Radiated Emissions of a Shielded Cable Excited by a Differential Voltage

The cables attached to a power converter are typically the main antennas for radiated emissions. The relevant current that leads to radiation is the total current on the cable, which is therefore called antenna mode current. A key part of EMC analysis is the understanding of the mechanism driving these antenna mode currents, in order to find proper shielding or filtering mechanism to reduce these currents. The imbalance difference theory allows to quantitatively describe the creation of antenna mode currents and is applied here to a setup consisting of a shielded cable with pigtails for different loads. Normal modes described by transmission line theory are converted to antenna modes causing radiation from the cable. Measurements, theoretical analysis, and full wave simulations of radiation are presented and are all in good agreement.