Temperature compensated high-Q dielectric resonators for long term stable low phase noise oscillators

High temperature superconductor (HTS)-shielded dielectric resonators with Q-values >10(5) at T=77K are promising candidates for applications in low phase noise oscillators. We have investigated feedback-oscillators at 5.6 and 10.2GHz and are currently setting up an oscillator at 23GHz. To achieve ultimate fl-values we have used TE01 delta- and whispering gallery mode resonators with the central dielectric made from sapphire or lanthanum aluminate (LaAlO3). Employing commercial MESFET-amplifiers we have determined the phase noise performance of feedback-oscillators at these frequencies. These results confirm the superior performance of HTS-shielded dielectric resonator stabilised oscillators. The long term stability of the oscillator is mainly determined by the temperature stability of the resonator frequency. Thermally induced variations of the permittivity epsilon Of the central dielectric puck cause frequency drifts of the resonator frequency. Rutile has successfully been used to build resonators with frequency stabilities <0.3ppm/K at 5.6GHz. To enable accurate positioning of the oscillator frequency we have investigated the effect of varying the distance between the central dielectric and superconducting end plate for a whispering gallery mode resonator at 23GHz. We have also started utilising a Stirling-type miniature cooler to cool the resonators. We present data on the influence of cooler vibrations on the purity of the oscillator frequency.