Oblique Incidence Analysis of FSS using a Dual-Section Parallel Plate Waveguide

Abstract

This paper presents the design and characterization of a parallel plate waveguide (PPW) system for analyzing the angular response of frequency selective surfaces (FSSs) under TE-polarized oblique incidence. The compact PPW structure, formed by two parallel metallic plates supporting the transverse electromagnetic (TEM) mode, enables accurate transmission and reflection measurements. A wideband absorber is used as a representative FSS, and its unit cell response is evaluated under both normal and oblique incidences. To introduce angular excitation, an initial approach rotates the FSS layer within the PPW. While this provides accurate transmission (S21) results, reflection (S11) is limited, as only part of the reflected wave returns to the input port. To overcome this, an improved setup is proposed by joining two identical PPW sections at an angle 2 θ, with the FSS inclined at θ. This configuration establishes a controlled excitation and reception path for both S11 and S21. The simulation results confirm that the proposed method enhances angular accuracy while maintaining a compact and low-complexity structure, offering an efficient alternative to conventional free-space setups for FSS evaluation. © 2025 IEEE.