Electromagnetic couplings in Unshielded Twisted Pairs.(Report)

1. Introduction

Magnetic couplings in twisted pairs are produced by magnetic fields that depend on time varying currents. Electric couplings in twisted pairs are produced by electric fields that depend on time varying voltages. Electromagnetic coupling is the sum of both, magnetic and electric couplings, and it is originated from a transmitted circuit in the neighboring of the receptor transmission line.

The analysis of electromagnetic coupling is a common problem in Electromagnetic Compatibility because higher frequency signals produce higher radiations. The most important factor in the mechanism of electromagnetic interference is the operation frequency, which will be from 10 KHz to 100 MHz. At this range of frequencies, the electromagnetic couplings are called crosstalk. Crosstalk is the unintended induced coupling of two circuits, a transmitted pair and a receiver pair. The term of crosstalk is reserved for interferences that take place within the same cable, it means intrasystem.

There are two techniques to determine the performance of cables, according with the location of the measure reference, either the nearest end or the farthest end of the source.

2. Simulation of Electromagnetic Coupling

Crosstalk in twisted pair cables has been simulated considering the following conditions:

* The propagation wave mode must be transverse.

* The line length ([L.sub.LT]) has been divided in strands.

* Every strand is constituted in two half strands.

* There are mutual inductances that model magnetic coupling in each half strand ([L.sub.m]).

* There are mutual capacitances that model electric coupling in each half strand ([L.sub.m]).

* The model approximates the crosstalk behavior, connecting both; mutual inductances and mutual capacitances in …