I'm designing an 8-layer PCB with 10 distinct region of power. To attain 50Ohm trace I used Stripline calculators (like this fancy EEWeb) and they work great If you know that you have a complete solid ground both on top and bottom of your signal.
The problem arises if you have copper pour between your signal and your holy ground which may be use as power signal. I already found in "reference plane doubt" that the power plane Can work as a reference plane in these magic Stripline calculators.
So now I have two question regard that. First, does this power plane need to be in the same circuit as signal? I mean suppose I'm routing a DDR signal. can the reference plane be some non-related power plane like 12V power plane?
Second does this plane should be fully continues under signal or split plane work too?
And third, I can't find any literature in transmission line theory that support the idea of "Any copper can work as reference plane". Does anybody see a formal calculation on this?