3-D Frequency-Selective Rasorber With Wide Upper Absorption Band

This communication presents a 3-D frequency-selective rasorber (FSR) that has a passband with a low insertion loss and two absorption bands at both sides of the passband. A lossless and two lossy resonators are employed in the unit cell of the periodic structure to produce the passband and the absorption bands, respectively. Utilizing the techniques of stepped impedance resonator and capacitor loading, the thickness of the resonators is reduced. Moreover, the capacitor loading also frees the tuning of each resonant frequency of the lossy resonator, which facilitates the FSR design. The multiresonances of the lossy resonators are also employed to obtain a wide upper absorption band. An equivalent circuit model is established for understanding the operating principle. A prototype of the proposed FSR is fabricated and measured. Good agreement between measured and simulated results validates our FSR design.