Another Field Decomposition for the Transmittance between OAM Antennas

This paper first provides an intuitive description of the spectral representations for the transmittance between two apertures. Then, two spectral representations of the transmittance between OAM antennas are compared. The first one makes use of the Modified Zernike function and has already been described in a previous publication. The second one is based on the Fourier-Bessel decomposition of the current distribution on the apertures. Both families of expansion functions are orthogonal on a disk and admit a closed form spectrum. In both cases, the transmittance in the far-field can be approximated in closed form if the current distribution is expressed in the basis. However, it is observed that the far-field behavior is fundamentally different, highlighting the complementarity between the two bases.