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

High temperature superconductor (HTS)-shielded dielectric resonators with Q-values >10⁵ at T=77 K are promising candidates for applications in low phase noise oscillators. We have investigated feedback-oscillators at 5.6 and 10.2 GHz and are currently setting up an oscillator at 23 GHz. To achieve ultimate e-values we have used TE_01δ- and whispering gallery mode resonators with the central dielectric made from sapphire or lanthanum aluminate (LaAlO ₃). 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 E of the central dielectric puck cause frequency drifts of the resonator frequency. Rutile has successfully been used to build resonators with frequency stabilities <0.3 ppm/K at 5.6 GHz. To enable accurate positioning of the oscillator frequency we have investigated the effect of varying the distance between the central dielectric and a superconducting end plate for a whispering gallery mode resonator at 23 GHz. 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