Realizing orbital angular momentum (OAM) beam with small divergence angle by luneberg lens

The antenna structure generating orbital angular momentum (OAM) beam with small divergence angle is described in this paper. Luneberg lens, always used to generate high gain beam, is utilized in this structure to focus the OAM beam generated by the source. Luneberg lens is discretized into layers. With simulations, the OAM beam's divergence angle with 19 degree is successfully decreased to 5 degree, meanwhile, the focused beam has the OAM properties with mode number l=-1.