Simultaneous Generation of Three OAM modes by using a RLSA Fed by a Waveguide Circuit for 60-GHz-band Radiative Near-field Region OAM Multiplexing

This article reports for the first time the design of a 60 GHz planar antenna system for radiative near-field region line-of-sight (LOS) link based on an orbital angular momentum (OAM) multiplexing. The antenna system is composed of a radial line slot array (RLSA) fed by a Butler network, made in post-wall waveguide technology, and located underneath the array. The network can launch different progressive phase states in the RLSA parallel-plate waveguide (PPW) to radiate three different OAM beams. To focalize each beam in the radiative near region, the use of a modified Laguerre–Gaussian aperture distribution is proposed to extend the range where the link is guaranteed. The design concept has been verified by prototyping and testing a 20 free-space wavelengths’ radius antenna. The measurements show that the proposed antenna can generate simultaneously the three OAM-mode states $n =0$ , −1, and +1.