Suppressed-Image ILS Glide Slope Antenna

Alfred Lopez

Abstract:	The Instrument Landing System, ILS, was to be replaced by the Microwave Landing System, MLS, in the 90’s. This is not the current plan. The FAA has canceled its MLS production contract and is moving rapidly toward implementing precision and Cat I approach and landing procedures using the Differential Global Positioning System, DGPS. The future role for MLS in the international community is not clear. It is envisioned that a Global Navigation Satellite System, GNSS, will ultimately provide approach and landing capability internationally. There are questions of when Cat II and Cat III service will be available and on the viability of Cat IIIC (autoland) using the GNSS. What is clear is that ILS will have a substantially extended life span. Therefore, improved ILS equipment should be of interest to the navigation community. The current FAA inventory of ILS glide slope antennas include image types (null-reference, capture effect, sideband-reference) and the non-image end fire antenna. All of these antennas are difficult to monitor and are sensitive to snow. The image-type antennas require large reflecting ground surfaces and can not be installed at some difficult sites. The end-fire antenna solves some of the difficult site problems but it has snow and ice problems. This paper describes a suppressed-image glide slope antenna that overcomes the existing problems with current glide slope antennas. It utilizes components in the current FAA inventory. This antenna is designed to suppress radiation in the direction of the ground image. It is based on a spatial-angle filter concept that is analogous to a stop-band frequency filter. A key requirement for this spatial-angle filter is that it have at least a second-order null in the direction of the ground image. The significant features of this antenna are: Not affected by snow Critical zone in front of antenna greatly reduced Low cost alternative for difficult sites Operates with standard glide slope transmitters Uses corner reflector antennas in FAA inventory Uses standard glide slope tower Aperture is reduced - a far field monitor is practical
Published in:	Proceedings of the 51st Annual Meeting of The Institute of Navigation (1995) June 5 - 7, 1995 Antlers Doubletree Hotel Colorado Springs, CO
Pages:	253 - 259
Cite this article:	Lopez, Alfred, "Suppressed-Image ILS Glide Slope Antenna," Proceedings of the 51st Annual Meeting of The Institute of Navigation (1995), Colorado Springs, CO, June 1995, pp. 253-259.
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