Phase Centre Variations in �Adaptive GNSS Antenna Arrays

Abstract

Adaptive antennas with digital beamforming is a promising technology for mitigation of radio interference and multipath effects in GNSS receivers. It is however well known that adaptive antennas may introduce biases in the pseudo-range and carrier phase measurements of a GNSS receiver. This effect can be interpreted as the deviation of the array phase centre from its nominal position. The array phase centre position is affected by the beamforming process as well as the properties of a single array element and electromagnetic coupling between the elements. Another factor affecting the position of the array phase centre are different characteristics of individual antenna channels (RF front ends), which requires accurate calibration. In the work to be presented, we investigated the phase centre variations of a 2x2 uniform rectangular adaptive antenna array by using the measured patterns of the antenna elements and applying different beamforming techniques. The array is designed for the reception of GPS/Galileo signals in the L1 band. The beamforming techniques are implemented in DLR in-house multi-antenna software GNSS receiver. The effect of phase centre variations on the positioning accuracy of a GNSS receiver as well as the possible compensation approaches are discussed.