| Summary: | Antenna array is one of the methods which can generate Orbital Angular Momentum (OAM) waves. However, OAM waves generated by different antenna arrays have different characteristics of Electric-field (E-field) components’ distribution and radiation patterns. In order to solve this problem, we derive E-field formulas of OAM waves generated by different kinds of dipole antenna array in this paper. The dipole antenna arrays are arranged by three methods: 1) antenna elements are in the same direction of y axis, 2) antenna elements are in the radial direction and 3) antenna elements are in the azimuthal direction. Results show that x components, y components and z components carry different OAM modes under the three conditions. Simulation results show that the same direction antenna array produces the best OAM waves because the y component is dominated by OAM mode l and RHCP/LHCP waves are negligible in energy, while the pure OAM waves carried by the z components generated by the other two antenna arrays have little energy. In addition, only the radiation pattern of l=0 produced by the same direction antenna array does not have a null zone in the propagation direction. Radiation patterns of l=±1 do not have null zones in the propagation direction generated by other two antenna arrays.
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