An equivalent circuit model of characteristic modes with lumped loads

Usage of lumped loads is an effective approach for mode manipulation, but the physical insights are not well disclosed. In this paper, an equivalent circuit model (ECM) is proposed to investigate the effects of lumped loads on the characteristic modes (CMs). This model can predict the modal admittance of a loaded antenna over a broad bandwidth. A scaling coefficient K is proposed to describe the discrepancy of the loading effects on different modes, thus providing a clear explanation of the resonant behaviors of CMs with lumped loads. Matrix perturbation theory is adopted to analyze the change of eigencurrents and eigenvalues upon lumped loads. The applicable boundaries of the ECM with regard to different lumped loads are given for the first time. The proposed ECM is potentially useful to assist mode manipulation.