parallel plate capacitor simulation using hfss
Luca,
I had a lot of work to do but I looked at your design this morning. I'm gonna sebd you a pm. Let's look at it.
Ciao
Added after 1 hours 21 minutes:
Luca, as you said in your last pm, the use of that ground plane is just for convenience but it does not represent the real situation. I think you'd better use lumped ports in this case: remove the ground plane (this one affects anyway the circuit behavior) and wave ports, draw a rectangular sheet, one for each capacitor terminal line, and create a lumped port for each rectangle, defining the correct current flow direction. Then draw a 2 very very thin rectangles (one for port) touching the side of the lumped port that doesn't touch the circuit terminals. Apply pec to these thin rectangles, which will behave as reference for ports. Enlarge the substrate in order to let the ports to be far enough from the borders (lumped ports are internal ports). Should be working.
Ciao