Antennas for generating electromagnetic waves bearing OAM momentum

Orbital angular momentum (OAM) has been proposed to improve spectral efficiency [1] [2] [3] in radio, by creating multiple sub-channels of communications corresponding to the twisting degree of the electromagnetic (EM) wave. Whereas the phase of a usual plane wave is constant on the wavefront, the phase α of OAM waves undergoes a linear variation along the angular coordinate φ (roll angle): α = ℓ.φ, where ℓ is an integer called the “topological charge” or the order of the OAM mode.