Optically Transparent Intelligent Reflecting Surface for 5G and Future 6G Coverage Enhancement

This paper presents an optically transparent intelligent reflecting surface (IRS) for 5G and future 6G network coverage enhancement using indium tin oxide (ITO) material. The proposed transparent IRS consists of a patterned ITO sheet with a surface impedance of 2.5 ohm/sq. Due to the high loss characteristics of ITO, a multilayer unit cell structure is employed to reduce dielectric losses. Simulating a single ITO-based unit cell revealed challenges in achieving a 360° phase shift with low reflection loss. Therefore, two unit cells are utilized to provide the required 360° phase compensation across the IRS aperture with less than 5 dB losses for both unit cells. An optically transparent IRS with 40x40 cells (200 mm×200 mm) is designed to reflect incoming signals from a base station 10 meters away toward a blind zone with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\theta_{i}=-15^{\circ}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\theta_{r}{ = }$</tex> -37°. Simulation results demonstrate that the proposed optically transparent IRS effectively covers the entire 5G millimeter-wave band from 24–30 GHz, maintaining stable beamforming performance throughout the frequency range.