## 1 Introduction  
In recent years, significant development of Europe's Global Navigation Satellite System (GNSS), Galileo, has been observed [1]. In 2011 and 2012, four In-Orbit Validation (IOV) satellites were launched, which comprised the first phase of Galileo. The next phase, Full Operational Capability (FOC), both started and launched the first two FOC satellites in 2014; however, these satellites went into the wrong orbit. Therefore, these satellites are no longer included as a part of the FOC phase of Galileo. Over the next few years, four pairs of FOC satellites were placed, and from the end of 2016, quadruple FOC satellites were placed simultaneously [2]. On 15 December, 2016, Early Operational Capability (EOC) was announced, and 12 new Galileo satellites were successfully launched between 2016 and 2018. Currently, the Galileo system has 26 satellites in space, including 22 operational, 2 with unhealthy and unavailable status, and 2 in the wrong orbit. The final launch of the satellites is expected to take place in 2020, complementing and placing spare satellites before FOC is announced. At the same time, Galileo Second Generation (G2G) satellites are already being prepared that can replace the old satellites. Together with such rapid development of the Galileo system, the International GNSS Service (IGS) provides repeatedly newer and better products [3]. These works are carried out as part of the Multi-GNSS Experiment (MGEX) project, which tracks, collates and analyzes all available GNSS signals. MGEX also generates high-accuracy products, such as orbits, clocks and site coordinates [2; 4; 5], and it has made Galileo-based products much more accurate than they were a few years ago--even more accurate in some aspects than GPS-based products, as shown by [6]. Such accuracy is also important for multi-GNSS absolute positioning, wherein measurement accuracy increases after adding Galileo observations [1; 7; 8]. To estimate precisely the point position, one should model properly the transceiver system. For each GNSS signal, one should know the position of the phase center antenna (PCA) for both the transmitter (satellite) and the receiver. It is widely accepted that the PCA can be described by mean offset with respect to the antenna reference point (ARP) and its direction-dependent variation. Therefore, two definitions are used: phase center offset (PCO) and phase center variation (PCV) [9]. The IGS Antenna Working Group provides the PCO/PCV tables for satellites and receiver antennas in the standardized ANTEX format [10]. This applies to each healthy satellite and most of the ground antennas. In this format, each frequency is coded by a satellite system flag (e.g., \"G\" for GPS and \"E\" for Galileo) and a frequency number code consistent with the RINEX definitions. Initially, the IGS estimated the Galileo values for transmitting antennas as similar to GPS and GLONASS [11]. The nadir-dependent phase center variation and offsets in the z-direction for each satellite were estimated by fixing the receiver antenna phase center corrections (PCCs) to robot-based calibrations. The situation had changed by the end of January, 2018, when the IGS tables were updated (IGSMAIL-7572). Since then, the tables contain calibrations for all five carrier signals for the Galileo satellite antennas provided by the European GNSS Agency (GSA) [12]. A completely new quality for antenna modeling has arisen, since the new values are chamber-calibrated PCO/PCV and cover more space than estimated ones [13]. However, as reported by the IGS Antenna Working Group [14; 15; 16], these calibrations disagree with the estimated values and are not consistent with the scale of the current release of IGS (IGS14/IGb14). This translates into coordinate inconsistency on the ground. For receiver antennas, the situation is also complicated. The official IGS products contain type mean corrections for most of the commonly used antenna types, which are mean corrections that were created on the basis of many calibrations of the same type of antenna.