# Phase Centre Corrections of GNSS Antennas and Their Consistency with ATX Catalogues
## 5 Discussion  
Modern manufactured antennas are of better repeatability than older models, i.e., exhibiting less deviation from the pattern (average) in antex files. This is the case for, e.g., the Trimble Zephyr Geodetic 2 (TRM57971.00 NONE) antenna used in the experiment. In selected stations (e.g., KRAW and BOGI), antennas are still being used that date back to the 1990s. Their characteristics may differ from the accepted standards. Therefore, it can be postulated that individual characteristics should be developed for them, so that they do not introduce errors to the network in which they work (IGS, EPN, etc.). However, their individual calibrations are a matter of debate due to costs. We checked the KRAW station based on a KRA1-KRAW overpass survey and the additional temporary stations KR01 and KR02. Archival materials from various authors were also collected. As a result of the analysis of these materials, it can be stated that the antenna (Ashtech ASH70195C_M SNOW) of the KRAW station has different characteristics from those revealed in the IGS files of the subsequent versions. Azimuth elevation is mostly dependent on the lowest-over-horizon satellites [4; 37], which have the smallest weights in processing. Thus, this aspect has the smallest impact. PPP processing shows a systematic shift in the KRAW-KRA1 height difference at the level of +1.8 mm, while measurements directly from levelling show a \(-\)6.2-mm difference. This may result in incorrect altitude results and have an adverse effect on, e.g., fitting the global geopotential model into the national height frame. Therefore, old stations that are included in the national (or transnational) permanent network need individual PCC. The tested network solutions, both PPP and baseline solutions [34; 35], were not resistant to the impact of real KRAW antenna characteristics, different from any analysed ATX catalogue. As a result, the permanent stations' ellipsoid heights in network solutions may be subject to systematic errors. Even using advanced and renowned software (Bernese GNSS Solutions), such errors cannot be detected. The analysis showed that a calculation strategy based on a short baseline L1-only solution may detect the error, even if the popular \"engineering\" software is used (Trimble Business Centres, GNSS Solutions, Geonet). The question arises as to what the optimal solution for old antennas is--the determination of individual characteristics (PCC) or replacement with a new antenna (also with  
Figure 10: Height difference (m) between the KRAW and KRA1 antenna reference points from precise levelling. individual PCC). In other words, should the old stations be partially or fully modernized? For the analysed station KRAW (antenna ASH70195C_M SNOW), a full upgrade had the advantage of introducing four GNSS systems compared to the existing GPS-only. Especially, introduction of the Galileo system may benefit the station solution [38; 39], e.g., decreasing the positioning error statistics for GPS + Galileo combinations [40] despite Galileo still not providing the same satellite availability as GPS [41]. Concluding the results and achievements in the investigation of PCC by other authors [16; 19; 21; 24], we are inclined to say that the time of antennas from the 1990s should be completed and full modernization carried out, despite the higher costs. Conceptualization, L.B. ; methodology, L.B. and J.K.; software, L.B. and J.K.; validation, L.B., J.K. and K.M. ; formal analysis, L.B., J.K. and K.M. ; investigation, L.B., J.K. and K.M. ; resources, L.B. and J.K.; data curation, L.B. and J.K.; writing--original draft preparation, L.B., J.K. and K.M. ; writing--review and editing, L.B., J.K., K.M., M.S. and B.K. ; visualization, L.B., J.K., B.K. and K.M. ; supervision, L.B., J.K., K.M. and M.S. ; project administration, L.B. ; and funding acquisition, L.B., J.K., M.S., B.K. and K.M. Percentage contributions: L.B., 60%; J.K., 15%; B.K., 5%; M.S., 5%; and K.M., 15%. All authors have read and agreed to the published version of the manuscript.