Generation of wideband vortex beam with different OAM modes using third-order meta-frequency selective surface

Orbital angular momentum (OAM) beam generators have attracted tremendous interests recently due to their excellent performance and potential applications in wireless communication. However, the existing transmissive OAM generators suffer from several limitations, such as narrow bandwidth, high profile and low efficiency. In this study, a new wideband third-order meta-frequency selective surface (meta-FSS) for generating focusing vortex beam is developed. The proposed meta-FSS element is designed at X- band with a third-order band-pass filter property, which exhibits the merits of low profile, high transmissivity, and large angular stability. By employing the proposed meta-FSS element, prototypes of OAM generators for + 1 and -2 modes are designed, fabricated, and measured. Experimental results verify the ability of the proposed design to convert an incident left/right-handed circularly polarized (L/RHCP) spherical wave into a transmitted R/LHCP vortex carrying OAM wave from 9.0 GHz to 11.0 GHz with high mode purity. A good agreement is achieved between the experimental and numerical results, which demonstrates that the proposed structure paves the wave for generating desired OAM modes, and provides new possibility for designing novel low-profile wireless communication devices.