Miniaturized Multibeam Antenna With Narrow Beam Based on Phase-Gradient Square Loop Metasurface

In this article, a new method to design multibeam antenna based on a phase-gradient metasurface (MS) is proposed and demonstrated through two cases of single source and multisource. The basic idea is to employ the feeding source operating in high-order TM20 (TM02) mode to generate split beams. Then, by loading an F–P cavity and a phase-gradient MS, the narrow main lobe is obtained. Also, the gain is raised and the sidelobe level (SLL) is cut down. In addition, for the single-source antenna, the impedance matching is improved and the gain is further enhanced by loading holes. Moreover, through adding a parasitic unit, the SLL is dropped. For the multisource antenna, by etching slots, the isolation between four ports is improved and the SLL is further reduced. Finally, both the simulated and measured results verify the proposed method. The realized single-source multibeam antenna operates in the range of 9.74–10.62 GHz and has a lower SLL of 21.28 dB. Four beams point to ( $\theta $ , $\phi$ ) = (57°, 0°), (57°, 90°), (57°, 180°), and (57°, 270°). For the multisource case, the antenna has a gain of 11.26 dBi, the isolation better than 20.52 dB, and the SLL of 12.16 dB. Also, the four main beams are steered to ( $\theta $ , $\phi$ ) = (12°, 2°), (12°, 92°), (12°, 182°), and (12°, 272°).