Due to the increase of electromagnetic pollution of the environment by electric and electronic applications on the one hand, and the tendency towards a decrease of operation levels, the problem of susceptibility becomes more destinct. Accordingly it is helpful at early design stages to gain information concerning the noise levels the logic has to face. Typically, such noise is either coupled directly into the circuit or is collected by the interconnects and transmitted to the gates of the circuitry. For estimation of the noise in the latter case simulation software has become quite popular in recent years.  While field solvers provide more detailed solutions, the modelling as well as the computational expense is prohibitive for many practical problems. Therefore many attempts have been made to reduce the effort by mapping the problem onto simpler approaches. Here, transmission line theory appears to be the base of one of the most important procedures, mainly due to its widespread use within the circuit designer and signal integrity community. One of the most traditional methods of transmission line modelling is based on the conception of equivalent source models for the signal transition having the great advantage of mapping the transmission line features onto the capibilities of a circuit simulator. The coupling of external electromagnetic fields to interconnects using transmission line theory thus far was restricted to canonical configurations because the coupling formulation was non--symmetrical. This means, though the angle of incidence of the plane wave might vary from the crazing case the perpendicular one, incidence was only allowed from one ``side'' of the transmission line, typically from the negative z--direction when the extend of the transmission line is identified with the positive z--direction. In the following a field coupling procedure based on retarded equivalent component models for transmission lines is presented that overcomes this restriction due to its symmetrical nature, thereby allowing for plane waves being incident from virtually everywhere. It will been shown that the results obtained by the presented method are in excellent agreement with those from other methods, but show better computational performance than those.