Effect of Beam Steering on the Performance of Misaligned Multi-Mode OAM Communications

Orbital angular momentum (OAM) at radio frequency (RF) provides a novel approach of multiplexing a set of orthogonal modes on the same frequency channel to achieve high spectral efficiencies. However, OAM communication system requires perfect alignment of the transmit and the receive antennas and this harsh precondition greatly challenges practical application of OAM mode multiplexing gain. In this paper, we first investigate the effect of non- parallel misalignment on the inter-mode interference of the RF-OAM communication system equipped with uniform circular array (UCA). Then, large-scale system analysis shows that increasing the number of antennas has little effect on the inter-mode interference induced by oblique angle, but beam steering approach could eliminate the inter-mode interference completely. Numerical simulations validate our conclusion on the effect of beam steering.