Complications in correlatability between test techniques due to directional emission patterns

Radiated emissions measurements are commonly performed in open area test sites (OATS), anechoic and semi-anechoic chambers, and GTEM and TEM cells. The OATS test results are typically regarded as the reference standard and all other techniques must be correlatable to the OATS data. The accepted procedures all determine the maximum emissions within some defined solid angle. Reverberation chambers, which measure total radiated power, are not currently accepted in any emission standard. Simple probing of general directional emission patterns can demonstrate what fraction of the total equipment-under-test (EUT) emissions are observed in a particular test technique. In this article, the emissions from two battery-powered laptop computers were investigated using a short wire antenna in the near field.