Anisotropic Bilayer Transmissive Huygens Metasurface for Generating Multi-OAM Beams With Orthogonal Modes and Polarizations

This letter proposes a bilayer transmissive Huygens metasurface with an independent phase response for two orthogonal polarizations to generate two distinct modes of orbital angular momentum (OAM) beams. The performance of the proposed unit cell is comprehensively investigated, and its efficiency in the near field is verified through an analytical approach. Then, the necessary theories for realizing converged OAM beams by merging the lens and OAM phase distributions are inclusively elaborated. Moreover, a dual-polarized quad-ridged open-ended waveguide antenna is designed to illuminate the metasurface. Ultimately, two scenarios are explored through the designed surface. The first strategy generates the second ($l_{x}=2$) and third ($l_{y}=3$) modes of the OAM beams in the x- and y-polarizations, respectively, while the second strategy produces modes $l_{x}=0$ and $l_{y}=2$ in two orthogonal polarizations. It appears that the suggested configuration managed to obtain a respectable level of agreement between simulation and measurement results.