Sapphire loaded cavity microwave oscillator with improved temperature stability

Poor frequency-temperature stability of sapphire "whispering gallery" resonators (SWGR) is the main drawback of modern ultra-low phase noise room-temperature microwave sources using such resonators. This paper describes a novel dual-mode oscillator temperature control network where an auxiliary RF reference signal is formed by output frequency division. It eliminates the additional RF source and simplifies the oscillator on the whole. The completed temperature stabilizing system looks basically like a familiar noise suppression circuit with the differences that its frequency discriminator operates now at the second SWGR\´s mode and a control signal governs the temperature. A variable infrared heater is suggested to improve the dynamic characteristics of the temperature control. Estimation shows that in such configuration the fractional frequency instability of the order of 5×10^-13 for measurement intervals from 1 to some hundred seconds is possible.