A dual-passband frequency-selective rasorber structure

A dual-passband frequency-selective rasorber (FSR) with high selectivity is proposed in this letter. By analyzing the equivalent circuit model (ECM), the design approach improving the selectivity of the dual-passband is introduced. The FSR is formed by a lossy layer and two frequency-selective surface (FSS) layers. The lossy layer is composed of two parallel resonance units embedded in a rhombic structure, which is connected with fourresistors loaded on the T-shape metal strips. The lossless layer consists of two layers of double square slots to provide highly selective passbands with second-order response. The simulated results show that two transmission bands are achieved at 7.2 and 10.8 GHz with the insertion loss of 0.86 and 0.57 dB. Both sides of the transmission bands exhibit steep roll drops. A prototype of the proposed FSR was fabricated and measured,