Design of a Pillbox Reflector based Millimeter-Wave Multi-beam OAM antenna

A multi-beam orbital angular momentum (OAM) antenna is proposed in this paper. The antenna is realized by the combination of a pillbox antenna beamforming network (BFN), dielectric phase delay elements (DPDEs), and a slotted waveguide antenna (SWA) array. The required phase distribution of the OAM beam is provided by the SWA array and the DPDEs. The DPDEs are stacked on the radiation slots of the SWA array to obtain the phase variation (PA) from 0 to 180°, and the position of the radiation slots on the waveguide can achieve another 0 or 180° PA, thus realizing 360° PA. The pillbox BFN is used to generate the phase gradients to the SWA array, steering the main beam direction of the OAM beams. To evaluate the performance of the antenna design, an antenna prototype is simulated at the center frequency of 24.0 GHz with +1 OAM mode. According to the results of the simulation, the antenna is able to produce 5 OAM beams with $\mathrm{a}\pm 20 ^{\circ}$ beam scanning range. The purity of the OAM mode is over 0.66 for all the multi beams.