Optically Transparent Reflectarray With Frequency Selective Surface Ground for High‐Gain Directive Radiation and Multiband Electromagnetic Stealth

ABSTRACT With the rapid development of wireless communication, optically transparent microwave devices are increasingly required in modern environments such as architectural glass, automotive windshields, and photovoltaic panels. However, high‐gain large‐aperture reflectarrays inherently conflict with scattering suppression, as they tend to increase the radar cross‐section (RCS). Optically transparent reflectarrays achieving both high‐gain directive radiation and low scattering remain scarcely explored. Here, we present a single‐layer reflectarray antenna employing a fine metal line (FML) based frequency selective surface (FSS) ground and a low‐loss modified cyclic olefin polymer (MCOP) substrate, which simultaneously delivers high optical transparency, efficient directive radiation, and multiband electromagnetic stealth. The proposed FSS ground replaces a continuous conductor, enabling in‐band reflection with minimal optical obstruction while allowing out‐of‐band microwave and visible‐light transmission. The fabricated prototype with subwavelength multi‐resonant element structure, operating at a center frequency of 45 GHz, achieves 83% optical transmittance, a maximum gain of 25.19 dBi, and 48.5% aperture efficiency with an 18.6% 1.5 dB gain bandwidth. Moreover, it exhibits out‐of‐band RCS reduction from 4 to 18 GHz, achieving dual stealth for both microwaves and visible light. This work demonstrates a transparent reflectarray with integrated high‐efficiency radiation and stealth functionalities, advancing the design of next‐generation multifunctional electromagnetic devices.