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

Abstract

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 ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{0}$ </tex-math></inline-formula> ) and third-order mode ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3f_{0}$ </tex-math></inline-formula> ) to provide two broad absorption bands. It transmits electromagnetic (EM) waves when the open-ended slotline operates in half-wavelength mode ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2f_{0}$ </tex-math></inline-formula> ). The 2-D lossy layer absorbs EM waves between the frequencies of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{0}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3f_{0}$ </tex-math></inline-formula> and provides a transmission window at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2f_{0}$ </tex-math></inline-formula> . The 2-D bandpass FSS has a broad transmission band at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2f_{0}$ </tex-math></inline-formula> 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.