Accurate model for GaAs HEMT for oscillator design
Depends on your foundry which you have intended.Every manufacturer/foundry chooses a proper model for their products,therefore you have compulsary to use their model approximation such as TOM,Angelov,Parker,EEHEMT,etc.
My problem is that I have a commercial phemt part and I am trying to figure out which model(already available with the ADS simulator) will be the best to use for designing/simulating an oscillator else which model I can take as reference to build a new model for the part which can be later used for designing the circuit. I have only the datasheet for the HEMT part available to me..no physical details.
If you have datasheet only, you have nothing to do but request nonlinear model from manufacturer.You can not achieve a nonlinear model from datasheet.
S-parameters can help you to start-up oscillator design but it will be a very limited aid.