A study on influence of guard band on common-mode current related to a microstrip line

Influence of guard band on common-mode (CM) current related to a microstrip line (trace) has been studied experimentally and FDTD simulation. As the guard band, copper tape is connected along the entire edge of the ground plane. It is cleared that a guard band parallel to and near a trace is most effective in suppressing the CM current. An empirical formula to quantify the relationship between the position of a trace and CM current of the case with a guard band is proposed. Calculated results using the empirical formula and FDTD modeling are in good agreement, which indicates this empirical formula should be useful for developing EMI design guidelines.