Split width effect of ground patterns on FM-band cross-talks between two parallel signal traces of printed circuit boards

Electromagnetic disturbances in vehicle-mounted radios are mainly caused by conducted noise currents flowing through wiring-harnesses from vehicle-mounted printed circuit boards (PCBs) with common slitted ground patterns. To investigate suppression of these kinds of noise currents, previous measurements from simple two-layer PCBs with two parallel signal traces with slitted and non-slitted ground patterns, and revealed that making slits with open ends on the ground patterns in parallel with the traces can reduce the conducted noise currents. It was also discovered that the noise currents from PCBs can be suppressed even if the size of the return ground is small. Furthermore, we performed finite-difference time-domain (FDTD) simulations, using eight simple two-layer PCB models in which the ground patterns were split into two parts with different widths and one PCB model with a plane ground pattern, and found that cross-talk decreases with widening the width of the ground pattern and has the smallest values at a specific width. In the present study, to confirm the above findings experimentally, we made actual PCB samples according to exactly the same specification as the models used in the FDTD simulation, and measured the cross-talk between the two parallel signal traces with respect to the different widths of ground patterns. The results approximately agreed with the simulation.