Space Dependence of Divided Ground Patterns on FM-Band Cross-Talk Characteristics between Two Parallel Signal Traces on Printed Circuit Boards for Vehicles

Abstract

Electromagnetic disturbances in vehicle-mounted FM radios are mainly caused by conducted noise currents flowing through wiring-harnesses from printed circuit boards (PCBs) with the slits of ground patterns. To suppress these kinds of noise currents from PCBs, we previously performed the FDTD simulation using eight simple two-layer PCB models in which the ground patterns were divided into two parts with different widths, which revealed that the cross-talk cannot always be reduced by widening the width of divided ground patters. In the present study, to confirm this finding, we made actual PCB samples, having the same geometry as that described above, and measured cross-talks between the two parallel signal traces with respect to the different widths of ground patterns. As a result, we confirmed that the measured results agree with the FDTD simulation, and also that the cross-talks have the smallest values at specific spaces between the divided ground patterns. In order to clarify the latter result, we calculated cross-talks from a simplified equivalent circuit model consisting of inductances, which were derived from their geometrical mean distance for the traces and ground patterns, and found that the circuit model can qualitatively explain the dependence of ground pattern width on cross-talks. The minimum reduction mechanism was found to come from the fact that a specific width of the ground pattern provides the smallest interlinking magnetic flux between the trace and the ground pattern.