High-efficient beam-converging for UCA based radio vortex wireless communications

Abstract

Orbital angular momentum (OAM) based radio vortex wireless communications, which provide the new angular orthogonal OAM-modes/states to significantly boost the spectrum efficiency, have received much attention recently. To achieve maximum spectrum efficiency, it is highly demanded that all OAM-modes need to be utilized. The uniform circular array (UCA), as a simple antenna structure for multiple OAM-modes transmissions, is convenient to be implemented for high spectrum efficiency radio vortex wireless communications. However, it has been shown that the OAM based electromagnetic waves are vortically hollow and divergent. Also, the divergence of corresponding electromagnetic wave increases as the order of OAM-mode increases. Therefore, if the order of OAM-mode is relatively large, it is impossible to use high order OAM-mode since the received corresponding signal-to-noise ratio (SNR) is very small. To efficiently utilize high order OAM-modes for spectrum efficiency enhancement, in this paper we propose the lens antenna based electromagnetic waves converging scheme, which keeps remain the angular-distinguishing property of multiple OAM-modes, for radio vortex wireless communications. We develop the novel bifocal lens antenna to not only converge the electromagnetic wave, but also decrease the attenuation corresponding to traditional electromagnetic waves. Simulation results are presented to show that the bifocal lens can converge the OAM waves into cylinder-like beams, which are expected to benefit the spectrum efficiency of wireless communications.