I am routing differential pairs in Altium 20 and using controlled impedance profiles. I am using microstrips on external layers only.
For instance, I want a 100 Ω controlled impedance pair, and have used "differential" before which seemed to work fine. Because the traces are together on the same layer (plane) I'm not sure how "coplanar" differs. Information on Altium's page about this is not really clearing it up for me.
What's the difference between "differential" and "differential-coplanar?"
With "differential", selecting the top layer provides this properties panel:
Using "differential-coplanar", selecting the top layer provides this properties panel:
I've always manually created a DRC rule to keep the ground pour on the same plane away from the differential trace by some amount. It appears that the coplanar option specifies a clearance (S) which aims to do the same thing. (Although the value provided is smaller than expected.)