Comparisons of planar versus spherical emission measurements for unintentional emitters

The emission patterns from electrically-large objects are complex and require time-consuming spherical scans to determine the emission maximums. A planar cut through the spherical pattern is a relatively easy measurement to make and resembles the techniques used in present EMC emissions and immunity standards. However, a planar cut is likely to miss the maximum emission from a test object. This paper explores how planar cut data can be used to estimate the spherical emissions maximum. Simulated data including both the full spherical radiation pattern and planar cut estimates for a random emitter are presented The key result is that, if planar cut data can be used to accurately approximate the mean radiation power, then directivity estimates for electrically large emitters can be used to accurately predict the maximum emissions. The results presented here have application to emissions and immunity measurements at frequencies above 1 GHz where most objects will be electrically large and have complex emissions and receiving patterns.