General application of characteristic mode equivalent circuit models in antenna design

Physics based equivalent circuits models for characteristic modes of a conducting chassis and their excitation by means of capacitive or inductive couplers are presented. As opposed to pure fitting models the topologies are derived from inspection of electromagnetic fields and most of the elements can directly be evaluated without numerical optimization. Special attention is given to the frequency dependent equivalent radiation resistance of a characteristic mode and a simple model is suggested which delivers frequency dependent modal radiation quality factors which are in good agreement with simulation results.