[IGSMAIL-8653] Updated antenna model for BDS-3/QZSS and BDS-3 signal switch to B1C/B2a

[Steigenberger, Peter]

Dear colleagues,

the operational IGS products currently cover GPS, GLONASS and Galileo. 
BeiDou and QZSS are only included in the products of the Multi-GNSS 
Pilot Project (MGEX). The inclusion of these constellations in the 
operational products is currently hampered by scale inconsistencies of 
the BDS and QZSS antenna models with the IGS20 reference frame scale.

In order to overcome these inconsistencies, the IGS Reference Frame 
Committee, Antenna Committee, and the Multi-GNSS Pilot Project together 
with ten IGS/MGEX ACs have generated a new BDS-3/QZSS antenna model 
aligned to the IGS20 scale. This model comprises:

BeiDou-3:
+ Block-specific estimated B1C/B2a phase patterns from COD, ESA, GFZ, 
SHA, TUM, WHU with extrapolation to 15 deg for BDS-3 MEO satellites
+ Block-specific estimated B1C/B2a phase patterns from COD, SHA, TUM, 
WHU with extrapolation to 10 deg for BDS-3 IGSO satellites
+ Retained x/y-PCOs and B1 z-PCOs from CSNO/TARC
+ Adjusted B2 and B3 z-PCOs of BDS-3 MEO and IGSO satellites to obtain 
SVN-specific B1C/B2a and B1I/B3I z-PCOs aligned to IGS20 as estimated by 
CAS, COD, GFZ, GRG, JGX, SHA, TUM, WHU (B1C/B2a) as well as DLR and WHU 
(B1I/B3I)
+ Multiple intervals are considered for selected SECM satellites with 
time-varying PCOs. In this case, no PCOs are provided prior to 01-Jan-2021
+ Preliminary z-PCOs of C232 and C233 are based on copied CSNO vales of 
C228 and IGS estimates
+ Preliminary z-PCOs of C234 and C235 are based on copied CSNO vales of 
C225 and DLR estimates only

QZSS:
+ limited to L1 and L5 as new QZSS Block III satellites do not transmit 
L2 anymore
+ satellite-specific phase patterns provided by Cabinet Office (except 
for J001)
+ satellite-specific x/y-PCOs provided by Cabinet Office
+ J003, J005, J007: z-PCOs provided by Cabinet Office
+ J001, J002, J004: Estimated L1/L5 z-PCOs by COD, GFZ, JGX, TUM

Further details can be found in the following presentations:
Phase pattern estimation, IGS Workshop 2024: 
https://elib.dlr.de/205651/1/IGSWS_2024_BDS_QZS_camp.pdf
PCO estimation, IAG Scientific Assembly 2025: 
https://elib.dlr.de/216593/1/IAG_2025_BDSant.pdf

This BDS-3 and QZSS antenna model update will be included in the IGS 
antenna model igs20.atx at the first day of GPS week 2405, i.e., 8 
February 2026. This ANTEX file is currently available at 
http://ftp.aiub.unibe.ch/awg/pcv_proposed/igs20_2405.atx.gz

At the same time, the MGEX ACs processing BeiDou will switch their 
signal selection from the legacy B1I/B3I signals to the modernized 
B1C/B2a signals. As the latter are only transmitted by BDS-3, this also 
means that BDS-2 satellites are not included anymore in the MGEX products.

Best regards,

Arturo Villiger, IGS Antenna Committee
Paul Rebischung, IGS Reference Frame Committee
Peter Steigenberger, IGS Multi-GNSS Pilot Project