Broadband Band-Absorptive Frequency-Selective Rasorber With a Hybrid 2-D and 3-D Structure

A novel frequency-selective rasorber (FSR) with a broad absorption band is proposed in this letter. The proposed FSR is realized by vertically cascading a two-dimensional (2-D) lossy layer with a 3-D band-stop frequency-selective structure (FSS). The 2-D lossy layer is composed of meandered square loops loaded with lumped resistors, and the 3-D band-stop FSS is constructed by parallel-plate waveguide arrays (PPWAs) stacked along the TE polarization direction (linear polarization perpendicular to the PPW). The band-absorptive FSR exhibits an absorption band (|S₁₁| ≤ -10 dB and |S₂₁| ≤ -10 dB) from 7.85 to 12.85 GHz and a low-pass band (|S₂₁| ≥ -1 dB) up to 3.8 GHz. Its transition efficiency of the transition band (FR_ap) is 2.1. A prototype is fabricated, and its measured results show that the proposed FSR has a low loss and flat low-pass band, a wide absorption band with high selectivity, and a steep transition band between the low-pass band and absorption band.

I. Introduction

Frequency-selective rasorbers (FSRs), as special frequency selective surfaces/structures (FSSs), have attracted growing attentions in recent years due to their unique characteristics [1]. Although FSSs can achieve good filter performance [2]–[4], they can only be used to reduce monostatic radar cross section (RCS) and unsuitable for bistatic/multistatic RCS reduction. By introducing additional lossy elements, FSRs are able to absorb the out-of-band electromagnetic (EM) waves instead of reflecting them, while they are transparent to in-band EM waves. Therefore, FSRs can be effective for monostatic and bistatic/multistatic RCS reduction.