Radiation Performance Synthesis for OAM Vortex Wave Generated by Reflective Metasurface

Abstract

The radiation performance of orbital angular momentum (OAM) vortex waves (OAMVWs) generated by reflective metasurface is comprehensively investigated. According to different incident sources, the issue is classified into two cases, namely, the plane-wave incidence and the focused incidence. In both cases, the radiation performance deteriorates with the increasing of topological charge <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$l$ </tex-math></inline-formula> . Moreover, the largest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$l$ </tex-math></inline-formula> that can be generated is limited by the scale of the metasurface. In addition, a detailed analysis reveals that phase quantization affects the lobe levels of OAMVWs but has no influence on the divergence angle of the main lobe. Nevertheless, for the case of plane-wave incidence, 1-bit phase quantization method is not able to generate OAMVWs in normal direction and will cause grating lobe when the beam scans. Meanwhile, the grating lobe carries OAM with opposite <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$l$ </tex-math></inline-formula> against the main lobe. Finally, a focused-feed metasurface based on 1-bit phase quantization is simulated and measured. The simulation and measurement results show that OAMVW with topological charge <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$l=1$ </tex-math></inline-formula> is successfully generated and detected, validating the effectiveness of phase quantization method in OAMVW generation. It is worth to point out that phase quantization is highly promising in electronic-controlled reconfigurable OAMVW generation.