This paper presents a polarization-insensitive frequency selective rasorber which has high in-band transmission at high frequency and wideband absorption at low frequency based on square-loop and parallel LC resonance. The rasorber consists of a bandpass FSS and a resistive sheet plus a slot-type metallic four-legged loaded element as the bandpass FSS element. The resistive element is realized by inserting several strip-type parallel LC structures into a resistor-loaded square-loop element, which allows the surface current to be controlled as necessary and the wave at the resonance frequency to be passed with minimum insertion loss. Wideband absorption is realized at low frequency, where the bandpass FSS is nearly totally reflected, and the FSR performs as an absorber. Simulation results show the transmission band at 9.9 GHz with transmissivity higher than 96% and the absorption band with absorptivity higher than 85% from 2.83 GHz to 8.6 GHz for TE-polarized 30˚ incidence and from 3.22 GHz to 8.48 GHz for TM-polarized 30˚ incidence. The absorptive/transmissive performance of the FSR structure is also verifieded by experimental measurements.
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