An Interpretation of Mode-Decoupled MIMO Antennas in Terms of Characteristic Port Modes

If N ports are defined on the moment method model of a radiating structure, so-called characteristic port modes may be computed, using the moment method operator matrix, with respect to these ports. This results in N port excitation vectors (each of length N). Each vector excites a radiated field which is orthogonal to the fields excited by any of the other N excitation vectors. It is shown that this may be usefully employed in the design of antennas for multiple-input multiple-output (MIMO) communications, and that recent multimodal/multipolar approaches for MIMO antenna design may be interpreted in terms of such port modes.