GB557870A - Improvements in and relating to radio communication systems for the navigation of aircraft - Google Patents

Abstract

557,870. Automatic control systems. HUGHES & SON, Ltd., H., SPROULE, D. O., and HUGHES, A. J. June 5, 1941, No. 7135. [Class 38 (iv)] [Also in Group XL] A navigation system for landing aircraft comprises means on the ground for formulating a radiation pattern the intensity of which continuously and periodically fluctuates about the desired flight path as an axis, and means on the aircraft by which its position relatively to the path can be determined from the amplitude and phase of the received signal and indicated as horizontal and vertical departures from the flight path. A beam AB, Fig. 3, inclined to the flight path AC, is continuously stated about that path as an axis, and an additional signal is transmitted in definite time relationship with the relation of the beam, in order to provide a reference phase with which the phase of the received signal may be compared. This additional signal may be a frequency modulation of the same beam or a short pulse, omitted from a second transmitter when the beam is in its uppermost position, controlling a continuous time base. If the aircraft is on the path AC, no change in intensity due to each rotation of the beam will be detected, but if the aircraft flies along some other part the received signal will be modulated in amplitude to an extent determined by its distance from the axis AC, and the phase of this signal will be determined by the angular position of the aircraft with reference to the axis. The combined amplitude modulated and frequency modulated signal is received by a standard superhet receiver 51, 52, 53, the frequency modulated component passing through a limiter 54, discriminator 56, and amplifier 57 to provide a reference phase for the centre zero dynamometer instruments 58, 59. The amplitude modulated component, the amplitude and phase of which is determined by the position of the aircraft, passes through detector 55 and amplifier 61 to the other coils of the instruments 58, 59. By the use of a 90 degrees phase shifter 60, and a suitable choice of the relative phase shifts of the two branches of the circuit, the instruments 58, 59 can be arranged to indicate respectively deviations from the desired path to right or left, and up or down, and the extent of such deviations. The transmitter may comprise a reflector and antenna mounted obliquely on the spindle of a constant speed motor which also carries a rotary condenser controlling the frequency modulation, Fig. 6 (not shown). For automatic steering, the instruments 58, 59 may be replaced by two phase motors controlling the steering and elevator mechanism of the aircraft.