Quality Analysis of GPS Signals Received on an Agusta Chopper: Influence of the Antenna Location

Alain Muls, Jean-Marie Sleewaegen and Carine Bruyninx

Abstract:	This paper describes the set-up and results of a static and kinematic test campaign carried out in order to evaluate the best location of a GPS antenna on an Agusta chopper of the Belgian Army. The chopper was initially equipped to have a GPS antenna installed on its tail. However, due to fissures in the vertical segment of the tail, an al- ternative antenna location on the nose of the chop- per was tested. This location presents two disadvan- tages. The first one is that the antenna is partially blocked by the cockpit and the second one is that the antenna is situated beneath the rotor having blades partially covered with a metallic protection layer.In order to address these problems two GPS Ash- tech Z-XII receivers were connected simultaneously to the two antennas on the chopper. The identical performances of both receivers were checked before- hand through a zero-baseline test. The investigations included a preliminary study, taking different chopper orientations into account, which demonstrated that for the antenna on the nose in average one satellite is lost due to the cockpit blocking. A static test examined the influence of the ro- tor blades on the GPS signal received at the nose antenna by operating the rotor of the chopper on an interrupted basis. The comparison of data avail- ability and quality at both the nose and tail anten- nas showed that the metallic shielding on the rotor blades did not prevent the GPS signals from arriving at. t he nose antenna. During a kinematic test the two Ashtech Z-XII receivers operated simultaneously during flight. A first flight path followed north-south and east-west directions in order to evaluate the influence of the cockpit blocking on the nose antenna. A second tactical flight evaluated the quality of the GPS signals and compared the code and phase solu- tions obtained from the nose and tail antennas dur- ing real combat situations. Results demonstrated that the nose antenna was less performant under high dynamic situations and tracked in general less satellites than the tail an- tenna. Although the phase data observed at the tail antenna were more noisy than the phase data for the nose antenna, the conclusion is that the top of the tail should be chosen as the future location for the GPS antenna.
Published in:	Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996) September 17 - 20, 1996 Kansas City, MO
Pages:	1865 - 1872
Cite this article:	Muls, Alain, Sleewaegen, Jean-Marie, Bruyninx, Carine, "Quality Analysis of GPS Signals Received on an Agusta Chopper: Influence of the Antenna Location," Proceedings of the 9th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1996), Kansas City, MO, September 1996, pp. 1865-1872.
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