How to simulate SAW devices packaging using HFSS?

Hello,

Some people have used HFSS to simulate SAW devices packaging.They first calculate SAW response with proprietary model,then obtaine scattering matrix representing the package using HFSS.The SAW response and the scattering matrix are combined in ADS or other RF circuit simulator.
Can anyone describe the details about the mentioned procedure?I am really interesting in the SAW devices packaging simulation,but know little about it.

Thanks!