Characterizing Phase-Center Motion of GNSS Antennas Used in High-Accuracy Positioning

Emerging transportation applications require positioning solutions with accuracy of a few centimeters. Current Global Navigation Satellite Systems (GNSS), such as GPS, GLONASS, and Galileo are, in some instances, capable of providing this level of accuracy. Real-Time Kinematic (RTK) techniques can generate solutions accurate to a few centimeters in a given locale. Precise Point Positioning (PPP) techniques promise to deliver RTK-level performance on a global scale. Even though low-cost, RTK-capable GNSS receivers are available today, antennas are a key component affecting quality of the positioning solution. Unless coupled with a high-quality (thus, more expensive) antenna, a low-cost receiver may not provide the centimeter-level accuracy needed for a safety-critical transportation application (e.g., autonomous vehicle, driver assist systems, etc.). Stability of the antenna phase-center is dependent on the antenna quality and can potentially move on the order of tens of mm if not centimeters. The purpose of the work reported here was to characterize the nature of this motion as a function of antenna quality. Anechoic chamber tests were performed using one high-cost and another low-cost GNSS antenna. The selected antennas represented "book ends" on the cost spectrum. These experiments showed that phase-center motion on the low-cost antenna can be a factor of four times larger than on high-quality antennas. Since anechoic chamber tests are not practical for each antenna installation in transportation applications, methods for antenna-specific, in-situ, phase-center motion calibration (modelling) methods have been suggested. Preliminary results suggested efficacy of these in-situ methods.