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

Abstract

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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$l=4$ </tex-math></inline-formula> mode at the designed frequency of 6 GHz. It is revealed that the radiation performance has been improved and mode purity for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$l=4$ </tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$l=4$ </tex-math></inline-formula> mode from 5 GHz to 7.5 GHz. The measured gain is 17.93 dBi which agrees well with the simulated gain.