Abstract
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.
Highlights
Electromagnetic waves carry angular momentum during propagation that has two components: spin angular momentum and orbital angular momentum (OAM)
The spin angular momentum relates to the states of polarization of electromagnetic waves, whereas the OAM corresponds to the distribution of the magnitude and wave front of the electromagnetic waves
Techniques to obtain multiple OAM modes by designing metasurfaces are limited to the aforementioned ones, which means that the orthogonal directions of the metasurface are designed separately
Summary
Electromagnetic waves carry angular momentum during propagation that has two components: spin angular momentum and orbital angular momentum (OAM). There are many ways to produce multiple OAM modes, including the patch antenna array, spiral antenna, resonant cavity, metasurfaces, and other planar devices.. It is easy to design the patch antennas, but difficult to plan the feeding networks Both the spiral antenna approach and the resonant cavity have the shortcoming of a bulky structure. In 2017, Li et al proposed a reflectarray to independently generate reconfigurable OAM-carrying waves in orthogonal directions of polarization in radio frequency.. In 2019, Qi et al proposed a transmissive metasurface for the generation of dual-mode polarized OAM.. In 2019, Qi et al proposed a transmissive metasurface for the generation of dual-mode polarized OAM.36 This structure is multilayered with three dielectric layers and four metal surfaces. Techniques to obtain multiple OAM modes by designing metasurfaces are limited to the aforementioned ones, which means that the orthogonal directions of the metasurface are designed separately
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