Check out this guy, http://lea.hamradio.si/~s53mv/zifssb/xband.html He made a 10ghz transceiver on diy FR4 board.
I really like stripline components. As soon as I have some time, I want to prototype some stuff on Fr408 board. The dielectric constant is not that bad.
I really like this guy S53MV, Matjaz Vidmar. He has made astounding machines with very little and simple components since the beginning of the 90ies in Slovenia.
He is a full professor with a PHD at the University of Lubljana, Slovenia, faculty of electric engineering.
From his designs, you can learn several things, among others, of course:
- modularize. Make separate units, test them independently, then combine them
- for homebrew, it does not need cutting edge components that are extremely hard to handle due to small size. If you are smart, even simple parts can work well.
Yes, he uses FR4 up to (in just one location, however) up to 10GHz. In order to reduce dielectric losses, he chose 0.8mm material instead of the normal 1.6mm,
the filters he made with it are rather broadband, and a few dB of filter losses were acceptable.
Another good thing with FR4 is that matching and reflections are not soo important because damping is so ample
Of course, FR4 and 10GHz can be done - if requirements are really relaxed (broadband, lossy, low accuracy and low power).
Narrowband, low noise, accurate, power stuff - better go for something else (PTFE, Rogers, ...).