The Validation of The Weak Coupling Assumption in Transmission Line Equations of Coaxial Cables

Abstract

The weak coupling assumption is frequently applied when solving coaxial shielded cable problems using transmission line equations. However, there are never enough justifications or no explicit indication of valid conditions. The purpose of this study is to provide the basis that supports the weak coupling assumption and a concise method to determine under what conditions the assumption holds. First, this paper summarizes the process of solving the shielded cable problem for different coupling methods. Further, this paper explores the conditions that must be met for the assumption by contrasting the weak coupling result with the numerical exact result. By comparing the weak-coupled model and the exact model under the electric short range, the ratio curve is obtained that can intuitively judge the weak coupling assumption validity. Then the coupling factors are proposed. And two examples are used as comparisons to validate. The ratio curves and coupling factors Kmin for determining the extent and degree of validity of the WCA are proposed, and validity is proved by examples.