Transmission Characteristics of a Twisted Radio Wave Based on Circular Traveling-Wave Antenna

A traveling-wave circular loop antenna with its phase distribution along the circle of lφ is demonstrated to generate the twisted radio wave. Theoretical formulations of its radiation fields are deduced in the cylindrical coordinate system and used to analyze its transmission characteristics, such as the radiation patterns, the evolution of the polarization states, and the angular momentum modes including the orbital angular momentum (OAM) modes and the spin angular momentum (SAM) modes. The prototype of a practical configuration for such antenna is proposed and conducted to validate the theoretical results. This theoretical analysis is applicable not only to radio waves but also to the whole electromagnetic spectrum.