Basics of high-frequency sources
This topic has not been dealt with very well on Microwaves101, our apologies! People tend to write textbooks about what they know, and I never really had to work on a source.
Modern sources use voltage controlled oscillators and phase-locked loops, with the output usually below 6 GHz. Then, mixers, multipliers or other nonlinear devices are used to achieve higher frequencies.
Bandwidth in a VCO is limited, maybe an octave. So for wideband, you will need more than one VCO, or more than one multipler, and then somehow mux it all together. Here's an example from Analog Devices
I am hopeful that someone smarter than I will add to this answer!
Steve (the Unknown Editor)