A 60-GHz RLSA fed by butler matrix carrying three OAM modes

We propose a 60-GHz radial line slot antenna (RLSA), which is fed by a Butler matrix, for orbital angular momentum (OAM) applications. The Butler matrix is placed at the lower layer and it is based on a post-wall waveguide structure. It has four input ports and it can launch different progressive phase states in the RLSA parallel plate waveguide (PPW). The RLSA in the upper layer is fed by the Butler matrix through four posts. The simulated results show that, at the design frequency, the proposed antenna can generate three OAM-mode states: l = 0, -1 and +1.