I have several boards with 50 ohm traces in 4-layer pcbs. my stack layer is usually top, ground, power, bottom. The 50 ohms traces should be in the top layer because is calculated between the top-prepreg-ground.
But what if I have to use a 50 ohm trace in the bottom layer? Can I use the same calculation but using power layer? (assuming power plane covers all the trace area). I remember in some class that when using RF model, GND and power are short-circuited, so, maybe gnd plane and power plane are the same for RF calculations.
Is that correct?
thank you very much