8.1 Rule 1: Trace placement symmetric to the enclosure symmetry reduces the coupling up to the second enclosure resonance

Figure 8.1(b) shows a radiated power reduction of 20dB below 1.2GHz and yet 10dB up to 1.5GHz, when the trace placement is changed from that of Trace A to that of Trace B, as depicted in Figure 8.1(a). It is recommended to place critical traces symmetric to the enclosure symmetry line. This must be considered when placing the driver and source IC on the PCB layout. Therefore, the rule cannot be used for every trace on the PCB and the designer should focus on critical signal lines, such as, for instance, fast clock signal traces.

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(a) Placement of Trace A and Trace B.
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(b) Overall radiated power from the enclosure slot.
Figure 8.1: 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.

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