Aircraft Antenna Calibration for the LAAS VHF Data Broadcast

Orville K. Nyhus, Trent A. Skidmore and Aaron A. Wilson

Abstract:	This paper provides a detailed look at an aircraft antenna calibration method for determining the performance of an installed aircraft antenna used in obtaining VHF data broadcast (VDB) information. The VDB is a critical element of the Local Area Augmentation System (LAAS) as well as the corresponding Ground Based Augmentation System (GBAS) developed by the International Civil Aviation Organization (ICAO). The VDB is used to transfer GPS (and GNSS) differential corrections, integrity, and final approach segment information from the LAAS (GBAS) ground facility to aircraft conducting approaches to the LAAS (GBAS) serviced airport. To aid in a successful LAAS installation, the VDB link budget must be closely adhered to. Subsequently, the antenna patterns of both the transmit antenna and the flight test aircraft antenna are required. Specifically, accurate knowledge of the signal path on the aircraft (including antenna, cables, connectors, and signal splitters) is necessary to insure an accurate evaluation of the field strength provided by the LAAS VDB transmitter. To determine the aircraft antenna pattern, the dipole comparison method (DCM) is used. The DCM first determines the coupling between two dipoles (horizontally and/or vertically polarized) that are located in an isolated area of the airfield where the aircraft is to be tested. A roving transmitter dipole serves as the signal source, while a stationary receiving dipole acts as the baseline. Next, the aircraft antenna under test is positioned where the stationary receiving dipole was located. Finally, measurements and computations are performed to determine the aircraft antenna gain relative to an isotropic antenna. This paper details all calculations as well as shows test results for several different aircraft measured using the DCM. Data is presented showing results for both horizontally and vertically polarized antennas, supporting elliptically polarized (EPOL) LAAS VDB antenna installations.
Published in:	Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001) June 11 - 13, 2001 Albuquerque, NM
Pages:	275 - 279
Cite this article:	Nyhus, Orville K., Skidmore, Trent A., Wilson, Aaron A., "Aircraft Antenna Calibration for the LAAS VHF Data Broadcast," Proceedings of the 57th Annual Meeting of The Institute of Navigation (2001), Albuquerque, NM, June 2001, pp. 275-279.
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