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To accommodate the ongoing user’s data explosion, many approaches like polarization multiplexing are proposed to increase the uplink communication capacity with limited bandwidth in user equipment (UE). This article proposes a novel dual-linearly polarized digital predistortion (DLP-DPD) scheme for DLP millimeter-wave (mmWave) phased array UE. Different from conventional single-polarized arrays, the DPD here not only aims to deal with the nonlinear distortion caused by power amplifiers (PAs) but also the cross-polarization interference which is a specific distortion in DLP phased array system. Theoretical analysis and system modeling of DLP phased array is presented, and a DLP-DPD model is proposed according to the derivation. Furthermore, in order to reduce the complexity of the DPD module, the proposed DLP-DPD scheme only needs to update a small part of coefficients when the user moves within a beam coverage. To validate the proposed DLP-DPD scheme, experiments were carried out on a 1 $\times $ 4 DLP mmWave phased array at 26.5 GHz. The experimental results show that DLP-DPD scheme can achieve good performance in DLP phased array dynamic scenario, dealing with the nonlinearity and cross-polarization interference well. [ABSTRACT FROM AUTHOR]

This article presents a novel built-in test equipment (BITE) for phase measurements in millimeter-wave integrated circuits (ICs). The BITE targets 5G New Radio (NR) applications. It is able to measure the phase in good agreement with $\mathbf {S_{21}}$ measurements and has a relative rms phase error lower than 6° over the frequency band of interest. Aside from the relative phase, this BITE also addresses the absolute phase difference of all ICs on the same phased array. To the authors’ best knowledge, this is the first BITE and built-in self-test (BIST) to do so. The BITE is able to reduce the absolute phase discrepancy by a factor of 3. To reduce the measurement complexity, the BITE is implemented as a homodyne architecture to output a dc voltage relative to the phase of the channel. A built-in algorithm is used, mitigating the impairments normally associated with a homodyne receiver. This reduces the design complexity and hence the area overhead. The BITE occupies an area of 480 $\mathbf {\mu m} \times 135\,\,\mathbf {\mu m}$ , facilitating easy integration. [ABSTRACT FROM AUTHOR]

We experimentally demonstrate the transmission of multiorder quadrature amplitude modulation (QAM) millimeter wave (MMW) orthogonal frequency division (OFDM) signal at 28 GHz radio frequency (RF). To overcome these unfavorable channel properties such as high path loss, propagation loss, rain fading, etc., 5G MMW phased array antenna has been used. Meanwhile, probabilistic shaping (PS) technology is applied to extend transmission distance, and Volterra nonlinearity compensation (VNC) technology is used to alleviate the system nonlinearity. Using 5G MMW phased array antennas and technologies of PS and VNC, 6.72 Gbit/s 1024-QAM OFDM signal at 28 GHz can be transmitted over 55-m wireless distance in our experiment, satisfying the normalized general mutual information (NGMI) threshold of 0.83 with 25% soft-decision forward-error-correction (SD-FEC) overhead. To the best of our knowledge, this is the first time to demonstrate the transmission of multiorder QAM OFDM signal at 28 GHz RF using 5G MMW phased array antenna. [ABSTRACT FROM AUTHOR]

In this research study, a novel hybrid approach to beam steering based on the combination of true time delay and phase shift to enable continuous beam steering with minimal beam squint in wideband mm-wave transceivers is investigated. With modern high-speed communication links in the mm-wave spectrum requiring ever higher bandwidths, and losses increasing with frequency, there is a need for steerable arrays in mobile applications. This steering capability is commonly realized by phase shifters, which enable continuous beam direction control, but produce significant beam squint at large bandwidths or steering directions. An alternative is to use a time-delayed control, which resolves the squint issue but covers only a limited number of beam directions, producing considerable loss and being large in size. This research work presents the first 2-bit time delay stage operating above 200 GHz. In addition, a novel approach is described to enable broadband continuous beam control with minimal beam squint; this is achieved by combining the time delay circuit with a 90° vector-sum phase shifter. To prove the concept, the circuit is realized in a 130-nm SiGe Bipolar Complementary Metal Oxide Semiconductor (CMOS) (BiCMOS) technology. At 4.33 mW of dc power consumption, the small-signal gain is −8.6 dB at a 3-dB band of 220–250 GHz, resulting in 12.8% of relative bandwidth. The time delay stage provides coarse beam direction control with a maximum steering angle of 43.9° resulting from a maximum delay of 1.47 ps with a resolution of 0.39 ps. Across all tuning states, the root-mean-square delay error is less than 23.7 fs. The following phase shifter enables fine direction control while also compensating ±1.5 dB of gain variation resulting from the time delay. This is achieved while reducing the area consumption to half of what is required for comparable true time delay circuits. In a minimal $2\times 1$ antenna array, this enables continuous beam direction control between ±54.6° while limiting the beam squint to less than 2.5°, equating to a more than 75% reduction in comparison to the common phase shift approach. [ABSTRACT FROM AUTHOR]

The nonlinearity of the fifth-generation (5G) millimeter-wave (mmWave) phased array transmitter (TX) depends on the variations in the beamforming coefficients, e.g., due to unwanted amplitude errors of the phase shifters or purposely introduced amplitude variations to shape the beam, as well as other analog component variations. Therefore, also the digital predistortion (DPD) coefficients depend on the beamforming coefficients and require a continuous update for different beamsteering directions in a conventional DPD. We propose a robust DPD approach that uses the average array response for DPD training. The average array response is estimated using the known experimental histogram of power amplifier (PA) input power variation resulting from the amplitude variations due to beamforming. The DPD training based on the average array response makes the DPD coefficients insensitive to beamforming variations. The proposed DPD strategy requires a shared feedback path for training and only a single set of DPD coefficients to linearize the array response in all beamsteering directions. The performance of the proposed DPD strategy is validated by over-the-air (OTA) measurements of a 28-GHz phased array TX over different steering angles. Experimental results show that the proposed DPD method using one set of DPD coefficients provides similar linearization performance across the steering angles compared with the DPD trained to all steering angles through the OTA reference antenna. [ABSTRACT FROM AUTHOR]

In this article, a novel passive vector-sum amplitude-variable phase shifter with integrated reconfigurable filtering function is proposed for the first time. It is constructed using conventional trisection filtering topology, with all the couplings between adjacent resonators being implemented with controllable mixed electric–magnetic couplings. This not only achieves a reconfigurable filtering response but also forms an intrinsic $I/Q$ signal generator inside the filter, which can be directly utilized to achieve continuous phase control based on the vector-sum mechanism. In such a manner, an integrated filtering phase shifter (FPS) without the need for an extra $I/Q$ generation network and individual filtering device is obtained. By properly choosing the coupling types and coupling strengths between adjacent resonators, a continuous phase control from 0° to 360°, covering the full four quadrants, is successfully realized. Closed-form equations associating the circuit parameters and insertion phase at center frequency are deduced, providing a quantitative theoretical guideline for determining the parameters of the FPS. Subsequently, a novel tuning mechanism for independent $Q$ -factor and resonant frequency control of the resonator is proposed and applied in the circuit to further exploit the amplitude control ability of the phase shifter. Measured results show that the proposed amplitude-variable FPS is capable of achieving a continuous phase control range of 360° and an amplitude control range of 10 dB within a center frequency tuning range of 0.75–0.95 GHz. The measured root-mean-square (rms) amplitude error and the rms phase error are less than 2.58 dB and 8.45°, respectively. [ABSTRACT FROM AUTHOR]

In this article, a dual-mode phase-conjugating/active Van Atta array using an integrated switchless phase-conjugating mixer/reflection amplifier is presented. The proposed array consists of $N$ dual-band mixer/reflection amplifiers (DMRAs), $N$ dual-mode hybrids, and $2N$ dual-band patch antennas. The novel integrated mixer/reflection amplifier comprises a single low-noise GaAs heterojunction field-effect transistor (HJ-FET) transistor with suitable input and output matching networks and identical power supply configuration at both modes. Switchless feature, not requiring external mixers, and improved backscatter communication are the main advantages of this component for the dual-mode retrodirective array design. Furthermore, to verify the proposed mixer/reflection amplifier, a DMRA is designed and fabricated at 3.55 and 5.8 GHz resulting in an acceptable performance in both modes. Meanwhile, the phase-conjugating/active Van Atta array microstrip prototype is fabricated. It is experimentally verified using the monostatic and bistatic radiation characteristics, which clearly shows the capability of the proposed architecture as a multimode retrodirective array. [ABSTRACT FROM AUTHOR]

Orbital angular momentum (OAM) carrying vortex beams has been studied and realized using different methods. However, the designed devices are usually capable of generating fixed OAM modes. Here, the concept of a modular radiating system based on tightly cascaded transmitarrays (TAs) provi- ding a compact and user-accessible modular radiating system suitable for affordable detecting and imaging systems is presented. The TA is based on a novel compact unit cell. The unit cell characteristics are explained and then cascaded for the TAs’ operation. Several prototype TA modules are realized, and their interactions for OAM mode interconversion are investigated. A restricted method for determining the OAM mode purity of the generated beams is employed. The simulated and experimental results are consistent with the theory, verifying the employed strategy. [ABSTRACT FROM AUTHOR]

An efficient, broadband SiGe HBT cascode nonuniform distributed power amplifier (NDPA) is presented for low-cost, fully integrated Si-based phased arrays. Optimum load impedances at each SiGe HBT cascode in a four-stage NDPA core are obtained by scaling the characteristic impedance ($Z_{0}$) of the collector transmission lines (TLs) and tapering the SiGe HBT emitter area simultaneously. A novel compact, lumped-element two-section $\lambda $ /4 output impedance transformer (OIT) is proposed to lower the NDPA load impedance ($Z_{L}$) from 50 to 25 $\Omega $ over more than one decade bandwidth (BW). Each $\lambda $ /4 impedance transformer is realized by four cascaded CLC $\pi $ -networks integrated into a single three-turn symmetric inductor in order to achieve compact size, high passive efficiency, and high LC cutoff frequency ($f_{c}$). The systematic design approach of a lumped-element $\lambda $ /4 impedance transformer with an arbitrary $Z_{0}$ is described in detail. The prototype NDPA was fabricated in 0.13- $\mu \text{m}$ SiGe HBT BiCMOS technology. The proposed SiGe HBT cascode NDPA supports both high linearity (HL) and high gain (HG) modes, each suited to a specific application. The NDPA attains a peak power gain of 10.3/12.5 dB, a saturated output power ($P_{\mathrm {out}}$) of 21.3/21.5 dBm, and a power added efficiency (PAE) of 12.2%/12.5%–21.6%/22.0% for HL/HG modes, with a 3-dB BW from 1.5 to 24.0 GHz. The NDPA delivers 13.0-dBm average $P_{\mathrm {out}}$ with a PAE of 10.0% at 6-Gbit/s data rate 64 QAM modulation. [ABSTRACT FROM AUTHOR]

Directional modulation (DM) is an attractive technique for securing wireless communication at the physical layer. DM systems usually require additional phase shifters or radio frequency vector modulators for beamforming. It thus inevitably introduces losses to the system. Due to the “time” degree of freedom, time-modulated array (TMA) has exhibited its unique features in DM system developments. Traditionally, periodic time sequence is always adopted in TMAs, which does not provide sufficient randomness for DM systems. In this work, a novel pseudorandom ascending phase (PS-AP) time sequence is proposed to enhance DM capability. The proposed PS-AP time sequence ensures maximum signal radiation power in desired directions and increases channel randomness in other undesired directions. Thus, the resultant DM system transmits nondistorted signals in desired directions, while it simultaneously distorts the signal constellation points by introducing randomly demodulated waveforms and minimizing radiation power along other undesired directions. Experimental results are presented along with theoretical and numerical analysis to validate the effectiveness of the PS-AP time sequence in TMA for DM systems. [ABSTRACT FROM AUTHOR]

A collocated phased-subarray multiple-input and multiple-output (MIMO) radar system that reduces the number of MIMO channels to implement a large antenna array is proposed. Both the transmitter (TX) and receiver (RX) arrays are divided into phased subarrays, which consist of several RF beamforming antenna elements. Each phased subarray is exploited as an MIMO channel. To estimate the angular information of targets, a hybrid beamforming technique that incorporates RF beamforming of the phased subarrays and digital beamforming of the MIMO virtual array is used. Antenna configurations of the phased-subarray MIMO radar and the corresponding virtual array are also presented. A space between the TX phased subarrays larger than one TX subarray aperture is introduced to facilitate the larger antenna aperture. Because this involves unwanted overall grating lobes, a grating lobe cancellation method is proposed using sum and difference RF subarray beams. This provides a higher angular resolution with the same number of antenna elements. The proposed phased-subarray MIMO radar concept with the corresponding grating lobe cancellation method is demonstrated by implementing a 60-GHz 16-element phased-subarray 2 ${\times }$ 2 MIMO frequency-modulated continuous-wave (FMCW) radar system. [ABSTRACT FROM AUTHOR]

In this study, we achieved a simple beam steering based on the hybrid configuration of traveling-wave and parallel feed circuits. The proposed antenna system provides a 2-D beam steering with the traveling-wave feeding using a two-way dc bias only. The traveling-wave feeding circuit and antenna units were designed and fabricated in this study. The input phases to the fabricated two-way traveling-wave antenna units were parallelly tuned using the two-way phase shifters. This antenna system consists of a hybrid configuration with the traveling-wave and parallel feedings, which contributed to a simple beam steering. In the demonstration using the designed and fabricated antenna, we confirmed the 77.8% parameter reduction compared with the conventional full-array antenna configuration. [ABSTRACT FROM AUTHOR]

Traditional methods for radio frequency (RF) beamforming require significant amounts of power, making them difficult to deploy in some low-power applications. A detailed analysis of RF beamforming utilizing transmission-line transformers (TLTs) and balanced impedance phase shifters (BIPSs) is presented. This technique enables ultralow-power RF beamformers by: 1) leveraging the RF feed lines to implement a low-loss TLT for signal combining and 2) using the balanced impedance tuning of shunt passives to implement simple, low-loss phase shifters. We highlight some of the key advantages of this beamforming approach for low-power systems and show how this idea can be expanded to arrays of more than two antenna elements by introducing a crossover switch into the phase shifters to extend the beam-steering range. In addition, a thorough comparison between the theoretical and measured performances of a simplified prototype system is provided for key system metrics, including loss and bandwidth. The prototype system is a fully passive 2-GHz two-element RF beamformer, utilizing TLTs and BIPS, realized with off-the-shelf components and a standard FR4 PCB. [ABSTRACT FROM AUTHOR]

This article presents a wideband scalable 27–31-GHz 1024-element $Ka$ -band SATCOM transmit (TX) phased array with embedded RF drivers and reconfigurable polarization. The phased array uses silicon TX beamformer (BF) chips and printed stacked-patch antennas on an FR-4 based printed circuit board (PCB) to TX either linear, rotated linear, circular clockwise, or anticlockwise polarization. It demonstrates a measured 3.5° half-power beamwidth (HPBW), 35-dB cross-polar discrimination (XPD), sub-1-dB axial ratio (AR), +49.5-dBW peak effective isotropic radiated power (EIRP) on axis, and the ability to scan to ±70° in all planes without grating lobes and $cos^{1-1.1}(\theta)$ scan loss. The measured error vector magnitude (EVM) of less than 2.3% and the adjacent channel power ratio (ACPR) of less than −32 dBc across all scans at $P_{1\,\text{dB}}$ make it suitable as a compact high-efficiency SATCOM transmitter. The array aperture measures 14.9 cm $\times14.9$ cm, and it is scalable to larger phased arrays with 4096 and a higher number of elements. To the best of our knowledge, this represents the highest level of integration at millimeter waves and with the highest measured EIRP from a SATCOM phased array. [ABSTRACT FROM AUTHOR]

This article presents a wideband scalable 17.7–20.2-GHz 1024-element $K$ -band satellite communication (SATCOM) receive (Rx) phased array with reconfigurable polarization. The phased array uses silicon Rx beamformer (BF) chips and silicon low-noise amplifiers (LNAs) and is able to receive either linear, rotated linear, circular clockwise, or anticlockwise polarization. It demonstrates a measured 3.47° half-power beamwidth (HPBW), more than 25-dB cross-polar discrimination (XPD), and +8.1-dB/K gain-to-noise (G/T) per polarization, and has more than 80-dB Tx-band isolation. The phased array is able to scan to ±70° in all planes without grating lobes and $\cos ^{1-1.2}(\theta)$ scan loss. The array aperture measures 22.4 cm $\times22.4$ cm. To our knowledge, this is the largest single printed circuit board (PCB) SATCOM $K$ -band phased-array receiver to date with the highest G/T and represents the highest level of integration at millimeter waves. [ABSTRACT FROM AUTHOR]

The focusing performance of an active short-range millimeter-wave imager is vulnerable to phase errors. As two major sources of phase error, delay uncertainty and array deformation are entangled when they are treated by conventional calibration methods, leading to defocusing. First, the defocusing effect caused by the array element position deviation (EPD) is graphically described in the form of ellipse deformation, indicating that the results of imaging a point target can inform on the distribution of EPD. Second, we analyze the phase error coupling problem to show that the EPD-caused phase error is spatially variant, therefore making the imaging performance sensitive to target location to varying extents bounded by the reference target location. Finally, a time-domain calibration method based on a constrained differential delay test is proposed to jointly mitigate the phase errors caused by both delay uncertainty and EPD. Numerical and experimental results demonstrate the efficacy of the proposed method. [ABSTRACT FROM AUTHOR]

This work presents a 15–57 GHz multiband/ multistandard phased-array architecture for the fifth-generation (5G) new radio (NR) frequency range 2 (FR2) bands. An eight-element phased-array receive module is demonstrated based on two four-channel wideband beamformer chips designed in the SiGe BiCMOS process and flipped on a low-cost printed circuit board. The SiGe Rx chip employs RF beamforming and is designed to interface to a wideband differential Vivaldi antenna array. Each channel consists of a low-noise amplifier (LNA), active phase shifter with 5-bit resolution, variable gain amplifier (VGA), and differential-to-single-ended stage. The four channels are combined using a wideband two-stage on-chip Wilkinson network. The beamformer has a peak electronic gain of 24–25 dB and a 4.7–6.2 dB noise figure (NF) with a −29 to −24 dBm input $P_{\boldsymbol {1\,dB}}$ at 20–40 GHz. The eight-element phased-array module also achieved ultra-wideband frequency response with flat gain and low-system NF. The phased array scans ±55° with $ < -12$ -dB sidelobes demonstrating multiband operation. A 1.2-m over-the-air (OTA) link measurement using the eight-element Rx module supports 400-MHz 256-QAM OFDMA modulation with < 2.76% error vector magnitude (EVM) at multiple 5G NR FR2 bands. To the author’s knowledge, this work achieves the widest bandwidth phased array enabling the construction of multistandard systems. [ABSTRACT FROM AUTHOR]

In this article, we present a new diagnostic technique for printed circuit boards (PCBs) and integrated circuits (ICs). This technique consists of an array-probe scanning system and the phaseless inverse source method with a joint regularization. Different from the single probe scanning system, a ground plane for array probes is applied to protect the RF transmission path from interference by other radiation in the array probes scanning system. In order to consider the influence of both PCB ground and array probes ground on electromagnetic near-field distributions, we use the method of moments to solve the surface integral equations in the forward problem. In the inverse problem, we establish a nonlinear cost function between the magnitude-only fields and equivalent sources. Because of the ill-posedness of the inverse problem, an efficient iterative method with a joint regularization framework is applied to reconstruct the equivalent sources on the source plane above the PCB ground. Different levels of noise are added to the simulated data to validate the algorithm. Laboratory experiments and numerical examples show the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This article reviews the recent advancements in the utilization of over-the-air combining techniques to enhance the efficiency of phased-array transmitters for signals with a high peak-to-average-power ratio. A methodological comparison between three spatial over-the-air combining techniques—Doherty, outphasing, and quadrature combining—is proposed, along with analysis of their spatial properties, such as a beamwidth angle for a given error vector magnitude (EVM) value, directivity, out-of-band emission, and sensitivity to amplitude and phase mismatches between the different streams. The analysis suggests that the Doherty technique has the widest spatial angle range with EVM under −30 dB and the lowest sensitivity to mismatches, while quadrature combining exhibits the lowest adjacent channel power ratio (ACPR). Also, the Doherty technique enables the largest efficiency enhancement and allows to trade off efficiency enhancement for out-of-band emission. The different methods were tested over-the-air at 28 GHz with a four-element integrated phased array fabricated in 65 nm to validate the analysis. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A new technique to realize miniaturized broadband multiway and polyphase differential phase shifters is proposed and studied in this article. In contrast to existing designs based on coupled-line and loaded stubs, the multiway phase dispersions are controlled by susceptances of multiple resonant tanks in this work, which can well enlarge the operation bandwidth (BW) and avoid the unachievable physical sizes in strip width and coupling gap over a large phase shift range on the universal reference line topology. In addition, its phase-shift range can be highly extended by properly allocating resonant frequencies of resonant tanks in each path to be specified different values. The theoretical analysis and design formula are studied, and the synthesis method is presented to determine all circuit parameters. By virtue of the quasi-lumped element technology, the proposed multiway phase shifter can be flexibly implemented on a single-layer printed circuit board (PCB) substrate with a very compact size. For demonstration, a five-way differential phase shifter in 0°–180° range has been designed, fabricated, and tested. Over a BW of 80.4%, the achieved phase shifts are 45° ± 4°, 90° ± 5°, 135° ± 5°, and 180° ± 6.3° with low insertion loss (IL) (<1.05 dB) and small amplitude imbalance (<0.29 dB). To the best of our knowledge, this is the tested widest multiway differential phase shifter in the 0°–180° range up until now. Meanwhile, the whole circuit size, including the substrate, is less than $0.30\lambda _{g} \times 0.26\lambda _{g}$. [ABSTRACT FROM AUTHOR]

This article presents a wideband ultralinear fully integrated power amplifier (PA) in 22-nm fully-depleted silicon-on-insulator (FD-SOI) technology for phased array-based $E$ -band backhaul networks. A novel amplitude to phase modulation (AMPM) compensation technique called NP (N-type P-type) matrix is presented. The performance of the proposed amplifier compared to a traditional N-type common-source (CS) PA is demonstrated in simulation across the corners and wide frequency range. The proposed PA occupies 0.084 mm2 core area and achieves peak 13.1-/13.7-dB gain, 61.8–83.7 GHz (21.9 GHz) 3-dB small signal bandwidth with 0.8 V/1 V supply. At 78 GHz, 13.8-/15.4-dBm peak saturated output power ($P_{\text {SAT}}$) with 13.1%/17% PAE from 0.8 V/1 V supply is measured, respectively. AMPM distortion at the output referred 1-dB compression point ($\text{OP}_{\text {1dB}}$) is less than 3.6° from 65 to 90 GHz. It achieves 18-/24-Gbit/s data rate with 10.7-/8.5-dBm average output power and 8%/4.9% average PAE at 73 GHz with 64/256 QAM modulation and a 0.8-V supply. [ABSTRACT FROM AUTHOR]

Code-modulated interferometry (CMI) enables a lens-less approach to imaging in which incoming signals are code modulated, combined, and processed through a shared hardware path; visibility functions are demodulated from an aggregate power-detected response; and an image is obtained using an inverse Fourier transform of the visibility samples. CMI allows the imager to be constructed using low-cost conventional beamforming hardware. This article presents the theory of operation of a code-modulated interferometer array intended for active imaging. This includes the selection of codes, the use of phase shifters for modulation, the demodulation of visibility functions, the necessary calibration, and the image processing. The architecture and design of an active imaging prototype is then presented, where it is created using a commercially available 16-element 8–16 GHz beamforming receiver along with a sparse antenna array that generates 169 distinct visibility samples. The imaging capabilities are demonstrated through the detection of multiple point sources at 10 GHz. Finally, the feasibility of creating a larger 64-element imager with 961 visibility samples is demonstrated through construction and measurements of a single row within that array. [ABSTRACT FROM AUTHOR]

We propose a 28.5-GHz channel sounder that switches through all antennas of multiple dual-polarized $8 \times 8$ phased arrays at the transmitter and receiver and performs beamforming in postprocessing through digital weights to synthesize a sweepable beam. To our knowledge, we are the first to implement—what we refer to as—switched beamforming with phased arrays for millimeter-wave channel sounding, realized through highly stable Rubidium clocks and local oscillators coupled with precision over-the-air calibration techniques developed in house. By circumventing the time-consuming programming of analog weights that is associated with analog beamforming—what phased arrays are designed for—we can sweep a 3-D double-omnidirectional dual-polarized channel in just 1.3 ms, for real-time sounding. By in turn circumventing the coarse precision of analog weights, we can synthesize ideal beam patterns thanks to the effectively infinite precision of digital weights, enabling fine weight calibration for the nonidealities of the system hardware and fine weight tapering for sidelobe suppression. This translates to average estimation errors of 0.47° in 3-D double-directional angle, 0.48 dB in co-polarized path gain, and 0.18 ns in delay, as substantiated by field measurements. [ABSTRACT FROM AUTHOR]

A high-efficiency 27–30 GHz 0.13- ${{\mu } \text {m}}$ BiCMOS transmitter front end for mobile satellite communication (SATCOM) phased arrays is presented. A system-level analysis for determining the key parameters of the RF front end for the case of a SATCOM user terminal for geostationary Earth orbit (GEO) is presented. The building blocks of the beamformer, consisting of a phase shifter, variable attenuator, and power amplifier, are fully characterized. A 360° phase shifter with an accuracy of 7 bits and amplitude error of ±1.5 dB is integrated with a variable attenuator that provides a gain variation of 16 dB with phase error of ±5°. The chip has a measured transducer gain of 23 dB and a power consumption of 45 mW at OP1dB of 10.8 dBm. The power-added efficiency (PAE) of 26.7% is measured for the entire channel at OP1dB. An error vector magnitude (EVM) of −28 dB at Pout,avg of 6 dBm and PAEavg of 12% is measured for a 400-MHz bandwidth 64-QAM modulated signal. The overall size of the chip is ${1.18} \times {2.23}\,\,\text {mm}^{{2}}$. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A new method of angle estimation of multiple targets using a distributed interferometric antenna array and wideband space–time modulation generating a dynamic array pattern is presented in this work. Interferometric array measurements of angle of arrival are generally ambiguous in the presence of two or more targets. We propose a new method of mitigating ambiguities in interferometric measurements by multiplying the angle pseudo-spectra from multiple antenna baselines, resulting in detections at only the angles of the targets. Using a single linear frequency-modulated transmitter and a receive interferometric array with $N$ elements, we show a simple and computationally efficient technique to estimate the angle of up to $\mathcal {O}(N^{2})$ targets. We describe the theory behind the technique, present detailed simulations, and provide an experimental verification using a three-element millimeter-wave measurement system. [ABSTRACT FROM AUTHOR]

Flexible phased arrays potentially enable diverse applications not permitted by rigid systems; however, they introduce ambiguity in antenna element positions. If this position ambiguity can be overcome, flexible arrays can perform the full suite of array functions: beam steering, wavefront engineering, and beam focusing. Furthermore, shape reconstructions of arrays can be used for applications beyond beamforming. We propose a framework to reconstruct the shape of a flexible array that only uses mutual coupling measurements and does not require additional sensors or functionalities in the system. We discuss the approach, a two-step algorithm, which is highly modular and can be implemented in a variety of phased array systems. To demonstrate the accuracy of the approach, we present results from two passive 2.5-GHz phased array setups using dipole and patch antennas, as well as a 10-GHz (active) integrated circuit flexible phased array, and demonstrate the accuracy of the approach in this system. In all cases, the algorithm reconstructs the antenna shape accurately, with average position errors of approximately 6% of the wavelength. This article can serve as the beginning of the broad study of shape reconstruction algorithms and their applications. [ABSTRACT FROM AUTHOR]

Power amplifier (PA) efficiency and linearity are among the key drivers to reduce energy consumption while enabling high data rates in the fifth-generation (5G) millimeter-wave phased array transmitters. Analog per-branch phase and amplitude control is used to steer the beam, suppress the sidelobes, and form zeros to the desired spatial directions. The amplitude control of individual PA inputs makes nonlinearity vary from antenna to antenna, which challenges the common digital predistortion (DPD) used to linearize the array. In this article, we implement an amplitude control for beamforming by tuning the PA gate bias. Varying the output powers via PA biasing makes the nonlinear characteristics observed at the individual PA outputs similar that helps the array DPD to linearize also individual PAs. The technique is validated by both simulations and measurements. As a measurement platform, we use a 28-GHz phased array transceiver equipped with 64 antenna elements and 16 radio frequency chains. The desired beam shape is synthesized by controlling the per-antenna over-the-air-power with PA gate bias. Then, the system is linearized by training DPD with a reference antenna. The DPD is demonstrated with 100-MHz-wide 5G new radio modulated waveform. The best example case showed −23.5-dB maximum sidelobe level (SLL) with 4.9% error vector magnitude and −40.8-dB total radiated adjacent channel power ratio with DPD. The proposed approach enables simultaneous reduction of beam pattern SLL, achieves good linearity in all directions, and maintains the PA efficiency. [ABSTRACT FROM AUTHOR]

In this article, a novel decoupling approach is proposed for large-scale patch antenna arrays. With the additional coupling path from the feeding line of an element to its adjacent element through a small aperture, the mutual coupling between the two elements can be well canceled. Completely different from the traditional transmission-line-based decoupling methods, the proposed approach does not employ direct transmission/coupling bridges between the feeding lines of the elements. Besides, there is no additional impedance matching network, resulting in a simple design procedure. For verification purposes, a decoupled dual-polarized 1 $\times $ 8 linear antenna array is developed and tested. Results denote that both the $E$ - and the $H$ -plane coupling are suppressed to less than −30 dB at the center frequency of 4.9 GHz. To further improve the decoupling bandwidth, a magnitude-compensation technique using a dual-aperture configuration is developed. A design example of a 4 $\times $ 4 single-polarized patch antenna array integrated with the decoupling method is measured. The results depict that the array is well-decoupled within the band from 4.7 to 5.04 GHz, with an isolation level of over 24.7 dB. The proposed decoupling approach features simple implementation and low profile, with almost no influence on element radiation performance, and can be utilized for 2-D large-scale arrays. [ABSTRACT FROM AUTHOR]

Recently, microwave imaging based on randomized illuminations has demonstrated promising potentials. The key to realize such imaging is to implement an imager with a reconfigurable, randomized aperture. In this work, we discuss the theory and the guidelines for implementing such an imager and demonstrate an experimental prototype working in the 24-GHz ISM band. It is realized with a board-integrated, space-fed, 400-element phased array capable of realizing independent 1-bit phase modulations for each element. The fields transmitting through this aperture can be deterministically randomized by simply controlling direct current bias voltages. Assisted by optimized system calibration and standard $\ell _{1}$ -norm regularization, experimental imaging with a notably improved quality can be obtained. The proposed solution can be used in wide applications, especially suitable for the massive personal security screenings in common public, government, and military areas. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 $ < -30$ 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. [ABSTRACT FROM AUTHOR]

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 0.52λ 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. [ABSTRACT FROM AUTHOR]

This article presents an ultralow-profile and lightweight Ku-band transmit phased array with 256 dual-polarized antenna elements for SATCOM on-the-move (SOTM) terminals. The antennas are placed in a square grid with λ/2 spacing at 14 GHz. At normal incidence, the phased array results in a measured effective isotropic radiated power (EIRP) of 64.5 and 66.5 dBm at P1~dB and Psat, respectively, per polarization. The measured patterns, in E- and H-planes, show almost ideal patterns with a wide scanning range of ±60°, a 3-dB instantaneous bandwidth of 13.0–14.6 GHz, and a cross-polarization isolation of 27 dB up to ±45° and 23 dB at ±60° scan angles. In the circular polarization mode, the measured axial ratio (AR) is <1.1 dB at 14–14.5 GHz. The phased array is also capable of synthesizing deep nulls (−30 to −40 dB) over a wide range of angles, thereby reducing unintended radiation to geostationary orbit (GEO) satellites. Transmit noise analysis is presented and shows that the array signal-to-noise ratio (SNR) is dominated by the block upconverter (BUC) and not by the beamformers. An error vector magnitude (EVM) of 2.8%–3.5% was achieved over a wide scan range for QPSK, 8-PSK, and 16-PSK waveforms with 100-MHz bandwidth. The array near-ideal performance, compact size, low profile with 3.5-mm thickness, and ultralightweight of 212 g make it ideal for affordable Ku-band SATCOM terminals. [ABSTRACT FROM AUTHOR]

A K-/Ka-band distributed attenuator in a 28-nm CMOS process is presented for a phased array. The proposed voltage-controlled distributed attenuator is designed using nonuniform varistors for a wide attenuation range with a compact size. An attenuation range of 25 dB was achieved with only three sections, which are 90° apart. The phase imbalance of the proposed attenuator is minimized using an artificial quarter-wave transmission line with series-connected varistors. The measured insertion loss of the proposed attenuator is 1.6–2.5 dB from 20 to 36 GHz. The insertion phase imbalance is less than 10° within the same bandwidth. The input 1-dB compression point is 10.6 dBm (defined as the 1-dB drop in the maximum attenuation range) at 28 GHz. The total chip size, including pads, is 0.77 × 0.42 mm2. The proposed attenuator has the highest attenuation range relative to the chip area compared with previously distributed attenuators. [ABSTRACT FROM AUTHOR]

In this work, we present a comprehensive analysis of port impedance effects on a signal coupled across two-port networks, derive an equation to evaluate the impedances for a specified coupling, and demonstrate two beam-shaping active array antenna prototypes to validate the theory. In this context, the generalized S-parameters are theoretically studied and verified through an example. Subsequently, a closed-form equation is derived to accurately evaluate the port impedances that enable the achievement of a desired magnitude and phase of the signal coupling across the two-port network. The meaningfulness of all the potential results and the additional capabilities of derived equations are then discussed. With this understanding, a general modeling procedure is formulated to achieve the simultaneous amplification and phase shifting only through the active devices, without resorting to any additional passive circuitry. As a proof of concept, two 1 × 5 active array antenna prototypes are developed and fabricated at 5 GHz: one for broadside radiation with a sidelobe level of less than −20 dB requirement, and the other for flat-top radiation beam between −10° and 30°. They are integrated with a 1 × 5 Wilkinson power divider that is designed for radiation pattern measurements, and the corresponding results agree reasonably well with the simulated counterparts and theory, thereby proving the developed concept. Such solutions demonstrate the inherent advantages of being low-loss, compact, and efficient, which are essential for the next generation of wireless systems. [ABSTRACT FROM AUTHOR]

A broadband SiGe power amplifier (PA) with double gain peaks for 5G applications is presented. The differential structure is widely adopted in millimeter-wave circuit design to decrease the impact of the source parasitic inductance that is induced by the bonding wires. Since differential PA results in a higher impedance transformation ratio of the matching network, differential PAs generally have narrower bandwidth than single-ended PAs. Through the bandwidth analysis of the matching network, the transformer used for interstage matching is elaborately designed to ease gain fluctuations. By controlling the stationary points of impedance transformation, the maximum available gain characteristic of a transistor, which decreases with increasing frequency, can be compensated. The gain curve of PA, thus, has double gain peaks within operational frequencies to make its frequency responses as flat as possible. The proposed PA for the frequency band from 27 to 37 GHz is fabricated in a standard 130-nm SiGe BiCMOS process, which occupies 0.36 mm2. Under the 2.5-V voltage supply, the SiGe PA exhibited a power gain of 33.5 dB and output power of 21.3 dBm with 24% power-added efficiency at 31 GHz. It achieves a 34% 3-dB small-signal S21 bandwidth from 27.3 to 38.5 GHz. [ABSTRACT FROM AUTHOR]

This article focuses on analyzing the aliasing artifact in millimeter-wave imaging systems, with a special focus on multistatic arrays. The current framework to analyze the behavior of multistatic structures is based on the effective aperture concept. Based on this framework, an equivalent monostatic array, approximating the position of each transmitter–receiver pair by its midpoint, is used to quantify the response and efficiency of the system. Although this framework helps to simplify the study of the complex characteristics of multistatic arrays, it suffers from vital deficiencies. Especially, it fails to describe the aliasing artifacts, seen in the image of some sparse multistatic configurations, where the study of their equivalent monostatic arrays proves that the Nyquist sampling rate is satisfied. In order to explain such behaviors, we propose a k-space-based framework to evaluate multistatic imaging systems. This framework not only explains the reason behind the aliasing artifacts but also estimates the locations where the aliasing happens. Moreover, this analysis can be beneficial to design multistatic configurations with reduced aliasing artifacts. The provided simulations and the experimental results prove the accuracy of the proposed framework that can effectively estimate the occurrence and the place of aliasing artifacts. [ABSTRACT FROM AUTHOR]

Intersymbol interference (ISI) is introduced in a phased array when the beam is scanned. The cause of the ISI is demonstrated and its dependence on the phased array dimensions, scan angle, and symbol rate is derived. A mathematical model is created to simulate the ISI effects on transmitted (or received) symbols, and an equalizer model is introduced and achieves near-perfect equalization of the ISI. Also, for wideband signals, it is shown that large phased arrays result in amplitude modulation versus frequency. The effect of ISI on the error vector magnitude (EVM) is simulated using complex modulated signals, and the EVM before and after equalization is compared, using an adaptive 17-tap linear equalizer implemented in MATLAB. The results show that ISI in large phased arrays can be equalized regardless of the modulation, bandwidth, scan angle, and symbol rate. The EVM of 16-, 64-, and 256-quadrature amplitude modulation (QAM) signals is measured for a 256-element array in the transmit mode. The measurements verify the derivations, eliminating ISI and resulting in low EVM values after equalization. The effect of array tapering on EVM is also presented, and the results show no difference in the EVM for uniform and tapered excitations. [ABSTRACT FROM AUTHOR]

This work proposes and demonstrates the scalable router array that eliminates the internal centralization of conventional arrays, unlocking scalability, and the potential for a system composed of spatially separated elements that do not share a common timing reference. Architectural variations are presented, and their specific tradeoffs are discussed. The general operation, steering capabilities, signal and noise considerations, and timing control advantages are evaluated through analysis, simulation, and measurements. An element-level CMOS radio frequency integrated circuit (RFIC) is developed and used to demonstrate a four-element 25 GHz prototype router. The RFIC’s programmable true time delay (TTD) control is used to correct path-length-difference-induced intersymbol interference (ISI) and improve a rerouted 270-Mb/s 64-QAM constellation from a completely scrambled state to an EVM of 4% rms (−28 dB). The prototype scalable router’s concurrent dual-beam capabilities are demonstrated by simultaneously steering two full power beams at 24.9 and 25 GHz in two different directions in a free-space electromagnetic setup. [ABSTRACT FROM AUTHOR]

We present improved methods for built-in test and calibration of phased arrays in free-space using a code-modulated embedded test (CoMET). Our approach employs the Cartesian modulation of test signals within each element using existing phase shifters, the combination of these signals into a code-multiplexed response, creation of code-modulated element-to-element “interference products” using a built-in power detector, demodulation of correlations from the digitized interference response, and parallel in situ extraction of amplitude and phase per element using an equation solver. In this article, we review CoMET’s methodology and then analyze the impact of noise within the system. To improve CoMET accuracy, a reference-element methodology is introduced, where all measurements are referred to as one element in the array whose phase is held constant. This is compared with another method in which the modulation axes are rotated to allow accurate extraction of phase near the original 0°/90°/180°/270° axes. Our techniques are demonstrated for both receive and transmit modes using an eight-element 8–16-GHz phased-array packaged and assembled together with patch antennas. Compared with network analyzer measurements, CoMET-extracted gain and phase using the reference-element method are accurate to within 0.4 dB and 2°–3° for free-space measurements, respectively. CoMET is then used within a calibration loop to equalize elemental gain and achieve a 7-bit phase resolution. In free space, the maximum gain and phase offsets between active antenna elements are reduced from 3.5 dB and 20°–90° to 1.1 dB and 0°, respectively. Calibrated beam patterns show significant improvement with peak-to-null ratios of >30 dB. [ABSTRACT FROM AUTHOR]

A new two-element phase-locked loop (PLL)-coupled array for the implementation of millimeter-wave (mm-wave) and subterahertz (sub-THz) phased arrays is presented. This architecture avoids using lossy phase shifter to create the required phase shift between the adjacent elements in a phased-array system. The required phase shift is generated by utilizing a dual nested loop PLL. The two PLL loops work together to stabilize the frequency and create the required phase shift. Moreover, it can be scaled simply by adding more unit cells to the architecture. A 112–121-GHz two-element phased array is designed and fabricated in a standard 65-nm CMOS process. It consumes 147-mW power and provides a phase shift of 46.7° ranging from 58.53° to 105.2° at 117 GHz. [ABSTRACT FROM AUTHOR]

This article presents a four-element 7.5–9-GHz phased-array receiver with 1–8 concurrent beams in a 65-nm CMOS technology. Each output beam utilizes all the input elements to maximize the beamforming gain. To realize a low-power and compact design, the multielement multibeam phased-array architecture features the gm-based variable-gain phase shifter (VG-PS) and the current-sharing active combiner. The VG-PS with 6-bit phase resolution achieves <2° root mean square (rms) phase error and <0.3 dB rms gain error at the maximum gain setting. The receiver demonstrates a 20-dB power gain, a 3.6-dB noise figure (NF), and a −19-dBm input 1-dB gain compression point (IP1dB) at 7.5–9 GHz for each element. The chip occupies $5.42\times3.62$ mm2 area excluding pads and consumes 860 mW, equivalent to the record low 27 mW per element per beam. To our knowledge, the receiver achieves the maximum number of simultaneously reconfigurable beams with the lowest power consumption per element per beam in RF phase shifting and combining receiver chips. [ABSTRACT FROM AUTHOR]

This article proposes a 28-GHz full-duplex (FD) phased arrays, which consists of 64-element transmitting and receiving arrays, and a 28-GHz radio frequency (RF) canceller. The phased arrays are designed with $2\times 2$ beamformer chips, and the transmitter (TX) and receiver (RX) arrays are oriented to have cross polarized configurations for high isolation. The 28-GHz RF canceller is based on an identical $2\times 2$ beamformer chip with two external different delay taps. Since the canceller is located at the input and output ports of arrays instead of antennas, it cannot eliminate the nonlinearities and noises in the phased arrays. Therefore, these nonlinearities and noise in the TX and RX arrays are experimentally analyzed to demonstrate that the proposed cross-polarized arrays have enough isolation to achieve suppression to the level of the RX noise floor. The FD phased-array system at 28.5–29.5 GHz has 57-dB isolation between the TX input and RX output ports, where the cross-polarization improves 10-dB isolation comparing to co-polarization and the RF canceller provide additional 10-dB self-interference (SI) suppression. Also, the nonlinearities and noise components of the received SI signals are lower than the noise floor at the output of the RX array. The system requires only 15.5-dB of additional digital cancellation to reduce the SI to the RX noise floor of 1-GHz bandwidth while maintaining the transmitting EIRP at 41 dBm. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A battery-less 5.8-GHz transmitter (TX), compact and lightweight enough to enable flight of $\sim 90$ mg honeybees and free roaming of bumblebees within their nest, was developed. The TX was coupled to a compact phased-array antenna receiver to achieve angle of arrival (AOA) estimation and bee localization through a received signal strength indicator approach (RSSI). The receiver was integrated into a commercial unmanned aerial vehicle (UAV) to support autonomous position updates based on the AOA estimates and a software development kit. A simple model predicting the system detection range was finally developed and is herein discussed. Our experimental results provide proof of concept toward autonomous tracking of tagged bees both in open air and in polytunnel settings. [ABSTRACT FROM AUTHOR]

The multichip packaging of an $E$ -band (71–76 GHz) millimeter-wave (mmWave) phased-array transceiver with an integrated $4 \times 4$ antenna array is described. Each unit is populated with four identical 2.1 mm $\times2.4$ mm transceiver dies assembled on the bottom side of an 8.01 mm $\times7.51$ mm substrate sized so that multiple units may be placed on a PCB to form a larger array while maintaining constant antenna pitch. Key features of the packaging solution include integrated stacked-patch antennas with measured $\vert S_{11}\vert $ less than −10 dB, die-to-antenna connection with simulated insertion loss less than 0.7 dB, on-package analog baseband splitters with 1-GHz bandwidth, and high-performance through-PCB cooling of the die, which are mounted to the bottom of the package. [ABSTRACT FROM AUTHOR]

We present an open-loop microwave distributed beamforming system using a self-mixing circuit for wireless frequency synchronization between two transmitting nodes in relative motion. Distributed beamforming on arrays of wireless nodes requires accurate coordination of the electrical states of each node to ensure that transmitted signals arrive at the desired destination with sufficient phase alignment for high signal gain. Of the necessary coordination parameters, synchronizing the frequencies of the internal oscillators is among the most crucial to ensure distributed coherence. In this work, we demonstrate distributed beamforming between separate microwave wireless transmitters using wireless frequency synchronization in a hierarchical coordination topology that is directly scalable to larger array sizes. The primary node transmits a spectrally sparse two-tone waveform that is received by a self-mixing circuit at the secondary node. A 10-MHz frequency reference of the primary node is modulated onto the tone separation of the waveform; upon self-mixing, the demodulated 10-MHz frequency reference is passed to a phase-locked loop to discipline the oscillator of the secondary node. We demonstrate beamforming at a 1.5-GHz carrier frequency between the two nodes, performed while moving the primary node, demonstrating the ability to maintain greater than 90% ideal distributed beamforming gain. [ABSTRACT FROM AUTHOR]