Based on the principles of microwave circuit interferometry we have constructed a Reduced Noise Amplifier (RNA) with power spectral density of phase, as well as amplitude, fluctuations close to -170 dBc/Hz at 1 kHz offset. The RNA has been incorporated with a cryogenic sapphire resonator as a loop oscillator whose noise performance is governed by the Leesons model. Following this model and using the results of in-situ measurements of gain and phase fluctuations of the RNA we inferred noise properties of the oscillator. In particular, for a signal transmitted through the resonator we found that power spectral density of its phase/amplitude fluctuations must be close to -185 dBc/Hz at offsets above 300 Hz. We discuss a few approaches that will allow direct measurements of such low levels of noise.
Download