Optimization in HFSS using measured return-loss!

Greetings,

I need to optimize my structure in HFSS to get the best fit between the simulation results and measured one. When, I import the measurement data in HFSS and try to make a subtraction from simulation results it seems that HFSS does not allow me to do this so.

I wonder if you guys to help me to find a solution for this problem!

Thanks!

Hamidreza