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This study proposes a design of a low-profile ultra wide-band cylindrical antenna array with plus/minus 45-degree dual polarization. The proposed compact cylindrical antenna array produces an omnidirectional radiation pattern in the azimuth plane to cover all directions. It consists of $20\times 4$ dual-polarized elements within a diameter of 131 mm and a height of 116 mm. The array elements are tightly coupled slant-polarized wideband dipole antennas, and hence, rotational symmetry of radiation patterns in the horizontal plane is achieved for the two orthogonal polarizations. Furthermore, a metasurface structure has been designed and placed over the interconnected array elements to achieve ultrawideband capabilities. The proposed array provides less than −10 dB reflection coefficient over a frequency band between 1.7 GHz and 5.9 GHz. The cross-polarization discrimination (XPD) is 15 dB at boresight in the azimuth plane. The electromagnetic characteristics of the cylindrical array and its corresponding planar array before bending have been evaluated and compared via simulations, and verified by measurements. The compact size, lightweight, and printable design of the proposed antenna array enable low-cost manufacturing and ease of installation. The proposed array design overcomes many challenges encountered in wide-band MIMO systems by covering the entire sub-6 GHz band while providing wide 360-degree coverage in the azimuth plane, hence, supporting multibeam applications.

In this paper, we develop a novel method to design the elements of an antenna array and their feed weights simultaneously. The method is based on formulating the design problem as a non-linear multi-objective optimization model that estimates the realized gain at certain angles as a function of the element-level port signals and impedances, and the array-level weights for the elements. This enables utilization of genetic algorithms to find optimal signals, impedances, and weights for given steering range requirements. As an example, an array consisting of multi-port antenna elements is simulated and modeled with its impedance and radiation matrices. These matrices are used in the calculation of realized gain with the model. The model is then applied as part of the method to find as wide scanning range for the array as possible. The antenna elements are designed such that the multi-port system can be reduced to a single feed with physically realizable matching components and a matching network. The array designed with the proposed method is also compared to a reference antenna array of the same size. Both the simulations and measurements verify that the method can provide substantial improvements in the scanning range as compared to the reference.

A reconfigurable phased array architecture utilizing a two-port half-loop antenna (THLA) is proposed and demonstrated at mmWave spectrum. The polarization, pattern, and beam steering can be freely reconfigured without any changes in the hardware by adjusting the weighting vectors of each port through software control. The proposed concept is demonstrated using an 8 RF port configuration and its isolation, gain, beam pattern, and beam steering resolutions are studied. Afterward, a $2\times 2$ THLA is exemplified as a proof-of-concept prototype for verifying its versatile radiation modes under realistic conditions. A low temperature co-fired ceramic process is applied to demonstrate its compatibility with conventional RF modules. Among the versatile modes of the $2\times 2$ THLA, 23 distinct radiation modes are selected and experimentally verified. The reflection and mutual coupling coefficients of the $2\times 2$ THLA are measured to be less than −10 dB at 28 GHz spectrum. Furthermore, the maximum gain of 8.47 dBi is confirmed at 28 GHz. This is the first to demonstrate a fully reconfigurable antenna which eliminates the need of any external and lumped components applicable for universal mmWave wireless applications.

Recent work has proposed that millimeter-wave beam steering antennas consisting of lens antenna subarrays (LASs) reduce hardware complexity. This manuscript extends the concept to 2D beam steering with extended hemispherical dielectric lenses (EHDLs). To accomplish this, we introduce a design process to maximize scan range and side lobe level (SLL) performance. The design process first employs the solution of the geometric disk covering problem to identify the initial positions of the feed antennas such that the subarray size, $M$ , is minimized. This process is followed by systematic 3D full-wave simulation-based parametric sweeps of lens geometry and feed antenna positions to maximize scan range and minimize SLL. Finally, we demonstrate this process with a 38 GHz antenna consisting of $L$ = 7 LASs and $M$ = 17 feed antennas per LAS. The resulting antenna has a ±36° field of view, −9.5 dB SLL, 5° half-power beamwidth, and ~20 dBi maximum realized gain. Compared to the existing literature on subarray-based beam-steering antennas, this antenna performs with a more extensive scan range while offering a comparable SLL performance.

In this paper, an optimization procedure for synthesizing shaped beams with an arbitrary geometry phased array system with real-time capability is presented. The algorithm involves a combination of an arbitrary extension of the Woodward-Lawson synthesis procedure with the magnitude least-squares optimization method. This simple combination significantly reduces the optimization time, enabling real-time beam shaping in response to changing requirements on beam shape or evolving geometry in distributed arrays. The technique places no restrictions on element positioning in all three spatial dimensions and is demonstrated to accurately reproduce the desired beam shape in both angular dimensions. The algorithm is demonstrated for multiple beam cases with a large, randomly generated array in computational simulation. The applicability of the algorithm to practical phased array hardware is also demonstrated using full-wave electromagnetic simulations and measurements of a realized arbitrary phased array system using a near-field scanner in an anechoic chamber.

This article presents a dual‐band shared‐aperture antenna array for a phased array system operating in the Ku/E‐bands with a large frequency ratio. A regular array arrangement is used to arrange single‐layer coupled microstrip patch elements that operate in the Ku‐band. E‐band elements using slot‐coupled microstrip patch antennas are arranged in a sparse concentric circular array configuration. In addition, E‐band transceiver/receiver (T/R) chips are attached to the back of the array's multilayer printed‐circuit board (PCB) to achieve high density with a low‐profile. In the shared‐aperture of the proposed antenna array, there are 64 elements in both Ku‐ and E‐bands. According to the results of our experiments, the Ku‐band array has a large scanning angle spanning from −45° to +45° with low gain drop and sidelobe level (SLL). It also exhibits a comparatively wide impedance bandwidth of 17.8% in the frequency range of 14.65–17.51 GHz. The E‐band array has a scanning angle of about ±20° in both the E‐ and H‐planes and a 7.7% simulated impedance bandwidth covers the frequency range of 75.8–81.9 GHz. [ABSTRACT FROM AUTHOR]

We present a 24–30-GHz 256-element dual-polarization transceiver (TRX) phased array based on a 16-element beamformer integrated circuit (BF-IC), 2-element frequency conversion integrated circuit (FC-IC), liquid crystal polymer (LCP)-based combiners and filters, and a tileable package with 64 embedded dual-polarized (dual-pol) antennas. The phased array presented in this work overcomes three key challenges in current 5G millimeter-wave (mmWave) antenna arrays: 1) it supports a dramatic increase in the number of supported fast-access beams; 2) it offers improved power efficiency; and 3) it provides a path to lower solution cost. 1) We enable fast switching among >30000 beams—orders of magnitude improvement over prior work—by employing an on-chip beam calculator in the BF-IC, achieving 200-ns beam setup and 8-ns over-the-air (OTA)-switching time. 2) We enable a module-level transmitter (TX) mode peak power added efficiency (PAE) of 20% using a modular architecture that preserves power amplifier (PA) linearity and efficiency as well as receiver (RX) mode low noise amplifier (LNA) noise figure (NF). The module achieves Psat effective isotropically radiated power (EIRP) of 68.5 dBm and BF-IC NF < 3.9 dB. 3) We lower the solution cost by enabling a wider steering range to reduce the number of phased arrays required in a sectorized coverage scheme, by reducing the IC and package area, and by avoiding calibration. The wider steering range is enabled by using an in-package magnetoelectric dipole antenna (for the first time in silicon-based phased arrays), resulting in steering over ±70° in H- and V-pol in both E- and H-planes without requiring any calibration. Moreover, the module achieves >20-dB cross-polarization isolation across the entire ±70° beam steering range. [ABSTRACT FROM AUTHOR]

In this letter, a novel design concept to achieve a low-cost wide-angle beam-scanning transmitarray (TA) using lens-loaded patch (LLP) elements is presented. In this design, each TA element consists of a beam switchable transmitting element, a group of receiving elements, and a signal via. The received powers of a 2×2 subarray are first combined and then transmitted to the corresponding LLP element, where the phases of the transmitted signals are manipulated for beamforming. Compared with the conventional designs, the phase shifters (PSs) can be multiplexed and the number of PSs is effectively eliminated by 75%, which significantly decreases the hardware cost. By employing multiple patches as the feed of the lenses, reconfigurable radiation patterns are obtained, and by properly choosing the transmitting patches, the developed TA achieves a wide-angle two-dimensional beam scanning within ±60° with stable gains. To validate the design concept, passive prototypes with a center frequency of 12.5 GHz are simulated, fabricated, and tested. The measured results show that the aperture efficiency is 30.1%, 19.4%, and 14.1% for beams steered to 0°, 30°, and 60° at 12.5 GHz, respectively. The beam coverage of ±60° with a less than 3.5 dB scanning loss in the H-plane is obtained. [ABSTRACT FROM AUTHOR]

This letter presents a dual-polarized low-profile linear phased array antenna design achieving one-dimensional wide-angle scanning with high polarization isolation. The dual-polarized antenna is constructed based on a metasurface serving different purposes for two polarization cases to achieve high polarization isolation while providing a low profile as a whole. It works as artificial magnetic conductor for x-polarization and radiator for y-polarization. To achieve wide-angle scanning, surface wave effect is exploited for x-polarization while for y-polarization widebeam active element patterns is implemented with a small array spacing of 0.42 λ0 applied. To verify the design, a 1×8 linear array was fabricated and tested. Measured and simulated results both demonstrate that, within a wide operating band, the proposed dual-polarized antenna has a high port-to-port polarization isolation over 29 dB with a low profile of 0.06 λ0. The measured results show that for x-polarization, the linear array can steer its main beam up to 81°, while for y-polarization, it can steer the main beam up to 70°. The cross-polarization levels can maintain below −20 dB during scanning in the general. [ABSTRACT FROM AUTHOR]

In this letter, a fast multinull steering technique is demonstrated by a linearly polarized linear antenna array. The new technique is based on the electric fields generated by each antenna element on a far-field arc of the antenna array, which are extracted in advance by simulation or measurement. The power transmission efficiency is used as the performance index to control the pattern nulls. By solving a matrix eigenvalue equation, in which the matrix is made up by selecting the corresponding electric fields on different positions on the arc standing for the null directions, the eigenvector corresponding to the zero eigenvalue is identified and used as the optimized distribution of excitations (ODEs) for the antenna array. Single-null and multinull patterns are tested from the ODEs and the results indicate that the number and directions of the multiple nulls can be controlled in the elevation space. The simulated and measured 2-D null patterns are shown in good agreement. [ABSTRACT FROM AUTHOR]

The complete multiple-input–multiple-output (MIMO) channel simulation in deterministic techniques can be a computationally intensive task, due to the inherent scenario's complexity and number of antennas. The spatial coherence among MIMO elements is a reasonable assumption to approximate the channel from a single point simulation. In this letter, a novel method to incorporate a geometrical approximation of the MIMO channel into a three-dimensional ray launching (3D-RL) algorithm is presented. The method is antenna type independent and the orientation of the array is embedded in the antenna representation. Relevant information of the MIMO channel characteristics like the root mean square (rms) delay spread, the maximum delay spread, phase and channel capacity are obtained and compared with the full 3D-RL simulation of the entire MIMO array, achieving 93.4% reduction in computational time. [ABSTRACT FROM AUTHOR]

Electromagnetic properties of an array antenna are inevitably affected by random magnitude and phase errors in the feeding network. Polynomial chaos expansion (PCE) method can analyze such problems, but the number of numerical quadrature grows rapidly with stochastic dimensionality for solving the PCE coefficients. An improved PCE algorithm is proposed to improve the computational efficiency. A large array is decomposed into several small groups those can be efficiently treated by the PCE method. Stochastic quantification of the whole array is achieved by the superposition of grouped results. In addition, the proposed method can integrate with the method of moments to treat real-world arrays. The results computed by this method agree with those of Monte Carlo, and the computational time is reduced by two orders of magnitude for a dipole array with 64 elements. [ABSTRACT FROM AUTHOR]

The papers in this special section focus on the state-of-the-art of applied and analytical research, including the latest technological advancements and the use of innovative materials and methods to disrupt the way beam-steering antennas are designed and to reveal novel approaches for the design and analysis of antennas for the next generation of satellite communication systems. [ABSTRACT FROM AUTHOR]

This letter proposes a self-deployable circularly polarized (CP) stacked Yagi–Uda phased antenna array operating at C-band (5.6–6.0 GHz). The proposed antenna system is composed of a 2×2 stacked CP Yagi–Uda antenna array and feeding networks consisting of a reflection-type phase shifter and a four-way Gysel power divider. The proposed phased antenna array is integrated into the top side of a 1U (10 $ \times $ 10 $ \times $ 10 cm3) CubeSat via fully three-dimensional (3-D) printed self-deployable spring hinges and frame. The volume of the proposed antenna is reduced by 69% when folded, and the antenna deploys to the desired shape without any actuators or power. The designed reflection-type phase shifter has 0°–373° analog phase-shifting range and the four-way Gysel power divider feeds each of the 2 $ \times $ 2 antenna array. The proposed self-deployable phased antenna array has 13.5 dBic left-handed circular polarized gain and +/−10° beam steering angle. [ABSTRACT FROM AUTHOR]

This letter presents a scalable multipolarized planar phased array for the low earth orbit satellite communication application. A dual-polarized aperture-coupled patch element antenna is proposed for designing the array, which can provide dual-linear polarization (LP) and dual-circular polarization (CP). The rotated feed technique is adopted to reduce the cross-polarization level. By using 8-channel beamformer chips and the multilayer printed circuit board technology, a phased array prototype with good electromagnetic shielding performance, high integration, and low cost is designed, fabricated, and measured. For dual-LP radiation, it steers up to the scan angles (±50°) with a scan loss less than 3.5 dB, and a cross-polarization level lower than −30 dB in azimuth/elevation plane and −15 dB in diagonal plane. For dual-CP radiation, it steers up to the scan angle (±50°) with a scan loss less than 3 dB and an axial ratio less than 3 dB. The phased array developed in this letter can be scaled to larger arrays and provides feasibility for the production of low-cost phased arrays. [ABSTRACT FROM AUTHOR]

An interferometric phase transmitarray is proposed for spatial power combining to enhance the equivalent isotropically radiated power (EIRP) of the millimeter-wave (mmW) transmitters. The study shows that the multiple beams emitting from the ideal point sources located at different positions are combined into one beam to radiate in the boresight direction of the transmitarray, namely, achieving spatial power combining. As an example, the prototyped transmitarray fed by two patch antennas operating over the bandwidth of 23–27 GHz shows that with the spatial power combining, the proposed antenna achieves the combined gain realized by two feeds of 19.6 dBi at boresight 2.5 dB higher than the realized gain of the single feed, so that the EIRP of the two-feed transmitarray is enhanced by 5.5 dB because of 2.5 dB from the gain enhancement of two-feed transmitarray and 3 dB by the two-way power combining. [ABSTRACT FROM AUTHOR]

A novel method of synthesizing shaped-beam cylindrical conformal array by rotating the antenna elements and optimizing their excitation phases is presented. Rotation of antennas on curved surface is mathematically described by rotating its vectorial active element pattern (VAEP) in its local coordinate system (LCS). Then the scalar patterns and polarization unit vectors of all the rotated VAEPs are properly transformed and then interpolated at a unified angle sampling grid in a common coordinate system, where they are summed to obtain an approximated array expression. With this expression, element rotations and phases can be optimized using the constriction factor particle swarm optimization (CF-PSO) to synthesize desired shaped-beam pattern with controlled sidelobe level (SLL) and cross-polarization level (XPL). However, since rotations on curved surface introduce considerable variations to the element curvature and mutual coupling (MC), the synthesized array pattern would have considerable errors. A refined strategy is adopted then to improve the synthesis accuracy. The proposed method uses uniform amplitude weighting, thus saving many unequal power dividers. Three typical shaped pattern synthesis examples are provided to show the effectiveness of the proposed method. A cylindrical array prototype with 24 rotated U-slot loaded patch antennas is fabricated and measured for practical validation. [ABSTRACT FROM AUTHOR]

A wideband high gain circularly polarized microstrip antenna (CP MSA) array is presented in this communication. In the proposed CP MSA array, the elements are designed at 3.5 and 5.8 GHz, which are sequentially rotated to form a planar array. The array elements are fed using the $TM_{110}$ and $TM_{210}$ modes of a center CP MSA. This arrangement achieves an axial ratio (AR) bandwidth of 63.7% (3.25–6.29 GHz) and improves gain over a wide bandwidth. The peak gain of the array is 17.77 dBic with a 3-dB gain bandwidth of 53.9%. The center MSA of the array is fed using four orthogonal printed L-probes with quadrature phase difference. The proposed CP MSA array has an $|S_{11}|\leq -10$ dB bandwidth of 63.3% (3.32–6.4 GHz). [ABSTRACT FROM AUTHOR]

In this communication, a dual-band shared-aperture reflectarray (RA) with a phased array is proposed for intersatellite links (ISLs). The Ka-band RA is integrated with an X-band phased array by a sharing mushroom patch structure. The high-frequency ratio allows the high-frequency RA and the low-frequency broadband phased array to operate independently to support high-speed communication of the geostationary orbit (GEO) relay nodes in the intersatellite network. To verify this concept, a prototype of the antenna is designed and fabricated, and its electrical performance is measured. The RA presents a peak gain of 30.1 dBi (28 GHz) and a 3 dB gain bandwidth of 11.4% (26.4–29.6 GHz). The phased array presents the peak gain of 21.7 dBi (9 GHz), and the relative bandwidth can reach 45.3% in the boresight direction. The scanning range can cover ±45°, and the H/E planes scan gain losses are less than 2.34 and 4.33 dB, respectively. [ABSTRACT FROM AUTHOR]

An efficient design of a 3-D printed dielectric dome array (DDA) antenna featuring ultrawide-angle beam scanning is presented in this article. Instead of using optimization tools, the inner and outer contours of the dielectric dome lens (DDL) are determined by the derived phase distribution $\phi (\theta)$ over a dome surface $r(\theta)$. The scan gain of the DDA can be manipulated by properly choosing the defined scan amplification factor $K(\theta)$ of the DDL. After determining the contours of the DDL, two finite-by-infinite 1-D DDA models are constructed to predict the E- and H-plane scanning performances, respectively, wherein both the full-wave performances of feed array and the effect of multiple reflections at the air–dielectric interfaces are considered. Since the phase distribution over the planar array is nonlinear due to the presence of the DDL, the array excitation phases are optimized by the particle swarm optimization (PSO) method with the optimization goal of the maximum gain at each scan angle. As a proof of concept, a 3-D printed DDL fed by an $8 \times 8$ E-shaped patch array at 20 GHz is manufactured and tested. When combined with the DDL, a ±60° scan range of the planar array can be extended to ±80° with relatively flat scan gain. The experimental results are in acceptable agreement with simulations, verifying the feasibility of the DDL design. [ABSTRACT FROM AUTHOR]

In this article, a wideband shared-aperture phased array antenna is proposed for synthetic aperture radar (SAR) applications. A metal cavity-backed slot antenna and a slot antenna are used as the L- and X-band antenna elements, respectively. Notably, the X-band antenna elements are mounted on top of the L-band ones, and their interactions are successfully isolated by loading a layer of frequency selective surface (FSS). The FSS layer reflects the electromagnetic waves in X-band and allows transmission of the L-band electromagnetic waves, making the shared-aperture antenna work properly in L- and X-bands. Furthermore, a circular patch is designed to improve the bandwidth of the X-band antenna. Simulations indicate that the proposed antenna has impedance bandwidths of 46% in X-band (7.5–12 GHz) and 21% in L-band (1.7–2.1 GHz). Moreover, the X-band antenna can scan up to ±60° in the E-plane and ±30° in the H-plane with voltage standing wave ratio (VSWR) below 3. To verify the design method, a shared-aperture antenna prototype, which consists of $6\times6$ X-band elements and one L-band element, has been fabricated and measured. Finally, the measured results agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

A novel coupling-cancellation method by loading planar path is proposed and applied in the millimeter-wave phased array for wide-angle scanning. By employing the improved decoupling stubs with weak radiation first, an extra introduced wideband equal-magnitude and anti-phase path is generated to cancel the inherent coupling path. The principle of the proposed method is investigated by the equivalent circuits and the full-wave simulation. Based on this method, a high-isolation 1-D phased array using low-temperature-cofired ceramic (LTCC) process is designed and fabricated. The planar paths are placed symmetrically between the subarrays and its radiation polarization is coincident with the antenna elements, resulting in high isolation and enhanced boresight radiation null-fill of subarrays. The measured isolation is below 20 dB within the relative bandwidth of 16.7% and the maximum scanning angle is ±60°. Moreover, the proposed method can be expectedly extended to large-scale arrays. [ABSTRACT FROM AUTHOR]

This article focused on broadening the azimuth plane scanning range of surface-mounted linear arrays. First, 14 kinds of basic radiation models were theoretically analyzed, and the basic model with a 180° covered main lobe was pointed out. Afterward, a wide-beam surface-mounted antenna was designed using an in-phase-reflection electromagnetic bandgap structure based on the selected element model. Finally, an azimuth plane wide-angle scanning linear array with wide-beam surface-mounted elements was arranged, decoupled, and evaluated. This array can scan its beam in the range of 90° ± 85° in the azimuth plane with a 3 dB gain fluctuation, which verified the effectiveness of the proposed theoretical model. [ABSTRACT FROM AUTHOR]

Infinite periodic arrays of antennas that can be individually described by means of spherical modes are analyzed starting from the generalized scattering matrix (GSM) of an isolated element. After computing the GSM of an isolated element with the finite-element method (FEM), a fast postprocessing can be carried out to calculate the response of the element in an infinite array environment by using addition theorems for spherical modes. For this purpose, an efficient computation of lattice sums of spherical harmonics is used. The main advantage of this method is that the antenna is analyzed only once whatever the array lattice or scan angle. In addition, fast frequency analysis can be performed since the starting point is the computation of the isolated antenna with the FEM, which is suitable for fast frequency sweep. The active reflection coefficient and the embedded radiation pattern of the infinite periodic array are calculated for several examples to show the capabilities of the proposed method. [ABSTRACT FROM AUTHOR]

This communication presents a vertically stacked substrate-integrated waveguide (SIW) antenna array that enables different array configurations with the minimum number of SIW layers. This achievement lies in the modular feature offered by the proposed design. Specifically, four distinct array configurations can be produced with only three different designs of SIW layers. Depending on the number of SIW layers employed in the stacked antenna, the directivity in the E-plane is modified. To obtain an equal and in-phase power distribution among the array elements, H- and E-plane corporate feeding networks are efficiently implemented in each array configuration. Array configurations of one, two, four, and eight radiating layers are offered by the proposed modular array, where each radiating layer is formed by eight H-plane horn antennas. The simulated directivity for the array configurations ranges from 15.8 to 23.8 dBi and the main beam direction remains fixed along the operating frequency range. The array design has been manufactured, and an agreement between simulated and measured results is observed. The measured impedance bandwidth in all the array configurations is from 35 to 41 GHz (15.79% bandwidth) with a reduction in the E-plane beamwidth as the number of radiating layers increases. [ABSTRACT FROM AUTHOR]

The “time” factor in time-modulated arrays (TMAs) offers a new degree of freedom for securing wireless communication. However, the widely used periodic time modulation introduces limited randomness for eavesdropping receivers, and thus gives weak security. To meet this challenge, this work proposes a TMA with chaotic-enabled phase modulation (CPM) for secure transmission. The proposed CPM technique offers the chaos features of high randomness, unpredictability, and initial condition sensitive characteristic, to increase the information uncertainty for eavesdropping receivers. An optimization-based time sequence design approach is introduced to design optimal CPM time sequences for secure transmission in a given direction. Thus, a variety of security strategies including beam scanning, directional modulation (DM), and chaotic encryption are simultaneously enabled by the optimized CPM time sequence. Moreover, the CPM is a radio frequency (RF)-domain security technique without requiring any baseband modulation modules, which exhibits a simplified hardware architecture. Numerical analysis and experimental results are presented to illustrate the effectiveness of the proposed CPM technique. The results indicate that the security is improved by lowering the bit error rate (BER) between the legitimate receiver and the transmitter, and reducing the mutual information between eavesdropping receivers and the transmitter. [ABSTRACT FROM AUTHOR]

A dual-polarized Ku-band and single-polarized Ka-band shared-aperture phased array antenna is proposed in this article. The endfire dipole antenna is designed as the radiating element of both bands. To eliminate the shading effect of the horizontal-polarized Ku-band antenna caused by the common ground, the director is loaded on the Ka-band antenna to increase the height of the equivalent phase center of the Ka-band antenna. The high-order mode of the horizontal-polarized Ku-band antenna is excited when the Ka-band antenna scans to a wide angle in H-plane within the frequency range of 33–34 GHz. An etched square ring is loaded on the Ku-band radiating arm to induce the reverse current to prevent such a high-order mode. The scanning blind spots occur at 33 and 35.8 GHz when the Ka-band antenna scans to 50° in E-plane owing to the mutual coupling between the Ka-band antenna and the vertical-polarized Ku-band antenna. A metallic strip is loaded on the vertical-polarized Ku-band antenna to eliminate the blind spot at 33 GHz. The feeding position of the vertical-polarized Ku-band antenna is elevated to eliminate the blind spot at 35.8 GHz. The periodic cell and finite array are simulated to verify the design proposed in this article. The results demonstrate that the design is effective and the beam-scanning coverage reaches $\pm \mathrm{50}^{\circ }$ at both bands. The active voltage standing wave ratio (VSWR) is not greater than 3.5 at 15–17 and 33–36 GHz in the whole beam-scanning coverage. A prototype of the 4 $\times $ 4 Ku-band and 8 $\times $ 8 Ka-band shared-aperture array is fabricated and measured. The measured results agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

In this communication, a reconfigurable 2-bit leaky-wave antenna (LWA) is proposed for low-cost fixed-frequency beam-steering applications. The proposed antenna consists of a microstrip transmission line loaded with several branches, a series of 2-bit phase shifters, and a $1\times 8$ patch array. Each phase shifter is built by selecting the feed directions on the branch and introducing slot perturbation on the patch, thus no phase delay line is used. Only three p-i-n diodes are needed to control the 0°, 90°, 180°, and 270° states of the element. The reference phase $\varphi _{0}$ , namely the phase of the first element, is utilized to enhance the peak gain of the array. The stopband effect of broadside beam is eliminated due to the perturbation on the patches. The prototype is tested at 3.6 GHz. The measured peak gain is 13.54 dBi, and the main beam can steer from $- \mathrm{48}^{\circ }$ to $+ \mathrm{46}^{\circ }$. [ABSTRACT FROM AUTHOR]

In this article, a millimeter-wave (mmWave) endfire phased array antenna with ±45° linear polarizations is proposed for fifth generation (5G)/B5G mobile communications. The proposed antenna achieves ±45° polarizations by utilizing a modified substrate integrated waveguide (SIW) slot polarizer. The polarizer generates dual orthogonal modes with equal amplitudes and a 0°/180° phase difference, thereby yielding $+ 45^{\circ }/- 45^{\circ }$ -polarization radiated waves in the far field. In a practical metal-framed mobile phone environment, the ±45 polarizations are verified to provide more balanced radiation patterns and, consequently, a higher polarization-multiple input multiple output (MIMO) efficiency. A prototype of the proposed 1 $\times $ 4 array is fabricated and measured, achieving a −10 dB impedance bandwidth of 23.4–30.0 GHz (covers 5G band of n257/n258), with an isolation better than 15.6 dB and a realized gain above 8.9 dBi in the operating bandwidth. A peak gain of 11.4 dBi and a 3 dB scanning range of 87° can be observed at 27.0 GHz. Furthermore, the prototype is characterized on a metal-framed mobile phone platform, experimentally demonstrating its superiority to conventional vertical/horizontal polarized (V-/H-pol) arrays. The validated advantages of the balanced radiation patterns and robust impedance matching make the proposed ±45°-polarization endfire antenna array a promising candidate for mobile terminals in the era of 5G/B5G. [ABSTRACT FROM AUTHOR]

Nonlinear ultrasonic emissions produced during a therapeutic ultrasound procedure can be detected, localized, and quantified through a class of methods that can be referred to as passive acoustic mapping (PAM). While a variety of PAM beamforming algorithms may be employed, they share a common limitation that a single sound speed is specified for both phase steering of array elements and for calculation of source power or energy. The specified value may be inadequate whether derived from B-mode-based metrics or literature values for constituent materials. This study employed experiments and simulations with linear and curvilinear array geometries to investigate the impact of in situ sound speed uncertainties on source localization in layered media. The data were also used to evaluate a new method for optimizing coregistration of PAM and B-mode images. Coregistration errors as large as 10 mm were observed with the curvilinear array, which also showed much greater sound speed sensitivity than the linear array. Errors with both array geometries were typically reduced to the order of 0.1 mm using the proposed optimization method regardless of beamformer choice or whether the array was calibrated. In a further step toward reliable implementation of PAM, the current work provides an approach that can help ensure that therapeutic ultrasound procedures are accurately guided by cavitation emissions. [ABSTRACT FROM AUTHOR]

Piezoelectric materials have been developed since early 1900s and many research had been conducted on the composition and process to obtain higher piezoelectric constants (${d}_{33}$). Within composition research, lead perovskite relaxor piezoelectric single crystals (SCs) of Pb(Mg1/3Nb2/3)O3–lead titanate PbTiO3 type have been actively studied since 1990s because of their outstanding ${d}_{33} >1500$ pC/N compared with those of the conventional Pb(Zr,Ti)O3 ceramics. A major driving force of these SC research has been promoted by mass production of ultrasound transducers and array probes for medical diagnostic systems since early 2000s. However, higher ${d}_{33}$ material and process research for these ultrasound devices are almost saturated. In this review article, we present a brief overview of the history, current situation, and future perspective of piezoelectric SCs. The authors believe that the main research in the next century is high ${d}_{33}$ SCs with a high composition uniformity and low-energy SC growth methods, such as solid-state SC growth, low-loss SC transducer manufacturing technique, and improved poling process. This is a big technical challenge for all the scientists; however, the relatively large market of medical ultrasound has been expanded year by year, and we hope that the community is motivated to solve such technical problems in the near future. [ABSTRACT FROM AUTHOR]

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]

Massive MIMO is a promising air interface technology for 5G wireless communications. Such antenna systems offer capabilities to utilize channel correlations to create beams suitable for user specific transmissions. Most of the prior research is devoted to user-specific transmission in such systems, where a narrow beam is formed towards a user to improve its reception. Meanwhile, public-channel transmission to multiple users at once by means of broad beams has been understudied. In this paper, we introduce the concept of array-size invariant (ASI) beamforming, enabling generation of broad beams from very large antenna arrays where all elements are transmitting at maximum power. The ASI technique offers the possibility to achieve a perfectly flat array factor by exploiting the additional degree of freedom coming from the dual-polarization beamforming. The proposed technique is applicable to both uniform linear and rectangular arrays. The benefits of the method are shown by means of several numerical examples. In particular, the practical usefulness of the ASI beamforming, in terms of coverage and energy efficiency, is illustrated on an example of designing a cell-specific broad beam for public-channel transmission in a realistic network deployment. [ABSTRACT FROM AUTHOR]

The high directionality of mmWave communication makes its line-of-sight (LoS) path susceptible to blockage when the user is moving. Most existing solutions have very stringent requirements on the antennas of the transmitter and the receiver, which are hardly met by today’s consumer-level commercial off-the-shelf (COTS) mmWave products. In reality, a COTS device uses low-resolution wide-beam antennas, and hence cannot support the aforementioned methods for NLoS beam switching in response to the LoS blockage. In this paper, we develop a new method to support high-resolution mmWave multi-path channel resolving based on coarse-grained wide-beam phased array antennas. We design a novel real-time beam-switching algorithm that allows COTS devices to estimate the location and reflection coefficient of the dominant reflectors. Whenever the current LoS is blocked, our algorithm can compute in real-time the best alternative beam direction based on estimated reflectors to establish a strong NLoS link. We implemented the proposed algorithm on a COTS mmWave device and evaluated the system’s performance on the physical and transport layer. Our experiments demonstrate the effectiveness of our algorithm on estimating dominant reflectors and calculating strong alternative beam directions, and its efficacy in providing robust connections for COTS mmWave devices. [ABSTRACT FROM AUTHOR]

The use of fifth-generation (5G) new radio (NR) spectrum around 26 GHz is currently raising the quest on its compatibility with the well-established Earth exploration-satellite service, which may be blinded by the spurious radiation emitted above the horizon (AtH) by base station (BS) antennas. Indeed, AtH grating lobes are often present during cell scanning due to the large interelement spacing in BS array antennas for achieving higher gains with a reduced number of RF chains. In this letter, we propose an approach based on an electrically thin metasurface-based dome for the reduction of AtH grating lobes in 5G-NR BS antennas. The proposed scanning range shifting approach exploits the natural lower amplitude of the grating lobes when the antenna array scans in an angular region closer to the broadside direction. The grating lobe reduction is here demonstrated considering a 1×4 phased linear antenna array operating under dual-liner ±45°-slant polarization. A simple design procedure for designing the metasurface dome is reported, together with the antenna performances, evaluated through a proper set of numerical experiments. It is shown that the grating lobe radiation toward the satellite region is significantly reduced, whereas the overall insertion loss is moderate. [ABSTRACT FROM AUTHOR]

This letter presents a microwave dielectric metasurface implementation comprising arrays of high permittivity pillars of varying diameter and height embedded in a lower permittivity slab. These dielectric arrays can provide a 490° transmission phase range with zero reflection and low loss and can be fabricated using additive manufacturing techniques in curved structures such as dome antennas. Full-wave simulations of a representative scan loss-reducing dome antenna agree well with analytic calculations that assume an ideal phase sheet. For simplicity, the example dome antenna is a two-dimensional (2-D) cylindrical dome; however, the dielectric metasurface implementation can be extended to 3-D dome designs. [ABSTRACT FROM AUTHOR]

A 28 GHz dual-mode phase-invariant wide-dynamic-range variable-gain amplifier (VGA) with adaptive phase compensators is presented for use as a gain control element in a beamforming IC, which must have a small chip size and low power consumption. It consists of a single-stage differential amplifier with main and auxiliary signal paths, where the auxiliary paths are introduced to achieve most-significant-bit (MSB) gain control. The wide-gain dynamic range is also covered through a least-significant-bit (LSB) gain-control scheme, which is implemented with bias control of common gate (CG) transistors in the main signal paths. In addition, the phase variations due to the gain controls are drastically reduced by introducing phase compensators for both gain controls. The proposed VGA shows a gain dynamic range of 24 dB, maximum gain of 13 dB and root-mean-square (RMS) phase error of 2.77 degrees at 28 GHz. The maximum DC power consumption is 24 mW at the maximum gain, the minimum is 4 mW at the minimum gain, and the chip size is 0.066 mm2. [ABSTRACT FROM AUTHOR]

We present measurements and analysis of self-interference in multi-panel millimeter wave (mmWave) full-duplex communication systems at 28 GHz. In an anechoic chamber, we measure the self-interference power between the input of a transmitting phased array and the output of a colocated receiving phased array, each of which is electronically steered across a number of directions in azimuth and elevation. These self-interference power measurements shed light on the potential for a full-duplex communication system to successfully receive a desired signal while transmitting in-band. Our nearly 6.5 million measurements illustrate that more self-interference tends to be coupled when the transmitting and receiving phased arrays steer their beams toward one another but that slight shifts in steering direction (on the order of one degree) can lead to significant fluctuations in self-interference power. We analyze these measurements to characterize the spatial variability of self-interference to better quantify and statistically model this sensitivity. Our analyses and statistical results can be useful references when developing and evaluating mmWave full-duplex systems and motivate a variety of future topics including beam selection, beamforming codebook design, and self-interference channel modeling. [ABSTRACT FROM AUTHOR]

An eight-channel phased array (PA) radiometer front-end is developed to serve video-rate passive millimeter wave (PMMW) imaging at ${V}$ -band. The front-end is implemented by multichip module (MCM), in which all active microwave functions are realized with GaAs monolithic microwave integrated circuits (MMICs) while passive devices and connection lines are designed on printed circuit board (PCB). All receiver channels are linearly arranged and equipped with waveguide-fed dielectric rod antennas (DRAs). By introducing a surface metallized bent structure into the DRA, the phase center of element antenna can be changed, which provides an effective approach to suppress grating lobes without a significant increase in structural complexity of the sparse array. Moreover, chip assembly details are presented together with the methods taken to mitigate the mismatch caused by wire-bond interconnections and MMICs. Single-channel (SC) and overall-module measurements are applied to the front-end, and the results reveal that the front-end achieves 50-dB gain, 5-dB noise figure (NF), ±24° field of view (FoV) and −10-dB side/grating lobes within the frequency band of 52–56 GHz. Finally, a passive imaging system is established using the proposed front-end and the primary imaging results verify the front-end design in system level. [ABSTRACT FROM AUTHOR]

The aperture-level simultaneous transmit and receive (ALSTAR) system uses full digital architecture with an observation channel to achieve remarkably effective isotropic isolation (EII). However, the number of observation channels must be the same as the number of transmit channels, which increases the system's complexity. To balance the system cost and performance of the ALSTAR, this paper proposes a joint design of sparse arrays and beamforming, which are achieved by a genetic algorithm and an alternating optimization algorithm, respectively. In the sparse design, we introduce beamforming technology to guarantee the EII while decreasing the corresponding elements of observation channel that contribute slightly to the EII. The simulation results are presented for a 32-element array that achieves 185.87 dB of the EII with 1000 W of transmit power. In the cases of sparsity rates at 0.875 and 0.75 (≥0.6), i.e., the number of observation channels decreases by 12.5% (2/16) and 25% (4/16), the reductions in EII do not exceed 1 dB and 3 dB, respectively. However, the EII decreases rapidly with a sparsity rate less than 0.25. Results demonstrate that our proposed joint design of sparse arrays and beamforming can reduce the system cost with little performance loss of EII. [ABSTRACT FROM AUTHOR]

A new far-field valid angle equation for rectilinear planar near-field measurements is derived. The new valid angle equation is derived by viewing the near-field to far-field transformation process as the generation of a pseudo plane wave by a synthetic phased array and subjecting the antenna-under-test (AUT) to the radiation from this synthetic array. The synthetic phased array does not physically exist; rather, the array is formed during the postprocessing of the planar near-field measurements. The resultant valid far-field angle computed with the new equation is compared against previously established and popularly accepted valid angle equations. A brief discussion is offered on the measurement of low-directivity antennas with a planar near-field measurement system and on amplitude tapering of the near-field measurements to improve the quality of the pseudo plane wave inside the test zone. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate an approach for local reduction of the electric field amplitude of the transmitted radio-frequency signal in ultrahigh-field magnetic resonance imaging (MRI). We excite a suitable combination of three coupled dipole hybrid resonances composing a single transmit antenna array element. Using numerical optimization, we designed a feeding network for three coupled dipoles placed over an electromagnetic phantom mimicking a human body. This network of discrete elements provides the appropriate amplitudes and phases of three dipole currents excited by a single input port. It allows controlling the electric field distribution in the vicinity of the antenna. Our goal was to obtain a minimum of the electric field at the given relatively small depth inside the phantom, where body implants are typically located while keeping a tolerable level of the magnetic field toward the phantom’s center. We designed and manufactured a three-dipole antenna prototype optimized for MRI of the human body at 7 T (proton Larmor frequency of 298 MHz). The experimental validation showed a 40 dB reduction of the electric field amplitude at a depth of 4 cm compared to a conventional single-dipole antenna. The coupling network can be rearranged to target different depths. Therefore, a principle of electric field minimization at a controllable position inside the body has been shown, which may be useful for designing transmit MRI antennas with improved safety of implants. [ABSTRACT FROM AUTHOR]

A systematic method for optimizing the time delay unit architecture (TDU-A) of a phased antenna array (PAA) is introduced. The problem is cast in the standard form of integer linear programming optimization with an objective function that targets minimizing the total number of TDUs within the RF fan-out while maintaining phase error and manufacturability constraints. The presented optimization method can reduce the cost, power, and complexity of a broadband PAA in contrast to prior methods that converge on a manufacturable architecture without considering the total number of TDUs. Three optimization examples are presented with a requirement of a maximum of 5° phase error. These examples clearly show that there are many TDU-As that can satisfy the phase error requirement, yet only one architecture is superior by exhibiting the minimum number of TDUs. The superior architecture is highly likely to be missed in a traditional design approach that places the TDUs in the RF fan-out as close as possible to the antenna elements if the presented optimization approach is omitted. [ABSTRACT FROM AUTHOR]

In this article, a technique to obtain a high-gain multibeam antenna for millimeter-wave (mmW) fifth-generation (5G) base stations (BSs) is proposed using the Fabry–Pérot Cavity (FPC) structures. A thin single metallodielectric layer is used as the partially reflective surface (PRS) layer to enhance the radiation performance of the FPC antenna (FPCA) and provide an off-axis pencil beam. As the feeding structure illuminating the PRS layer, a cylindrical cavity is designed using a right-angle-type semi-waveguide (RATSW) structure. An array of coaxial probes is used to obtain beam switching at the azimuth plane by exciting different probes. To confirm the functionality of the proposed FPCA, a prototype is fabricated with five coaxial probes to generate five radiation beams; however, the structure can be extended to provide more antenna beams using higher number of probes. The cavity structure of the proposed antenna is fabricated by the 3-D printing technology as an easy manufacturing process. The measurement results show that multiple switchable beams with high antenna gain are obtained over the desired frequency bandwidth of 27–30 GHz. The maximum measured gain is 19 dBi at 27.5 GHz when a single probe is excited. A conceptional scenario for the potential applications of the proposed antenna in the 5G BSs is presented. [ABSTRACT FROM AUTHOR]

This article presents 3-D printed metal-only dual-band millimeter-wave circularly polarized (CP) reflectarrays (RAs). The RAs’ unit cell (UC) is made of an anisotropic metal brick mounted on a full metal ground. In-plane rotating the metal brick introduces geometric Pancharatnam–Berry (PB) phase shifting, and vertically adjusting the position of the UC provides propagation phase shifting. The geometric PB and propagation phase shifting offer two different degrees of freedom, enabling independent wavefront shaping of CP wave over dual-band. Specifically, the low-band CP beam shaping solely depends on the propagation phase. In contrast, the high-band CP beam shaping depends on the geometric PB and the propagation phases. The coupling issue between dual-band is minimal because of the unique dual-band phase-shifting methods. In addition, 3-D printed dual-band left-hand CP (LHCP) horn antennas are designed, printed, and used as the feed. To demonstrate, two RA antennas with different dual-band CP beam directions are fabricated and measured. [ABSTRACT FROM AUTHOR]

We propose an RF front-end architecture with simultaneous direct antenna modulation and beam steering capability based on space-time-coding (STC) arrays. In an STC array, digital codes control the state of each array element. The element state determines the amplitude and phase of the radiated wave, and in a time scale over which the state of the elements is changed by a few successive codes, the frequency harmonics are generated. We first introduce a vector representation of bits in a code and their effects on the resultant harmonic wavefront. We show that by choosing proper codes with a minimum of two repetitions, one can modulate data on the phase and amplitude of a desired far-field harmonic where proof-of-concept simulations are given for a 16-APSK digital modulation scheme. We investigate the data rate, spectral efficiency, and the limitation of switching speed in our proposed scheme. Moreover, it is shown that the harmonic beam patterns of an STC array can be easily steered by a consecutive shifting of bits in the code without affecting the transmitted data symbols. Through cosimulation of digital design and coded antenna array, we calculate the constellation of the QPSK digital modulation scheme for a steered beam and study its angular dependency. Finally, we provide an upper bound for the efficiency of STC arrays. [ABSTRACT FROM AUTHOR]

Angle of arrival (AoA) for target echo signal detection is crucial in vehicular radar systems, where the estimation of signal parameters via rotational invariance (ESPRIT) provides a high-resolution estimation. A subarray decomposition strategy is presented in this article to create two ESPRIT antenna arrays with enhanced echo signal strengths, applicable to multi-input–multioutput (MIMO) operations for creating a large virtual array. The concept intends to maximize the echo signal’s strength with minimum signal interferences by increasing the aperture sizes of the two ESPRIT antenna arrays. The decomposition produces two virtually overlapped subarrays to increase the subarray aperture sizes in the spatial or spectral representations. It is applied to the MIMO-based arrays for two-way radiation patterns for ESPRIT estimation of AoA. Numerical simulation examples are shown to validate the feasibility and demonstrate the applications. [ABSTRACT FROM AUTHOR]

This article presents a novel metamaterial-inspired, miniaturized, vertically polarized (VP), pattern reconfigurable dielectric resonator (DR) antenna/phased array for sub-6 GHz fifth-generation (5G) beam-steering applications. The proposed antenna is miniaturized by creatively loading the mushroom structure on the DR, and the beam steering/scanning function is realized using a pattern reconfigurable configuration. Owing to the extra loading capacitance and inductance from the VP mushroom, the resonance frequency of the DR shifts to the lower region. Based on the classical Huygens radiation principle and image theory, a novel miniaturized Huygens form with a tilted pattern is developed. Then, by exploring a switchable magnetic current source, a pattern reconfigurable Huygens design is proposed and studied. For verification, a pattern reconfigurable DR antenna with eight beams and a low-cost 4 $\times4$ wide-angle beam-scanning phased array using the reconfigurable DR cells for 5G microcell and macro-base station demands are fabricated and measured, respectively. The measured −10 dB impedance bandwidth and peak gain are 3.30–3.75 GHz (12.8%) and 4.8 dBi, respectively. Also, the proposed 2-D phased array can scan up to ±60° and supports a 3 dB beam coverage up to ±80° in each region. The proposed beam-steering antenna/array is a promising candidate for 5G microcell and macro-base station applications. [ABSTRACT FROM AUTHOR]

A novel metamaterial-loaded, miniaturized, broadband, wide-beam dielectric resonator (DR) antenna is presented for low-cost wide-angle beam-scanning applications. The mushroom structure is loaded on the DR structure, so the proposed DR radiator reduces the size reduction (low profile, $0.09\lambda _{0}$) and achieves a broadened bandwidth with a dual-mode response. The realized 3 dB beamwidth of the DR radiator is widened from 90° to 194° by introducing a pair of miniaturized equal-amplitude and out-of-phase Huygens sources. Owing to its compact size and wide beamwidth, a five-element low-cost wide-angle beam-scanning phased array is presented by using the proposed wide-beam DR elements. The measured −10 dB impedance bandwidth covers the 5G-78 band well (3.30–3.80 GHz, 14.1%). The realized scanning angle of the fabricated linear array can be extended from ±36° to ±65°, and its 3 dB beamwidth scanning coverage can up to ±90°. In virtue of miniaturized size, wideband, low cost, and good beam-scanning ability, the presented element, and the resulting wide-angle beam-scanning array are promising candidates for wireless communication and low-cost phased array applications. [ABSTRACT FROM AUTHOR]