Circularly polarised OAM antenna using an aperture-coupled uniform circular array

Circularly polarised (CP) orbital angular momentum (OAM) antennas using aperture-coupled uniform circular array (UCA) are proposed to avoid the polarisation mismatch during the mobility and/or the space communications. A comprehensive derivation for ideal CP UCA is derived and numerical simulations are performed for further analysis. To validate the theoretical result and explore explicitly, the proposed prototype for +/- 1, +/- 2 mode OAM antennas with right-hand and left-hand circular polarisations are proposed and fabricated with measurements conducted, respectively. Measured radiation patterns, axial ratio versus elevation angle and the helical phase wavefronts are all favourable and exhibited. The transmission characteristics versus frequency f, relative azimuthal angel phi and distance D are all measured and analysed, which shows high isolations between different channels.