Investigation into the influence of ground plane insulation thickness on radiated emission from mains cable of EUT

In the emission standard CISPR32 for multimedia equipment (MME), the specification provided for cabling on the reference ground plane (RGP) stipulates that the thickness of the insulation shall not be more than 150 mm. However, the emission standard does not specify a minimum insulation thickness. Therefore, it is assumed that measurements will be conducted at various insulation thicknesses across various test sites. Thus, the cable impedance varies with the degree of coupling with the RGP, which may significantly degrade the reproducibility of measurements. This investigation verifies that varying insulation thickness does impact AC cable-radiated emission. A very high frequency Une impedance stabilization network (VHF-LISN) representing the common-mode impedance of an AC outlet supplying power to the equipment under test (EUT) in the actual test site was used. The test results have verified that the radiated emission changes much at an insulation thickness of 2 mm or less and the change gradually decreases as the thickness increases (5 dB or less at a thickness of 12 mm or more and 2 dB or less at a thickness of 30 mm).