Group Delay Characterization of Multipath Limiting Ground Station Antennas for Enhanced GBAS Performance

Kurzfassung

The Ground Based Augmentation System (GBAS) provides precision approach guidance for aircraft by enhancing the integrity, accuracy, continuity, and availability of Global Navigation Satellite Systems (GNSS) signals. Current efforts aim to extend the operation of GBAS installations from within a single frequency band (L1) of GPS to a dual-frequency and multi-constellation (DFMC) operation. A key component of GBAS is multipath-limiting antennas (MLAs), which mitigate signal reflections to ensure reliable corrections and integrity parameters. However, such antennas are traditionally optimized and characterized for operation in the GPS L1 band. Therefore, little knowledge about their performance in other GNSS frequency bands is available which presents a significant hurdle in estimating their performance for future GBAS systems. This study provides a comprehensive evaluation of two GBAS MLAs (Bae Systems ARL-1900) by analyzing their realized gain, phase center variations (PCV), and group delay variations (GDV) across GPS L1/L5 and Galileo E1/E5a frequency bands using a compact antenna test range (CATR). Results indicate that the antennas perform optimally in the L1/E1 band but exhibit significant GDV oscillations in the L5/E5a band, potentially affecting DFMC GBAS performance. The findings suggest that intrinsic antenna biases must be accounted for in future GBAS error models to ensure robust navigation solutions.