Unexpected loadline in ADS simulation
Why negative values? Stored energy. 

And the Vgs source has 50 ohm impedance. Thus distortion inside the amplifier can reflect back onto the Vgs input.

========================================= May 26, 2020

To exit the 1rst quadrant, either voltages or currents MUST become Negative.
Or both.

That suggests phase_flipping caused by energy storage in resonators.