Wideband dual-polarized linear-circular and linear-cross angular stable THz reflective polarizer based on a modified square loop FSS

Abstract

A simple wideband reflective type linear-cross and linear-circular polarization converter for terahertz (THz) applications is proposed in this paper. The top frequency selective surface (FSS) consists of a thin gold coated figure of eight square loop with the connected strip line corners on a thin grounded polyamide dielectric substrate. For the y / x -polarized incidence, the design exhibits linear-circular conversion with an axial ratio ( ≤ 3 d B ) from 0.49–0.50, 0.60–0.83, 1.16–1.62, and 1.81–1.85 THz with 2.02%, 32.17%, 33.09%, and 2.19% fractional bandwidth (FBW), respectively. In addition, it also performs the linear-cross conversion with a minimum 90% polarization conversion ratio (PCR) from 0.53–0.56, 0.92–1.07, and 1.69–1.75 THz having 5.50%, 15.08%, and 3.49% FBW, respectively. Multiple plasmonic resonances are the reason behind different polarization conversions and are confirmed with surface current distribution profiles of the FSS and ground. The metasurface’s performance is stable up to 45° for both transverse electric (TE) and transverse magnetic (TM) oblique incidences. The polarizer’s unit cell architecture is compact with structural dimensions of 0.121 × 0.121 × 0.041 λ L 3 , where λ L is the lowest operating frequency’s free-space wavelength. The authors believe this design is compact, with angular stable multi-band multi-conversion ability that will significantly impact the THz applications in real time.