A Transmissive Metasurface for OAM Vortex Beam Generation in the 77-GHz Automotive Radar Band

Abstract

This letter presents a transmissive metasurface for generating orbital angular momentum (OAM) vortex beams in the 77-GHz automotive radar band. The unit cell features a central cross-shaped patch surrounded by a circular resonant ring, implemented on a multilayer Rogers RT/duroid 5880 substrate. This configuration enables continuous $0\pi $ – $2\pi $ transmission phase coverage with an amplitude above 0.7 across 76–81 GHz. A $21\times 21$ -element array was fabricated and characterized experimentally. Measurements confirm the generation of a +1-mode OAM beam over the full automotive band, with mode purity exceeding 70%, a half-power beamwidth of approximately 9°, and a peak gain exceeding 20 dBi.