Mode Measurement of a Dual-Mode Radio Frequency Orbital Angular Momentum Beam by Circular Phase Gradient Method

A measurement method of dual-mode radio frequency orbital angular momentum (RF-OAM) beams is proposed, dedicated to meeting the practical needs of the orbital angular momentum mode-division multiplexing (OAM-MDM) in free-space communication. Theoretical analysis and numerical simulations are conducted to demonstrate that a dual-mode OAM beam can be unambiguously measured by gathering the phase gradient function of a circle around the OAM beam axis and calculating its average value and PV (peak/valley) factor. A proof-of-concept experiment is presented, which employs a single receiving antenna on a rotatable plane to measure mode +1 and -2 of a dual-mode OAM beam.