Circuit Modeling of Near-Field Coupled Undersea Antennas Using Impedance Double Expansion Method

This study addresses circuit modeling of near-field coupled antennas that are separately enclosed in lossless dielectrics and immersed in seawater, which are intended for applications such as undersea wireless power transfer (WPT) systems. To accomplish this, a circuit modeling technique called the impedance expansion method (IEM) is extended to consider lossy dielectrics with a loss tangent greater than unity. Unlike the conventional IEM, the extended method first expands the coefficient matrices derived by the method of moments (MoM) into the Laurent series with respect to propagation constants and then further expands them with respect to the complex angular frequency. Based on this feature, the extended method is called the impedance double expansion method (IDEM). By applying the IDEM to the undersea dipole and loop antennas with pure water covers, their circuit models are obtained. Comparison with the full-wave MoM and finite-difference time-domain (FDTD) calculations shows that these circuit models reasonably approximate not only the reflection and transmission coefficients between the antennas with matching circuits (MCs) but also the radiation loss.