Sinusoidal time-modulated uniform circular array for generating orbital angular momentum modes

Time Modulated Uniform Circular Arrays (TMUCA) can produce Orbital Angular Momentum (OAM) modes using relatively inexpensive hardware. For enhanced spectral efficiency in line-of-sight links, it is desirable to produce multiple OAM modes simultaneously. TMUCA typically suffer from leakage of energy into all the other available OAM modes, which is undesirable because it increases crosstalk between the channels. This paper proposes a modified approach to TMUCA that overcomes the energy-leakage limitation. We adopt a time-modulation scheme that can be viewed as similar to intermediate frequency beamforming, although we do not use it for its beam-forming properties. Here, only the fundamental harmonic of the time-switching signal is applied to the system, eliminating unwanted spectral and spatial mode leakage in the ideal case. Simulations are presented in support of our proposal.