Bandwidth and Gain Improvement of a Circularly Polarized Slot Antenna Using Nonuniform Metasurface

This paper presents a novel design of a circularly polarized antenna based on a nonuniform metasurface (NMS). The original antenna comprises a uniform metasurface (UMS) layer and a slot antenna below. In order to achieve circularly polarized (CP) radiation, an oblique slot is etched on the center patch, and the size ratio between the center patch and the surrounding patches is adjusted to create the NMS. To further enhance the CP properties, an improved NMS (INMS) is proposed, consisting of four units with corners removed, building upon the original NMS design. Simulation results demonstrate that the proposed antenna design offers an S11 bandwidth ranging from 4.39 to 7.21 GHz, with a 3 dB axial ratio (AR) bandwidth spanning from 5.43 GHz to 6.76 GHz. Compared to the original UMS-based antenna, the INMS design shows an average gain increase of 1.21 dB, with a peak gain of 9.49 dBic. Furthermore, utilizing characteristic mode analysis (CMA), this paper explores the modal behaviors when applying the NMS to the antenna. The results indicate that this configuration excites two orthogonal modes, leading to CP radiation and the emergence of an additional AR minimum point. These factors contribute to the broader bandwidth observed in the proposed antenna design. The outstanding radiation performance of the proposed antenna design makes it suitable for various applications, including military and civilian communication, as well as point-to-point links.