If you want to see some local oscillator phase noise performance comparisons between an HP8568B and something like the classic 26.5GHz Agilent E4440A PSA analyser I can show you if that helps?
I don't have the newer PXA here (I wish I did!) but I do have an old E4440A PSA that I could fire up and I still have my HP8568B. The Agilent PSA analyser range was the best we had at work 15 or so years ago. They are a bit long in the tooth now and most people prefer to use the PXA or the MXA or something from the Tek RTSA range. These modern analysers can capture and process >80MHz bandwidth and are suitable for modern digital signals. This old PSA only captures up to about 10MHz and it has limited capture memory.
It represents a crossover between the flagship 8566/8 swept analysers and today's modern signal analysers as it can work both as an ultra high performance swept spectrum analyser and also as a fairly restricted VSA (Vector Signal Analyser) with about 10MHz capture bandwidth.
https://www.keysight.com/en/pcx-x205...0&cc=GB&lc=eng
I have the 26.5GHz E4440A version in the link above and there should be loads of literature on the Keysight website that will include technical descriptions and block diagrams for the YIG based LO system.