Low phase noise microwave oscillators based on HTS shielded dielectric resonators

To meet the specifications of future radar and communication systems we developed a low phase noise microwave oscillator. This feedback oscillator consists of a commercial MESFET-amplifier at room temperature and a LaAlO3 dielectric resonator with high temperature superconducting (HTS) shielding at 63K. The resonator operating at a resonance frequency of 5.6GHz showed unloaded quality factors in the 10(5) to 10(6) range. By means of a strong resonator coupling (\S-21\=6dB) and an amplifier gain of 20dB we obtained an output power of +15dBm. The phase noise L(f(m)) of the oscillator was below the detection limit for offset frequencies beyond 10kHz. For offset frequencies below 5kHz measurements revealed perfect L(f(m))proportional to f(m)(-3)-behaviour according to the Leeson model. The phase noise was -110dBc/Hz at 1kHz offset and -130dBc/Hz at 10kHz. This phase noise performance is superior to state of the art SAW- or quartz oscillators for f(m)>10kHz. To further reduce the phase noise performance close to the carrier we investigated the implementation of a phase locked loop (PLL). The long term temperature stability of the oscillator frequency can be enhanced by introducing a central cylinder made from rutile (TiO2). We will present numerical and experimental results on this compensation.