoM) formulation with distributed line impedance is used to solve for their coupled currents. The accuracy of the in-house solver is validated against the commercial MoM and the finite element method (FEM) solvers over a broad range of frequencies (from 1 GHz to 10 THz) and for a wide range of dielectric slab properties. Examples of 100 nm-long vertical and horizontal CNTs embedded in a 1 $mu text{m}$ -thick lossy dielectric substrate are presented. The in-house solver provides more than $50times $ speed up while solving the vertical CNT and more than $570times $ speed up while solving the horizontal CNT than a commercial MoM solver over the GHz-to-THz frequency range.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Spectrally-Accurate Analysis of EM Scattering by Material and
           Metamaterial, Isotropic or Anisotropic, Radially Inhomogeneous Spherical
           Objects

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      Authors: John L. Tsalamengas;
      Pages: 6934 - 6943
      Abstract: We study electromagnetic (EM) plane wave scattering by material and metamaterial radially inhomogeneous spherical objects that are either isotropic or uniaxially anisotropic with radial anisotropy. Using field representations in terms of scalar Hertz potentials, we reformulate Maxwell’s equations into two systems of first-order ordinary differential equations, which we then convert into equivalent second-kind linear Volterra matrix integral equations. The discretization scheme uses a high-order, entire domain, Nystrom method that employs the Gauss–Legendre–Radau quadrature rule. The proposed algorithms have spectral convergence and apply to either single-layer or multilayer structures with continuous or sectionally continuous profiles.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Fast O(N log N) Algorithm for Generating Rank-Minimized H2-Representation
           of Electrically Large Volume Integral Equations

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      Authors: Yifan Wang;Dan Jiao;
      Pages: 6944 - 6956
      Abstract: In this article, we propose a fast algorithm to generate a rank-minimized $mathcal {H}^{2}$ -representation for solving electrically large volume integral equations (VIEs). Unlike existing methods whose complexity is as high as quadratic, the proposed algorithm has linearithmic complexity, and thus, it can handle problems with large electrical sizes. Furthermore, the algorithm is purely algebraic and kernel independent. Numerical experiments on electrically large 3-D arrays of dielectric cubes having over 33 million unknowns demonstrate the efficiency and accuracy of the proposed algorithm.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • An Appraisal of Numerical Approaches for a VED Over the Earth or Ocean

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      Authors: Francisco Mesa;David R. Jackson;
      Pages: 6957 - 6972
      Abstract: The numerical solution of the classical Sommerfeld problem is thoroughly discussed in this work. In particular, the computation of the vertical electric field excited by a vertical electric dipole (VED) is taken as a paradigm to discuss some different approaches that have been proposed in the literature (with some new variations included). A detailed study is carried out on the pros and cons of each method as well as their range of numerical efficiency in terms of frequency, ground losses, height of the dipole, and distance to the observation point. We finally propose a numerical implementation of the steepest descent method as a good overall method in terms of accuracy, computational efficiency, and extended range of validity. Asymptotic closed-form expressions for the far-field region are also provided.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Estimating the Attenuation of ELF-Band Radio Waves in the Earth’s
           Crust by Q-Bursts

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      Authors: József Bór;Karolina Szabóné André;Tamás Bozóki;Janusz Mlynarczyk;Péter Steinbach;Attila Novák;István Lemperger;
      Pages: 6973 - 6982
      Abstract: Q-bursts are extremely low-frequency (ELF) wave packets spawned by exceptionally powerful lightning strokes. As the Earth’s surface bears finite conductivity, ELF-band radio waves can also be detected under the ground. Q-bursts detected in the magnetic field near the surface and at a depth of 140 m were compared to characterize signal attenuation in the Earth’s crust. The applied analysis incorporates data from permanent ELF measuring sites and the World Wide Lightning Location Network so that simultaneous surface and underground measurements were not needed. The analysis in the 2–140 Hz frequency band yielded $sim !70 ~Omega mathrm{m} $ bulk resistivity. The corresponding skin depths, 1470, 1100, and 920 m for the lowest three Schumann resonance (SR) modes at 7.8, 14.1, and 20.0 Hz, respectively, were found to decrease at a rate proportional to the inverse of the square root of the frequency. A well conductive clay-rich ground layer under the surface can explain the obtained relatively low resistivity compared to known values of local andesitic bedrock. Incorporating independently obtained near-surface ground resistivity values in the evaluation of magnetotelluric (MT) surveys is suggested to improve results for the upper crust layers. The advantages of using Q-bursts in surveying the properties of the Earth’s crust by electromagnetic (EM) methods are pointed out.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Scattering by Arbitrary Cross-Section Cylinders Based on the T-Matrix
           Approach and Cylindrical to Plane Waves Transformation

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      Authors: Jesús Rubio;Juan R. Mosig;Rafael Gómez-Alcalá;Miguel Ángel González de Aza;
      Pages: 6983 - 6991
      Abstract: Multiple scattering of parallel cylinders with arbitrary cross section is computed using the T-matrix of each single scatterer and the general translational matrix for cylindrical waves. Usually, the recommended golden rule to compute the translational matrix is Graf’s addition theorem. However, this approach cannot be properly implemented for some geometries, such as in a two-cylinder case when the center of one of them falls within the minimum circular cylinder that circumscribes the other one. In order to overcome this limitation, a transformation between cylindrical waves and plane waves, followed by propagation of the latter, is proposed. The new approach succeeds due to an adequate truncation of the evanescent plane wave spectrum. This strategy is demonstrated by studying the scattering of three infinite elliptic metallic cylinders for different electrical sizes and observing the convergence of the results as a function of the truncated spectrum. Finally, to conclusively show the interest and applicability of the approach, two more complex problems are treated: a group of infinite elliptic metallic cylinders where two different sizes are combined and a practical real-life filter in substrate integrated waveguide (SIW) technology, including several groups of rectangular dielectric cylinders.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Virtual Antenna Array With Directional Antennas for Millimeter-Wave
           Channel Characterization

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      Authors: Mengting Li;Fengchun Zhang;Yilin Ji;Wei Fan;
      Pages: 6992 - 7003
      Abstract: Millimeter-wave (mm-Wave) band channel modeling and characterization are essential for system design and analysis in the fifth generation (5G) and future communication systems. Reliable channel sounding in the deployment scenarios is required for accurate and realistic channel modeling and characterization. In the state of the art, directional scanning sounding (DSS) and virtual antenna array (VAA) sounding are two popular methods due to their simplicity and cost-effectiveness. The DSS and the VAA methods are typically based on mechanically rotatable directional antennas and mechanically movable omnidirectional antennas, respectively. However, the spatial resolution is limited by the directivity and high sidelobes of the directional antennas used in the DSS method. The conventional VAA method also has limitations in terms of the low signal-to-noise ratio (SNR) and the unavailability of suitable omnidirectional antennas that support mmWave (above 60 GHz) band measurements and wideband horizontal polarization measurements. In this article, a novel directional antenna-based VAA framework in combination with the associated beamforming algorithm is proposed. Compared to the state-of-the-art methods, the proposed framework can achieve high angular resolution and high SNR for mm-Wave channel measurements without introducing additional cost and measurement time. Furthermore, it is a generic solution that can be applicable for arbitrary frequency bands and polarizations, unlike the conventional VAA method. To validate the effectiveness and robustness of the proposed method, experiments in two scenarios (a clean anechoic chamber and a realistic indoor meeting room) were conducted over 28–30 GHz with two types of directional antennas (i.e., a horn antenna and a corrugated antenna). Besides, the advantages of the proposed method are highlighted with a comparison to the conventional VAA and DSS methods.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Quantized Tensor Train Method for High-Frequency Scattering Problems
           Involving Heterogeneous Dielectric Layers

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      Authors: Matthias Baray;David Levadoux;Jean-René Poirier;
      Pages: 7004 - 7010
      Abstract: We present a new numerical scheme to solve efficiently scattering problems involving an elongated and flat heterogeneous dielectric material assumed to be invariant along a direction of space. The technique consists of compressing the integral operators of an integro-differential formulation with a so-called quantized tensor train (QTT) algorithm whose use is rather original in this context. We show that it allows to compute and store operators with a notably small memory footprint while having at the same time a fast matrix-vector product (MVP) leading to a competitive method compared with the more classical $mathcal {H}$ -matrix approach.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Scattering Properties of Spherical Time-Varying Conductive Shells

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      Authors: Kurt Schab;Bradley Shirley;K. C. Kerby-Patel;
      Pages: 7011 - 7023
      Abstract: Harmonic generation in the scattered fields produced by a dielectric sphere coated with a time-varying conductive shell is studied using a Mie theory approach hybridized with conversion matrix methods. Analytic results are derived for plane wave incidence as well as general external excitation using transition matrix techniques. An equivalent transmission line approach is also discussed. Numerical examples validate the derived expressions through comparison with purely numerical methods and convergence characteristics are explored. Several additional examples illustrate unique trends in far- and near-field scattering.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Antenna De-Embedding Using Deconvolution With Tikhonov Regularization for
           mmWave Channel Measurement

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      Authors: Congle Ge;Ruonan Zhang;Yi Jiang;Lin Cai;Bin Li;
      Pages: 7024 - 7036
      Abstract: Antenna-free channel models can reflect real multipath propagation and can be applied widely for performance analysis, simulation, and physical emulation, combined with specific antennas used in the communication systems. However, the millimeter-wave (mmWave) channel measurement is usually performed by steering horn antennas, and the measured channel responses are actually spatial convolution of the channel propagation models and antenna pattern, which is commonly referred to as the antenna embedding effect. In this work, we propose a novel antenna de-embedding algorithm based on the deconvolution with Tikhonov regularization. By suppressing parts of the observed responses which are disguised by noise, the Tikhonov regularization facilitates the deconvolution of antenna pattern and enables the extraction of propagation models. In particular, in order to minimize the impact of deconvolved noise, we design an optimization algorithm to obtain the appropriate regularization factor with low computational complexity. To validate the proposed approach, we have performed an indoor mmWave channel measurement campaign using two different steering horn antennas. The principal peaks in the synthesized channel responses are accurately reconstructed, and the signal-to-noise ratio (SNR) is improved. The experiments verify that the proposed scheme de-embeds effectively the antenna effect and leads to the antenna-free channel models.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Efficient Yield Estimation of Multiband Patch Antennas Using NLPLS-Based
           PCE

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      Authors: Dieter Klink;Petrie Meyer;Werner Steyn;
      Pages: 7037 - 7045
      Abstract: For high-volume manufacturing, yield estimation is an important design step to determine the effects of uncertainties in the fabrication process. The tolerances associated with the fabrication process are applied to the statistically significant system parameters, and a Monte Carlo (MC) simulation is historically done to accurately estimate the yield. This process becomes computationally very expensive when the number of statistically significant system parameters are either too difficult to intuitively determine or are too high. A nonlinear partial-least-squares-based polynomial chaos expansion (NLPLSs-based PCE) is proposed as a solution for complex antenna yield analysis. NLPLS-based PCE effectively reduces the system dimensionality using NLPLS and simultaneously extracts the statistical information on the same sample set, that is, yield, using PCE. It is also possible to perform a global sensitivity analysis using NLPLS-based PCE surrogates, providing an additional advantage. This method is illustrated using an eight-variable single-frequency patch antenna, an eight-variable dual-band patch antenna, and a 37-variable diplexer requiring 30, 10, and 30 analysis points, respectively, to obtain converged yield estimates.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Efficient Secure Communication in 4-D Antenna Arrays Through Joint
           Space–Time Modulation

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      Authors: Kejin Chen;Shiwen Yang;Deqiang Yang;Yikai Chen;Shi-Wei Qu;Jun Hu;
      Pages: 7046 - 7056
      Abstract: Traditional directional modulation techniques always sacrifice the effective radiated power in order to produce the effect of directional modulation, thus resulting in low radiation efficiency and leading to low channel capacity or short transmission distance. Generally, a signal is first modulated at the baseband and then modulated again at the antenna. The two modulations are always regarded as two separate steps. Therefore, these directional modulation techniques fail to maximize their modulation efficiency, resulting in possible performance degradation. Aimed at this problem, this article proposed a novel secure transmission approach named joint space–time modulation (JSTM) for improving the transmission efficiency of secure communication by using 4-D antenna arrays. By selecting the appropriate modulation strategy, the space–time degrees of freedom are integrated and the signal modulation can be completed with high efficiency, thus being able to reduce the attenuation in the signal modulation process. The proposed approach is able to improve the overall gain of the 4-D arrays close to that of the phased arrays while ensuring good security performance. Numerical and experimental results demonstrate the effectiveness of the proposed approach.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Independent Component Analysis for the Multitag Detection of
           Frequency-Coded Chipless RFID

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      Authors: Wen-Sen Li;Cong-Zhi Peng;Fei-Peng Lai;Pin-Sung Lai;Yen-Sheng Chen;
      Pages: 7057 - 7072
      Abstract: A multitag detection technique is proposed for frequency-coded chipless radio frequency identification (RFID) to achieve minimum separations of tags, enhanced data capacity, and calibration-free features. Previous attempts for multitag detection include signal processing, comparisons with a database, and space-division multiple access (SDMA); nevertheless, these techniques rise to the challenges of large separations of tags, reduced capacity, and the complexity due to a phased array or beamforming technology, respectively. In contrast, the proposed technique overcomes these limitations by a new framework that integrates signal processing and SDMA. The capability is derived from the independent component analysis (ICA), which transforms mixing backscattering fields into an optimization model; by using the Newton method to maximize non-Gaussianity, the original resonances of each tag can be recovered. Furthermore, the proposed technique eliminates the procedure of calibration. An 8 bit system is designed and tested over 2.0–5.0 GHz. When two tags are separated by 0, 10, and 20 mm, ICA shows average reliability of 80.4%, 90.4%, and 91.5%, respectively. Thus, closely adjacent tags can be detected without calibration even for a high-density system. Real-world implementation issues, including four-tag detection, orientation mismatch, and a displacement of tags, are also analyzed to validate the proposed technique.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Feasibility Study of Quasi-Optical MIMO Antennas for Radiative Near-Field
           Links

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      Authors: Nuria Llombart;Shahab Oddin Dabironezare;
      Pages: 7073 - 7083
      Abstract: This article presents a feasibility study of single feed per beam quasi-optical (QO) antennas for enabling incoherent multiple-input multiple-output (MIMO) array front-end architectures at 270 GHz. The objective is to reach ultrafast and radiated energy efficient point-to-point (PtP) wireless links by exploiting the multimode capacity of radiative (Fresnel region) near-field links. In this article, we present a feasibility study of the number of independent links achievable with QO MIMO incoherent arrays. For this purpose, we present theoretical curves of the level of EM co-coupling and interference between the multiple modes versus the link distance. The study focuses at the 252–325 GHz spectral bandwidth defined by the new IEEE 802.15.3d standard. A specific and new MIMO array architecture operating at 270 GHz based on a $2 times 2$ array of parabolic reflectors is proposed for a link distance of 100 m. The proposed PtP MIMO system is capable of generating 16 dual-polarized modes in a 70 GHz bandwidth with signal-to-interference ratio >17 dB and a power co-coupling coefficient of −3 dB without the need for interference cancelation techniques. Combining this architecture with wideband front ends could potentially lead to an aggregated data rate in the order of terabit per second in a PtP wireless line-of-sight link, not previously achieved experimentally to the best of authors’ knowledge.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Achieving Wireless Cable Testing for MIMO Terminals Based on Maximum RSRP
           Measurement

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      Authors: Fengchun Zhang;Mengting Li;Xiang Zhang;Zhengpeng Wang;Wei Fan;
      Pages: 7084 - 7093
      Abstract: It is essential to perform end-to-end performance testing of multiple-input–multiple-output (MIMO) systems under realistic propagation channel conditions. However, due to the highly integrated and compact radio frequency (RF) system design, the traditional conducted cable testing method is getting more and more problematic. The wireless cable solution, which can achieve the equivalent functionality of the conducted cable testing without actual RF coaxial cables, has attracted huge attention from the industry and standardization for over-the-air (OTA) testing in recent years. However, the state-of-the-art solutions to achieve wireless cable testing necessitate at least reference signal received power (RSRP) reporting per device under test (DUT) antenna port for MIMO capable terminals, which is demanding and might not be accessible for commercial DUTs. In this work, a novel wireless cable solution based only on the maximum RSRP measurement of all DUT antenna ports is proposed, which can significantly alleviate the requirement of DUT RSRP reporting. To achieve the wireless cable testing, a novel calibration procedure is proposed to determine the transfer matrix between the probe antenna ports and the DUT antenna ports based on the DUT maximum reported RSRP measurement. The proposed algorithm is theoretically derived and experimentally validated for a $2times 2$ MIMO system, where the isolation of above 25 dB is achieved for the measurement setup. The numerical simulation and experimental validation demonstrate the efficiency and robustness of the proposed algorithm.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Multi-Antenna System for In-Line Food Imaging at Microwave Frequencies

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      Authors: Marco Ricci;Jorge A. Tobón Vasquez;Rosa Scapaticci;Lorenzo Crocco;Francesca Vipiana;
      Pages: 7094 - 7105
      Abstract: This work presents the design and numerical assessment of a novel microwave imaging (MWI) system, capable of providing a full 3-D image of food/beverage products content in order to disclose the possible presence of physical contaminants, such as plastic fragments. The system here presented exploits the dielectric contrast between the food content and possible intrusions at microwave frequencies; it is based on an antenna array architecture inspecting the items in motion along a conveyor belt without interrupting the production process. The inversion problem is solved by means of linearization, assuming the viability of the Born approximation thanks to the localized intrusions, and regularization, based on the singular value decomposition of the discretized scattering operator. Furthermore, an algorithm, to balance the illumination of the considered scenario due to the nonuniform radiation of the employed antennas, is presented to enhance imaging. The system is first assessed considering an ideal case and then extended to a more realistic approach, for two different kinds of food products, with completely different dielectric properties and considering the performance of existing instrumentation for the purpose. The obtained results lay the foundations for the realization of an actual prototype.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Compact Dual-Band Base-Station Antenna Using Filtering Elements

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      Authors: Sheng Jie Yang;Wen Duan;Yi Yang Liu;Hua Ye;Hua Yang;Xiu Yin Zhang;
      Pages: 7106 - 7111
      Abstract: This communication presents a compact dual-band dual-polarized filtering antenna for base-station applications. The proposed dual-band antenna consists of a high-band (HB) dipole element and a low-band (LB) patch element, both with filtering responses. The HB element is embedded into the LB element, minimizing the overall size. The strong mutual coupling between the HB and LB elements is reduced by employing filtering HB and LB elements. For demonstration, a prototype of the dual-band antenna operating at LTE band 41 (2.5–2.7 GHz) as well as LTE bands 42 and 43 (3.3–3.8 GHz) is fabricated and measured. The antenna features a compact size of 41 $times,,41$ mm2 ( $0.52,,lambda _{hh} ,,times0.52,,lambda _{hh}$ , where $lambda _{hh}$ denotes the guided wavelength at the highest frequency of HB). The cross-band isolation is higher than 27 dB without using extra filtering or decoupling circuits. In addition, a measured average gain of 7.8 dBi in LB and 7.7 dBi in HB is achieved. These merits make the proposed antenna suitable for 5G multiband aperture-shared array application.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Magnetoelectric Dipole Antennas Loaded With Meta-Lens for 5G MIMO Pattern
           Diversity Applications

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      Authors: Mehri Borhani-Kakhki;Abdolmehdi Dadgarpour;Marco A. Antoniades;Abdel R. Sebak;Tayeb A. Denidni;
      Pages: 7112 - 7117
      Abstract: This communication presents a unique design of a dual-polarized wideband passive beam-switching antenna at millimeter-wave (mm-wave) bands for multiple-input–multiple-output (MIMO) pattern diversity applications, which exhibits low correlation between the ports and a broad tilt bandwidth (BW). A magnetoelectric (ME) dipole fed by a printed ridge gap waveguide (PRGW) as a quasi-TE source is considered as the elementary antenna in the Ka-band. To achieve beam deflection in each quadrant, a four-port MIMO prototype consisting of four ME-dipoles, positioned perpendicular to each other, is integrated with a meta-lens that consists of three layers of $12times12$ dual-polarized split-ring resonators (SRRs) offset from the center of each antenna. The beamforming structure is able to generate four fixed beams, one in each quadrant at an elevation angle of $sim 40^{circ }$ with respect to the broadside direction by exciting each port sequentially, while the other ports are terminated. Moreover, the proposed orthogonal structure contributes to low correlation between the four ports, while achieving dual-polarization, which highlights the suitability of the antenna for 5G mm-wave applications. The measured results from a fabricated prototype demonstrate a −10 dB impedance BW of 40% over 24–36 GHz, tilting BW of 32.2%, and a peak gain of 13.4 dBi at 29 GHz, while an isolation better than 30 dB is achieved over the whole frequency band. Moreover, a measured radiation efficiency in excess of 85% is obtained, due to the use of the low-loss PRGW feedlines.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Wideband Monopole-Like Cup Dielectric Resonator Antenna With Coil Feeding
           Structure

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      Authors: Shuxin Zheng;Zhen-Yuan Zhang;Xiaoming Chen;Ahmed A. Kishk;
      Pages: 7118 - 7123
      Abstract: A wideband cup dielectric resonator antenna (CDRA) with a monopole-like mode is presented. A new coil feeding structure is used, creating an equivalent magnetic current loop above the ground plane, exciting the CDRA $textrm {TM}_{01 delta } $ mode and an equivalent electric dipole at the adjacent frequency band. Thus, a broad bandwidth is achieved from two adjacent resonances. A CDRA with $0.25lambda _{0} $ diameter and $0.23lambda _{0} $ height ( $lambda _{0} $ is the center frequency free-space wavelength) is fabricated and measured. About 29% of −10 dB matching bandwidth (2.98–4.00 GHz) is achieved. The structure has a low cross-polarization level and stable radiation patterns within the entire operating bandwidth.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Theory of Arbitrarily Oriented VLF Linear Antennas With Lumped Loadings in
           Ionospheric Plasma

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      Authors: Hui Ran Zeng;Tong He;Kai Li;
      Pages: 7124 - 7129
      Abstract: For very low frequency (VLF: 3–30 kHz) space-borne transmitting systems, the antenna loading technology provides a new technical scheme in boosting the antenna efficiency by optimizing its current distribution and input impedance. This communication studies the theory of VLF linear antennas applied with the lumped loadings in the ionospheric plasma. By considering the influences of ordinary and extraordinary waves and using Kirchhoff’s laws, the integral equation of the antenna under the effect of lumped loadings in an ionospheric plasma is derived and calculated by the method of moments (MoM). Calculations indicate that after loading capacitance, the overall current of the antenna increases while the input impedance decreases. It is also found that loading resistance and inductance will make the antenna current smaller. Theoretical results are compared with those simulated by commercial software, and the agreement demonstrates the validity of the approach. By comparing the input impedances of loaded and unloaded antennas, we observed that loaded antennas are more efficient than unloaded ones when the capacitance is appropriately deployed.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Experimental Realization of Silicon Micromachined Terahertz
           Diplexer-Antenna Module for Heterodyne Receiver

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      Authors: Hongda Lu;Zhipeng Liu;Pengfei Zhao;Yong Liu;Xin Lv;
      Pages: 7130 - 7135
      Abstract: A novel integrated silicon micromachined diplexer-antenna module for compact terahertz (THz) heterodyne receiver is proposed. The module is composed of a radio frequency (RF) antenna, a local oscillator (LO) antenna, and a waveguide diplexer which are realized by using the silicon micromachining technology and stacking nine equal-thickness layers. The corrugated conical horn antenna and quasi-diagonal horn antenna are applied as the RF- and LO-antenna, respectively. The diplexer is composed of two third-order waveguide bandpass filters and an H-plane T-junction, providing the isolated RF and LO channels. An experimental study is carried out in the 340 GHz band, demonstrating its application potential in THz heterodyne receiver element and array.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Four-Port Cylindrical Pattern- and Polarization-Diversity Dielectric
           Resonator Antenna for MIMO Application

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      Authors: Bing Zhang;Jian Ren;Yu-Xiang Sun;Ying Liu;Yingzeng Yin;
      Pages: 7136 - 7141
      Abstract: In this communication, a four-port cylindrical pattern-diversity and polarization-diversity dielectric resonator antenna (DRA) for multiple-input multiple-output (MIMO) applications is presented for the first time. The design utilizes two degenerate $mathrm {HEM}_{12 delta + 1 }$ modes and two degenerate $mathrm {HEM}_{21 delta }$ modes of the cylindrical DRA, with unidirectional radiation and quasi-omnidirectional radiation, respectively. The resonant frequencies of four modes can be predicted by the radar cross section characteristic of an isolated DRA. By optimizing the dimension of DRA and loading technology, the $mathrm {HEM}_{12 delta + 1}$ and $mathrm {HEM}_{21 delta }$ modes can operate in the same band. The $mathrm {HEM}_{12 delta + 1}$ modes are effectively excited by two polarization orthogonal slot pairs while two coaxial probes are utilized for exciting the $mathrm {HEM}_{21 delta }$ modes. The power divider with tapered end is presented to expand bandwidth of $mathrm {HEM}_{21 delta }$ modes. In addition, the method based on mode orthogonal to utilize two degenerate $mathrm {HEM}_{21 delta }$ modes with high isolation is proposed. To verify design, a four-port diversity DRA operating at 2.4 GHz band (2.4–2.48 GHz) was simulated, fabricated, and measured. The S parameters and radiation characteristics were measured and discussed. Moreover, the c-lculated indoor communication performance including the envelop correlation coefficient (ECC), mean effective gain (MEG), and channel capacity as the proposed four-port DRA used for MIMO element are given and discussed.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Method to Evaluate the Performance of Ultra-Wideband Antennas for the
           Radiation of High-Power Electromagnetic Pulses

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      Authors: Shao-Fei Wang;Yan-Zhao Xie;
      Pages: 7142 - 7146
      Abstract: In this communication, a time-frequency joint method is proposed to evaluate the performance of ultrawideband (UWB) antennas for the radiation of high-power (HP) electromagnetic pulses. First, conventional antenna parameters, such as the efficiency, gain, and so on, are translated to UWB pulsed antennas from the energy perspective, so as to get several scalar antenna parameters, since energy in one pulse is finite. Thus, the power-spectrum weighted efficiency ( $eta _{e}$ ), directivity ( $D_{e}$ ), and gain ( $G_{e}$ ) are proposed. Then, several electromagnetic norms of the radiating pulse are selected to characterize the sensitive parameters of the equipment under test (EUT). Based on these, several other scalar antenna parameters are proposed, which are the effective potential gain ( $G_{ep}$ ), pulse sharpening factor (PSF), and peaking impulse gain ( $G_{PI}$ ). Thus, a set of time-domain scalar criteria are proposed to evaluate the performance of HP-UWB antennas. These criteria can be calculated with the frequency functions of conventional antenna parameters, which demonstrate the inherent properties of one antenna. Finally, the performance of two kinds of typical HP-UWB antennas, namely the impulse radiating antenna and the combined antenna, is measured and compared with the proposed method. It indicates that, with the proposed method, one can not only get the inherent properties of one antenna in the frequency domain but also quantitatively compare the performance of different antennas with a given exciting pulse in the time domain with the proposed scalar antenna parameters.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Circularly Polarized Dielectric Resonator Antenna Based on
           Quasi-Self-Complementary Metasurface

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      Authors: Ge Zhao;Yi Zhou;Jing Rui Wang;Mei Song Tong;
      Pages: 7147 - 7151
      Abstract: In this communication, a circularly polarized (CP) dielectric resonator antenna (DRA) based on quasi-self-complementary metasurface (MS) has been proposed. Due to the quasi-self-complementary characteristic of the proposed MS, the phase difference of the transmission coefficients between two orthogonal linear polarizations is 90° in the frequency band from 25.5 to 26.5 GHz. The DRA with the proposed MS can realize the transformation from linear polarization to circular polarization at 25.6–25.99 GHz. The proposed MS significantly increases the gain and CP bandwidth of the DRA. The working bandwidth of the proposed antenna is included in the New Radio FR2 frequency band totally, which is considered as the follow-up expansion frequency of fifth-generation (5G) communication. The proposed MS-based antenna has realized the linear-to-circular polarization transformation in millimeter frequency band without additional substrate, which has not been researched yet.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Low-Profile, Electrically Small, Ultrawideband Antenna Enabled With an
           Inductive Grid Array Metasurface

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      Authors: Qingli Lin;Ming-Chun Tang;Xiaoming Chen;Da Yi;Mei Li;Richard W. Ziolkowski;
      Pages: 7152 - 7157
      Abstract: A low-profile, electrically small, ultrawideband (UWB) antenna enabled with a grid array metasurface is presented. The design incorporates a driven dipole, an electric near-field resonant parasitic (NFRP) element, and a grid array structure which operates as an inductive metasurface. The NFRP element is an Egyptian axe dipole (EAD) that is excited by the driven dipole. This combination itself is an electrically small NFRP dipole antenna. In contrast to previous versions, its operation in both its first and third resonant modes is established. The presence of the grid, which consists of identical interconnected rectangular loops, then provides a new dipole mode and facilitates the reduction of the frequency ratio of the NFRP dipole’s modes. The resulting overlap of these three resonant modes yields the UWB operation. The electrically small (ka = 0.92), low-profile ( $0.003lambda _{0}$ ) antenna exhibits uniform radiation patterns and stable and high radiation efficiency (RE) performance characteristics. The antenna was optimized, fabricated, and tested. The measured results, in good agreement with their simulated values, demonstrate that the antenna yields an ultrawide, 67.7%, −10 dB impedance bandwidth with stable realized gain (RG) values, ~1.6 dBi, and high RE values, RE >77%, over its entire operational bandwidth.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Fully Metallic Glide-Symmetric Leaky-Wave Antenna at Kₐ-Band With
           Lens-Augmented Scanning

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      Authors: Xianliang Zeng;Qiao Chen;Oskar Zetterstrom;Oscar Quevedo-Teruel;
      Pages: 7158 - 7163
      Abstract: A fully metallic leaky-wave antenna (LWA) with enhanced scanning rate is presented. The leaky waveguide is implemented in groove gap waveguide technology and is periodically loaded to produce backward radiation. Furthermore, glide-symmetric pins are placed inside the leaky waveguide to increase the dispersion. A parallel-plate waveguide metasurface prism lens is used to disperse the backward radiation and increase the scanning rate of the LWA. The designed antenna can steer the radiation from −26° to 26° from 27 to 35 GHz, and an average total efficiency of 74% is achieved. A prototype of the designed antenna is manufactured, and measurements corroborate the simulated results. The proposed concept is applicable to other frequency-scanning antennas and can be used to increase the scanning rate in radar and imaging systems.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Feed Mismatch Due to Reflectors Revisited

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      Authors: Trevor S. Bird;
      Pages: 7164 - 7168
      Abstract: An expression for the reflection coefficient in a feed resulting from scattering from a neighboring reflector is derived from the reaction theorem. This expression includes the influence of an external interfering source as well. An asymptotic formula for this reflection coefficient is derived, which simplifies for an arbitrary shaped symmetrical reflector. This formula is shown to be accurate to second order. For a paraboloid, this is identical to the one derived originally by Silver (1949) except for an additional 180° phase factor. The results are given for a parent parabola, one loaded with a cone at its vertex and another for a reflector that is shaped to minimize reflection while maintaining efficiency over a 20% bandwidth. The effect of an interfering on- axis source on the mismatch is described through an asymptotic approximation.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Wideband Polarization Agile Dielectric Resonator Antenna With
           Reconfigurable Broadside and Conical Beams

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      Authors: Yuan Ji;Lei Ge;Yujian Li;Jianpeng Wang;
      Pages: 7169 - 7174
      Abstract: A new broadside and conical beam reconfigurable dielectric resonator antenna (DRA) with three orthogonal linear polarizations (LPs) and two orthogonal circular polarizations (CPs) agility is presented. It consists of a quad-strip-fed DRA element and a reconfigurable feeding network. First, the DRA element is designed to make unidirectional ${mathrm{HEM}}_{11 delta }$ mode and omnidirectional ${mathrm{TM}}_{01 delta }$ mode operate in the same wide band by tactfully removing a concentric annular column from its interior. Furthermore, a center-loaded metal post helps to improve the impedance matching of the ${mathrm{TM}}_{01 delta }$ resonance significantly. Afterward, the switchable feed network is designed to implement diverse phase distributions of four output ports, i.e., providing the quad-port in-phase excitation, dual-port differential excitations, and quad-port sequentially rotated phase excitation strategies for a vertical LP, ±45° slant horizontal LPs, and two CPs, respectively. Finally, a fully functional prototype is designed, fabricated, and measured to validate the design. The measured results show that the overlapping impedance bandwidth of 36.8% for all the states and the axial-ratio bandwidth of 33.8% for the CPs are obtained.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Multifunctional Low-Profile Fabry–Perot Resonator Antenna
           Integrated With Solar Cells

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      Authors: Zhen-Guo Liu;Chao Zhang;Ren-Jie Yin;Wei-Bing Lu;
      Pages: 7175 - 7180
      Abstract: A novel multifunctional low-profile Fabry–Perot resonator (FPR) antenna integrated with solar cells (SCs) is proposed in this communication. It is mainly composed of a transparent partially reflective surface (PRS), a patch radiator, and an artificial magnetic conductor (AMC) made of SCs array. On the upper layer, the PRS is made of the transparent copper microgrid to perform the function of partial reflection as well as ensure that sufficient solar energy can be captured by the SCs. Here, the SCs array acting as AMC can reduce the profile of the FPR antenna, on the other hand, it can collect solar energy and convert it into direct current (dc) power to provide energy supply of the device. Through this design, the SCs and FPR antenna are well combined compatibly together. The proposed antenna is fabricated and verified, the measured results demonstrate that the proposed multifunctional FPR antenna has a realized gain of 11.5 dBi with high aperture efficiency of 58.3% and a good low-profile characteristic (approximately $lambda _{0}$ /6). The measured output power of SCs can reach to 600 $mu text{w}$ . The work proposed in this communication illustrates the multifunctional requirements of antenna with high radiation properties, low profile, and the capability of power harvesting, simultaneously. It may be a good scheme for self-powered occasions, such as outdoor and satellite communication devices.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Low-Profile High-Gain Endfire Antenna With Circular Polarization

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      Authors: Shangkun Ge;Qingfeng Zhang;Amir K. Rashid;Yujie Zhang;Ming Yu;Ross Murch;
      Pages: 7181 - 7186
      Abstract: A circularly-polarized (CP) traveling-wave endfire antenna featuring low profile, high gain, and simple feeding structure is presented in this communication. Offset parallel strips with proper dielectric loading are employed in a low-profile substrate to achieve two orthogonal electric field components with equal magnitude and 90° phase difference for CP endfire radiation. Meanwhile, periodic phase-loading technique is used to achieve a proper phase constant for high endfire gain. A prototype is designed and fabricated to verify the proposed method. Experimental results demonstrate CP endfire radiation within a frequency band of 9.78–10.09 GHz. The average endfire gain is 10.3 dBic with an average efficiency of 62.5%.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Longitudinally Miniaturized H-Plane Horn Antenna With −30 dB Sidelobes
           Realized by Simple Blocks Redistributing the Aperture Field

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      Authors: Jing-Ya Deng;Rui-Qing Luo;Wei Lin;Yin Zhang;Zhijiao Chen;Li-Xin Guo;
      Pages: 7187 - 7192
      Abstract: A longitudinally miniaturized H-plane horn antenna with suppressed sidelobes by redistributing the field on the radiating aperture is proposed by loading a few rectangular blocks. The substantial longitudinal length reduction (around 50% of an optimal horn) will cause a nonuniform phase and nontapering magnitude distributions of the electric fields on the horn aperture, resulting in high sidelobes and decreased gain. Four pairs of rectangular blocks perturbing the fields are loaded near the radiating aperture, realizing a field redistribution for a tapered magnitude distribution and relatively uniform phase distribution on the aperture. Thus, the sidelobes are noticeably reduced to lower than −30 dB, and 10.6 dBi average gain in the frequency band of 10.5–15 GHz is achieved. A prototype of the proposed miniaturized H-plane horn antenna is manufactured and measured, and good agreements between the measured and simulated results are obtained. The proposed miniaturized H-plane horn has two advantages over other reported miniaturized horn antennas: 1) simple geometry resulting in easy fabrication and low cost and 2) −30 dB ultralow sidelobe level (SLL).
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Enhanced-Stopband Dual-Polarized Filtenna Without Extra Circuit for Tile
           Array Applications

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      Authors: Weiheng Chen;Zhiqiang Yu;Xuan He;Jianyi Zhou;Wei Hong;
      Pages: 7193 - 7198
      Abstract: In this communication, a dual polarized (DP) stacked patch filtenna (filtering antenna) with a wide stopband is developed for tile array applications. The bandpass filtering property is realized by improving the feeding network and patch without adding extra bandpass circuit or size. An elaborate feeding structure with complementary pair of a short-circuited stub and an open-circuited stub (CSSOS) is developed, which generates two transmission nulls effectively enhancing the selectivity and suppressing the harmonic. Moreover, CSSOS has a small size and broadens the impedance bandwidth apparently by introducing an in-band resonance. By properly etching four U-shaped slots on the driven patch, a radiation null in the upper stopband is also generated. The nulls generated by the two approaches can be adjusted independently in wide ranges. For further harmonic suppression, bandstop striplines (BSSs) with ultralow insertion loss are developed. Measured results show that the filtenna performs a wide operating band (3.10–3.95 GHz) and a wide stopband up to 8 GHz with a rejection level higher than 16 dB. Besides, a 32-element tile phased array employing the filtennas is also fabricated and measured. A compact configuration, high selectivity, and good beam steering capacity are exhibited.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Compact, Broadband, Monopole-Like Endfire Antenna With Reconfigurable
           Patterns for 5G Applications

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      Authors: Zhan Wang;Shuxuan Liu;Yuandan Dong;
      Pages: 7199 - 7204
      Abstract: This communication presents a novel compact, broadband, monopole-like endfire antenna with reconfigurable radiation patterns for 5G applications. Based on the mirror principle, a half-size monopole-like endfire structure with a wideband response is firstly proposed and analyzed. By switching the ON/OFF states of p-i-n diodes embedded in the passive stub lines, the monopole-like endfire structure achieves omnidirectional and endfire beam switching. Since the structure has a stable and broadband frequency response, a novel flexible pattern diversity antenna with omnidirectional coverage and directional scanned radiation is easily implemented by loading multiple stub lines. To validate the working principle, a nine-mode pattern reconfigurable antenna with a compact size of $0.31,,lambda _{0},,times ,,0.31,,lambda _{0},,times ,,0.19,,lambda _{0}$ ( $lambda _{0}$ is the free space wavelength at 3.75 GHz, radiator only) is designed and fabricated. The measured overlapped −10 dB impedance bandwidth for the nine modes is from 3.30 to 4.20 GHz (>24.0%), which well covers the 5G N77/N78 band. Besides, their measured gain is greater than 4.0/5.30 dBi. The proposed antenna has the merits of a compact size, simple design, wideband, good radiation performance, and flexible multibeam switching capacity. It is a good candidate for 5G new radio and other sub-6 GHz applications.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Frequency-Reconfigurable Circularly Polarized Omnidirectional Antenna

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      Authors: Ken Paramayudha;Shengjian Jammy Chen;Withawat Withayachumnankul;Christophe Fumeaux;
      Pages: 7205 - 7210
      Abstract: A concept of frequency-reconfigurable circularly polarized (CP) antenna with omnidirectional radiation characteristics is introduced. The antenna is based on a center-fed circular patch with shorting vias, surrounded by three arc-shaped arms. Omnidirectional CP is attained through its two orthogonal radiators with a quadrature phase difference. Three varactor-loaded meandered slots are etched onto the top patch to miniaturize the antenna and empower it with reconfigurability. The resonance frequency of the vertically and horizontally polarized modes can be simultaneously tuned by varying the bias voltage applied to the varactors, and thus frequency-reconfigurable CP is achieved. The realization demonstrates a wide CP tuning range of 28.5% from 3.55 to 4.73 GHz. Stable omnidirectional patterns in the azimuth plane are achieved across the tuning range. All these results suggest that the antenna is suitable for communication systems that require an omnidirectional CP antenna with a frequency-tunable feature.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Shorted Trapezoidal SIW Antenna With Quasi-Hemispherical Pattern for 2D
           Wide Scanning Planar Phased Array Antenna

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      Authors: Hyunyoung Cho;Hye-Won Jo;Jeong-Wook Kim;Kwang-Seok Kim;Ju-Ik Oh;Jong-Won Yu;
      Pages: 7211 - 7216
      Abstract: This communication presents a shorted trapezoidal substrate integrated waveguide (SIW) antenna with a quasi-hemispherical pattern composed of a 64-element (8 $times $ 8) 2-D planar phased array. The proposed low-profile SIW antenna is analyzed in terms of resonating mode and magnetic current and is simulated. The proposed antenna is composed of a trapezoidal patch and shorting vias. The upper side of the trapezoid is the shorting wall, and the middle of the bottom side provides shorting with a via. The resonance produced by the structure causes the magnetic currents to have three different directions. Hence, the single element has a quasi-hemispherical beam pattern on a large ground. The 64-element (8 $times $ 8) 2-D planar phased array was implemented and measured. Because the constituent elements have a quasi-hemispherical pattern, the phased array antenna has a wide scanning range in all azimuth directions. The measured scanning range with 5 dB gain fluctuation in the $phi = 0^circ $ plane, $phi = 45^circ $ plane, and $phi = 90^circ $ plane are 170°, 143°, and 168°, respectively.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Design of an Air-Filled Slot Antenna and Array for Millimeter-Wave
           Applications

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      Authors: Qing-Yi Guo;Hang Wong;
      Pages: 7217 - 7222
      Abstract: This communication introduces a new structure of wideband slot antenna with high gain and stable radiation patterns for millimeter-wave (mmW) applications. It is the first attempt to apply an air-filled I-shape slot excited by a substrate-integrated-waveguide (SIW) feed. The slot can achieve lower $Q$ -factor contributing to a wider bandwidth. In addition, the feature of even electric field distributions across the operating bandwidth produces very stable gain performance for the proposed antenna. The proposed antenna is realized using a single-layered PCB substrate with plated-through-hole technology, which is cost effective and easy to fabricate. In addition, a $1times8$ antenna array based on the proposed antenna element is developed with a planar 1–8 SIW feeding network. The measurement results show that the proposed array can achieve an impedance bandwidth of 36.6% from 58 to 84 GHz with a peak gain of 16 dBi. These performances ensure that the proposed antenna array is a promising candidate for mmW communications.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Multifunctional Drone-Based Antenna for Satellite Communication

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      Authors: Saman Zarbakhsh;Abdel R. Sebak;
      Pages: 7223 - 7227
      Abstract: This communication presents a drone-to-satellite beam-forming antenna with multifunctional purposes. A glass material with a gradient coating configuration is exploited to realize a transparent structure. Beam tilting is obtained by controlling the phase distribution of an antenna by means of an inexpensive and passive surface. Simultaneously, solar cells are implemented on the proposed structure for solar energy harvesting using the transparency feature of the surface. The sputtering physical vapor deposition process is used to layer a thin coat of indium tin oxide (ITO) onto the glass. A conceptual beam tilting with a multipurpose design is introduced for drone2sat communication and energy harvest. The proposed communication structure works at a frequency of 3 GHz and covers a 60° spatial beamwidth. The directivity and propagation characteristics are preserved by this configuration. To validate the design performance, a prototype has been fabricated and a satisfactory agreement between the numerical results and experimental ones is achieved. The proposed structure can enhance the multifunctional designs, which could offer advantages for real-world space drone communications.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Design of Coupled-Resonator Array Antenna for Steering Beam With Extremely
           High Scanning Rat

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      Authors: Hongxin Zhou;Yujie Zhang;Qingfeng Zhang;Ming Yu;Hong Wang;Ross D. Murch;
      Pages: 7228 - 7233
      Abstract: An extremely high scanning-rate beam-steering antenna based on coupled resonators is proposed in this communication. Coupling resonators in a controlled manner provides a sharp phase variation across a narrow frequency band, which contributes to the extremely high scanning rate. To steer the beam across broadside, alternating +90° and −90° impedance inverters are employed in the topology. Such a coupled-resonator array antenna is modeled and analyzed by coupling matrix technique, which was conventionally used in filter design. To illustrate the proposed technique, two examples with 50 and 100 MHz bandwidths are designed. Experimental validation is also provided for the 50 MHz bandwidth example, which demonstrates that the proposed antenna reaches a high relative scanning rate of $52.8^{circ }/%BW$ with efficiency of 75%.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Model Construction, Theoretical Analysis, and Miniaturized Implementation
           of High-Order Deflected Multivortex Beams With Uniform Elliptical Array

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      Authors: Hao Xue;Ruijie Li;Peng Xu;Haixia Liu;Long Li;
      Pages: 7234 - 7239
      Abstract: This work proposes a miniaturized uniform elliptical array (UEA) to generate high-order multivortex beams with mixed orbital angular momentum (OAM) modes in different directions. First, the construction method of the UEA model is proposed, and different miniaturized UEA models are designed to generate multivortex beams. On this basis, the UEA and uniform circular array (UCA) models are compared, and the modified radiation pattern product theorem is proposed to design high-order deflected vortex beams with fewer elements. Then, a miniaturized elliptical ring patch antenna is analyzed according to the theory of characteristic modes at 5.8 GHz. Finally, a miniaturized UEA is constructed by the miniaturized patch antennas under the guidance of the proposed UEA model and the modified radiation pattern product theorem. The UEA with four elements and corresponding feed networks generates four vortex beams with different directions and mixed modes, including the OAM modes of ±2. The designed device can generate high-order deflected multivortex beams by significantly reducing the number of elements to reduce system complexity and cost. The vortex beams with different directions and mixed modes expand the coverage of the vortex beams and provide the possibility for high-capacity OAM radio frequency communication.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Compact Omnidirectional Parabolic Shape Tilted Dipole Array With
           Improved Axial Ratio Bandwidth

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      Authors: Hao-Liang Chen;Yu-Zhi Chen;Yi-Fan Xiong;Jiang Xiong;
      Pages: 7240 - 7245
      Abstract: Current omnidirectional circularly polarized (CP) antennas meet the difficulty of limited bandwidth and bulky configuration. An exact analytical far-field solution for a conventional tilted dipole array (TDA) has been proposed, where the origin of axial ratio (AR) bandwidth limitation has been investigated. Then, it has been shown that the AR bandwidth can be efficiently improved when a conventional straight dipole is folded into a multi-segment one, where the deviation of two perpendicular far-field components, $E_{theta }$ and $E_{phi }$ , can be reduced at both the lower and higher frequencies. The dipole was further modified to be of a parabolic shape, a continuous and optimized variation for the multisegment one, which brings about an even wider AR bandwidth. For a compatible wide impedance bandwidth, several impedance matching techniques like radiator tapering, parasitic loading, and feeding network design have been applied. Measured results show the proposed TDA has a 3 dB AR bandwidth (also the antenna usable bandwidth) of 65%, within which the desired omnidirectional radiation is well maintained. Compared with the performances of some recent omnidirectional CP antennas, our design has a much wider usable bandwidth, and is also superior in the compact size, simple structure, and ease of fabrication.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • High-Gain 100 GHz Antenna Array Based on Mixed PCB and Machining Technique

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      Authors: Wenjie Feng;Xiaoyu Ni;Ruilian Shen;Hui Wang;Zhiyu Qian;Yongrong Shi;
      Pages: 7246 - 7251
      Abstract: A W-band 8 $times $ 8 slot-enhanced antenna array with high gain and high aperture efficiency is proposed based on the mixed printed circuit board (PCB) and machining technique. The antenna array consists of 16 2 $times $ 2 antenna subarrays. The substrate-integrated waveguide (SIW) cavity is used to feed the antenna subarray, where electromagnetic fields distribute in the TE220 mode. The SIW cavity is fabricated by the PCB technology for low cost, low profile, and lightweight. To reduce the loss of the feeding network, a constant-amplitude in- phase power divider based on ridge gap waveguide (RGW) is adopted to feed the SIW subarray using the machining technique. Besides, the standard WR-10 waveguide to the RGW transition structure is designed for measurement. The entire antenna array is integrated and packaged in a metal box. The measured results show that the impedance bandwidth of the antenna array is 97.8–107 GHz with a reflection coefficient lower than −10 dB. Within the impedance bandwidth, the antenna array gain is higher than 24.0 dBi, and the peak gain is 26.5 dBi. Moreover, an aperture efficiency of the antenna is larger than 75%.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Design of Filtering Dielectric Resonator Antenna Arrays Using Simple
           Feeding Networks

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      Authors: Chen Xi Zhao;Yong Mei Pan;Guo Dong Su;
      Pages: 7252 - 7257
      Abstract: A 1 $times $ 3 filtering dielectric resonator antenna (DRA) array is investigated in this communication. The central DRA is excited by a microstrip-coupled slot, while the two side DRA elements are, respectively, excited by the central DRA via a low-profile patch-loaded dielectric bridge laid between them. In order to integrate the filtering function, the open stub of the microstrip feed line is elaborately designed to generate a radiation null at the upper band edge, while two vertical metallic strips are added onto the sidewalls of the central DRA to provide another radiation null at the lower band edge. On the other hand, in order to achieve an enhanced gain in the operating passband, the higher order TE113 mode of the DRA elements is excited. It is found that due to the loading effects of metallic patches and conformal strips, three stepping resonances of the TE113 mode are generated in the passband, leading to a wide impedance bandwidth of 13.7% and a stable gain of 11.4 dBi. As a result, both good radiation and filtering performance are achieved without requiring complex filtering circuits. To demonstrate the extensibility of the array, a larger 3 $times $ 3 filtering DRA array with a high peak gain of 14.7 dBi is further designed by just using a three-way power dividing network.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A D-Band Corporate-Feed Gap-Cavity Slot Array Antenna Using Virtual PEC
           Method

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      Authors: Teng Li;Akanksha Bhutani;Thomas Zwick;
      Pages: 7258 - 7263
      Abstract: A D-band corporate-feed gap-cavity slot array is proposed with wide bandwidth and high aperture efficiency. The cavity with higher order modes is implemented by using the gap waveguide (WG) technology, namely, a gap cavity. To ensure that the gap cavity is operating with the desired higher order mode over a wide bandwidth, the corporate-feed architecture is applied for uniform excitation and with alternating-phase between adjacent slots. The gap cavity is split into multiple elements by using zero-thickness virtual perfect electric conductor (PEC) walls. With this unique approach, the design, fabrication, and assembly complexities are reduced. For experimental verification, a gap cavity with an 8 $times $ 8 slot array is designed in the 120 GHz band, and an E-plane WG feeding network is proposed to excite the TE880-mode. Two metal fences are introduced on either side of the radiating slot, and an inductive metal pin is introduced below the radiating slot to improve the radiation performance and broaden the bandwidth. The measured impedance matching bandwidth is around 110–144.8 GHz (27.3%). The measured peak gain is 26.22 dBi at 137.64 GHz, and the measured peak aperture efficiency is 86.2% at 115.325 GHz. The 3 dB gain bandwidth is the same as the impedance matching bandwidth.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Scanning Angle Extension of a Millimeter-Wave Antenna Array Using
           Electromagnetic Band Gap Ground

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      Authors: Luyu Zhao;Yuqi He;Ge Zhao;Xiaoming Chen;Guan-Long Huang;Wei Lin;
      Pages: 7264 - 7269
      Abstract: A compact phased array with extended beam steering characteristics for the millimeter-waveband of the fifth-generation (5G) applications is presented in this communication. An E-shaped patch antenna placed on an electromagnetic bandgap ground (EBGG) with operating bandwidth of 24.2–27.5 GHz is used as the basic building block of the eight-element linear array. The array utilizes both the in-phase reflection characteristic for broad element radiation pattern and the bandgap characteristic for mutual coupling reduction for limited inter-element spacing of the proposed array. The existence of the EBGG enables a compact array with the inter-element spacing of around 0.4 wavelengths at the center frequency, yet the isolation between each element is still above 17 dB within the whole band of interest, which also helps to increase the array directivity at large scanning angles. The scanning angle of the array with the electromagnetic bandgap (EBG) structure ranges from −75° to 75° at 26 GHz within 3 dB scanning loss. The proposed EBGG extends the antenna array’s spatial coverage and enables a compact size of the array, which is very attractive for 5G millimeter-wave (mm-wave) application.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Broadband Millimeter-Wave Endfire Circularly Polarized Array With a
           Low-Profile Feeding Structure

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      Authors: Yingrui Yu;Zhi Hao Jiang;Jin-Dong Zhang;Wen Wu;
      Pages: 7270 - 7275
      Abstract: In this communication, a broadband endfire circularly polarized (CP) antenna with a low-profile feeding structure is proposed for millimeter-wave (mmW) applications. The array element consists of a horizontally oriented printed electric dipole and a vertically aligned tapered slot radiator, exciting two orthogonal radiated electric-field components simultaneously. The amplitude and phase relationships between these two field components can be adjusted by balancing the response of the tapered slot and dipole radiators, thereby producing a CP radiated wave. Importantly, a parasitic director is introduced near the printed dipole to compensate for the gain degradation of the dipole element at higher frequencies, thus significantly expanding the axial ratio (AR) bandwidth of the CP element. Compared with other reported endfire CP antennas, the proposed antenna owns a lower profile of feeding substrate (0.508 mm $sim 0.056~lambda _{0}$ ), making it amenable for convenient integration with planar front-end circuits. As a demonstration, a $1times8$ array prototype is designed and measured, exhibiting an impedance bandwidth of 42.1% (27.45–42.1 GHz) and a 3 dB AR bandwidth of 35.8% (27.5–39.5 GHz). The demonstrated CP array is a promising candidate for wideband mmW applications due to its advantages of wideband, ease of integration with planar circuits, and low fabrication cost.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Wide-Angle, Ultra-Wideband, Polarization-Independent Circuit Analog
           Absorbers

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      Authors: Zhixin Yao;Shaoqiu Xiao;Yan Li;Bing-Zhong Wang;
      Pages: 7276 - 7281
      Abstract: In the analysis of most circuit analog (CA) absorbers, it is only the absorption performance under normal incidence that is taken seriously, leading to a much worse absorption with the increase of incident angle, especially when it is larger than 30°. In this communication, a novel absorber, which consists of a conductive square-loop (SL) array embedded with lumped resistors and a well-designed wide-angle impedance matching (WAIM) layer, is proposed. Equivalent circuit (EC) and strict formula derivations are introduced to present a great insight into the deterioration of absorption performance under oblique incidence and the effect of WAIM layer. An absorber sample is further fabricated and measured for verification. It is shown through measurement that the structure has a fractional bandwidth of 137.1% for at least 10 dB reflection reduction under normal incidence. When the incidence angle is increased to 45°, the overlapped bandwidth for both transverse electrical (TE) and transverse magnetic (TM) polarizations is still measured to be 110.5%.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Second-Order, Single-Band and Dual-Band Bandstop Frequency Selective
           Surfaces at Millimeter Wave Regime

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      Authors: Soumik Dey;Sukomal Dey;Shiban K. Koul;
      Pages: 7282 - 7287
      Abstract: This communication presents the miniaturized low-profile second-order (SO) bandstop frequency selective surfaces (FSSs) for single- and dual-band resonances. The unit cell comprises two identical first-order (FO) elements in a back-to-back configuration with the metal grid in between. Two thin dielectric substrates separate the three metal layers. The proposed FO unit cell consists of intercell-connected spiral resonators (SRs) with capacitively coupled cross loop dipole. The SO filter response of the proposed FSS exhibits a wide stopband ( $S_{21} < -10$ dB) bandwidth (BW) of 27.6%. The unit cell has the periodicity of $0.162lambda _{0}$ , where $lambda _{0}$ is the free space wavelength at the lower passband. The novelty of the proposed work is a miniaturized simple unit cell geometry, at the millimeter-waveband but not limited to it, with polarization insensitive and high angular stable filter response up to 60° with small variations in the BW. An unconventional four-unit cell element FSS is designed for dual-band SO stopband resonances with the BWs of 8.3% and 13.8%. Prototypes of both FSSs were fabricated and their measured results were found consistent with the simulated filter responses.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Extremely Wideband and Omnidirectional RCS Reduction for Wide-Angle
           Oblique Incidence

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      Authors: Meijun Qu;Chenyang Zhang;Jianxun Su;Jinbo Liu;Zengrui Li;
      Pages: 7288 - 7293
      Abstract: In this communication, a novel metasurface with multiple unit cells of different thicknesses based on optimized multielement phase cancellation (OMEPC) is proposed for extremely wideband, omnidirectional, and polarization-independent radar cross section (RCS) reduction under wide-angle oblique incidence. Omnidirectional characteristic refers to the capability of RCS reduction under all azimuth angles ( $varphi ^{i}$ ) at certain elevation angles ( $theta ^{i}$ ). The equivalent circuit model of the square patch unit cell is analyzed under both normal and oblique incidences. Unit cells of multiple thicknesses are adopted to solve the in-phase reflection at certain frequencies. The scattered fields of the proposed multiple-element metasurface under different frequencies, polarizations, and incident angles are jointly optimized and simultaneously suppressed by OMEPC. When the range of incident angles is increased from 0° to 40°, the proposed multiple-element metasurface can achieve the 10 dB specular RCS reduction from 7.34 to 64.85 GHz with a ratio bandwidth of 8.84:1 for both TE and TM polarizations, and the 8 dB RCS reduction bandwidth is approximately 6.76–83.70 GHz. The measurement results are in agreement with the theoretical analysis and simulation results.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Operating Band Shifting of Resistor-Loaded Antenna-Based Absorber by Using
           Parasitic Element Concept

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      Authors: Stanislav Stefanov Zhekov;Peng Mei;Gert Frølund Pedersen;Wei Fan;
      Pages: 7294 - 7299
      Abstract: The size of an electromagnetic (EM) absorber is a critical design parameter since it determines the operating frequency band. The realization of lower starting frequency requires enlargement of the absorber which often is not desired. In this communication, a technique for overcoming this problem in the case of an absorber, constructed of a resistor-loaded wideband bowtie antenna, is studied. The method is about placing parasitic elements around the antenna in order to change its input impedance and thus to realize large shifting of the operating band of both single- and dual-polarized absorbers. Without using parasitic elements large move of the operating band can only be achieved by a considerable increase in the absorber’s size. However, the used method for absorption band shifting leads to shrinking of the bandwidth which means a compromise is to be made between these two parameters. For validation purposes, prototypes are fabricated and tested, and a good agreement between the simulation and measurement results is obtained.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Discrete Huygens’ Metasurface: Realizing Anomalous Refraction and
           Diffraction Mode Circulation With a Robust, Broadband and Simple Design

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      Authors: Chu Qi;Alex M. H. Wong;
      Pages: 7300 - 7305
      Abstract: Metasurfaces composed of subwavelength unit cells usually require a large number of unit cells which lead to complicated design and optimization. Aggressive discretization in metasurface designs can significantly reduce the number of unit cells within a period, resulting in large unit cell sizes. The enlarged unit cells will encounter negligible mutual couplings when combined together, hence making straightforward the process of metasurface design. These advantages combine to allow the design of a novel class of metasurfaces which support the high efficiency redirection of electromagnetic (EM) waves over a wide bandwidth and operation angle. Moreover, an aggressively discretized metasurface can realize diffraction mode circulation. In this work, we propose a simple transmissive metasurface which can realize diffraction mode circulation by refracting plane waves from angles of $mathrm {-45^{circ }}$ , $mathrm {0^{circ }}$ , and $mathrm {45^{circ }}$ to angles of $mathrm {0^{circ }}$ , $mathrm {45^{circ }}$ , and $mathrm {-45^{circ }}$ , respectively. The power efficiency of each anomalous refraction is more than 80% at the design frequency of 28 GHz, and the 3 dB power efficiency bandwidth is 11%. We fabricated and measured the metasurface, the experiment results agree well with the simulation results.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Polarization-Independent Broadband Angular Selectivity Based on
           Anisotropic Diamagnetic Metamaterial

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      Authors: Yuan Gao;Binghui Li;Rui Wang;Qinghui Yan;Jiangtao Huangfu;Dexin Ye;
      Pages: 7306 - 7310
      Abstract: Achieving broadband angular selectivity has been attracting much interest from both scientists and engineers in recent years. Previous experimental demonstrations have been limited to the $p$ -polarized incidence. Here, we propose a universal approach to achieve polarization-independent broadband angular selectivity by introducing electrically and magnetically anisotropic diamagnetic medium into multiple 1-D photonic crystal stacks. Such stacks have a broadband angular photonic bandgap for both $s$ - and $p$ -polarized waves. The anisotropic diamagnetic medium is artificially constructed with periodically arranged close metallic ring arrays, which exhibits a negligible frequency dispersion in an ultrawide band. As a proof of principle, one stack of photonic structures for the normal-incidence-selective case is fabricated and measured in the microwave region. The proposed approach is simple, robust, and scalable from near-zero frequencies to terahertz frequencies, showing promising practical applications such as spatial filters and anti-jamming communications.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Design and Analysis of an Electronically Tunable Magnet-Free
           Non-Reciprocal Metamaterial

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      Authors: Swadesh Poddar;Alexander M. Holmes;George W. Hanson;
      Pages: 7311 - 7315
      Abstract: In this communication, we develop and experimentally test a fully tunable magnet-free, non-reciprocal, split-ring resonator-based metamaterial. Non-reciprocity in the material response is introduced by bridging the split-ring gap with a biased field-effect transistor (FET) transistor, which allows the non-reciprocity to be tuned with respect to gate–source and drain–source bias conditions. As a measure of non-reciprocity, we consider the Faraday rotation of a normally incident linearly polarized planewave, which is a function of the co-polarized and cross-polarized $S$ -parameters associated with two horn antennas that transmit and receive the wave. Faraday rotation is calculated with respect to the operating frequency of the horn antennas and manually measured with respect to drain–source current at the resonant frequency. Interestingly, we find a linear relationship between Faraday rotation and drain–source current at the resonance.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Dispersion-Assisted Dual-Phase Hybrid Meta-Mirror for Dual-Band
           Independent Amplitude and Phase Controls

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      Authors: Zhenfei Li;Jurui Qi;Wenman Hu;Ji Liu;Jin Zhang;Linda Shao;Chiben Zhang;Xiong Wang;Ronghong Jin;Weiren Zhu;
      Pages: 7316 - 7321
      Abstract: Frequency-multiplexing metasurfaces are typically attributed to the integration of multiple resonators, where mode coupling may significantly affect their performances. In this communication, we develop a dispersion-assisted dual-phase hybrid strategy for dual-frequency independent control of amplitude and phase with a single resonance. Therein, the frequency and phase decoupling can be achieved by precise dispersion control between two frequency states, while the amplitude distribution of each meta-atom can be controlled by properly allocating the energy of copolarized and cross-polarized waves. As a proof of concept, a bi-functional meta-mirror shaping multifocal points at two different frequencies have been experimentally demonstrated. The measured results are in good agreement with simulated results, showing the diffraction efficiencies (DEs) of 38% and 45%, and a signal-to-noise ratio (SNR) of 8.36 and 10.35 at $f_{1}$ and $f_{2}$ , respectively. In addition, another three meta-mirrors with tailorable amplitudes at dual frequencies are designed to further verify our strategy. This method offers an alternative platform for designing high-performance devices with dual-frequency wavefront manipulations, which may find potential applications in microwave integrated systems and wireless communication systems.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Convergence Acceleration of Characteristic Mode-Based Basis Function
           Method for Connected Array Structures

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      Authors: Chunlai Jia;Pengfei Gu;Zi He;Rushan Chen;
      Pages: 7322 - 7327
      Abstract: The characteristic mode (CM)-based basis function method for connected array structures has been proven to be an efficient numerical approach. However, it generates a matrix equation for which iterative methods will only slowly converge due to the truncation effect of discarding buffers. Singular value decomposition (SVD) is first implemented to enhance the orthogonality between the characteristic currents of the connected array elements. The original characteristic currents are replaced by the newly constructed global basis functions so that the condition number of resultant reduced-order matrix is greatly reduced. In addition, a preconditioner is applied for the reduced-order impedance matrix, which can greatly improve the convergence speed of iterative method. Numerical examples are given to show that the proposed methods can significantly reduce the iterative steps and the calculation time with encouraging accuracy.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Dispersive Formulation of Time-Domain Meshless Method With PML Absorbing
           Boundary Condition for Analysis of Left-Handed Materials

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      Authors: Sheyda Shams;Farzad Mohajeri;Masoud Movahhedi;
      Pages: 7328 - 7333
      Abstract: We have proposed a dispersive formulation of scalar-based meshless method for time-domain analysis of electromagnetic wave propagation through left-handed materials (LHMs). Moreover, we have incorporated Berenger’s perfectly matched layer (PML) absorbing boundary condition (ABC) into the dispersive formulation to truncate open-domain structures. In general, the dispersive formulations of conventional numerical methods are proper tools for analysis of left-handed (LH) media, whenever the LH media can be characterized by considering spatial or frequency dispersion effect for the constitutive parameters. In comparison to the grid-based numerical methods, it is proven that meshless methods not only are strong tools for accurate approximation of derivatives in Maxwell’s equations but also can provide more flexibility in modeling the spatial domain of problems. However, we have not seen any reports on using dispersive forms of meshless methods for simulation of wave propagation in metamaterials and applying any PML ABCs to dispersive formulation of meshless method. The proposed formulation enables us to take advantage of meshless methods in analysis of LH media with frequency-dependent parameters. For modeling the frequency behavior of the medium, we have used auxiliary differential equation (ADE) method based on the relations between electromagnetic fields intensities and current densities. Effectiveness of the proposed formulation is verified by analysis of 2-D and 3-D numerical examples; also, some basic factors which affect the accuracy, stability, and computational cost of the simulations are studied.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • A Unified View of DI- and ETD-FDTD Methods for Drude Media

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      Authors: José A. Pereda;Ana Grande;
      Pages: 7334 - 7337
      Abstract: A unified view of direct-integration (DI) and exponential-time-differencing (ETD) methods to incorporate Drude media, such as isotropic plasma and microwave graphene, into finite-difference time-domain (FDTD) simulators is provided. To this end, the Drude constitutive relation is expressed in integral form and the DI integrators are obtained by applying quadrature rules. Analogously, the ETD integrators are obtained by starting from the variation of constants formula and applying the same quadrature rules as in the DI case. This approach allows one to directly compare the two families of methods. In addition, the accuracy of each integrator is discussed and the stability condition of the resulting FDTD schemes is derived in exact closed form by applying the von Neumann method.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • 2-D Green’s Function for an Elliptically Layered Cylindrical PEC
           Enclosure

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      Authors: Andrea Randazzo;Alessandro Fedeli;Matteo Pastorino;
      Pages: 7338 - 7343
      Abstract: In this communication, a semianalytical solution for the computation of the 2-D Green’s function for a cylindrical perfect electric conducting (PEC) enclosure containing an arbitrary number of confocal elliptic dielectric layers is provided. The approach relies on an expansion of the Green’s function into Mathieu functions, whose coefficients are found in an efficient way through a recursive procedure. The effectiveness of the technique is evaluated by comparisons with analytical formulas and against the results provided by independent numerical solvers. Moreover, the applicability of the solution to forward scattering problems using integral formulations is also assessed. In all the considered cases, the developed approach has been found to provide accurate results.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • RCS Estimation of Drone Motion Using Mesh-Element Rotation in MoM and
           Micro-Doppler Signatures

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      Authors: Dong-Yeob Lee;Jae-In Lee;Dong-Wook Seo;
      Pages: 7344 - 7349
      Abstract: For an automatic recognition system, a huge number of micro-Doppler signature images is required to train a classifier. However, in general, measurements are only possible for hovering drones, so the dynamic radar cross section (RCS) of a drone with various motions is estimated through EM simulation and converted into a micro-Doppler signature image. In this work, we use far-field approximation and mesh-element rotation in the method of moments to quickly estimate the dynamic RCS of a drone in various motions. First, 3-D meshes and the impedance matrix of a single propeller are generated only once. Instead of rotating the propeller, the position information of the mesh elements is rotated without recreating 3-D meshes or the impedance matrix. Next, using the mirror-image symmetric characteristics of drone propellers and the far-field approximation, the dynamic RCS of multiple propellers is synthesized from that of a single propeller. Finally, the dynamic RCS was estimated at 3 and 9 GHz and converted to micro-Doppler signatures, spectrogram, and cadence-velocity diagram (CVD). As a result, it was more accurate to estimate the dynamic RCS at 9 GHz, and it was easier to obtain the rotation frequency at 3 GHz in the CVD.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Communication Bistatic RCS Estimation Using Monostatic Scattering Centers
           With Compressive Sensing

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      Authors: Yeong-Hoon Noh;Hyeong Rae Im;Woobin Kim;Ic-Pyo Hong;Jong-Gwan Yook;
      Pages: 7350 - 7355
      Abstract: This communication presents a novel technique for obtaining bistatic radar cross sections (RCSs) extracted from a monostatic scattering field dataset using a discrete scattering center model and basis pursuit denoising (BPDN) algorithm, which is compressive sensing (CS) technique. With the high-frequency assumption, a complex vector of independent point sources is formulated in a monostatic configuration for a geometrical relationship among the transmitter, receiver, and equivalent scatterers. A matrix equation for the scattering problem of an underdetermined form is effectively calculated by an iterative BPDN solver. Then, compensating the phase difference in the bistatic condition can derive the bistatic RCS at specific frequency points and observation angles. The accuracy of the proposed method for extracting bistatic results is verified using two numerical examples, and the performance of the method in terms of measurement efficiency and data resolution in frequency and angle domains is compared with that of conventional method.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Nonuniform Field Sampling in Circumference Geometries

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      Authors: Giovanni Leone;Fortuna Munno;Raffele Solimene;Rocco Pierri;
      Pages: 7356 - 7361
      Abstract: Proper field sampling strategies are important in antenna measurements and diagnostics applications to reduce the overall testing time. We investigate the role of source dimension in determining sampling points’ locations by referring to circumference geometries. An inverse problem approach is adopted, and spectral decomposition of the relevant operator is considered for a 2-D geometry. First, we introduce and discuss an approximation of the resulting point spread functions (PSFs), on which we found our approach. Next, a numerical strategy to discretize the field observation domain is presented, which results in a nonuniform angular step depending, in turn, on source extension. Some numerical examples of source characterization show the effectiveness of the approach in comparison to uniform angular sampling.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Reliable Linearized Phase Retrieval for Near-Field Antenna Measurements
           With Truncated Measurement Surfaces

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      Authors: Alexander Paulus;Josef Knapp;Jonas Kornprobst;Thomas F. Eibert;
      Pages: 7362 - 7367
      Abstract: Most methods tackling the phase retrieval problem of magnitude-only antenna measurements suffer from unrealistic sampling requirements, from unfeasible computational complexities, and, most severely, from the lacking reliability of nonlinear and nonconvex formulations. As an alternative, we propose a partially coherent multiprobe measurement technique and an associated linear reconstruction method which mitigate all these issues. Hence, reliable and accurate phase retrieval can be achieved in near-field far-field transformations (NFFFTs). In particular, we resolve the issues related to open measurement surfaces (as they may emerge in drone-based measurement setups) and we highlight the importance of considering the measurement setup and the phaseless NFFFT simultaneously. Specifically, the influence of special multiprobe arrangements on the reconstruction quality of partially coherent solvers is shown..
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
  • Call for Papers: Frontiers in Computational Electromagnetics

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      Pages: 7368 - 7368
      Abstract: Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers.
      PubDate: Aug. 2022
      Issue No: Vol. 70, No. 8 (2022)
       
 
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