Effects of roofing materials on propagation of air navigation signal have generally been determined. Firstly the research revealed that roofing materials have little effect on navaids signal strength particularly in the transmission path. However the effects were very significant in the reflective path. Secondly it was found that some materials interacted with navaids signal and caused decrease in received signal strength (RSS) while others caused increase in RSS over similar transmission distance but these effects were not significant. Lastly the research established that roofing materials have no significant effect on wave polarization.
This study found that decra roofing material offered highest attenuation and reflection to the navaids signals. It showed that 90% of the radio signal that interacted with decra was lost, out of which 60% was due to reflection. This characteristic had little effect on the ICAO recommended specification (ICAO, 2012) which requires that minimum signal strength in the designated operational coverage should be minus 28dBmV/M. The mean field strength recorded for decra interaction was 57dBmV/M which is well above the recommended minimum. Therefore the selected roofing materials had no significant effect on navaids signal strength in the transmission path. However decra and steel provided the highest reflected mean signal strength at 73dBm/V whereas iron showed the lowest reflected signal strength at 61dBm/V. For decra, this translated to the lowest desired-to-undesired (D/U) signal ratio of minus 16dB which is far below the recommended value of 20dB. It was therefore deduced that roofing materials have significant effect on navaids signal strength particularly in the reflective path.
The highest and lowest mean attenuation occurred at angles of incidence of 90 and 135 degrees respectively. It was shown that the lowest received signal strength occurred on decra material at an angle of 135 degrees while the highest occurred on iron at 90 degrees. The attenuation ratio decreased as the angle of incidence was varied from 0 degrees to 90 degree. The highest and lowest mean reflection occurred at angles of incidence of 90 and 135 degrees respectively. It was shown that the lowest reflected signal strength occurred on clay material at an angle of 135 degrees while the highest occurred on steel at 90 degrees. Generally the reflected received signal ratio increased as angle of incidence varied from 0 degrees to 90 degrees across all materials. It was therefore deduced that angle of incidence has significant effect on navaids signal strength in both transmission and reflective paths.
The relationship between roofing materials and transmission distance was determined by the correlation factor r. The correlation factors of plastic (r = -0.996), clay (r = -0.911) and steel (r = -0.801) were determined and found to be negative. Thus radio navigation signal via plastic, clay and steel roofing materials decreased with distance. However, the radio navigation signal via decra (r = +0.723), aluminum (r = +0.988) and iron (r = +0.695) increased with distance. The strength of a radio signal that interacts with plastic and clay structures decreases rapidly with distance as shown in this study. It therefore means that radio navigation systems positioned in such environments require extra power to attain a certain range. Further the study found that the signal via aluminum structures increase rapidly with distance in the near field. This rapid increase in signal strength with respect to distance is likely to create errors in systems like (ILS) whose intelligence is contained in the signal strength. However all navaids are positioned in far field regions and therefore such characteristics of aluminum will be less significant.
The path loss exponent factor for all the six test materials was found to be well above the free space path loss exponent of factor 2. Decra and steel provided the highest value at 3.7 whereas clay was lowest at 3.0. This meant that the rate at which the signal propagated via these structures was significantly slower than propagation in free space.
Effects of roofing materials on transmission distance varied depending on the selected material. It also depended on whether the operation was in the near-field or far-field regions. The general trend was that signal strength decreased slowly with increase in transmission distance thus providing a low negative correlation factor (r = -0.280).
It has been observed that the interaction of roofing materials with navaids signals has no significant effect on recommended minimum signal strength in the transmission path except in the reflective path. For distances that were considered in these experiments, these materials had no significant effect on transmission distance since the received signal was within the recommended signal strength.
The effects of roofing materials on wave polarization showed that Iron and clay provided higher propagation level than the rest whereas plastic showed the highest propagation in vertical and circular polarization modes. It was also found that horizontal, vertical and circular polarization modes have different maximum propagation angles positioned at 90, 60 and 150 degrees respectively.
Despite the differences a statistical analysis revealed that roofing materials have little effect on wave polarization. It can be concluded that roofing materials have no significant effect on radiation patterns. Therefore a radiation pattern which is a prime variable in the operation of navaids systems cannot be altered by the presence of roofing materials in the propagation path.
Further results showed that there was a strong negative correlation (r = -0.9944) between attenuated and reflected signals at various angles assuming constant effect of roofing material. This implies that angles that provide high attenuation exhibit low reflections and vise versa when material-type is constant. A correlation factor of 0.9611 showed that there was a strong positive correlation between attenuated and reflected signals across roofing materials assuming a constant angle of incidence. It implies that materials that provide high attenuation exhibit high reflections at constant angle,
It is recommended that building and avionics industries develop a compromise roofing material that has little effect on flight navigation. Similarly the angle at which roofs are inclined should be designed to minimize reflections as per the data provided in this research.
Relationship between path loss exponent of a roofing material and transmission distance need to be studied further so as to explain why there is a mix of positive and negative correlation.
Further studies should be directed in conducting experiments in open fields and factoring in sources of variability arising from the environment so as to actualize the scenario of flight navigation.
It is also recommended that similar studies should be conducted on roofing materials other than those considered in this research.