Design of Radar Absorbing Materials Based on Connected Frequency Selective Surfaces

This article derives design guidelines for radar absorbing materials (RAM) integrating connected, fishnet-like, resistive frequency selective surfaces (R-FSSs). While R-FSSs have been long used in the radar signature and electromagnetic interferences reduction, nevertheless the configuration where all the unit-cells are physically connected has not been yet thoroughly investigated for this aim. Indeed, the fishnet-like arrangement can guarantee extraordinary key advantages in terms of RAMs fabrication, especially for large production scales. Therefore, this article, by resorting to significant test-cases, aims at deriving practical design procedures to realize advantageous connections among adjacent FSS unit-cells. Specifically, the effects on the overall FSS impedance behavior of the geometrical variations in the unit-cell connections are deeply explored. To ensure the broad applicability of the presented guidelines, the study has been carried out by recurring to an equivalent circuit analysis, based on the transmission line theory, and on accurate full-wave simulations. To prove the practical significance of the developed guidelines, two prototypes of the same RAM based on a resistive and connected FSS have been fabricated. Both in a small flat panel and in a large-scale conformal arrangement, the electromagnetic reflection was drastically reduced in the band between 6 and 18 GHz, while significantly simplifying the fabrication process. In conclusion, the proposed research exhibits promising potential to enable an efficient large-scale fabrication for RAMs, by addressing the difficulties associated with the design of connected unit-cells.