Marianna V. Ivashina

This paper presents a compact dual-band substrate integrated waveguide-to-rectangular waveguide frequency-selective transition (FST). This FST is a key enabler of future dual-band systems, such as automotive radar operating at 77 GHz and 130 GHz. The proposed structure enables efficient signal routing from a single beamforming integrated circuit to two separate antenna arrays, leveraging waveguide-based filtering for high-frequency integration. A vertical transition topology is adopted to enhance mechanical robustness and to simplify assembly. This robustness is validated by performing a sensitivity analysis on the assembly. The structure is fabricated using aluminum-based laser powder-bed fusion, enabling monolithic integration of complex millimeter-wave features. Experimental results demonstrate insertion loss around 2.5 dB for the low and high bands of the FST, with measured isolation exceeding 30 dB in the high band. The results validate the feasibility of the proposed FST and highlight the impact of manufacturing tolerances on millimeter-wave performance. This work contributes a scalable, low-loss packaging solution for dual-band radar front ends in next-generation automotive and 6G sensing applications.

We present a W-band (92–96 GHz) electronically steerable reflector antenna system for 6G backhaul that cointegrates a GaAs multi-channel transmitter (Tx) with a compact waveguide focal-plane array (FPA) via a quasi-optical multi-input feeding network (QOFN). Unlike conventional architectures that separate power amplifier (PA) power combining and beamforming into distinct modules, or switch a single PA among QOFN inputs, the proposed QOFN simultaneously combines the power of all PAs while synthesizing the required FPA excitation for electronic beam steering. This eliminates a separate lossy switch/combiner stage and equalizes per-channel power, critical for maintaining high Tx efficiency. Methodologically, we develop an active-system modeling framework that extends conventional passive antenna array formulations by incorporating PA output mismatch effects, channel-to-channel variations, and discrete phase-shifter states into the beam synthesis. The formulation yields closed-form realized-gain and EIRP (Effective Isotropic Radiated Power) maximization solutions under realistic PA constraints. To compensate for mast swaying, a rim-extended offset parabolic reflector is co-designed with the FPA, providing ∼ 50 dBi gain with ETSI Class 3 sidelobe mask compliance over a 2-half-power-beamwidth 2-D steering range. A prototype with six Tx PAs shows that across 92–96 GHz and multiple beams, the minimum measured EIRP is ≥ 75 dBm, the on-axis beam reaches ∼ 80 dBm, and the QOFN insertion loss is 2.3–3.7 dB. The results experimentally validate a unified architectural and modeling approach to high-EIRP W-band backhaul transmitters, demonstrating a compact and scalable alternative to large silicon-based phased arrays that typically peak near 60 dBm EIRP.

This work presents a machine-learning-driven framework for designing single- and dual-polarized, four-port MIMO antennas for in-band full-duplex (FD MIMO) operation. A symmetry-constrained, pixel-based layout enables efficient exploration of the design space. A multi-task convolutional neural network (CNN) surrogate is trained to jointly predict return loss and multi-port coupling from symmetric pixel layouts, accurately modeling the amplitude of the $4\times 4$ S-parameter matrix across 5–8 GHz. By embedding this surrogate within a binary genetic algorithm, the framework synthesizes antenna layouts that simultaneously achieve impedance matching and high inter-port isolation across the operating band. Fabricated prototypes show close agreement with predictions and simulations, achieving a return loss greater than 10 dB, isolation up to 36.25 dB, and realized gain of 7.7 dBi at 6.2 GHz. Unlike prior multi-port designs, the approach delivers low loss and robust isolation without relying on additional decoupling structures such as defected ground planes, resonators, or stacked patches, establishing a scalable methodology for next-generation FD MIMO antenna systems.

This work introduces a dual-polarized (DP) slot-excited dielectric-filled cavity antenna phased array designed for 5G and beyond AiP solutions using low-temperature co-fired ceramic (LTCC) technology. The primary challenge is to maximize a two-dimensional (2-D) beamsteering range with a compact form factor in a DP operation. Most reported LTCC AiP arrays have ≤ 55° beamsteering range at 5G mmWave frequencies and lack experimental validation for DP 2-D beamsteering operation. In contrast, the proposed antenna element in the infinite array enables ±60° 2-D beamsteering in the 5G n261 (27.5-28.35 GHz) band with the form factor as small as 5mm×5mm×1.3mm. 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 4×4 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° (with a scan loss marginally above 3 dB) at 27.5-29.5 GHz. Measurements confirm simulations for all relevant performance metrics in ±60° 2D-range.

Fast optimization of arbitrary-shaped antennas is enabled by a neural network model, trained by a Method of Moments (MoM) framework capable of evaluating large sets of pixel-based antenna metal layouts. The MoM matrix equation is constructed once for a fully metalized pattern. Matrix rows and columns are selectively removed to reflect the absence of metal pixels. Fixed regions, such as the ground plane, dielectric, and meshed port are accounted for through the Schur complement. Using this framework, a dataset of 2,000,000 antenna configurations is generated in 19 hours—a speedup of 13.5 times compared to a plain MoM approach. Meshing is done only once, as opposed to commercial solvers, including meshing the speed advantage is 270 times. A convolutional neural network is trained on this dataset and combined with a genetic algorithm to synthesize various triple-band Wi-Fi 7 antennas, which are experimentally validated. These results demonstrate the realworld applicability of the proposed MoM framework for MLbased optimization of arbitrary-shaped antennas

This paper presents a reconfigurable intelligent surface (RIS) unit cell (UC) with independent amplitude-phase control, crucial for complex field shaping in RIS-assisted over-the-air testing. Unlike conventional phase-only tuning UCs, the proposed design enables continuous control from reflective to absorptive states for advanced field synthesis. To quantify reconfigurability, we introduce a generalized complex-plane representation, termed Γ-coverage, mapping both amplitude and phase over all bias states. For the first time at millimeter-wave frequencies, a loop-embedded end-folded UC integrating a forward-biased p-i-n diode and a reverse-biased varactor diode is developed to maximize Γ-coverage. The UC achieves a 0–0.5 amplitude tuning range (equivalent to a controllable loss from complete attenuation to 6 dB) and a −180°–+180° phase tuning range at 28 GHz. The maximum incident angle reaches 45° within ±48° phase fluctuations, extending to 60° with full-phase tuning under a 12 dB loss criterion. We derive empirical circuit models for both diodes to account for high-frequency parasitic effects and formulate a semi-analytical UC equivalent circuit model. The UC prototype is evaluated using a waveguide simulator. The operational bandwidths for reconfigurability are 25.8–28.0 GHz with a relative Γ-coverage area exceeding 25%, and 26.5–27.7 GHz for 360° phase control with 8.4–12 dB losses. The instantaneous bandwidth for stable operation spans 27.3–27.7 GHz, maintaining ±50° phase fluctuations within 5.6–13.4 dB losses. The UC is analyzed in an RIS-assisted near-field plane-wave generation scenario for a compact antenna test range (CATR), achieving high field uniformity (< 0.6 dB and < 2.5° errors). Despite intrinsic UC losses, the RIS-based CATR reduces total system loss by 22.8 dB compared to a far-field test range.

We introduce a novel joint transmit (Tx) and receive (Rx) beamforming method and relevant performance metrics for in-band full-duplex (IBFD) antenna systems, addressing two major challenges: self-interference (SI) leakage from the transmitter to the receiver and non-linear gain compression in the receiver's low-noise amplifiers (LNAs). Conventional methods treat Tx and Rx beamforming separately, often failing to balance SI suppression with sufficient Tx gain. In contrast, our approach achieves two key objectives. First, it maximizes Tx array antenna gain while ensuring that SI at the LNA input remains below a predefined threshold, preventing saturation and maintaining linearity. Second, it suppresses residual SI at the receiver output, improving the signal-to-SI ratio by effectively separating the desired signal from residual interference. This method is validated using a commercial RF system-on-chip evaluation board and 3×5 Tx and Rx Vivaldi antenna arrays operating in the 3–6 GHz band. Experimental results show that the conventional Tx maxGain beamformer achieves approximately 22 dB isolation between closely spaced Tx and Rx arrays. In contrast, the proposed Tx beamforming method provides over 45 dB isolation, with a Tx array gain of up to 10 dBi. Overall, the joint Tx-Rx beamforming method achieves more than 80 dB isolation with a 10 dBi Rx array gain for the IBFD system, representing a significant improvement over conventional methods.

This work presents a novel W-band ( $92-96$ GHz) focal plane array (FPA) for 50 dBi-reflector antennas intended for the next-generation point-to-point communication links with antenna mast sway compensation. The FPA comprises seven metal waveguide elements arranged in a hexagonal lattice, ensuring the cross-over level of the corresponding reflector beams above $-6$ dB. The primary challenge of this design is to realize efficient illumination of the reflector for the on-axis and off-axis beams, while keeping a minimum beamforming complexity (i.e., one element per beam) and overcoming array implementation challenges associated with high frequencies. This is accomplished by (i) a high decoupling level of the FPA elements ( $< -24$ dB) and shaping their individual element patterns via a dedicated aperture pin structure between them; and (ii) encircling the FPA aperture with a periodically perforated choke ring pair to further improve the illumination by off-set elements. The FPA performance, evaluated on an offset parabolic reflector with $F/D=0.35$ , exhibits $52-68\%$ efficiency, close beam overlap, and good impedance matching. Measurements of the FPA prototype verify the results for all characteristics; the latter are competitive with state-of-the-art solutions.