Satellite navigation has become ubiquitous in our everyday life and plays a crucial role also in geodesy. In order for the users to obtain optimal performance, reference stations are key elements: they allow to monitor satellite signals, providing alerts for malfunctioning as well as constantly estimating propagation errors and possibly distributing this information (through augmentation systems) to the users.

Antennas drive the obtainable performance of reference stations: with the development of antennas with always better performance (for instance in terms of phase center and group delay variations), research has also focused in the last years on how to achieve highest accuracy by minimizing the intrinsic errors of the antennas.

Near-field effects are among the largest remaining influencing variables in GNSS positioning. All objects in the direct vicinity of the antenna (near field) influence the reception behaviour of the antenna, effectively turning the antenna “standalone” pattern into an “installed” pattern, different for each installation. The strength of the near-field influence depends, among other things, on the size, geometry, position and material of the closeby objects. This variability of the antenna properties has a detrimental effect for precise geodetic measurement, as it introduces a not-known error, limiting the achievable accuracy.

Efforts to precisely characterize the antenna intrinsic-errors, such as phase centre and group delay variation, do not bring in this framework the wished improvement, as antennas are typically characterized in “standalone” configuration, i.e. not considering the actual objects (mast, pillar) they will be installed on in the final configuration.

Near-field effects are among the largest remaining influencing variables in GNSS positioning. All objects in the direct vicinity of the antenna (near field) influence the reception behaviour of the antenna, effectively turning the antenna “standalone” pattern into an “installed” pattern, different for each installation. The strength of the near-field influence depends, among other things, on the size, geometry, position and material of an interfering object. This variability of the antenna properties has a detrimental effect for precise and geodetic measurement, as it introduces a not-known error, limiting the achievable accuracy.

This paper aims at shedding insight into the influence of mounting structures on GNSS antenna performance, mostly in terms of PCV and GDV, and proposing possible countermeasures. To do so, we will use a mixture of electromagnetic measurement and simulation, to be able to visualize the effect of mounting structures on the antenna fields and then validate our observations on real antennas.

Authors: Stefano Caizzone, Stefan Ionita, Wahid Elmarissi