Transparent Wide-Bandpass FSS with High Selectivity on Windows Glass for mm-Wave Wireless Communication

This study presents a simple design of a bandpass frequency selective surface (FSS) that achieves high optical transparency (OT), stability under varying incident angle, and enhanced electromagnetic wave transmission with a wide selective bandwidth, specifically intended for glass windows in 5G mm-wave wireless communication (n257, n258, and n261 frequency bands). These FSS structures, applied to glass windows and referred to as glass-penetrating transparent surfaces (GPTS), are designed using meta-surface technology to remain visually unobtrusive in environments where signal transmission control is required. To optimize the OT of 61%, square loop (SL) and grid wire (GW) structures were employed, both utilizing miniaturized metallics. These elements were vertically stacked to minimize the impact of metallic coverage on transparency, resulting in a three-layer FSS configuration with an SL/GW/SL arrangement. Strong interlayer coupling is generated between the layers, enhancing both the transmission, with a peak insertion loss of 0.74 dB at the center frequency (27 GHz), and the − 3dB bandwidth (BW) achieving 5 GHz (24.6–29.6 GHz, 18.4%). Additionally, the proposed design features a compact unit cell size of 0.148 0.148 and a symmetric configuration, which contributes to stable performance under various incident angles up to 45. Results indicate that the proposed FSS design holds promise as an effective solution for mm-wave signal filtering on glass windows, providing conditions for high data-rate communications.