Design of A Small-Divergence-Angle and High- Purity OAM Metasurface Antenna

Circular phased antenna array (CPAA) is a typical structure to generate vortex beams. However, the CPAA presents disadvantages such as low efficiency, impure orbital angular momentum (OAM) mode and large divergence angle. Herein, a metasurface antenna is proposed to generate small-divergence- angle and high-purity vortex beams carrying OAM. The designed antenna consists of 17 x 17 multilayer unit cells with a good transmission coefficient. Simulation results show that OAM beams can be generated at 5.8 GHz with a mode purity over 93%. The divergence angles of OAM mode l=+1 and l =+3 are 7° and 12° respectively, which are validated by both simulations and experiments. This compact antenna increases the feasibility of practical applications using OAM beams.