Broadband High-Order OAM Reflective Metasurface With High Mode Purity Using Subwavelength Element and Circular Aperture

In this paper, high-order orbital angular momentum (OAM) vortex beams (OAMVBs) are generated using reflective metasurface. Generating high-order OAMVBs using traditional reflective metasurface methods deteriorates the radiation performance that affects the mode purity of OAMVBs. A reflective metasurface is proposed to generate the OAMVBs with
$l=4$
mode at the designed frequency of 6 GHz. It is revealed that the radiation performance has been improved and mode purity for
$l=4$
is increased 12.6% by using quarter wavelength unit cell and circular aperture metasurface as compared to the conventional metasurface at the designed frequency. Moreover, the reflective metasurface can generate the OAMVBs with
$l=4$
mode from 5 GHz to 7.5 GHz. The measured gain is 17.93 dBi which agrees well with the simulated gain.