Characterization of the Antenna Group Delay Variation for a Multi-Frequency/ Multi-Constellation Antenna as a Function of Azimuth and Elevation Angles and its Effect on the Multi-Constellation GBAS
Anurag Raghuvanshi and Frank van Graas, Ohio University
The modernization of GPS is underway, and the control, space and user segments are being updated to enable new and expanded civil applications. The modernized GPS has a new civil signal at L5, in the spectrum band that is allocated to Aeronautical Radionavigation Service (ARNS), thus, unlike L2, it can be used for airborne aviation applications. A dual frequency Ground Based Augmentation System (GBAS), dual frequency Space Based Augmentation System (SBAS) and Advanced RAIM (ARAIM) have been proposed with the advent of new civil signals. Moreover, other satellite navigation systems such as Galileo, GLONASS, QZSS and Beidou are also updating or creating their constellations. Therefore, a Multi-Constellation GBAS is also being considered for future aviation applications.
The most recent update of the Minimum Operational Performance Standards (MOPS) for a single frequency airborne antenna  documents requirements for Antenna Group Delay Variations (AGDV) as a function of arrival angle. The AGDV is included in the airborne ranging standard deviation together with airborne multipath and noise. The impact of the AGDV on GBAS operations was shown in . The treatment of the AGDV for multi-frequency and multi-constellation applications needs to be addressed next. Also, with Small Unmanned Aircraft System (SUAS) applications on the rise, the additional constraint of small antenna systems needs to be included in the AGDV evaluation.
In this research, a combination of in-flight and ground-based characterization of AGDV for a multi-frequency/ multi-constellation antenna, a single frequency antenna and a small size multi-frequency/ multi-constellation antenna are proposed. The multipath and AGDV are difficult to separate using in-flight, so the in-flight characterization will be a combination of the multipath and the AGDV. The ground experiment is designed to separate multipath and AGDV, but suffers from a higher level of noise. The combination of the in-flight and ground data provide a complete characterization of the AGDV. The effect of the ADGV on the Divergence free and the Ionosphere free measurements will also be analyzed. Finally, the effect of AGDV on future multi-constellation Vertical Protection Level (VPL) calculations will be studied.
1. RTCA, Inc., Minimum Operational Performance Standards for Global Navigation Satellite System (GNSS) Airborne Active Antenna Equipment for the L1 Frequency Band, DO-301, 2006.
2. Harris, M., Miltner, M., Murphy, T., Raghuvanshi, A., van Graas, F., Bounding GPS L1 Antenna Group Delay Variation for GNSS Landing System Integrity, Proceedings of the 2017 International Technical Meeting of The Institute of Navigation, Monterey, California, January 2017, pp. 591-605.