In designing for EMC, details matter. A lot!
A simple example is ribbon cables.
Most often, to save on costs (only apparent), we cut down on things that we think are "unnecessary."
In the case of ribbon cables, and of course also in the case of regular wires, we often choose to get rid of a few return reference path connections because we think "we only need one thicker cable" or even just one that "handles the current" to work as a "sink" for the current.
The problem in this case is that we are not considering what happens to the EM fields.
Then we try to certify the products, and we see some high peaks in the frequency spectrum during the radiated emission test (typically above the 300 MHz range).
Keeping the return reference path for the signal (which is not a sink!) adjacent to the cable or wire, will ensure that the fields are well contained, and that the loop area enclosed by the signal and its return current, is as small as possible.
The reason why I prefer to obsess about keeping the area of the loop as small as possible, is that radiation from differential mode current, or radiation from the normal current required for the operation of the device, is directly proportional to the area of the loop.
This means the larger the area, the larger the emission from differential mode currents.
So next time you are planning for connections, remember that the signal needs the return path to be adjacent to it.
My advice: save some cash on EMC certifications (or attempts) rather than on connectors.
I hope this helps,
Dario
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