Oscillators based on high-Q sapphire resonators and interferometric noise suppression systems have produced the lowest noise microwave oscillators to date. [1-3] Such oscillators operate at room temperature and 8 to 10 GHz have achieved noise as low as -160 dBc/Hz at 1kHz and -175 dBc/Hz at 10 kHz offset frequency. The success of such low noise is mainly due to the high-Q cavity and the intricate design of the phase detection circuitry, which is used to cancel the phase noise. The phase detection is based on an interferometer, which carrier suppresses the microwave signal during phase detection. In this way the signal can be amplified free of flicker noise. Details will be presented along with details of the design of the sapphire resonators. Cryogenic versions have also been built with ultra-stable frequency stability and will be presented. To attain millimeter wave frequencies multiplication of the signals with low noise chains can lead to successful high frequency low noise oscillators. [4-5]
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 EN Ivanov, ME Tobar, “Low Phase Noise Sapphire Crystal Microwave Oscillators: Current Status,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, vol. 56, no. 2, pp. 263-269, 2009.
 R Bara-Maillet, SR Parker, N Nand, Nitin, J-M le Floch, ME Tobar, “Microwave to Millimetre Wave Synthesis Chain Phase Noise Performance,” IEEE Trans. UFFC, vol. 62, no. 10, pp. 1895-1900, 2015.
 R Bara, J-M Le Floch, ME Tobar, PL Stanwix, S Parker, JG Hartnett, EN Ivanov, "Generation of 103.75 GHz CW Source with 5.10-16 Frequency Instability Using Cryogenic Sapphire Oscillators" IEEE Microw. Wireless Comp. Lett., vol. 22, no 2, pp. 85-87, 2012.