Simulation of the Stochastic Electromagnetic Field Coupling to an Unshielded Twisted Pair of Wires

The twisting of signal pairs in cables is among shielding a typical countermeasure against the coupling of external fields into transmission lines. For the simulation a twisted pair can be modeled as a bifilar helix and the incident field can be approximated by a plane wave. With these simplifications the field-to-wire coupling can be calculated analytically. This method, which is based on classical transmission line theory, is known from the literature and is validated against a numerical simulation using the method of moments. In a next step the analytical method is used to calculate the coupling of stochastic electromagnetic fields into a twisted pair cable. Therefore the incident field is modeled by a superposition of plane waves. As a result also the coupled current becomes a stochastic quantity, whose statistical properties and dependencies are analyzed.