Thin-Flexible Broad-Band Resistive Frequency Selective Surface Radar Absorbing Material for Low Observable Aircraft Air Intake Application

An aircraft consists of various cavities including air intake ducts, cockpit, radome, inlet and exhaust of heat exchangers, passage for engine bay/other bay for cooling of aircraft systems etc. These cavities are the prime contributors for aircraft radar cross-section (RCS). These cavities are of different cross-sectional areas as well as different lengths depending on the applications on aircraft. The RCS reductions of these cavities are very important to achieve a low observable aircraft configuration. In this paper, a thin-flexible resistive frequency selective surface (FSS) based radar absorbing material (RAM) design is presented. The proposed FSS-RAM is of 0.15mm thickness. Computational result shows > 10dB RCS reduction from 12.5GHz to 40GHz on a flat radar absorbing structure (RAS) panel of 2.0mm thickness with metal backing. The results are further validated with experiments from 8 to 18GHz of frequencies. This FSS based RAS is then computationally implemented on different circular cavities with varying L/D ratios and its performance are compared with the conventional non-RAS cavities. Significant RCS reduction demonstrates possible application of FSS based RAS on various cavities of futuristic aircraft platform for achieving very low observability. Lastly, the performance of the FSS-RAM based RAS of thickness 2.0mm is also demonstrated on an open-source CAD model of conventional fighter aircraft. Aircraft frontal sector of 0 ⁰ to 15 ⁰ shows ~ 7.75Db median RCS reduction and 0 ⁰ to 60 ⁰ shows ~ 8.72dB median RCS reduction from 8GHz to 18GHz frequencies using the proposed FSS RAM based RAS of 2.0mm thickness.