Recent progress on RF orbital angular momentum antennas

In the last five years or so, there has been a great interest in RF OAM to address the contradiction between the lack of wireless spectrum resources and the continually growing demands of the bandwidth. Recent developments and technological advancements in antenna design, material science, and integrated circuits have enabled miniaturized, multiple modes, tunable in radio frequency (RF) orbital angular momentum (OAM) antenna designs. From conventional methods such as spiral phase plate and reflector antenna to antenna array and metasurface, the working principle and structures are introduced. To improve the performance of RF OAM antennas, several innovative physical concepts have been explored for the designs of RF OAM antenna designs. In this paper, we present an up-to-date survey on the development of RF OAM antenna technologies. Open issues and development trends are explored as a source of inspiration towards the future better outcome of RF OAM antenna designs.