I want to use E5071B to characterize a differential saw filter and use the ADS loading the S4P file measured by network analyzer so that I can do the impedance matching for this device. Originally, I save the S4P file without turn on the balun which is in fixture simulator and cannot obtain the same response plotted in datasheet. Then I turn on the balun function saving the S4P file again and use the same ADS simulation setup, the result is very close to the datasheet. I have consult with the FAE in TAIWAN and they say that it should be no difference between these two S4P file and they think the difference I saw before is just because of different sweep time. I don't think so since I have done many try to confirm my operation. If they are different just because of different sweep time, how could the power levels between two S4P files after impedance matching have 10dB difference? Could anybody tell me what's difference between these S4P file?
You might see a difference if you used any fixture simulator features besides balanced. For example, if you used impedance transformation or port matching. Impedance transformation and port matching are applied to the single-ended S-parameters before the S4P (I think, not 100% sure), so if you turn fixture simulator off, these impedance matching elements will not be in the S4P data. However, you don't mention if you use this, so this is a wild guess.
If you want a better answer, you might try posting your results with a detailed description of the analyzer settings (everything that you set after preset). Also, for a saw filter, you really should use stepped sweep mode on the analyzer.