A Multifunctional Frequency Selective Surface With a Wide Incident Angle for X-/K-/Ka-Band Applications

In this letter, we propose a multifunctional frequency selective surface (FSS) designed for wide incident angles optimized for X-band reflection and K-/Ka-band transmission. To verify its applicability, we analyzed the performance variations of the FSS with respect to polarizations and incidence angles. The proposed FSS facilitates space communication in the K/Ka-band, while simultaneously minimizing electromagnetic interference for X-band defense applications. The pixelated structures of the FSS are optimized to realize fine frequency selectivity in the target frequency bands. The proposed FSS is implemented in a double layer to provide higher-order characteristics. To validate its performance, measurements are conducted in a free-space measurement system with spot-focusing lens horn antennas. The proposed structure demonstrates a -1.5 dB bandwidth from 17.41 GHz to 20.97 GHz in the pass band of the K-band and 30.09 GHz to 33.24 GHz in the pass band of the Ka-band, with fractional bandwidths of 18.6% and 9.9%, respectively. Additionally, it satisfies -15 dB blocking performance across the entire X-band.