In this paper, we theoretically propose and experimentally demonstrate a compact, optically-transparent metasurface radome with asymmetric electromagnetic absorption for making low-radar cross section (RCS) and gain-enhanced multifunctional antennas. The proposed unseeable metasurface has a bilayer structure consisting of periodically patterned and unpatterned transparent conductive films separated by a thin acrylic layer. Such a bilayer metasurface is highly reflective when illuminated by microwave from one side, while exhibit a high absorption when illuminated from the other side. Moreover, when the optically-transparent, weather-proofing bilayer metasurface acts as a radome, it can greatly enhance the gain and reduce RCS of the solar panel-integrated microstrip antenna without affecting the performance of optical devices (e.g., photovoltaic panels, flat panel displays, or light emitting devices). We provide the analytical formulation and design guidelines for the bilayer metasurface and the integrated cavity antenna. Our experimental results show that the realized gain of the microstrip antenna can be increased by 6.1 dBi and its RCS can be reduced by more than 20 dB around the operating frequency of 8.1 GHz. The proposed low-profile, flexible, hydrophobic, and optically-transparent bilayer metasurface may be beneficial for many applications, including the next-generation radomes, self-powered 5G/6G base stations, satellite communication (CubSat), and other compact, multifunctional RF and microwave modulus integrated with optical sensors, lidar, displays, and solar panels.

This research presents a high-performance design for a multiple-input multiple-output (MIMO) antenna intended for operation within the 28 GHz band. The four-port MIMO antenna configuration, featuring 1 × 8 series-fed arrays for each port, has demonstrated peak gains of 15.5 dBi and bandwidths of 2 GHz. This improved antenna performance results from carefully optimized antenna spacing and a decoupling approach involving well-designed metamaterial cells, effectively minimizing interference between antenna elements. The system exhibits remarkably low mutual coupling, measuring below −40 dB, with envelope correlation coefficients of 0.00010, diversity gains nearing 10 dB, and a channel loss capacity of 0.11 bit/s/Hz across the frequency spectrum under investigation. Experimental evaluations have confirmed these improvements, establishing the proposed design as a robust candidate suitable for a wide range of millimeter-wave communication systems.

This research introduces a novel, high-performance multiple-input–multiple-output (MIMO) antenna designed to operate in allocated millimeter-wave (mmWave) 5G wireless communications. Operating in the tri-band, 28, 35, and 38 GHz, the four-port MIMO antenna possesses a compact size—measuring just 50 × 50 × 0.787 mm³ (4.67λ_o × 4.67λ_o × 0.73λ_o). The antenna delivers a remarkable performance, achieving peak gains of 9.6, 7.8, and 13.7 dBi in the tri-band, respectively. The realized bandwidths are 1.1, 2.2, and 3.7 GHz, at the tri-band frequencies. The antenna’s performance was significantly improved by carefully spacing the elements and employing a decoupling technique using metamaterial cells. This minimized interference between the antenna elements, resulting in efficient MIMO operation with a low envelope correlation coefficient of 0.00015 and a high diversity gain approaching 10 dB, and high isolation of 34.5, 22, and 30 dB, in the tri-band. This proposed design is confirmed with experimental measurements and offers a promising candidate for multi-band use of mmWave communication systems.

This work presents the design and experimental validation of a high-performance 6-port MIMO antenna array designed for radar applications in the 24 GHz Industrial, Scientific, and Medical (ISM) band. The proposed design, configured as a 1 × 10 series-fed microstrip patch array on an RT/Duroid 5880 substrate, is engineered to meet the demanding requirements of automotive and industrial radar systems, where high resolution and target discrimination are critical. A key challenge in such dense MIMO arrays is mutual coupling, which was addressed by integrating novel metamaterial structures between the radiating elements. These structures effectively suppress surface waves, resulting in exceptional inter-port isolation exceeding 46 dB at 24.3 GHz. The antenna achieves a peak gain of 17.4 dBi, ensuring sufficient range for sensing applications. Furthermore, the radiation pattern exhibits a simulated low side lobe level (SLL) of −24.6 dB in the E-plane, and −15.8 dB in the H-plane, a critical parameter for minimizing false detections and enhancing accuracy in cluttered environments. With an operational bandwidth of 0.71 GHz, the proposed design demonstrates comprehensive performance metrics—high gain, outstanding isolation, and low SLL—that surpass many existing MIMO solutions. The results confirm the antenna’s strong potential for advanced MIMO radar systems operating in the 24 GHz-ISM band, paving the way for reliable high-resolution sensing.

This paper presents a versatile metasurface (MS) structure for enhancing the radiation performance of multiple microstrip patch antenna topologies operating in the 5.8 GHz ISM band. Unlike conventional metasurface-assisted antenna designs that are optimized for a single radiator, the proposed MS is systematically integrated with four fundamentally different antenna configurations, including a conventional rectangular patch antenna, an ultra-wideband (UWB) patch antenna, a 1 × 4 corporate-fed patch array, and a coplanar MS-loaded 1 × 4 array, thereby demonstrating its applicability across diverse antenna architectures. The electromagnetic characteristics of the proposed unit cell are first investigated through full-wave simulations and constitutive-parameter retrieval, revealing resonant magnetic behavior, strong reflective characteristics, and a negative refractive index region around the operating frequency. The metasurface is subsequently employed as either a reflective superstrate or an in-plane loading structure to manipulate the radiated wavefront, improve aperture utilization, and enhance radiation directivity. Across the antenna configurations investigated, realized gain improvements ranging from 1.0 to 6.3 dB are achieved without significant degradation of impedance matching, corresponding to relative improvements between 8.3% and 315%. The highest realized gain of 15.7 dBi is obtained for the superstrate-loaded 1 × 4 array, while the coplanar-loaded array achieves 14.3 dBi with half-power beamwidths of approximately 17° and 37° in the principal planes. Prototype fabrication and experimental characterization demonstrate good agreement with full-wave simulations, confirming the effectiveness and robustness of the proposed metasurface. The presented approach establishes a practical and scalable metasurface platform for improving the radiation characteristics of different patch antenna topologies, making it attractive for high-performance wireless communication, radar, sensing, and emerging microwave systems.