A Transmissive Metasurface Producing Wideband Higher-Order Vortex Modes to Increase the the Information-Carrying Capacity of Wireless Systems

High-order, broadband OAM-vortex beams have great potential to increase the information-carrying capacity of wireless systems, but their practical application is constrained by issues with low gain, limited bandwidth, and low mode purity in higher-order modes. To address these requirements, in this paper, we propose a symmetric transmit unit cell that achieves full 360-degree phase coverage with acceptable transmission loss and a uniform configuration suitable for dual-polarized applications, which consists of four conductive layers interleaved with substrate layers. Experimental testing of higher-order modes on the manufactured transmissive prototype verifies broadband vortex-beam formation, which is consistent with the simulation results. Across the 26.5 to 40.5 GHz frequency span, the proposed design demonstrates a consistently high OAM-vortex mode purity exceeding 86% and covering 46.6% of the OAM bandwidth. It is also observed that the fabricated prototype achieves a peak realized gain of 21.7 dBi for the +2 mode, resulting in an aperture efficiency of 13.6%. With the implementation of the proposed transmitarray prototype, future wireless systems can attain significantly improved information-carrying capacity.