Design and analysis of an X-band low-RCS A-sandwich radome based on double-layer frequency-selective surface for modern defence systems

This article presents the design of an X-band A-sandwich radome based on a double-layer frequency-selective surface (FSS) to reduce the radar cross-section (RCS) of the co-designed antenna. The proposed radome is designed with bandstop FSS elements on the top and bottom surfaces of the skin layers. The radome wall thickness is optimised to 0.285λ0 to achieve low insertion loss and minimise reflections in the desired RCS reduction band. Initially, a basic radome structure was implemented utilising a T-shaped monopole element, which exhibits a 10 dB monostatic RCS bandwidth of only 0.95 GHz, ranging from 9 to 9.95 GHz. Therefore, to achieve wider RCS bandwidth and high angular stability, a modified radome structure was later designed with a convoluted geometry of the basic FSS elements. This design shows an improved bandwidth of 2.58 GHz (7.32–9.90 GHz) and stable angular performance up to 70°. The proposed radome is integrated into a linearly polarised microstrip patch antenna for out-of-band RCS reduction measures. An 8 × 8-element FSS-based radome prototype of size 112 mm × 112 mm has been fabricated for experimental verification. The measured results achieve a peak out-of-band monostatic RCS reduction of 16.86 dB for the x-polarisation and around 13 dB for the y-polarisation while maintaining other antenna parameters. Furthermore, a 2-D bistatic RCS reduction of more than 20 dB has also been achieved for a boresight angle of ±20°.