IGS BDS-3 satellite antenna calibration campaign

A new antenna model for BeiDou-3 satellites in medium Earth orbit (MEO) and inclined geosynchronous orbit (IGSO) is presented. This model enables consistent processing of BeiDou-3 with other GNSSs in the IGS20 reference frame and has been adopted for use within the International GNSS Service (IGS) in February 2026. The model introduces estimated phase patterns for four different blocks of BeiDou-3 satellites and provides satellite- and frequency-specific phase center offsets (PCOs) for the B1, B2, and B3 bands. B1C/B2a phase patterns and PCOs are obtained as weighted averages of individual estimates from up to nine IGS analysis centers (ACs) to minimize the dependence on AC-specific models and processing standards. In order to support users of the B1I/B3I legacy signals, satellite-specific PCOs for this linear combination have been determined by two ACs. As part of the antenna model development, temporal variations of PCOs at the few decimeter level were observed over the 2021–2024 time frame for selected satellites built by the Shanghai Engineering Center for Microsatellites (SECM), which are handled as piece-wise constant PCOs in the new IGS antenna model for the affected satellites. The new phase center model is aligned to the IGS20 reference frame and ensures consistency between GPS, GLONASS, Galileo, and BeiDou-3 in multi-GNSS processing. A precise point positioning validation of the new antenna model with B1C/B2a observations confirms a 0.11 ppb scale consistency of BeiDou-3 with the IGS20 reference frame.