There are many examples included with ADS.
Start with examples on S-parameter simulation (linear simulation, S-parameter models at one specific operating point, no bias or supply voltage required in simulation)
Also search for "ads circuit design cookbook"
Authors specify 30mA drain current, set the gate voltage as required for 30mA. Use voltage and current probe in ADS. There is also a DC curve tracer template in ADS.
But that is for non-linear simulation. Make sure to understand linear (S-parameter) simulation where the S2P transistor model has built-in the response at one specific bias. We don't need bias or supply sources in linear simulation with "S-Paramter simulation" controller.
From 20 years experience in simulation: It often happens that published simulation results cannot be reproduced because some detail in the paper is wrong or missing (by mistake or on purpose).