Dielectric resonators with Q-values > 10~6 at T = 77K have been employed to build oscillators at 23GHz and 24.68GHz. To achieve ultimate g-values we have used sapphire "Whispering Gallery Mode resonators. We have optimised these resonators to suppress low-Q housing modes and ensure oscillator operation on high-Q modes only. Employing a commercial MESFET-amplifier we have determined the phase noise performance of the oscillators. To accurately set the oscillator frequency we have investigated the performance of a mechanical tuning mechanism by an HTS end plate. This tuning mechanism also allows for active compensation of long term frequency drifts by means of a piezoelectric fine-tune element. Also, we have incorporated this oscillator on a Stirling-type miniature cooler.
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