An Asymptotic Model of Multiconductor Transmission Lines in a High-Frequency Region Considering the Lossy Ground

The classical transmission line (TL) theory may normally fail when analyzing the multiconductor TLs (MTLs) with high-frequency excitations, which is mainly due to the unsatisfactory quasi-TEM approximation. In comparison, the asymptotic method can be applied to address this problem efficiently and accurately. However, when taking into account the finitely conductive ground, Sommerfeld-Goubau (surface wave) propagation may appear in the high-frequency region, which may result in the degradation of the accuracy of the asymptotic method. This letter proposes a new asymptotic method with complete formulas to take into account the ground loss. The proposed method was validated with the case that MTLs are excited by the lumped source above the lossy ground. The validation examples show that the asymptotic method with the complete formulas could lower the attenuation in the propagation constant; thus, the solutions in the high-frequency region can be presented in a better way.