On Reception Sampling Region of OAM Radio Beams Using Concentric Circular Arrays

Orbital angular momentum (OAM) supplies a new degree of freedom for the electromagnetic (EM) wave, which can be used to increase communication capacity. The amplitude of the OAM wave is null in the center of the beam and the distribution of the electric field intensity is not uniform, so the study of the optimal receiving location of single OAM wave is necessary. Furthermore, in order to efficiently receive OAM waves with different OAM modes simultaneously on single receiving antenna, the common reception sampling region of multi-mode OAM waves should also be studied. However, few experiments study the region of multi-mode OAM waves. Here, concentric circular arrays are proposed to generate OAM waves with different OAM modes. Based on theoretical formulations of its radiation fields in the cylindrical coordinate system, its transmission and reception characteristics would be analyzed. Basically, the common reception sampling region of multimode OAM waves can be confirmed by calculating function formulas of the upper and lower boundaries of the region or analyzing amplitudes and phases of the axial ratio of optimal receiving location of multiple OAM waves. Numerical results show that methods of confirming the region are feasible and simple. When other parameters besides frequency are the same and the optimal receiving location of certain OAM mode wave at certain frequency is known, optimal receiving locations of certain OAM mode wave at other frequencies can be confirmed easily, according to the formula related to the optimal receiving location and frequency.