Analysis of Termination Impedance Influence to Radiated Emission from AC Cable with CMAD

The method of stabilizing termination impedance at AC cables is discussed to improve the reproducibility of test results between test sites. The common-mode absorbing device (CMAD) and the VHF band line impedance stabilization network (VHF-LISN) were investigated as the devices which can stabilize the termination impedance, and the investigation indicated that the deviation between test sites depended on the type of equipment when CMAD was used as the device. The phenomenon was studied by connecting the artificial network (AN) to the AC cable end. Comb generator and PC were used for the study as EUT. The termination impedance of the AC cable was changed by the AN, and then, the radiated electric field strength and the common-mode current were measured. The investigation indicated that the standard deviation of the field strength is similar to that of the common-mode current. The AC cable with CMAD and the AN were presented by an equivalent circuit, and the circuit parameters were determined from the measurement value of S-parameters. The equivalent circuit and disturbance sources of EUT were determined from the measured currents intensity and S-parameters. The common-mode current was calculated when the termination impedance of the AC cable was changed, and the standard deviation of the common-mode current was estimated. The comparison with the measurement value showed that the type of EUT influenced the deviation between test sites.