Space qualified microwave source for cold atom clock operating in orbit

The space cold atom clock (CAC) suffers more degradation of frequency stability from the local oscillator noise compared with fountain clocks operating on the ground because of the larger dead time of the clock cycle. Therefore, low phase noise is required for the microwave source of the space CAC in addition to robustness, compactness, and adaptability to the space environment. This paper presents the design and measurements of a low-phase-noise space qualified microwave source for the cold atom clock experiment in space CAC operating in the Tiangong-2 Chinese space laboratory. At frequencies near the carrier, a phase noise level of 10−6.7 × f−1.5 rad2/Hz (f is the Fourier frequency) is achieved. This guarantees a frequency stability of 1.4 × 10−13 τ−1/2 (τ is the average time in seconds) for the typical space CAC operation cycle.