On the Estimation of Radiated Emissions from Common Mode Cable Currents

This article quantifies an aspect that every EMC engineer is intuitively aware of: At low frequencies, as long as the boxes are electrically small, one can estimate the far field from the cable currents, but engineers may not know how to do this, and how good is that estimate? The paper compares different methods that can be used to estimate the radiated fields from the currents. The analysis is based on about 100 different geometries, cable and ground plane termination impedances. Full-wave simulation is used to calculate the currents and the far field, and estimation methods that use the cable current to obtain the far field are compared. It is shown that a combination of methods leads to average estimation errors of less than 4 dB for a frequency range of 30 MHz to 500 MHz, with lower errors in the 30 MHz to 300 MHz range.