A Hybrid Element Triband Frequency Selective Surface With High Angular Stability and Polarization Insensitivity

Abstract

In this article, a triband frequency selective surface (TBFSS) with narrow band separation is proposed. Pass band frequencies of this TBFSS are 6.9, 8.63 and 10.3 GHz with fractional band width (FBW) of $\text{15.8}\%$ , $\text{13.5}\%$ , and $\text{10.9}\%$ , respectively. Low insertion losses of 0.5, 0.2, and 0.4 dB are observed in the pass bands. These resonant frequencies are adjusted in C and X bands. The unit cell (UC) dimension is $0.2\lambda _0\times 0.2\lambda _0$ which is calculated at lowest transmission zero. Hybrid structural elements are etched on two sides of Rogers 4003 C substrate with $\varepsilon _r$ of 3.38 and thickness of substrate is selected to be 0.406 mm. This design is highly obliquely stable upto $\text{75}^\circ$ . It also shows polarization insensitivity to transverse electric (TE) and transverse magnetic (TM) modes of the plane wave. An equivalent circuit is presented for better understanding of the structure and tuning purpose. A prototype is fabricated to measure the frequency response of the TBFSS. Measured and simulated scattering parameter S $_{21}$ exhibit very good match.