Showing papers in "IEEE Transactions on Microwave Theory and Techniques in 2021"
TL;DR: In this paper, a dual-polarized vortex beam generator based on metasurface and metagrating (MG) is proposed, where the phase is modulated through moving the position of meta-atoms instead of varying the geometrical parameters or rotating the unit cells.
Abstract: Traditional methods of generating vortex beams based on metasurfaces consist mainly in modulating propagation phase or geometric phase. Here, by introducing detour phase, we propose the construction of dual-polarized vortex beam generators in the form of metasurface and metagrating (MG). The phase is modulated through moving the position of meta-atoms instead of varying the geometrical parameters or rotating the unit cells. To use detour phase, two kinds of unit cells are designed to achieve specific diffraction order. Each unit can arbitrarily and independently adjust the operation frequency and diffraction angle of transverse electric (TE) and transverse magnetic (TM) polarizations. Two vortex beam generators are designed and fabricated with different topological charges carried by orthogonal polarizations. To demonstrate the ability to independently manipulate, two polarizations of the generator based on MG are designed in different frequency bands. Both the simulation and experimental results validate the proposed method, showing great potential for polarization division multiplexing in orbital angular momentum (OAM) communication systems.
88 citations
TL;DR: In this article, the authors systematically introduced the information metasurface (IM) with its application in wireless communications, in which the meta-atoms are represented by using digital codes "0" and "1" to characterize the EM responses.
Abstract: Metasurface has great capabilities in tailoring the electromagnetic (EM) waves in a controllable way owing to the carefully designed and arranged subwavelength meta-atoms In this review paper, the digital version of metasurface, information metasurface (IM), is systematically introduced with its application in wireless communications IM extends the research scope of metasurface from physics to the information perspective, in which the meta-atoms are represented by using digital codes “0” and “1” to characterize the EM responses It can achieve programmable controls of EM waves in real time by integrating with the field-programmable gate array (FPGA) On the other hand, the digital coding strategy bridges the physical world and digital world, and further make the metasurface realize direct information processing With the outstanding advantages, IMs have shown great potentials to bring revolutionary applications in wireless communications In this article, the basic concepts and principles of IMs and their programmable features are presented first Then it focuses on the IM-based new architecture transmitters, as well as the IM-integrated wireless networks in more detail Finally, the current progress and the future directions of IMs in the wireless communications are respectively summarized
70 citations
TL;DR: In this article, a dual-band and polarization-angle-independent rectifying metasurface (MS) with a miniaturized dimension and a wide incident angle range is presented.
Abstract: A dual-band and polarization-angle-independent rectifying metasurface (MS) with a miniaturized dimension and a wide incident angle range are presented in this article. The proposed structure consists of a single layer of periodic cell arrays with integrated diodes, a $dc$ feed, and a load. A novel method of incorporating surface-mount components (e.g., diodes) into the texture is developed to simplify the structure. The matching network between MS and the nonlinear rectifier can be eliminated directly due to the multimode resonance and adjustable high-impedance characteristics of the MS. Moreover, the proposed MS can maintain high conversion efficiency by using different diodes without changing the overall topology. In addition, the proposed design can effectively capture incoming waves with arbitrary polarizations and a wide incident angle range of 60°. The $4\times 4$ MS array is fabricated and measured. Experimental results show that the proposed structure can achieve maximum efficiency of 58% at 2.4 GHz and 50% at 5.8 GHz with an input power of 0 dBm under different polarizations and incident angles. Importantly, it is also shown that the rectifying MS can maintain high efficiency over a wide power range from −3 to 10 dBm. The proposed design concept is very suitable for the adaptive wireless power supply of portable devices.
54 citations
TL;DR: In this paper, a wide-angle and broadband rasorber is presented incorporating several advances, such as frequency selective surface (FSS), which increases the upper and lower absorption bandwidths while reducing the insertion loss at transmission window.
Abstract: A novel wide-angle and broadband rasorber is presented incorporating several advances. To broaden the bandwidth, we introduce a new type of frequency selective surface (FSS) in the bottom layer of the rasorber. This strategy increases the upper and lower absorption bandwidths while reducing the insertion loss at transmission window. Furthermore, a new top resistive layer is proposed via the loading of electric field coupled resonator elements on a cross-dipole structure. The proposed design offers both, an angularly stable performance and a thin structure that can be fabricated on a single dielectric substrate. To enable switchability, p-i-n diodes are employed and a reconfigurable rasorber/absorber is designed where a new concept of “lossy/lossless” top layer is investigated and established as the best choice among other switchable designs. Equivalent circuit models are constructed for both active and passive designs to provide physical insight into their operation. Finally, to enable deployment of the rasorber over curved geometries, these advances are incorporated into a conformal structure. Three separate prototypes are fabricated and good agreement is obtained between design predictions and experimental results.
52 citations
TL;DR: To the best of the authors' knowledge, this work is the first 5G 37-/39-GHz phased array Tx/Rx using the scalable brick array configuration and demonstrating competitive performances compared with previous works.
Abstract: This article presents the 38-GHz phased array 32-element Tx and 16-element Rx with 2-GHz IF and 5-GHz LO for fifth-generation (5G) millimeter-wave (MMW) communications. The Tx and Rx beamformers and upconverters/downconverters are fabricated in 65-nm CMOS. The PAs and LNAs near antenna ends are fabricated in 0.15- $\mu \text{m}$ GaAs pHEMT. The eight-element Tx and four-element Rx phased array printed circuit board (PCB) modules integrated with multiple integrated circuits (ICs) and endfire antennas are implemented as unit cells. Four pieces of Tx modules are vertically stacked to construct an $8\times {4}$ brick array (planar array), while four Rx modules are to construct a $4\times {4}$ array. According to 38-GHz over-the-air (OTA) measurements, the 32-element Tx shows 47.5-dBm equivalent isotropic radiated power (EIRP) at OP $_{\mathrm {1 ~dB}}$ with −35.2-dB image rejection ratio (IMRR) and −37.4-dB $\times 8$ LORR. The 16-element Rx at 38 GHz shows −4-dBm OP $_{\mathrm {1~dB}}$ with −28-dB IMRR and −36.6-dB LORR. The Tx and Rx support the beam scanning around ±60° azimuth and ±30° elevation planes. The Tx-to-Rx wireless data link demonstrates 64 quadrature amplitude modulation (QAM)/400 M-BR, 256 QAM/200 M-BR, and 512 QAM/100 M-BR in 20 m. To the best of our knowledge, this work is the first 5G 37-/39-GHz phased array Tx/Rx using the scalable brick array configuration and demonstrating competitive performances compared with previous works.
52 citations
TL;DR: In this paper, the authors presented a 23.5-29.5 GHz TRX quad-beamformer with 6 bit phase control and 8 bit gain control for wideband multistandard applications, which achieved an effective isotropic radiated power (EIRP) of 54.8 dBm at P1dB with a 3-dB bandwidth of 23. 5-30 GHz and can scan to ±60° in the azimuth plane and +/40° in elevation plane with excellent patterns with a single point calibration at 27 GHz.
Abstract: This article presents a 23.5–29.5-GHz $8\times 8$ phased array for wideband multistandard applications. The array is based on wideband high-performance $2\times 2$ transmit/receive (TRX) quad-beamformer chips with 6 bit of phase control and 8 bit of gain control. The antenna is designed using a stacked-patch structure combined with a two-stage impedance matching network to enhance its bandwidth. The $8\times 8$ phased array achieves an effective isotropic radiated power (EIRP) of 54.8 dBm at P1dB with a 3-dB bandwidth of 23.5–30.5 GHz and can scan to ±60° in the azimuth plane and +/40° in the elevation plane with excellent patterns with a single-point calibration at 27 GHz. Measured error vector magnitude (EVM) for a 64-QAM 200 and 800-Mbaud waveforms result in a system EVM of 5% (−26 dB) in the TX mode at an average EIRP of 46–47 dBm at 24.5–29.5 GHz. Also, the wideband array is capable of 16-QAM 24-Gb/s links with an EVM <16% over all scan angles. An interband carrier aggregation (CA) system is also demonstrated with the wideband array using 200-Mbaud 64-QAM waveforms with 25- and 29-GHz carriers. The phased-array phase and amplitude settings are chosen such that the 25- and 29-GHz waveforms are radiating simultaneously at the same angle with low scan loss, resulting in an efficient system. Also, the out-of-band third-order intermodulation products generated by the power amplifier on each element are filtered out by the antenna. CA measurements with up to 50° scan angles are demonstrated with low EVM. To the best of our knowledge, this is the first demonstration of CA in millimeter-wave fifth-generation (5G) systems.
52 citations
TL;DR: In this article, a 15°Y-X LiNbO3/SiO2/SiC multilayered substrate was designed and fabricated to suppress spurious resonance due to Rayleigh-mode and transverse-mode responses, and one-port resonators with a clean spectrum, a high electromechanical coupling coefficient of 22.00%, and an admittance ratio (impedance ratio) over 65 dB were successfully implemented.
Abstract: The rapid development of the fifth-generation (5G) wireless system is driving strong demand for high-performance radio frequency filters. This work studies shear horizontal surface acoustic wave (SAW) devices using 15°-rotated $Y$ -cut $X$ -propagating (15°Y-X) LiNbO3/SiO2/SiC multilayered substrates. Single-crystalline 15°Y-X LiNbO3 films are bonded to SiO2/SiC handling substrates by the smart cut technology. On the basis of accurate finite-element-method simulations, LiNbO3/SiO2/SiC wafer configurations are optimized to suppress spurious resonance due to Rayleigh-mode and transverse-mode responses, and one-port resonators with a clean spectrum, a high electromechanical coupling coefficient of 22.00%, and an admittance ratio (impedance ratio) over 65 dB are successfully implemented. Based on the characteristics of the resonators, high-performance filters with a center frequency of 1.28 GHz, a large 3-dB fractional bandwidth of 16.65%, and a low minimum insertion loss of 1.02 dB are successfully designed and fabricated. Furthermore, no ripples in the passband of the filters are observed. Additionally, the filters exhibit a temperature coefficient of center frequency of −63.8 ppm/°C and a large power durability of 33.2 dBm. This work confirms the high performances of the SAW devices using the 15°Y-X LiNbO3/SiO2/SiC multilayered substrate, and this type of SAW device exhibits a prospect of commercial applications in the 5G wireless system.
50 citations
TL;DR: In this article, the authors presented a new load-modulation power amplifier (PA) architecture called asymmetrical load-modified balanced amplifier (ALMBA), which can be designed with arbitrary load modulation (LM) ratio by offsetting the symmetry of two sub-amplifiers (BA1 and BA2) in the balanced topology.
Abstract: This article presents a new load-modulation power amplifier (PA) architecture—asymmetrical load-modulated balanced amplifier (ALMBA). It is for the first time discovered that the control amplifier (CA) of LMBA can be designed with arbitrary load modulation (LM) ratio by offsetting the symmetry of two sub-amplifiers (BA1 and BA2) in the balanced topology. The rigorous analytical derivation reveals a unification of the quadrature-coupler-based LM PA theory, which inclusively covers the recently reported LMBA within this generalized framework. Through pseudo-Doherty (PD) biasing of the asymmetric BA1 & BA2 (peaking) and the CA (carrier) combined with proper amplitude and phase controls, the optimal LM behaviors of three amplifiers can be achieved independently overextended power back-off range and ultrawide RF bandwidth. Importantly, the LM of CA effectively mitigates the over-driving issue imposed on symmetrical PD-LMBA, leading to enhanced overall reliability and linearity. Based on the proposed theory, an RF-input PD-ALMBA is designed and implemented using commercial GaN transistors. The developed prototype experimentally demonstrates dual-octave bandwidth from 0.55 to 2.2 GHz, which is the widest bandwidth ever reported for load-modulation PAs. The measurement exhibits an efficiency of 49–82% for peak output power and 40–64% for 10-dB OBO within the design bandwidth. When stimulated by a 20-MHz long-term evolution (LTE) signal with 10.5-dB peak to average power ratio (PAPR), an average efficiency of 47–63% is measured over the entire bandwidth at an average output power around 33 dBm.
49 citations
TL;DR: In this paper, the progress of silicon-germanium (SiGe) bipolar-complementary metal-oxide-semiconductor (BiCMOS) technology-based integrated circuits (ICs) during the last two decades is reviewed.
Abstract: This invited paper reviews the progress of silicon–germanium (SiGe) bipolar-complementary metal–oxide–semiconductor (BiCMOS) technology-based integrated circuits (ICs) during the last two decades. Focus is set on various transceiver (TRX) realizations in the millimeter-wave range from 60 GHz and at terahertz (THz) frequencies above 300 GHz. This article discusses the development of SiGe technologies and ICs with the latter focusing on the commercially most important applications of radar and beyond 5G wireless communications. A variety of examples ranging from 77-GHz automotive radar to THz sensing as well as the beginnings of 60-GHz wireless communication up to THz chipsets for 100-Gb/s data transmission are recapitulated. This article closes with an outlook on emerging fields of research for future advancement of SiGe TRX performance.
48 citations
TL;DR: In this article, the sensitivity in reflective-mode phase-variation sensors based on an open-ended transmission line with a step-impedance discontinuity is studied, and the authors provide the design guidelines to achieve a sensor with high sensitivity compared with the one based on a uniform (uniform) line.
Abstract: This article presents an exhaustive study of the sensitivity in reflective-mode phase-variation sensors based on an open-ended transmission line with a step-impedance discontinuity. Such discontinuity delimits the sensing region (which extends up to the open end of the so-called sensing line), from the transmission line section connected to the input port (design line), which is used to enhance the sensitivity. The theoretical analysis provides the design guidelines to achieve a sensor with high sensitivity compared with the one based on an ordinary (uniform) line with a similar length. In particular, it is shown that for sensitivity optimization, the electrical length of the design line must be set to 90° (or an odd multiple), whereas either a 90° (or an odd multiple) or a 180° (or an even or odd multiple) sensing line can be alternatively used in order to maximize the sensitivity. It is shown that the impedance contrast, defined as the ratio between the characteristic impedances of the design and sensing line, is a key parameter for sensitivity enhancement, and it must be as low or as high as possible for the 90° or 180° sensing lines, respectively. For validation purposes, two prototype devices (one with a 90° and the other one with a 180° sensing line) have been designed and fabricated following the design guidelines. Such devices have been tested by loading the sensing region with several materials with different dielectric constants. Compared with the ordinary line-based sensors, it is found that the maximum sensitivity is enhanced by a factor of 19.7 and 11.4 in the phase-variation sensor based on a 90° and 180° sensing line, respectively. Finally, the sensor concept is generalized to a multisection step-impedance transmission line as a means of further increasing the sensitivity, and a prototype device exhibiting 528.7° maximum sensitivity is implemented.
47 citations
TL;DR: Multilayer perceptron (MLP) and support vector machine (SVM) are identified as the best performing algorithms for classification of material types followed by their corresponding temperature in a temperature compensation technique for microwave sensors.
Abstract: The planar nature of microwave sensors leaves them vulnerable to ambient temperature changes with potential impact on the perception of the material under test. A temperature compensation technique is required to consider its direct effect on the dielectric property of materials. In this article, machine learning algorithms are employed in two configurations of classifier and regressor on frequency response of a split-ring resonator operating at 1.19 GHz. A wide range of dielectric constant is covered with concentrations of [0:20%:100%]-methanol/acetone in water with a temperature cycle of 25 °C–50 °C. This broad variety of cases captures the complicacy of entangled trends that are recognized using classifiers regardless of the measurement temperature. In the next step, the ambient temperature is extracted from the same measured data. This is accomplished by cascading the classifier with a regressor pool that contains trained parameters for individual classes. Highly accurate classification of material types followed by their corresponding temperature (using linear regression with $R^{2}=97$ % averaged over tenfold cross validation and a mean absolute error of 0.58 °C) leads to investigating limit of detection in the proposed scheme. This step, through testing of [0:1%:5%] methanol in water, identified multilayer perceptron (MLP) and support vector machine (SVM) as the best performing algorithms. Final hyperparameter optimization yields parameters for these two models that provide accuracy of 0.97 and 0.99, respectively.
TL;DR: In this article, the inversion of S-parameter data collected in a metallic chamber is performed with a nonlinear inversion strategy in Lebesgue spaces with nonconstant exponents.
Abstract: Stroke identification by means of microwave tomography requires a very accurate reconstruction of the dielectric properties inside patient’s head. This is possible when a precise measurement system is combined with a full nonlinear inversion method. In this article, the inversion of S-parameter data collected in a metallic chamber is performed with a nonlinear inversion strategy in Lebesgue spaces with nonconstant exponents. This is the first time that this kind of nonlinear S-parameter electromagnetic formulation has been applied to this problem. The inverse-scattering method incorporates a 2-D electromagnetic model of the imaging chamber based on a finite-element formulation, which has led to a complete redefinition of the solving procedure with respect to previous works. This allows a suitable description of the multistatic S-parameters due to the interactions between the incident radiation and the structure under test. The developed inversion procedure is first assessed by means of numerical simulations. The experimental results, obtained with a clinical microwave system prototype containing a liquid-filled 3-D SAM phantom with an inhomogeneity mimicking a hemorrhagic stroke, further prove the effectiveness of the proposed approach.
TL;DR: The proposed WPTS is composed of a self-diplexing implantable antenna, efficient rectifier, and WPT transmitter and proves that the proposed scheme is suitable for biotelemetry and wireless powering of biomedical implants.
Abstract: This article proposes an efficient and complete wireless power transfer (WPT) system (WPTS) for multipurpose biomedical implants The WPTS is composed of a self-diplexing implantable antenna, efficient rectifier, and WPT transmitter (WPT Tx) The proposed system is capable of simultaneously transmitting recorded data and recharging the batteries of the devices (so as to elongate the implant life) The WPT Tx occupies dimensions of $50 \times 50 \times 16$ mm3 and is optimized to effectively transfer power at 1470 MHz to a 55-mm deep implantable device An efficient and compact ( $34 \times 67$ mm2) rectifier is used at 1470 MHz to convert the harvested RF power into a useful direct current (dc) power The proposed rectifier circuit exhibits a high conversion efficiency of 50% even at an input power of −14 dBm and maximum efficiency of 761% at 2 dBm The proposed self-diplexing implantable antenna occupies small dimensions (94 mm3) and operates at 915 and 1470 MHz by exciting ports 1 and 2, respectively The biotelemetry operation is performed using a 915 MHz band (port 1), and the rectifier circuit is connected to port 2 (1470 MHz) to perform wireless powering The simulated results are validated by examining the individual elements (WPT Tx, rectifier, and self-diplexing antenna) and overall WPTS in a saline solution and minced pork The results prove that the proposed scheme is suitable for biotelemetry and wireless powering of biomedical implants
TL;DR: In this article, the authors proposed an optically transparent reflection-type metasurface based on indium tin oxide (ITO) material for simultaneously achieving high transmission of visible light and near-field focusing of microwave, demonstrating its potential for wireless power transfer (WPT) and harvesting applications.
Abstract: We propose a novel optically transparent reflection-type metasurface based on indium tin oxide (ITO) material for simultaneously achieving high transmission of visible light and near-field focusing (NNF) of microwave, demonstrating its potential for wireless power transfer (WPT) and harvesting applications. By achieving high impedance of the metasurface, this work overcomes the main challenge in designing metasurface with lossy metal materials, i.e., optimizing the tradeoff between phase shift characteristics and efficiency loss. We propose a new element with two degrees of freedom to ensure that the phase shift range can reach 350° while keeping $\vert S_{11}\vert $ less than −2.5 dB. In addition, we adopt the grid ground (GND) instead of the complete GND plane to further improve the light transmittance. Based on the above considerations, we design two types of metasurfaces for deployments in ambient wireless energy harvesting (plane-wave feeding) and WPT (horn feeding), respectively. Its NNF transfer efficiency can reach more than 60% of the metasurface based on good conductor materials. The relative bandwidth with 50% transfer efficiency can reach 34.5% (4.9–6.9 GHz). We fabricate an ITO-based prototype of the metasurface with the dimension of $342 \times 342 \times 4.4$ mm3 ( $6.6 \times 6.6 \times 0.08\lambda _{0}^{3}$ ) with the sheet impedance of $1~\Omega $ /sq and a light transmittance of 60%. We also perform near-field scanning measurements to verify that the focusing position is accurate. Finally, through WPT and harvesting tests, we achieve a WPT and receiving efficiency (from power source to receiving antenna) of 12.6% and a rectification efficiency of 55%, confirming the practicability and effectiveness of the proposed work.
TL;DR: In this article, a 220-GHz four-channel, non-contiguous, and manifold-coupled waveguide multiplexer for future terahertz (THz) multichannel communication application is presented.
Abstract: This article presents a 220-GHz four-channel, noncontiguous, and manifold-coupled waveguide multiplexer for future terahertz (THz) multichannel communication application. The multiplexer is composed of four Chebyshev bandpass filters based on metal waveguide technology. Through a unique design in which the tuning dimensional variables are reduced to 14 and a co-design of low-order electromagnetic (EM) distributed models and full-wave EM models, the design optimization is achieved with a good computational efficiency and design accuracy. The proposed multiplexer is fabricated by high-precision computer numerical control (CNC) milling technology, in which the fabrication errors are evaluated to be within ±3 μm. The measured results exhibit 1.7 dB of in-band insertion loss and better than 15 dB of average common-port return loss for each of the channel filter. The measured results are all in good agreement with the simulated ones, thereby validating the complete design procedure.
TL;DR: An overview of distributed phased arrays, the principal challenges involved in their coordination, and recent research progress addressing these challenges are presented.
Abstract: There has been significant research devoted to the development of distributed microwave wireless systems in recent years. The progression from large, single-platform wireless systems to collections of smaller, coordinated systems on separate platforms enables significant benefits for radar, remote sensing, communications, and other applications. The ultimate level of coordination between platforms is at the wavelength level, where separate platforms operate as a coherent distributed system. Wireless coherent distributed systems operate in essence as distributed phased arrays, and the signal gains that can be achieved scale proportionally to the number of transmitters squared multiplied by the number of receivers, providing potentially dramatic increases in wireless system capabilities enabled by increasing the number of nodes in the array. Coordinating the operations of nodes in a distributed array requires accurate control of the relative electrical states of the nodes. The basic challenge is the synchronization and stability of the relative phases of the signals transmitted or received. Generally, such control requires wireless frequency synchronization, phase calibration, and time alignment. For radar operations, phase control also requires high-accuracy knowledge of the relative positions of the nodes in the array to support beamforming. Various technologies have been developed in recent years to address the coordination challenges for closed-loop applications, such as distributed communications, and more recently, there has been growing interest in new technologies for open-loop applications, such as radar and remote sensing. This article presents an overview of distributed phased arrays, the principal challenges involved in their coordination, and recent research progress addressing these challenges.
TL;DR: The lightweight, low-cost PCB with all silicon chips and a thickness of 3.4 mm presents a viable candidate for Ku-band SATCOM ground and Satcom-On-The-Move (SOTM) terminals.
Abstract: This article presents a 1024-element dual-polarized Ku-band (10.7–12.7 GHz) satellite communication (SATCOM) receive (RX) phased array. The array consists of four 16 $\times16$ subarray tiles, each of which comprises 64 eight-channel beamformer chips, 256 dual-channel low-noise amplifiers (LNAs), and 256 dual-polarized antennas built on an affordable printed circuit board (PCB). The antennas spaced at $\lambda $ /2 spacing at 12.2 GHz in an equilateral triangular grid allow scanning up to x±70° in all planes while maintaining a cross-polarization level $ dB. The use of LNAs just after the antennas enables a low-noise operation with an antenna gain-to-noise temperature (G/T) of 10.5 dB/K ( $T_{\mathrm {ant}} =20$ K) at broadside while maintaining a directivity of 34 dB at 11.7 GHz. Also, a two-pole/two-zero filter is placed between the LNA and the beamformer chip to greatly attenuate any transmit leakage signal at 14–14.5 GHz. The lightweight, low-cost PCB with all silicon chips and a thickness of 3.4 mm presents a viable candidate for Ku-band SATCOM ground and Satcom-On-The-Move (SOTM) terminals.
TL;DR: In this article, a machine learning-based framework for automated and computationally efficient design of metasurfaces realizing broadband RCS reduction is introduced, which is a three-stage procedure that involves global surrogate assisted optimization of the unit cells, followed by their local refinement.
Abstract: Popularity of metasurfaces has been continuously growing due to their attractive properties including the ability to effectively manipulate electromagnetic (EM) waves. Metasurfaces comprise optimized geometries of unit cells arranged as a periodic lattice to obtain a desired EM response. One of their emerging application areas is the stealth technology, in particular, realization of radar cross section (RCS) reduction. Despite potential benefits, a practical obstacle hindering widespread metasurface utilization is the lack of systematic design procedures. Conventional approaches are largely intuition-inspired and demand heavy designer’s interaction while exploring the parameter space and pursuing optimum unit cell geometries. Not surprisingly, these are unable to identify truly optimum solutions. In this article, we introduce a novel machine-learning-based framework for automated and computationally efficient design of metasurfaces realizing broadband RCS reduction. Our methodology is a three-stage procedure that involves global surrogate-assisted optimization of the unit cells, followed by their local refinement. The last stage is direct EM-driven maximization of the RCS reduction bandwidth, facilitated by appropriate formulation of the objective function involving regularization terms. The appealing feature of the proposed framework is that it optimizes the RCS reduction bandwidth directly at the level of the entire metasurface as opposed to merely optimizing unit cell geometries. Computational feasibility of the optimization process, especially its last stage, is ensured by high-quality initial designs rendered during the first two stages. To corroborate the utility of our procedure, it has been applied to several metasurface designs reported in the literature, leading to the RCS reduction bandwidth improvement by 15%–25% when compared with the original designs. Furthermore, it was used to design a novel metasurface featuring over 100% of relative bandwidth. Although the procedure has been used in the context of RCS design, it can be generalized to handle metasurface development for other application areas.
TL;DR: This article presents a dual-polarized phased-array receiver with simultaneous dual-beam reception capability for make-before-break connections and for multi-satellite reception systems, such as simultaneous television (TV) reception and connectivity.
Abstract: This article presents a $16\times 16$ dual-polarized $Ku$ -band (10.7–12.7 GHz) satellite communications (SATCOM) phased-array receiver with simultaneous dual-beam reception capability. The array incorporates 64 16-channel beamformer chips and 256 dual-polarized antennas. A dual-channel low noise amplifier (LNA) is employed on every antenna to lower the system noise figure (NF) and increase the antenna gain-to-noise temperature (G/T). The phased-array is built on a low-cost printed circuit board (PCB), with an antenna spacing of $\lambda $ /2 at 12.2 GHz in an equilateral triangular grid to result in ±70° scan volume, and is capable of receiving two concurrent data-streams with a distinct direction of arrival (DOA) since it employs two 64:1 Wilkinson combiner networks. A transmit band (14–14.5 GHz) filter is also implemented between the LNA and the beamformer chip. The 256-element array has a directivity of 28 dB at mid-band with a G/T of 5 dB/K ( $T_{\mathrm{ ant}}=20$ K), which results in a G/T of 11 dB/K for a 1024-element array. This array is a feasible solution for make-before-break connections and for multi-satellite reception systems, such as simultaneous television (TV) reception and connectivity.
TL;DR: In this article, the authors present a 1024-element planar phased-array system with high EIRP for Ku-band satellite communication (SATCOM) mobile transmitter terminals.
Abstract: This article presents a 1024-element Ku-band phased-array transmitter for mobile satellite communications. The array is based on eight-channel transmit (TX) SiGe beamformer chips. Dual-polarized stacked-patch antennas enable the array to synthesize linear, rotated-linear, and left- and right-hand circular polarization. The array consists of four quadrants of 256-element subarrays, each of which has 64 beamformer chips and a driver chip assembled on a printed circuit board (PCB). The array achieves an effective isotropic radiated power (EIRP) of 75 dBm per polarization (78-dBm circular polarization) and scans to ±75° in all planes. This is achieved using an antenna spacing of $\lambda $ /2 at 14.4 GHz in an equilateral triangular grid. The array also results in 30-dB cross-polarization rejection up to 60° scan angles. Measured error vector magnitude (EVM) for 50-, 100-, 200-, and 500-MBd QPSK and 8 phase-shift keying (8PSK) waveforms results in at most 1.5%rms and 2.5%rms at $P_{1\textrm {dB}}$ and $P_{\mathrm{ sat}}$ , respectively, at 14 GHz over all scan angles. Also, the adjacent channel power ratio (ACPR) was measured as −32 dB for 200- and 500-MBd QPSK and 8 phase-shift keying (8PSK) waveforms at $P_{1\textrm {dB}}$ at 14 GHz. To the authors’ knowledge, this work presents a state-of-the-art planar phased-array system with high EIRP for Ku-band satellite communication (SATCOM) mobile transmitter terminals.
TL;DR: The experimental results demonstrate that the proposed MIMO 2-D imaging radar system can locate chest areas of multiple targets, suppress the clutters, and make vital signs measurement, heartbeat measurement in particular, more robust compared with single-input–multiple-output (SIMO) radar system in complex environment.
Abstract: Simultaneous multitarget vital signs measurement has become a hot issue for noncontact vital signs perception. However, there is still challenge in the multitarget heartbeat measurement due to the weakness of heartbeat signal and interference from complex environment. In this article, a new multiple-input–multiple-output (MIMO) continuous-wave (CW) radar system equipped with 2-D digital beamforming (DBF) is presented to measure the respiration and heartbeat of multiple human subjects at unknown positions simultaneously. Through 2-D beam scanning of the whole scene, a 2-D radar image is generated. From the image, the chest motion of multiple targets is accurately located. Then, the vital signs of targets are obtained through forming individual beams focusing on the chests of targets. Moreover, the low intermediate frequency (low-IF) architecture is adopted to minimize the impact of flicker noise in low-frequency amplifier stages. The experimental results demonstrate that the proposed MIMO 2-D imaging radar system can locate chest areas of multiple targets, suppress the clutters, and make vital signs measurement, heartbeat measurement in particular, more robust compared with single-input–multiple-output (SIMO) radar system in complex environment.
TL;DR: In this article, a monolithically integrated reflective-type phase shifter (RTPS) utilizing silicon-on-insulator (SOI) radio frequency (RF) microelectromechanical systems (MEMS) is presented.
Abstract: This article presents a monolithically integrated reflective-type phase shifter (RTPS) utilizing silicon-on-insulator (SOI) radio frequency (RF) microelectromechanical systems (MEMS). The analog phase shifter employs a hybrid coupler and two identical reflective loads optimized to achieve a large phase shift range. The hybrid coupler is designed using two CPW-based couplers connected in a folded tandem configuration to achieve a compact size design. Various reflective load topologies are studied for optimum phase shift range and phase linearity over the bandwidth of interest. Measurement results demonstrate a continuous 120° tunable range from 26 to 30 GHz. The mmWave phase shifter exhibits a low insertion loss of 5.35 dB ± 0.6 dB at 28 GHz. The fabricated phase shifter has an overall device footprint of 4.0 $\text {mm}\times 2.6$ mm. All the components of the phase shifter module are co-fabricated in the 20 $\mu \text{m}$ device layer of a SOI wafer, which provides the flexibility of monolithic integration with other RF modules in phased array antenna systems. Contactless thermally actuated MEMS varactors are used in the reflective loads which do not suffer from the conventional contact-based reliability issues.
TL;DR: In this article, the authors presented a Ku-band phased-array receive tile with 256 elements, which is based on 64 dual-polarized beamformer chips assembled on a printed circuit board (PCB).
Abstract: This article presents a Ku-band phased-array receive tile with 256 elements. The design is based on 64 dual-polarized beamformer chips assembled on a printed circuit board (PCB) with dual-polarized antennas and an integrated Wilkinson combiner network and can operate at any polarization (linear, rotated-linear, and circular). The 256 elements are spaced $0.52\lambda $ apart at 12.7 GHz in the $x$ - and $y$ -directions. The measured patterns show near ideal patterns with a wide beam scanning range of ±70° (V- and H-pol) and a high cross-polarization rejection of 27 dB. The array has a 3-dB instantaneous scanning bandwidth of 10.6–12.5 GHz. In circular polarization mode, the measured axial ratio (AR) is 0.5 dB at 11.75 GHz for both left- and right-hand circular polarizations. The tile design is scalable to allow large-scale phased-array construction with 1024 elements or higher. Extensive measurements are presented, showing the versatility of this approach. Also, the dual-polarization feeds can be optimized to result in very low cross-polarization for circular and slanted-linear polarizations at all scan angles. The array performance, compact size, ultralightweight of 258 g, and low profile with 3.5-mm thickness make it suitable for affordable mobile Ku-band SATCOM on the move (SOTM) terminals.
TL;DR: In this article, a dual-probe filtering antenna with a cascaded triplet (CT) filter and a cascade quadruplet (CQ) filter was designed for verification.
Abstract: In this article, we present a design method of high-selectivity filtering antennas based on a dual-probe feeding structure. The first stage of the filtering circuit consists of two or three coupled resonators which are then coupled to the radiating patch acting as the last resonator of the filter. Cross-coupling is used to obtain transmission zero, and thus the selectivity of the filtering antennas is improved. A cascaded triplet (CT) filtering patch antenna, which produces a radiation zero at the high-frequency edge of the passband, and a cascaded quadruplet (CQ) filtering patch antenna, which produces radiation zeros at both edges of the passband, are designed for verification. The process of designing the filtering patch antenna is given in detail. The designed CT filtering patch antenna has a bandwidth of 1.029–1.17 GHz and a radiation zero at 1.19 GHz. The designed CQ filtering patch antenna has a bandwidth of 1.029–1.17 GHz and two radiation zeros at 1.012 and 1.19 GHz, respectively. The peak gain of the CT filtering patch antenna is 9.35 dBi and that of the CQ filtering patch antenna is 9.16 dBi. A dual-polarized CQ filtering patch antenna is fabricated, showing a good performance in measurement.
TL;DR: In this article, the implementation of 80 and 160 GHz four-channel radar sensors employing the modular scalable platform based on a single relaxed 40-GHz local oscillator and cascadable transceiver chips is demonstrated.
Abstract: This article demonstrates the implementation of 80- and 160-GHz four-channel radar sensors employing the modular scalable platform based on a single relaxed 40-GHz local oscillator and cascadable transceiver chips. The first two channels synthesize $2 \times 2$ multiple-input–multiple-output (MIMO) radar at 80 GHz with onboard $8 \times 1$ patch arrays for enhanced angular resolution, whereas the other two channels employ 160-GHz system-on-chip transceivers with integrated wideband 6-dBi micromachined on-chip antennas for enhanced range resolution. Configurable modulators in each transceiver offer ranging, direction-of-arrival (DoA) estimation, velocity/vibrations measurement, and data communication applications. Frequency-modulated continuous wave (FMCW) is demonstrated with 4-/8-GHz sweep bandwidth at 80/160 GHz corresponding to 3.75-/1.875-cm range resolution. Chirp-sequence FMCW is employed to measure the heartbeat rate of a human, and 78 bpm is measured with 0.06-Hz Doppler resolution. Mechanical vibration rate from a loudspeaker is measured using the CW radar technique, whereas phase-modulated continuous wave is employed for distant selective vibrations measurement. Time-division multiplexing MIMO radar is configured at 80 GHz in a multitarget scenario for DoA estimation, and the targets are distinguished with 25° effective angular resolution. Frequency-division multiplexing MIMO radar technique is demonstrated based on $\Delta \Sigma $ -modulation and binary phase shift keying (BPSK) modulators. Furthermore, the 10-Mb/s BPSK data communication link is evaluated at 80 GHz with a 20-dB signal-to-noise ratio at 1 m. The 160-GHz vector modulators offer additional modulations.
TL;DR: In this article, an approach to design RF all-port-reflectionless quasi-elliptic-type single/dual-band bandpass filters (BPFs) and diplexers with frequency-adaptive constant-absolute-bandwidth (ABW) response is reported.
Abstract: An approach to design RF all-port-reflectionless quasi-elliptic-type single-/dual-band bandpass filters (BPFs) and diplexers with frequency-adaptive constant-absolute-bandwidth (ABW) response is reported. The tunable reflectionless BPF case is first addressed, where a balanced-circuit scheme composed of two identical wideband 3-dB quadrature couplers and two equal reflective-type BPF units with synchronous center-frequency agility is exploited. The input signal is split into the two BPF units with equal amplitude and 90° phase shift by the first coupler and then recombined at the output node of the second coupler after being processed by the balanced-circuit branches. In this manner, the signals reflected at the stopband regions of the BPF units are mutually canceled at the coupler input port and absorbed at the isolated port by its loading resistor. This allows a symmetrical low-reflection behavior to be attained in the overall circuit, whose filtering transfer function is the one determined by the BPF units. Furthermore, by using dual-band BPFs in the balanced-circuit branches, this concept is readily extended to frequency-tunable constant-ABW dual-band BPFs whose passbands can be separately switched OFF (i.e., absorptive switched-OFF states) as an added reconfiguration capability. For practical-demonstration purposes, starting from theoretical design guidelines followed by an optimization step, the third- and second-order microstrip prototypes of reflectionless frequency-controllable single- and dual-band BPFs with predefined constant ABW, respectively, are developed and tested. Afterward, inspired by the devised tunable absorptive BPF structure, an all-port-reflectionless diplexer with frequency-adjustable constant-ABW channels is shown. This controllable multiport-absorptive filtering device is also verified with the fabrication and testing of a microstrip prototype. All the constructed circuits employ varactor diodes for electronic tuning, showing close agreement between simulation and measurements.
TL;DR: A Ka-band CMOS cascode power amplifier (PA) linearized with a cold-FET-based interstage matching network is presented, which is designed in a 65-nm CMOS process and improves the linearity and the input and output impedance matchings.
Abstract: A Ka-band CMOS cascode power amplifier (PA) linearized with a cold-FET-based interstage matching network is presented, which is designed in a 65-nm CMOS process. Since it is difficult to make a cascode PA matched to the optimum output and input impedances at high frequencies, a matching network has to be introduced at the node between the common-source (CS) and common-gate (CG) stages. The cold-FET-based matching network improves the linearity and the input and output impedance matchings, which is analyzed and optimized with its simple model. It makes the PA have gain expansion and phase lag with the power, which allows the PA to have less amplitude-to-amplitude (AM–AM) and amplitude-to-phase (AM–PM) distortions. In addition, it improves the return losses of the PA by making the impedances for power matching and conjugate matching located closely. The implemented PA achieves the peak power-added efficiency (PAE) of 38.2% and the saturated output power ( $P_{\mathrm {sat}}$ ) of 17.1 dBm at 31 GHz while occupying the chip area of 0.16 mm2. It is also shown that the OP1 dB is improved by 1.7 dB, and the AM–PM distortion is reduced to only 1.1° due to the linearization technique. It is tested with 64-quadrature amplitude modulation (QAM) signals, which has a 400-MHz channel bandwidth (BW) and a 9.7-dB peak-to-average power ratio (PAPR). It achieves average output powers of 9.6/7.7 dBm with error vector magnitudes (EVMs) of −25/−30 dB for 64-QAM OFDM signals, efficiencies of 17.7%/12%, and the adjacent channel leakage ratio (ACLR) of −28.2/−32.8 dBc, respectively.
TL;DR: In this paper, the authors proposed a novel technique to remove the radar self-motion effects (RSMs) for an accurate detection of human vital signs, which does not require any additional sensor and instead extracts the RSM from the signals reflected by stationary clutters.
Abstract: This article presents a novel technique to remove the radar self-motion effects (RSMs) for an accurate detection of human vital signs. As opposed to the commonly used techniques, the proposed approach does not require any additional sensor, and instead, it extracts the RSM from the signals reflected by stationary clutters. Since the proposed technique requires to accurately identify the clutter range, two procedures for its automatic identification are proposed, aimed to detect both small and large radar motions. Besides allowing precise and reliable vital sign detection, it provides a compact, lightweight, comfortable, and cost-effective solution since potentially intrusive additional sensors are not required. Simulations have been carried out for validating the proposed approach, with an insight on the influence of different clutter radar cross sections on the sensitivity. Moreover, the effectiveness of the RSM cancellation has been experimentally demonstrated, showing its suitability for different applications, e.g., radar on moving platforms, vibrating tools, handheld devices, unmanned aerial vehicles, and cars.
TL;DR: In this article, a 5.8 GHz band highly efficient 1-W rectenna was proposed, which consists of a bridge diode, directly connected to a short-stub-connected high-impedance dipole antenna.
Abstract: This article describes a 5.8-GHz band highly efficient 1-W rectenna that consists of a bridge diode, directly connected to a short-stub-connected high-impedance dipole antenna, with a designed antenna resistance of $580~\Omega $ . The proposed antenna topology realizes circuit functionalities of impedance transform, impedance matching, harmonic reaction, and dc blocking while maintaining a high antenna radiation efficiency. Lossy circuit components between the antenna radiator and the bridge diode can be eliminated for a highly efficient rectification. In experimental investigations, the measured rectification efficiency of the 5.8-GHz band rectifier is 92.8% at an input power of 1 W, and the estimated antenna radiation efficiency from the measured antenna gain is 96.9%, including loss due to circuit functionalities and interconnection. With lesser additional losses, the proposed antenna can be integrated with circuit functionalities to achieve a highly efficient rectenna. The measured rectification efficiency is almost the same as the fundamental limitation restricted by the rectifier diodes’ performance.
TL;DR: Wang et al. as discussed by the authors proposed an end-to-end sequence-based network that consists of a shallow convolutional neural network, a bidirectional long short-term memory (Bi-LSTM) network strengthening with a self-attention mechanism, and a dense neural network is constructed to recognize eight kinds of intrapulse modulations of radar signals.
Abstract: As the electromagnetic environment in battlefields is more and more complex, automatic modulation recognition for radar signals is becoming vital and challenging. Traditional methods are more likely to cause lower recognition accuracy with higher computational complexity in low signal-to-noise ratio (SNR). Feature redundancy especially for handcrafted features is one of the shortcomings of deep-learning-based methods. In this article, a novel end-to-end sequence-based network that consists of a shallow convolutional neural network, a bidirectional long short-term memory (Bi-LSTM) network strengthening with a self-attention mechanism, and a dense neural network is constructed to recognize eight kinds of intrapulse modulations of radar signals. The autocorrelation functions of received radar signals are first calculated as autocorrelation features. Then, these features are employed as inputs of the proposed network which owns significant sequence processing advantages and adaptive selection ability of features. Finally, the proposed network outputs prediction modulations directly. The simulation results verify the robustness and effectiveness of autocorrelation features. And the proposed network achieves about 61.25% accuracy at −20 dB and more than 95% accuracy at −10 dB. Compared with four state-of-the-art networks, the proposed network has better recognition performance especially at low SNRs with much lower computational complexity. Results on measured signals also demonstrate that the proposed network outperforms these four networks.