Broadband microwave absorber composed of sandwich structure with a lossless medium as the intermediate layer

Abstract

A broadband microwave absorber with a sandwich structure has been designed, creatively taking lossless medium (paraffin or air) as the intermediate layer. The paraffin layer effectively adjusted the impedance of the absorber, especially at the high-frequency region, hence observably raising the upper limit of the effective absorption region from 14.5 GHz to 18 GHz. As a result, the effective absorption bandwidth (EAB, reflection loss less than −10 dB) is broadened to 10.1 GHz, covering the entire Ku band and the entire X band, with a total thickness of only 2.5 mm, among which the paraffin intermediate layer has a thickness of 0.8 mm. Based on Maxwell's equations, normalized Poynting vector and loss analysis are given, which reveals the paraffin layer can enhance the total loss, though paraffin is lossless. In addition, the intermediate paraffin layer can also be replaced with air or even vacuum, providing a new perspective for the design of a high-performance absorber with lighter weight.