Multi-facility GNSS antenna calibration

Abstract Accurate antenna calibrations are a cornerstone of high-quality global navigation satellite systems (GNSS) positioning, time and frequency transfer, precise orbits, and troposphere estimates. The international GNSS service (IGS) antenna committee maintains antenna phase center corrections in the ANTEX file relying on five calibration facilities. Since new calibration facilities have been set up and user demands have grown along with hardware and software updates of GNSS, we organized an international inter-comparison across nine facilities, using both anechoic chambers and field robots. Six antennas with different designs were calibrated by each facility and compared with the Geo++ robot solution (GPP4), a proxy for the IGS ANTEX. Where available, we also considered the IGS type means. We examined differences between the antenna patterns and subsequent differences in station coordinates. To this end, we used a standardized forward simulation as well as multi-GNSS PPP solutions using the GNSS toolbox developed at Leibniz University Hannover, Institut für Erdmessung (IfE). Our study yields several important results. We found that multi-GNSS antenna calibrations exhibit frequency- and elevation-dependent variations, with deviations of up to 3 mm to 4 mm at low elevations. We show that organizations like Topcon (TPS), national geodetic survey (NGS), and Wuhan GNSS Research Center (WHU) yield calibration results that are in very good agreement with those of IGS accepted facilities such as GPP, IfE, and to some extent geoscience Australia (GA). These differences result in position deviations of a few millimeters, with the Up component being the dominant contributor.