Uniform Circular Arrays for Generating Mode 1/-1 OAM Beams Without a Radiation Vortex

In this paper, uniform circular arrays (UCA) capable of generating mode 1/-1 orbital angular momentum (OAM) beams without a radiation vortex are designed and simulated. The generated OAM beams have the characteristic helical phase front, but the radiation pattern does not have a null at the center in the direction of propagation. This is in contrast to the typical OAM beams, which not only carry the helical phase fronts but also have a null at the center of their radiation patterns. This is achieved by applying the OAM mode 1/-1 excitation phases to the antenna elements and sequentially rotating the antenna elements of the UCA by an amount equal to their excitation phases. Several examples of such arrays designed at 17.55 GHz operating frequency are presented via full-wave simulations in the CST Microwave Studio software. Such OAM beams without a radiation vortex could enable high data rate long-range communications by multiplexing several beams.