Diffraction Path Losses Measurements for Low Altitude UAVs

The maximum altitude of flight for medium and small size UAVs is limited to a maximum height of 120m. Therefore these vehicles frequently fly close to the rooftop of buildings in urban or semi-urban environments, while the control station is 1-2km away. On this conditions, the low flying height moderately affects the propagation by introducing additional losses by diffraction. In this paper we present a detailed analysis of the additional diffraction losses for UAV fliying on semi-urban environment. Diffraction losses are based on the ITU for the normal flight conditions of UAVs. Measurements have been made with a medium-sized UAV in a suburban environment at two frequencies: 440Mhz and 1000Mhz, under normal flight conditions with control station on the top of a building. The results allow to analyze the accuracy of the diffraction model and the additional losses when the UAV flies near the roofs of the buildings.