Selection of a Localizer Array for Use When Large Buildings are Present

Richard H. McFarland and David Quinet

Abstract:	The contemporary instrument landing system (ILS) has served the civil aviation community extremely well for over 50 years. Work performed by industry and the government in the late 1930’s culminated in four systems being commissioned for public use at Indianapolis[ 11. The localizer is that component of the ILS which provides the lateral guidance for an airplane flying the approach path. It operates between 108 and 112 MHz in the VHF band. Presently there are over 1,000 commissioned localizers serving the public[2]. The localizer signal, as is the case with most navigation and communication radio signals, can be corrupted by noise. One of the common sources of noise is atmospheric such as that generated by lightning discharges. This was a major reason why navigation radio carrier signals were moved from the low frequency band (200-400 KHz) to VHF. With shorter wavelengths (2.7 meters) assigned to the localizer the issue of man-made reflecting objects then became an issue. Power lines and hangar surfaces, objects often found on or near an airdrome, become concerns. As those familiar with the EM theory know, the effectiveness of the reflector is related to its dimensions in terms of wavelength. When the dimensions of the reflector are large with respect to wavelength, optical type considerations can be applied. These reflectors, sometimes called scatterers are commonly referred to as multipath sources. Many airport boundaries are constrained and the only real estate available for construction of major buildings is near the runway. Desired additional real estate is frequently not available either due to cost of acquiring, natural boundaries such as rivers, roadways, or constraints imposed by environmental concerns. Economic factors become strong drivers because the buildings are needed to meet commercial, revenue- producing needs and in some cases there is the additional motive of job creation. There is a tendency, too, by airport planners to regard the constraints due to the physical obstructions as being the dominant and only concern. Few planners seem to take into account the vulnerability of the local&r course to multipath. This is typically left to the engineer to fii after the fact. The ILS siting engineer must make an appropriate choice as to what specific array meets the needs of the airport runway considering its environment. The tradeoffs are basically those of costs versus capability. One purpose of this paper is to aid in providing an engineeringbasis for making the choice of the localizer array considering tradeoffs.
Published in:	Proceedings of the 1994 National Technical Meeting of The Institute of Navigation January 24 - 26, 1994 Catamaran Resort Hotel San Diego, CA
Pages:	219 - 229
Cite this article:	McFarland, Richard H., Quinet, David, "Selection of a Localizer Array for Use When Large Buildings are Present," Proceedings of the 1994 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1994, pp. 219-229.
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