group delay time s parameters

I need to optimize the group delay time for 2-port circuit in ADS.
But I don't know - What Goal expression I must to write in "Expr" row of GOAL component.
Please, give an advice.

As I know ADS calculates the group delay from S parameters using the function. What you can probably do is to put in your schematic a simulation measurement equation item and calculate for each point the group delay as
-diff(unwrap(phaserad(S(2,1),pi) )/ (2*pi)
Then you should be able to access the delay as you normally access s-params in the optimizer.
Success

Leron