Comparison of cylindrical mock-up path loss data to operational aircraft data. Determining path loss variations with distance and radius at VHF, L band and GPS/Satcom

Abstract

This paper compares aircraft ComNav systems path loss data taken from operational aircraft to data taken on an idealized aircraft mock up. This comparison was performed in order to increase the understanding of the path loss dependence on aircraft radius and the distance between the aircraft windows and the top and bottom mounted ComNav systems antennas. Ten operational aircraft GPS data sets were selected to compare to mockup data having the same radius and distance parameters. Likewise 24 L-band and 25 VHF cases were compared. The comparison showed general correspondence of path loss with distance between the mockup and aircraft data. However, the aircraft path loss was larger. The best correspondence occurred at GPS frequency where the mockup had about 6 dB path loss and the two curves tracked each other closely. The 6 dB separation was also seen in the L-band top antenna comparison but the two data sets corresponded less precisely. The L-band bottom antenna and both top and bottom VHF comparison showed wide variations up to 31 dB. The correspondence was varied in detail. Some reasons were found that can be used to improve the fit by correcting the loss and gain factors based on improved aircraft information and data. The major finding, that of variation in path loss with distance and radius is irregular and remains unexplained. This has led to a series of recommendations for the development of mathematical models. These models may explain the phenomena and lead to an improved understanding of path loss dependency.