Design of Passive and Wideband Radar Absorbing Materials Comprising Resistive Frequency Selective Surfaces

In this study, we present general guidelines for the design of wideband radar absorbing materials that incorporate resistive frequency selective surfaces (FSSs). We first describe the design analytical methodology, based on the transmission line equivalent circuit. We therefore apply the proposed approach to numerical case studies, aimed at demonstrating the effectiveness of the equivalent circuital approach. Specifically, we conceived two radar absorbing materials by employing commercial dielectric substrates and particular FSS patterns based on continuous fishnet structures. These design choices have been preferred in order to enhance the practical applicability and to facilitate the fabrication step. For the first design, the obtained numerical results demonstrate that the absorption is below-10 dB in the frequency range from 2 to 6 GHz, which corresponds to a fractional bandwidth of 100%, under normal incidence. Conversely, the second absorber covers the -10 dB absorption band from 5 to 19 GHz, with a fractional bandwidth of 116%, always under normal incidence. Therefore, the proposed analytical approach can be extremely useful for the designer in order to rapidly prototype broadband and passive radar absorbing materials which include frequency selective surfaces. Moreover, fundamental practical design aspects, as the use of commercial dielectric substrates and fishnet FSS patterns, which facilitates the fabrication of the developed RAMs, can be taken as well into account.