Physics-Based circuit models for MIMO antennas using characteristic modes

Using characteristic mode theory, we develop a general broadband circuit model for the admittance of a multi-input, multi-output antenna. Each accessible port couples into radiation modes and to the other ports in a way that can be represented analytically or as a circuit block. This physics-based approach offers a systematic method to build a model of a complicated multiport antenna using simple building blocks. An example of a strip dipole antenna shows that a circuit model made from simple building blocks can model the multi-port S-parameters of the antenna within a few percent over a 10:1 frequency range.