Microwave Vortex-Beam Emitter Based on Spoof Surface Plasmon Polaritons

Since orbital angular momentum (OAM) being investigated intensively in the optical region, there have been growing interests in employing OAM to solve the problem in wireless communications as a new method. It is found that the independence between different OAM modes is crucial to wireless communications. Motivated by the tremendous potential of OAM in communication systems, a novel method to generate vortex beams by spoof surface plasmon polariton (SPP) is proposed. A looped double-layer spoof SPP waveguide is applied to realize the transmission of electromagnetic waves. Beam emitting is accomplished through a series of circular patches, whose role is not only the radiation units but also resonators giving rise to the phase shifts required by the vortex beam. The proposed method is validated by both numerical simulation and experiment. The measured results show that spoof SPP are radiated by the circular patches and vortex beams carrying different OAM modes are observed at different frequencies. The proposed method possesses smaller size and is much easier to be integrated into systems and integrated circuits. The simple structure and design procedure make the proposed method promising in future wireless communication systems.