Bandpass Absorptive Frequency-Selective Structures With Wide Absorption Bands Based on Hybrid 2-D and 3-D Structures

This article proposes a bandpass absorptive frequency-selective structure (AFSS) with wide absorption bands based on the hybrid two-dimensional (2-D) and three-dimensional (3-D) structures. It consists of a 3-D lossy structure, a 2-D lossy layer, and a 2-D bandpass frequency-selective surface (FSS). The 3-D lossy structure functions in its fundamental mode (f(0)) and third-order mode (3f(0)) to provide two broad absorption bands. It transmits electromagnetic (EM) waves when the openended slotline operates in half-wavelength mode (2f(0)). The 2-D lossy layer absorbs EM waves between the frequencies of f(0) and 3f(0) and provides a transmission window at 2f(0). The 2-D bandpass FSS has a broad transmission band at 2f(0) and a broad rejection band outside of the band. The operating principle of AFSS is investigated in depth based on an accurate equivalent circuit model (ECM). A prototype is fabricated and assembled to demonstrate the viability of the principle. The experimental results indicate a wide passband with low insertion loss. The bandwidth of lower and upper wide absorption bands is 120.3% and 43.5%, respectively. In addition, both the simulated and measured outcomes exhibit that the proposed AFSS has stable performance under oblique incidence.