Antenna specific IfE-robot based code phase delays and its impact on positioning and navigation

The Institut für Erdmessung (IfE) is an official IGS calibration institution, calibrating phase center variations (PCV) for receiver antennae routinely in the field, using the actual GNSS satellite signals in space. Current research activities focus on the antenna code phase calibration with the Hannover Concept of absolute antenna calibration. The receiving antenna as a part of a reception chain can introduce systematic effects, currently known as Group Delay Variations (GDV), i.e. azimuth and elevation dependent code-phase delays. This error introduces additional range variations along the line-of-sight for every satellite depending on the corresponding incident angle in the antennas body frame. Depending on the antenna design, suitable for specific applications, GDV can degrade the accuracy of code based applications, such as precise landing approaches as well as for time and frequency transfer. The paper can be subdivided into two major parts: In the first part, we focus on the current investigations on receiver antenna GDV calibration. Beside the theoretical background of a concept to determine GDV for different GPS antennae based on the Hannover Concept of absolute antenna calibration, the obtained GDV from several antennae with different characteristics will be presented and critically discussed. The second part focuses on the consequent analysis of the impact of the determined GDV on position and navigation applications. The contribution of GDV on the observation and position domain can be shown by using a special experimental set-up. In addition, GDV for a real C/A based autonomous navigation approach are investigated and critically discussed.