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IEEE Transactions on Antennas and Propagation
Journal Prestige (SJR): 1.309
Citation Impact (citeScore): 5
Number of Followers: 81  
 
  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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      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • IEEE Transactions on Antennas and Propagation

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      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Institutional Listings

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      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Low-Profile Wideband Circularly Polarized Complementary Antenna and Arrays
           for Millimeter-Wave Communications

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      Authors: Jun Xu;Kwai-Man Luk;Wei Hong;
      Pages: 2052 - 2063
      Abstract: Low-profile millimeter-wave (mm-Wave) arrays using wideband complementary element combining circularly polarized (CP) electric and magnetic sources are proposed in this article. A pair of centrosymmetric printed $ {Gamma }$ -shaped strips serve as a CP electric source, and a modified narrow slot with two etched centrosymmetric stubs can be treated as a CP magnetic source. The combination of them can provide a wide 3 dB axial ratio (AR) bandwidth. Operating mechanism of the proposed CP radiating element is investigated and provided. Two differently constructed CP arrays, i.e., a sequentially rotated $4times4$ CP array and a full-corporate fed $8times8$ CP array, are then designed based on the proposed CP radiating element, to confirm the expandability of the proposed CP radiating element. Prototypes of these two arrays were fabricated and measured. According to the measured data, the sequentially rotated fed $4times4$ CP array exhibits an impedance bandwidth ( $vert S_{11}vert < -10$ dB) better than 57.1% (i.e., 25–45 GHz), a 3 dB AR bandwidth better than 31.4% (i.e., 29–40 GHz), and a maximum gain of 16.4 dBic, while the corresponding results for the full-corporate fed $8times8$ CP array are 25.8% (i.e., 29–37.5 GHz), 19.1% (i.e., 29.8–36 GHz), and 24.3 dBic. These competitive performances together with merits, such as compact size, low profile, low cost, and direct -ntegration ability, make these two arrays promising candidates for mm-Wave communications.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Wing Conformal Load-Bearing Endfire Phased Array Antenna Skin Technology

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      Authors: Zhao Li;Kan Wang;Yuelong Lv;Shengxia Qian;Xudong Zhang;Xiao Cui;
      Pages: 2064 - 2069
      Abstract: In this article, a phased array antenna skin is proposed for conformally assembling scenarios and wide scanning applications. Planar inverted F antenna (PIFA) is used as a radiation element of the proposed array due to its low profile and omnidirectional radiation pattern. The PIFA element is conformally assembled in a wing of an aircraft and is designed and fabricated with the technology of composite material, which makes the PIFA element load bearing. The endfire beam synthesis is also investigated, and the proposed array supports wide-angle beam scanning in both forward and backward regions. An array of 240 PIFA elements are designed, simulated, fabricated, and experimentally tested. The fabricated sample is able to bear an overload of 1 g in the mechanical test, and all the electronic experiment results agree well with the simulation data.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Dual-Band Patch Antenna Employing a Folded Probe Feed for Nonlinear
           Radar Applications

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      Authors: Alex Bouvy;Gregory J. Mazzaro;Kyle A. Gallagher;Kelly Sherbondy;Nader Behdad;
      Pages: 2070 - 2081
      Abstract: In this work, we design a novel, integrated transmit (TX)/receive (RX) dual-band folded-probe-fed patch (DFPFP) antenna to improve nonlinear radar (NLR) system performance. Designed for down-looking, airborne NLR applications, the DFPFP antenna occupies an improved form factor ( $0.9lambda times 0.9lambda times 0.1lambda $ , 1.8 kg) over existing commercial-off-the-shelf (COTS) designs and additionally offers minimal drag in airborne applications due to its low profile. The DFPFP antenna is simulated, fabricated, and tested, and excellent gain (9 dBi) and bandwidth (15%) performance are demonstrated. Iterations of the design from single, standalone TX and RX antennas to the final, integrated design are presented and discussed. The final DFPFP is compared to a pair of COTS antennas that are currently used for NLR system testing. Evaluated in the context of an NLR system, the custom DFPFP antenna significantly outperforms the COTS antennas, with signal-to-noise ratio (SNR) improvements as high as 17 dB, while offering significantly improved size, weight, and power (SWaP) performance.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Long-Range EM Communication Underwater With Ultracompact ELF
           Magneto-Mechanical Antenna

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      Authors: Silei Yang;Junping Geng;Han Zhou;Kun Wang;Xiaonan Zhao;Jingzheng Lu;Rui Zhao;Xudong Tang;Yangzhou Zhang;Da Su;Ao Zhang;Haotian Li;Ronghong Jin;
      Pages: 2082 - 2097
      Abstract: In this article, a long-range underwater electromagnetic (EM) communication system is proposed based on an ultracompact extremely low-frequency (ELF) magnetomechanical transmission antenna (UEMTA). The transmitter mainly includes a waveform generator, a variable frequency drive (VFD), and a three-phase induction motor. The receiver consists of a 200-turn coil and signal analyzer. Based on the equivalent model of a rotating magnetic dipole, the principles of the EM transmission underwater and across the interface of water and air are analyzed. ELF wave propagating underwater in the adjacent area was stronger and decays slowly, which was certificated by the experiment and simulation. Thus, the long-range transmission underwater in the ELF band with digital coding modulation based on the UEMTA is realized, and the longest distance can reach 210 m underwater in the experiment. The transmission of ELF wave across water–air medium based on the system is also tested by the experiment too. The long-range transmission of digital coding modulation across the water–air interface is realized with the longest distance of about 210 m. The ELF transmission technology based on the UEMTA can greatly promote flexible long-distance underwater transmission, the development of satellite-to-submarine communication, and ocean exploration.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Theoretic Study of Antenna Scattering Problems Based on Characteristic
           Modes and its Applications in Reducing Antenna Scattering

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      Authors: Gang Shi;Yongtao Jia;Ying Liu;Yi Chen Zhong;Yang Wu;Biao Du;Dan Jia;Tie Jun Cui;
      Pages: 2098 - 2109
      Abstract: A new antenna scattering theory based on characteristic modes (AST-CMs) is proposed to analyze the antenna scattering mechanism and guide the design of antenna scattering reduction in this article. A specific set of modal electric fields, which of an antenna loaded with a short circuit, is used to express the structure mode and antenna mode scattering fields of the antenna with arbitrary loads. The contribution of each characteristic mode to the structure mode and antenna mode scattering fields can be clearly analyzed, which efficiently guides the antenna scattering reduction under the incident plane waves with arbitrary propagation direction and polarization. A typical microstrip antenna is given as an example to validate the proposed AST-CM. The radar cross section (RCS) of the microstrip antenna calculated by AST-CM agrees well with the result simulated by commercial simulation software Altair FEKO. Moreover, the design procedure based on AST-CM is used to guide the in- band RCS reduction of the microstrip antenna under both ${x}$ - and ${y}$ -polarized normally incident plane waves. Compared with the reference antenna, the proposed antenna achieves a notable RCS reduction in its operation band with the radiation performance well preserved. The proposed low-RCS antenna is fabricated and measured, and the experimental results are in good agreement with the numerical simulated results.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Beyond-Decade Ultrawideband Quad-Ridge Flared Horn With Dielectric Load
           From 1 to 20 GHz

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      Authors: Jonas Flygare;Jian Yang;Alexander W. Pollak;Robert E. J. Watkins;Fiona Hillier;Leif Helldner;Sven-Erik Ferm;
      Pages: 2110 - 2125
      Abstract: In this article, we present a novel dielectrically loaded quad-ridge flared horn (QRFH) as a reflector feed with beyond-decade ultrawideband performance. The dielectric is machined in a low-loss, space-grade polyimide specified with low outgassing for a vacuum environment. The feed covers 1–20 GHz bandwidth with a measured band-average input reflection of −13.6 and 41.5 dB isolation between two orthogonal polarized ports. Predicted performance in a paraboloidal reflector with a 60° half-subtended angle is 62% aperture efficiency average over the band. The ridges of the horn are designed with analytic-spline-hybrid 3-D profiles with thickness flaring outwards toward the feed aperture, improving low-frequency polarization properties. The QRFH was manufactured in four quarters for accurate ridge-to-ridge alignment and a reduced number of interfaces for good thermal properties in cryogenic applications. A prototype feed has been installed and tested with promising results in one of the 6 m offset Gregorian reflectors of the Allen Telescope Array (ATA) located at the Hat Creek Observatory, Hat Creek, CA, USA.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Self-Decoupling Method for MIMO Antenna Array Using Characteristic Mode
           of Ground Plane

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      Authors: Qi Xuan Lai;Yong Mei Pan;Shao Yong Zheng;
      Pages: 2126 - 2135
      Abstract: A self-decoupling method for the multiinput multioutput (MIMO) antenna array is investigated. This method is based on the specific characteristic mode (CM) of the ground plane, which features two or multiple parallel null-field regions. By using one antenna element to excite such a mode on the ground plane while placing the other one/ones in a way that their feed points are located in the null-field region, very high isolation between antenna elements can be obtained naturally. To validate the feasibility of this decoupling method, a $1times $ 2 microstrip patch antenna (MPA) array is simulated, fabricated, and measured. It has been shown that a maximum isolation level of 57 dB is achieved without any extra decoupling structure. Moreover, this self-decoupling method shows strong universality and extensibility, and it applies to different types of antenna arrays and multielement arrays.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • 140-GHz Wideband Array Antenna-in-Package Using Multimode Resonance

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      Authors: Hyunjin Kim;Jungsuek Oh;
      Pages: 2136 - 2144
      Abstract: A 140-GHz wideband array antenna-in-package (AiP) that uses multimode resonance is proposed based on a low-profile multilayer printed circuit board (PCB), which can be incorporated with flip-chip technology and an integrated transceiver. Using the multiple resonances of a patch and $lambda $ /4 monopole-type feeder, a simulated impedance bandwidth of 53% and stable radiation performance over the operating band were achieved. A $4times $ 4 antenna array achieves a gain of up to 18.1 dBi, a radiation efficiency of 80%, and a cross-polarization discrimination (XPD) of over 20 dB. By combining the elements with a feed network composed of striplines, single and $4times $ 4 antenna arrays were designed and fabricated. The capacitance caused by the limitations of the fabrication process was analyzed and overcome using a novel capped-cavity structure. From the experiment, a −10 dB impedance bandwidth of 31% was measured.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Dual-Band Differential Intraoral Antenna and System for Wireless Data
           and Radiative Near-Field Power Transfer

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      Authors: Sarita Ahlawat;Neeta Singh;Binod Kumar Kanaujia;Karumudi Rambabu;
      Pages: 2145 - 2157
      Abstract: Intraoral tongue drive system (iTDS) is a promising assistive technology for rehabilitating disabled persons. This article proposes a radiative near field power transfer (RNF-PT) system comprising an intraoral differential rectenna (rectifying antenna) and external power transmitter (RNF-Tx). A dual-band compact differential intraoral antenna operating in the Industrial, Scientific and Medical (ISM) band (2.45 GHz) and midfield band (1.9 GHz) is proposed for the data and power transmission modes, respectively. The proposed differential antenna and rectifier were designed and fabricated individually using a Rogers RT/duroid 6010 substrate. The differential rectifier shows a simulated conversion efficiency of 89.3% for a radio frequency (RF) input power of 14.78 dBm at 1.9 GHz with a 2 $text{k}Omega $ load. The maximum transmission coefficient of −25.95 and −24.93 dB was achieved at a separation of 22 mm for the closed and opened mouth conditions, respectively. The measured impedance bandwidths of the proposed antenna in both the closed and open mouth of the test subject are around 10% in the midfield band and around 9.5% in the ISM band, respectively. The measured peak gain in the minced pork and saline solution was −20.48 dBic, −18.25 dBic at the frequency of 1.9 GHz and −18.54 dBi, and −16.88 dBi at the frequency of 2.45 GHz, respectively. The specific absorption rate (SAR) values have also been analyzed through simulations for both data and power transmission modes and are found acceptable in the closed and open mouth placements. Based on these acceptable SAR values, the link margin was theoretically calculated where it could communicate over a reasonable distance. Thus, the proposed intraoral differential antenna with a -ectifier is ideal for data and PT support in iTDS-based applications.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A W-Band Self-Packaged SIW-Based Slot Antenna With Gain and Bandwidth
           Enhancement

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      Authors: Yin-Shan Huang;Liang Zhou;Qi-Hao Xu;Jun-Fa Mao;
      Pages: 2158 - 2166
      Abstract: This study presents the design of a self-packaged substrate integrated waveguide (SIW)-based slot antenna with a low profile at the W-band. A $1times $ 4 SIW slot antenna array is developed using a standard printed circuit board (PCB) process. Then, the array is embedded in a silicon wafer. The loss of the benzocyclobutene (BCB)-based coplanar waveguide with ground (CPWG) to PCB-based SIW transition is investigated and measured to interconnect and integrate the antenna array with other components. The performance of the SIW-based slot antenna is enhanced about 2 dB without extra feeding networks by using a novel method of parasitic folded patches, and the fractional impedance bandwidth is increased from 10% to 15% by changing the metallic posts besides the SIW. The antennas are fabricated using our in-house silicon-based MEMS photosensitive composite film BCB fabrication process, which is described in detail. The proposed antenna has a measured maximum gain of 11.7 dBi at 98 GHz, with a fractional impedance bandwidth of 17%. Measured results show a close relationship with the simulated values. Compared with other antennas, our proposed antenna exhibits excellent performance, such as high gain, low profile, low loss interconnection structure, and broad bandwidth. Finally, a novel heterogeneous integration transceiver application is introduced. In this application, self-packaged SIW-based slot antennas are integrated with different types of chips. This 1 transmitter and 2 receivers (1T2R) transceiver can be further used in long-range radar detection, vital sign monitoring, and synthetic aperture radar imaging.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Very-Low-Frequency Magnetoelectric Antennas for Portable Underwater
           Communication: Theory and Experiment

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      Authors: Yongjun Du;Yiwei Xu;Jingen Wu;Jiacheng Qiao;Zhiguang Wang;Zhongqiang Hu;Zhuangde Jiang;Ming Liu;
      Pages: 2167 - 2181
      Abstract: Finding an efficient way for underwater communication with a portable antenna at very low frequency (VLF 3–30 kHz) is challenging since the conventional electrical antennas require the size to be larger than 1/10 of the wavelength. Recently, acoustically driven antennas were proposed to realize portable VLF communication in air but lack the demonstration in a lossy environment. Here, we reported the first VLF underwater communication system based on a pair of acoustically actuated magnetoelectric (ME) antennas with small size of 10 cm in length. A theoretical analysis of reflection and radiation performance of the ME antenna was conducted, where the electromechanical resonance (EMR) frequency and effective magnetic dipole moment were estimated, and a near-field coupling model of a pair of ME antennas was further established. The results of theoretical predictions and finite element model (FEM) simulations were then compared with experimental measurements and their differences were discussed. A prototype of underwater communication system based on the ME antenna pair was finally presented, where a binary digital modulation with a bit rate of 100 b/s has been demonstrated, confirming the feasibility of ME antennas for portable underwater communication.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Decoupling of Antenna Pairs Based on Equal Modal Conductance by
           Antenna-Shape Modification

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      Authors: Qi-Yu Zeng;Xiao Zhang;Lei Zhu;Qiong-Sen Wu;Tao Yuan;
      Pages: 2182 - 2193
      Abstract: In this article, a fundamental method based on mutual conductance elimination is proposed for the ultimate decoupling of closely spaced antenna pairs. First, the mutual coupling between radiators is characterized by lossy J/K inverters, and the analysis with circuit models shows that the traditional lumped loading method can only suppress the mutual susceptance. Particularly, the decoupling will not be ultimate unless the mutual conductance is further eliminated, which requires equal modal conductance of the odd and even modes of the antenna pair. After that, a method based on antenna-shape modification is proposed, and three types of antennas are designed with characteristic mode analysis (CMA). As for the single-band and wideband patch antenna pairs, by changing the patch shape into a parallelogram and adjusting the patch angle, the modal conductance of the odd and even modes are regulated to be equal, and the isolation is thus significantly improved when compared with the traditional ones to be loaded with lumped elements. As for the inverted-F antenna (IFA) pair, enhanced isolation is achieved by changing the bending configuration, coupling gap, and ground length of the antenna. Good agreement between simulated and measured results shows that all these antennas have achieved isolation over 20 dB.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Go-Caterpillar Mutation and Its Optimization Algorithm for Synthesis of
           Large-Scale Sparse Planar Arrays

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      Authors: Heng Zhao;Yong-Ling Ban;Yanhui Liu;Jun Hu;Zaiping Nie;
      Pages: 2194 - 2207
      Abstract: Optimizing the layout of sparse planar arrays constrained by minimum element spacing to reduce the peak sidelobe level (PSLL) is a difficult and challenging task in engineering applications. Here, a new sparse array design method is proposed under the constraints of aperture size, the number of array elements, and minimum spacing between elements. The approach is based on a new element mutation method which is proposed for mutating the position of any element within the aperture without changing the position of other elements. Because a mutating element can be thought of as being placed inside the board like a black/white stone in go or crawling somewhere nearby like a caterpillar, we call it go-caterpillar-mutation (GCM). Based on GCM, a stochastic optimization algorithm (GCM-OA) is proposed to optimize the layout of sparse planar arrays. Several examples demonstrate the robustness and rapidity of GCM-OA in reducing PSLL by adjusting the array element positions under various constraints.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Beamforming Phased-Array-Fed Lenses With0.5λ-Spaced Elements

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      Authors: Wei Wang;Nicholas Estes;Nicolas C. Garcia;Matthew Roddy;Andrew K. Bolstad;Jonathan D. Chisum;
      Pages: 2208 - 2223
      Abstract: We propose a phased-array-fed lens (PAFL) antenna that is capable of beamforming like a phased array but with array elements spaced beyond $0.5lambda $ . The PAFL produces high-quality scanned beams using only five active feeds. This architecture represents dramatic cost and power savings over conventional phased arrays while providing many of the features. We present an optimal beamforming method to achieve the maximum gain at any angle using a subset of feeds and a multiobjective optimizer using particle swarm optimization for more granular pattern control. The method is applied to several simulated state-of-the-art lens antennas with good performance confirming the generality of the method. The theory is demonstrated with a prototype PAFL comprising a 4 inch aperture gradient-index (GRIN) lens antenna, an 8-element $0.725lambda $ -spaced linear patch array operating at 29 GHz, and a commercial Ka-band SATCOM beamformer integrated circuit (IC). The prototype achieves the maximum gain at all angles and improves the scan loss by 4 dB at ±50°.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Characteristic-Mode-Analysis-Aided Design of Filtering Patch Antennas

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      Authors: Xiang Jie Chen;Qi Xuan Lai;Yong Mei Pan;
      Pages: 2224 - 2234
      Abstract: A characteristic-mode-analysis (CMA)-aided design method for filtering patch antennas is proposed in this article. The method mainly includes three parts: first, use the theory of characteristic mode (TCM) to analyze the filtering antenna without feed structure (i.e., the radiator) to find the resonant modes in the passband and predict the positions of the inherent radiation nulls, which are then utilized to obtain the suitable size of the radiator and filtering elements; second, use modal analysis to find the best feed position to excite the resonant modes and simultaneously generate the inherent radiation nulls; and third, optimize the filtering antenna to obtain the optimal overall performance. For demonstration, two different types of filtering patch antennas are investigated using the proposed method. It has been shown that the method can truly realize the independent analysis and design of the radiator structure and the feed with the help of characteristic modal analysis, making the design process of both filtering antennas clearer and more efficient. In addition, the proposed method can find out and fully utilize the inherent radiation nulls, including the modal nulls and the nonmodal nulls of the radiator itself.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Impedance Matching at Skin–Air Interface for Transmission-Range
           Improvement of Implantable Antennas

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      Authors: Li-Jie Xu;Lei Zhu;Mingyu Liang;
      Pages: 2235 - 2246
      Abstract: This article presents a novel impedance matching layer (IML) placed on skin tissue to enhance the transmission ability for implantable antenna. The IML is designed with a particular dielectric constant to mitigate the reflection occurred at skin–air interface at 2.45 GHz Industrial Scientific and Medical (ISM) band. To obtain this targeted effective dielectric constant, periodic posts are inserted into a 3-D printed substrate to increase its shunt capacitance, forming an IML with a height of 17 mm for enhancement of transmission ability. Furthermore, a slow wave structure is adopted to lower the profile of IML further to 7 mm, making it more comfortable for routine wearing. To testify the property of the proposed IML, a slot implantable antenna is designed, and its gains with and without IML are comparatively studied. The simulated results exhibit a gain enhancement of over 5 dB with IML loaded, providing a promising solution for a typical communication link for implantable application.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Wideband 3-D-Printed Metal-Only Reflectarray for Controlling Orthogonal
           Linear Polarizations

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      Authors: Ángel Palomares-Caballero;Carlos Molero;Pablo Padilla;María García-Vigueras;Raphaël Gillard;
      Pages: 2247 - 2258
      Abstract: This article presents a metal-only reflectarray that enables the control of incident orthogonal polarizations in a large bandwidth. The proposed reflectarray is based on a unit cell whose tuning elements allow the independent control of the reflection phase value for the vertical and horizontal impinging polarizations. Due to the symmetry of the unit cell, the same performance is produced by each polarization when its reflection phase response is modified. The proposed unit cell provides a fairly linear phase response along the frequency with a phase variation in the orthogonal polarization of ±1°. The performance under oblique incidence and the frequency limitation of the unit cell are also investigated. From this unit cell, a metal-only reflectarray that produces circular polarization from a linear polarization is designed. The reflectarray presents a simulated directivity greater than 27 dBi with an axial ratio (AR) below 1.5 dB from 32 to 50 GHz (43.9% of bandwidth). A prototype is fabricated and the measured results agree well with the simulated ones. The obtained aperture efficiency is between 56% and 41% in the considered frequency band. The measured realized gain ranges from 27 to 30.3 dBi where the achieved radiation efficiency is greater than 97%.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Kind of Tightly Coupled Array With Nonuniform Short-Circuited Branches
           for the Radiation of UWB Pulses

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      Authors: Shao-Fei Wang;Yan-Zhao Xie;Yang-Xin Qiu;
      Pages: 2259 - 2267
      Abstract: In this article, a kind of tightly coupled array (TCA) with nonuniform short-circuited branches (NSCBs) is proposed. It indicates that the introduction of the NSCBs fundamentally changes the working principle of the TCA and makes it operate like an electromagnetic combined antenna. Arms of the array elements, the short-circuited branches (SCBs), together with the ground plane, compose current loops, which act as magnetic dipoles, and the array elements themselves are electric dipoles, so the TCA becomes an array of electromagnetic combined dipoles in theory. Thus, the backplane short-circuited effect (BSE) and the edge truncation effect (ETE), which limit the working band of the TCA, are avoided simultaneously. Therefore, the working band of TCA remarkably improves, so that it can be applied to radiate the ultrawideband (UWB) pulses with band ratio over 10:1. Then, based on the theory of electromagnetic combined dipoles, the TCA with NSCBs is designed and optimized. A practical such TCA integrated with feeding baluns is developed and measured. The developed TCA with NSCBs has a working band of 287 MHz–6.45 GHz, and the band ratio is 22.5:1. The distance between the array and the ground plate is 20 mm, and the total height of the array antenna is 35 mm, which is only 3.4% of the wavelength of the lower cutoff frequency, which makes a low-profile UWB antenna. Finally, the TCA is excited by a UWB pulse with an amplitude of 3.06 kV, and the performance is measured and calculated in the pulse mode. It indicates that the UWB pulse radiating system has an effective potential of 3.54 kV, and the effective potential gain is 1.16.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Methodology and Implementation of Beam Steering Using C-Shaped Split Rings
           for Fabry–Perot Antennas

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      Authors: Gaojing Zhang;Ming Su;Yanming Zhang;Anna Wang;Chengkang Pan;
      Pages: 2268 - 2277
      Abstract: The design process of beam-steering partially reflective surface (PRS) made up of C-shaped split-ring resonators (CSRRs) is presented in this article. Through analyzing the transmission characteristics of CSRRs with variable opening angles and orientations, spatially abrupt phase and magnitude are introduced over PRS to reshape the wavefronts of linear polarization waves. Based on the designed two distributions and the two control methods, four arrangements of $5times $ 5 CSRRs are fabricated to validate the design methodology of beam steering. Furthermore, two reconfigurable Fabry–Perot (FP) antennas are proposed based on liquid-metal and mechanically rotating reconfiguration. An agreement between simulated and measured results shows higher aperture efficiency and desirable radiation patterns while demonstrating excellent reconfiguration reliability. Besides, an eight-element phased array combined with liquid-metal PRS is fabricated and shows improved scanning performance and stable gain fluctuation.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Dual-Polarized Shared-Aperture Antenna With Conical Radiation Patterns
           and High Gain for 5G Millimeter-Wave Ceiling Communications

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      Authors: Botao Feng;Jiexin Lai;Liangying Li;Chow-Yen-Desmond Sim;Li Deng;Xiao Ding;
      Pages: 2278 - 2289
      Abstract: A dual-polarized (DP) antenna with a conical radiation pattern and high gain characteristics is proposed. It is mainly comprised of a horizontally polarized (HP) array, a vertically polarized (VP) element, a fence, and a feeding network. In the HP direction, a rotatable stacked substrate-integrated waveguide (SIW)-to-coaxial-to-SIW transition (SCST) is meticulously designed to yield omnidirectional radiation with low gain variations and low transmission loss. As for the VP direction, two orthogonal substrates that are arranged above the VP radiating element act as a holder to fix the director, resulting in gain enhancement. Here, the VP element is placed in the center of the HP array to share the aperture for size reduction. Moreover, the top-hat-shaped metal fence collaborates with the large-size ground plane to yield dual conical beams with high gain in DP directions. From the measured results, the HP direction has exhibited desirable bandwidth of 11.4% (24.8–27.8 GHz) with a peak gain of 11.6 dBi, and the VP direction has demonstrated wider bandwidth of 13.7% (24.5–28.1 GHz) with a corresponding gain up to 8.1 dBi. Notably, low gain variations of ±0.65 and ±0.8 dBi are also realized for the HP and VP directions, respectively. Therefore, a DP antenna with high-gain conical beams and low gain variations can be obtained for the fifth-generation (5G) millimeter-wave (MMW) ceiling communications.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Fast and Efficient Calibration Method for Phased Array Antennas Using
           Fourier-Structured Excitation Matrix

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      Authors: Si Tang;Zhengpeng Wang;Chong Pan;Rui Su;Wei Fan;Steven Gao;
      Pages: 2290 - 2299
      Abstract: This article presents a novel phased array antenna calibration method. Unlike conventional phased array calibration methods equipped with only one probe antenna in the far-field setup, multiple measurement probes are introduced in the proposed algorithm to significantly improve the measurement efficiency. Specifically, a novel construction method for an excitation matrix (which contains excitation coefficients for phased array elements) is proposed, where phase differences introduced by the spatial locations of the multiple probes are perfectly incorporated into the Fourier-structured excitation matrix, thereby presenting the best measurement efficiency without sacrificing the array calibration accuracy. The proposed method can offer robust array calibration results (guaranteed by the low condition number of the constructed excitation matrix with Fourier structure) and high measurement efficiency (offered by multiprobe setups). To experimentally validate the proposed algorithm, a multichannel (i.e., multiprobe) far-field measurement setup was utilized. A four-element open-ended waveguide array operating at 2.6 GHz and two-probe far-field systems were employed as the antenna under test (AUT) and multiple probes, respectively, to validate the effectiveness and robustness of the proposed phased array calibration algorithm. The proposed algorithm will be highly valuable for efficient phased array calibration, especially for future antenna systems equipped with large-scale antenna configurations.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Rotating-Permanent-Magnet Array for ULF Through-the-Sea Magnetic
           Communications

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      Authors: Feng Zhang;Zhaoqian Gong;Shun Wang;Yicai Ji;Guangyou Fang;
      Pages: 2300 - 2310
      Abstract: To realize magnetic induction (MI) communication through seawater, a rotating-permanent-magnet array (RPMA) operating in the ultralow frequency (ULF) band is proposed. The array consists of $5times $ 5 cylindrical Nd–Fe–B magnets driven by servo motors. To maximize the transmitting magnetic moment, the motors are controlled to rotate synchronously through network communication. The design of the magnet and array configuration is implemented by analyzing the torque and magnetic moment. Magnetic forces between the array magnets are analyzed by using the equivalent static magnetic dipole model. Permalloy sleeves are used to reduce the influence of magnetic force on the synchronization of magnets. The total transmitting magnetic moment of the RPMA is 360 A $cdot ~text{m}^{2}$ , and its power efficiency is 14.4 times higher than the conventional transmitting system using coils. Binary frequency shift keying (BFSK) modulation is realized by switching the rotating speed of the magnets and verified by an indoor test. The equivalent orthogonal horizontal magnetic dipole (HMD) model of the array is used, and the magnetic field distribution in layered media is simulated using FEKO. The calculated MI is 100 fT in the position with a distance of 1 km and a depth of 5 m in the sea. The results of the through-the-sea experiment show that the magnetic field of the RPMA can be detected in a range of 500 m by magnetic inductive sensors immersed at a depth of 5 m in seawater and agree well with the simulated results. Transmission bit rates of 10 and 5 b/s can be achieved in the positions of 60 and 110 m.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Compact Cylinder Luneburg-Lens Antennas Based on 3-D-Printing Technology

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      Authors: Yi Xuan Zheng;Bing Jie Xiang;Yong Mei Pan;Shao Yong Zheng;
      Pages: 2311 - 2320
      Abstract: The Luneburg-lens is a prospective candidate for implementing multibeam antennas. However, the size of the conventional configuration is bulky, and most reported works are linearly polarized (LP), leading to some inconvenience in the practical applications. To deal with these problems, a new approach to realize a compact LP Luneburg-lens antenna is proposed first, and then, a method for implementing circular polarization (CP) property is further proposed. An air-coated dielectric cylinder is rotated around the center axis to form different layers of an equivalent cylindrical Luneburg-lens. The corresponding theoretical model to calculate the equivalent permittivity is given. Based on this approach, a Luneburg-lens is constructed using one dielectric cylinder and nine dielectric rings with the same permittivity but different dimensions. The proposed lens can be easily fabricated through the 3-D printing technology with low manufacturing complexity. For validation, an LP and a CP Luneburg-lens antenna operating at the Ka-band were designed, fabricated, and measured. A good consistency between simulated results and measured ones can be found. The LP antenna achieves a wide-scanning range of 174° and a bandwidth of 28.6%. Also, the CP one exhibits a scanning range of 134° and an AR bandwidth of 17.4%.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Design, Array, and Test of Super-Low-Frequency Mechanical Antenna Based on
           Permanent Magnet

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      Authors: Wenhou Zhang;Zhenxin Cao;Xiaoyu Wang;Xin Quan;Mengjiang Sun;
      Pages: 2321 - 2329
      Abstract: As a new type of super-low-frequency (SLF, 30–300 Hz) magnetic antenna, the permanent magnetic mechanical antenna (PMMA) has great potential for applications in underwater communication, underground communication, and earthquake prediction. PMMAs use large-volume permanent magnets to enhance the signal, posing a significant challenge to power consumption of the mechanical drive structure. We optimize the permanent magnets in terms of magnetization structure, magnetic material, and form factor to determine the optimal permanent magnet structure. We establish an analytical model of the magnetic torque of the array elements and the radiated field of the array to determine the optimal array form. Based on the analytical model, we analyze the effects of the array element spacing, the phase difference of the array elements, and the number of array elements on the radiated time-varying magnetic field. Finally, a 3-D array prototype operating in the frequency band of 75–125 Hz is developed for testing. The test results show that when the phase difference is less than $mathrm{26}^{circ} $ , the effect on the radiation intensity of the array is negligible. When the array element spacing is 0.15 m, the motor cannot drive the mechanical structure, and when the array element spacing increases to 0.3 m, it can operate normally. Communication experiments were conducted, and the transmission rate could reach 2 bps.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Geodesic Half-Maxwell Fish-Eye-Lens Antenna

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      Authors: Shiyi Yang;Qiao Chen;Francisco Mesa;Nelson J. G. Fonseca;Oscar Quevedo-Teruel;
      Pages: 2330 - 2338
      Abstract: We propose and implement a geodesic half-Maxwell fish-eye (MFE)-lens antenna. The lens was optimized using an in-house physical optics (PO) code adapted for generalized geodesic lenses. The final antenna design was validated with commercial electromagnetic simulation software. The antenna combines a modulated geodesic half-MFE lens and a transition to a linear flare, which is needed to preserve the linear polarization in the aperture. The antenna prototype, designed to operate in the $text{K}_{mathrm {a}}$ -band, was manufactured with computer numerical control (CNC) milling and measured in an anechoic chamber. The design provides continuous beam scanning because of a mechanically actuated feed. Promising beam scanning properties are demonstrated in an angular range of ±45° with a scan loss below 3 dB, as well as good frequency stability from 26 to 32 GHz. Since the antenna is fully metallic, its radiation efficiency is high (approximately 90%).
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Millimeter-Wave Patch Antennas With Ultralow Profile of 20 μm on
           Flexible Substrate

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      Authors: Feng Wang;Jian Zhou;Yanzhao Li;Xiaoguang Xu;
      Pages: 2339 - 2349
      Abstract: In applications of flexible communication electronics, the requirement for ultralow profile of antenna is gradually approaching a limit. In order to achieve a higher flexibility, it is necessitated to limit the vertical distance to 10 $mu text{m}$ scale between the integrated antennas and the electrode ground (GND). Such a small Section height results in a severely reduced radiation efficiency and a narrowed bandwidth. In this article, the enhancement of radiation efficiency and bandwidth of a millimeter-wave (mmWave) patch antenna with 20 $mu text{m}$ profile height are studied. On the metal GND, by properly opening two (or one) resonant slots with a width of 100 $mu text{m}$ , strong resonance coupling between the patch antenna and the slots can be induced, leading to a greatly enhanced radiation efficiency. Meanwhile, the spectra width of TM10 mode of the patch antenna can also be effectively broadened by the mode coupling, giving rise to a greatly improved radiation bandwidth. The physical mechanism and the sensitive factors to maximize bandwidth, antenna gain, and front-to-back ratio are discussed.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Near-Field Angular Scan Enhancement of Antenna Arrays Using Metasurfaces

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      Authors: Gleb A. Egorov;George V. Eleftheriades;
      Pages: 2350 - 2362
      Abstract: In this publication, we continue our previous work on extending the angular scan range of phased arrays using metasurfaces. We consider in detail scan enhancement using a single metasurface lens in the near-field of a source and provide analytical expressions for source excitation to obtain a desired beam. We show that such a device suffers from the same directivity degradation as in the case of far-field lens placement. Moreover, we discuss in detail that this approach has limitations, and one cannot place the lens arbitrarily close to the source array. We then propose a two-lens near-field scan enhancer which is not subject to the same limitations, although still subject to the same directivity degradation. Finally, we propose a binary metasurface concept which theoretically achieves desired scan enhancement without directivity degradation. Some theoretical claims are then verified via full-field simulations.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Millimeter-Wave Spoof-Surface-Plasmon-Polaritons-Fed Dual-Polarized
           Microstrip Patch Antenna Array

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      Authors: Di Cao;Yujian Li;Junhong Wang;Lei Ge;
      Pages: 2363 - 2374
      Abstract: A novel millimeter-wave spoof surface plasmon polaritons (SSPPs)-fed dual-polarized microstrip patch antenna array is proposed in this article. A dual-polarized single-layered square patch antenna fed by SSPPs is investigated first acting as the radiators. A method of directly connecting two orthogonal SSPPs with two edges of the square patch is introduced to excite the TM10 and TM01 modes and to achieve promising performance simultaneously. The fabricated antenna element has a measured overlapped impedance bandwidth of 13.7%, an isolation of more than 15 dB between the two inputs, a gain of up to about 6 dBi, and stable dual-polarized radiation patterns. With the use of two SSPPs branches printed on different sides of the substrate, a compact SSPPs power divider with adjustable power dividing ratio is then investigated for realizing the series SSPPs feed network, whose design considerations are discussed in detail. By combining the feed network with the patch elements, a $1times $ 4 SSPPs-fed dual-polarized microstrip patch antenna array is fulfilled. The fabricated prototype confirms a bandwidth of 15% and dual-polarized broadside radiations. Benefitted from the simple single-layered geometry without the metallic ground plane over the major region of array geometry and the dual-polarized unidirectional radiation, the presented designs are valuable to emerging millimeter-wave applications.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Study on Millimeter-Wave Magneto-Electric Dipole Phased Arrays for 5G
           Dual-Band Applications

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      Authors: Liyue Zhao;Yujian Li;Junhong Wang;Lei Ge;
      Pages: 2375 - 2384
      Abstract: Beam steering characteristics of millimeter-wave substrate-integrated magneto-electric (ME) dipole phased arrays with large sizes are investigated in this article. The formation mechanism of the guided waves traveling along the planar ME-dipole array geometry is revealed with the use of a linear array model in simulation, which not only provides an effective method of predicting the blind angles for the ME-dipole phased arrays but also confirms the superior wide-angle scanning performance of the arrays. An 8 × 8 ME-dipole phased array is then designed, fabricated, and tested, whose measured beam scanning range without the blindness in both the E- and H-planes is ±60° over the frequency range between 23.5 and 27.5 GHz and is ±50° over the range between 27.5 and 29.5 GHz. A gain of up to 23.6 dBi and stable radiation patterns are also achieved. With the simple single-layered configuration and the wide-angle scanning ability over the wide operating band of 22.6%, the ME-dipole phased array would be an attractive candidate for the millimeter-wave dual-band applications in the fifth generation (5G) mobile communications.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Ka-Band Multibeam Patch Antenna Array Fed by
           Spoof-Surface-Plasmon-Polariton Butler Matrix

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      Authors: Di Cao;Yujian Li;Junhong Wang;
      Pages: 2385 - 2395
      Abstract: A novel Ka-band spoof-surface-plasmon-polaritons (SSPPs) Butler-matrix-fed multibeam patch antenna array is proposed. An SSPPs-fed single-layered microstrip patch antenna with suppressed cross-polarization is investigated acting as the radiator. By using SSPPs etched on both sides of a substrate, a 3 dB coupler, a crossover, two phase shifters, and a vertical interconnection with compact geometries and promising performance are designed and investigated. By connecting the devices together, an SSPPs Butler matrix is realized, whose topology is modified in order to compensate for the phase influence of the SSPPs couplers that are different from traditional results. The $1times4$ multibeam patch array fed by the SSPPs Butler matrix is fabricated and measured. An impedance bandwidth of 15.4%, a gain of up to 12 dBi, and stable radiation beams are obtained. Benefitting from the small ratio between the metal area and the overall array area and the promising operating performance, the proposed SSPPs fed multibeam array may find potential applications in millimeter-wave systems where the absence of a large ground is preferred.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A 1-bit Time-Modulated Reflectarray for Reconfigurable-Intelligent-Surface
           Applications

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      Authors: Xianbo Cao;Qiang Chen;Toru Tanaka;Masaki Kozai;Hiroya Minami;
      Pages: 2396 - 2408
      Abstract: The development of reconfigurable intelligent surfaces (RISs) is important to facilitate advances in beyond 5G and 6G technologies. However, the difficulty of controlling the reflected amplitude of the widely studied 1-bit reflectarray (RA) makes it difficult to meet the requirements of RIS for multiple application scenarios, and the change of the operating frequency in emerging time modulation (TM) technology-based RAs makes them unsuited to existing systems. Considering the observed the intrinsic similarities between the reflection states of 1-bit RA and logic states of 1-bit time function, a 1-bit time-modulated RA (1-bit TMRA) was designed based on a conventional 1-bit RA and TM technology in this study, and then was verified experimentally. The 1-bit RA characteristic was verified by realizing beam scanning, and the TM characteristic was verified by a shaping scattering pattern with ultralow sidelobe levels (SLLs). The results show that the proposed 1-bit TMRA is capable of realizing an extra TM characteristic without significantly increasing the system complexity of the 1-bit RA. Unlike most time-modulated arrays, the proposed 1-bit TMRA operates at the center frequency, making it suitable for direct application in existing wireless communication systems. These advantages highlight the potential of the proposed 1-bit TMRA for practical applications in RISs.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Broad-Angle Multichannel Metagrating Diffusers

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      Authors: Yarden Yashno;Ariel Epstein;
      Pages: 2409 - 2420
      Abstract: We present a semianalytical scheme for the design of broad-angle multichannel metagratings (MGs), sparse periodic arrangements of loaded conducting strips (meta-atoms), embedded in a multilayer printed circuit board (PCB) configuration. By judicious choice of periodicity and angles of incidence, scattering off such an MG can be described via a multiport network, where the input and output ports correspond to different illumination and reflection directions associated with the same set of propagating Floquet–Bloch (FB) modes. Since each of these possible scattering scenarios can be modeled analytically, constraints can be conveniently applied on the modal reflection coefficients (scattering matrix entries) to yield a diffusive response, which, when resolved, produce the required MG geometry. We show that by demanding a symmetric MG configuration, the number of independent S parameters can be dramatically reduced, enabling satisfaction of multiple such constraints using a single sparse MG. Without any full-wave optimization, this procedure results in a fabrication-ready layout of a multichannel MG, enabling retroreflection suppression and diffusive scattering from numerous angles of incidence simultaneously. This concept, verified experimentally via a five-channel MG prototype, offers an innovative solution to both monostatic and bistatic radar cross Section (RCS) reduction, avoiding design and implementation challenges associated with dense metasurfaces used for this purpose.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • 1-bit Coding Reconfigurable Array for 2-D Wide-Angle Scanning

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      Authors: Shangyang Li;Yan Wang;Feng Xu;
      Pages: 2421 - 2432
      Abstract: In this article, an $8,,{times }$ 8 array with 2-D wide-angle scanning is proposed and studied. By integrating two p-i-n diodes on the feeding line, the radiated electric field of the element can present two different phase states of 0° and −180°. By introducing the elaborately designed two groups of fixed phase delay (FPD) in horizontal and vertical directions, the grating lobe of the 1-bit array is effectively mitigated. Simulated and measured results indicate that the proposed array can cover the beam from −60° to 60° with no grating lobe within a 2-D scanning scope from 9 to 10 GHz. The peak gain of the array is 17.3 dBi and the cross-polarization level at the main lobe is less than −20 dB. The proposed array has the advantages of being lightweight, low-cost, and easy to integrate. These features enable its applications in space-limited scenarios such as base stations and unmanned aerial vehicles.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Wideband Dual Linearly Polarized Hollow- Waveguide Septum Antenna Array
           for Ku-Band Satellite Communications

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      Authors: Yunlong Lu;Shuhao Shen;Yang You;Jun Xu;Jifu Huang;
      Pages: 2433 - 2442
      Abstract: This article presents a Ku-band full-corporate-feed dual linearly polarized (LP) hollow-waveguide (HW) septum antenna array. A modified low-profile septum polarizer, worked as the radiating element, is designed to push the radiation nulls out of the desired passband upon odd-mode excitation, which helps to achieve stable and consistent radiation performance for both H-pol and V-pol. Square coaxial lines are employed to realize two sets of full-corporate feeding networks with compact size, enabling close spacing between the two adjacent radiating elements. A magic-T based on the single-ridge waveguide is designed to provide in-phase and out-of-phase responses for the feeding networks so that the dual LPs can be achieved. A prototype covering 10.5–14.5 GHz is designed, fabricated, and measured for demonstration. Experimental results show that more than 17.3 dBi peak gain and better than 79% antenna efficiency for both polarizations are achieved within the desired frequency band. In addition, the antenna is free from grating lobes over the same frequency band.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Dual-Polarized SIW Lens Antenna Array for Rx-/Tx-Integration at
           K/Ka-Band

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      Authors: Thomas Jaschke;Arne F. Jacob;
      Pages: 2443 - 2453
      Abstract: The terminal antenna with dual-circular polarization reported here operates around 20 and 30 GHz, that is, in the down- and uplink frequency bands of current satellite communication systems. The passive array, this work focuses on, integrates the receive and the transmit (Rx/Tx) paths in a single aperture. This approach is shown to be advantageous compared to classical solutions with two separate antennas. The modules, the array consists of, are formed by a stack of eight linear subarrays that themselves are composed of an alternating series of four Tx-only and four combined Rx/Tx endfire antenna elements. The resulting brick architecture provides enough real estate for the future implementation of phased-array electronics. The array is implemented in substrate-integrated waveguide (SIW) technology. For improved matching, it is covered with a periodically shaped dielectric lens. A technique is proposed to mitigate cross-polarization in the pointing direction. A module is realized using standard technologies. The relevant array parameters are measured. The module patterns are synthesized from the individual element responses. They confirm the simulated results and, in particular, a bandwidth of more than 2.5 GHz for both Rx and Tx.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Broadband Statistically Designed Thinned-Binned Array Antennas

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      Authors: Giovanni Buonanno;Sandra Costanzo;Raffaele Solimene;
      Pages: 2454 - 2466
      Abstract: Statistically thinned arrays are obtained by thinning a reference filled array, according to a probabilistic law that is dictated by the reference current. The remaining radiators are still separated by commensurable distances, even if randomly located. Hence, wideband operations are prevented by grating lobes’ occurrence. To overcome the above limitation, a new and simple strategy is presented in this article for randomly deploying the elemental radiators across the array aperture. More in detail, unlike classic thinned arrays, elements surviving the thinning are not positioned on a priori fixed deterministic lattice. Instead, their positions are modeled as random variables, which are determined by exploiting the binned strategy. Numerical examples reveal that the new proposed scheme allows for a considerable enlargement of the frequency band, without incurring in grating lobes’ appearance.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Tightly Coupled Huygens Element-Based Conformal Transmitarray for E-Band
           Airborne Communication Systems

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      Authors: Xuan Wang;Pei-Yuan Qin;Li-Zhao Song;Ronghong Jin;Y. Jay Guo;
      Pages: 2467 - 2475
      Abstract: In this article, a wideband conformal transmitarray employing dual-layer tightly coupled Huygens elements is proposed at E-band. The element consists of five pairs of partly overlapped metallic strips with different lengths printed on two sides of a dielectric substrate. It can support tightly coupled Huygens resonances with a high transmission efficiency and a nearly full phase coverage in a wide bandwidth from 71 to 87 GHz. Equivalent circuit models are created to analyze the tightly coupled Huygens element, which has good agreement with that from full-wave simulations. In order to validate the proposed element, a cylindrically conformal transmitarray at 78 GHz is designed, fabricated, and measured. Good agreement between the measured and simulated results has been obtained, showing a peak realized gain of 26.6 dBi with an aperture efficiency of 37.2% from measurement. A measured 3 dB gain bandwidth of 20.4% is achieved from 71 to 87 GHz, fully covering the E-band spectrum.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A 3-D-printed Wideband Millimeter-Wave Fan-Beam Antenna With Flat-Top,
           Sharp Cutoff Patterns, and Beam-Scanning Capability

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      Authors: Xue Ren;Dashuang Liao;Shaowei Liao;Quan Xue;Kai Xue;Wenlong He;
      Pages: 2476 - 2486
      Abstract: This article presents a wideband millimeter-wave (MMW) fan-beam antenna with a flat-top, rapid cutoff radiation pattern, and beam-scanning capability through the use of 3-D printer technology. The proposed antenna, consisting of several periodic structures that composed of dielectric and air slabs, is fed by the WR-28 waveguide. By tuning the ratio of dielectric slab thickness to that of unit cell, the effective permittivity is controlled flexibly. The phase distribution on the aperture is carefully modulated in this way to devote high-quality flat-top patterns. In addition, the beam can be continuously scanned within the angle range of 70° without scarifying the gain performance dramatically. For demonstration, a prototype with boresight fan-beam radiation is first fabricated and measured. The proposed antenna achieves an impedance bandwidth of 50% from 24 to 40 GHz. Measured results indicate that the wide beamwidth patterns show flat-top and sharp cutoff performance. Both E-plane and H-plane patterns draw low cross polarization (smaller than −22 dB). Another prototype, aiming to verify the beam-scanning capability, is investigated. Measured results demonstrate the performances of the proposed antennas. With such favorable electrical performance, simple structure, and low-cost fabrication, the proposed antenna is a promising candidate for 5G MMW and satellite applications.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Toward High-Power Beam-Steerable Reflectarrays Using Tunable-Height
           Dielectric

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      Authors: Kendrick Q. Henderson;Walter Disharoon;Nima Ghalichechian;
      Pages: 2487 - 2496
      Abstract: A novel method for a high-power reconfigurable reflectarray (RRA) with a moderate 30° beam scanning is demonstrated. The proposed technique eliminates the need for mechanical steering of reflectors for satellite communication. A small mechanical movement of a patterned dielectric structure under multislot elements achieves beam steering by changing the coupling. Due to the unique shape of the multislot element, the unit cell is capable of tuning the phase for both linear polarization and circular polarization (CP) within a single design operating at 20 GHz. The maximum phase range obtained in this design is a continuous 280° for RHCP, LHCP, and two linear polarizations at 20 GHz. The phase of the reconfigurable unit cell is verified and measured using a waveguide simulator attached to a micromotor. Maximum element loss is simulated to be 0.5 dB. To demonstrate beam steering, three reflectarrays with frozen dielectrics and square array lattices composed of 400 elements ( $10lambda _{0},,times 10lambda _{0}$ ) are fabricated. The frozen reflectarrays demonstrate beams at 0°, 15°, and 30°. The measured gain is found to be 23.2 dB at broadside with 21.8 and 23.3 dB, respectively, when scanned to 15° and 30°. The 1 dB gain bandwidth is measured to be 7.45% with a 3 dB axial ratio bandwidth of 12.1%. Unlike other architectures that use nonlinear semiconductor devices, the proposed reflectarray uses a dielectric insert with a height that can be controlled by a micromotor suitable for high-power applications supporting up to 80 MW/ $text{m}^{2}$ .
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Wideband Dual-Polarized Microwave Absorber at Extremely Oblique Incidence

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      Authors: Qihao Lv;Cheng Jin;Binchao Zhang;Pengyu Zhang;Junwei Wang;Na Kang;Buning Tian;
      Pages: 2497 - 2506
      Abstract: In this article, a novel method for developing a dual-polarized broadband microwave absorber (MA) for use at an extremely oblique incidence angle is presented. A detailed theoretical analysis is performed and formulas are derived to obtain the required relative permittivity and permeability tensors to achieve dual-polarized absorption at an arbitrary oblique incidence angle. As a proof of concept, a broadband dual-polarized MA operating at an oblique angle of $75~{}^{circ }$ is designed whose unit cell consists of a pair of rectangular patches and a rectangular loop embedded with four resistors. A prototype is fabricated and measured for verification. Both the measured and simulated results demonstrate that the proposed MA achieves more than 90% absorption within a broad frequency with a relative bandwidth of 61.2% for both transverse electric (TE) and transverse magnetic (TM) polarizations at an extremely oblique incidence angle of $75~{}^{circ }$ .
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Effective Constitutive Parameters Extraction of Bianisotropic
           Metamaterials Using Bloch Modes

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      Authors: Parisa Karimi;Behzad Rejaei;Amin Khavasi;
      Pages: 2507 - 2514
      Abstract: In this article, a method is proposed to extract the effective constitutive parameters of bianisotropic metamaterials using Bloch modes. We consider 3-D structures that are realized by stacking identical unit layers, where each unit layer is a 2-D periodic array of metallic or dielectric elements of arbitrary shape embedded in a background dielectric medium. Bianisotropic metamaterials do not satisfy the condition of reflection symmetry of unit layers considered in previous studies. The eigenvectors and eigenvalues of the generalized transfer matrix of a unit layer are related to the Bloch modes of the structure. When only two dominant Bloch modes exist, closed-form expressions are found for effective permittivity, permeability, and magnetoelectric tensors of the medium. The effects of nondominant Bloch modes are taken into account as interface surface impedance matrices. The calculated scattering parameters of a slab of bianisotropic metamaterial are shown to be in good agreement with the results obtained from full-wave electromagnetic simulations using commercial solvers.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Metamaterial-Based Pattern-Switchable Linear Array for 2-D Discrete
           Beam-Scanning Using Hybrid Digital Coding Method

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      Authors: Zhan Wang;Yuandan Dong;
      Pages: 2515 - 2526
      Abstract: A new low-cost, pattern-switchable, metamaterial-inspired, dielectric resonator (DR) 1-D linear array for 2-D beam-steering is presented by using a hybrid digital coding method. By loading the metasurface on the DR, a low-profile DR radiator is developed. To realize both phase and pattern digital coding, a beam-switching metasurface-loaded 1 bit DR antenna is explored by using a symmetrical feeding scheme and a Yagi-like endfire radiation mechanism. The novel hybrid digital coding method is realized by using p-i-n diodes to co-control the phase (1 bit, 0°/180°) and radiation states (three-beam). Based on the hybrid digital coding method, the developed 1-D linear array creatively achieves low-cost quasi-2-D discrete beam scanning. The pattern reconfiguration technique contributes to the E-plane beam scanning, while the H-plane beam steering is attributed to the phase digital coding sequence. To validate this working mechanism, a four-element linear array is implemented and tested. The realized overlapped −10 dB impedance bandwidth is about 17.6% (covering LTE B42/43 bands), and the realized peak gain is 9.05 dBi. By controlling the switch states of 16 p-i-n diodes, the proposed four-element linear array achieves digital 2-D beam steering (12 beams). The presented antenna features a miniaturized size, wideband, low cost, and good 2-D beam-steering capacity. It provides a new and feasible solution for low-cost 2-D beam scanning, demonstrating a good application potential for intelligent communication systems and low-cost arrays.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Time-Domain Modelling of Pulsed Photoconducting Sources—Part I: The
           Norton Equivalent Circuit

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      Authors: Andrea Neto;Nuria Llombart Juan;Angelo Freni;
      Pages: 2527 - 2535
      Abstract: In the circuit theory, the Norton and Thevenin equivalent generators are tools that simplify the solutions of networks involving passive or active components. They have been extensively used in the frequency domain to describe time-harmonic sources. A time-stepped evolution is instead typically used to include transient sources. As a particular case of the latter, the Norton equivalent circuit is extended here to investigate pulsed photoconducting sources, where a dc bias voltage and a pulsed optical laser are combined to generate terahertz (THz) bursts. The proposed derivation relies on the application of the electromagnetic (EM) equivalence theorem. The main conclusion of this derivation is the understanding that, from the three different spectral regions (dc, THz, and optics), only the THz radiation is to be explicitly included in the equivalent circuit. The theory is validated by a campaign of measurements reported in a connected paper.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Time-Domain Modelling of Pulsed Photoconducting Sources—Part II:
           Characterization of an LT GaAs Bow-Tie Antenna

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      Authors: Arturo Fiorellini Bernardis;Paolo Maria Sberna;Juan Bueno;Huasheng Zhang;Nuria Llombart;Andrea Neto;
      Pages: 2536 - 2545
      Abstract: Drude’s description of the response of low-temperature gallium arsenide to optical pulse excitation is used to evaluate the components of a time-domain Norton equivalent circuit of a photoconductive antenna (PCA) source. The saturation of the terahertz (THz) radiated power occurring at large optical excitation levels was previously associated by the scientific community to radiation and charge screening of the bias. With the present circuit, we are able to model accurately the measured saturation as only due to the EM feedback from the antenna to the bias. The predicted THz radiated power is shown to match very accurately the measurements when the circuit is combined with an accurate description of the experimental conditions and the modeling of the THz quasi-optical (QO) channel.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • The Fast Physical Optics Method With the Linear Amplitude and Quadratic
           Phase Terms

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      Authors: Feng Li Song;Yu Mao Wu;Ya-Qiu Jin;Zhi Qiang Li;Jun Hu;
      Pages: 2546 - 2555
      Abstract: The physical optics (PO) scattered fields from the electrically large scatterers contain slowly varying amplitude and highly oscillatory phase terms. In this work, first, we consider quadratic approximations for the phase term of the PO scattered fields. Second, the linear amplitude of the PO scattered fields [linear-fast PO (L-FPO)] is proposed. The simplification of the linear amplitude term is adopted for two reasons. One is that the contributions of the PO scattered fields mainly come from the high-frequency critical points, that is, the stationary phase points, the boundary phase points, and the vertex points. When the wave frequency goes large, the linearization of the amplitude term could guarantee the accuracy of the PO scattered fields from the high-frequency critical points. The other reason is that the L-FPO method proposed in this work avoids the time-consuming and complicated calculation of Fresnel integrals. The computational cost of the Fresnel integrals is shrunk drastically. For the aircraft model, the CPU time of the proposed method is reduced by one order of magnitude compared with Gordon’s method and nearly half compared with the Q-FPO method. In the process of the PO method of determining the lit region of the scatterer, the new shadowing technique pairing a quadratic quadrilateral patch into two subtriangles achieves high accuracy in the determination of the shadow boundary.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • The Shannon Information Capacity of an Arbitrary Radiating Surface: An
           Electromagnetic Approach

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      Authors: Said Mikki;
      Pages: 2556 - 2570
      Abstract: Utilizing a cross-disciplinary approach, we explore Shannon information-theoretic characterizations of the information capacity limits of generic electromagnetic (EM) surfaces intended for possible use in wireless communication links. Our principal task is to first formulate at a general and rigorous level the EM theory of the information that can be extracted from the Maxwellian fields radiated by an arbitrarily shaped continuous surface. This is then followed by a detailed derivation and illustration of practical physics-informed algorithms for computing approximations of the Shannon capacity of surfaces with any given geometry operating in Gaussian channels. Our formalism can address both near- and far-field information capacity scenarios, with a mathematical treatment that includes a complete characterization of the source-field polarization structure, mutual coupling, and interactions.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • On a Low-Frequency and Contrast-Stabilized Full-Wave Volume Integral
           Equation Solver for Lossy Media

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      Authors: Clément Henry;Adrien Merlini;Lyes Rahmouni;Francesco P. Andriulli;
      Pages: 2571 - 2586
      Abstract: In this article, we present a new regularized electric flux volume integral equation (D-VIE) for modeling high-contrast conductive dielectric objects in a broad frequency range. This new formulation is particularly suitable for modeling biological tissues at low frequencies, as it is required by brain epileptogenic area imaging, but also at higher ones, as it is required by several applications, including, but not limited to, deep brain stimulation (DBS). When modeling inhomogeneous objects with high complex permittivities at low frequencies, the traditional D-VIE is ill-conditioned and suffers from numerical instabilities that result in slower convergence and less accurate solutions. In this work, we address these shortcomings by leveraging a new set of volume quasi-Helmholtz projectors. Their scaling by the material permittivity matrix allows for the rebalancing of the equation when applied to inhomogeneous scatterers and, thereby, makes the proposed method accurate and stable even for high complex permittivity objects until arbitrarily low frequencies. Numerical results, canonical and realistic, corroborate the theory and confirm the stability and the accuracy of this new method both in the quasi-static regime and at higher frequencies.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Recompressed Nested Cross Approximation for Electrically Large Bodies

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      Authors: Nathan M. Parzuchowski;Brenton Hall;Isroel M. Mandel;Ian Holloway;Eli Lansey;
      Pages: 2587 - 2595
      Abstract: A recompressed nested cross approximation (rNCA) based closely on the recent fast nested cross approximation (fNCA) algorithm is formulated in this article. The proposed method builds on previous work in which the fNCA was formulated in a purely algebraic and kernel-independent fashion, using a top-down recursive application of the adaptive cross-approximation (ACA). Our proposed method employs ACA recompression to avoid the need to compute low-rank approximations of excessively large far-field matrices, and thus mitigates the effects of high-frequency rank growth on run-time scaling for electrically large models. The low run-time and memory cost allows for efficient parallel computation of $mathcal {H}^{2}$ -matrices for systems of excessive electrical sizes. Radar cross sections (RCSs) are evaluated for electrically large instances of a perfectly conducting sphere and the NASA Almond. We observe near-linear scaling of memory cost and construction time.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Path Loss Over Irregular Terrain

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      Authors: Terence Wong;
      Pages: 2596 - 2605
      Abstract: A method for computing the path loss over irregular terrains due to diffraction and reflection is described. The mathematical technique used is the discrete Fresnel transform and its inverse. The transform pair is applied to the problem of diffraction due to multiple knife edges. The shadow region of a terrain is then modeled as a set of infinitesimally spaced knife edges. The method is shown to be equivalent to the small-angle parabolic equation. It is tested against the established theoretical and experimental results. Differences between this and other methods are discussed in the Appendix.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • An Accurate Echo-Acquisition Method for PEC/Coated Targets by GTD-Based
           Gridless Compressed Sensing

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      Authors: Zi He;Xiao Huang;Sheng-Kai Sun;Hua Yan;Da-Zhi Ding;Hong-Cheng Yin;
      Pages: 2606 - 2612
      Abstract: A novel geometrical theory of diffraction (GTD)-based echo-generation approach for perfectly electromagnetic conducting (PEC) and coated targets is proposed, which applies gridless compressed sensing (CS). First, the GTD model for both the PEC and coated targets is established. These GTD models can thus be used to obtain the scattering-echo. The gridless CS method is then used to estimate the GTD model’s phase information, offering a continuous parametric estimation. Next, the genetic algorithm (GA) is used to determine the amplitude and frequency dependency. Finally, the scattering echo at various observed angles can be quickly recorded, yielding high-resolution range profile imaging results. The numerical results show that the proposed method predicts echo more accurately than traditional optimization methods.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • An Efficient and Error-Controllable Angular Sweep Algorithm for
           Electromagnetic Wave Scattering and its Analysis

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      Authors: Chung Hyun Lee;Joseph D. Kotulski;Vinh Q. Dang;Jin-Fa Lee;
      Pages: 2613 - 2625
      Abstract: The angular sweep of electromagnetic wave scattering is formulated as a matrix equation with multiple right-hand sides (RHSs). Although the low-rank approximation of an RHS matrix is a popular choice for reducing the computational costs of multiple RHSs, only a small amount of research has been conducted to explore how this approximation impacts the solution quality. Furthermore, there has not been sufficient research on the quality of the solution as a function of the accuracy of the iterative solver. We present an error analysis of the approximated solution considering both the reduced number of RHSs and the tolerance of the iterative solver. Based on the error analysis, a new angular sweep algorithm is proposed with fine-tuned tolerances of the iterative solver for individual singular vectors. The different tolerances for each singular vector increase the efficiency of the proposed algorithm. Another benefit of the proposed algorithm is that the error can be bounded by a user-defined global tolerance. In addition, a variant of the generalized conjugate residual method for multiple RHSs is introduced to accelerate iterative solvers. Finally, numerical validation is conducted with three examples in which the discontinuous Galerkin surface integral equation method is applied. The experiments support two conclusions: tight upper and lower bounds of the solution error exist, and fine-tuning the tolerances reduces the computational costs.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Generalized Surface-Integral-Equation-Based Sub-Structure
           Characteristic-Mode Solution to Composite Objects

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      Authors: Shaode Huang;Chao-Fu Wang;Ming-Chun Tang;
      Pages: 2626 - 2639
      Abstract: Characteristic mode analysis (CMA) is becoming a popular tool to analyze radiation and scattering problems. However, some preliminary studies revealed that the conventional full-structure characteristic modes (CMs) had troubles identifying the desirable modal solutions to some antenna problems, e.g., dielectric resonator antennas (DRAs) with a finite ground plane. In order to remedy the drawback of full-structure CMs and then expand the application scope of CMA, we herein propose a generalized surface integral equation (SIE)-based sub-structure CM formulation for composite objects with arbitrary metallic-dielectric combinations. For the computation of sub-structure CMs, the composite object is handily decomposed into two parts with different functions, namely, the main radiator and passive loading. The distinctive feature of the sub-structure CMs is to accurately capture the resonant modes that belong to the main radiator in the presence of the passive loading. Numerical results of several typical antennas validate that the sub-structure CMs can provide flexible and useful modal solutions to some antenna problems in which the resonant modes confined to designated regions are desirable.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Ray-Tracing Model for Generalized Geodesic-Lens Multiple-Beam Antennas

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      Authors: Qingbi Liao;Nelson J. G. Fonseca;Miguel Camacho;Ángel Palomares-Caballero;Francisco Mesa;Oscar Quevedo-Teruel;
      Pages: 2640 - 2651
      Abstract: geodesic-lenses are a compelling alternative to traditional planar dielectric lens antennas, as they are low loss and can be manufactured with a simple mechanical design. However, a general approach for the design and analysis of more advanced geodesic-lens antennas has been elusive, limiting the available tools to rotationally symmetric surfaces. In this article, we present a fast and efficient implementation built on geometrical optics and scalar diffraction theory. A numerical calculation of the shortest ray path (geodesic) using an open-source library helps quantify the phase of the electric field in the lens aperture, while the amplitude is evaluated by applying ray-tube power conservation theory. The Kirchhoff-Fresnel diffraction formula is then employed to compute the far field of the lens antenna. This approach is validated by comparing the radiation patterns of a transversely compressed geodesic Luneburg lens (elliptical base instead of circular) with the ones computed using commercial full-wave simulators, demonstrating a substantial reduction in computational resources. The proposed method is then used in combination with an optimization procedure to study possible compact alternatives of the geodesic Luneburg lens with size reduction in both the transverse and vertical directions.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Full-Vectorial Spectral Element Method With Generalized Sheet Transition
           Conditions for High-Efficiency Metasurface/Metafilm Simulation

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      Authors: Guoxiong Cai;Xuehan Liu;Tingting Shen;Jie Liu;Na Liu;Qing Huo Liu;
      Pages: 2652 - 2660
      Abstract: Recently, metasurfaces as 2-D metamaterials have been widely applied due to their advantages in low loss, ease of fabrication, and tunability in the phase, magnitude, and polarization of incident electromagnetic waves. However, due to the subwavelength-thickness properties of metasurfaces, their direct modeling and simulation are challenging because of the heavy computational burden. In this work, a high-efficiency spectral element method with generalized sheet transition conditions (SEM-GSTCs) is proposed by replacing finite thickness metasurfaces with zero-thickness equivalent boundary conditions to avoid dense elements and the associated enormous number of unknowns. Moreover, both the scalar and the full-vectorial SEM-GSTC are implemented. Some illustrative numerical examples are shown to verify that the proposed SEM-GSTC not only can obtain highly accurate numerical results but also is effective in addressing complex functions ranging from isotropic to fully bianisotropic metasurfaces.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Benchmarking Computational Electromagnetics With the Large Resonant
           Circular Array of Electrically Short and Thick Dipoles

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      Authors: Orestis Christogeorgos;Anastasios Papathanasopoulos;Panagiotis J. Papakanellos;George Fikioris;
      Pages: 2661 - 2673
      Abstract: The phenomenon of resonances in large circular arrays of electrically short and thick dipoles was studied intensively in the nineties by Harvard’s Antenna Group, led by R. W. P. King and T. T. Wu. Here, we propose these arrays as a benchmark for modern 3-D computational electromagnetics (CEM) solvers. Our proposed benchmark is challenging because it exhibits resonances which, for judicious choices of the parameters, can be extremely narrow. We present exploratory simulations of our proposed benchmark using COMSOL multiphysics and ANSYS HFSS and give detailed comparisons with previously published results.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Measurements and Analysis of Maritime Wireless Channel at 8 GHz in the
           South China Sea Region

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      Authors: Qi Zhang;Shuwen Wang;Yang Shi;Kunde Yang;
      Pages: 2674 - 2681
      Abstract: This article presents the measurement results of maritime wireless propagation channel at 8 GHz in the South China Sea (SCS) region. Large-scale path loss (PL) and small-scale fading of channels between a marine observation platform and a moving vessel are investigated. For large-scale PL, comparisons are conducted among the free space model, the two-ray model, the parabolic equation model (PEM), and the log-distance model with the measured PL data. The results show that the log-distance model agrees well with the general trend of the measured data, whereas the PEM has a better ability to capture the variations of the interference nulls. In addition, the free space model and the two-ray model have larger deviation from the empirical data, implying that they are not suitable for the desired scenario. For small-scale fading, various distributions are considered to fit the fading. Based on the criteria of Kolmogorov–Smirnov statistics, the Rician distribution has the best goodness of fit, compared with the Rayleigh, Nakagami-m, Welbull, or lognormal distributions. These research can provide good guidance for efficient designing and future deployments of distributed buoy networks (DBNs) in the SCS region.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Unification of LoS, Non-LoS, and Quasi-LoS Signal Propagation in
           Wireless Channels

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      Authors: Jonathan W. Browning;Simon L. Cotton;Paschalis C. Sofotasios;David Morales-Jimenez;Michel Daoud Yacoub;
      Pages: 2682 - 2696
      Abstract: The modeling of wireless communication channels is often broken down into two distinct states, defined according to the optical viewpoints of the transmitter (TX) and receiver (RX) antennas, namely, line-of-sight (LoS) and non-LoS (NLoS). Movement of the TX, RX, both and/or objects in the surrounding environment means that channel conditions may transition between LoS and NLoS leading to a third state of signal propagation, namely, quasi-LoS (QLoS). Unfortunately, this state is largely ignored in the analysis of signal propagation in wireless channels. We, therefore, propose a new statistical framework that unifies signal propagation for LoS, NLoS, and QLoS channel conditions, leading to the creation of the three-state model (TSM). The TSM has a strong physical motivation, whereby the signal propagation mechanisms underlying each state are considered to be similar to those responsible for Rician fading. However, in the TSM, the dominant signal component, if present, can be subject to shadowing. To support the use of the TSM, we develop novel formulations for the probability density functions of the in-phase and quadrature components of the complex received signal, the received signal envelope, and the received signal phase. In addition, we derive an expression for the complex autocorrelation function of the TSM, which will be of particular importance in understanding and simulating its time correlation properties. Finally, we show that the TSM provides a good fit to field measurements obtained for two different body-centric wireless channels operating at 2.45 GHz, which are known to be subject to the phenomena underlying the TSM.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Transmission and Scattering Characteristics in Plasma Sheaths of Re-Entry
           Vehicles Due to Multieffect Synergy

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      Authors: Xin Ai;Qiuyue Nie;Zhonglin Zhang;Peiqi Chen;Changshi Yan;Guoqiang Wei;
      Pages: 2697 - 2709
      Abstract: The interaction between electromagnetic (EM) waves and plasma sheaths of reentry vehicles has attracted widespread attention for solving the blackout problem in reentry control and communication. In this article, an integrated model is proposed to study EM wave transmission and scattering characteristics in plasma sheaths for typical altitude and velocity regimes. The key plasma parameters and their distributions of the plasma sheath are investigated based on the previously reported flying data. Reflection, transmission, and absorption coefficients as well as radar cross sections (RCSs) in studied cases are calculated by the integrated model. The results show that multieffects of the plasma sheath, including the high-density, strong-collision, wide-dispersion, subwavelength thickness, etc., can synergistically affect the transmission and scattering characteristics. EM signals of control and communication are then reflected, transmitted, or absorbed differently in various parameter regimes of the plasma sheath. The backward RCS of reentry vehicles may decrease or increase due to variations of feature EM shapes of the plasma sheath. Communication and control properties of the reentry vehicles are also revealed by synergy of multieffects of the sheath on EM waves in various regimes.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Plasma and Terahertz-Wave Propagation Characteristics in
           Atmospheric-Pressure Plasma Jet Under Different Operating Conditions

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      Authors: Wenchong OuYang;Qi Liu;Wenzhe Mao;Shuzhan Gao;Zhengwei Wu;
      Pages: 2710 - 2718
      Abstract: High-density plasma source device is of great significance for ground experiment verification of vehicle reentry communication. atmospheric-pressure plasma jet (APPJ), as a high-density plasma source, has received little attention in ground experiments on vehicle communications. In this article, terahertz (THz) wave propagation characteristics in APPJ are investigated by joint simulation of APPJ discharge and THz transport model and related experimental measurements. THz interferometer (THz-IF) system is used to diagnose the electron density and THz transmission characteristics of APPJ for the first time, and the measured results are in good agreement with the simulation results of a joint simulation model in this article and the measured results of THz time-domain spectroscopy (THz-TDS) system of other researchers. Sheath thickness and electron density produced by self-designed APPJ are highly matched with the plasma sheath environment of the HIFIRE-5b vehicle. Further analysis of the influence of different voltages and needle electrode radius on the THz transmission characteristics shows that the absorption effect plays a major role in THz-wave attenuation in APPJ, and the contribution of the collision effect almost disappears, which is completely consistent with the phenomenon observed in HIFIRE-5b vehicle. The joint simulation model and THZ-IF method developed in this article are of great significance for the ground test verification of reentry communication schemes.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • T-Matrix Backprojection Imaging for Scalar and Vector Electromagnetic
           Waves

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      Authors: Mark S. Haynes;Ines Fenni;
      Pages: 2719 - 2734
      Abstract: Expressions for the ideal free-space backprojected image of an object with known transition matrix (T-matrix) are derived for scalar and vector electromagnetic waves in bistatic and monostatic geometries. Discrete backprojection sums are extended to continuous integrals over source/receiver spheres. Images are formed without the need to generate or process scattered field data. The final expressions only depend on regular wave functions in the frame of the object and the object T-matrix. The formulation is validated numerically using the aggregate T-matrix solution for a collection of acoustic and dielectric spheres. Applications include assessment and validation of free-space focusing and T-matrix scattering solutions.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Wideband High-Selective Linear Polarization Converter and Its Application
           in Bifunctional Metasurface for Reduced Isolation Band

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      Authors: Lei-Lei Qiu;Shuguang Fang;Lei Zhu;Lianwen Deng;Shengxiang Huang;Yueyang Wu;Xiaohui Gao;Xiao Zhang;
      Pages: 2735 - 2744
      Abstract: In this article, a wideband high-selectivity filtering linear polarization converter is proposed and applied for ultranarrow isolation-band bifunctional metasurface. As the contribution of this work, the developed polarization converter based on slot-line loaded triangular resonator unit not only achieves the in-band multimode resonant characteristic, but also introduces two additional controllable zeros out-of-band, so as to enable simultaneous implementation of the wideband and high selectivity features. With the detailed analysis of the modes, field, and surface current distributions, the mechanisms of wideband, high selectivity, and polarization conversion are revealed. Finally, the linear polarization converter as well as the bifunctional metasurface are fabricated for demonstration. The linear polarization converter can attain a conversion bandwidth of 45% under a polarization conversion ratio of >90%. Due to the excellent filtering characteristic of the proposed linear polarization converter, the constructed bifunctional metasurface can reduce its isolation band to only 2.7%. As expected, the proposed converter has the attractive advantages of wideband operation and high selectivity, which are of great significance for reducing the isolation-band and improving the spectral utilization in various applications of multifunctional metasurfaces.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Systematic Method for Efficient Wireless Powering to Implantable
           Biomedical Devices

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      Authors: Xianbo Cao;Hiroyasu Sato;Kai-Da Xu;Wen Jiang;Shuxi Gong;Qiang Chen;
      Pages: 2745 - 2757
      Abstract: Wireless power transfer (WPT) technology has played a vital role in the rapid development of biomedical devices. While several single methods to improve WPT efficiency have been reported, the lack of integrality in these single methods limits the effect of the improvements. In this investigation, we analyze the physical process of a typical WPT scenario and find that the high propagation loss consisting of in-tissue attenuation and interface reflection degrades the WPT performance. A systematic method to comprehensively improve WPT efficiency is then proposed. Specifically, a Fresnel zone plate (FZP) is applied against the attenuation of inner biological tissue, and a practical air layer-artificial matching layer (AL-AML) is applied to decrease the reflection on the surface of biological tissue. According to a simulation of possible analytical models, the efficiency is significantly improved when using the proposed method. In an experiment with an implant depth of 20 mm, the proposed systematic method is found to enhance maximum relative received power by 12 dB, with an almost 15-fold increase in efficiency over the conventional system with just a transmitter (Tx) and a receiver (Rx). It is also verified that the improvement in efficiency is greater in the systematic method than in single methods. Also, various misalignment tolerances between the proposed structures and the Rx are determined from the coupling strength of the proposed WPT system. The results of this investigation show the potential of the proposed systematic method for further improvements in WPT efficiency.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Multihop Strategy for the Planning of EM Skins in a Smart
           Electromagnetic Environment

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      Authors: Marco Salucci;Arianna Benoni;Giacomo Oliveri;Paolo Rocca;Baozhu Li;Andrea Massa;
      Pages: 2758 - 2767
      Abstract: This article deals with the electromagnetic (EM) planning of static and passive EM skins (EMSs) in complex urban scenarios to improve the EM coverage of the base-station (BTS) antenna by means of a set of multihop (MH) cascaded reflections. Toward this end, an innovative system-by-design (SbD)-based method is developed where wireless links of arbitrary “depth,” which are implemented through multiple anomalous cascaded reflections, are optimized. Representative numerical results, concerned with real-world scenarios, are analyzed to assess the capabilities and the potentialities of such an instance of the so- called smart EM environment (SEME).
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Focusing and Linear-to-Circular Polarization Conversion of a Hemispherical
           Metasurface

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      Authors: Yuping Shang;Lixin Dang;Ju Feng;Cheng Liao;
      Pages: 2768 - 2777
      Abstract: With the aim of enhancing the radiation of the antenna system conventionally containing a protective dome, a transmission-type linear-to-circular polarization conversion electromagnetic metasurface lens which approximates a hemispherical shell profile is presented in this study. The presented design bearing structural compatibility with the existing dome geometry can facilitate the link enhancement of compact system through its potential for a circularly-polarized high gain antenna. To fulfill both the focusing and polarization conversion requirements, transmission phase distribution on the hemispherical surface is analyzed first. Then, polarization-dependent unit cell geometry is designed to achieve the objective transmission phase distribution. The hemispherical metasurface is thus obtained through building all unit cells with determined dimensions and orientations onto the corresponding hemispherical surface positions. Finally, using an aperture-coupled linearly-polarized patch antenna as the primary radiating source of the metasurface, enhanced main lobe gain and circularly-polarized secondary radiation is observed within a wide band. The agreement between simulation and measurement validates the design.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Single-Cut Far-Field Pattern Determination of Polarized Linear Antenna
           Array via Quasi-Far-Field Mathematical Absorber Reflection Suppression

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      Authors: Xi Li;Guangqun Niu;Bing Zhao;Lin Yang;
      Pages: 2778 - 2783
      Abstract: In this work, a method for rapidly and accurately determining the single-cut far-field (FF) patterns of any polarized linear antenna array, termed as quasi-far-field mathematical absorber reflection suppression (QFF-MARS), is introduced. The proposed QFF-MARS method takes advantage of the cylindrical wave expansion (CWE) theory and is able to exclude interference from scatters at the QFF range. In this method, probe compensation is not needed, owing to the fact that the measurement procedure is the same as that for FF. It is only required that the measurement distance for an antenna under test (AUT) satisfies the FF and QFF conditions for its smaller and larger dimensions, respectively. To validate the proposed method, a 45° polarized antenna array and a phased array have been simulated. The results obtained by the proposed approach are consistent with both theoretical and measured results. This indicates that the proposed approach can directly obtain the single-cut FF patterns of polarized linear antenna arrays at a QFF range, while identifying and extracting range-related multipath effects.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Aperture-Shared All-Metal Endfire High-Gain Parabolic Antenna for
           Millimeter-Wave Multibeam and Sub-6-GHz Communication Applications

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      Authors: Jianfeng Zhu;Yang Yang;Zhangju Hou;Shaowei Liao;Quan Xue;
      Pages: 2784 - 2789
      Abstract: This communication demonstrates an endfire aperture-shared antenna for millimeter-wave (mm-wave) multibeam and sub-6-GHz communication applications. High-gains are achieved based on the parabolic reflectors (PRs) that can collimate the electromagnetic (EM) wave radiated from the feeds at the focal points. In contrast to the full metal-based PR in the sub-6-GHz band, the mm-wave PR is implemented using periodic metal gratings, which shows a bandgap in the mm-wave band while allowing the sub-6-GHz EM wave free to pass. In this way, the sub-6-GHz and mm-wave parabolic antennas share the same radiating aperture with near 100% aperture reuse efficiency and tiny mutual interference. Multiple mm-wave feeds are used to achieve multibeam radiation without a complicated feed network. The radiating aperture is gradually enlarged in a flared structure to enhance the gain further while maintaining a high aperture efficiency. In contrast to the state-of-the-art printed circuit board (PCB) designs, the proposed antenna is an all-metal one with the advantage of no dielectric loss. A prototype operating at the C- and Ka-bands is designed, prototyped, and measured.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Low-Cost, Dual Circularly Polarized 2-bit Phased Array Antenna at
           X-Band

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      Authors: Lu Yin;Peng Yang;Qianwei Zeng;Peng Zhang;Tao Dong;Jun Hu;Zaiping Nie;
      Pages: 2790 - 2795
      Abstract: A low-cost, dual-circularly-polarized (CP) 2 bit antenna working at 10 GHz is reported in this work. The antenna element utilizes a square-ring patch as a radiator. By selecting the feeding direction of the T-shaped coupling microstrip line and the position of the perturbation corner, the 2 bit phase of 0°, 90°, 180°, 270° and the CP reconfigurability can be realized. An eight-element linear array is used to verify the beam scanning performance. By controlling the “ON” or “OFF” of the p-i-n diodes, the prototype array can steer the main beam from 0° to 40°. Within these steering beams, simulated and measured results have a good agreement, which verifies the functions of the antenna.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Wide Bandwidth Ratio of 10-to-1 CPW-Fed Whip Antenna With Improved
           Radiation Patterns

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      Authors: Zhi-Min Du;Sai-Wai Wong;Rui-Sen Chen;Yin Li;Lin-Ping Feng;Kam-Weng Tam;
      Pages: 2796 - 2801
      Abstract: In this communication, a novel compact single whip wideband antenna with an improved omnidirectional wideband antenna is proposed. First, a single whip antenna is designed on a thin flexible printed circuit (FPC) with a tapered coplanar waveguide feed line. This proposed antenna shows a wide impedance matching performance in a frequency range from 194 to 2124 MHz with a bandwidth ratio of 10:1, while a measured return loss is better than 10 dB within the desired passband. The single whip antenna has demonstrated an ultrawide bandwidth with satisfactory radiation properties in the lower frequency band. However, the omnidirectional radiation pattern deteriorated in the higher frequency band. Three whipped antennas are codesigned to form an improved omnidirectional radiation pattern. Finally, the measured performance of the fabricated antenna shows a good agreement with that obtained through simulation results.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Dual-Band Decoupling for Two Back-to-Back PIFAs

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      Authors: Weiquan Zhang;Yue Li;Kunpeng Wei;Zhijun Zhang;
      Pages: 2802 - 2807
      Abstract: In this communication, two dual-band back-to-back planar inverted-F antennas (PIFAs) are presented for wireless local area network (WLAN) applications. By simply etching a slot on the PIFA, the PIFA can simultaneously radiate at the WLAN 2.4 GHz (2.4–2.484 GHz) and WLAN 5 GHz (5.15–5.835 GHz) bands. To reduce the mutual coupling at the two independent bands in a guided way, long and short slots are successively engraved on the ground. The detailed decoupling process is given and discussed. The antenna was fabricated and measured. The measured results show that the two PIFAs cover the 2.4 and 5 GHz WLAN bands and the isolation can be improved to higher than 20 dB at the two independent bands.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Low-Scattering X-Band Planar Phased Vivaldi Array Antenna

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      Authors: Shi-Gang Fang;Shi-Wei Qu;Shiwen Yang;Jun Hu;
      Pages: 2808 - 2813
      Abstract: A low-scattering X-band planar phased Vivaldi array antenna is proposed in this communication. To reduce the scattering cross section (SCS) of the antenna, two types of Vivaldi elements with the defected ground structures (DGSs) are designed, as well as an embedded absorbing array. Under the normal co-polarized (co-pol) incident waves, the reflections of the two Vivaldi elements are close in magnitude but out of phase. Hence, the scattering of the two elements cancels out in the normal direction. Besides, the problem of obvious bistatic SCS peaks, which always arise when utilizing the phase cancellation method to achieve SCS reduction (SCSR), is solved by the interlacing arrangement of the two elements. Under the cross-polarized (cr-pol) incident waves, the incident power is mostly received and absorbed by the absorbing array, which is composed of the dipole elements in the array center and the slot elements on two edges. According to the measured results, the proposed phased Vivaldi array antenna achieves notable cr-pol SCSR over 6–18 GHz, and the average in-band co-pol SCSR reaches 20 dB simultaneously, without any deterioration on the radiation and scanning performances compared to a referenced one.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Compactly Placed High-Isolated Antenna Pair With Independent Control of
           Decoupling Amplitude and Phase

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      Authors: Aofang Zhang;Kunpeng Wei;Qiao Guan;Yiwu Hu;
      Pages: 2814 - 2819
      Abstract: We propose a compactly placed high-isolated antenna pair through the decoupling of the transmission line (TL) for the application of mobile terminals. Especially, the TL, loaded with a decoupling branch and a phase shift circuit, is employed to create two transmission paths, where the coupling powers through such two paths are capable of being counteracted perfectly. By adjusting the decoupling branch and the phase shift circuit, the decoupling amplitude and phase could be controlled independently, thus realizing a very high isolation of such antenna pair. Both measured and simulated results show that the isolation of the antenna pair, with compact distance from 1/ $40 lambda _{0} $ to 1/ $8 lambda _{0} $ , is better than 25 dB in Wi-Fi 2.4G/Bluetooth band with a peak value of over than 40 dB. Furthermore, the decoupling technique is extended to multi-element and dual-band operations. Our proposed design, with independent control of decoupling amplitude and phase, should provide promising values for the application of multiple-input multiple-output (MIMO) and diversity systems.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Uniformly Improved Cross-Polar Discrimination in a Dielectric Resonator
           Antenna by Conduction-Current Control

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      Authors: Sk Rafidul;Puneet Kumar Mishra;Rajat Bose;Debatosh Guha;
      Pages: 2820 - 2825
      Abstract: This work, for the first time, investigates the comprehensive sources of cross-polarized (XP) radiation from a dielectric resonator antenna (DRA). The study uses a recently developed theory on DRA radiation and models the XP sources with the help of well-known definition by Ludwig. This eventually focuses on the conduction-current distribution on the metallic ground. The interpretation leads to a concept of synthesizing effective conduction current in order to satisfy the required condition of low XP fields. A representative prototype of a cylindrical DRA on engineered ground plane has been realized to operate in C-band. It exhibits nearly 12% matching bandwidth with more than 25 dB co-to-cross polar discrimination over both orthogonal (H-) and diagonal (D-) planes. Relative improvement in XP level promised by the measured data is $sim $ 15 dB in D- and $sim $ 10 dB in H-planes. This proof of concept may now be extended to other DRA geometries and for practical applications in the near future.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A Dual-Band Antenna for LTE/mmWave Mobile Terminal Applications

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      Authors: Xin-Hao Ding;Qing-Hu Zhang;Wen-Wen Yang;Wei Qin;Lei Guo;Jian-Xin Chen;
      Pages: 2826 - 2831
      Abstract: In this communication, a dual-band antenna is proposed, which integrates a millimeter-wave (MMW) substrate-integrated dielectric resonator antenna (SIDRA) beam-steerable array and long-term evolution (LTE) folded monopole antenna (FMA). The SIDRA, which is a $1times4$ tightly arranged DRA array with zero edge-to-edge spacing, is developed in the clearance area of the FMA. Hence, the two antennas not only share the same substrate but also share the same aperture. The performance of FMA will not deteriorate by properly locating the SIDRA array. An antenna prototype was fabricated and measured, and the rationality of the design was verified. The LTE FMA can cover the band of 1.78–2.62 GHz (38.2%) and achieve a peak gain of 3.9 dBi, while the MMW array can cover the band of 26.4–29.8 GHz (12.2%) and achieve a peak gain of 10 dBi. The MMW array can support beam-steering angles of ±45°. The high space utilization of the proposed design strategy makes the dual-band antenna suitable for the fifth-generation (5G) mobile terminal applications.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Modeling and Analysis of Wideband Multilayer Metasurface Antenna Array
           Using Characteristic-Mode Analysis

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      Authors: Jia Fan Gao;Feng Han Lin;
      Pages: 2832 - 2836
      Abstract: Conventional single-layer homogeneous impedance-sheet models (ISMs) for single-layer metasurface (MTS) antenna elements cannot handle multi-layer inhomogeneous MTS antenna arrays of local field inhomogeneity caused by loadings and feedings. In this communication, a hybrid ISM is proposed to overcome the above challenge with the aid of characteristic mode analysis (CMA). For proof of concept, a wideband multilayer MTS antenna array (MAA) is designed, where capacitive loading is further proposed to manipulate the frequency interval of desired modes for bandwidth improvement. With an element width of $0.29lambda _{0}$ and an overall size of $0.70lambda _{0} times 0.70lambda _{0} times 0.08lambda _{0}$ ( $lambda _{0}$ is the wavelength in free space at 3.5 GHz), the proposed four-element MAA achieves a measured impedance bandwidth of 17.8% with $vert S_{11}vert < -10$ dB, a gain of 9.1–12 dBi, and a least front-to-back ratio of 25 dB. The proposed method extends the application of CMA from MTS antenna elements (MAEs) to MAAs, by enabling advanced mode manipulation techniques for simultaneous antenna miniaturization and bandwidth enhancement.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Metasurfaces Design Using Primary Elements and Characteristic Models:
           Connection Between SSM/SPM and Circuit Quantities

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      Authors: Xiao Jia;Xunwang Dang;Xiaotian Pan;Mingjiang Wang;
      Pages: 2837 - 2842
      Abstract: This study proposes a metasurface-designing framework using a pre-established database of primary elements and characteristic models, which avoids tedious optimization during metasurface design. We adopt the surface susceptibility model (SSM) and surface porosity model (SPM) as primary characteristic models, and patch-like and fishnet-aperture unit cells as primary elements. First, we connect the efficient characteristic model of metasurfaces, SSM for patch-like unit cells, and SPM for fishnet-aperture unit cells, to $LC$ circuit components. Then, we extend the scale of SSM/SPM of the patch/fishnet-like unit cells with a periodicity in the order of $0.1lambda _{0}$ , to establish a primary database. Finally, we design metasurfaces of various functionality using the pre-established database of the primary elements and characteristic models with the aid of classical circuit and transmission line theories.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Null Steering in Linear Array Antennas With Electronically Displaced Phase
           Center Dual-Mode Antenna Elements

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      Authors: Tanzeela Mitha;Maria Pour;
      Pages: 2843 - 2848
      Abstract: The potential of dynamically steering the null locations in equally spaced linear scanning array antennas using the electronically displaced phase center antenna (E-DPCA) technique is investigated for the first time in this communication. The relative coordinates, and thus, the element spacing, of the equally spaced linear array antennas are electronically varied using the E-DPCA technique to adaptively steer the null locations without any physical displacement while maintaining the same overall array length. The versatility of the proposed technique is further explored by: 1) generating consecutive nulls with a minimum resolution of 1° between them and 2) simultaneously steering the null locations and scanning the main beam.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Plasma-Based Reflective Surface for Polarization Conversion

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      Authors: Mirko Magarotto;Luca Schenato;Paola De Carlo;Antonio-Daniele Capobianco;
      Pages: 2849 - 2854
      Abstract: This study analyses, for the first time, the use of reflective surfaces based on magnetized plasmas for polarization conversion. The feasibility of this concept has been assessed via a theoretical model. Moreover, the numerical design of a plasma-based reflective surface is presented. The latter enables linear-to-linear (LP-to-LP) and linear-to-circular polarization (LP-to-CP) conversion over a broad frequency range, from 7.5 to 13 GHz. To this end, the applied magnetic field intensity has to be tunable over 55–140 mT and its direction steerable toward three mutual orthogonal axes. At the same time, the plasma density has to be controlled up to ${2times 10^{18}},,text{m}{^{-3}}$ . These requirements are consistent with the plasma technology at the state-of-the-art.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Ultrawideband Dual-Polarized Frequency-Selective Absorber With Tunable
           Reflective Notch

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      Authors: Yudi Fan;Da Li;Hanzhi Ma;Jiaqi Xing;Yijie Gu;Lay Kee Ang;Er-Ping Li;
      Pages: 2855 - 2860
      Abstract: An ultrawideband dual-polarized frequency-selective absorber (FSA) with a tunable reflective notch is proposed in this communication. The structure is constructed by combining a broadband FSA as well as a tunable lossless frequency-selective surface (FSS). The FSA consists of a lossy layer and an air spacer, which is backed with a metal plane. Varactors are employed in the lossless FSS and a dc bias is applied to adjust the frequency of the reflective notch. An equivalent circuit model (ECM) of the notch-tunable FSA is established to explain the operating principle, and the impedance condition of the ultrawide absorptive band is discussed. The ECM results agree well with the frequency-domain simulation results. The absorption band with a reflection coefficient below −10 dB extends from 2 to 8 GHz. It is worth mentioning that the reflective notch with nearly perfect reflection is demonstrated to be tuned from 2.24 to 4.56 GHz. A prototype of the structure is fabricated and measured to validate the design concept. Its measured absorption band from 2.5 to 8 GHz is in favorable agreement with the simulated results. These findings will be useful for designing intelligent antenna reflector systems with out-of-band radar cross section (RCS) reduction.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Critical Angle Formulation of Nonuniform Plane Waves for Determining
           Correct Refraction Angles at Planar Interface

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      Authors: Yongwan Kim;Hyunjun Yang;Jungsuek Oh;
      Pages: 2861 - 2866
      Abstract: The expressions and properties of the critical angles of nonuniform plane waves for determining the correct refraction angle at the infinite planar interface of two linear, isotropic, and homogeneous media are presented. The two media could be lossless or lossy. For the case where the complex wave vector of Adler–Chu–Fano formulation and the normal vector to the interface are coplanar, a critical angle equation, which is simpler than the extant one, under the condition that one or two critical angles exist, is formulated. In addition, for the case where the complex wave vector and normal vector to the interface are noncoplanar, a critical angle equation is formulated, rendering the 3-D nonuniform plane wave refraction feasible for utilization in many areas of optics. The presented critical angle equations were validated for various nonuniform plane waves and media.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Solving Electromagnetic Inverse Scattering Problems in Inhomogeneous Media
           by Deep Convolutional Encoder–Decoder Structure

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      Authors: Huan Huan Zhang;He Ming Yao;Lijun Jiang;Michael Ng;
      Pages: 2867 - 2872
      Abstract: This communication proposes a novel deep learning (DL) approach to solve electromagnetic inverse scattering (EMIS) problems in inhomogeneous media. The conventional approaches for solving inhomogeneous EMIS problems generally have to consider inhomogeneous Green’s functions or conduct approximation operations to media, which inevitably introduces various challenges, including complex mathematical derivation, high computation cost, unavoidable nonlinearity, and even strong ill-posedness. To avoid these challenges, we propose a DL approach based on the complex-valued deep convolutional neural networks (DConvNets), which comprise the deep convolutional encoder–decoder (DCED) structure. Its training data are collected based on the simple synthetic dataset. While the scattered fields received in the measurement domain are utilized as the input for the encoder to extract feature fragments, the final output for the counterpart decoder is the contrasts (permittivities) of dielectric scatterers in the target domain. In this way, unlike the conventional methods, the unknown domain between the target domain and measurement domain never has to be considered to compute inhomogeneous Green’s functions. Consequently, the inhomogeneous EMIS problems could be solved with higher accuracy even for extremely high-contrast targets. Numerical examples illustrate the feasibility of the proposed DL approach. It acts as a new candidate for solving EMIS problems in inhomogeneous media.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Pixel Antenna Optimization Using the Adjoint Method and the Method of
           Moving Asymptote

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      Authors: Tianrui Qiao;Fan Jiang;Shanpu Shen;Zhen Zhang;Min Li;Chi-Yuk Chiu;Qingsha S. Cheng;Ross Murch;
      Pages: 2873 - 2878
      Abstract: The pixel concept offers a convenient and efficient method for antenna design. To meet the given specified antenna requirements or constraints, heuristic algorithms are often used to optimize the connection states for the hardwires between pixels, which are usually assumed to have the binary states, “short” or “open”. An alternative optimization strategy is proposed in this work, where the Boolean constraints on the hardwires are first relaxed to continuously tunable resistances and the globally convergent method of moving asymptotes (GCMMA) is applied to optimize the resistances. To speed up the computation, the adjoint method is used to simplify the calculation of the gradient information required in GCMMA. Resistances that are found as being above or below a certain threshold are then judged as “open” or “short”, respectively. Finally, the remaining intermediate resistance states are binarized using the successive exhaustive Boolean optimization (SEBO) method. Four different optimization strategies are proposed in terms of the objective function implemented in GCMMA and whether the second-stage SEBO is iterative or not. Two broadband endfire pixel antennas having horizontal linear polarization and high radiation efficiency are designed and fabricated correspondingly to demonstrate the feasibility of our proposed methods.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Suppressing White-Noise Interference for Orbital Angular Momentum Waves
           via the Forward–Backward Dynamic Mode Decomposition

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      Authors: Yanming Zhang;Lijun Jiang;
      Pages: 2879 - 2884
      Abstract: When the orbital angular momentum (OAM)-carrying beam propagates in a highly boisterous environment, it causes the degradation of the OAM modes’ purity, which brings the crosstalk in the demultiplexing process. To address this issue, we extend the dynamic mode decomposition (DMD) method to suppress white-noise interferences of OAM by using the forward–backward DMD (FBDMD) approach. The FBDMD-based scheme retrieves the noise-free DMD mapping matrix corresponding to the actual OAM’s topological charges by combining the forward and backward DMD mapping matrix in the noisy environment and consequently reduces the crosstalk, particularly for sorting the superposed OAM modes. Numerical examples are provided to demonstrate the effectiveness and advantages of the proposed approach. It is found that the white-noise interference can be significantly suppressed in sorting the OAM modes process compared with previous works. Also, FBDMD is feasible for the whole aperture receiving and partial aperture receiving (PAR). This work offers a practical tool for OAM coaxial demultiplexing in a noisy environment.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • A 3-D-Printed Ultrawideband and Ultralow-Scattering Water-Based
           Metasurface

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      Authors: Jianxun Su;Yujiao Li;Meijun Qu;Hang Yu;Qingxin Guo;Zengrui Li;
      Pages: 2885 - 2890
      Abstract: In this communication, a water-based metasurface is proposed using hybrid mechanisms of absorption and phase cancellation for ultrawideband and ultralow scattering. Pure water as the lossy material is utilized in our work due to its high-dielectric loss and easy accessibility. In addition, 16 water-based unit cells with different parameters are selected according to optimized multielement phase cancellation (OMEPC). The best backward scattering reduction can thus be acquired since the combination of different unit cells can achieve the desired phase difference condition in ultrawideband. The 3-D radar cross-sectional (RCS) patterns and the ratio of energy dissipation demonstrate that the ultrawideband and ultralow backward scattering of the proposed design is due to the combined effect of absorption and diffusion. The simulated 10 dB (15 dB) RCS reduction bandwidth is from 2 to 100 GHz (9.7–100 GHz). The RCS reduction results can maintain stable under wide-angle incidence up to 60°. Finally, a prototype with $4times4$ arrays based on 3-D printing technology is fabricated and measured for demonstration. Each array is a subarray of 5 $times5$ unit cells with the same parameters to facilitate processing. The measured results are in good agreement with the simulated ones.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Resolution Analysis of Coincidence Imaging Based on OAM Beams With Equal
           Divergence Angle

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      Authors: Xue Li;Ningning Zhou;Shitao Zhu;Xiaoming Chen;Mengran Zhao;Anxue Zhang;
      Pages: 2891 - 2896
      Abstract: The multi-mode orbital angular momentum (OAM) beams can be effectively applied in target detection when the divergence angles are equal. The resolution threshold of the coincidence imaging system with multi-mode OAM is analyzed assisted by the subspace projection method. First, the relationship between the imaging resolution and the correlation function (CF) of the measurement mode is obtained based on the first-order correlation algorithm for the multi-mode OAM-based coincidence imaging (MM-OAMCI). Then, the feature vector of each imaging unit is extracted to distinguish the imaging point in the discretized imaging plane. Finally, the resolution threshold is given based on three factors, i.e., the feature vector, the noise, and the reconstruction algorithm. Specifically, the resolution of the MM-OAMCI system is determined by the deployment of the transmitting array, the reconstruction algorithm and the noise caused by the system design, the imaging modeling, and the environment noise. The super-resolution capability of the multi-mode OAM coincidence imaging system is validated by the simulations and experiments. The imaging results show that the resolutions in elevation and azimuth of the reconstructed image can be improved largely compared with the traditional microwave coincidence imaging (TMCI) methods, which is consistent with the theoretical analysis results.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Comments on “Correction Analysis of ‘Frequency Diverse Array Radar
           About Time’”

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      Authors: Kejin Chen;Shiwen Yang;Yikai Chen;Shi-Wei Qu;
      Pages: 2897 - 2898
      Abstract: In recent years, frequency diverse arrays (FDAs) have been receiving much attention due to their high degrees of freedom for beamforming [1]. Essentially, the beampatterns of FDA are related to angle, time, and range [1], [2], [3], [4]. However, the time-varying property has limited the practical application of FDAs. Thus, there has been a lot of discussion about the time-varying property of FDAs [3], [4], [5], [6], [7], [8].
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Reply to Comments on “Correction Analysis of ‘Frequency Diverse Array
           Radar About Time”’

    • Free pre-print version: Loading...

      Authors: Ming Tan;Chunyang Wang;
      Pages: 2899 - 2902
      Abstract: Similar to the analysis method of dividing the actual time into “fast time” and “slow time” introduced in the signal processing community, dividing the actual time into “the transmit delay” and “the time index within pulse” is a new analysis method from a new perspective to facilitate the analysis of the time-varying property of frequency diverse array (FDA) radar. It does not break the nature of the unity of time. In this reply, the importance of our new findings and contributions are presented again in a more concisely way.
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • Special Issue Measurement Technologies for Emerging 5G and Beyond Channel
           Characterization and Antenna Systems

    • Free pre-print version: Loading...

      Pages: 2903 - 2903
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
  • IEEE Open Access

    • Free pre-print version: Loading...

      Pages: 2904 - 2904
      PubDate: March 2023
      Issue No: Vol. 71, No. 3 (2023)
       
 
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