Multimode OAM antenna with reduced beam divergence for 6G networks

Orbital angular momentum (OAM) in microwave frequencies introduces a promising new dimension for enhancing channel capacity in future 6G wireless communication systems. However, the practical use of OAM waves for long-distance transmission is limited by their inherent beam divergence, which reduces signal strength over distance. This paper proposes a transmissive metasurface lens designed to reduce the divergence of an OAM beam generated by a multimode uniform circular array (UCA) operating at 6 GHz. The design of the metasurface lens is based on the optical converging axicon concept, which is used to achieve the required phase-shift distribution across the metasurface. The UCA generates OAM modes of l = − 1, + 1, and 0 through distinct feed excitations. Comprehensive evaluations comparing the UCA performance with and without the metasurface lens were carried out based on radiation patterns, S11, electric field amplitude, and phase distribution. The results demonstrate a significant improvement: the beam divergence is reduced from 18° to 10°, and the maximum gain is increased from 10.7 dBi to 14.1 dBi. These improvements indicate a more focused and directional OAM beam, enhancing the practicality of OAM-based communication systems for extended-range applications.