A compact single-layer reflective metasurface for high-efficiency polarisation conversion applications in C and X bands

The authors design and experimentally analyse an anisotropic metasurface for the simultaneous conversions of linear cross and circular polarisations in the C and partial X bands. The proposed compact structure utilises a dual-cut square-ring resonator and a square patch on an FR4 substrate above a ground plane. The full-wave simulations exhibit over 92% efficiency in cross-conversion over a fractional bandwidth (BW) of 52.3%. The proposed metasurface efficiently converts linear to circular polarisation in two different bands, achieving left-hand circularly polarised and right-hand circularly polarised efficiencies exceeding 93% and 89%, respectively. The compact unit-cell with dimension 0.22λ × 0.22λ attains stable polarisation transformation efficiency rates exceeding 80% up to 40° incident angles. The design is adaptable for efficient wide BW across both lower and higher (millimetre-wave) frequencies through scaling. A prototype of the proposed polarisation converter (PC) was realised and validated effectively in measurements, aligning well with simulations. This PC features a novel and simple structure with multifunctional wideband operation, stable incident angle output, polarisation insensitivity, and scalability, making it an efficient front-end for various radio frequency applications, including polarisation control and polarisation transformers.