Low phase noise sapphire disk dielectric resonator oscillator with combined stabilization

This paper deals with a theoretical analysis of a low phase noise microwave transistor oscillator stabilized with a sapphire “whispering gallery” mode disk dielectric resonator which used both as a filter in the oscillator feedback circuit and as a dispersive element of a frequency discriminator in the AFC loop providing additional noise degeneration. It is found that in many cases a noise floor of the AFC system is determined with residual flicker noise of a ferrite circulator used as a part of the discriminator circuitry. Replacing the circulator by a 3-dB hybrid and adding the auxiliary amplifier(s) at the phase detector input(s) open a possibility to reduce the AFC system noise floor as much as 30-35 dB and thus to get impressive improvement in the oscillator close-in phase noise