Microwave oscillators for superior short term stability and ultra-low phase noise

A survey is presented of the wide variety of available microwave oscillator capabilities, with emphasis on their phase noise and short term frequency stability. These oscillators show unique capabilities for frequency generation, making possible the lowest phase noise floors and short term stabilities of any technology. They range in complexity from a free-running transistor oscillator with an ultra-low noise floor, to cryogenic oscillators with higher frequency stability than any other source for measuring times up to ≈100 s. Their advantages derive primarily from high operating frequency and from recent advances in resonator and circuit technology