On the Transmittance Between OAM Antennas

A quasi-analytical solution is derived for the transmittance between two OAM antennas. It makes use of the properties of the modified circle polynomials, related to Zernike functions, and of integration in the complex plane of the radial spectral coordinate. The resulting formulation can be estimated extremely fast and is shown to exhibit several expected properties. An asymptotic expression is proposed and validated.