I have found no way to save the S-parameters of a PSP analysis directly. In ViVA we can not really plot a complex waveform, since we have only two dimensions, so exporting a trace will not work. I think that is why the SP analyses had an option for output file. Unfortunately PSP does not have this. Opening the Results browser and selecting export for S11, I got the very same dialog as for exporting a trace, i.e. no Snp file.
I have a circuit, which has a periodic behaviour and I want to compare my simulation data with the measurement one. It would be much more easier to compare two sNp files.
PS: of course I could export the magnitude and the phase into a vcsv file and write a program which converts it into S parameter and then dump it into sNp file. I am looking for a ready to use solution. There must be such an option, I just don't find it.