Microwave oscillators incorporating cryogenic sapphire dielectric resonators

Progress is reported on efforts to develop a commercially viable high-purity X-band signal source incorporating a cryogenic sapphire dielectric resonator. The resonator design is of the whispering gallery type to take advantage of the excellent electromagnetic field confinement offered by this geometry. Complications resulting from the high spurious mode density of this type of resonator have been eliminated by developing a very accurate and complete mode analysis program which fully incorporates the dielectric anisotropies of the sapphire ring. This program allows the design of a window in the frequency domain where no unwanted modes exist, with accurate placement of the desired mode at the center of this region. The phase noise properties of simple oscillators incorporating these resonators have been evaluated. Two-oscillator phase noise comparison measurements have yielded extremely encouraging results