Analysis of the Impact of UCA Element’s Radiation Pattern on the OAM Communication Performance

Orbital Angular Momentum (OAM) based wireless communications can greatly increase the channel capacity due to its mode degree of freedom (DOF) besides time and frequency. Currently, OAM generation based on Uniform Circular Arrays (UCAs) draws much attention because it can flexibly perform OAM mode multiplexing. Channel models of UCA based OAM communications in the previous researches were built without consideration of radiation patterns of antenna elements in the UCA. In order to further explore the impact of UCA element’s radiation pattern on the OAM communication performance, in this paper, we consider the radiation pattern of antenna elements in both the transmit and receive UCAs and reconstruct the channel model of UCA based OAM communications in the line of sight (LOS) and coaxial scenarios. For the antenna element’s radiation pattern function $G(\theta,\phi)$, we theoretically prove that only when $G(\theta,\phi)$ is symmetric in the dimension of $\phi$ can the orthogonality among each OAM mode be maintained. The simulations indicate that the mode isolation, the channel capacity and the bit error rate (BER) performance all decline sharply when $G(\theta,\phi)$ is not symmetric in the dimension of $\phi$. Our research provides useful insights for the designing of antenna elements for CA based OAM communications.