Dipole antenna incorporated with metasurface and cavity reflector for wideband circular polarisation and high gain

This paper presents the design of a low-profile dipole antenna incorporating a polarisation converter metasurface and cavity reflector for wideband circular polarisation and high-gain performance. The antenna comprises a modified dipole structure with two parasitic patches placed on the bottom side of the substrate in a coplanar configuration, and a metasurface comprising four modified square metal patches in a 2 × 2 layout, with a centrally positioned cross-shaped strip printed on the top side of the substrate. A modified cavity reflector with truncated corners and four triangular extensions at the top corners of the cavity was introduced beneath the dipole to enhance gain. Each unit cell of the metasurface included a complementary patch structure formed by etching two diagonally oriented C-shaped slots onto a square metal patch, resulting in a distinct chiseled pattern. These diagonal slots are critical for generating a 90° phase difference and balancing the amplitude of the orthogonal polarisation components, thus facilitating the conversion from linear to circular polarisation. The proposed antenna achieves a global bandwidth of 49.7% (4.0-6.73 GHz), simultaneously satisfying impedance matching, axial ratio, and gain requirements with a peak gain of 10.8 dBic and a radiation efficiency exceeding 92%.