Precise phase synchronization of a cryogenic microwave oscillator

We developed a novel technique for accurate phase synchronization of microwave oscillators based on sapphire dielectric resonators cooled to liquid nitrogen temperature. The achieved quality of phase synchronization (a few milliradians) enables the accurate measurements of extremely weak phase fluctuations expected from the next generation of ultralow phase noise microwave oscillators. (C) 2010 American Institute of Physics. [doi:10.1063/1.3433475]