Reducing the Orbital Angular Momentum Waves Divergence with a Lens to the Utilized Antenna Array

One of the major obstacles to use non-zero orbital angular momentum (OAM) systems is the strong divergence of OAM modes with increasing range. This paper discusses a way to reduce the divergence of OAM modes using dielectric lenses. A square antenna array (AA) on printed patches operating in the frequency range of 9 to 10 GHz was used as the source of OAM. AAs are capable of generating OAMs of modes 0, -1, +1. Two types of dielectric lenses were modelled for the AAs: conventional and hyperbolic. The distributions of amplitudes and phases of the electric field strength vector in different planes and at different ranges were analysed. For the experiment, 2 samples of dielectric hyperbolic lenses with diameters of 180 mm and 220 mm were fabricated using 3D printing technology. During the experiment, the transmission coefficient was measured at different distances between the antenna systems and the lenses. As a result of the experiment, the distance dependence of the transmission coefficient was obtained for all combinations of different modes. Conclusions were drawn about the possibility of using dielectric lenses to reduce the divergence of OAM waves. During the experiment, the effective distance of the OAM antennas using the designed lens increased from 130 cm to 210 cm.