Unmanned Aerial System Inspection of Instrument Landing System Radio Signals

Abstract

This study investigates the use of a unmanned aerial system (UAS) for instrument landing system (ILS) signal inspection. A model of expected equivalent isotropic receiver power was built. A 10-meter radio tower was constructed to be used as the test ILS source. Then, empirical channel power measurements were made with antennas and a spectrum analyzer mounted on the prototype vehicle in a simulated ILS environment. Channel power measurements were made by the prototype UAS at various altitudes 19.4 km (12.1 miles) from the base station. Comparisons are made between model and empirical data. The model reasonably predicted signal level and lobing patterns for two of the three ILS component signals. A method of channel power correction based on aircraft orientation was attempted but was ineffective due to UAS pitch data suspected to be inaccurate. This study finds that signal level inspection of ILS can be done by UAS with a reasonable level of repeatability and that measurement accuracies of ±1.0 dB and ±1.5 dB were achievable for localizer and glideslope respectively. Larger changes in signal levels can be observed on a day-to-day basis. This is likely due to changing atmospheric conditions and tear-down and reassembly of the base station.