GB557903A - Improvements in and relating to radio communication systems for the navigation of aircraft - Google Patents

Abstract

557,903. Automatic control systems. HUGHES & SON, Ltd., H., SPROULE, D. O., and HUGHES, A. J. June 5, 1941, No. 17407/42. Divided out of 557,870. [Class 38 (iv)] [Also in Group XL] A radio navigation system for aircraft comprises means on the ground for radiating in succession four spaced beams which overlap to define a flight path, and means on the aircraft whereby its position may be found by determining the intensity and phase of the received signals. Two or more of the four beams A, B, C, D, radiated in succession, are given different modulation frequencies, beams A, C defining the flight path in a vertical plane (left right) and beams B, D in a horizontal plane (up down). When the aircraft is following the defined path, all four beams are received in equal strength, but when it deviates from the vertical plane, say, the signals from beams A, C are unequal in amplitude, and are caused to produce an alternating current whose amplitude depends upon the difference in amplitude of the received signals and whose phase depends upon which is greater, Figs. 4 to 14 (not shown). This alternating current is measured with the aid of a reference phase derived from the beams B, D, the signals from which are passed through limiters (so as to produce pulses of equal intensity even if the signals received from B and D are unequal) and caused to produce an alternating current of fixed phase and amplitude. Similarly, if the aircraft deviates from the horizontal plane, the signals from beams B, D are unequal in amplitude and produce an altenating current of phase and amplitude determined by the direction and amount of deviation this current being measured with the aid of a reference current of fixed phase derived from the beams A.C. Fig. 2 shows the apparatus on the ground for producing the four spaced beams, comprising what may be regarded as a localizing transmitter A1 and a glide path transmitter A2, each having two radiating positions. Transmitter A1 is at one end of the approach path R and is oscillated to radiate in the directions B1, D1 on each side of the path R, a switch 27 connecting up modulating frequencies N1, N3 in the two extreme positions, so that the beams are modulated respectively at these two frequencies, which may be 1000 and 3000. The glide path transmitter A2 is at one side of the approach path, and oscillates in a vertical plane, radiating in two directions beams modulated at 2000 and 4000. The two transmitters are synchronized so that the four signals of frequencies 1000, 2000, 3000, 4000 are received in regular sequence being used as described above. In a modified system, only two modulation frequencies are used. Figs. 18 to 26 (not shown). The signals may be led to centre zero dynamometer indicators, or may control two phase motors for automatic steering of the aircraft.