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 paper 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.