the difference between HFSS's and ADS's sNp files.

3-D Fullwave
Ansoft HFSS: Finite Element Method


2.5-D Fullwave
Agilent ADS Momentum: Moment Method

I don't thinks there is any difference. When you export the touchstone file from hfss, make sure you select re/im

what i remember is that, they do have a little difference
for DC. as in dc s-parameter has no meaning, they defined it differently. the result is for a short circuit in HFSS, it become open circuit in ADS or the other way.