Superbroadband Diffuse Wave Scattering Based on Coding Metasurfaces: Polarization Conversion Metasurfaces

In this article, a wideband metasurface for radar cross-section (RCS) reduction based on a polarization conversion is presented. The unit cell is composed of a two-layer metasurface based on frequency-selective surfaces (FSSs) backed by a thin-grounded dielectric substrate. The metasurface is able to rotate the polarization by 90° using special binary elements "0" and "1" in combination. The elements are arranged using a binary coding matrix formed by a group search optimization (GSO) algorithm. The optimized arrangement resulted in the distribution of scattered electromagnetic (EM) waves and suppression of the maximum bistatic RCS of the metasurface over a broadband of incident angles for both polarizations. Additionally, a polarization conversion ratio (PCR) of nearly 131% with an efficiency higher than 90% is achieved. The reflective two-layer metasurface is designed in such a way to generate a reflection phase difference of 180° between elements 0 and 1 on a broad frequency band. A theoretical analysis is performed on the ratio of the 0 and 1 elements using the least square error (LSE) method to find the best ratio value. The simulated and experimental results show that the structure can significantly reduce the RCS by 10 dB over a wide frequency range from 5.1 to 22.1 GHz (125%) at the normal incidence for both polarizations.