High-Q frequency stable dual-mode whispering gallery sapphire resonator

The design and experimental test of a dual mode high-Q Whispering Gallery (WG) sapphire resonator is presented. Dual mode operation is realized by designing the WGE/sub 7,0,0/ and the WGH/sub 9,0,0/ mode near 9 GHz and separated in frequency by approximately 80 MHz. Design was achieved by implementing finite element software, which is shown to agree very well with measurement, Due to the anisotropy of sapphire, WGH and WGE modes have different temperature coefficient of frequency (TCF). We show that the difference frequency can be used to stabilize the temperature, resulting in a temperature limited frequency stability of better than one part in 10/sup 13/. This type of resonator has the potential to improve substantially the close to the carrier phase noise in current state-of-the-art low noise oscillators.