A Novel FSS-Based Bandstop Filter for TE/TM Polarization

A novel miniaturized unit-cell frequency-selective surface (FSS)-based bandstop filter (BSF) is presented in this letter. The proposed structure exhibits negative refractive index (NRI) characteristics by designing an epsilon-negative FSS. This design gives a 10-dB rejection bandwidth from 3.13 to 4.75 GHz and its unit cell has an electrical length of $0.125\,\,\lambda _{0} \times 0.125\,\,\lambda _{0}$ . In addition, the designed BSF has a center frequency of 3.96 GHz and an NRI value for a range of 220 MHz, starting from 4.07 to 4.29 GHz. Furthermore, its equivalent circuit model and surface current distribution are elucidated to explain the behavior of the proposed FSS. The structure manifests polarization-independent characteristics and provides a stable frequency response for normal and oblique angles under both transverse electric (TE) and transverse magnetic (TM) incident polarization. To validate the results, the BSF is fabricated, and good agreement between the simulated and measured responses is observed.