Wideband high-purity dual-mode circularly polarized vortex antenna for OAM multiplexing

An ultra-wideband high-purity dual-mode circularly polarized (CP) vortex antenna is proposed to generate orbital angular momentum (OAM) vortex beams with modes ±l. The proposed antenna consists of a uniform circular array (UCA), an in-phase feeding network and a metasurface. Different from traditional OAM multiplexing antennas composed of multiple UCAs arranged in concentric rings, the proposed design only utilizes one UCA to generate two OAM modes. A dual-port ultra-wideband CP antenna is designed using characteristic mode analysis and exploited as the array element. In addition, the feeding phase of each array element is provided by its rotation angle, enabling to have a more compact-size multiplexed structure, a less complex feeding network and to generate two high-purity OAM beams. Moreover, a metasurface is used to increase the isolation between the two ports, and two ultra-wideband 1 × 8 power dividers are also designed as the in-phase feeding network. A proof-of-concept prototype of the proposed antenna is fabricated and measured. The measurement results confirm that the proposed antenna can generate both l = + 1 and −1 modes simultaneously through two ports, with −3 dB axial ratio (AR) bandwidths up to 67.9% and 52.4% respectively, and peak gains of 13.8 dBi and 13.9 dBi respectively. The proposed antenna can provide a new trajectory for OAM multiplexing antenna design in wireless communication systems.