GNSS Receiver Antenna Absolute Field Calibration System Development: Testing and Preliminary Results

Abstract

For high-precision Global Navigation Satellite Systems (GNSS) positioning based on carrier-phase measurements, knowledge of the GNSS receiver antenna electrical signal reception characteristics, i.e., phase center, is crucial. Numerous studies have led to the understanding of the influence of GNSS receiver antenna phase center corrections (PCCs) on GNSS positioning accuracy and other estimated parameters (e.g., receiver clock estimates, ambiguities, etc.). With the goal of determining the PCC model of GNSS receiver antennas, only a few antenna calibration systems/facilities are in operation or under development worldwide. The International GNSS Service (IGS) publishes type-mean PCC models for almost all geodetic-grade GNSS antennas. However, the type-mean models are not perfect and do not fully reflect the signal reception properties of individual GNSS receiver antennas. Relevant published scientific research has shown that the application of individual PCC models significantly improves the accuracy of GNSS positioning and other estimated parameters. In this article, the new automated GNSS antenna calibration system, recently developed at the Laboratory for Measurements and Measuring Technique (LMMT) of the Faculty of Geodesy of the University of Zagreb in Croatia, is presented. The developed system is an absolute field calibration system based on the utilization of a Mitsubishi MELFA 6-axis industrial robot. During calibration, the robot tilts and rotates the GNSS antenna under test (AUT) around a fixed point within the antenna. The antenna PCC modelling is based on time-differenced double-difference carrier-phase observations. Our preliminary results for the Global Positioning System (GPS) L1 (G01) frequency show a submillimeter repeatability of the estimated PCC model and a submillimeter agreement with the Geo++ GmbH calibration results.

Early Results on GNSS Receiver Antenna Calibration System Development

“…For an in-depth description of the antenna calibration methodology at LMMT, an interested reader is referred to Tupek et al [14].…”

“…To fulfill the requirements of high-accuracy positioning applications, the receiver antenna PCCs must be determined. In line with the IGS convention, and as depicted in Figure 1, PCC is divided into the phase center offset (PCO) vector and the azimuth-and elevation-dependent phase center variation (PCV) [4,6,[10][11][12]14]:…”

“…The inhouse custom-made software components of the calibration system, all written in Python, are the antenna calibration module (ACM), time synchronization module (TISY), and the PCC estimation module. An in-depth description of the calibration system operation can be found in Tupek et al [14].…”

“…Only a few calibration systems utilizing a precise robot are operational or under development worldwide [5][6][7][8][9][10][11][12], and even fewer are accredited by the International GNSS Service (IGS) to provide antenna calibration results [13]. Since this topic is of high interest to the scientific antenna community, and a new calibration system is highly desirable, at the Laboratory for Measurements and Measuring Technique (LMMT) of the Faculty of Geodesy of the University of Zagreb in Croatia, a new antenna calibration system has been developed [14]. In this article, preliminary antenna calibration results for the Global Positioning System (GPS) L1 frequency (G01) are presented and elaborated.…”