Generation of orbital angular momentum multiplexing millimeter waves based on a circular traveling wave antenna

Orbital angular momentum (OAM) has recently attracted extensive attention in the radio frequency domain due to its potential applications in various areas. In the OAM-based communication system, the development of the OAM-generating antennas lies at the heart of the matter to generate and receive vortex beams. In this work, a multiplexing/demultiplexing millimeter-wave OAM antenna based on the traveling-wave circular loop structure is proposed and experimentally demonstrated. The feeding networks are implemented using waveguide ports which are inherent integration in millimeter wave communication systems. A prototype with OAM states l = +/- 3 carried by the z polarization and l = +/- 2 for the x and y polarizations at 60 GHz is fabricated and measured. Measured near-field distributions and far-field radiation patterns show excellent agreement with the simulated ones. Furthermore, based on the designer strategy, four coaxially propagating waves with OAM modes l = +/- 3 and +/- 5 for the z polarization component and l = +/- 2 and +/- 4 for the x, y polarization components are investigated, respectively. The antenna will have a positive effect on the application potential of OAM-based wireless communication.