I. Introduction
The problem of electromagnetic (EM) field coupling to a transmission line (TL) falls into the category of direct EM scattering problems that can be solved by means of EM integral equations and dedicated numerical procedures (see, e.g., [1, Ch. 12]). In order to avoid the relatively high computational burden associated with the solution of the full scattering problem, several approximate models have been put forward [2], [3]. Among the most popular approaches in this respect are EM-field-to-line coupling models based on TL theory (see, e.g., [4]) that are mostly tackled numerically via a finite-difference technique (see [5] and [6]).