Correct information on GPS antenna and use of accurate model of phase center variation (PCV) is must for accurate GPS processing. GPS antenna model (including satellite antenna) has been updated. To know the timing of the update is important to avoid false interpretation of nature based on GPS solutions. It's always good to check the possibility of antenna, antenna model, and reference frame changes when we find jump is GPS solutions.
IGS Antenna Working Group： Detailed description of IGS antenna files
National Geodetic Survey - Antenna Calibrations： Antenna model made by NOAA NGS