Design of Angle-stable and High-transmittance Frequency Selective Rasorber Based on Bilateral Connected Interdigital Resonator

This paper presents a novel frequency selective rasorber (FSR) design with a highly transparent window. FSR is a two-dimensional periodic structure consisting of a lossless FSS layer, an air layer, and a lossy resistive thin layer. The lossless bandpass layer consists of a bimetallic square ring. It provides a bandpass response with double transmission zeros by parallel resonance. The impedance layer consists of bilaterally connected interdigital resonator (BCIR) and crossed metal wires loaded with resistors. Among them, the BCIR can produce parallel resonance. When the lossless layer coincides with the parallel resonance frequency of the lossy layer, the FSR can produce a high transmittance window. The whole structure can produce a frequency response with low-frequency absorption and high-frequency transmission. The simulation results show that the structure has almost the same response under both TM and TE polarization conditions. the reflection coefficient of the FSR in the band of 5.03–11.61 GHz under TE polarization is below −10 dB. The transmission coefficient of the FSR in the 8.57–9.73 GHz band is higher than −3 dB, where the minimum insertion loss of the transmission window can reach −0.00652 dB near 9.12 GHz. Meanwhile, the FSR has good angular stability up to 40° angle of incidence. Finally, the equivalent circuit model (ECM) of FSR is also presented.