8.3 Rule 3: Trace placement in the middle of the enclosure slot reduces the EMI at
the first resonance
(a) Placement of Trace A and Trace B.
(b) Overall radiated power from the enclosure slot.
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
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.