Beam Steering for the Misalignment in UCA-Based OAM Communication Systems

Radio frequency-orbital angular momentum (RF-OAM) is a technique that provides extra degrees of freedom to improve spectrum efficiency of wireless communications. However, OAM requires perfect alignment of the transmit and the receive antennas and this harsh precondition greatly challenges practical applications of RF-OAM. In this paper, we first investigate the effect of non-parallel misalignment on the channel capacity of the RF-OAM communication system equipped with uniform circular array (UCA). Then, we propose a transmit/receive beam steering approach to circumvent the large performance degradation in not only non-parallel case but also off-axis and other general misalignment cases. The effectiveness of the beam steering approach is validated through both mathematical analysis and numerical simulations.