A co-aperture dual-band linearly polarized slot array based on ridge gap waveguide (RGW), operating at the 74-78- and 102-106-GHz bands, is designed. In each subarray, two groups of longitudinal slots for two frequency bands are excited by a single RGW channel to achieve dual-band unidirectional radiation. Additionally, grooves and notches are implemented inside the RGW structure to improve dual-band matching, and two bandpass filters (BPFs) are incorporated at each side of the subarray to realize independent dual-band feeding while also providing filtering characteristics. The proposed subarray operates as a single channel. It can expand into a multichannel array, enabling multiple-input multiple-output (MIMO) when each subarray is individually excited or broadside radiation when all subarrays are simultaneously excited. A planar array of four subarray columns was fabricated to validate the dual-band concept and its broadside radiation performance. The simulated and measured results show good agreement.

An all-metal 3D-printed circularly polarized (CP) Ka-band phased array is presented. Each array element consists of a square waveguide with parallel double ridges, while the radiating aperture incorporates a stepped profile along the x-axis and a notched structure along the y-axis. These features generate two orthogonal field components with nearly equal amplitudes and a 90° phase difference in the xoz- and yoz-planes, resulting in right-hand circular polarization (RHCP). The element is excited through a Subminiature screw mount probe (SSMP) connector. To alleviate the coupling effects inherent in array operation, the height difference between the parallel double ridges is a key design parameter and is systematically investigated. Experimental validation is performed using two phased-array prototypes: one fabricated by computer numerical control (CNC) machining and the other by metal 3D printing. The array achieves beam scanning up to ±60° over 27.5–31 GHz, with moderate axial-ratio degradation near the scan limit. In addition, thermal analysis demonstrates the improved heat-dissipation capability of the 3D-printed prototype, highlighting its potential for compact Ka-band satellite communication (SATCOM) phased-array front ends.

This study introduces a novel, optically transparent, and passive smart electromagnetic skin (EMS) designed for millimeter-wave 5G signal redirection to enhance coverage in dense urban environments of smart cities. The proposed EMS targets 5G frequency bands n258 (24.25 GHz to 27.5 GHz) and n257 (26.5 GHz to 29.5 GHz), utilizing transparent indium tin oxide (ITO) conductive films with a sheet resistance of 2.5 Omega/sq, deposited on soda-lime glass substrates. The structure comprises a 40 x 40 array of subwavelength ITO unit cells, each capable of providing a full 0 degrees to 360 degrees reflection phase shift. The array features periodicities of 0.42 lambda at 26 GHz and 0.45 lambda at 28 GHz, with total dimensions of 200 mm x 200 mm x 2.1 mm. A case study demonstrates the EMS's ability to redirect incident 5G signals, establishing a virtual line-of-sight link between a hypothetical base station located 10 m away at a 15 degrees incidence angle and mobile users positioned at a 37 degrees reflection angle. Both simulation and experimental results confirm stable and efficient signal redirection across the 24 GHz to 30 GHz band, maintaining a consistent reflection angle of 37 degrees +/- 3 degrees. Furthermore, the EMS achieves a measured optical transparency of 73.7% in the visible spectrum (380 nm to 760 nm), allowing near-invisible integration onto urban surfaces such as windows without requiring any external power source.

Dense direct-current (DC) bias routing and numerous radio-frequency (RF) choke inductors pose major challenges to the practical implementation of phase-shifter-free beam steering using PIN-controlled phase switching. To address this issue, a compact vertical DC biasing network is proposed, in which most DC bias lines are routed beneath the ground plane. The DC signals are fed to the PIN diodes through vertical bias lines passing through metallized vias in the dielectric substrate. This arrangement reduces routing congestion and simplifies array-level bias integration. The number of required RF choke inductors is decreased from 112 to 22 per dual-polarized element while preserving the required beam-steering functionality. For experimental validation, a 1 × 3 prototype operating at 3.5 GHz is fabricated and measured. The measured beam directions of −14°, 0°, and +14° agree well with simulations, confirming that the proposed bias network provides the phase control required for beam steering. The proposed network, therefore, offers a compact, low-complexity, and practical solution for scalable phase-shifter-free beam-steering systems.

A scalable measurement setup for PCB-based, wide-scanning phased arrays operating in the SATCOM Ka-band $(27.5-31 \text{GHz})$ is designed. This setup addresses the critical challenges of dense element spacing in dual-polarization configurations as well as the non-ideal performance of commercial surface-mount device (SMD) resistors at millimeter-wave frequencies. The measurement setup uses SMD connectors and resistors, eliminating the need for additional fixtures and/or PCB conductor layers. The footprint required for the connector transition is minimized by shaping the connector pad, reducing the number of pad-grounding vias needed, and increasing the flexibility in connector pad placement. Miniaturized terminations using SMD resistors are designed by co-simulating transmission lines, grounding vias and resistor equivalent models. The designed terminations and transition are used in the fabrication of phased array prototypes. Test boards for the transition and terminations are fabricated and their S-parameters measured. The measurement results validate the repeatable performance of the designed components.

An 8 x 8 antenna array composed of 2 x 2 printed patch antenna subarrays is designed for dual-band operation in the K- and Ka-bands, at 24 and 28 GHz, respectively. The key features of the design are a diplexer-splitter integrated with the feed network and a wideband subarray. The feed network is designed using inverted microstrip gap waveguide (IMGW) technology, simplifying manufacturing while still achieving low losses, and the radiating layer is also made using printed technology. The antenna achieves a realized gain of more than 25 dBi across the two bands, making it suitable for 5G networks and other high-frequency applications that require efficient and flexible dual-band operation. Experimental validation shows good agreement with the simulated results. This is the first example of an antenna designed using gap aveguide (GW) technology on a PCB with no grounded vias in either the feed network or the radiating layer.

A dual-circularly polarized (D-CP) low-profile folded reflectarray (FRA) capable of simultaneous 2-D beam scanning is proposed. The FRA consists of a planar feed embedded within the lower reflectarray (RA) and an upper spin-decoupled circularly polarized selective metasurface (CPSM). The RA is responsible for the beam deflection, whereas the spin-decoupled CPSM imparts opposite phase gradients to the left-hand and right-hand circular polarization (LHCP and RHCP) waves and consequently produces D-CP beams. Leveraging its polarization selectivity, the CPSM effectively reduces the antenna profile to half the focal length of the RA. Furthermore, based on the Risley prism principle, simultaneous D-CP 2-D beam scanning is achieved by appropriately rotating both the RA and CPSM. To validate the design methodology, a prototype operating at X-band is fabricated and characterized. The measured results indicate that the FRA can achieve satisfactory beam scanning of +/- 42 degrees in the elevation plane and 0 degrees-360 degrees in the azimuthal plane for both LHCP and RHCP beams. Additionally, a total peak aperture efficiency of 37% is achieved during beam steering.

We present a comprehensive review of computational optimization techniques for the design of RF circuits. Important design techniques used to optimize RF circuits, such as genetic algorithms (GAs), particle swarm optimization (PSO), reinforcement learning (RL), Bayesian optimization (BO), and space mapping (SM), are discussed. The basics of the techniques, their merits, and their drawbacks are covered so that new researchers can understand the relevant theories of the techniques. A comparative analysis of design techniques is included. This article also provides insights into the present state and future directions of the optimization techniques.

Fully isolated crossover equivalent (FICE) models septum polarizers (SPs) in the back-to-back (BTB) configuration, representing their symmetric crossover behavior as a perfectly isolated equivalent. The underlying linear interdependence among the FICE’s scattering parameters facilitates the exact retrieval of a single unit S-matrix. SP terminated with high-reflective loads is presented as a virtual BTB setup, enabling the theoretical derivation of the FICE using a single SP unit. The proposed technique considers all critical parameters, thereby avoiding limitations in the present BTB-based analyses with reduced measurement requirements, a simple retrieval procedure, and provides accurate and comprehensive retrieved functionality. Full-wave validation examples are provided and compared with the state-of-the-art techniques. The proposed technique is experimentally validated and compared with recent methods using a broadband SP with an irregular common port cross section.

This work introduces a dual-polarized (DP) slot-excited dielectric-filled cavity antenna phased array designed for 5G and beyond antenna-in-package (AiP) solutions using low-temperature co-fired ceramic (LTCC) technology. The primary challenge is to maximize a 2-D beamsteering range with a compact form factor in a DP operation. Most reported LTCC AiP arrays have <= 55 degrees beamsteering range at 5G mmWave frequencies and lack experimental validation for DP 2-D beam-steering operation. In contrast, the proposed antenna element in the infinite array enables +/- 60 degrees 2-D beamsteering in the 5G n261 (27.5-28.35 GHz) band with the form factor as small as 5 & times; 5 & times; 1.3 mm. This performance is achieved by introducing a wide-angle impedance matching (WAIM) structure directly at the antenna aperture, comprising a dual-layer metasurface formed by periodically arranged electrically small patches in a staggered configuration. The antenna is jointly optimized with a DP feeding network to minimize parasitics in the multilayer LTCC stack and a co-integrated printed circuit board (PCB) carrier to mitigate package-carrier coupling often neglected in previous works. It is fabricated in a single LTCC process without air gaps to ensure precise layer-to-layer alignment and eliminate losses from additional support structures inherent to conventional air-gap WAIM stacks. A custom equivalent-circuit model enables efficient analysis of scan-dependent impedance matching for the optimization. A 128-element AiP prototype employs 4 & times; 4 subarrays of four DP elements on the PCB carrier and is packaged with ball grid arrays (BGAs) to facilitate integration. This modular approach allows scaling to large arrays while considering the critical effects of the package stack-up and DP feeding. The simulated active reflection coefficient is < -8.5 dB within +/- 60 degrees (with a scan loss marginally above 3 dB) at 27.5-29.5 GHz. Measurements confirm simulations for all relevant performance metrics in +/- 60 degrees 2-D range.

A compact, efficiency-enhanced feed architecture is proposed for 140-150 GHz for continuous-transverse-stub (CTS) arrays. The design cascades four hard-wall feed channels, each realized with artificial magnetic conductor (AMC) boundaries to produce a uniform aperture distribution (magnitude and phase) across a center-fed aperture, thereby eliminating the need for a large corporate divider network. This architecture can reduce the number of power dividers in the feeding network resulting in a reduction of the insertion loss and gain improvement. The proposed feed has amplitude and phase balance of $\boldsymbol{\pm} \mathbf{1. 5 ~ d B}$ and $\boldsymbol{\pm} \mathbf{1 2}^{\boldsymbol{\circ}}$. When the proposed feeding is used to excite the CTS subarray, a realized gain of 27.8 dBi with radiation efficiency above 82% is achieved for gold plated structure with surface roughness of $\mathbf{0. 9} \boldsymbol{\mu} \mathbf{m}$. The fully metallic AMC structure ensures low ohmic loss and simple fabrication without dielectric loading or precision alignment. The proposed compact, low-loss feed is scalable to realize high-gain antennas for sub-THz band.

The discovery of high-magnetization soft ferrites is highly beneficial for a wide range of applications supporting satellites and radar systems by enabling nonreciprocal microwave devices to efficiently operate at millimeter-wave and sub-terahertz frequency spectrums. However, the maximum available ferrites in the microwave and space industries have a magnetization saturation of approximately 5300(G), which limits the development of nonreciprocal microwave devices above 40 GHz. Here, we investigate a soft ferrite disk with a high magnetization 4πMs exceeding 11250(G), which is more than double that of the currently commercially available materials in the microwave and space industries. The high saturation magnetization of a Nickel-Zinc ferrite Ni0.5Zn0.5Fe2O4 powder is achieved by heating at 1100 °C for 4 h in a Nitrogen + 3% H2 gas environment. The magnetic and structural properties are demonstrated by X-ray diffraction (XRD) and vibration sample magnetometer (VSM), which show a high magnetization saturation of 174 emu/g. Later, electromagnetic investigations using the Vector Network Analyzer (VNA) exhibit a loss tangent of 0.00115 and a dielectric constant of 14.5. This newly proposed fabrication technique for producing Nickel-Zinc ferrites will mark a significant breakthrough in the microwave and space industry supporting various future applications in the millimeter-wave spectrum.

Advanced wireless integrated systems are highly based on Printed Circuit Board (PCB) technology. Thus, antennas should be designed based on the same technology for full and straightforward integration with these systems. On the other hand, antennas with waveguides and metallic feeds are very bulky and hard to integrate with PCB-based solutions, as they require complex transitions that increase the system cost and losses. Therefore, we shed the light and review thoroughly the challenges and the main strategies and techniques used to design low-cost, high-gain PCB-based antenna solutions for sensing and Internet of Things (IoT) millimeter-Wave (mm-Wave) applications. Several crucial techniques to counter the design impairments of PCB antennas at mm-Wave frequencies are discussed, this includes: (1) The utilization of diffracted fields to increase the main radiating element gain, and reduce the feeding network size. (2) The utilization of Microstrip Line (MSL) radiation losses to implement high gain radiating antenna elements. (3) The utilization of high characteristic impedance lines to feed antenna array elements, and reduce drastically the radiation effects of the feeding network. (4) The utilization of superstrates and polarizers to enlarge the elements spacing in an array configuration, and enhance the gain and side-lobe level performance. An elaborate design and analysis example of a packaged printed feed with symmetric radiation characteristics is detailed out, capitalizing on the advantages of such feed as a replacement for horn antennas and open-ended waveguide feeds for lenses and reflectors.

Part II investigates phase modulation as a low-complexity alternative to conventional phase shifters in pattern-reconfigurable antenna (PRA) arrays. In the proposed architecture, phase formation originates from the direct reconfiguration of the driven radiation current and the induced parasitic current within each radiating element. This is achieved through a dual-phase control mechanism that independently tunes the intrinsic and deflection phases using separately biased PIN diodes integrated into the feeding branches and parasitic comb structures. The resulting discrete phase states (PSs) provide a phase tuning range of up to 116 degrees and enable subarray-level beamforming without continuous elementwise phase synthesis. Based on this concept, a six-element discretized subarray is developed as the fundamental beamforming unit, offering three fixed beam states with simplified bias control. By adopting subarray-level beam-state selection, an 8 x 24 sparse dual-polarized array is constructed, enabling wide-angle 2-D scanning (+/- 60 degrees azimuth, +/- 10 degrees elevation) while significantly reducing the number of RF chains. Despite the reduced channel count, the proposed architecture maintains comparable channel capacity, as validated through simulations and measurements, demonstrating its practicality for large-scale base station (BS) antenna arrays.

A unified reconfigurable array architecture is proposed, supporting two-phase modulation mechanisms: element rotation and initial phase modulation. Both approaches enable subarray-level beam steering without needing phase shifters or complex feeding networks, facilitating large-scale array beam scanning with fewer radio frequency (RF) channels. An innovative beamforming method is introduced in part I, leveraging element rotation within an Ns-element (six-element) linear subarray. Vertical partition scanning within +/-theta(max) (+/- 10 degrees) is achieved by presetting the tilt angles of the elements in the N-s-element sub-array (six-element). A longer linear array of Ny-elements formed by M-s-subarrays is formed (Ny = M-s & times; Ns). A high-profile Nx & times; Ny array (8 & times; 24) of Yagi elements achieves 2-D beam scanning at 4.5 GHz with a grating lobe suppression algorithm. To generalize this approach, a theoretical framework is established that incorporates concepts such as phase smoothing region, deflection phase, intrinsic phase, and initial phase modulation, ultimately extending the rotation-based method into a universal initial phase control scheme. Simulation and measurement results confirm that replacing conventional small-ratio power dividers with 1-to-Ns equal-dividers preserves low sidelobe levels (SLLs) in vertical scanning, maintains original horizontal scanning performance, and achieves channel capacity parity with full-channel systems. Part II will further validate the approach by designing and implementing a dual-polarized base station antenna element with electronically tunable initial phase control.

A large-scale parallel strategy for the finite-difference time-domain (FDTD) method on heterogeneous architectures is presented. A multilevel cooperative parallel framework is developed on heterogeneous accelerator platforms to improve load-balancing efficiency and intersubdomain communication efficiency. An asynchronous remote communication optimization strategy based on temporal updates is proposed to address the high communication intensity of FDTD. With the multilevel cooperative parallel framework, load-balancing efficiency is improved by approximately 40% in weak scaling tests, and a maximum acceleration ratio of about $2\times $ can be achieved as the number of nodes increases. With the asynchronous remote communication optimization, the communication overhead is reduced from 69% to 11%, and a maximum acceleration ratio of $2.49\times $ is achieved. Finally, the combined optimization strategy is validated through electromagnetic scattering simulations, demonstrating that the algorithm sustains approximately 61% strong-scaling efficiency when scaling from 2800 processes (1.15 million cores) to 28 000 processes (11.5 million cores) on the Tianhe supercomputing platform.

This study addresses the challenge of balancing high hardware cost and radiation performance in a hemispherical circularly polarized conformal phased array by proposing an innovative optimization design method based on zoning and hybrid grouping strategies. The design employs a 10-layer concentric ring topology with a radius of 3.2λ₀, comprising 272 elements. By introducing the maximum local scan angle αmax as a dynamic partitioning criterion, the array is divided into a main excitation region (MER) containing high-activation-frequency elements with independently configured (transmit/receive) T/R modules, and a sub-excitation region (SER) containing low-activation-frequency elements with shared T/R modules. For the SER, two novel grouping strategies are proposed: the same-layer different-sector grouping method (applicable for αmax ≤ 50°) and the layer-sector hybrid grouping method (effective up to αmax = 70°), achieving optimized antenna T/R module matching. Results demonstrate a 33% reduction in T/R modules (from 272 to 180) while maintaining a -20 dB sidelobe level (SLL). The layer-sector hybrid scheme achieves optimal performance at αmax = 65°, improving gain by 1.35 dBi compared to a conventional 180-element array. Fault analysis validates the design’s robustness, confirming stable sidelobe suppression even with up to 20% T/R module failures. This work provides a cost-effective methodology for wide-angle scanning systems, highlighting its potential in satellite radar and airborne communications.

This article introduces a novel metasurface design methodology that achieves wideband, polarization-insensitive, and angle-stable radar cross section (RCS) reduction by leveraging a phase distribution inspired by the Ackley function, applied for the first time in electromagnetic scattering control. The proposed Ackley function-based phase profile is inherently frequency-independent and mimics quasi-random phase coding, resulting in strong diffusive scattering across a broad frequency range. Notably, the design process eliminates the need for time-consuming optimization algorithms and the computer resources typically required for RCS reduction metasurfaces in the literature, enabling fast and efficient implementation. A single-layer metasurface prototype is developed with a 0°–360° Ackley function-based phase profile. Simulated and measured results demonstrate more than 10 dB of RCS reduction from 12 to 32 GHz under the incidence of far-field radar waves of linear and circular polarization, confirming their polarization-insensitive behavior. Moreover, the Ackley metasurfaces maintain a consistent 10-dB RCS reduction fractional bandwidth of 90% and up to 75° in azimuth and elevation planes, showcasing exceptional angular robustness.

Signal degradation at handheld terminals within base station coverage areas often arises from conventional sector antenna arrays that lack beam-shaping capability and therefore have nonuniform signal strength over the target coverage. To address this issue, this letter presents a planar antenna array operating at 3.5 GHz in the 5G N78 band, designed based on the extended method of maximum power transmission efficiency to synthesize a 3-D radiation pattern with combined cosecant-squared (CSC2) and flat-top characteristics. In the target region, testing point sources are introduced with weighting coefficients for both the main-beam shaping and sidelobe suppression. Using this approach, the fabricated antenna array achieves a CSC2 beam in the elevation plane with a -15 dB gain decrease over 30 degrees coverage, a ripple below 0.7 dB, and sidelobe levels less than -24.1 dB, while simultaneously producing a 60 degrees flat-top beam in the azimuth plane with only 0.7 dB gain fluctuation. The measured results show good agreement with simulations, validating the effectiveness of the proposed design for precise 3-D beam-shaping in 5G base station applications.

A novel circularly polarized (CP) wideband high-gain reflectarray antenna (WHG-RA) is designed to cater to the requirements of future vehicle-to-everything (V2X) communication links. The WHG-RA offers a gain bandwidth spanning from 12 GHz to 32 GHz, encompassing crucial V2X frequency bands, including vehicle-to-satellite (V2S) Ku/Ka downlinks and uplinks frequencies (12.25 GHz to 12.75 GHz, 14.0 GHz to 14.5 GHz, 19.6 GHz to 21.2 GHz, and 29.4 GHz to 31.0 GHz), the 24.25 GHz to 26.65 GHz range designated for vehicle-to-vehicle (V2V) short-range radars, and all 5G millimeter-wave spectrums, such as n258 (24.25 GHz to 27.5 GHz) and n257 (26.5 GHz to 29.5 GHz), intended for vehicle-to-5G networks (V2N) links. The design of the wideband unit cell within the WHG-RA is rooted in a rotational technique grounded in geometric phase theory and has multiple resonances. As a proof-of-concept, a 180 mm x 180 mm planar WHG-RA consisting of 900 unit cells is designed, fabricated, and rigorously tested across the 12 GHz to 32 GHz frequency range. Both simulation and measurement results affirm the WHG-RA's prowess, showcasing consistent radiation patterns, a commendable peak aperture efficiency (41.1%), a high gain of 30.3 dBi, and sidelobe levels (<-17.2 dB) averaged over 12 GHz to 32 GHz, offering a substantial 3 dB and 4 dB gain bandwidths of 51% and 91%.