You have connected the DC bias direct to the gate of the CREE transistor. The DC bias is a voltage source and will appear as a perfect short on the smith chart.
Also you have connected it straight to port 1 without a DC blocking capacitor.
-2V into 50 ohm is -40mA.
Same for port 2.
Try putting an inductor in series with the DC source and a series blocking capacitor on port 1 and port 2.
Better still, if you are serious (are you serious or is this just a windup?) about playing with CREE GaN transistors then contact a CREE rep for assistance. They can offer you basic MWO startup schematics.
Your schematic is also wrong because you have placed a 12 ohm resistor (?) in the drain and also you are only running from 15V. I think you will be advised by CREE to run these devices at at least 20V drain voltage (and probably less than 32V)
What spec amplifier are you hoping to design?
I've designed several broadband amplifiers with these devices.