A study on the correspondence of common-mode current in electromagnetic radiation from a PCB with a guard-band

A PCB, in which the ground plane has a finite width and the trace has unbalanced positioning, can result in common-mode (CM) radiation. So far, CM current which is generated by the unbalance of a trace and ground plane has been investigated by experiment and numerical method. It was clarified that CM current is well explained the radiation from PCB up to a few hundred megahertz, and addition of a guard band geometry, which is well connected to the ground plane, can be effective in suppressing the CM current. But it seems to be an insufficient description for the phenomena observed at higher frequency. This study newly focuses on the correspondence of the CM current in total electromagnetic (EM) radiation from a PCB with a guard band up to 5 GHz. In results, although total radiated power and near electric field up to 1 GHz were related to CM current, the increase in EM radiation in higher frequencies (a few gigahertz) could not be predicted from only the frequency response of CM current. This should suggest two radiation components for a PCB configuration; radiation as a result of a CM current due to the current driven mechanism, and direct radiation from a trace. At the higher frequencies, direct radiation from the trace may be more significant relative to the radiation due to the CM current. This research is very useful and applicable to estimate the detail of EMC radiation problem from PCB with attached cables.