Bidirectional multi-mode microwave vortex beam generation enabled by spoof surface plasmon polaritons

The microwave spectrum has become more and more crowded, motivating the investigation of new techniques to increase the communication capacity. Vortex beams carrying orbital angular momentum (OAM) have the capability for providing an extra degree of freedom to increase the channel and capacity of the wireless communication system. In this Letter, we demonstrate an effective route to achieving efficient bidirectional multi-mode microwave circularly polarized vortex beam generation enabled by spoof surface plasmon polariton (spoof SPPs, SSPPs). According to the dispersion relation of the SSPP waveguide and the radiation principle for a leaky-wave antenna, multi-OAM-mode vortex beams with different topological charges can be generated by changing the operating frequency without changing the structure. Interestingly, the emitter simultaneously radiates the right-hand circularly polarized and the left-hand circularly polarized vortex beams with opposite topological charge values upward and downward, respectively. Simulation and experimental results show that this planar SSPP vortex emitter has the advantages of single-fed, bidirectional, multi-mode, and integration compatibility.