Optically Transparent Dual-Ring Resonant Frequency Selective Surface Based on ITO Film for Sub-6 GHz Indoor Communication

With the rapid development of wireless communications, electromagnetic interference (EMI) in complex environments has become a critical factor affecting communication quality. Addressing the EMI issues caused by multi-band coexistence in indoor scenarios, traditional metallic resonant structures, while effective in filtering, often compromise optical transparency due to light blockage. To resolve this trade-off, this paper proposes a dual-ring resonant frequency-selective surface (FSS) based on Indium Tin Oxide (ITO) films. This design aims to achieve efficient transmission in specific C-band frequencies and suppress out-of-band interference, realizing excellent optical transmittance while ensuring electromagnetic shielding effectiveness. The designed metasurface targets a passband of 5.35–5.40 GHz for sub-6 GHz indoor communications. Experimental results confirm superior transmission in this range and significant out-of-band suppression. Furthermore, featuring high optical transparency, the structure can be directly integrated onto glass surfaces. It is not only suitable for optically transparent devices but also provides a compact passive solution for anti-EMI applications in smart buildings and sub-6 GHz indoor communications.