Examining the effect of source type on the accuracy of inverse distance fall-off for radiated EMI measurements

Inverse distance fall-off theory is often used to project radiated emission measurements from one distance to another, such as 1, 3, 5 and 10 meters. This commonly-used technique can result in errors of up to 14 dB. Simulations are performed with six different source types to examine the effect of source type on the accuracy and suitability of the inverse distance fall-off technique. Results show that even for simple sources substantial errors can result from using inverse distance fall-off for correlation of measurements made at different test distances and any correction factor would be a very complex function of frequency.