Controlling Radiation from External Cables

Abstract

As soon as an equipment is fitted with external cables whose length exceeds the largest box dimension, it is highly probable that these cables will become the largest contributors to radiated emissions (and susceptibility, as well). We have seen (in Sections 2.4 and 2.5) that two types of excitation drive theses cables as radiating antennas:

• 1. Differential-mode (DM) excitation, where the currents are balanced (equal and opposite) in the wire pairs. Unless the outgoing and return carriers are spaced very far apart and untwisted, this mode is a minor contributor, though measurable.

• 2. Common-mode (CM) excitation, where the unbalanced portion of the current flows in the whole cable-to-ground loop. Due to the huge size of the antenna, this mode largely dominates DM excitation.

The online version of the original chapter can be found at http://dx.doi.org/10.1007/978-1-4615-3102-9_21