Hybrid frequency‐selective rasorber with wide passband based on spiral resonator

Abstract

A hybrid frequency-selective rasorber (HFSR) with low-frequency absorption and high-frequency polarization conversion based on rectangular spiral resonator (RSR) is designed, which implements a broad transmission band in the middle band, simultaneously. The HFSR is made up of three components, which are separated by two air gaps. A bandpass frequency-selective surface (FSS) is employed to realize a broad transmission window at the bottom layer, serving as a metal background of the top layer. The middle lossy layer is composed of the RSR and T-type metallic strips with four resistors, which is used to absorb the electromagnetic waves (EMWs) in the low-frequency band and provide a broadband transmission band. The top layer is formed by a pair of arrows to achieve the linear polarization conversion at the high-frequency band. A four-port equivalent circuit model (FP-ECM) with absorbing function is established to explain the physical principle of the proposed HFSR. The simulation results reveal that the 1 dB transmission band is obtained in 7.67-12.06 GHz with a 44.5% fractional bandwidth (FBW). Besides, the co-polarized reflection coefficients (S 11 < À10 dB) are achieved in 4.51-15.81 GHz with a 111.2% FBW. Moreover, the HFSR has a stable oblique incident angle of 30 under TE-and TM-polarized waves. In addition, the radar cross-section (RCS) of the HFSR can be reduced from 3.0 to 16.0 GHz, which has a 136.8% FBW. Finally, the archetype of the designed HFSR is fabricated and tested to validate the reliability of the simulation results.