Quasi-Elliptic Bandpass Frequency Selective Surface Based on Coupled Stubs-Loaded Ring Resonators

In this paper, a novel design of frequency-selective surface (FSS) based on coupled stubs-loaded ring resonators (SLRRs) is proposed. The proposed FSS exhibits quasi-elliptic bandpass filtering characteristic at C-band. And each unit cell of the structure is composed of two SLRRs coupled by a circular aperture. A novel method of transmission line (TL) model is proposed to investigate the operating principle of a single SLRR under normal incidence plane wave. Moreover, the operating mechanism of the proposed FSS is further researched with the aid of the equivalent circuit model (ECM) analysis method. Due to the symmetric and low-profile physical structure, the FSS keeps stable frequency response under oblique incident plane wave for both transverse electric (TE) and transverse magnetic (TM) polarizations. Finally, the designed FSS is fabricated and measured. The measured results agree well with the simulated results. The measured results indicate that the proposed FSS exhibits a dual-polarized and stable bandpass frequency response with two transmission zeros (TZs) at around 5.71 and 6.87 GHz under different incident angles up to 40°.