Reduction effects of geometrical configuration on FM-band cross-talks between two parallel signal traces on vehicle-mounted printed circuit boards

Electromagnetic disturbances in vehicle-mounted FM radios are mainly caused by conducted noise currents flowing through wiring-harnesses from printed circuit boards (PCBs). To suppress these kinds of noise currents, we previously investigated the FM-band cross-talks between two parallel signal traces on two-layer PCBs with slit ground patterns, and showed that the cross-talks cannot always be reduced by widening the width of the divided ground patterns from finite-difference time-domain (FDTD) simulations and measurements. In this paper, to examine geometrical configuration effects in reducing the FM-band cross-talks, we further performed the FDTD simulations for new-type PCBs on which two signal traces were kept in the centre of their corresponding ground patterns. The result showed that the wider the ground slit width is, the smaller the cross-talks become. To explain the difference between the above findings, we calculated the mutual inductances `M´ between the two signal trace circuits for the previous and new-type PCBs, which largely affect the cross-talks, and found that both Ms have the same dependence of the ground slit width as the cross-talks.