Dual-Polarization Absorptive/Transmissive Frequency-Selective Surface With Tunable Passband

A dual-polarization frequency-selective structure with a tunable passband and two absorptive bands is presented. Based on an equivalent circuit model (ECM), the working principle is investigated first. The values of components in the ECM are derived from the required performances and are mapped to the structure of an initial design, which is designed by cascading of an absorptive frequency-selective surface (FSS) realized with dipole-like elements and a lossless bandpass FSS achieved with square ring slot. For tuning the passband, varactors and biasing networks are added into the initial design. The adding of the varactors and biasing networks significantly affects the performance, and brings about the emergence of singular resonances. The approaches for mitigating the effects and the techniques for suppressing the singular resonances are proposed. Simulated results show that, between two absorptive bands, a passband is tuned from 3.33 to 5.13 GHz if the capacitances are decreased from 0.5 to 0.15 pF. A prototype is fabricated and measured. Measured results show that the passband is altered from 3.56 to 4.35 GHz as the reverse bias voltage of the used varactors is increased from 6 to 18 V.