High-resolution flicker-noise-free frequency measurements of weak microwave signals

Abstract

Amplification is usually necessary when measuring the frequency instability of microwave signals. In this work, we develop a flicker-noise-free frequency measurement system based on a common or shared amplifier. First, we show that correlated flicker phase noise can be cancelled in such a system. We then compare the new system with the conventional system by simultaneously measuring the beat frequency from two cryogenic sapphire oscillators (CSOs) with parts in 1015 fractional frequency instability. We determine for low power, below -80 dBm, the measurements were not limited by correlated noise processes, but by thermal noise of the readout amplifier. In this regime, we show that the new rea..