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IEEE Transactions on Antennas and Propagation
Journal Prestige (SJR): 1.309
Citation Impact (citeScore): 5
Number of Followers: 79  
 
  Full-text available via subscription Subscription journal
ISSN (Print) 0018-926X
Published by IEEE Homepage  [228 journals]
  • IEEE Transactions on Antennas and Propagation

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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: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • IEEE Transactions on Antennas and Propagation

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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: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Institutional Listings

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      Abstract: Presents a listing of institutions relevant for this issue of the publication.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Editorial Outstanding Associate Editors and Top Reviewers

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      Authors: Danilo Erricolo;
      Pages: 4946 - 4947
      Abstract: The IEEE Transactions on Antennas and Propagation is one of the most influential publications of IEEE. Its scientific contributions attract a lot of interest and are among the most downloaded across all IEEE publications. In 2021, the IEEE Transactions on Antennas and Propagation ranked third out of 389 publications available on IEEE Xplore for total number of downloads. The IEEE Transactions on Antennas and Propagation ranks second for total number of downloads out of all IEEE publications, when open access journals are excluded. In addition, the bibliometric measures released by Clarivate for year 2021 indicate that the journal performance has set a new record in its history, with an impact factor of 4.824, a 5-year impact factor that reached 5.005, an eigenfactor score of 0.041, and article influence score of 1.048.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Guest Editorial Machine Learning in Antenna Design, Modeling, and
           Measurements

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      Authors: Francesco Andriulli;Pai-Yen Chen;Danilo Erricolo;Jian-Ming Jin;
      Pages: 4948 - 4952
      Abstract: Machine learning (ML) is the study of computational methods for improving performance by mechanizing the acquisition of knowledge from experience. As a modern data-driven optimization and applied regression methodology, ML aims to provide increasing levels of automation in the knowledge engineering process, replacing much time-consuming human activity with automatic techniques that improve accuracy and/or efficiency by discovering and exploiting regularities in training data. Indeed, many ML and data-driven methods, such as conventional artificial neural networks (ANNs), were introduced and studied within electromagnetics a few decades ago. However, these past studies did not benefit from the most recent advances in ML, which have been driven by the present confluence of improved hardware performance at lower cost, advanced network algorithms and architectures, data science, and considerable efforts dedicated to advancing the computational electromagnetics (CEM) benchmark. Today, a broader family of ML techniques based on ANNs has been developed. Examples include deep neural network (DNN), convolutional neural network (CNN), recurrent neural network, generative adversarial network, and deep reinforcement learning, which have been successfully applied to different engineering and science problems, ranging from image and video recognition, social media services, virtual personal assistant to autonomous vehicles, to name a few. This naturally suggests that applying ML to real-world electromagnetic problems could be one of the emerging trends in ML and artificial intelligence (AI) [1]–[4]. Indeed, ML has been becoming an important complement to existing experimental, computational, and theoretical aspects of electromagnetics.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Efficient Online Data-Driven Enhanced-XGBoost Method for Antenna
           Optimization

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      Authors: Wen Tao Li;Hao Sen Tang;Can Cui;Yong Qiang Hei;Xiao Wei Shi;
      Pages: 4953 - 4964
      Abstract: The tremendous progress in artificial intelligence promotes the wide application of machine learning (ML) technology in the field of electronic science. Recently ML-based antenna optimization provides a distinct candidate and attracts considerable attention. However, the large number of training samples generated through time-consuming EM simulations becomes a significant challenge. In this article, an efficient online data-driven enhanced-XGBoost (E-XGBoost) method for antenna optimization is proposed, which is mainly composed of two parts, i.e., an input variable filter module (IVFM) and an antenna optimization module (AOM). Specifically, IVFM serves as a variable sensitivity analyzer, which is accomplished by E-XGBoost to efficiently reduce the dimension of design variable and hence save the training samples. Next, the design variables obtained by IVFM are fed into AOM to find the near-optimal solution. In AOM, an online learning strategy is proposed to train a local E-XGBoost model to evaluate the population in the metaheuristic optimization algorithm (MOA). Compared to the global ML model that can mimic the entire design space, this local E-XGBoost model can further cut down the training samples. To verify the performance of the proposed method, several different antenna examples, i.e., U-slot patch antenna, Fabry–Perot resonant antenna, and dual-polarized cross dipole antenna and 5G MIMO antenna array, are simulated. Numerical results support the proposed method in terms of its superior performance and potential advantage of saving computational overhead.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Intelligent Antenna Synthesis Method Based on Machine Learning

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      Authors: Dan Shi;Cheng Lian;Keyi Cui;Yazhou Chen;Xiaoyong Liu;
      Pages: 4965 - 4976
      Abstract: An intelligent antenna synthesis method is proposed to automatically select suitable antenna type and provide optimal geometric parameters according to the requirement of antenna performance. The performance characteristics of different antennas are analyzed, and a smart antenna selection model is established to recommend the appropriate antenna by using support vector machine (SVM). Then, the stacking ensemble model is built by combining five primary learners to give full play to the advantages of each type of learners and, finally, the geometric parameters of the antenna are provided. Microstrip patch antenna, spiral antenna, and horn antenna are used to demonstrate the accuracy and efficiency of the model. The system shows a great ability of antenna classification with accuracy over 99% and parameter prediction with a mean absolute percentage error (MAPE) of less than 6%. Moreover, the results are compared with the traditional data-driven model, and the key parameters of the model are comprehensively discussed. The proposed method could be widely used in intelligent antenna design in practice.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Efficient Surrogate Assisted Particle Swarm Optimization for Antenna
           Synthesis

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      Authors: Kai Fu;Xiwen Cai;Bo Yuan;Yang Yang;Xin Yao;
      Pages: 4977 - 4984
      Abstract: By virtue of the prediction abilities of machine learning (ML) methods, the ML-assisted evolutionary algorithm has been treated as an efficient solution for antenna design automation. This article presents an efficient ML-based surrogate-assisted particle swarm optimization (SAPSO). The proposed algorithm closely combines the particle swarm optimization (PSO) with two ML-based approximation models. Then, a novel mixed prescreening (mixP) strategy is proposed to pick out promising individuals for full-wave electromagnetic (EM) simulations. As the optimization procedure progresses, the ML models are dynamically updated once new training data are obtained. Finally, the proposed algorithm is verified by three real-world antenna examples. The results show that the proposed SAPSO-mixP can find favorable results with a much smaller number of EM simulations than other methods.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Multibranch Machine Learning-Assisted Optimization and Its Application to
           Antenna Design

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      Authors: Weiqi Chen;Qi Wu;Chen Yu;Haiming Wang;Wei Hong;
      Pages: 4985 - 4996
      Abstract: To satisfy certain requirements for an antenna design, many full-wave electromagnetic (EM) simulations are required, and they involve a considerable computational burden. A multibranch machine learning-assisted optimization (MB-MLAO) method is proposed to dramatically reduce the computational complexity in this task. Then, this method is applied to antenna design and worst case performance (WCP) searching under a practical manufacturing tolerance. In the conventional Gaussian process regression (GPR)-based MLAO method, a lower confidence bound (LCB) prescreening strategy with an empirical LCB constant is used to weigh the predicted value and predicted uncertainty. Using a variable-fidelity machine learning method, an adaptive LCB variable, and a retraining and repredicting method, the proposed MB-MLAO method can strike a delicate balance between exploitation and exploration in searching. Moreover, variable-fidelity data from full-wave EM simulations are used in the multifidelity GPR machine learning method to further reduce the computational burden. Finally, two test functions and three types of antennas are selected as examples to illustrate the superiority of the proposed MB-MLAO method.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Machine Learning Methods-Based Modeling and Optimization of 3-D-Printed
           Dielectrics Around Monopole Antenna

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      Authors: Yashika Sharma;Xi Chen;Junqiang Wu;Qiang Zhou;Hao Helen Zhang;Hao Xin;
      Pages: 4997 - 5006
      Abstract: In this article, we propose using new machine learning (ML)-based optimization methods as an alternative to traditional optimization methods, for complex antenna designs. This is an efficient methodology to tackle computational challenges, as it is capable of handling a large number of design parameters and is more efficient as well as informative. The proposed technique is applied for modeling the gain performance in the principal plane of a monopole antenna when its radiation properties are modified by placing spatially dependent dielectric material around it. Using the proposed methodology, the dielectric constant values are mapped to the gain pattern of the design. We use two ML techniques for this purpose, namely Gaussian process (GP) regression and artificial neural network (ANN). Once each of these models is obtained, they are further used for estimating the dielectric constant values that can suggest optimal directions to modify gain patterns for single-beam and multiple-beam patterns rather than the conventional omnidirectional pattern of a monopole antenna. The performance of this technique is compared with heuristic optimization techniques, such as genetic algorithms (GAs). The proposed method proves to be quite accurate in spite of being a high-dimensional nonlinear problem. A prototype of a monopole design with three-beam gain pattern is fabricated and tested. The measurement results agree well with the simulation results. The proposed methodology can provide useful and scalable optimization tools for computationally intensive antenna design problems.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Efficient Knowledge-Based Artificial Neural Network for the Design of
           Circularly Polarized 3-D-Printed Lens Antenna

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      Authors: Yan-Fang Liu;Lin Peng;Wei Shao;
      Pages: 5007 - 5014
      Abstract: An efficient knowledge-based artificial neural network (KBANN) is proposed, and it is used for the design of circularly polarized (CP) lens antenna in this article. In this KBANN, forward neural network (FNN) and inverse neural network (INN) are included. In this model, INN is the major component to predict the antenna structure parameters. As multiple performance indices are required, INN requires a large number of training samples to deduce complex mapping relationship. To solve this problem, FNN is introduced to provide prior knowledge for INN. FNN generates a huge training dataset for INN training, and then the trained INN can directly output the geometric parameters by feeding the target electromagnetic responses as input. This article solves the problem of multiple performance indices in antenna design, and a CP lens antenna with wideband, good axial ratio, and high gain is designed and fabricated to verify the effectiveness of the KBANN model.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Consensus Deep Neural Networks for Antenna Design and Optimization

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      Authors: Zoran Ž. Stanković;Dragan I. Olćan;Nebojša S. Dončov;Branko M. Kolundžija;
      Pages: 5015 - 5023
      Abstract: We present a general approach for antenna design and optimization based on consensus of results from a number of independently trained deep neural networks (DNNs). The aim of using the consensus is to reduce the uncertainty of results from a single DNN. The approach leads to several orders of magnitude faster antenna optimization and design compared to the optimization based on a full-wave solver and allows a compromise between the analysis speed and its accuracy. The used DNNs are multilayer perceptrons (MLP) with multiple fully connected hidden layers. As an example, we consider the Yagi–Uda antenna with four design parameters and optimize it for the maximal forward gain. The training of neural networks is done on datasets of several sizes, up to 1 million antenna samples. The samples are generated either randomly or at a uniform grid over the design space using the method of moments.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Prior-Knowledge-Guided Deep-Learning-Enabled Synthesis for Broadband and
           Large Phase Shift Range Metacells in Metalens Antenna

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      Authors: Peiqin Liu;Liushifeng Chen;Zhi Ning Chen;
      Pages: 5024 - 5034
      Abstract: A prior-knowledge-guided deep-learning-enabled (PK-DL) synthesis method is proposed for enhancing the transmission bandwidth and phase shift range of metacells used for the design of metalens antennas. The algorithm of conditional deep convolutional generative adversarial network (cDCGAN) is utilized in the proposed deep-learning (DL) method. Prior knowledge, including well-known fundamental electromagnetic theorems and experience in antenna design, is purposely applied at the early stage of the proposed method to strategically guide and speed up the synthesis. The proposed intelligent method provides the design of pixelated metacells with high degrees of freedom so that the key performance of the synthesized metacells exceeds the existing limit of conventional design methods by generating a rich profusion of cell patterns. For example, the synthesized triple-layer metacell achieves the −1 dB phase shift range of 330° breaking the limit of 308° derived by existing techniques. The proposed synthesis method also provides the additional capability to flexibly control the phase shift not only at the center frequency but also over a frequency range of interest. A Ku-band metalens antenna formed with the synthesized metacells demonstrates the achieved 1 and 3 dB gain bandwidths increase by 52.2% and 42.6%, respectively, compared to the metalens antenna using the well-known Jerusalem cross (JC) metacells. The proposed method extends the capability for the synthesis of metacells and metalens antennas with enhanced performance.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Design for Array-Fed Beam-Scanning Reflector Antennas With Maximum
           Radiated Power Efficiency Based on Near-Field Pattern Synthesis by Support
           Vector Machine

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      Authors: Lun Wei Mou;Yu Jian Cheng;Ya Fei Wu;Ming Hua Zhao;Hai Ning Yang;
      Pages: 5035 - 5043
      Abstract: The maximum radiation efficiency can be obtained when the feed array excitation of a reflector antenna is synthesized by the conjugate field matching (CFM) method. However, the CFM method can only get the strongly tapered feeding power distribution. This will lead to most of power amplifiers (PAs) working in low efficiency states and reduce the equivalent isotropic radiated power (EIRP) with the limited power consumption. In this work, combining the radiation efficiency and the PA efficiency, the radiated power efficiency (RPE) is defined as the new design goal and is to be raised to achieve higher EIRP. For this reason, a method based on the near-field pattern synthesis is proposed. In this method, all the ON-state PAs are required to work in the highest efficiency state. Then, with well-trained support vector machine (SVM), the ON–OFF states of the PAs are adjusted so that the reflected focal field can be better synthesized by the near-field pattern of the feed array. Thus, the loss of the radiation efficiency is minimized. As a result, the RPE is about 22% higher than that of the CFM method and about 10% higher than that of the optimum CFM truncation case.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Robust and Efficient Fault Diagnosis of mm-Wave Active Phased Arrays Using
           Baseband Signal

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      Authors: Martin H. Nielsen;Yufeng Zhang;Changbin Xue;Jian Ren;Yingzeng Yin;Ming Shen;Gert Frølund Pedersen;
      Pages: 5044 - 5053
      Abstract: One key communication block in 5G and 6G radios is the active phased array (APA). To ensure reliable operation, efficient and timely fault diagnosis of APAs on-site is crucial. To date, fault diagnosis has relied on measurement of frequency domain radiation patterns using costly equipment and multiple strictly controlled measurement probes, which are time consuming, complex, and therefore infeasible for on-site deployment. This article proposes a novel method exploiting a deep neural network (DNN) tailored to extract the features hidden in the baseband in-phase and quadrature signals for classifying the different faults. It requires only a single probe in one measurement point for fast and accurate diagnosis of the faulty elements and components in APAs. Validation of the proposed method is done using a commercial 28 GHz APA. Accuracies of 99% and 80% have been demonstrated for single- and multi-element failure detection, respectively. Three different test scenarios are investigated: ON-OFF antenna elements, phase variations, and magnitude attenuation variations. In a low signal-to-noise ratio (SNR) of 4 dB, stable fault detection accuracy above 90% is maintained. This is all achieved with a detection time of milliseconds (e.g., 6 ms), showing a high potential for on-site deployment.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Machine Learning-Assisted Array Synthesis Using Active Base Element
           Modeling

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      Authors: Qi Wu;Weiqi Chen;Chen Yu;Haiming Wang;Wei Hong;
      Pages: 5054 - 5065
      Abstract: Array synthesis under practical constraints is a vital design task. Traditional array synthesis methods usually deal with isolated antenna elements without considering mutual coupling (MC) or mounting-platform effects, which results in unacceptable degradation in practical array designs. An efficient machine learning-assisted array synthesis (MLAAS) method is introduced using efficient active base element modeling (ABEM). This method greatly extends the boundaries of practical antenna array synthesis from the perspectives of both accuracy and design freedom. Using much fewer samples than those in conventional MLAAS methods, all possible element designs are accurately modeled into one active base element (ABE). Compared with conventional active element pattern (AEP)-based methods, the ABEM aims to predict AEPs for elements with arbitrary allocations and electromagnetic (EM) surroundings, therefore offering more degrees of freedom for practical array designs. Four array design examples are used to verify the effectiveness of the proposed method.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Ultra-Wide-Scanning Conformal Heterogeneous Phased Array Antenna Based on
           Deep Deterministic Policy Gradient Algorithm

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      Authors: Binchao Zhang;Cheng Jin;Kaiqi Cao;Qihao Lv;Pengyu Zhang;Yan Li;Maokun Li;
      Pages: 5066 - 5077
      Abstract: This article investigates the pattern synthesis of the conformal phased array antenna (PAA) by using the deep deterministic policy gradient (DDPG) algorithm, and a nearly full solid angle for beam steering is realized. The beam steering capability of the planar and conformal PAAs is theoretically compared at first, and a conclusion is obtained that conformed to the conical-and-cylindrical structure can help to achieve ultrawide-angle beam steering. Next, a typical deep reinforcement learning algorithm, which is the DDPG algorithm, is utilized to deal with the fast beam steering problem of the conformal heterogeneous PAA. By virtue of the strong fitting ability of the DDPG algorithm for high-dimensional continuous nonlinear problems, the performance of fast beam steering is achieved within a wide-angle range within (−150°, 150°). Finally, a prototype of $1times17$ conformal PAA is fabricated for measurement and verification, and the measured results are in good agreement with the simulation results.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Towards Efficient Reflectarray Digital Twins - An EM-Driven Machine
           Learning Perspective

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      Authors: Giacomo Oliveri;Marco Salucci;Andrea Massa;
      Pages: 5078 - 5093
      Abstract: The concept of digital twins (DTs) for reflectarray (RA) unit cells (UCs) is discussed and implemented by exploiting electromagnetic-driven machine learning (ML) techniques. Toward this end, several open challenges are addressed, such as the reliability and the effectiveness of using surrogates for modeling different, in terms of descriptors and complexity, UCs, the accuracy in predicting the scattering matrix entries of both single- and dual-polarization elements, the implementation of effective and efficient strategies for the setup of the training set, and the definition of generalized and robust guidelines for the use of popular ML techniques to the problem at hand. Representative results of an extensive numerical validation are presented to assess the performance and the potentialities of DTs when dealing with different RA modeling problems and training sets.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Cognitive Conformal Antenna Array Exploiting Deep Reinforcement Learning
           Method

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      Authors: Binchao Zhang;Cheng Jin;Kaiqi Cao;Qihao Lv;Raj Mittra;
      Pages: 5094 - 5104
      Abstract: A cognitive antenna array, which is designed by using deep reinforcement learning (DRL) is proposed in this article to adapt to the complex electromagnetic environment. Specifically, the phased array antenna is utilized as the manipulatable component to achieve the characteristic of beam steering with the help of the DRL algorithm. We begin by establishing a DRL-based framework, which is comprised of a microprogrammed control unit, power divider, digital phase shifter, and the patch antenna array. In the DRL algorithm, the desired beam steering is obtained through trial-and-error interactions with the environment, which is required to observe predefined rewards based on the current state and action. Next, the system is trained to perform beam steering, and a set of hyperparameters of the deep neural network are obtained and stored for practical usage. A good agreement is achieved between the simulated and measured radiation patterns of the planar phased array antenna, which validates the DRL-based phase distribution regulation algorithm. Finally, the algorithm is implemented in the design process of a conformal phased array antenna, and it is shown that the measured radiation performance of the array is satisfactory for different beam scan angles.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Combined Machine-Learning/Optimization-Based Approach for Inverse Design
           of Nonuniform Bianisotropic Metasurfaces

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      Authors: Parinaz Naseri;Stewart Pearson;Zhengzheng Wang;Sean V. Hum;
      Pages: 5105 - 5119
      Abstract: Electromagnetic metasurface (EMMS) design based on far-field (FF) constraints without the complete knowledge of the fields on both sides of the metasurface is typically a time-consuming and iterative process, which relies heavily on heuristics and ad hoc methods. This article proposes an end-to-end systematic and efficient approach where the designer inputs high-level FF constraints, such as nulls, sidelobe levels, and main beam level(s), and a three-layer nonuniform passive, lossless, and omega-type bianisotropic EMMS design to satisfy them is returned. The surface parameters to realize the FF criteria are found using the alternating direction method of multipliers on a homogenized model derived from the method of moments (MoM). This model incorporates edge effects of the finite surface and intercell mutual coupling in the inhomogeneous impedance sheet. Optimization through the physical unit cell space integrated with machine-learning-based surrogate models is used to realize the desired surface parameters from physical meta-atom (or unit cell) designs. Two passive lossless examples with different feeding systems and FF constraints are shown to demonstrate the effectiveness of this method.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Equivalent Circuit Theory-Assisted Deep Learning for Accelerated
           Generative Design of Metasurfaces

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      Authors: Zhaohui Wei;Zhao Zhou;Peng Wang;Jian Ren;Yingzeng Yin;Gert Frølund Pedersen;Ming Shen;
      Pages: 5120 - 5129
      Abstract: In this article, we propose an equivalent circuit theory-assisted deep learning approach to accelerate the design of metasurfaces. By combining the filter equivalent circuit theory and a sophisticated deep learning model, designers can achieve efficient metasurface designs. Compared with most existing metasurface generative design methods that rely on arbitrarily generated training dataset (TDS), the proposed method can adaptively produce highly relevant and low-noise training samples under the guidance of filter equivalent circuit theory, resulting in a significantly narrowed target solution space and improved model training efficiency. Furthermore, we select the variational autoencoder (VAE) as a generative model, which can compress the raw training samples into a lower-dimensional latent space where optimization methods, such as genetic algorithm, can be more efficiently executed to find the optimal design than a brute-force search. To verify the effectiveness of the proposed method, we apply it in the creation of three examples of frequency selective surfaces (FSSs), presenting wide-band, dual-band, and band-stop responses. Experimental results show that the proposed method can realize much faster and more stable convergence than deep learning design methods without domain knowledge.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Fourier Subspace-Based Deep Learning Method for Inverse Design of
           Frequency Selective Surface

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      Authors: Enze Zhu;Zhun Wei;Xingxing Xu;Wen-Yan Yin;
      Pages: 5130 - 5143
      Abstract: Frequency selective surface (FSS) is critical for electromagnetic (EM) radiation protection due to its high spatial filtering performance, especially for active FSS. Recently, the artificial neural network (ANN) has shown great potential in solving EM inverse problems and rapid industrial design. In such an inverse model with ANN, it establishes the relationship between the given inputs of S-parameters and the desired structure parameters or material parameters. However, faced with applications where S-parameters vary in a large frequency range with different curve shapes, such as multiband microwave devices, equal interval sampling may result in high-dimensional inputs and will require a more complicated neural network. In this work, we present a Fourier subspace-based deep learning method (FS-BDLM) for FSS inverse design, where the dimension of the input is largely reduced by using Fourier subspace to represent the most salient features of the desired S-parameter performance. Compared with existing deep learning methods, the proposed technique makes inverse neural models more compact and more stable to noise contaminations. The validation of the proposed FS-BDLM is conducted both numerically and experimentally through two dual-passband FSS design examples, where the well-designed FSS is fabricated to validate the technique.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Electric Flux Density Learning Method for Solving 3-D Electromagnetic
           Scattering Problems

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      Authors: Tiantian Yin;Chao-Fu Wang;Kuiwen Xu;Yulong Zhou;Yu Zhong;Xudong Chen;
      Pages: 5144 - 5155
      Abstract: Inspired by a discretized formulation resulting from volume integral equation and method of moments, we propose an electric flux density learning method (EFDLM) using cascaded neural networks to solve 3-D electromagnetic (EM) scattering problems that involve lossless dielectric objects. The inputs of the proposed EFDLM consist of the contrast of the objects, the projections of incident field, and the first-order scattered field onto the testing functions, and the output is chosen as the normalized electric flux density. Analyses on the computational complexity, computation time, and memory usage of the EFDLM are conducted to fully understand its fundamental features. Numerical simulations clearly show that the proposed method outperforms black-box learning method, which chooses the contrast and incident field as its inputs and the total electric field as its output. It is also demonstrated that the EFDLM is able to solve the scattering problems of dielectric objects with higher contrasts by increasing the number of subnetworks. Further, the pros and cons of the proposed learning approach for solving EM scattering problems are discussed, where some caveats are provided to avoid using learning approaches in a black-box way.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Rapid Subentire-Domain Basis Functions Method Based on Adaptive Artificial
           Neural Networks

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      Authors: Wei Xiang;Zhe Zhang;Wenming Zheng;Jiaqi Li;Wu Yang;Weibing Lu;
      Pages: 5156 - 5164
      Abstract: The subentire-domain (SED) basis functions method has shown its efficiency in solving the electromagnetic problem of large-scale finite periodic structures (LFPSs). However, calculating the expansion coefficients of SED basis functions is very time-consuming due to the consideration of the mutual coupling between all the elements in LFPSs, even after accelerated by conjugate-gradient fast Fourier transform (CG-FFT) and/or fast multipole method (FMM). In this article, based on the physics locations of observation cells, the adaptive artificial neural networks (AANNs) have been employed to rapidly predict the expansion coefficients of SED basis functions on interior cells, edge cells, and corner cells. By involving the AANNs, the mutual coupling between all the elements can be accounted into the neural networks without the construction of the mutual coupling matrix, and the expansion coefficients of SED basis functions can be obtained rapidly. Numerical experiments prove the accuracy and efficiency of the AANN-assisted SED basis functions method.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Fast Multi-Physics Simulation of Microwave Filters via Deep Hybrid Neural
           Network

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      Authors: Yuanguo Zhou;Jianan Xie;Qiang Ren;Huan Huan Zhang;Qing Huo Liu;
      Pages: 5165 - 5178
      Abstract: One fundamental difficulty in multiphysics numerical simulation is the complex interactions between different physics domains leading to plenty of computational costs. Although neural networks have recently been introduced in multiphysics simulations, the modeling complexity and the enormous amount of training data required may still pose significant challenges to researchers. In this work, we introduce a low-cost, electromagnetic-centric, multiphysics modeling approach to simulate microwave filters. With ground-truth datasets being generated from the finite element method, a novel deep hybrid neural network (DHNN) model structure is introduced, which uses the sigmoid and the ReLU functions as activators to mimic the diversity of biological neurons. A new, more feasible training algorithm is proposed for the efficient development of the DHNN model. The algorithm adopts the design-of-experiment (DOE) sampling technique and is specifically designed for the simulation of multiphysics responses. The strong approximation ability of the DHNN can lead to high-accuracy modeling with fewer training data and less resource consumption. Another advantage of this approach is that the modeling process is more concise and easier to apply compared with other modeling technologies. Numerical examples show that the DHNN can achieve higher accurate results with much less training data compared to traditional ANNs. The advantages of the proposed method in computational efficiency are more pronounced, especially when the amount of input data increases.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Data-Free Solution of Electromagnetic PDEs Using Neural Networks and
           Extension to Transfer Learning

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      Authors: Shubhendu Bhardwaj;Pawan Gaire;
      Pages: 5179 - 5188
      Abstract: In this article, we present a data-free method to solve differential equation using artificial neural networks (ANN). This method exploits the universal function approximation nature of a neural network to mimic a specified partial differential equation (PDE) and provide its solution. Specifically, use of simple feed-forward artificial neural network (FF-ANN) is shown to demonstrate the solution of 1-D second-order differential equations without use of any prior data. The article also demonstrates that the similarity in two PDEs is akin to similarity in the optimized weight matrices attained after the solution using FF-ANN. This property is then utilized for a transferred learning to enable faster convergence of a new PDE, based on the prior solution of a similar PDE. The concept is shown while considering a general form of second-order PDE, and considering specific cases of scalar in-homogeneous wave equation form and Poisson Equation form. Error convergence below 10−6 is shown and the transferred learning process shows typical time acceleration by a factor of 1.5–3 for the considered equations.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Compact Machine Learning Architecture for Wideband Amplitude-Only
           Direction Finding

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      Authors: Gaeron R. Friedrichs;Mohamed A. Elmansouri;Dejan S. Filipovic;
      Pages: 5189 - 5198
      Abstract: A generalized, reduced-size machine learning architecture for single-snapshot amplitude-only direction finding (AODF) is proposed for uniform circular arrays. A method for reusing angle of arrival (AoA) estimation models that are accurate over narrower fields of view is described. The efficacy of the proposed method is demonstrated using an ultrawideband circular array of miniaturized transverse electromagnetic (TEM) horns covering 1.5–5.5 GHz. Reasonable azimuth estimations performed on this retrofitted system are obtained over 2.6:1 bandwidth (1.5–4.0 GHz). Antenna performance features that impact the accuracy of AODF are also recognized. Root mean square error less than 5° is achieved in simulation above 15 dB signal-to-noise ratio (SNR) and above 20 dB SNR in measurement. The improved accuracy over the conventional correlation method of 52%–85% is demonstrated in an SNR domain of 10–40 dB. This performance improvement is obtained while maintaining a footprint reduction of 80%–95%, and an AoA estimation time speed-up of at least 85%.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Machine Learning-Based Matching Medium Design for Implant Communications

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      Authors: Erdem Cil;Cemre Cadir;Omer A. Kati;H. Birkan Yilmaz;Sema Dumanli;
      Pages: 5199 - 5208
      Abstract: Matching media are used in various applications to increase the power transmitted into the human body. The selection of the optimum matching medium (MM) permittivity is not a straightforward task, as the optimum value maximizing the transmitted power depends on the thickness of the MM and the electromagnetic properties of the target tissue. In this article, a computationally heavy empirical approach and a machine learning (ML)-based approach are utilized for the selection of the MM. The empirical approach demonstrates that the MM can increase the $ S_{21} $ values up to 8 dB, which is validated with measurements. Next, an ML-based tool is proposed to predict the optimum MM permittivity for any target tissue and any MM thickness. A 1-D convolutional neural network followed by a multilayer perceptron is trained with the simulated average Poynting vector magnitudes (APVMs) for muscle and fat as target tissues. The APVM and the dipole length for given system parameters are predicted by the trained artificial neural network. The accuracy is calculated by comparison with the results of the empirical analysis and found to be 1% and 12.3% mean absolute percentage error for dipole length and APVM, respectively. The proposed tool decreases the time required to milliseconds.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Mode Recognition of Rectangular Dielectric Resonator Antenna Using
           Artificial Neural Network

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      Authors: Yuqi Xiao;Kwok Wa Leung;Kai Lu;Chi-Sing Leung;
      Pages: 5209 - 5216
      Abstract: A new method powered by an artificial neural network (ANN) is studied for resonant-mode recognitions of a rectangular dielectric resonator antenna (DRA). Different rectangular DRAs were simulated with ANSYS HFSS to generate a large dataset for training the model. Their resonance frequencies, dimensions, and 3-D electric fields are input to the ANN. The output end is a 12-element array representing the corresponding probabilities of 12 different resonant modes. Using this trained ANN model, the mode recognition accuracy can reach 96.74%. Apart from identifying the resonant modes, our proposed approach can suggest how to modify a rectangular DRA to improve the purity of a resonant mode for better antenna performance.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Cone-Shaped Space Target Inertia Characteristics Identification by Deep
           Learning With Compressed Dataset

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      Authors: Shaoran Wang;Mengmeng Li;Tian Yang;Xia Ai;Jiaqi Liu;Francesco P. Andriulli;Dazhi Ding;
      Pages: 5217 - 5226
      Abstract: An effective method for identifying inertia characteristics of cone-shaped space target based on deep learning is proposed. The inertia ratio is determined by the time-varying scattering fields from the cone-shaped targets. The multistatic method is introduced to reduce the evaluation time of time-varying scattering fields. The micro-Doppler spectrogram (MDS) dataset is constructed by the time–frequency analysis with numerical simulation method, point scattering model, and experimental tests. The compressed dataset is further achieved by truncated singular value decomposition (SVD). Finally, the micromotion parameter identification model is constructed to identify the inertia ratio for the cone-shaped space target. The interaction loss function and the feedforward denoising convolutional neural networks (DnCNNs) are employed to improve the identification accuracy. Parameters identification of the precession frequency, precession angle, spin frequency, and inertia ratio with both simulation and experiment datasets demonstrate the validity of the proposed method.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Two-Port Microstrip Antenna With High Isolation for Wi-Fi 6 and Wi-Fi 6E
           Applications

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      Authors: Weiquan Zhang;Yue Li;Kunpeng Wei;Zhijun Zhang;
      Pages: 5227 - 5234
      Abstract: In this article, a two-port microstrip antenna (MSA) with high isolation is presented for simultaneously supporting wireless fidelity 6 (Wi-Fi 6) and wireless fidelity 6E (Wi-Fi 6E) applications. Due to the narrow guard band between Wi-Fi 6 (5.15–5.83 GHz) and Wi-Fi 6E (5.92–7.125 GHz), the mutual coupling near common edge frequencies cannot be sufficiently suppressed by existing filters. To mitigate the mutual coupling over the guard band of a symmetrical two-port MSA, the common-mode (CM)/differential-mode (DM) cancellation theory was utilized. Then, the operating frequencies of two ports were tuned to Wi-Fi 6 and Wi-Fi 6E bands, without deteriorating the original decoupling performance. Finally, two filters were loaded to realize high isolation over the whole working bandwidth. For the demonstration, a prototype was fabricated and measured. The measured results show that the proposed two-port MSA achieves the impedance bandwidth of 5.49–5.9 and 5.89–7.14 GHz and the isolation over 20 dB across the whole band. The results indicate that the proposed antenna is a promising candidate for Wi-Fi 6 and Wi-Fi 6E applications.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Depolarizing Chipless RFID Tag Made Orientation Insensitive by Using
           Ground Plane Interaction

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      Authors: Zeshan Ali;Olivier Rance;Nicolas Barbot;Etienne Perret;
      Pages: 5235 - 5245
      Abstract: The ground plane has never been considered as a degree of freedom to be used for chipless radio frequency (RF) identification (RFID) tag design purposes. For the first time, we show that the interaction with the ground plane can be exploited to achieve challenging designs, such as depolarizing tag insensitive to orientation (i.e., nonzero cross polar for any roll angle). The principle relies on the perturbation of the ground plane symmetry with merely one microstrip dipole placed near the edge of the substrate. Chipless RFID tags are realized using three different shapes of the substrate (square, octagonal, and circular) to achieve multiple edges. The measurements are performed in a semianechoic and office environment with tag attached to objects (cardboard box and metallic plate). The measured results of the square chipless RFID tags present magnitude variations (< 10 dB) but are detectable over a full 360° even in real environment yielding an “orientation-insensitive” detection system. Compared to previous designs, the frequency variability of the peaks is negligible.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Textile UHF-RFID Antenna Embroidered on Surgical Masks for Future Textile
           Sensing Applications

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      Authors: Chengyang Luo;Ignacio Gil;Raúl Fernández-García;
      Pages: 5246 - 5253
      Abstract: Ultrahigh frequency (UHF, 865–868 MHz) radio frequency identification (RFID) devices are expected to be implemented in many health-caring areas. In this article, we present three progressive designs of textile UHF-RFID antennas on surgical masks using a function-extensible integrated circuit (IC) chip (Rocky 100). The simulated and measured resonance curves of the designs all match well ( $ S_{11} < -20$ dB at 868 MHz) and the maximum realized gain are improved progressively in order to overcome the difficulty of the chip low sensitivity and increase the maximum read range. The best type (Design 3) is selected and its read range measured by the RFID reader (M6E Kit) can reach 2.5 m in air. In addition, several reliability validation measurements are performed, such as bending and skin contact, and maximum read range can reach 1.1 m considering the on-body worn worst case. The proposed Design 3 allows common use as a tag for tracking or safe distance alert under an epidemic situation. Alternatively, for the used function-extensible chip, the design can be applied to many different types of sensors for various application scenarios.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Wideband Back-Cover Antenna Design Using Dual Characteristic Modes With
           High Isolation for 5G MIMO Smartphone

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      Authors: Wei Hu;Zhan Chen;Long Qian;Lehu Wen;Qi Luo;Rui Xu;Wen Jiang;Steven Gao;
      Pages: 5254 - 5265
      Abstract: A novel method of designing a wideband high-isolated dual-antenna pair using dual-characteristic modes (CMs) is presented for fifth-generation (5G) multiple-input multiple-output (MIMO) smartphone applications. A set of orthogonal CMs resonating from the square-loop slot is first introduced and works for the lower band. Then, another set of orthogonal CMs resonating from the edge branches is introduced with a shared compact radiator and works for the higher band. In combination with two sets of degenerated CMs and a capacitive coupling feeding structure, the proposed dual-antenna pair achieves a broad impedance bandwidth and high isolation without the need for any external decoupling structures. Based on this dual-antenna pair, an $8times $ 8 MIMO array is developed and integrated into the back cover of a smartphone, which realizes zero ground clearance on the system circuit board. To verify the design concept, prototypes of the antenna pair and MIMO array were fabricated and measured. It shows that experimental results agree well with the simulation results. More importantly, the presented $8times $ 8 MIMO array has high isolation of more than 20 dB is achieved across the operating band of 3.3–3.8 GHz.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Orientation-Insensitive Chipless RFID Achieved in Multiple Rotational
           Degrees of Freedom

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      Authors: Ying-Hsiu Cho;Fei-Peng Lai;Yen-Sheng Chen;
      Pages: 5266 - 5277
      Abstract: Frequency-coded chipless radio frequency identification (RFID) suffers from resonant frequency detuning caused by misaligned orientations. The literature has employed topological symmetry to prevent shape variations; however, this scheme is effective only for the orientation in roll and cannot address other rotational degrees of freedom, including pitch and yaw. This study takes the first step to cope with the orientation mismatch against arbitrary roll, pitch, and yaw angles. The proposed technique requires the design of tag and new reader architecture, eliminating complex signal processing. The tag comprises resonators with the pattern of a short dipole. Two reader antennas are placed orthogonally and fed with equal power, illuminating co-polarized electromagnetic waves toward the tag. Based on the Pythagorean trigonometric identity, the sum of the backscattering power is unvarying against the rotations in pitch or yaw. The proposed technique is experimentally validated using a 6.97 bit system. When orientation mismatch in yaw appears, the proposed scheme improves the read reliability from 54.3% to 93.5%. Moreover, when mismatch in both roll and yaw occurs, the reliability is improved from 43.8% to 91.8%. Practical aspects, including various detection zones and the loading effect, are also analyzed.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Low-RCS and High-Gain Planar Circularly Polarized Cassegrain
           Meta-Antenna

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      Authors: Shaojie Wang;He-Xiu Xu;Mingzhao Wang;Chaohui Wang;Yanzhao Wang;Xiaohui Ling;
      Pages: 5278 - 5287
      Abstract: Achieving highly directive radiation with broadband operation, low scattering, and thin profile for a circularly polarized (CP) antenna is particularly challenging and yet rarely reported. Here, we propose a strategy of a CP Cassegrain meta-antenna by combining a planar helical antenna, a metasurface main reflector, and a metamaterial subreflector. The main reflector is designed to achieve focusing for CP waves at 13 GHz. The subreflector is chessboard-configured chiral metamaterial slab composed of two different types of chiral meta-atoms, aiming to achieve spin- and direction-selective CP transmissions and reflections. The distance between two reflectors is half of focal length, which enables our antenna to be dubbed as a folded reflectarray. The low radar cross section (RCS) is achieved based on scattering cancellation technique by realizing near 180° reflection phase difference between two neighboring chessboard submeta-atoms. Thanks to the architecture of the two reflectors, the proposed antenna exhibits high gain and low profile simultaneously according to image theory. For verification, a planar CP Cassegrain antenna, excited by a left-handed CP (LCP) planar helical antenna, is numerically studied, fabricated, and experimentally measured. Numerical results are in good agreement with the experimental ones, showing a peak right-handed CP (RCP) gain of 26.6 dBi at 12.6 GHz. Furthermore, the backward monostatic RCS of the antenna is dramatically reduced over −10 dB in a broad bandwidth from 8.4 to 15.7 GHz when it is illuminated by an LCP planar wave. Our proposed Cassegrain antenna features simultaneously broadband, high gain, low profile, and low RCS, providing a new avenue to low-profile CP reflectarrays with invisibility.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Multipole-Based Electrically Small Unidirectional Antenna With
           Exceptionally High Realized Gain

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      Authors: Ting Shi;Ming-Chun Tang;Ruolei Chai;Richard W. Ziolkowski;
      Pages: 5288 - 5301
      Abstract: Electrically small, high-directivity antennas are in demand for a variety of current and future wireless applications. An electrically small directive antenna (ESDA) that requires only one specially engineered port to excite a set of multipoles is demonstrated in this article. Four 90° copper sectors are combined with additional structures and fed with a coaxial cable. Two resonant quadrupoles (equivalent to two pairs of resonant electric dipoles) and one magnetic dipole are excited. Both high radiation efficiency and good impedance matching are achieved. Theoretical calculations, numerical simulations, and experimental measurements are shown to be in good agreement. An optimized prototype is designed, fabricated, and tested. The measured results confirm that it is a supergain system. The unidirectional ESDA has a peak directivity of 6.71 dBi, a peak realized gain of 6.31 dBi, radiation efficiency of 94.5%, and a front-to-back ratio of 14.89 dB at its resonance frequency, 814 MHz. Its height is $0.06 lambda _{mathrm{ res}}$ , and $ka = 0.98$ . These measured realized gain and directivity values exceed both the Harrington and Kildal–Best $ka$ -based upper limits.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Multi-Turn Coil Antenna With Nonuniform Clustered Turns Optimized Using
           Q-Assisted MMSE Procedure to Enhance Misalignment Tolerance in WPT Systems
           

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      Authors: Ananth Bharadwaj;Ashwani Sharma;Chakradhar C. Reddy;
      Pages: 5302 - 5311
      Abstract: In this article, an optimized non-uniformly distributed turn (NUDT) coil antenna is proposed to mitigate the lateral misalignment problem in wireless power transfer (WPT) systems. The proposed $ {Q}$ -assisted ${H}$ -field forming technique is analytically implemented using a minimum mean square error (mmse)-based algorithm. This results in an optimized transmitter (Tx) coil with clustered turns achieving a widespread uniformity of the ${H}$ -field in the receiver (Rx) working region. The proposed optimal design shows a consistent mutual inductance and power transfer efficiency (PTE) irrespective of the Rx misalignment which is realized using the circuit parameters. The analytical and simulated results of the proposed Tx coil designed using the $ {Q}$ -assisted mmse-based ${H}$ -field forming technique is experimentally verified. The misalignment tolerance of the proposed antenna is improved over the existing design by 224%. The proposed design proves its advantage to realize misalignment tolerant wireless charging platforms for WPT applications.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Analysis and Design of Stable-Performance Circularly-Polarized Antennas
           Based on Coupled Radiators for Smart Watches

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      Authors: Xiao Zhang;Qi-Yu Zeng;Zeng-Pei Zhong;Qiong-Sen Wu;Lei Zhu;Tao Yuan;Qing-Hua Jiang;Bo Mei;
      Pages: 5312 - 5323
      Abstract: A singly fed circularly polarized (CP) antenna based on coupled radiator pair with stable CP performance is proposed for the accurate positioning of smart watches in this article. It is first demonstrated that two identical coupled monopoles sharing a finite ground can be equivalent as a second-order filter network consisting of composite J/K inverters. The coupled radiators will produce a pair of even and odd modes, whose resonant frequencies and bandwidths are determined by the coupling strength. After that, the characteristic mode analysis (CMA) is conducted to verify the circuit model, and it reveals that the even and odd modes are orthogonal to each other, which are candidates for CP radiation. In particular, the phase difference of the two modes is determined by the coupling coefficient, and it can be elaborately manipulated by properly changing the current distribution of characteristic modes through ground size, slot loading, and radiator length. At last, two antenna prototypes are designed, implemented, and measured to validate the working principle. Different from conventional CP antennas operating in degenerate modes, the proposed antennas are insensitive to perturbation segments and can maintain stable CP performance, which is highly demanded in smart watches under wearing conditions.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Improving Compact Short Backfire Antenna Gain and Cross-Polarization Using
           Choke and Ring Cavity Loading

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      Authors: Amirbahador Mansoori;Dustin Isleifson;Lotfollah Shafai;
      Pages: 5324 - 5334
      Abstract: We present two designs that improve the gain and cross-polarization performance of the waveguide-fed short backfire (SBF) antenna by introducing a choke (SBF-2) and by loading the cavity with a metallic ring feature (SBF-2-Ring). A series of parametric simulation studies on antenna dimensions provides information on how to improve the antenna gain and cross-polarization performance while simultaneously extending the impedance bandwidth. For SBF-2, the peak gain was 16.6 dBi, the minimum cross-polarization ratio was −23.8 dB, and the maximum impedance bandwidth was 27.3%, with a gain bandwidth of 19.2%. For SBF-2-Ring, the peak gain was 15.8 dBi, the minimum cross-polarization ratio was −29.1 dB, and the maximum impedance bandwidth was 43.5%, with a gain bandwidth of 31.8%. The concepts were verified by designing, fabricating, and testing two prototypes in the microwave C-band. Excellent agreement between simulation and measurement was achieved. The measured gain for SBF-2-Ring was >14 dBi for 4.7–6.2 GHz and the worst case cross polarization in the diagonal plane was $< -22$ dB for 5.3–5.8 GHz. Cross-polarization in the principal planes has significantly greater bandwidth and the worst case analysis is presented to give limitations on the performance.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Wideband Millimeter-Wave Substrate-Integrated Waveguide-Fed Metasurface
           Antenna

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      Authors: Ji-Wei Lian;Dazhi Ding;Rushan Chen;
      Pages: 5335 - 5344
      Abstract: A wideband metasurface antenna operating at millimeter-wave spectrum in substrate-integrated waveguide (SIW) technology is proposed. Coupled by a slot etched on an SIW section, the proposed metasurface antenna achieves a wide 10 dB impedance bandwidth in simulation from 19.2 to 42.4 GHz, indicating a fractional bandwidth of 75%. The development of the proposed metasurface antenna can be divided into four stages, i.e., a slot antenna, dielectric loading, adding covered metasurface, and connecting to a transition. The input impedance and the resonance of these stages are elaborated in detail to explain the working mechanism. Parametric study is carried out to inspect into the design process. By analyzing the $E$ -field distributions, the proposed metasurface antenna is characterized by TM10 mode, antiphase TM20 mode, and TM30 mode. Compared with other similar designs in the open literatures, the proposed metasurface antenna displays a widest impedance bandwidth. The dimension of the proposed metasurface antenna is $0.80,,lambda _{0} times 0.72,,lambda _{0} times 0.24,,lambda _{0}$ , where $lambda _{0}$ is the free-space wavelength at 30 GHz. The maximum gain within the interested frequency spectrum is 7.0 dBi.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Design of Broadband Aperture-Coupled Stacked Microstrip Antennas Using
           Second-Order Filter Theory

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      Authors: Nieves García-Alcaide;Armando Fernández-Prieto;Rafael R. Boix;Vicente Losada;Jesús Martel;Francisco Medina;
      Pages: 5345 - 5356
      Abstract: In this article, the authors propose a lumped circuit methodology for the design of broadband stacked microstrip patch antennas fed through an aperture. First, an equivalent circuit (EC) is introduced for the antenna. The EC consists of an $LC$ series resonator modeling the feed plus two capacitively coupled $LC$ parallel resonators accounting for the radiating patches. Then, a deembedding procedure based on total least squares method is introduced to determine all the parameters of the antenna EC. Second, the circuit stage modeling the patches is designed as a second-order Chebyshev filter based on coupled resonators. Since the standard Chebyshev approach leads to circuit parameters that cannot be physically obtained in practice, a modified second-order quasi-Chebyshev design is presented, which can be physically implemented by stacking one conventional rectangular patch above one rectangular patch with both inner and meandering slots. The proposed methodology is used to design an antenna with over 30% bandwidth at a center frequency of 5.57 GHz. A prototype has been fabricated and measured, and good agreement has been found between simulations and experiments.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • UWB Bowtie Antenna for Medical Microwave Imaging Applications

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      Authors: Ondrej Fiser;Vojtech Hruby;Jan Vrba;Tomas Drizdal;Jan Tesarik;Jan Vrba Jr;David Vrba;
      Pages: 5357 - 5372
      Abstract: This work presents a design and experimental validation of a compact ultrawideband (UWB) bowtie antenna and balanced-to-unbalanced (balun) circuit for medical microwave imaging (MWI) applications working in the frequency band of 1–6 GHz. The UWB balun is perpendicularly attached to the planar bowtie arms, whose dimensions were miniaturized by rounding the bowtie edges. The antenna reflection coefficient was lower than −12 dB for tissues with a higher water content. The antenna possesses a high radiation efficiency (over 80%) and very low backward radiation. The predicted and measured specific absorption rate (SAR) distributions together with the electric field $vert Evert $ distribution proved a symmetrical radiation pattern. The potential of the presented antenna element was demonstrated by successful reconstruction of the images from the measured data by MWI methods. For this purpose, an MWI system equipped with eight antennas was implemented. The radar approach was used to determine the region of interest (ROI) where the area for microwave tomography reconstruction was identified. The dielectric properties within the ROI were reconstructed by using the Born approximation method at 1 GHz. This confirmed that the antenna can be used as the basis for more accurate multifrequency MWI systems and can be implemented in UWB MWI hybrid systems.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Novel Differentially Fed Dual-Polarized Filtering Magneto-Electric
           Dipole Antenna for 5G Base Station Applications

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      Authors: Dong Yang;Huiqing Zhai;Chaozong Guo;Chang Ma;
      Pages: 5373 - 5382
      Abstract: In this article, a compact differentially fed ±45° dual-polarized filtering magneto-electric (ME) dipole antenna with improved harmonic suppression is proposed and analyzed. First, the fusion of loop-slot dipole and half-wave vibrator is calculated and mentioned to furnish theoretical guidance. Then, by reasonably placing two pairs of second-order step impedance feedlines and a loop-slot patch, a corresponding two-mode loop-vibrator combination filtering antenna with an upper radiation null is naturally constructed. Moreover, simply by loading four open-circuit stubs at the center of octagonal slot patch edge, another extra resonance mode and radiation null in the upper band can be simultaneously obtained. Later, through hiring the reconstructed third-order stub-loaded-resonator (SLR) feedlines, wideband harmonic suppression along with a third radiation null is unaffectedly achieved. Finally, the optimized antenna is fabricated and tested. The measured results reveal it realizes a wideband impedance bandwidth of 42.0% (2.78–4.26 GHz) and a high port isolation of 35 dB. Also, the length of its harmonic suppression is measured from 4.56 to 7 GHz, while the depth reaches more than 20 dB. In addition, the measured gain and radiation efficiency curves in the operating band are relatively stable and both are at a high average value (8.2 dBi, 85%).
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Switched and Steered Beam End-Fire Antenna Array Fed by Wideband Via-Less
           Butler Matrix and Tunable Phase Shifters Based on Liquid Crystal
           Technology

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      Authors: Dongwei Wang;Ersin Polat;Henning Tesmer;Holger Maune;Rolf Jakoby;
      Pages: 5383 - 5392
      Abstract: This article presents the design of a Ka-band beam-switchable and beam-steerable endfire planar Yagi–Uda antenna array fed by a wideband Butler matrix, combining continuously tunable phase shifters based on a liquid crystal (LC) technology. The proposed array consists of four wideband 3 dB 90° branch-line couplers, two novel wideband via-less crossovers, LC-based 135° microstrip (MS) delay line phase shifters, and planar endfire Yagi–Uda antennas. The Butler matrix realizes beam switching, while LC phase shifters enable continuous beam steering inbetween the discrete beam positions. In this way, long delay line phase shifters are avoided for achieving 360°, reducing the phase shifter insertion losses (IL). Besides, such a hybrid beam steering method is expected to respond faster and more accurate. The array has two metallized layers, which can be easily fabricated by standard photolithography procedures. The fabricated array demonstrator is measured in terms of $S$ -parameters and far-field patterns. The measured return loss and isolation of the array are both ≥15 dB from 26 to 30 GHz. The beam is switchable among ±15° and ±45° in E-plane. By applying bias voltage up to 5 V to the LC phase shifters, the beam can be further continuously steered, covering almost −60° to +60° with acceptable sidelobe level. The maximum gain of the array is estimated to be 5.6 dBi. The radiation efficiency is 12%.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Dual Circularly Polarized 3-D Printed Broadband Dielectric Reflectarray
           With a Linearly Polarized Feed

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      Authors: Qiao Cheng;Yang Hao;Jack McGhee;William G. Whittow;J. C. Vardaxoglou;Raj Mittra;Shiyu Zhang;
      Pages: 5393 - 5403
      Abstract: A broadband dual circularly polarized (dual-CP) reflectarray based on 3-D printed dielectric materials is proposed in this article. A novel 3-D dielectric array element that enables the broadband linearly polarization (LP) to CP transformation is proposed. The unit cell consists of two orthogonal dielectric cuboids that adjust the phases of the two orthogonal LP waves independently and then combine them into a CP wave. The innovative unit cell design provides an extra degree of freedom in varying the geometries of the array elements in all three dimensions, which enables us to independently control the phases of the two LP waves. This maintains an equal amplitude and 90° phase difference condition across the entire reflectarray surface, realizing a broadband and high gain LP–CP reflectarray. The placement of the feed is also optimized to achieve the highest aperture efficiency. Finally, an off-set reflectarray was designed and fabricated using lost-cost 3-D printing. The reflectarray is able to provide both left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP), with just an LP feed. The measurements agree well with simulated results where the maximum realized gain and directivity at 34 GHz are measured as 27.9 and 28.1 dBi, respectively. The measured 3 dB gain bandwidth and aperture efficiency are 30% and up to 38%, respectively. More importantly, a broad 3 dB axial ratio (AR) bandwidth greater than 40% has been achieved for both LHCP and RHCP, covering almost the entire frequency band of interest, ranging from 26 to 40 GHz.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Dual-Wideband Dual-Circularly-Polarized Shared-Aperture Reflectarrays With
           a Single Functional Substrate for K-/Ka-Band Applications

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      Authors: Xuanfeng Tong;Zhi Hao Jiang;Yuan Li;Fan Wu;Ronan Sauleau;Wei Hong;
      Pages: 5404 - 5417
      Abstract: We report, here, the design and experiments of dual-wideband dual-circularly polarized (dual-CP) shared-aperture reflectarrays (RAs) operating at the K-/Ka-band utilizing a single functional substrate. By coupling the adjacent but separated resonances of the H-shaped aperture and circular patch, and utilizing the shorted microstrip phase delay lines, the proposed RA cells can offer wideband performance. Then, these RA cells are interleaved in a shared aperture for the dual-band operation. By combining the dynamic phase and Berry phase compensation techniques, the RA cells can independently control the reflective phase delay of orthogonal CP beams at both of the targeted bands, providing four degrees of freedom for beamforming. The diffractive property of an infinite periodic gradient array of the interleaved K- and Ka- band cells is investigated, which verifies the wideband performance of the proposed cells. Two RAs with a thin panel thickness of $0.27lambda _{K}$ ( $lambda _{K}$ is the free-space wavelength at the K-band) are fabricated and characterized, generating symmetrically and asymmetrically distributed dual-wideband dual-CP beams at the K-/Ka-band, respectively. The measured bandwidths for the two RAs are wider than 14.1% for the K-band right-handed CP (RHCP)/left-handed CP (LHCP) beams and about 11% for the Ka- band RHCP/LHCP beams with both the gain variation and axial ratio of smaller than 2 dB.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Wideband Differentially-Fed Slot Antenna and Array With Circularly
           Polarized Radiation for Millimeter-Wave Applications

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      Authors: Lehu Wen;Steven Gao;Wei Hu;Qi Luo;Xue-Xia Yang;Benito Sanz-Izquierdo;
      Pages: 5418 - 5429
      Abstract: A wideband differentially-fed slot antenna is presented for millimeter-wave (mmWave) applications. A novel method of using stepped corner-shaped slot is first utilized to establish the wideband circularly polarized (CP) radiation. In the configuration of corner-shaped slot, two wide open slots at the ends are utilized for effective orthogonal radiation, while the narrow slot at the center is utilized for power transmission and quadrature phase delay. An equivalent circuit is given to illustrate the inner working principle for CP radiation. In addition, square cuts are etched on the four corners of the radiating patches to further increase the axial ratio (AR) and impedance bandwidth. Based on this design concept, the antenna element was first designed and fabricated for performance verification. Then, a $1times $ 4 linear array with beam-scanning performance and a $4times $ 4 planar array with high gain and stable radiation were designed and fabricated. Both the simulated and measured results show that the $1times $ 4 linear array and $4times $ 4 planar array can have the wide overlapped impedance and AR bandwidths of 30.6% and 33.6% with a thickness of $0.16lambda _{0}$ , respectively. The advantages of compact size and wide bandwidth make the presented antenna a good candidate for mmWave applications.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Design of Beam-Steerable Aperiodic Linear Array Antenna With Improved Peak
           SLL Using Strip-Projection Method

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      Authors: Pratik Mevada;Sanjeev Gupta;Soumyabrata Chakrabarty;Milind Mahajan;
      Pages: 5430 - 5436
      Abstract: This article discusses the design of the beam-steerable aperiodic linear array antenna with improved sidelobe level (SLL), using the strip-projection method. The strip projection method uses the area of rotated higher-dimensional lattice and projects it to lower dimensions to generate an aperiodic array. This article describes the modeling and analysis of such an array and its optimization for the desired far-field performance. The aperiodic arrays are also generated using various evolutionary optimization algorithms, namely genetic algorithm (GA), particle swarm optimization (PSO), and Jaya algorithms. The far-field performance of the generated aperiodic arrays is compared with the conventional periodic array. The proposed 21-element aperiodic array is also populated with a X-band electromagnetically coupled patch antenna and phase shifter designed using varying width of the high dielectric material. The aperiodic patch array antenna is also developed and characterized for various beam scan angles. A significant improvement of 5.72 dB in peak SLL is achieved at ±30° beam scan angle.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Analysis, Rigorous Design, and Characterization of a Three-Layer
           Anisotropic Transmitarray at 300 GHz

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      Authors: Orestis Koutsos;Francesco Foglia Manzillo;Antonio Clemente;Ronan Sauleau;
      Pages: 5437 - 5446
      Abstract: A novel approach for studying and designing low-cost anisotropic transmitarrays (TAs) at sub-THz frequencies is presented here. The array comprises three metal layers and two interleaved dielectric spacers. A four-port equivalent circuit model is derived to accurately model the anisotropic behavior of the unit cell (UC). The analysis proves theoretically that nearly perfect transmission and complete phase control can be achieved at the same time. A systematic procedure optimizing the admittance tensor of the inner layer is described for the UC design. A 3 bit TA antenna at 300 GHz is fabricated using a standard printed circuit board (PCB) process. The measured results demonstrate that the design methodology is effective even under strict technological constraints. The antenna achieves a peak gain of 32.2 dBi with 36.5% aperture efficiency and 70.4 GHz of 3 dB bandwidth.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Two-Dimensional Scanning Phased Array With Large Element Spacing Using
           Pattern Reconfigurable Stacked Patch Antenna at Ka-Band

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      Authors: Ziheng Ding;Jingfeng Chen;Han Zhou;Ronghong Jin;
      Pages: 5447 - 5457
      Abstract: A 2-D scanning phased array with large element spacing using pattern reconfigurable stacked patch antenna at Ka-band is presented. The pattern reconfigurable stacked patch antenna is composed of four patches on the top integrated with four p-i-n diodes and a driven patch on the lower layer, where the top patches are located along the diagonals of the proposed antenna. By switching the reverse/forward bias states of p-i-n diodes, the phase gradients in different directions are generated and beam steering on the E-, D-(diagonal), and H-planes can be delivered. Subsequently, a 2-D scanning $4times 4$ phased array with large element spacing is proposed by applying the pattern reconfigurable stacked patch antenna. The 2-D space is divided into nine subsets and covered by nine states of the proposed antenna. The measured results show that a scanning range of ±55° on the E-, D-, and H-planes can be provided. The maximum realized gain is 20.9 dBi at 26.5 GHz with an aperture efficiency of 62.0%. Compared with conventional half-wavelength phased array, the complexity and cost can be reduced for 2-D scanning phased array by introducing the proposed pattern reconfigurable stacked patch antenna.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A New High Aperture Efficiency Transmitarray Antenna Based on Huygens
           Metasurfaces

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      Authors: Iman Derafshi;Nader Komjani;
      Pages: 5458 - 5467
      Abstract: In this article, a new transmitarray (TA) antenna is designed and fabricated based on Huygens metasurfaces (HMSs). An analytical method has been used to achieve the distribution of surface parameters equivalent to HMS. In this method, the required equations for computing the surface parameters are derived using ray tracing, generalized sheet transition conditions, and two conditions of local power consumption and local impedance equalization. In order to implement these surface parameters, wire and loop unit cells are utilized, which are exposed to the radiation transversely. The array of these unit cells offers high aperture efficiency broadband TA antennas in low aperture profile. The fabricated TA antenna with a low aperture thickness of $0.2lambda $ exhibits the bandwidth, sidelobe level (SLL), and cross-polarization level of 14%, −19 dB, and −19 dB, respectively. In addition, the high aperture efficiency of 65% is reached with this TA, which shows great improvement in comparison to previous works.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Innovative Inverse Source Approach for the Feasibility-Driven Design of
           Reflectarrays

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      Authors: Marco Salucci;Giacomo Oliveri;Andrea Massa;
      Pages: 5468 - 5480
      Abstract: The design of feasible surface currents in reflectarray (RA) antenna is addressed. By exploiting the nonuniqueness of the associated inverse source problem, an innovative synthesis method is proposed to simultaneously match radiation requirements and constraints on the surface currents. First, the surface current of the RA is expressed as the linear combination of a “preimage” term, which is computed with a truncated singular value decomposition of the RA radiation operator, and a suitable “null-space” component. A customized multiagent global optimization is applied to set the latter. A set of numerical experiments, concerned with different RA apertures and radiation objectives, are presented to illustrate the features of the proposed approach as well as to assess its potentialities and current limitations.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Low-Scattering-Cross Section Thinned Phased Array Antenna Based on Active
           Cancellation Technique

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      Authors: Peng-Fa Li;Shi-Wei Qu;Shiwen Yang;Jun Hu;
      Pages: 5481 - 5490
      Abstract: In this article, a novel approach to simultaneously reduce the scattering cross section (SCS) and lower sidelobe level (SLL) as well as the cost of a phased array is proposed, which is a combination of active cancellation and array thinning techniques. Two 10 $times,,10$ planar microstrip phased arrays are designed to validate the proposed concept, including a full array and a thinned array with 20 passive elements. In the thinned array, the passive elements are made use of and terminated at an optimized position with short-circuited loads to generate scattering fields with the required magnitude and phase for cancellation of the scattering fields from the active elements. Furthermore, the positions of the passive elements are optimized by a multiple dimensional discrete particle swarm optimization (MDDPSO) algorithm to achieve a low SLL. It is theoretically predicted that the thinned array features a low SLL below −18 dB in a scan range of ±45°, and SCS reductions of 21 and 9.1 dB in 7.3–10.1 GHz compared to an equal-sized metallic plate and a full array, respectively, which are further verified in simulations and measurements. It is also remarkable that the array cost is reduced due to array thinning, at the cost of an approximately 1 dB gain drop.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Optimal Capacity-Driven Design of Aperiodic Clustered Phased Arrays for
           Multi-User MIMO Communication Systems

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      Authors: Nicola Anselmi;Paolo Rocca;Stefan Feuchtinger;Bruno Biscontini;Alejandro Murillo Barrera;Andrea Massa;
      Pages: 5491 - 5505
      Abstract: The optimal design of aperiodic/irregular clustered phased arrays (PAs) for base stations (BSs) in multi-user (UE) multiple-input–multiple-output (MU-MIMO) communication systems is addressed. This article proposes an ad hoc synthesis method aimed at maximizing the UEs traffic capacity within the cell served by the BS while guaranteeing a sufficient level of the signal at the terminals. Toward this end, the search of the optimal aperiodic clustering is carried out through a customized tiling technique able to consider both single and multiple tile shapes and assure the complete coverage of the antenna aperture for the maximization of the directivity. Representative results, from a wide set of numerical examples concerned with realistic antenna models and benchmark Third Generation Partnership Project (3GPP) scenarios, are reported to assess the advantages of the irregular array architectures in comparison with regular/periodic layouts proposed by the standard development organizations as well.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Wide-Angle Impedance Matching Layer-Enhanced Dual-Polarization sub-6 GHz
           Wide-Scan Array for Next-Generation Base Stations

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      Authors: Giacomo Oliveri;Marco Salucci;Renato Lombardi;Roberto Flamini;Christian Mazzucco;Stefano Verzura;Andrea Massa;
      Pages: 5506 - 5520
      Abstract: A new sub-6 GHz antenna array that supports slant ±45° dual-polarization multiple-input multiple-output (MIMO) communications with high interport isolation and stable radiation performance over wide scan angles and bandwidths is designed. An architecturally inexpensive solution, which combines a standard truncated waveguide array and a single-layer patterned metasurface superstrate with wave manipulation capabilities, is proposed. A task-oriented formulation is adopted to mathematically formulate the EM associated multiscale design problem, then solved with an innovative instance of the system-by-design (SbD) paradigm where the fast and reliable modeling of the device is yielded by an ad hoc artificial intelligence-based surrogate. The final layout of the antenna array is validated with industry-standard full-wave numerical simulators.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Hybrid Approach for the Synthesis of Nonuniformly Spaced and Excited
           Linear Arrays With Strict Element Spacing Constraints

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      Authors: Jianhua Yang;Peng Yang;Feng Yang;Zhiyu Xing;
      Pages: 5521 - 5533
      Abstract: A hybrid methodology for the synthesis of nonuniformly spaced and excited linear arrays is proposed. At first, a modified genetic algorithm (GA) named linear-constraint genetic algorithm (LCGA) is discussed in this article to adapt to generalized linear-constraint optimization problems. Then, by nesting the technique of convex programming (CP) into LCGA, a hybrid optimization implementation is developed to jointly optimize the position and excitation variables. Due to the linear-constraint character of LCGA, array layouts can be exactly constrained with element spacings and the aperture size. A set of representative numerical experiments shows the effectiveness of this method to obtain very high-quality solutions.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Multistability in Coupled Nonlinear Metasurfaces

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      Authors: Constantinos Valagiannopoulos;
      Pages: 5534 - 5540
      Abstract: Multistability, namely, the property of obtaining different outputs depending on the past values of the input, is the key effect behind memory components in a variety of electronic, chemical, biological, and quantum systems. Two electromagnetic metasurfaces, with nonlinear admittances of Kerr type, are found to manifest significant multistability regarding their transmissivity. Such a feature is owed to the discontinuous variation of the response once the nature of the material changes from dielectric to plasmonic and vice versa, occurring at different levels of incoming power. The conditions for giving sizable hysteresis loops, with respect to either the input intensity or its operational wavelength, are determined. The reported results are expected to assist the modeling of nonlinear metasurfaces and open unexplored opportunities toward the efficient design of photonic memory elements.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Non-Uniform Gratings That Radiate Preselected Plane Waves

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      Authors: Thorkild B. Hansen;
      Pages: 5541 - 5554
      Abstract: A generalized Poisson summation formula produces exact expressions for the locations and strengths of line currents that radiate preselected plane waves. The line currents can be in free space or placed above a perfectly conducting ground plane. Closed-form expressions are obtained for the line current locations and amplitudes when the plane-wave parameters have periodic amplitudes and propagation vectors. A corresponding wire-impedance solution is derived that employs thin-wire approximations and takes into account all multiple interactions between wires. Remarkably, this solution holds even when the required impedance values are nonperiodic. The plane-wave parameters within one period determine the period of the impedance values and, thus, determine how many different types of loaded wires are required. For general nonperiodic plane-wave parameters, the line-source locations and amplitudes can be determined from an FFT approach involving a complex-contour integral, and the corresponding wire impedances can be computed numerically. With these impedance solutions, the number of degrees of freedom for the planar grating has been increased significantly to allow for the creation of a wide range of plane-wave fields.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Efficient Bloch Analysis of General Periodic Structures With a Linearized
           Multimodal Transfer-Matrix Approach

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      Authors: Federico Giusti;Qiao Chen;Francisco Mesa;Matteo Albani;Oscar Quevedo-Teruel;
      Pages: 5555 - 5562
      Abstract: A systematic and efficient multimodal transfer-matrix approach is proposed for the comprehensive Bloch analysis of general 1-D/2-D/3-D periodic structures. We provide a linearization procedure for transforming the original nonlinear eigenvalue problem associated with 2-D/3-D structures to a standard one that can easily be solved without the need of a zero-searching algorithm in the complex plane. The proposed approach has been validated with bounded/open structures with complex geometries and/or inhomogeneous lossless/lossy materials. It demonstrates a significantly reduced computational time and leverages the strengths of full-wave simulators to deal with general problems and ad hoc quasi-analytical methods to give a fundamental understanding of the behavior of the structure. Also, it allows for an accurate evaluation of the imaginary part of the wavenumber, which offers information of material dissipation, stopband rejection, leakage, and complex modes.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Design of In-Phase and Quadrature Two Paths Space-Time-Modulated
           Metasurfaces

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      Authors: Xinyu Fang;Mengmeng Li;Dazhi Ding;Filiberto Bilotti;Rushan Chen;
      Pages: 5563 - 5573
      Abstract: Space-time-modulated metasurfaces can manipulate electromagnetic waves in space and frequency domains simultaneously. In this article, an analytical design of space-time-modulated metasurfaces with modulation elements composed of two paths, In-phase (I) and Quadrature (Q), is proposed. The model is derived analytically, the space-/frequency-domain manipulations are achieved by designing the dimension and time sequence of I and Q paths. In the specular reflection direction, an objective frequency shift of the reflected first-order harmonic can be obtained. While, in other directions, the opposite first-order harmonic can be easily controlled by changing the dimension of I/Q paths, and the objective first-order harmonic remains unchanged. Furthermore, with a small dimension of I/Q paths, the first-order harmonic can be used for beam scanning by predesigning the start time of the modulation element. To realize the space-time-modulated metasurface with the required periodically time-varying responses, 2 bit unit cells loaded with dynamically switchable pin diodes are used as I/Q modulation. Both the analytical and numerical results demonstrate that space- and frequency-domain manipulations of the reflected fields by the first-order harmonics can be simultaneously obtained. The proposed designs have potential applications in wireless communications, radar camouflaging, and cloaking.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Transparent and Broadband Diffusion Metasurface With High Transparency and
           High Shielding Effectiveness Using Metallic Mesh

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      Authors: Jianzhong Chen;Yaqi Wei;Yutong Zhao;Lei Lin;Liang Li;Tao Su;
      Pages: 5574 - 5583
      Abstract: A novel transparent and broadband diffusion metasurface that is composed of digital coding elements is presented. A coding unit shares a symmetric circular quasi-Minkowski closed-loop shape that is capable of generating 1 bit coding (with two phase states of 0° and 180°) elements by using different geometric scales. To improve the optical transmittance of metasurface, the top layer of the coding elements adopts the metal rings with ultrathin linewidth with the optical transmittance of above 97% theoretically, whereas the bottom layer adopts hexagonal ring mesh metallic film with the optical transmittance of 95.4% and high electromagnetic interference (EMI) shielding effectiveness. Moreover, an optimized random distribution of coding elements is elaborately designed to realize diffusion patterns with numerous uniform grating lobes resulting in significant suppression of the backward peak energy level. Finally, a prototype diffusion metasurface is fabricated and good agreement between the simulated and the measured results is obtained. The results demonstrate a significant polarization-insensitive diffusion property with about 10 dB scattering reduction in a broadband from 10.5 to 19.5 GHz, reaching a fractional bandwidth of 60%, as well as show good scattering reduction properties for oblique incident waves. The proposed optical transparent diffusion metasurface has further advantages of opening up a new route for tailoring the exotic microwave scattering features with simultaneously high transmittance such as window and other transparent applications in visible frequencies and can be extended for imaging and communications.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Dual-Band Circular Polarizers With Versatile Polarization Conversions
           Based on Aperture-Coupled Patch Resonators

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      Authors: Jin-Ming Xie;Bo Li;Lei Zhu;
      Pages: 5584 - 5596
      Abstract: In this article, a class of low-profile dual-band circular polarizers based on aperture-coupled patch resonators (ACPRs) are proposed to achieve versatile linear-to-circular polarization (LP-to-CP) conversions. Initially, a dual-band dual-polarized bandpass frequency-selective surface (FSS), consisting of a composite array of two independent ACPRs subelements, is presented to obtain the desired transmission properties for vertically and horizontally polarized incident waves. The equivalent circuit model is then introduced to analyze the proposed FSS, exhibiting that transmission magnitude properties of vertically and horizontally polarized transmitted waves can be independently designed within these two passbands. Furthermore, two pairs of rectangular slots are introduced in the patches of these ACPRs subelements and extensively investigated to demonstrate that versatile phase differences between vertically and horizontally polarized transmitted waves with equal magnitude can be achieved. Based on this concept, within these two passbands, a right- or left-hand circularly polarized (RHCP or LHCP) transmitted wave is then attained by designing the vertical and horizontal components of a 45° tilted LP incident wave with equal magnitudes and ±90° phase difference, thus leading to dual-band LP-to-CP polarization conversions. To validate the design concept, two prototypes of dual-band circular polarizers with orthogonally and identically LP-to-CP conversions in each operation band are designed, fabricated, and measured. Experimental results have well revealed that our proposed structure has a few attractive advantages of ultrathin profile, low axial ratio, and flexible designs in LP-to-CP conversions and frequency band ratios.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Orthogonality Properties of Characteristic Modes for Lossy Structures

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      Authors: Matti Kuosmanen;Pasi Ylä-Oijala;Jari Holopainen;Ville Viikari;
      Pages: 5597 - 5605
      Abstract: Orthogonality of the characteristic modes with respect to the weight operator of the generalized eigenvalue equation (GEE), and in the far-field, is investigated in the case of lossy conducting and dielectric objects. Linking the weight operator to radiated power is shown to provide orthogonal far fields in the lossless case. In the lossy case, both the orthogonality of the characteristic far fields and the weight operator orthogonality of the modal currents are satisfied with respect to the Hermitian inner products only for sufficiently symmetric geometries, such as a sphere. For irregular lossy shapes, independent of the symmetry of the formulation, the far-field orthogonality can be obtained only with respect to the symmetric (non-Hermitian) product. The weight operator orthogonality can be satisfied with (complex) symmetric formulations, but again only with respect to the symmetric product. Since the symmetric products are not related to any physical power quantity, the modes do not form a (radiated) power orthogonal set in the lossy case. Hence, for lossy structures, characteristic modes (CMs) do not satisfy their classical definition and they need to be redefined.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Absorptive Frequency-Selective Transmission Structures Based on Hybrid FSS
           and Absorber

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      Authors: Hao Huang;Changzhou Hua;Zhongxiang Shen;
      Pages: 5606 - 5613
      Abstract: The replacement of lumped resistors with absorbing materials for absorptive frequency-selective transmission (AFST) structures enables a wider range of applications in low radar cross section (RCS) radomes. However, the transmission band within the absorption band for most absorbers is naturally nonexistent. It is shown that such a limitation can be overcome with the engineered frequency-selective surfaces (FSSs) and microwave absorbers to obtain a frequency response of absorption–transmission–absorption. In particular, a transmission window of low insertion loss within the absorption band is introduced by the integration of bandpass FSS and wideband absorber, while a bandstop FSS in the front minimizes the insertion loss in the passband. This design methodology is successfully demonstrated by two examples of AFST structures with single and dual polarizations.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Broadband Chiral-Type Linear to Linear Reflecting Polarizer With Minimal
           Bandwidth Reduction at Higher Oblique Angles for Satellite Applications

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      Authors: Mohammad Abdul Shukoor;Sukomal Dey;Shiban K. Koul;
      Pages: 5614 - 5622
      Abstract: This work presents a broadband linear–cross polarizer for K- and Ka-band applications. The design consists of a simple asymmetric width-based meander-line metasurface printed on a thin FR-4 grounded dielectric substrate. Normal incidence demonstrates 90% polarization conversion ratio (PCR) bandwidth (BW) of 20.64 GHz from 18.31 to 38.95 GHz with 72.1% fractional BW (FBW). Due to the destructive interference involved at greater oblique angles, reflective polarizers experience severe degradation of 90% PCR BW response. The proposed polarizer’s performance is obliquely stable up to 43° for transverse electric (TE) and 45° for transverse magnetic (TM) incidence with minimal 90% PCR BW reduction of only 13.95% (TE) and 15.25% (TM) compared with normal incidence. For the first time, transfer matrix method (TMM)-based equivalent surface impedance technique is modeled for oblique incidence analytically, closely resembling the full-wave analysis. The design is compact with a periodicity of $lambda text{o}$ /5.98 and a thickness of $lambda text{o}$ /13.69. The surface current patterns at resonant frequencies illustrate the reason behind broadband behavior. Bistatic radar cross section (RCS) analysis of the proposed converter is studied with reference to PEC. To the best of the author’s knowledge, this structure demonstrates broadband response with wide angular stability with less than 90% PCR BW reduction at higher oblique angles reported so far.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Hierarchical Curl-Conforming Vector Bases for Pyramid Cells

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      Authors: Roberto D. Graglia;Paolo Petrini;
      Pages: 5623 - 5635
      Abstract: Advanced applications of the finite-element method use hybrid meshes of differently shaped elements that need transition cells between quadrilateral- and triangular-faced elements. The greatest ease of construction is obtained when, in addition to triangular prisms, one uses also pyramids with a quadrilateral base, as these are the transition elements with the fewest possible faces and edges. A distinctive geometric feature of the pyramid is that its vertex is the point in common with four of its faces, while the other canonical elements have vertices in common with three edges and three faces, and that is why pyramids’ vector bases have hitherto been obtained with complex procedures. Here, we present a much simpler and more straightforward procedure by shifting to a new paradigm that requires mapping the pyramidal cell into a cube and then directly enforcing the conformity of the vector bases with those used on adjacent differently shaped cells (tetrahedra, hexahedra, and triangular prisms). The hierarchical curl-conforming vector bases derived here have simple and easy to implement mathematical expressions, including those of their curls. Base completeness is demonstrated for the first time, and results confirming the avoidance of spurious modes and faster convergence are also reported.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Tolerance-Aware Multi-Objective Optimization of Antennas by Means of
           Feature-Based Regression Surrogates

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      Authors: Slawomir Koziel;Anna Pietrenko-Dabrowska;
      Pages: 5636 - 5646
      Abstract: Assessing the immunity of antenna design to fabrication tolerances is an important consideration, especially when the manufacturing process has not been predetermined. At the same time, the antenna parameter tuning should be oriented toward improving the performance figures pertinent to both electrical (e.g., input matching) and field properties (e.g., axial ratio bandwidth) as much as possible. Identification of available tradeoffs between the robustness and nominal performance can be realized through multi-objective optimization (MO), which is an intricate and computationally expensive task. This article proposes a novel technique for fast tolerance-aware MO of antenna structures. The key component of the presented methodology is a feature-based regression surrogate, established based on the characteristic points of antenna responses extracted from its electromagnetic (EM)-simulation data, and employed for a rapid estimation of the maximum allowed input tolerance levels for given values of performance parameters of interest. Subsequent tradeoff designs are generated by tuning the antenna parameters for various assumed values of relevant figures of interest (e.g., the operating bandwidth). As demonstrated using three microstrip antennas, a rendition of performance-robustness tradeoff designs can be accomplished at the cost of just about forty (for six-parameter antenna) to about 80 (for 14-parameter antenna) per design EM analyses of the respective structure. The reliability of the approach is validated through direct EM-driven Monte Carlo analysis of the selected designs.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Efficient Integral Equation Method for Full-Wave Analysis of
           Inhomogeneous Electromagnetic Surfaces With Connected Conductors

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      Authors: Reza Gholami;Parinaz Naseri;Piero Triverio;Sean Victor Hum;
      Pages: 5647 - 5658
      Abstract: In this article, a generalized macromodeling approach is presented to simulate complex electromagnetic (EM) surfaces consisting of unit cells with connected conductors. Macromodels of each unit cell are produced by applying the equivalence principle on fictitious surfaces encapsulating them. Unit cells often consist of multiple dielectric layers and conductor traces, featuring multiscale structures. Challenges arise when a current-carrying conductor trace traverses the fictitious surface. Hence, a new method based on half Rao–Wilton–Glisson basis functions is proposed to accurately ensure the continuity of the surface currents and avoid singularities at the intersections. The accuracy of the proposed approach is validated by comparing the results with commercial solvers for different EM surfaces.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • EM-WaveHoltz: A Flexible Frequency-Domain Method Built From Time-Domain
           Solvers

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      Authors: Zhichao Peng;Daniel Appelö;
      Pages: 5659 - 5671
      Abstract: A novel approach to computing time-harmonic solutions of Maxwell’s equations by time-domain simulations is presented. The method, electromagnetic-WaveHoltz (EM-WaveHoltz), results in a positive definite system of equations, which makes it amenable to iterative solution with the conjugate gradient method or with generalized minimal residual method (GMRES). Theoretical results guaranteeing the convergence of the method away from resonances are presented. Numerical examples illustrating the properties of EM-WaveHoltz are given.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Solving Electromagnetic Scattering Problems With Tens of Billions of
           Unknowns Using GPU Accelerated Massively Parallel MLFMA

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      Authors: Wei-Jia He;Zeng Yang;Xiao-Wei Huang;Wu Wang;Ming-Lin Yang;Xin-Qing Sheng;
      Pages: 5672 - 5682
      Abstract: In this article, a massively parallel approach of the multilevel fast multipole algorithm (PMLFMA) on graphics processing unit (GPU) heterogeneous platform, noted as GPU-PMLFMA, is presented for solving extremely large electromagnetic scattering problems involving tens of billions of unknowns, In this approach, the flexible and efficient ternary partitioning scheme is employed at first to partition the MLFMA octree among message-passing interface (MPI) processes. Then, the computationally intensive parts of the PMLFMA on each MPI process, matrix filling, aggregation and disaggregation, and so on are accelerated by using the GPU. Different parallelization strategies in coincidence with the ternary parallel MLFMA approach are designed for GPU to ensure high computational throughput. Special memory usage strategy is designed to improve computational efficiency and benefit data reusing. The CPU/GPU asynchronous computing pattern is designed with the OpenMP and compute unified device architecture (CUDA), respectively, for accelerating the CPU and GPU execution parts and computation time overlapped. GPU architecture-based optimization strategies are implemented to further improve the computational efficiency. Numerical results demonstrate that the proposed GPU-PMLFMA can achieve over three times speedup, compared with the eight-threaded conventional PMLFMA. Solutions of scattering by electrically large and complicated objects with about 24 000 wavelengths and over 41.8 billion unknowns are presented.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Fast Computation of Electromagnetic Scattering From Dielectric Objects
           Using Quadrilateral Piecewise Sinusoidal Basis and Characteristic Basis
           Function Method

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      Authors: Chao Li;Mohammad S. Sharawi;Raj Mittra;
      Pages: 5683 - 5692
      Abstract: A method of moments (MoM)-based procedure is developed to calculate the scattering from homogeneous dielectric bodies. The technique uses quadrilaterals for the approximation of geometry and piecewise sinusoidal (PS) basis functions for the approximation of surface currents. The notable advantage of the PS basis is its radiated fields can be expressed in closed-form. The proposed approach therefore circumvents the need to use Green’s function in formulating the integral equations. Combined with a simple testing procedure, the matrix filling time is reduced and the concern of singularity is removed. To further reduce the computational complexity and enhance the performance, a characteristic basis function method (CBFM) is implemented and embellished with a new characteristic basis function (CBF) generation strategy. Specifically, a cubical surface bounding the entire target is first specified and discretized. A set of auxiliary sources are then defined in a manner similar to that done for a scattering body. These auxiliary sources are defined once and shared by different blocks. In comparison to the traditional plane wave spectrum (PWS) method, the CBFs generated by the new approach are valid not only for plane wave excitations but also for localized excitations. Numerical results are provided to validate the efficacy of the proposed algorithm.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Millimeter Wavelength Prime Resonance Spectra for High and
           Low-Conductivity Fibrous Aerosols

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      Authors: Charles W. Bruce;Al V. Jelinek;Sharhabeel Alyones;
      Pages: 5693 - 5698
      Abstract: Spectral dependence of the millimeter wavelength extinction due to two fibrous aerosols were measured over a frequency range spanning the primary attenuation peak. For contrast, two conductivities were selected, one representing polyacrylonitrile (PAN) graphite and the other is a metal-coated version incorporating the PAN core. Aerosol densities were measured to determine the mass-specific values of extinction. Aerosol length and diameter distributions were measured to provide parameters for comparison with theory. Both measurements and theory show a much stronger attenuation resonance for the higher conductivity material. At the resonance frequency, for which the particle length is approximately one-half the wavelength, the extinction efficiencies differ by about a factor of 3.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Entire-Structure-Oriented Work-Energy Theorem (ES-WET)-Based
           Characteristic Mode Theory for Material Scattering Objects

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      Authors: Ren-Zun Lian;Xing-Yue Guo;Ming-Yao Xia;
      Pages: 5699 - 5714
      Abstract: Entire-structure-oriented work-energy theorem (WET) framework is used to establish the characteristic mode theory (CMT) for material scatterers. Diagonalizing driving power operator (DPO) method is proposed to calculate characteristic modes (CMs). Solution domain compression (SDC) scheme is introduced to suppress spurious modes. An electromagnetic energy characteristic equation similar to the energy eigen-equation in quantum mechanics is derived for unifying the modal analysis theories of classical electrodynamics and quantum mechanics. Using the concept of driving power in the WET framework, the physical meaning of characteristic values is revealed; the reason leading to the nonorthogonal characteristic far fields of lossy scatterers is provided; it is explained why the conventional CMT fails to analyze some classical transmitting antennas; the physical interpretation for normalizing modal real power to 1 is given; the Parseval’s identity in CMT is derived; the classical concept of quality factor ( $Q$ -factor) is generalized to a novel concept of field-current phase-mismatching factor ( $Theta $ -factor). Using the diagonalizing DPO method with the SDC scheme, the spurious modes outputted from the conventional diagonalizing impedance matrix operator method are suppressed. Both the novel SDC and conventional dependent variable elimination schemes confirm the same conclusion that the spurious modes originate from overlooking the dependence relationships among the currents in CM-generating operator.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Analysis of High-Frequency Atmospheric Windows for Terahertz Transmission
           Along Earth-Space Paths

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      Authors: Xiang-Chun Cao;Jian-Hong Hao;Qiang Zhao;Fang Zhang;Jie-Qing Fan;Zhi-Wei Dong;
      Pages: 5715 - 5724
      Abstract: The atmospheric absorption effect greatly increases the transmission loss of terahertz (THz) waves, which limits the transmission distance. In this article, with the support of sufficient antenna gain, a series of high-frequency THz transmission windows in the ground-satellite link are presented. First, the more ideal ground-based site is determined. Based on the path loss model and the layered transmission theory, the total path loss is obtained. Combined with signal transmit power, antenna gain, signal-to-noise ratio, and noise power, total usable bandwidths and transmission windows in the 0.2–15 THz corresponding to antenna gain from 0 to 100 dBi are given. By taking the high-altitude platform as a relay link, the usable transmission windows are also given. The first six transmission windows are identified as [0.4776–0.48645 THz], [0.4906–0.49975 THz], [0.6618–0.6811 THz], [12.1015–12.10355 THz], [12.10425–12.11285 THz], and [12.11505–12.14355 THz] bands against 100 dBi gain near 1 and 10 THz bands, respectively. Furthermore, the influence of ice clouds on the transmission characteristics is analyzed. The additional attenuation in the partial usable atmospheric window frequency range can reach 1.84 dB typical, which is directly related to the effective radius and shape of particles.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Performance of Beamforming for a Handheld Device in Measured 21.5 GHz
           Indoor Channels

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      Authors: Jesper Ødum Nielsen;Gert Frølund Pedersen;
      Pages: 5725 - 5735
      Abstract: This article presents an evaluation of the performance of two different approaches for beamforming (BF) in a fifth generation (5G) handset, based on measured channels from a dual-polarized transmitter (Tx) to a mockup handset with a seven-element receiver (Rx) array. The measurements at 21.5 GHz include both small-scale and large-scale channel changes and were conducted for different users holding the mockup at different locations in an indoor corridor environment. The unique measurements enable novel results based on the statistics of the power achieved with BF, using channel state information (CSI) measured at a 90 Hz rate, and both when using beam scanning (BS) and the equal gain combining (EGC) reference case. For the case of ideal CSI knowledge, BF gains of up to about 18 dB were found. However, when the density of the angle scanning grid is reduced and the CSI is delayed to realistic values, the average performance decreases by 8 dB. More results are given in the article.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Pulsed Electromagnetic Diffraction by a Semi-Infinite Sheet With
           Conductive and Dielectric Properties

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      Authors: Martin Štumpf;
      Pages: 5736 - 5743
      Abstract: The 2-D diffraction of a pulsed electromagnetic (EM) plane wave by a semi-infinite sheet with conductive and dielectric properties is analyzed analytically with the aid of the Wiener–Hopf technique and the Cagniard–DeHoop technique. Novel exact analytical expressions describing the time-domain (TD) EM field in the presence of the conductive half-plane are derived. Moreover, closed-form approximate TD expressions are arrived at via Koiter’s approximate method of factorization. Illustrative numerical examples are presented.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Study on the Electromagnetic Scattering Characteristics of High-Speed
           Target With Non-Uniform Plasma via the FCC-FDTD Method

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      Authors: Wei Chen;Liufeng Wang;Zhenhua Wu;Ming Fang;Qingqing Deng;Anqi Wang;Zhixiang Huang;Xianliang Wu;Lixin Guo;Lixia Yang;
      Pages: 5744 - 5757
      Abstract: The face-centered cube (FCC) grid has more sampling points than the traditional Yee cell (as it contains a total of 14 grid points, of which six are center points and eight are vertices, and each grid point has three field components). Thus, FCC is better than the former in dealing with the dispersion error of anisotropic media. On the basis of this feature, this article first derived the FCC-finite-difference time-domain (FDTD) iterative formula for nonuniform plasma on the basis of FCC grid and verifies the accuracy of the algorithm. This algorithm is combined with the nonuniform plasma flow field model of hypersonic vehicles, and the backward single-station radar cross sections (RCSs) of vertical polarization (VV) and horizontal polarization (HH) are calculated under different flight altitudes, flight velocities, and external conditions. Results showed that as flying height increased or flying speed decreased, it results in an increase in RCS. Different external magnetic fields and incident angles also had an obvious impact on the electromagnetic scattering characteristics. From the perspective of electromagnetic wave polarization, both VV polarization and HH polarization have a great impact on RCS. These results provide a theoretical basis for studying the electromagnetic scattering characteristics of nonuniform plasma targets.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Multi-Modal Scattering and Propagation Through Several Close Periodic
           Grids

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      Authors: Christoph Kohlberger;Andreas Stelzer;
      Pages: 5758 - 5769
      Abstract: The presented method describes reflection and transmission of electromagnetic waves at multiple closely stacked metal grids using multimodal S-parameter propagation. For that, the periodic surface admittance curve of every metal layer was determined through a novel semianalytic approach that uses simple Fourier transformations instead of solving an integral equation. The modal components of this surface admittance were used to express the generalized scattering matrices of the individual grids. By applying multimodal propagation techniques to the resulting scattering parameters, it was possible to model the electromagnetic interactions within a multilayer stack of periodic impedance sheets. Resulting reflection and transmission parameters perfectly matched the corresponding full-wave simulations even above the grating lobe regime. In the end, the universal mode propagation method enabled modeling of a layer stack, connected to lumped components.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A New Model for Estimating Troposcatter Loss and Delays Based on
           Ray-Tracing and Beam Splitting With ERA5

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      Authors: Shuang Zhang;Xi-Hong Chen;Qiang Liu;Xin-Ping Mi;
      Pages: 5770 - 5783
      Abstract: The atmospheric environment is one of the critical factors affecting troposcatter transmission loss and propagation delay. This article proposes a new estimation model that can accurately calculate troposcatter transmission loss and propagation delay with a numerical weather model (NWM). The ERA5 reanalysis data as the NWM are applied to construct the new model. The 3-D ray-tracing and beam splitting are used to calculate propagation paths and delays. Compared with the existing methods, the new model thoroughly considered the bending and delaying effects of the atmospheric environment on electromagnetic waves, resulting in more accurate estimates. The transmission loss calculation capability of the new model is compared with the International Telecommunication Union (ITU) model and the terrestrial trans-horizon propagation loss data banks. The propagation delay calculation capability is compared with the Bello model. These comparison results show that the new model sufficiently reflects the meteorological environment’s influence on transmission loss and propagation delay. Finally, the daily variation characteristics of losses and delays are analyzed using the new model and further validate the model performance.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Geometry-Based Stochastic Line-of-Sight Probability Model for A2G Channels
           Under Urban Scenarios

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      Authors: Qiuming Zhu;Fei Bai;Minghui Pang;Jie Li;Weizhi Zhong;Xiaomin Chen;Kai Mao;
      Pages: 5784 - 5794
      Abstract: Line-of-sight (LoS) path is essential for the reliability of air-to-ground (A2G) communications, but the existence of the LoS path is difficult to predict due to random obstacles on the ground. Based on the statistical geographic information and Fresnel clearance zone, a general stochastic LoS probability model for 3-D A2G channels under urban scenarios is developed. By considering the factors, that is, building height distribution, building width, building space, carrier frequency, and transceiver’s heights, the proposed model is suitable for different frequencies and altitudes. Moreover, in order to get a closed-form expression and reduce the computational complexity, an approximate parametric model is also built with the machine-learning (ML) method to estimate the model parameters. The simulation results show that the proposed model has good consistency with existing models at low altitude. When the altitude increases, it has a better performance by comparing with that of the ray-tracing (RT) Monte-Carlo simulation data. The analytical results of the proposed model are helpful for the channel modeling and performance analyses such as cell coverage, outage probability, and bit error rate in A2G communications.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Over-the-Horizon Channel of Radio Communication at VHF Band via Artificial
           Plasma Clouds

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      Authors: Hai-Sheng Zhao;Zheng-Wen Xu;Yao-Wu Wang;Shou-Zhi Xie;Kun Xue;Cheng Wang;Jian Wu;Jing-Fan Gao;Zhao-Hui Xu;Yan-Shuai Zheng;
      Pages: 5795 - 5803
      Abstract: Metal cesium (Cs) vapor, released at an altitude in the upper atmosphere, generates an artificial space plasma cloud with high electron density. It can act as a scatter to realize radio communication across an over-the-horizon distance. A full-life model of radio propagation via an artificial plasma cloud is established based on its space–time evolution in this article. In addition, this model is verified by the sounding data of the rocket release experiment carried out in the United States. The multipath effect of plasma cloud scattering is studied by using ray tracing, and then, the coherent bandwidth is estimated for this spatial channel. Also, the theoretical channel model of artificial plasma cloud is established by using its space–time evolution and atmospheric wind field parameters. Considering common modulation modes and receiver noise levels, the potential communication performance is evaluated by using the proposed channel model, such as the transmission rate, the bit error rate (BER), and the available time for building up and maintaining communication links. It is shown that the maximal communication rate is up to 200 kb/s, BER overall maintains below 10−7, and the available time for a single release is about 30–60 min; for the case of this article, they are release mass of 2–10 kg, communication distances of 400–1200 km, and radio frequencies of 30–70 MHz at the VHF band. This demonstrates that the artificial channel can propagate radio waves at a much higher frequency, wider bandwidth, and higher rate than those of HF communication. Hopefully, it could be a solution to overcome the intolerable shortcoming and adverse effects on HF communication due to ionospheric disturbances especially in cases of maritime, emergency, and minimum communications
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Integrated Terrain and Clutter Propagation Model for 1.7 GHz and 3.5
           GHz Spectrum Sharing

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      Authors: Christopher R. Anderson;
      Pages: 5804 - 5818
      Abstract: Over the past decade, spectrum sharing has evolved into viable commercial systems poised to meet the ever-increasing spectrum demand from service providers and end users. The key to the success of these systems is accurate and reliable propagation models that will simultaneously maximize the number of users able to access the spectrum and minimize the interference to incumbent or protected users. The classical propagation models currently utilized by these systems—the irregular terrain model (ITM) and extended hata (eHata)—do not account for features, such as foliage or endpoint clutter that can have a large impact on propagation loss. This article presents a measurement-based framework for updating these classical models and proposes a new integrated terrain and clutter model using publicly available geographic information system datasets. Over 400 000 path loss measurements were recorded in nine diverse locations across the United States at 1.7 and 3.5 GHz. Our updates improved the rms difference between measurements and model by 3–7 dB for ITM and 3–14 dB for eHata. In addition, we demonstrate several integrated terrain and clutter models that have rms differences ranging from 9.5 to 17.8 dB. Finally, cross validation was used to demonstrate the generalizability of our models to a wide variety of propagation environments.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • High Frequency Land Backscatter Coefficients Over Northern Australia and
           the Effects of Various Surface Properties

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      Authors: Danielle J. Edwards;Manuel A. Cervera;Andrew D. MacKinnon;
      Pages: 5819 - 5830
      Abstract: Over-the-horizon radars (OTHRs) utilize the refractive properties of the ionosphere to illuminate targets beyond the Earth’s horizon. Consequently, the performance of this type of radar is highly dependent on the ionosphere. Reliable models of the radar ground backscatter are required to accurately assess the ionospheric propagation conditions and, thus, the expected performance of OTHRs. The ground backscatter coefficient characterizes the amount of radiation scattered back from a surface toward a receiver per unit area. While the backscatter coefficient of the sea is well understood and may be calculated from theory if the sea state is known, the backscatter coefficient of land at high frequencies is not well understood. To calculate the land backscatter coefficients over Northern Australia, a methodology that compares observed backscatter ionograms to those synthesized using high-frequency (HF) radio wave ray-tracing techniques through model ionospheres was developed. Maps of the backscatter coefficients across Northern Australia were produced. The effects of surface properties, including topography, soil moisture, and vegetation cover on the backscatter coefficients, were investigated. A weak positive correlation between the backscatter coefficient and the soil moisture and surface roughness was observed; however, it was found that the vegetation had the largest effect on the backscatter coefficient.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Far-Field Radar Cross Section Determination From Near-Field 3-D Synthetic
           Aperture Imaging With Arbitrary Antenna-Scanning Surfaces

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      Authors: Takuma Watanabe;Hiroyoshi Yamada;
      Pages: 5831 - 5840
      Abstract: In this study, we propose a generalized algorithm for far-field radar cross section determination by using 3-D synthetic aperture imaging with arbitrary antenna-scanning surfaces. This method belongs to a class of techniques called image-based near-field-to-far-field transformation. The previous image-based approaches have been formulated based on a specific antenna-scanning trajectory or surface, such as a line, plane, circle, cylinder, and sphere; the majority of these approaches consider 2-D radar images to determine the azimuth radar cross section. We generalize the conventional image-based technique to accommodate an arbitrary antenna-scanning surface and consider a 3-D radar image for radar cross section prediction in both the azimuth and zenith directions. We validate the proposed algorithm by performing numerical simulations and anechoic chamber measurements.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Robust Method for Solving the Modal Fields in Radially Unbounded
           Cylindrical Waveguides With Two Layers Under Extreme Conductive Conditions
           

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      Authors: Guilherme S. Rosa;
      Pages: 5841 - 5848
      Abstract: In this article, we present a numerically stable formulation for the electromagnetic analysis of lossy circular waveguides. The associated boundary value problem is solved analytically via an appropriate set of scaled cylindrical functions. A new numerically stable characteristic equation that simplifies the application of Cauchy’s argument principle is introduced. Numerical results are presented and show that the proposed approach can solve modal fields even in extreme lossy scenarios.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Portable 5.8 GHz Dual Circularly Polarized Interferometric Radar Sensor
           for Short-Range Motion Sensing

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      Authors: Jingyun Lu;Zijian Shao;Changzhi Li;Changzhan Gu;Junfa Mao;
      Pages: 5849 - 5859
      Abstract: The conventional short-range interferometric radar sensors usually employ two separate transmitting (TX) and receiving (RX) antennas for improved TX–RX isolation. However, they are subject to increased system size and misalignment of the TX/RX radiation patterns. In this article, a portable 5.8 GHz dual circularly polarized (CP) interferometric radar sensor is presented, which leverages the proposed dual CP common-aperture antenna that reduces the size of the entire radar system. The common-aperture nature gets rid of the radiation pattern misalignment and ensures that the object can be in the optimal boresight direction. Cross polarization, i.e., right-hand CP (RHCP) for TX and left-hand CP (LHCP) for RX or vice versa, was employed based on the sequentially rotated array (SRA), which not only improves the TX–RX isolation but also adapts with the polarization change in radar sensing. Moreover, a near-field cancellation technique was proposed to further increase the TX–RX isolation in the small form factor. A portable 5.8 GHz radar sensor integrated with the proposed dual CP antenna was custom-designed. Compared to the conventional two-antenna architecture, the proposed radar sensor is reduced in size by 140% but can still achieve a high TX–RX isolation of >60 dB at 5.8 GHz. Experiments were carried and the results illustrate that the proposed radar sensor has high micrometer accuracy in detecting the predefined displacement motions and is able to precisely track the human vital signs in the office environment.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Correlated Sample-Based Prior in Bayesian Inversion Framework for
           Microwave Tomography

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      Authors: Rahul Yadav;Adel Omrani;Guido Link;Marko Vauhkonen;Timo Lähivaara;
      Pages: 5860 - 5872
      Abstract: When using the statistical inversion framework in microwave tomography (MWT), generally, the real and imaginary parts of the unknown dielectric constant are treated as uncorrelated and independent random variables. Thereby, in the maximum a posteriori estimates, the two recovered variables may show different structural changes inside the imaging domain. In this work, a correlated sample-based prior model is presented to incorporate the correlation of the real part with the imaginary part of the dielectric constant in the statistical inversion framework. The method is used to estimate the inhomogeneous moisture distribution (as dielectric constant) in a large cross section of polymer foam. The targeted application of MWT is in industrial drying to derive intelligent control methods based on tomographic inputs for selective heating purposes. One of the features of the proposed method shows how to integrate lab-based dielectric characterization, often available in MWT application cases, in the prior modeling. The method is validated with numerical and experimental MWT data for the considered moisture distributions.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Adaptive Data Acquisition Technique to Enhance the Speed of Near-Field
           Antenna Measurement

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      Authors: Rezvan Rafiee Alavi;Rashid Mirzavand;Ali Kiaee;Pedram Mousavi;
      Pages: 5873 - 5883
      Abstract: In this article, a new approach is proposed to improve the speed of near-field measurement of antennas. The near-field measurements are mainly performed using a planar near-field scanner, named RFX2. In RFX2, which is an electronically switched probe array, the probes in the $x$ and $y$ directions cannot be fabricated at the same place. At each point, only one tangential component of the magnetic field is measured, and the other component is estimated numerically using an interpolation technique. Here, an adaptive data acquisition technique is proposed that sequentially collects samples from the field in the areas with highly dynamic behavior and skips the regions that have smooth near-field variations. Since the newly introduced points at each iteration of the algorithm are not necessarily laid on the probe locations of the RFX2, the values of the data at these points are calculated using an interpolation method. The proposed adaptive algorithm in this work requires remarkably fewer samples to reach the same accuracy as uniform sampling. This method is also utilized in spherical NF measurement over $theta $ and $phi $ plane. The validity of the approach is verified using various numerical and measurement results.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Imaging Properties of Nonperiodic Time-Varying Active Frequency Selective
           Surface

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      Authors: Junjie Wang;Dejun Feng;Yameng Kong;Sinong Quan;Shiqi Xing;
      Pages: 5884 - 5891
      Abstract: The rapid development of artificial electromagnetic (EM) materials provides unprecedented freedom to manipulate EM waves. In recent years, reflective spectrum conversion technology based on EM materials has been widely studied due to its multiharmonic generation capability. The possibility of its application in wireless communication is explored. However, the research on spectrum conversion is mainly based on periodic modulation waveforms. The modulation effect of nonperiodic for EM materials has not been studied so far. In this article, a nonperiodic time-varying active frequency selective surface (AFSS) is proposed to manipulate the spectral distribution of harmonics. By dynamically controlling the amplitude of the reflected echo, a continuous Doppler spectrum is generated. On this basis, the imaging characteristics of nonperiodic time-varying AFSS are analyzed in detail, and the defocusing phenomenon of the target image is discovered. Finally, the radar imaging experiments for nonperiodic time-varying AFSS are conducted to verify the validity of the proposed method.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • CRLH-TL Based Reconfigurable Antennas With Multiple Parameter
           Reconfigurability

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      Authors: Kalyanbrata Ghosh;Sushrut Das;
      Pages: 5892 - 5896
      Abstract: In this communication, two composite right-/left-handed transmission line (CRLH-TL)-based reconfigurable antennas with multiple-parameter reconfiguration capability have been presented. In antenna I, the polarization is switched between circular polarization and linear polarization. In antenna II, a split-ring resonator (SRR) is introduced that is connected with the ground through another p-i-n diode D2. In the D2 OFF-state, the metamaterial behavior of the SRR establishes. Due to negative permeability at the frequency of operation, it produces magnetic coupling with the antenna and the antenna starts radiating at a new band (5.2 GHz), forming dual-band characteristics with circular polarization. Antenna II is capable of providing band/frequency and polarization/band, frequency, and polarization reconfiguration using different ON/OFF combination states of diodes D1 and D2. The antennas are suitable for 2.4/5.2 GHz WLAN and 3.5/3.6 GHz WiMAX applications.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Design, Uncertainty Analysis, and Measurement of a Silicon-Based Platelet
           THz Corrugated Horn

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      Authors: Jie Hu;Wei-Tao Lv;Hao-Tian Zhu;Zheng Lou;Dong Liu;Jiang-Qiao Ding;Sheng-Cai Shi;
      Pages: 5897 - 5901
      Abstract: Platelets corrugated horn is a promising technology for its scalability to a large corrugated horn array. In this communication, we present the design, fabrication, measurement, and uncertainty analysis of a wideband 170–320 GHz platelet corrugated horn that features with low sidelobe across the band (
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Broadband High Gain and Low Cross-Polarization Double Cavity-Backed
           Stacked Microstrip Antenna

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      Authors: Krishnendu Raha;K. P. Ray;
      Pages: 5902 - 5906
      Abstract: This communication presents a novel stacked multi-resonator two-layered suspended rectangular microstrip antenna (MSA) backed by double-cavity, which yields a wide bandwidth (BW) of 64% at the center frequency of 2.6 GHz, due to additional resonances introduced by the cavity. The proposed antenna has high radiation efficiency above 89.5% throughout the band yielding a maximum gain of 14.7 dBi and an average gain of 12.5 dBi. It has a stable radiation pattern and low cross-polarization better than −45 dB and yields uniform isolation better than 40 dB between two such antennas. Compared to without cavity-backed configuration, the proposed double cavity-backed configuration yields 82% more BW, 1.8 dB more gain, and 10 dB more isolation between the antennas. Simulated results are validated by measurements with a close agreement. Improved characteristics of the proposed antenna make it suitable for several applications including through the wall and ground penetrating radars (GPR).
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Broadband Circularly Polarized Magnetoelectric Dipole Antenna and Array
           for K-Band and Ka-Band Satellite Communications

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      Authors: Jiawang Li;Yun Hu;Lei Xiang;Weiyang Kong;Wei Hong;
      Pages: 5907 - 5912
      Abstract: A circularly polarized (CP) magnetoelectric dipole (ME-dipole) antenna with a wide impedance bandwidth and 3 dB axial ratio (AR) bandwidth is proposed. The antenna is fed by a microstrip line and coupled through a modified cross-slot on the ground plane. Based on the conventional linearly polarized (LP) ME-dipole, the proposed electric dipoles and the coupling slots are modified to generate the CP radiation. Simulated results of the antenna element show an impedance bandwidth of 72.8% from 16.35 to 35.08 GHz and a 3 dB AR bandwidth of 39.2% from 21.53 to 30.07 GHz. To enhance the gain of the antenna for practical application, a 4 $times $ 4 antenna array with full-corporate feeding network is designed, fabricated, and measured. The measured results show that an impedance bandwidth of 66.95% from 17.26 to 34.63 GHz and a 3 dB AR bandwidth of 41.1% from 19.25 to 29.25 GHz are achieved. The proposed antenna can be applied to K-band, Ka-band satellite communications or fifth-generation (5G) millimeter wave (mmWave) communications at n257 (26.5–29.5 GHz) and n258 (24.25–27.5 GHz) bands.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Asymmetric Endfire Frequency Scanning Tapered Slot Antenna With Spoof
           Surface Plasmon Polaritons

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      Authors: Hongxin Zhao;Feiyu Ge;Qiuyi Zhang;Shunli Li;Xiaoxing Yin;
      Pages: 5913 - 5917
      Abstract: An endfire frequency scanning tapered slot antenna (FSTSA) is proposed and investigated. The proposed FSTSA is a two-conductor structure with a gradient slots array etched only on one of two inner edges in the FSTAS. The asymmetrical inner edges enable the antenna to excite two modes with different phase constants simultaneously along the two inner edges. Due to dispersion characteristics of spoof surface plasmon polaritons (SSPPs), the phase difference between the EM waves along the two conductors changes versus frequencies, which enables the main lobe of the FSTSA to scan through the endfire direction. An analysis model is conceived to provide insights into the design, which accurately predicts main lobe directions and initial values of the proposed antenna. The proposed antenna is fabricated, and the measured results show that the main lobe of the antenna scans from −15° to 14° (endfire direction at 0°) from 6.60 to 7.70 GHz, with the scanning rate of 26.4°/GHz. This antenna could be suitable for radar, plane integrated communication system, and certain other beam-scanning applications.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • High Gain Planar Segmented Antenna for mmWave Phased Array Applications

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      Authors: Jinwoo Kim;Han Lim Lee;
      Pages: 5918 - 5922
      Abstract: A new high-gain antenna structure is proposed for mmWave 5G and potentially for B5G and 6G applications. The proposed antenna is configured by a planar segmented patch structure that has a radiator size comparable to the conventional patch but achieves more than 3 dB gain enhancement without a help of superstrate stack-up layer. The proposed planar segmented antenna (PSA) induces multiple magnetic currents through multiple segmented conductors, resulting in a strong magnetic field circulation around the conductors. Only one conductor requires an excitation port and each segmented conductor has a shorting pin to synchronize resonance currents. To verify the PSA operation, several prototypes were fabricated at 28 GHz with the identical volume of $1.213,,lambda _{0} times 1.213,,lambda _{0} times 0.113,,lambda _{0}$ , including the ground plane. The maximum measured impedance bandwidth of the single PSA was 23.1%. Furthermore, the measured maximum antenna gain was 11.5 dBi, whereas the same sized reference patch antenna showed only 6.3 dBi.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Ultra-Miniaturized Antenna With Ultra-Wide Bandwidth for Future Cardiac
           Leadless Pacemaker

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      Authors: Farooq Faisal;Muhammad Zada;Hyoungsuk Yoo;Ismail Ben Mabrouk;Mohamed Chaker;Tarek Djerafi;
      Pages: 5923 - 5928
      Abstract: The detuning owing to the complex in-body operating scenarios, environmental factors, and circuitry of the implantable medical devices (IMDs) are the primary concerns in integrating implantable antennas with their corresponding systems. The wide bandwidth achievement for avoiding the detuning challenges is constrained by device specifications and antenna miniaturization. This study presents an ultra-miniaturized antenna of only 10.66 mm3 volume with an ultra-wide bandwidth of 3040 MHz (0.79–3.83 GHz) for a leadless pacemaker (LP). The proposed antenna encompasses the five important bands: ISM (868–868.6 MHz, 902–928 MHz, and 2.4–2.48 GHz), Wireless Medical Telemetry Service (WMTS) (1395–1400 MHz), and the midfield (1.45–1.6 GHz) bands. To consider a practical operating scenario, the antenna was integrated with a battery and controlling electronics of an LP. In a homogeneous heart phantom (HHP), the proposed antenna showed a higher gain of −28.7, −20.02, and −16.7 dBi at 915 MHz, 1.4 GHz, and 2.45 GHz, respectively. The specific absorption rate (SAR) evaluation in the heart of a realistic model guaranteed patient safety by satisfying the IEEE C95.1-2005 and C95.1-1999 guidelines. The antenna is experimentally validated through measurements in minced pork. The strength of the received signal in the measurements confirms a stable biotelemetric link of the proposed ultra-wideband (UWB) antenna with an external monitoring system. The results obtained through simulations and in vitro testing emphasized that the proposed ultra-miniaturized and UWB antenna could operate more efficiently in the heart, thus establishing itself as a suitable candidate for the LPs.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Antenna-on-Display Concept on an Extremely Thin Substrate for Sub-6 GHz
           Wireless Applications

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      Authors: Myoungsun Kim;Dongseop Lee;Yerim Oh;Jae-Yeong Lee;Bumhyun Kim;Junho Park;Dongpil Park;Wonbin Hong;
      Pages: 5929 - 5934
      Abstract: This communication presents a concept of a sub-6 GHz antenna-on-display (AoD) that can eventually be integrated into the transparent area of a display panel of various wireless devices for the first time in the literature. The transparency of the proposed microwave AoD is realized using metal mesh conductive film and features optical transparency, which is compatible with high-resolution liquid crystal display (LCD)/organic light-emitting diode (OLED) display panel requirements. To maximize the radiation efficiency despite the extremely thin substrate ( $0.0048lambda _{0}$ ), a traveling-wave antenna topology is inspired and further modified to incorporate the inherent structural limitations of modern-day high-resolution display panels. Eventually designed to operate in a leaky-wave mode, a novella dedicated feeding mechanism is introduced to minimize undesired coupling between the antenna structure and the display panel. The composite right-/left-handed (CRLH) unit cell employs a single shunt inductor topology to maximize the radiation efficiency. The measured 6 dB impedance bandwidth of the proposed microwave AoD is from 2.36 to 6.17 GHz, which is consistent with the fast wave region of the proposed unit cell. The measured realized gain of the microwave AoD consisting of 13 unit cells is 2.68 dBi at 5.5 GHz with a radiation efficiency of 62.5%. This is the first demonstration to ascertain that an AoD topology can be applicable at microwave applications while reducing the antenna-to-ground distance by approximately a factor of 20 compared to previous studies.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Compact Wideband and Variable Impedance Transformation Ratio Balun for
           Folded Dipole

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      Authors: Wang Yao;Huotao Gao;Ying Tian;
      Pages: 5935 - 5940
      Abstract: Aiming at dipoles with different impedances, a wideband balun with adjustable impedance for the balanced port is proposed in this communication. The balun is directly connected to the dipole to form an antenna element, so it also needs to meet: no connection line is required; the overall size is less than a quarter of the wavelength. The proposed balun realizes balanced–unbalanced conversion through aperture coupling, and dual slot ensures its wide-band characteristics. Due to the high-impedance characteristics of the folded dipole (FD), the balun has achieved impedance conversion ratios of 6:1, 8:1, 10:1, and 12:1, and the corresponding bandwidths are 82.1%, 67.1%, 53.7%, and 44.4%, respectively. Finally, three types of wideband dipoles with different characteristic impedances are fabricated to verify the versatility of the balun.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Compact Dual-Polarized Filtering Antenna With Steep Cut-Off for
           Base-Station Applications

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      Authors: Xuekang Liu;Steven Gao;Wei Hu;Lehu Wen;Qi Luo;Benito Sanz-Izquierdo;Xiaodong Chen;Long Qian;Josaphat Tetuko Sri Sumantyo;Xue-Xia Yang;
      Pages: 5941 - 5946
      Abstract: A dual-polarized filtering antenna with steep cut-off and compact size is developed for base-station applications. In this design, four controllable radiation nulls are obtained by utilizing split rings, slotted T-shaped branches, a single-stub tuner, and a parasitic loop. Split rings are first used as the dipole arms to obtain the first radiation null at upper out-of-band. Four T-shaped branches working as DGS are printed under the crossed dipoles to achieve the second radiation null. The connected outer conductors of the differential feed structure acting as a single-stub tuner can provide the third radiation null to further enhance the upper band rejection. Finally, a parasitic loop is incorporated around the split rings, and the out-of-band rejection of the lower band is further enhanced by the fourth radiation null. More importantly, the impedance bandwidth of the antenna can be expended with two newly introduced resonant modes. As a result, a compact filtering antenna with a wide operational bandwidth of 1.7–3.01 GHz (56%) is realized for $vert text{S}_{dd11}vert < -15$ dB with the isolation higher than 38 dB. The out-of-band suppression is higher than 18.4 dB in 3.1–4.5 GHz and more than 47 dB in 0.8–1.1 GHz.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Broadband High-Gain SIW Horn Antenna Loaded With Tapered Multistrip
           Transition and Dielectric Slab for mm-Wave Application

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      Authors: Yaling Chen;Long Zhang;Yejun He;Chunxu Mao;Sai-Wai Wong;Wenting Li;Peng Chu;Steven Gao;
      Pages: 5947 - 5952
      Abstract: A substrate integrated waveguide (SIW) H-plane horn antenna loaded with tapered multistrip transition and dielectric slab is proposed for broadband high-gain operation. The broadband characteristic of the proposed antenna is obtained by loading a tapered multistrip transition. The theory of coupled resonator is introduced to reveal the mechanism of bandwidth enhancement. On the other hand, a dielectric slab is used to enhance the gain of the proposed antenna. The optimal length of this dielectric slab is determined based on the design principles of a dielectric rod with maximum gain. Besides, the tapered multistrip transition also contributes to the gain improvement by suppressing the feed radiation and prompting the transverse expansion of the surface wave. To verify the design theory and concept, a prototype operating at the K- and Ka-bands is fabricated and measured. The measurement results show that the impedance bandwidth of the proposed antenna is from 20.6 to 38.4 GHz (60%). Within the operating band, a peak realized gain of 19.1 dBi and excellent endfire radiation patterns with low cross polarization (20 dB) are achieved simultaneously. With its broad bandwidth, high gain, low cross polarization, and high FBR, the proposed antenna is promising for various millimeter-wave applications.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Design of Wideband Base Station Antenna by Involving Fragment-Type
           Structures on Dipole Arms

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      Authors: Dong Wang;Gang Wang;Diqun Lu;Nan Yang;Qingfu Zhang;
      Pages: 5953 - 5958
      Abstract: Base station antenna usually requires dual-polarization operation with satisfactory input return loss, adequate dual-polarization isolation, stable gain, and half-power beamwidth (HPBW) in a wide bandwidth covering the entire or part of the mobile communication bands. Such comprehensive requirements provoke great challenges in antenna design. A novel design scheme is proposed by involving fragment-type structures (FTSs) in antenna and seeking for the optimal FTS by multiobjective optimization searching. The technique is demonstrated by improving crossed dipoles for operation in band ranging from 1.7 to 3.8 GHz. Part of the dipole arms can be gridded into cells and reconfigured by using FTS elements. For automatic optimization searching, a binary coding scheme for both the FTS distributions and canonical dipole structure dimensions is proposed. Simulation and measurement show that the optimal crossed dipole antenna may acquire a wide operation bandwidth of 76.3%, with the return loss higher than 15 dB, isolation higher than 30 dB, HPBW of 65° ± 5°, and gain of 9 dBi ± 0.65 dBi for ±45° polarizations.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Compact Vertically Polarized Fully Metallic Quasi-Yagi Antenna With High
           Endfire Gain

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      Authors: Changjiang Deng;Weihua Yu;Kamal Sarabandi;
      Pages: 5959 - 5964
      Abstract: A compact fully metallic antenna with high endfire gain and vertical polarization is presented for applications that require the antenna to be mounted on large metallic platforms. The proposed structure includes one driven element on a ground plane, in addition to several parasitic directors and reflectors. The antenna behaves like a Yagi array, but with vertical polarization, where multiple directors and reflectors are used to enhance the endfire gain in the plane that contains the ground surface. The driven element is an upside-down U-shaped metallic strip with short vertical sides connected to the ground plane. The radiation is predominantly emitted from these vertical sides giving the antenna its vertical polarization radiation. Directors and reflectors are designed based on the driven element, with directors having the center of the U-shaped strip connected to the ground plane and reflectors without shorting pins in the middle. A prototype is fabricated with a volume of 104 $times 55times $ 6 mm3. The measured bandwidth is 18% (5.32–6.38 GHz). The variation of endfire gain is 2 dB around the nominal gain of 10.3 dBi across the bandwidth.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • High-Order Mode Resonant Planar Dual-Sense Bidirectional Circularly
           Polarized Antenna With Arbitrary Orthogonal Polarization Flared Angles

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      Authors: Shan-Shan Gu;Wen-Jun Lu;Xiao-Hui Mao;Lei Zhu;
      Pages: 5965 - 5970
      Abstract: A design approach to a planar dual-sense bidirectional circularly polarized (CP) antenna is advanced. The resultant antenna can exhibit orthogonal CP radiations in arbitrary directions between 90° and 180°, i.e., the flared angle formed by pure left-handed CP (LHCP) and right-handed CP (RHCP) directions could be set in a wide range from 90° to 180°. The operational principle is revealed by an equivalent source model at first. Then, prototype antennas are advanced by incorporating a high-order mode resonant, V-shape dipole to a planar magnetic dipole, and a parasitic electric dipole. As numerically simulated and experimentally validated, the flared angle formed by LHCP and RHCP directions can be adjusted as 90° and 135°. In the 90° case, the presented bidirectional CP antennas can exhibit impedance bandwidth of 6.6%, 3 dB axial ratio (AR) bandwidth of 13.0% in the $+ x$ -axis, and 8.9% in the +z-axis. The advanced low-profile (height < 0.05 wavelength) antenna can simultaneously provide spatial and polarization diversity abilities in one principal-cut elevation plane. Therefore, it would be a promising colocated, spatial/polarization diversity antenna in future wireless systems.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • 3-D-Printed Wideband Circularly Polarized Dielectric Resonator Antenna
           With Two Printing Materials

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      Authors: Zhen-Xing Xia;Kwok Wa Leung;
      Pages: 5971 - 5976
      Abstract: A new 3-D-printed wideband circularly polarized (CP) dielectric resonator antenna (DRA) with two printing materials is investigated. The DRA has a multilayer comb-shaped structure at its top for generating CP fields. Three dielectric strips are embedded inside the DRA body to support multiple transverse-electric (TE) DRA modes to widen the DRA bandwidth. To slightly improve the axial-ratio (AR) performance, the DRA is twisted in the horizontal plane. For demonstration, a prototype operating in C-band was designed and printed with two different materials. The reflection coefficient, AR, radiation pattern, antenna gain, and efficiency of the antenna are measured, and reasonable agreement between the measured and simulated results is observed. The prototype has a measured 10 dB impedance bandwidth of 69.7% (4.80–9.94 GHz) and 3 dB AR bandwidth of 68.6% (4.52–9.24 GHz), achieving a wide overlapping bandwidth of 63.2% (4.80–9.24 GHz). Both the AR and overlapping bandwidths are record-high for a single-fed CP DRA. The prototype has a measured peak antenna gain of 8.3 dBic inside the overlapped passband.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Single Layer Dual Circularly Polarized Antenna Array Based on Ridge Gap
           Waveguide for 77 GHz Automotive Radar

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      Authors: Zhaorui Zang;Ashraf Uz Zaman;Jian Yang;
      Pages: 5977 - 5982
      Abstract: A single layer 77 GHz dual circularly polarized (CP) antenna array is proposed based on ridge gap waveguides (RGWs) technology. The antenna consists of eight U-shaped slots, fed by two feeding networks for generation of dual CP. The proposed antenna array has been fabricated and measured. The experimental results show good agreement with the simulations. The axial ratio is below 2 dB, and the return loss and port isolation are better than 13 and 18.6 dB over 76–81 GHz, respectively. The measured gain for the integrated array is 14.8 dBi at the center frequency of 78.5 GHz. With integration of feeding networks and the radiating elements in a single layer, this antenna has potential to be used in automotive radars.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Low-Profile Dual-Band Circularly Polarized Antenna Combining Transmitarray
           and Reflectarray for Satellite Communications

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      Authors: Shuyang Yang;Zehong Yan;Mingbo Cai;Xi Li;
      Pages: 5983 - 5988
      Abstract: This communication proposes a low-profile dual-band circularly polarized (CP) antenna for satellite communication at K- and Ka-bands. The antenna consists of a folded transmitarray (TA) operating at 20 GHz and a multi-feed reflectarray (RA) operating at 30 GHz. The dual split rings are used as the TA and RA elements. The TA is placed above the RA. The TA acts as the phase-controlling surface at 20 GHz and does not affect the transmission of plane waves at 30 GHz generated by the RA. The RA simultaneously serves as the phase-controlling surface at 30 GHz and as the ground for the folded TA at 20 GHz. Owing to the combination of the folded TA and multi-feed RA with a small focal length-to-diameter ratio, the antenna profile is reduced, and the height-to-diameter ratio is only 0.4. Compared with the traditional horn feed system, the CP patch arrays integrated on the TA surface are used as the feeds in this design. The orthomode transducer (OMT) and circular polarizer are not needed, which significantly saves space and cost. The antenna was manufactured and measured to verify its performance. The measured results keep good consistent with the simulated results.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Single-Layer Dual-Band Dual-Circularly Polarized Reflectarray for Space
           Communication

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      Authors: Roger L. Farias;Custódio Peixeiro;Marcos V. T. Heckler;
      Pages: 5989 - 5994
      Abstract: This communication proposes a novel unit cell for the design of dual-band dual-circularly polarized reflectarrays for space communications. The main advantage of the proposed cell is the use of one single layer for the antenna fabrication, hence yielding lower costs and fabrication with lower complexity in comparison to multilayer antennas. The proposed cell is used to design a dual-band dual-circularly polarized reflectarray with widely separated bands. Due to the physical symmetry, it provides very good polarization characteristics. The antenna performance is validated by far-field measurements and very good agreement between simulated and measured results has been verified.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Focused Connected Array Antenna as a Broadband Beam-Steering Feed for
           Quasi-Optical System

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      Authors: Alejandro Pascual Laguna;Daniele Cavallo;Jochem J. A. Baselmans;Nuria Llombart;
      Pages: 5995 - 6000
      Abstract: This communication proposes a broadband and efficient integrated focal plane array solution based on a near-field focused connected array of slots. The focused aperture provides: 1) broadband and highly efficient illumination of the quasi-optical system and 2) scanning capabilities within a focusing system. The connected array antenna in turn allows for a fully integrated solution that can synthesize a focused aperture while providing broadband impedance matching. Focused connected array antennas enable the coupling to a reflector system over bandwidths in excess of one octave and with aperture efficiencies in excess of 60%. To demonstrate the concept, we present two printed circuit board (PCB) prototypes operating in the band 3–6 GHz and yielding more than 60% reflector aperture efficiency under broadside illumination and allowing to scan one beamwidth at the lowest frequency with a frequency-averaged scan loss of 0.2 dB. The feasibility of scaling this concept to THz frequencies and with dynamic beam-steering capabilities is discussed in the context of a superconducting device.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Wideband Polarization Rotation Transmitarray Using Arrow-Shaped FSS at
           W-Band

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      Authors: Suyang Shi;Qing Lu;Wenjie Feng;Wenjun Chen;
      Pages: 6001 - 6005
      Abstract: Based on the passband characteristics of frequency selective surface (FSS), a wideband transmitarray (TA) with linear polarization rotation at W-band is proposed. The middle layer of the unit cell is a pattern of arrow-shaped structure, which can rotate the incoming wave by 90°. A pair of parallel strip polarizers is employed to enhance the polarization conversion efficiency. The prototype of $25times 25$ -element TA is fabricated by the standard PCB technology. Within the 3 dB gain bandwidth of 20%, the measured peak gain of 28.7 dB with the corresponding aperture efficiency of 38.2% is achieved. The error analysis is also conducted by comparing the simulation and measurement. The performance of the proposed TA demonstrates that it is a suitable solution for wideband and low-cost applications in the millimeter-wave spectrum.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A New Multi-Band Multi-Array Antenna Configuration With Scattering
           Suppression for Radiation Pattern Distortion Mitigation of Base Station

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      Authors: Feifei Jia;Zhilun Zheng;Qiang Wang;Peitao Liu;Shaowei Liao;Wenquan Che;Quan Xue;
      Pages: 6006 - 6011
      Abstract: This communication presents a new multiband multiarray (MBMA) scattering suppression antenna configuration for a dual-band and dual-polarized antenna array with reduced radiation distortion. The proposed antenna array configuration consists of a low-band (LB) antenna element working in the 690–960 MHz band and four high-band (HB) antenna elements working in the 1.7–2.7 GHz band. The LB antenna introduces U-shape structures to the radiation element to neutralize HB scattering currents. On the other hand, the HB antenna involves an LC resonant structure between its radiation arm and feeding balun to suppress LB scattering currents. An antenna array using the proposed LB and HB elements is designed to achieve MBMA functions. Experimental results show that the radiation distortions in both LB and HB bands are improved significantly. The VSWR of less than 1.5, the isolation of more than 25 dB, and the symmetrical radiation pattern are obtained in both bands.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Circularly-Polarized Multi-Beam Magneto-Electric Dipole Transmitarray
           With Linearly-Polarized Feeds for Millimeter-Wave Applications

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      Authors: Jun Hu;Hang Wong;Lei Ge;
      Pages: 6012 - 6017
      Abstract: This communication presents the design of a wideband circularly polarized (CP) multibeam transmitarray with a cluster of linearly polarized (LP) feeds for millimeter-wave applications. A novel receiving/transmitting (Tx) unit cell, composed of one LP and one CP magnetoelectric (ME) dipoles, is designed with capability of converting the incident wave from LP source to CP radiation and enabling to provide a full 360° geometric phase coverage by rotating the CP element. The geometric phase compensation is realized by setting the space-dependent rotation angle for the Tx array such that it exhibits a wide frequency response in producing directive CP beam radiation with improved axial ratio (AR) performance. Moreover, a bifocal strategy is employed in the design of the multibeam transmitarray to achieve a small scanning loss. To verify our proposed methodology, a prototype of the bifocal multibeam transmitarray with seven LP ME dipole source radiators is fabricated and measured. The obtained results show that the seven beams can cover a range of ±33° with a peak gain of 21.5 dBic and a scanning loss of 2 dB. Meanwhile, the overlapped bandwidth for the reflection coefficient ( $vert S_{11}vert le -10$ dB), the 3 dB AR, and the half-power gain is around 33.3% (23–32 GHz).
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Mutual Coupling Compensation for Compact MIMO Radar

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      Authors: Zhou Jianxiong;Zhu Rongqiang;Li Haorun;
      Pages: 6018 - 6023
      Abstract: A calibration method to compensate for the mutual coupling and channel imbalance in a compact multi-input multi-output (MIMO) radar array based on turn table measurements is proposed. Two mutual coupling matrices, one for the transmit array and the other for the receive array, are used to model the relationship between the ideal manifold and the measured manifold. The practical factors such as the nonisotropic element pattern and the displacement of the array phase center are also taken into account. All the unknowns are determined by solving the nonlinear least-squares fitting problem iteratively. Using two coupling matrices consists of the mutual coupling mechanism in an MIMO array and has better calibration performance than using one matrix for the virtual array. It also reduces the dimension of the matrix and hence the computation load of calibration. Measurements by a microstrip array with two transmitters and four receivers are used to verify its effectiveness in angle estimation, beamforming, and superresolution of close targets.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Self-Decoupled Dual-Band Shared-Aperture Base Station Antenna Array

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      Authors: Yixin Li;Qing-Xin Chu;
      Pages: 6024 - 6029
      Abstract: A new decoupling concept for dual-band shared-aperture base station antenna arrays is proposed. By loading arrow-shaped decoupling structures in the hollowed regions of the low-band (LB) loop dipole arms, the LB antenna can yield partial reflection to the high-band (HB) antennas, canceling the HB-coupled wave. A dual-band base station antenna array is designed, fabricated, and measured based on this decoupling concept. With decoupling, the HB radiation patterns are restored. The copolarized in-band couplings between the HB antennas are reduced by about 9 dB, reaching >26.9 dB. The proposed antenna array possesses both cross-band and in-band decoupling abilities, without extra decoupling layer.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Method of Introducing Coupling Null by Shorting Pins for Stacked
           Microstrip Patch Antenna Array

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      Authors: Yulin Fang;Lin-Sheng Wu;Liang-Feng Qiu;Yue Ping Zhang;
      Pages: 6030 - 6035
      Abstract: In this communication, a method is proposed to generate coupling null by introducing shorting pins into a stacked microstrip patch antenna (S-MPA) array, named shorted S-MPA (SS-MPA). The currents on different regions of the driven patch, with approximately equal amplitude but out of phase, are formed, due to the shorting pins, which makes the electric field component $E_{x}$ canceled, introducing a new dip near the lower resonant frequency. The new dip works with the inherent dip produced by the radiation cancellation between two patches near the higher resonant frequency. High isolation is achieved over the wide impedance bandwidth of the SS-MPA array. Expected results are obtained from the fabricated two-element SS-MPA array. Moreover, the proposed scheme is employed to a three-element array successfully.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Folded Comb-Line Array for Backscattering-Based Bodycentric Communications
           in the 5G Sub-6 GHz Band

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      Authors: Cecilia Occhiuzzi;Jack D. Hughes;Francesco R. Venturi;John Batchelor;Gaetano Marrocco;
      Pages: 6036 - 6041
      Abstract: Growing interest in Internet of Things (IoT) and health care pushes the exploration of innovative solutions for connecting our bodies to external systems. The need for devices interoperability combined with data rate considerations, and low-power consumption make 5G backscattering-based communications a promising opportunity, especially in the low sub-6 GHz band. Starting from a monolithic array, this communication proposes a skin-mountable miniaturized antenna suitable for 3.6 GHz body-centric backscattering communications. The array is an improved version of the comb-line antenna, which simultaneously optimizes size and radiation features. The horizontal segments are folded such to place the radiating dipoles closer and increase the radiation efficiency of the structure by co-phasing a single component of the surface currents. Parametric analysis obtains optimal configurations in terms of gain and size. Compared to conventional layout, the miniaturized array has an efficiency 6 dB higher and an area 80% smaller while the improved structure provides a theoretical read distance of more than 4 m. Measurements on a volunteer corroborate the improved performance.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Circular Array of Endfire Yagi-Uda Monopoles With a Full 360°
           Azimuthal Beam Scanning

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      Authors: Yubo Wen;Pei-Yuan Qin;Geng-Ming Wei;Richard W. Ziolkowski;
      Pages: 6042 - 6047
      Abstract: A multiport circular array of endfire Yagi–Uda monopoles with a full beam coverage of the azimuth plane is developed in this communication. The known issue that a vertical monopole antenna on a finite-sized horizontal ground plane radiates an elevated beam is investigated. It is demonstrated that this effect can be mitigated by inserting resonant structures, i.e., slots, into the ground plane to redirect the radiated beam back to the horizontal direction. An endfire monopole-based Yagi–Uda antenna is then developed that radiates a directed endfire beam. A multiport circular array of these antennas is optimized to provide beam coverage over the full 360° azimuthal plane. A sector of this circular array of monopole-based Yagi–Uda antennas was simulated, fabricated, and measured to verify the concepts. Good agreement between the simulated and measured results is confirmed.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Dual-Band Aperture Shared Antenna Array With Decreased Radiation Pattern
           Distortion

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      Authors: Wei Niu;Baohua Sun;Gaonan Zhou;Zhepeng Lan;
      Pages: 6048 - 6053
      Abstract: In this communication, a dual-band aperture-shared antenna array (ASAA) is developed for base station. This ASAA contains a 4 $times $ 4 high-band (HB) antenna array, which operates from 3.4 to 3.8 GHz, and low-band (LB) antenna, which operates from 0.69 to 0.96 GHz. For decreasing pattern distortion of HB array due to the induced current in the LB element, a method following two side chokes (TSC) is proposed. By loading the TSC, the LB element exhibits a cross-band scattering suppression performance in HB. Furthermore, ASAA is fabricated and measured. Measured results show that the proposed ASAA exhibits stable radiation performance in both LB and HB. Also, the LB antenna can cover 0.69–0.96 GHz (VSWR < 1.5). Hence, the antenna array can be a good candidate for future 5G and 2G/3G/4G aperture-shared base station antenna array.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Dual-Band Dual-Rotational-Direction Angular Stable Linear-to-Circular
           Polarization Converter

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      Authors: Xiaoming Liu;Yixin Zhou;Chen Wang;Lu Gan;Xiaofan Yang;Lijun Sun;
      Pages: 6054 - 6059
      Abstract: A dual-band dual-rotational-direction reflective linear-to-circular polarization converter based on metasurface is designed, fabricated, and measured. The unit cell consists of an open ring and a square patch. The open ring creates two resonances, and the square patch is used to improve the axial ratio (AR). It is shown that this design can be working at two frequency bands, i.e., 29.0–41.5 GHz and 52.5–61.5 GHz. Interestingly, it is found that the linearly polarized wave in $x(y)$ -direction can be converted into right(left)-handed circularly polarized wave at the former band, and into left(right)-handed circularly polarized wave at the later band. Compared to other designs in the literature, this design demonstrates 45° angular stability for 3 dB AR over two operational bands. In addition, this design is realized on a single substrate, making it easier to be fabricated. Furthermore, the insertion loss can be as low as 0.5 dB, showing a very low-loss property. Lastly, the unit cell is less than 0.2 wavelength at the lower frequency band. The measured results show good agreement with simulation. Potential applications can be envisaged in dual-band and dual-polarization communication.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Design of Conformal Array of Rectangular Waveguide-Fed Metasurfaces

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      Authors: Insang Yoo;David R. Smith;
      Pages: 6060 - 6065
      Abstract: We present a systematic design method for a cylindrical conformal array of rectangular waveguide-fed metasurfaces. The conformal metasurface consists of multiple curved rectangular waveguides loaded with metamaterial elements—electrically small apertures—inserted into the upper conducting walls of the waveguides. Each element radiates energy into free space to contribute to an overall radiation pattern. Thus, the geometry or electrical configuration of each of the elements needs to be tailored to generate a desired pattern. Generally, due to difficulties in modeling the effect of curvature, the design of conformal metasurface arrays has relied on full-wave simulations or experiments. In this study, we propose a design method utilizing the semianalytical model of a planar metasurface accounting for metamaterial elements’ locations and orientations over a curved surface. Although approximate, we demonstrate that the alteration along with the framework of dipolar modeling of planar elements can be used for the analysis of conformal arrays with small curvature. We then design a conformal array metasurface using the method combined with the covariance matrix adaptation evolution strategy (CMA-ES) optimizer. Through numerical simulations, we confirm the validity of the proposed design method. Applications include the design of metasurfaces for radar, communications, and imaging systems for mobile platforms.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Note on Representation of Electromagnetic Plane Wave Polarization State

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      Authors: Izuru Naito;
      Pages: 6066 - 6071
      Abstract: Representations are studied for both natural and intuitive grasp of electromagnetic plane wave polarization states. The representations have been established, but unfortunately, the detailed definitions have variations depending on the references. These circumstances could cause unnecessary confusion. In order to resolve the confusion, representations are presented taking correspondence into consideration with both natural and intuitive grasp of polarization states. The presented representations are confirmed to be consistent with those in the references.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Transmission–Reflection-Integrated Metasurfaces Design for Simultaneous
           Manipulation of Phase and Amplitude

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      Authors: Guoqiang Li;Hongyu Shi;Jianjia Yi;Bolin Li;Anxue Zhang;Zhuo Xu;
      Pages: 6072 - 6077
      Abstract: A kind of transmission–reflection-integrated elements and metasurfaces (MSs) are proposed to achieve full-space manipulation of amplitudes, phases, and polarization states of electromagnetic (EM) waves. The elements of MSs are designed to control the reflection and transmission under the same incident wave. By introducing an amplitude–phase regulation structure to each element, the amplitudes, phases, and polarization states of reflection and transmission can be simultaneously controlled by three geometric parameters of the proposed elements, respectively. To demonstrate the abilities of elements to regulate EM waves, the MSs working in the reflection mode, transmission mode, and transmission–reflection-integrated mode are designed and simulated, and their simulation results verify the designs. The transmission–reflection-integrated MS is also fabricated and experimentally measured. Its simulation and measurement results show that deflective vortex beams with different values of topological charge can be generated simultaneously and independently in both the reflection and transmission modes.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Solution of Volume–Surface Integral Equation Accelerated by MLFMA
           and Skeletonization

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      Authors: Yan-Nan Liu;Xiao-Min Pan;
      Pages: 6078 - 6083
      Abstract: A fast algorithm for solving large multi-scale scattering problems by the volume–surface integral equation (VSIE) is proposed. The sub-matrices of the near-field interactions (NFIs) in terms of the multi-level fast multipole algorithm (MLFMA) are compressed by the skeletonization after the theoretical and numerical investigations on their low-rankness are carried out. A block-diagonal preconditioner (BDP) based on the recursive skeletonization (RS) is developed to improve the conditioning of the impedance matrix of the VSIE. The rules to select hyperparameters in the proposed method are given. Numerical experiments conducted on scattering problems show the performance of the proposed algorithm.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Contour Smoothing for Super-Algebraically Convergent Algorithms of 2-D
           Diffraction Problems

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      Authors: Yury A. Tuchkin;Farhad Mazlumi;Emrah Sever;Fatih Dikmen;
      Pages: 6084 - 6088
      Abstract: A new method extending the scope of the superalgebraically convergent 2-D wave diffraction algorithms is proposed. The principal tool is the construction of an infinitely smooth approximation to the boundary contour. The construction is based on the ideas of Tikhonov’s regularization to the stable summation of the Fourier series and the evaluation of unbounded operators. Both the algorithms for smoothing and the nonsaturated solutions for integral equations together provide the superalgebraic (faster than any algebraic) convergence. The comparison of the algorithms using the original (noninfinitely smooth) parameterization and the infinitely smooth one demonstrates the essential advantage of the latter over the former with respect to accuracy and time consumption.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Explicit Time-Domain Finite-Element Boundary Integral Method for
           Analysis of Electromagnetic Scattering

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      Authors: Ming Dong;Liang Chen;Lijun Jiang;Ping Li;Hakan Bagci;
      Pages: 6089 - 6094
      Abstract: A numerical scheme, which hybridizes the element-level dual-field time-domain finite-element domain decomposition method (ELDDM) and the time-domain boundary integral (TDBI) method to accurately and efficiently analyze open-region transient electromagnetic scattering problems, is proposed. Element-level decomposition decouples Maxwell equations on a discretization element from those on its neighboring elements using equivalent currents defined on their faces. For any element inside the computation domain, the equivalent currents are obtained from fields in the neighboring elements. For any element on the boundary of the computation domain, the equivalent currents are obtained using the fields generated by TDBI. To generate these fields, TDBI “radiates” equivalent currents on a Huygens surface enclosing the scatterer. This approach when combined with a leapfrog-type time updates results in a fully explicit numerical scheme that allows ELDDM and TDBI to use different time steps. Numerical results that demonstrate the applicability of the proposed method to concave and disconnected scatterers are presented.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • A Slot Antenna Array With Reconfigurable RCS Using Liquid Absorber

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      Authors: Yukun Zou;Xiangkun Kong;Lei Xing;Shunliu Jiang;Xuemeng Wang;He Wang;Zhiming Liu;Yongjiu Zhao;Jens Bornemann;
      Pages: 6095 - 6100
      Abstract: A method is presented to achieve a slot antenna array with a reconfigurable radar cross section (RCS) by injecting and extracting ethanol. In a complex communication system, this can be used to switch between the detection and stealth modes. The antenna system is formed by combining a liquid absorber with a $2times $ 2 slot antenna array. The liquid absorber consists of a polymethyl methacrylate (PMMA) container, 45% ethanol layer, and metal ground, which is attached to the surface of the slot antenna array. The incident wave can be absorbed by the absorber rather than reflected in other directions when the PMMA container is filled with ethanol, which reduces the monostatic and bistatic RCS. Thus, the RCS of the antenna can be changed by injecting and extracting ethanol while sustaining the antenna’s radiation performance in terms of bandwidth, radiation patterns, and gain. The mechanism of the absorber is investigated. The simulated results show that the antenna with this absorber has monostatic and bistatic RCS reduction bands from 2.0 to 18.0 GHz and a maximum RCS reduction of 35 dB with an average RCS reduction of 13.28 dB. Without ethanol, the antenna realizes a gain of 12.1 dBi, which drops by 2 dB when the lossy ethanol is injected. The measured and simulated results agree well.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • From Spatial Urban Site Data to Path Loss Prediction: An Ensemble Learning
           Approach

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      Authors: Sotirios P. Sotiroudis;Achilles D. Boursianis;Sotirios K. Goudos;Katherine Siakavara;
      Pages: 6101 - 6105
      Abstract: Machine learning (ML) models have become increasingly popular in the field of path loss prediction. Their performance depends profoundly on the data they use as their input. The work at hand proposes and evaluates new input features for urban propagation. These features were obtained via image processing tools. Moreover, we propose a new two-level ensemble model using the concept of stacked generalization. The proposed model is based on seven different basic ML models. To the best of the authors knowledge, this is the first time that a two-level ensemble method is applied to a modeling problem in electromagnetics. The results demonstrate that the new input features, coupled with the new ensemble, provide improved prediction performance.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Planar Array Diagnosis Based on Bayesian Learning With a
           Bernoulli–Gaussian Prior Model

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      Authors: Fang-Fang Wang;Yu-Hui Xu;Qing Huo Liu;
      Pages: 6106 - 6110
      Abstract: A new approach is proposed for the planar array failure diagnosis from a set of far-field measurements. Under the framework of Bayesian learning, a Bernoulli–Gaussian (BG) model is constructed to exploit the binary prior information of the unknown failure elements. Subsequently, the variational expectation maximization (EM) strategy is used to perform the Bayesian inference. Moreover, the damped generalized approximate message passing (GAMP) is further adopted to circumvent the matrix inversion in the variational EM procedure, thus making the overall process computationally very efficient. A set of representative numerical experiments are provided to validate the accuracy, efficiency, and flexibility of the proposed method.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • An Efficient Maximum-Likelihood-Like Algorithm for Near-Field Coherent
           Source Localization

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      Authors: Cheng Cheng;Songyong Liu;Hongzhuang Wu;Ying Zhang;
      Pages: 6111 - 6116
      Abstract: This communication presents an efficient iterative approach for locating the near-field (NF) coherent sources. In each iteration, the covariance matrices only containing single source information are constructed by using alternating oblique projection. Then based on the principle of vector dot products, a new iterative direction-of-arrival (DOA) estimator is proposed. After the DOA of each separated signal is estimated, the paired ranges are obtained from the 1-D maximum likelihood (ML) estimator. The proposed algorithm avoids high-dimensional spectral searches, subspace extraction, and any preprocessing such as spatial smoothing, leading to low computational complexities and high estimation accuracy. Comparative simulations show the efficiency and merits of the proposed method.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Accelerating Hydraulic Fracture Imaging by Deep Transfer Learning

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      Authors: Runren Zhang;Qingtao Sun;Yiqian Mao;Liangze Cui;Yongze Jia;Wei-Feng Huang;Mohsen Ahmadian;Qing Huo Liu;
      Pages: 6117 - 6121
      Abstract: Deep transfer learning has a great success story in computer vision (CV), natural language processing, and many other fields. In this communication, we are going to push forward the deep transfer learning to the hydraulic fracture imaging problem by proposing a two-step approach: 1) train a convolutional neural network (CNN) to reconstruct target geometries by a relatively large amount of approximated field patterns generated from a simplified model and 2) fine-tune the top layers of transferred CNN by a small amount of true field patterns generated through a full model. The advantages include the rapid generation of large amount of data through the simplified model and the high reconstruction accuracy through a careful design of the deep transfer learning. The CNN trained through the deep transfer learning can accurately reconstruct the lateral extent and direction of fractures with unseen conductivity and white Gaussian noise, showing a notable acceleration/accuracy enhancement over the previous CNN trained by mixing a small number of true data into the approximated data as data augmentation.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Frontiers in Computational Electromagnetics

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      Pages: 6122 - 6122
      Abstract: Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • Introducing IEEE Collabratec

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      Pages: 6123 - 6123
      Abstract: Advertisement.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
  • IEEE Open Access

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      Pages: 6124 - 6124
      Abstract: Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers.
      PubDate: July 2022
      Issue No: Vol. 70, No. 7 (2022)
       
 
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