A Tunable Bandstop Frequency Selective Surface with Polarization-Insensitive Characteristic

In this paper, a low-profile tunable bandstop frequency selective surface (FSS) is presented for S-band applications. The FSS consists of square loops connected through varactor diodes across the diagonals. By controlling the reverse voltage of the varactors, the resonance frequency can be tuned for a wide frequency range. Full-wave simulation shows 21% tuning range from 2.31 GHz to 2.79 GHz with respect to lower resonance frequency. The novelty of the design lies in its fourfold symmetry, which makes the structure polarization-insensitive. The FSS is also angularly stable under oblique incidence for both TE and TM polarizations. Additionally, an equivalent circuit model has been introduced to explain the resonance mechanism of the proposed FSS. The structure is also fabricated and measured, where good agreement is observed between simulated and measured responses.