Simulation of helical modulation in a focal plane array

In various experiments it had been positively demonstrated that the ability to perform helical modulation, by exploiting the Orbital Angular Momentum (OAM) states of the electromagnetic (EM) waves, is a feasible scheme of digital modulation in the bandwidth-constrained regions of the spectrum. In this paper we shall show that by changing the EM properties to an antenna array, at the focal plane of a parabolic antenna (instead of changing the geometry of the entire aperture), a factor of vorticity can be introduced in the radio waves. The problem becomes relevant in cases where the antenna has larger radial dimensions. At the focal plane of the antenna phase changes are incorporated in the successive elements of the array. Circular arrays made up of discrete elements arranged in different configurations are being used in this exercise. Results from the different arrangements are compared in terms of antenna parameters, and the radiation patterns are obtained for various optimal representations of the OAM states.