Distance measuring apparatus integrated in an aircraft landing system of the ILS type which utilizes the differential measuring technique wherein a deviation signal is alternately applied and suppressed to a network of lateral aerials of a glide station. The distance measuring apparatus measures the bearing angle of the approaching aircraft with respect to the glide station, and includes at the glide station a pair of lateral aerials associated with the low aerial of the glide station arranged for intermittently emitting side bands corresponding to the modulation of the glide signal at a low frequency which is sufficiently high with respect to the conventional ILS frequencies of 90 and 150 Hz, for example, 960 Hz. On board the aircraft, the distance measuring apparatus includes distance indicating devices connected to the low frequency output of a conventional ILS receiver for providing a distance indication in accordance with the variation in the degree of modulation of the 960 Hz signal received by the ILS receiver.
A guidance system for landing an aircraft is described which uses a source of signals identifiable with the aircraft and a ground station which is linked to the aircraft. Specifically, the ground station includes a receiver which is connected to one or more pairs of antennas having a fixed, overlapping, directional sensitive pattern symmetically located relative to the center of the landing path, a receiver and a processor for measuring the relative sensitivity of the signals received at the antennas and for using the relative signal intensity to determine the location of the aircraft relative to the center of the landing path.
