I have just found the program SATSAGEN by Alberto IU1KVL on the web.
It turns a Pluto into a very useful measuring device. A generator and a spectrum analyzer were realized, whereby the entire frequency range of the Pluto is supported.
In the "Spectrum Analyzer w/Tracking" mode, for example, filter passband curves can be determined very easily. As a very first test I measured a 2.4GHz filter, see screenshot. For tuning and matching of antennas, only a suitable directional coupler would be required in addition.
At Albertos blog you find the download page and also a video with helpful explanations:
Thanks to Alberto, who provides SATSAGEN to the HAM Radio community free of charge.
73 de Roland