Twisted Beams With Variable OAM Order and Consistent Beam Angle via Single Uniform Circular Arrays

A planar antenna radiating twisted beams with different azimuthal order and a consistent beam angle is designed by employing a single uniform circular array embedded in a Fabry-Perot cavity. Circular phased arrays placed in free space are commonly employed to radiate conical beams carrying orbital angular momentum. However, the beam angle depends on both the array radius and the azimuthal order of the beam, thus requiring the use of multiple concentric circular arrays in order to produce beams with different azimuthal order and a common beam angle. In the proposed design, this is simply achieved by exciting higher-order cylindrical leaky waves through a single circular array feeding a Fabry-Perot cavity. Such waves radiate conical patterns whose beam angle is mainly determined by the relevant radial wavenumber and only weakly depends on the azimuthal order. In particular, we propose here an antenna design capable of radiating beams with azimuthal orders 0, +/- 1, +/- 2, and +/- 3 in the microwave range. The cavity is fed by an array of coaxial probes optimized for input matching through the inclusion of parasitic metal pins. Numerical full-wave simulations validate the effectiveness of the proposed design in terms of radiation patterns, passive input scattering parameters, and active input reflection coefficients.