Abstract: Spaceborne atomic clock is a key part of satellite navigation system, which provides stable and reliable high-precision time-frequency signals for the system. Its performance determines the user's navigation, positioning and timing accuracy, so it is particularly important to carry out comprehensive performance evaluation of spaceborne atomic clock. This paper introduces the main methods and principles of the performance evaluation of spaceborne atomic clocks and the pre-processing process, and summarizes and analyzes the frequency characteristics, fitting precision, frequency accuracy, frequency drift rate and frequency stability of the clock difference data of spaceborne atomic clocks. A comprehensive performance evaluation of GNSS spaceborne atomic clocks is carried out with the after-the-fact precision clock difference products provided by GFZ. The results show that the fitting accuracy of Galileo spaceborne hydrogen clock is the best, and more than half of them are better than 0.1 ns. Galileo and BDS-3 spaceborne hydrogen clocks perform well in frequency accuracy analysis and frequency drift rate analysis. In terms of stability, Galileo spaceborne hydrogen clock, BDS-3 spaceborne hydrogen clock and GPS Ⅲ-A spaceborne rubidium clock are basically in the order of 10^-15/d. The research in this paper is of great significance in improving the reliability and stability of PNT.

Key words: GNSS, spaceborne atomic clock, performance evaluation, frequency accuracy, frequency drift rate