Effect of ground layer patterns with slits in suppressing cross-talks between two parallel signal traces on printed circuit board

For electromagnetic (EM) disturbances in vehicle-mounted radios, the main source is known to be conducted noise currents flowing through wiring-harnesses from vehicle-mounted multi-layer printed circuit boards (PCBs). To investigate a design method that can suppress the conducted noise currents, we previously measured noise current outflows from four types of simple three-layer PCBs having two perpendicular signal traces and different ground patterns with/without slits, and showed that slits on a ground pattern allow conducted noise currents to flow out from PCBs, while the levels for the symmetric two slits ground types are smaller compared to the case for the asymmetric two slits ground types. In the present study, to further confirm the above finding, we fabricated six types of simple two-layer PCBs having two parallel signal traces and different ground patterns with/without slits, and measured the cross-talks between the traces to evaluate the noise current outflows from the PCBs. As a result, we found that the ground pattern with the slits perpendicular to the traces cause noise current outflows larger by 19-42 dB at 100 MHz than the ground pattern with no slits, while the ground patterns with the slits in parallel with the traces can provide current noise levels slightly smaller by 2.5-5 dB compared to the case for the no-slit ground pattern. These results were confirmed by the FDTD simulation, and were also qualitatively explained from an equivalent circuit model we previously proposed.