a question about transmission line simulationA60GHz

Hello, I am a new guy here.
I hope to compare the Q value of microstrip and cpw.
I met a problem when i simulated microstrip (with a shielded ground plane between the alumina layer and the 15Ohm-cm Si substrate) and conduct-back cpw transmission line by ADS Momentum. In the simulation, i have to connect the shielded ground in Microstrip line and the surface ground in CPW to the lower ground plane. Of course, using the ground port in Momentum can define any layer to be a ground reference. But when I tried to use vias which are very close to each other to connect the ground plane, it gave me wrong results of the Q value at very high freqs(>30GHz).
Could you give me some ideas about how to use vias to define a ground layer correctly at very high freqs (by ads momentum)?

Thank you very much

hi vonleo,
the help of ADS-momentum itself is quite helpful, read it carefully, and vias should be there of course but i havent worked with them b4

Hi,

Try to use staggered vias instead of one straight via.

Gud luck!