Active Frequency Selective Surface to Switch Between Absorption and Transmission Band With Additional Frequency Tuning Capability

This study realized a polarization-insensitive active frequency selective surface (AFSS) that simultaneously exhibited mode switching and frequency tunable capacity. Its geometry comprised periodic metallic patterns printed on opposite sides of a dielectric substrate, with varactors and p-i-n diodes mounted on the top and bottom layers, respectively. The proposed AFSS switches between transmission and absorption modes by regulating the p-i-n diodes (OFF and ON states). Transmission and absorption frequencies can also be continuously tuned by changing the bias voltage across the varactor diodes. To realize polarization independence, metallic patterns, lumped components, and biasing configurations were symmetrically patterned. The equivalent circuit and parametric studies were considered to explain AFSS switching and tuning behaviors. The proposed multifunction and frequency tuning responses were experimentally demonstrated by fabricating a prototype with 17 × 17 unit cells. The bandpass frequency can be tuned from 3.70 to 4.27 GHz with a 1.96-4.30 dB insertion loss in the transmission mode, and the absorption frequency can be regulated from 4.28 to 5.12 GHz with 78.77%-90.78% absorptivity.