The working principle of DME rangefinder used in civil aviation aircraft is that the transponder on the aircraft sends out an inquiry signal, and the DME receiver receives the response signal from the DME station on the ground and measures the distance according to the time difference. DME rangefinder is a short-range navigation equipment specified by ICAO, which provides the inclined distance of the aircraft relative to the DME platform on the ground. Usually, there is a VOR navigation station near DME station, which together form a range-azimuth polar coordinate system to directly locate the aircraft.