The rapid advancement of telecommunication systems demands antennas with reduced mass and size. Wire-grid structures serve as effective alternatives to traditional solid metal antennas by significantly reducing their mass. The Optimal Current Grid Approximation recently proposed approach has introduced sparse wire-grid structures with further mass reduction but poses fabrication challenges, prompting modified approaches. However, the previously proposed modified approaches only focused on overcoming the difficulties in fabrication, without considering the current distribution, resulting in structures with characteristics different from those of the original wire-grid structure. To overcome these limitations, we propose the“Maximum Current-based”Optimal Current Grid Approximation, a novel approach that selectively reconnects wires with maximum current, improving the radiation performance of the sparse structure and aligning antenna characteristics more closely to those of the original wire-grid structure. Applied to a UHF-horn antenna, the sparse structures generated using the proposed approach were analyzed and their antenna characteristics were compared with those of the sparse structures obtained using other approaches and the original wire-grid structure, which in turn were compared with those from previous studies obtained numerically by different methods and experimentally for solid antenna prototypes. The performed comparative analysis confirmed that the proposed approach generates sparse wire-grid structures with antenna characteristics closer to those of the original wire-grid than other approaches, demonstrating its effectiveness. In addition, based on the simulation results, the sparse wire-grid structure is generated to verify the effectiveness of the proposed approach. The obtained experimental results demonstrate the effectiveness of the proposed approach in generating sparse wire-grid antenna with mass 1.41 times less than the original wire-grid antenna and 7.63 times less than the solid antenna while maintaining the required characteristics.

As 6G and beyond technologies are stepping into the spotlight, phased arrays are becoming increasingly promising candidates for agile antenna systems. In particular, aperiodic phased arrays provide many desirable traits for such technologies, such as reduced mutual coupling, sidelobe suppression, and grating lobe elimination. However, the design of such systems creates a complex, high-dimensional optimization space due to the competing traits. Traditional optimization methods often fail to scale well when applied to such high-dimensional problems. To this end, three promising algorithms that claim to perform well for such complex and large problems have been identified: Trust region Bayesian optimization (TuRBO), hybrid remora crayfish optimization algorithm (HRCOA), and the zeroth-order optimization toolbox (ZOOpt) featuring a sequential randomized coordinate shrinking classification algorithm (RACOS). The study allows maximal freedom in optimization through using free-floating elements and suggested minimum spacing through weights in the cost function. Two cases of 256 and 625 element arrays, 512 and 1250 variables, respectively, are studied using these three algorithms and compared against the covariance matrix adaptation evolutionary strategy (CMA-ES). The convergence characteristics of each algorithm are analyzed, and their robustness for application in high-dimensional antenna array optimization problems is examined.

A metasurface-based ultralow profile folded transmitarray antenna (FTA) is proposed. An integrated feed source, a reflective polarizer, and a polarization-selective metasurface together form the FTA. Both the reflective polarizer and the polarization-selective metasurface have stable EM responses over a wide angle. The integrated feed source is a rectangular waveguide antenna that is used to provide a low-gain and wide-coverage beam. The final design of the FTA has an ultralow profile with height-to-diameter (H/D) ratio of only 0.16 while maintaining good radiation performance. The measured results include a peak gain of 28.82 dBi at 28.2 GHz with an aperture efficiency of 35.2% and a 3-dB gain bandwidth of 6.8%. The proposed FTA can find significant applications in radar systems and satellite communications.

A scalable and cost-effective phased array architecture based on dielectric resonator antenna (DRA) technology is presented for millimeter-wave applications. The proposed dome-on-cylinder DRA elements, encapsulated in a thermally conductive metal frame and excited through a suitable feeding network integrated into a multilayer PCB stack-up, enable two-dimensional wide-angle beam steering with minimized scan loss. A 64-element array prototype operating in the 24-GHz ISM radar band demonstrates 2D beam scanning up to ±70° in the E-plane and ±65° in the H-plane, with H-plane scan loss following an approximate cos<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.4</sup>(θ<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">_s</i>) dependence, significantly lower than the conventional cosine law. The same metal frame and high-thermal-conductivity DRA cores provide an efficient heat removal path, yielding at least an eightfold decrease in thermal resistance compared to an equivalent stacked microstrip patch array architecture, so that the aperture acts as a complementary heatsink. The electromagnetic and thermal performance of the array are validated through full-wave simulations and measurements of S-parameters, embedded-element and scanned-beam patterns, and steady-state temperature distributions, confirming the suitability of the proposed platform for high-power, wide-angle mm-wave communication and remote sensing systems.

The stringent reliability and latency requirements of industrial networks are challenged by harsh propagation environments. To design effective communication systems, a thorough understanding of the underlying channel characteristics is essential. Deploying multiple, spatially distributed Access Points (APs) is a promising strategy to overcome these challenges by creating resilient communication links through macro-diversity. This paper presents an experimental characterization of a multi-AP radio channel in a representative industrial laboratory environment, focusing on the 6 GHz band (upper FR1), enabling the investigation of frequency-dependent propagation mechanisms beyond traditional sub-6 GHz cellular bands. We analyze key statistical properties, including inter-link correlation, coherence distance, and coherence bandwidth, to assess the potential for both macro- and micro-diversity. The results demonstrate that the channels from distributed APs are largely uncorrelated, highlighting a significant opportunity for macro-diversity. Conversely, the measured coherence distances far exceed typical device dimensions, suggesting limited returns from single-device spatial diversity. An evaluation of selection combining, equal-gain combining, and maximal-ratio combining techniques confirms that distributed APs can provide substantial diversity gains, ranging from 2.6 dB to 23.1 dB. These findings validate the deployment of coordinated, distributed AP architectures as a crucial strategy for achieving robust, low-latency connectivity in future industrial settings.

This paper presents a low-profile transmitarray using multi-feed technology. The element of the transmitarray adopts two orthogonally arranged slots on the bottom and upper layer of the cavity as received and transmitted structure, and is constructed using only a single-layer laminate. The element achieves 1-bit phase state by locating the transmitting slots at two different positions which are symmetrical. The element has an extended bandwidth by incorporating a center shorting pin in the cavity. Four slots excited by one-to-four metal waveguide feeding network are introduced to feed the transmitarray, effectively reducing the height-to-diameter ratio (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H/D</i>). Finally, a low-profile transmitarray antenna with 24 × 24 elements is designed, fabricated, and measured. The overall antenna has an aperture size of 13.09 13.09 λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">₀</sub> × 13.09 λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">₀</sub>, and an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H/D</i> ratio of 0.18. Measured results indicate that the proposed antenna achieves a peak gain of 24.5 dBi and a 3-dB gain bandwidth of 12.2%. The proposed antenna is a promising candidate for spaceborne and satellite communications.

This paper introduces a compact wideband Reconfigurable Intelligent Surface (RIS) leveraging Schiffman phase shifters to overcome the traditional narrowband limitations of RIS technology. The proposed design achieves ±15∘ phase balance across a broad frequency range of 7.5–13 GHz, addressing a key challenge in RIS design. The proposed RIS features a compact unit cell, with dimensions of (0.25λ×0.25λ) at 10.25 GHz, integrating a single PIN diode and a tailored internal geometry to enable efficient phase control and scalable implementation. Experimental validation is carried out in two phases: initially, the unit cell is characterized using a waveguide setup; subsequently, a 30cm×30cm RIS panel is fabricated and tested under horn antenna excitation. The measured data exhibit strong agreement with simulations, demonstrating the accuracy and robustness of the proposed design. The full RIS surface is further evaluated for its reconfigurability and ability to generate Orbital Angular Momentum (OAM) beam scanning. These findings highlight the design’s potential for enabling key 6G communication features, offering a compact and wideband RIS solution through the integration of Schiffman phase shifters and contributing to advancements in next-generation wireless systems.

Ray tracing method (RT) is a computational method for modeling light propagation and interaction, which can be used to simulate communication signal propagation, path loss, etc. in unmanned aerial vehicles(UAV). However, the ray tracing method may face some challenges in real-time simulation of multi-UAVs. In this paper, we propose a low-complexity deterministic path loss prediction model based on RT and backpropagation neural network (BPNN) for online decision-making systems of multiple UAVs in urban environments. The dataset is built by calculating the path loss (PL) between each pair of receivers and transmitters in a deterministic urban scenario via RT. However, numerical results show the high complexity when using the path loss dataset directly to train the neural network. To address this, we simplify the PL dataset by incorporating communication system parameters (e.g., receiver sensitivity and transmission power) and categorizing the path loss severity into four levels: Low Path Loss, Moderate Path Loss, High Path Loss, and Severe Path Loss. The resulting low-complexity path loss prediction model, trained with BPNN and the simplified dataset, achieves efficient PL prediction while maintaining high accuracy. Compared to RT, the proposed model is computationally less time-consuming and can effectively predict the degree of path loss attenuation across various UAV distributions and operating frequencies. Furthermore, it provides a practical solution for assessing communication performance under dynamic urban propagation environments and varying signal conditions, including channel fading.

In sixth-generation (6G) application scenarios like industry 5.0, augmented reality (AR), autonomous transportation, and eHealth, there is a growing demand for Human Activity Recognition (HAR). Meanwhile, with the deployment of millimeter-wave (mmWave) technologies in fifth-generation (5G) cellular communications, higher-resolution sensing becomes feasible. Utilizing mmWave for communication and HAR has garnered attention, necessitating accurate modeling of sensing channels. This paper proposes a mmWave scattering channel model for indoor HAR, which facilitates system design, optimization, and implementation. In the proposed model, we integrate primitive-based human body scattering where the human body is indicated by a set of primitives, and cluster-based environment scattering models, enabling detailed modeling of self-shadowing and double-bounce environment scattering. Additionally, we develop a simulation framework encompassing signal transmission, sensing channels, and processing, allowing adjustment of system parameters. Simulation results indicated by micro-Doppler signatures including multi-link effects show good agreements with measurements, validating the effectiveness of the proposed model. Meanwhile, the time consumption of the proposed simulation workflow for generating micro-Doppler signatures for most human activities is within 10 minutes.