Multimode orbital angular momentum antenna based on four-arm planar spiral

An orbital angular momentum (OAM) antenna based on four-arm planar spiral for multiple OAM modes generation is proposed in this Letter. There are four OAM modes generated by employing different phase feeding arrangements for the four ports. By adjusting the branch between the feeding port and the corresponding spiral arm, a good match can be easily obtained. The characteristics of the OAM antenna with modes of ${l}=0\comma\; -1\comma\; -2\comma\; -3$l=0,−1,−2,−3 at the operating frequency of 5.8 GHz are presented both in simulation and experiment, with 10-dB return loss from 5.6 to 6.0 GHz. The measured near-field phase distributions clearly indicate the OAM vortex characteristic which are consistent with the simulations. The proposed design shows great potential for the application of reconfigurable OAM wireless communication systems.