8.3 Rule 3: Trace placement in the middle of the enclosure slot reduces the EMI at the first resonance

\includegraphics[height=5 cm]{pics/MotorSG.eps}
(a) Placement of Trace A and Trace B.
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(b) Overall radiated power from the enclosure slot.
Figure 8.6: The trace width is 0.2mm, the trace height above the ground plane is 0.65mm. A 10mV voltage source with an impedance equal to the characteristic impedance of the trace $ Z_w$ drives the trace which is terminated with a 10pF capacitance.

Figure 8.6 shows a reduction of the emission at several resonances of more than 20dB. However, the radiated emission is increased in the frequency range below the first resonance. Therefore such a trace placement should only be selected in the case of enough margin to the EMC compliance limit at low frequencies and a known EMI problem at the first resonance of the enclosure.

C. Poschalko: The Simulation of Emission from Printed Circuit Boards under a Metallic Cover