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Momentum port setup at transistor input above 100 GHz

Question asked by kron on Aug 3, 2015
Hello all,

I am currently designing an MMIC LNA above 100 GHz. For simulating transmission lines, differential port setup with Metal1 referenced ports without any calibration works just fine. However I am confused about how to setup ports at transistor terminals. Reference pins at PEC give unphysical results so I place them at the closest ground plane (Metal1). This gives 'meaningful' results but I'm not sure if this is the correct port setup since I'm grounding the reference pins at schematic level but my real grounding point is further away. 

Attached files show the layout and schematic. It feels like with this setup I'm omitting the resistive path to my real ground but other setups I've tried did not work. What is the best way to define ports (and ground) in this situation?  

Other question is about the ground pin in momentum. I did not see any difference in results when I place this component in the layout so I'm wondering what exactly does this ground pin do?