High-Selectivity Bandpass Frequency-Selective Surface in Terahertz Band

A terahertz (THz) bandpass frequency-selective surface (FSS) with high selectivity is proposed in this work. The three-layered FSS filter consists of identical tripole resonators located on the top and bottom layers and rectangular coupling apertures etched on a conducting plane in between. Multiple signal paths exist between the top and bottom resonators through the coupling apertures. Therefore, this aperture-coupled resonator (ACR) structure exhibits a narrow bandpass response, and two transmission zeros appear near the skirts of the passband. These zero points considerably improve the frequency selectivity and suppress the sidebands of the FSS. For demonstration, a micro-fabrication process was used to realize an ACR FSS at 850 GHz. The frequency performance of the ACR FSS in terms of insertion loss is investigated numerically and experimentally. The measured transmission responses at normal incidence based on time-domain as well as frequency-domain measurements agree well with the simulated one, thus verifying the proposed design. Furthermore, the frequency-domain measurement reveals that the FSS response remains stable at various incident angles for both TE and TM polarizations.