Broadband AT Rasorber for Radome Application

This paper presents compact Absorptive-Transmissive (AT) frequency-selective rasorber, providing more than 90% absorption of electromagnetic (EM) waves from 3.88 GHz to 8.43 GHz and a good insertion loss at 9.48 GHz. The structure is simple, consisting of a top lossy layer and a bottom frequency selective surface (FSS) layer, isolated by an air spacer. The design methodology of the proposed structure and its detailed analysis using S-parameters is discussed. The lossy layer consists of four octagonal rings symmetrically placed at corners and connected through a common larger-sized central octagonal ring of copper with resistors. The FSS layer consists of a single dielectric octagonal ring cut over uniform copper. Based on equivalent circuit model, the EM characteristics of frequency selective rasorber is presented. The effect of resistance and the height of substrate on EM performance of rasorber are analysed. Finally, the rasorber is fabricated and measured to experimentally validate the performance of proposed design.