Generating dual-polarized orbital angular momentum radio beams with dual-bowtie cell

In this paper, we propose a reflectarray metasurface to generate two modes of orbital angular momentum (OAM) in two orthogonal directions of polarization. The metasurface comprises dual-bowtie elements of various sizes. By varying the size of the geometry, the element can simultaneously alter the phases of reflection of both polarizations. In the design, equivalent circuit models of the unit cell in both the orthogonal direction and the direction of excitation are built and discussed. These models are used to explain the results of the simulation and can help accelerate the optimization process when designing other reflective metasurfaces. Both the first- and second-order metasurface reflectarrays were simulated and measured at 10 GHz, and the results confirmed that different OAM modes can be generated in two orthogonal directions of polarization. Compared with the prevalent design, the proposed one is more compact as it has only one layer and does not require active components. We also simulated and measured the first-order metasurface reflectarray at multiple frequencies, and the results from 9.2 to 10.5 GHz show that it can generate the two polarized OAMs independently in broadband.