Generation of OAM Beams Using Circular Ring Array With In-Phase Feed

Efficient generation of orbital angular momentum (OAM) modes is a key foundation for electromagnetic vortex wave communications or radar applications. The usual OAM generation methods based on phase-shifted circular ring arrays require a complex feed network. In this article, a ring array with low-order OAM single antennas as the array elements of in-phase feed is proposed to simplify the array structure and increase the practicality. The theoretical analysis shows that the phase singularity of the radiation fields appears in the array boresight direction. The region just close to the array axis radiates only the first-order OAM mode, independent of the antenna element OAM order. Outer these regions, however, $1-N$ order vortex waves determined only by the array element number $N$ can be realized. The hexagonal array of the fifth-order OAM has experimentally confirmed these conclusions. Clearly, for this kind of array, higher order OAM modes are easily achieved, and the order can be controlled by regulating the number of array elements. Since it is fed in phase, this construction method for OAM antenna array is very practical.