The Optimum Operating Frequency for Near-Field Coupled Small Antennas

The optimum operating frequency of wireless power transfer is investigated for near-field coupled resonant small antennas. The existence of the frequency can be inferred from the equivalent circuit representation for coupled small antennas, based on mode-based analysis using the addition theorem, and the frequency dependence of the radiation efficiency. From the EM simulation results, it is demonstrated that there is an optimum operating frequency for maximum matched gain. In addition, it is shown that the optimum frequency can be accurately estimated using the addition theorem and the EM simulation results of a single antenna.