An X-Band Frequency Selective Rasorber Based on Concentric Split Ring Slots

This paper presents a frequency selective rasorber (FSR) with absorption-transmission-absorption (A-T-A) capabilities at X-band. The proposed FSR consists of a dual-layer array, where the unit cell of the first layer contains three concentric split ring slots with resonant frequencies located within the X band. The inner and the outer rings are loaded with lumped resistors to increase the absorptivity at the lower and upper bands, while the middle ring is not loaded to allow a passband for the center frequencies. The second layer contains miniaturized ring slots to provide high transmission to the center passband. Due to the proximity between frequencies, the resonance’s selectivity of the second layer needs to be high; therefore, a unit cell with four small ring slots loaded by capacitors is used. Simulated results show that this FSR demonstrates absorption peaks of $87.4 \%$ and $94.4 \%$ at the lower and upper absorptive bands, respectively, and insertion loss lower than 2 dB is obtained at the transmissive band from 9.59 to 9.86 GHz. One can conclude that this design can reach very high absorption rates without increasing insertion loss at the transmission window.