Low‐sidelobe orbital angular momentum beam for donut‐shaped amplitude‐and‐phase metasurface based on Bayliss synthesis method

Abstract

In this letter, a method for generating low‐sidelobe orbital angular momentum (OAM) beam is presented using a donut‐shaped amplitude and phase metasurface (DS‐APM). Building upon conventional phase‐only metasurface, the Bayliss synthesis method is employed to adjust the amplitude distribution on the metasurface. Thereby, the amplitude and phase metasurface (APM) can reduce the sidelobe level of the OAM beam. Subsequently, considering the Nyquist conditions and momentum constraints, a hollow modification is implemented on the APM array aperture center. The adjustment of the hollow dimension renders the DS‐APM compatible with the corresponding OAM beam mode number. Furthermore, a modified I‐shaped element is proposed, which enables independent modulation of the amplitude and phase of reflected cross‐polarized waves. Utilizing the proposed elements, a DS‐APM applied to generate a second‐order OAM beam operating at 15 GHz was designed, fabricated, and measured. The measurement results align with the full‐wave simulations, thereby validating the rationality of the proposed method.