Recent Articles
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A Robust Machine Learning Approach to Path Loss Prediction for a Low Altitude UAV-to-Ground Urban Scenario
24 June 2026 Achilleas Theocharopoulos, Nektarios Moraitis, Athanasios D. Panagopoulos present a machine learning-based approach for the prediction of path loss of a 2×2 dual-polarized (DP) multiple-input-multiple-output (MIMO) channel. The communication scenario takes into account the link established between an unmanned aerial vehicle (UAV) and a ground terminal in an urban environment. The proposed machine learning (ML) methodology is thoroughly analyzed, giving particular emphasis on the hazards induced by the sequential nature of the measurement procedure. It is demonstrated that, due to the temporal correlation between the data samples, the conventional random splitting of the dataset leads to substantial overfitting and a biased performance evaluation. To counteract this issue, an alternative partitioning scheme that is based on continuous trajectory segments is proposed and statistically validated.
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A Millimeter-Wave Flat-Top Fan-Beam Antenna Array Based on a Geometry-Independent Resonant Cavity
15 June 2026 Evandro C. Vilas Boas, Sofia B. De Vasconcellos, Arismar Cerqueira Sodré, Felipe A. P. de Figueiredo present a novel antenna design capable of producing a flat-top fan-beam profile through the integration of slotted apertures and a geometry-independent resonator. Starting with a three-slot cavity-backed design, the radiator is reconfigured into a five-slot structure by reshaping its geometry while preserving the original cross-sectional area, converting a pencil beam into a fan-shaped beam without shifting the resonant operating frequency. The cavity is loaded with an FR4 dielectric slab to achieve impedance matching, and metallic rods are placed around the slab to suppress undesired mode coupling. In addition, a stepped profile is utilized around the slot apertures to increase the flat-top beamwidth. The prototype exhibits a measured −10 dB bandwidth over 1.11 GHz, a 1 dB beamwidth directivity with ripple below 0.71 dB over 60∘ −70∘ , a 3 dB beamwidth over 80°, a peak realized gain of 7.84 dBi, and sidelobe levels below −10.02 dB.
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Planar CP ME-Dipole Antenna With Surface-Wave Compensation for Symmetric Axial-Ratio Beamwidth in mm-Wave Frontend Systems
08 June 2026 Arpan Desai, Nirbhay Bhojani, Yi-Fan Tsao, and Heng-Tung Hsu present a planar embedded magneto-electric (ME) circularly polarized (CP) dipole antenna achieving symmetrical axial-ratio (AR) beamwidth for mm-wave Satcom applications. Although AR beamwidth is a critical parameter governing polarization stability over wide angular coverage, it is often overlooked in favor of impedance and AR bandwidth. While maintaining symmetric AR beamwdith along two principal cutplanes is preferred for certain applications, such issues have rarely been discussed. In conventional air-cavity-based ME dipoles, the absence of dielectric loading results in symmetrical AR beamwidth across both principal planes due to negligible surface-wave (SW) excitation, thereby preserving a stable quadrature condition. In contrast, planar embedded ME dipoles, which are more suitable for compact front-end integration, introduce significant SW modes at mm-wave frequencies.
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High-Gain Microstrip Patch Arrays Using Odd TMZM0 Modes
02 June 2026 Fábio S. Borges, Letícia T. Lima, Tales C. Pimenta, Daniel C. Nascimento, and Renan A. Santos present a general spectral-domain synthesis framework for high-gain microstrip patch antenna arrays operating in arbitrary odd TMzm0 modes. Unlike previous higher-order-mode antennas, whose designs are typically geometry- and mode-dependent, the proposed approach establishes a systematic and scalable methodology that directly links surface-current distribution to radiation characteristics. Within this framework, a conventional TMzm0 patch is synthesized into a high-gain radiator through suppression of out-of-phase current regions and introduction of parasitic sections that enlarge the effective in-phase radiating aperture, leading to enhanced directivity and reduced sidelobes. To experimentally validate the proposed methodology, a TMz70 -like element is designed and implemented, achieving a measured impedance bandwidth of 1.63% (7.92–8.05 GHz) for |S11|≤−10 dB, a realized gain of 15.3 dBi, and sidelobe levels below −16.6 dB.
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Multi-Task Learning for Real-Time Atmospheric Duct Characterization in Wireless Propagation Channels
01 June 2026 Mohammed Banafaa and Ali Hussein Muqaibel introduces a multi-task learning (MTL) framework to address the challenges of characterizing atmospheric ducts, which significantly influence radio wave propagation, particularly in maritime and desert regions. Rapid refractive-index variations critically affect signal propagation, especially for next-generation systems operating in the sub-6 GHz and higher frequency bands. Existing atmospheric duct models are often limited in scope, typically focusing on single-output prediction tasks and relying on synthetic or surface-level inputs that do not fully capture the vertical refractivity structure required for flight-level duct characterization. To address this gap, the proposed framework combines convolutional neural networks (CNNs) with bidirectional long short-term memory (BiLSTM) networks to sequentially detect duct occurrence, classify duct types, and predict essential duct characteristics. The model is trained and evaluated using two years of vertical profile data for a coastal region, with stratified 5-fold cross-validation (CV) and an independent hold-out test set.
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Pedestrian Activity Recognition and Prediction With Multi-Dimensional Point Cloud-Based Deep Learning for Millimeter Wave Radar
01 June 2026 Zihang Zhou and Shouhei Kidera present a multidimensional point cloud-based pedestrian activity recognition framework for millimeter-wave (mmW) pedestrian collision avoidance sensors. While many existing methods exploit range-velocity-angle data through Fourier-based processing along array or slow-time dimensions, such approaches face fundamental limitations including a high-frequency mmW radar systems, particularly in the 79-GHz band. These include across-range-unit (ARU) range walk due to high range resolution, a limited unambiguous velocity range, and the inherent tradeoff between temporal and velocity resolutions. To address these issues, we propose a k -decomposed weighted kernel density (WKD)-based range-Doppler velocity estimation method that directly extracts the range, Doppler velocity, direction-of-arrival (DOA) angles, and reflection intensity from point cloud data to overcome the shortcomings of short-time Fourier transform (STFT)-based analysis.
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Site-Specific Channel Modeling and Optimization of RIS-Assisted Multiuser MISO Systems
25 May 2026 Ziqi Liu, Wei Yu and Sean Victor Hum present a physics-based channel modeling and optimization framework for reconfigurable intelligent surface (RIS)-assisted downlink multi-user multiple-input single-output (MU-MISO) communication systems in site-specific environments. A hybrid ray-tracing (RT) and full-wave electromagnetic analysis approach is developed to construct a deterministic channel model that explicitly captures multipath propagation, RIS scattering behavior, and mutual coupling effects through a non-diagonal load impedance representation. Based on this model, an alternating optimization scheme jointly updates the base-station (BS) beamformer and RIS load impedances to maximize the minimum achievable rate under a total transmit power constraint and practical capacitance limits. The objective of the proposed framework is to provide a reliable initial assessment of the system-level impact of RIS deployment in realistic propagation scenarios.
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Design of Optimal Gain Mask for Phased Array-Fed Offset Reflectors
25 May 2026 Minsang Yoon, Changhyeon Im, Changsung Kim, Wongu Seo, Seulgi Park, and Hosung Choo propose a method to derive an optimal gain mask to enhance the aperture efficiency of phased array-fed reflectors (PAFRs). The optimal gain mask is obtained to uniformly illuminate the offset reflector’s surface. The optimal gain mask is derived based on the square of the distances from the feed antenna to each point on the offset reflector surface. To generate a feed pattern similar to the optimal gain mask, a 4×8 array antenna is used as the feed antenna. Using this array antenna, beam synthesis is applied through the superposition of array patterns sampled at 1° intervals in both θ and φ . In addition, to achieve sidelobe suppression, quadratic taper function is applied to the derived optimal gain mask.
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A Dual-Polarized Fully-Planar Inverted-L Element (DP-FILE) Array
22 May 2026 Christos Exadaktylos, Muhammad Hamza, Constantinos L. Zekios, and Stavros V. Georgakopoulos introduces the first, to our knowledge, PCB-based dual-polarized antenna array covering the Q (33-50 GHZ), V (50-75 GHZ), and part of the W-band (75-110 GHZ), called the dual-polarized fully planar inverted-L element (DP-FILE) array. To enable operation at high mmWave frequencies (> 50 GHz), the DP-FILE array employs an extremely compact unit-cell architecture composed of two orthogonal FILE radiators and a common ground via (CGV), requiring only three vias per unit cell. According to infinite array predictions, the DP-FILE array achieves common mode and scan blindness-free performance from 34 GHz to 94 GHz (2.75:1 bandwidth ratio), while scanning up to ±45° in all principal planes and preserving its VSWR < 3. To experimentally validate the array’s performance, a finite 25×25 DP-FILE prototype is fabricated and measured. Excellent agreement is observed between the measured and simulated results.
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Multi-Beam Conformal Leaky-Wave Antenna Fed by an Integrated Quasi-Optical System
18 May 2026 Michael Dittman, Ethan Neitzke, Brian Wright, John Papapolymerou, and Mauro Ettorre present a fully conformal antenna system composed of an integrated multi-layer quasi-optical system and a conformal leaky-wave antenna (CLWA). The conformal system enables simultaneous beam steering in the E- and H-principal planes, multi-beam capability, and mitigation of geometric defocusing. The work represents a novel integration of quasi-optical structures with CLWAs. The CLWA is constructed from an array of slots on a double-grounded substrate illuminated by the conformal quasi-optical system. The antenna system operates in the band of 22 GHz to 26 GHz with a design frequency of 24.15 GHz . The radiation patterns in the E- and H-planes of the CLWA are controlled by the leaky-wave mode and the quasi-optical system, respectively.
