Compact 2-D Passive Beam-Scanning Multibeam Antenna Based on Rotman Lens and Mechanical Sweeping Phase Gradient Metasurface

Abstract

A compact multibeam antenna is proposed with passive 2-D beam scanning capability. The antenna is composed of a Rotman lens beamformer, a slotted waveguide array (SWA), and a mechanical sweeping phase gradient metasurface (PGM). The Rotman lens and the PGM together provide a wide range of scanning angles, enabling 2-D beam steering. To improve the crossover level (COL) and the sidelobe level (SLL) of the beams steered by the Rotman lens, the technology of dual sources excitation (DSE) is used, optimizing the COL and the SLL by the tapered magnitude distribution from the sources. Numerical analysis and full-wave simulation are used to verify the performance variations with different source aperture sizes. Since the SWA array can generate a quasi-plane wave above its aperture, the PGM can be fitted close to the SWAs with low spillover loss, resulting in a low antenna profile ( $\lt 0.41\lambda $ ). Then, the phase distributions of the PGM are optimized to suppress the edge negative phase mutation, further optimizing the gain and SLL. To verify the feasibility, a prototype is designed and fabricated at 5.8 GHz. The measured results show that ±50° and ±40° beam scanning ranges in the multibeam and PGM mechanical sweeping planes are realized with the minimum COL and SLL of −2.6 and −8.8 dB. With the wide angle 2-D beam scanning range, low SLL, and COL, the proposed antenna would be attractive for low-cost sensing and communication applications.