Ultra-Wideband Low-RCS Circularly Polarized Antennas Realized by Bilayer Polarization Conversion Metasurfaces and Novel Feeding Networks

This article introduces a chessboard metasurface comprising four orthogonally arranged elements designed to create a broadband circularly polarized (CP) antenna with ultra-wideband radar cross section reduction (RCSR). Each element is a bilayer structure consisting of a polarization rotation surface (PRS) and a phase-controlled surface (PCS). The PCS effectively modulates the phases of co-polarized and cross-polarized reflective waves, resulting in a considerable bandwidth expansion for polarization conversion. To achieve CP radiation, the chessboard metasurface is fed sequentially with rotational input, with each output port featuring a double-V-shaped slot coupled by a fork-shaped microstrip. This feeding approach significantly suppresses scattering modes within the working band, thereby enhancing in-band RCSR. In addition, eight microslots are further etched onto the ground plane to achieve a full in-band RCSR exceeding 10 dB. Simulation results demonstrate an impedance bandwidth of 54.5% (6-10.5 GHz) and a 3-dB axial ratio bandwidth of 32.9% (6.6-9.2 GHz), with a peak gain of 11.9 dBic. Besides, the antenna exhibits 10-dB out-of-band and full in-band RCSR in the ultra-wideband range from 6.6 to 22.4 GHz. Experimental results corroborate the findings of the simulations.