Active Dual-Band Frequency Selective Surfaces with Close Band Spacing Based on Switchable Ring Slots

This letter presents active dual-band frequency selective surfaces (AFSS) with close band spacing based on two switchable ring slots loaded by PIN diode switches. The close band response is achieved by splitting the outer ring slot, and then shifting upward its fundamental resonance beyond the resonance of the inner ring slot. The proposed AFSS can provide four states of operation including lower single-band, upper single-band, dual-band with close band spacing, and reflective mode. Experimental results based on the waveguide simulator show that a frequency ratio of 1.14, with insertion loss lower than 0.82 dB at resonant frequencies, is obtained in the X-band.