Effects of selected roofing materials on air navigation signal propagation

Abstract

The environment around radio navigation aids systems (navaids) includes buildings whose roofing materials interfere with signal propagation. This interference may cause partial loss of intelligence in communication between navaids and flying aircrafts. Buildings around airports have been restricted partly because they pose threats to flight navigation. This restriction as captured in the Laws of Kenya has not been supported by sufficient data. Previous studies have shown that about half of air accidents occur during landing. However, no data has been availed to determine the contribution of navaids to these accidents. The purpose of this research was to study effects of roofing materials on air navigation signal propagation. The method involved use of a 9.4GHz transmitter, a receiver and a computer to measure signal level transmitted through roofing materials at various angles of incidence. The study considered effects of decra (aluminum-zinc stone-chip coated steel), iron, steel, aluminum, plastic and clay materials on navaids signal strength, transmission distance and wave polarization. Decra gave the highest attenuation whereby 98% of the signal propagated was lost, out of which 53% was due to reflection. Decra also exhibited the lowest desired-to-undesired signal ratio of -27dB which was far below International Civil Aviation Organization recommended value of 20dB. Only iron and clay reported significant figures above the recommended value. Variation of signal strength with transmission distance depended on type of roofing material but generally a negative correlation was registered. Roofing materials had no significant effect on wave polarization. The study challenged flight navigation authorities and construction industry to isolate and develop a compromise roofing material that will have little effect on navaids signal propagation.