Development and Flight Testing of a Low Cost VHF Datalink Antenna for the Ground-Based Regional Augmentation System

William S. Ely

Abstract:	Since 1997, Airservices Australia has been developing a Ground-based Regional Augmentation System (GRAS) utilising a Very High Frequency (VHF) data link as a low cost option to providing wide area augmentation services similar to Satellite Based Augmentation Systems such as the American developed Wide Area Augmentation System (WAAS). In 2000, Airservices Australia, in conjunction with the Global Navigation Satellite Systems Panel (GNSSP) of the International Civil Aviation Organisation (ICAO), commenced work on Standards and Recommended Practices (SARPs) which describe the technical nature of GRAS. These SARPs have adopted the same data link standard for GRAS as is used for Ground Based Augmentation Systems (GBAS) such as the Federal Aviation Administration's (FAA) Local Area Augmentation System (LAAS). To ensure compatibility with aircraft equipment, the same data link standards and antenna polarisation have been agreed for GBAS and GRAS. Until early 2003, the Australian GRAS test bed had utilised a low cost vertically polarised antenna for flight testing. Until this time, the lack of a cost effective, commercially available horizontally polarised antenna, and the high cost of elliptically polarised antennas, had compromised one of the basic objectives for GRAS, low cost. Antennas varying in price from US$2K to US$10K were identified, but all were considered excessive for the low cost GRAS solution. Airservices Australia staff were able to identify and modify a simple horizontally polarised antenna design, which has been successfully constructed and shown to provide data link coverage capable of supporting GRAS operations to Approach with Vertical Guidance level one (APV-I), and potentially level two (APV-II). These prototype antennas have been produced for less than US$100. This paper covers the development and flight testing of the low cost antenna during enroute, terminal and APV operations.
Published in:	Proceedings of the 2004 National Technical Meeting of The Institute of Navigation January 26 - 28, 2004 The Catamaran Resort Hotel San Diego, CA
Pages:	409 - 419
Cite this article:	Ely, William S., "Development and Flight Testing of a Low Cost VHF Datalink Antenna for the Ground-Based Regional Augmentation System," Proceedings of the 2004 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2004, pp. 409-419.
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