Experimental Evaluation of 3D Printed Spiral Phase Plates for Orbital Angular Momentum Waves Generation

The use of orbital angular momentum waves can improve the efficiency of communication systems as well as other radio systems, but the range and divergence problems of OAM waves must be solved before successful application and implementation. Despite the many ways of generating OAM waves, the question of optimal solutions is still under research and discussion. One such method is the use of spiral phase plates along with traditional horn antennas. The authors of this paper chose this method of generating OAM waves for the experiment, for which two SPPs were modeled and fabricated to verify the generation of OAM modes and their orthogonality in practice. A propagation ratio measurement experiment was conducted, where a set of previously fabricated antenna arrays were used as second antennas, and measurements were performed in the distance range from 40 cm to 400 cm. There have been positive experiences with the fabrication of such SPPs by means of 3D printing, FDM technology in particular. Two different SPPs demonstrated the generation of two OAM modes: +1 and -1. A decoupling between these modes was obtained in the order of 10 dB for short distances (up to one meter) and $0..5 \mathrm{~dB}$ for further distances.