Theoretical Analysis on Generating Composite-Orbital Angular Momentum Beam

For orbital angular momentum (OAM) based practical applications in radio frequency, inherent puzzles of traditional OAM carrying waves will be encountered inevitably, such as the inherent dark zone in the beam center and severe beam divergence. To solve the problem, some specific beams, which are directional beams with high gain, retaining the vorticity and orthogonality of conventional OAM carrying beams have been put forward. They are termed as composite-orbital angular momentum (c-OAM) beam for the first time in this paper. Continuous arc source model (CASM) and discrete arc source model (DASM) are proposed to generate c-OAM beams, which are composed of several OAM waves with different weights. Mathematical models of CASM and DASM are demonstrated, and the field expressions are derived. Numerical simulations are conducted to analyze the characteristics of the c-OAM beams, including directivity, vorticity, orthogonality, etc., and certify the validity of the proposed model. In all, CASM and DASM are capable of generating c-OAM beams, which are more suitable for OAM property based practical applications. Since beamforming is one of the key technologies in 5G systems, c-OAM beams are beneficial to be applied in current communication systems.