Frequency-Selective Rasorber with Tunable Passband Based on Loaded Rings

This paper presents a frequency selective rasorber (FSR) with a tunable passband between two absorptive bands. The X-band FSR consists of two layers separated by an air gap. One layer is an absorptive surface designed by resistive-loaded meandered rings, and the second layer is a bandpass frequency selective surface (FSS) realized with capacitive-loaded ring slots. Simulation results show that the central frequency of the passband decreases from 11.22 to 9.12 GHz as the capacitive load increases from 0.030 to 0.065 pF. The FSR design was validated using the waveguide simulator method. A demonstrator containing two unit cells was designed, fabricated and tested. The capacitive loading was implemented using interdigital capacitors to obtain a frozen state of the tunable FSR. There is a good agreement between simulated and measured results.