Ultra-Thin Broadband Circular Polarization Conversion Metasurface for Full-Space Wavefront Manipulation Application

In this article, we introduced an ultra-thin broadband single-layer metasurface (MS) comprising an S-shaped resonator (SSR) structure enclosed by a circular cover adhered on a dielectric substrate. The MS exhibits remarkable capabilities in achieving simultaneous half-transmission and half-reflection for broadband circular polarization (CP) conversion, as well as full-space wavefront manipulation in the microwave frequency range. Through simulations and experiments, we demonstrated that the orthogonal CP coefficients for both transmission and reflection exceed 0.35 for normal incidence of left-handed circular polarizations (LCP) and right-handed circular polarizations (RCP) waves from 6.2 GHz to 15 GHz, with a relative bandwidth of about 87.1%. This results in a polarization conversion efficiency of approximately 22%, which approaches the theoretical limit (25%) of the single layer MS structure around 8 GHz. Moreover, utilizing the principle of geometrical phase modulation, the desired full 2π phase-shift of orthogonal CP waves in both transmission and reflection can be achieved by solely adjusting the orientation angle of the SSR structure. Numerical simulations substantiate this concept by demonstrating anomalous reflection and refraction, vortex beam generation, and planar focusing, showcasing the comprehensive control of wavefronts in all spatial directions. Our design offers valuable insights for the practical implementation of broadband full-space CP and wavefront manipulation in various applications.