Design and equivalent circuit model extraction of a third-order band-pass frequency selective surface filter for terahertz applications

In this paper, a third-order band-pass frequency selective surface (FSS) filter is proposed for terahertz applications. The presented FSS filter is designed based on miniaturized unit cells and a fractional bandwidth of 72% around 0.775 THz is achieved. In addition, a high transmission magnitude is obtained with an acceptable flatness in comparison to previous reports. In order to verify the numerical results, an equivalent circuit model of the proposed spatial filter is introduced considering both normal and oblique incident angles. The sensitivity of the filter with respect to the incident wave angle is investigated in the range of 0–60° whereas the obtained performance is acceptable for various incident angles in the mentioned range. Moreover, the effects of altering different geometrical parameters are studied and justified based on the extracted equivalent circuit model.