Radiated Emissions from a PCB in an enclosure, a practical case

Emmanuel Leroux



In order to teach Best Practice in EMC regarding the design of PCBs, a realistic demonstrator board was layouted and measured at the company FESTO.

The board consists of two layouts placed on the same substrate. It is basically two boards: one with a good EMC design and one with a bad EMC design. Both designs use the same driver components but the layout is quite different. As a first step we analyze the performance of differential pairs, the bad design is routed over some splits in the reference layer below. Both designs were measured in a semi anechoic chamber at FESTOs HQ.

In order to have a good comparison between measurements and simulations we show how it is important to use a realistic model for the source and to incorporate the PDN into the simulation. In the second part of the work we consider a simple PCB placed in an enclosure. We measure and simulate the Shield Effectiveness and realize that two peaks are originated from the slot between to top cover and the body of the enclosure. We add screws to the model and re-simulate and clearly observe how the peaks do disappear.

The screws used in this simulation were ideally conducting. We then study in the simulation how the shielding is affected if the screws do not ideally conduct, but there is some contact resistance.