A Novel High-Precision Satellite–Ground Frequency Synchronization Method Based on Beacon Transponder

High-precision frequency standards underpinning signal synchronization and data consistency are essential for satellites. Navigation satellites use atomic clocks as time and frequency standards; however, limitations in size, weight, and cost constrain their performance. Geostationary Earth orbit (GEO) communication satellites typically rely on onboard oscillators as references, whose performance is generally poor. Moreover, satellite–ground links can be used for frequency synchronization between GEO satellites and ground stations. However, phase drift in onboard oscillators restricts improvements in synchronization precision. This paper introduces a frequency synchronization method based on a beacon transponder that enables ground stations to calculate and eliminate satellite oscillator phase drift. This design achieves high-precision frequency synchronization through real-time carrier-phase compensation and replicates the ground station’s frequency standard onboard. Ground-based experiments validated the method using a beacon transponder prototype in motion. The standard deviation of the phase synchronization error between the replicated clock and ground-station frequency standard was 2.97 ps over 24 h. The stability was better than 2.61 × 10−12 and 9.98 × 10−16 for averaging times of 1 s and 10,000 s, respectively. These results demonstrate this method’s potential for high-precision frequency synchronization between satellites and ground stations, crucial for establishing an integrated space–air–ground frequency synchronization network.