While working on a new design, we had to route Ethernet signals on our PCB. My colleague and I has some discussion on how we should handle the grounding around the Ethernet signals, and their return path.
The signals are routed from the PHY to the magnetics, travel some distance on the PCB, and exit through the Ethernet connector. Our discussion was for the part after the magnetics and up to the connector.
My colleague proposed that we shall add a proper ground plane under these signals, and pay attention to the return paths.
I, on the other hand, proposed that we don't need this, as the Ethernet signals are magnetically coupled, and essentially galvanically isolated. Its like having an unrelated cable just happening to be close to the PCB, without any actual electrical connection.
So, is it actually needed to have a return path for the Ethernet signals?