Hybrid cubic-chessboard metasurfaces for wideband angle-independent diffusive scattering and enhanced stealth.

Because of the shortcomings associated with their scattering patterns, both the chessboard and cubic phased metasurfaces show non-perfect diffusion and hence sub-optimal radar cross section reduction (RCSR) properties. This paper presents a novel and powerful hybrid RCSR design approach for diffusive scattering by combining the unique attributes of cubic phase and chessboard phase profiles. The hybrid phase distribution is achieved by simultaneously imposing two distinct phase profiles (chessboard and cubic) on the hybrid metasurface area with the aid of geometric phase theory to further enhance the diffusive scattering and RCSR. It is shown in this paper that through the integration of cubic and chessboard phase profiles, a metasurface with the hybrid phase mask successfully overcomes all the above issues and shortcomings related to the RCSR of both chessboard and cubic metasurfaces. In addition, the proposed design leverages the unique scattering properties offered by these distinct phase profiles to achieve enhanced stealth capabilities over wide frequency ranges and for large incidence angles. Simulation and measurement results show that the designed hybrid metasurfaces using the proposed strategy achieved RCSR and low-level diffused scattering patterns from 12-28 GHz (80%) for normal incidence of a far-field CP radar plane wave. The hybrid metasurface shows a stable angular diffusion and RCSR performance when the azimuthal and elevation incidence angles are in the range of 0° → ± 75° which is wider than other designs in the literature. Therefore, this work can make objects significantly less detectable in complex radar environments when enhanced stealth is required.

Exploring the EM-wave diffusion capabilities of axicon coding metasurfaces for stealth applications.

Coding metasurfaces for diffusion scattering of electromagnetic (EM) waves are important for stealth applications and have recently attracted researchers in physics and engineering communities. Typically, the available design approaches of coding metasurfaces lack a coding sequence design formula and sometimes cannot simultaneously ensure uniform diffusion and low reflected power intensity without extensive computational optimization. To the authors' best knowledge, the diffusion and radar-cross-section reduction (RCSR) of 2D axicon metasurfaces for cloaking and stealth applications have not been explored before. This article presents a single-layer coding metasurface design that exhibits an axicon phase mask on its aperture for efficient diffusion of EM-waves and RCSR of metallic objects. The proposed approach is robust and ensures greater than 10 dB of RCSR for normal incidence and a wide-range of off-normal incident angles. Theoretical calculations, numerical simulations, and experimental validations of the proposed axicon coding metasurface demonstrate that the 10 dB RCSR covers the frequency range of 15 to 35 GHz (fractional bandwidth is 80%) under normal incidence. Under off-normal incidence, the RCSR and the diffusive scattering behavior are preserved up to 60° regardless of the polarization of the far-field incident radar wave. Compared to other available approaches, the presented design approach is fast, robust, and can achieve more uniform diffusive scattering patterns with remarkable RCSR, which makes it very attractive for potential stealth applications.