This dissertation introduces a mixed-mode matrix generalization of scattering parameters which is suitable for the investigation of wireless communication based on orbital angular momentum (OAM), and antenna arrays that radiate electromagnetic fields showing OAM are being studied to provide an explanation of the generation of OAM based on fields. To this purpose a unitary transformation matrix is defined that contains as basis vectors the transmitted and received amplitudes that correspond to OAM-based communication between two antenna arrays. The mixed-mode matrix is then obtained from the corresponding similarity transformation of the standard scattering matrix available e.g. from numerical simulations or measurements. The mixed-mode matrix allows better physical insight into OAM-based communication by clearly separating all modes and is more efficient than post-processing of single-antenna results in a system simulator. Mode conversion/isolation and proper mode termination can be easily quantified. Also, it allows to generalize the interpretation of OAM-based communication by focusing on the property of a constant phase difference within each antenna array. The usefulness of this approach is demonstrated using Method of Moments (MoM) simulations of dipole radiators in various arrangements of a transmitting and a receiving array. Systematic parameter studies that reveal dependencies of OAM-based communication are possible by using the mixed-mode matrix. As an application, the communication pattern is studied to obtain the suitable position and relative orientation in free space for good mode isolation or communication.
