Patent GB-1435174-A (GB)
Title: Ranging system for the measurement by radio transmission of a distance between two stations
IPC: G01S13/32
Filed: 1973-08-01
Abstract: 1435174 Radar ELECTRONIQUE MARCEL DASSAULT 1 Aug 1973 [2 Aug 1972] 36543/73 Heading H4D In a ranging system, a first signal is transmitted from a first station to a second station which thereupon transmits a second signal to the first station. Each station includes a pseudonoise (PN) code generator for phase modulating the signals and means for correlating the PN generated code with the PN modulated received signal in order to derive at the first station the distance between the two stations by generating the correlations of two successive PN codes spaced apart by one period of the PN code bit sequence and by controlling a delay-lock tracking loop by the difference between the two correlations. A psuedo-noise (PN) code utilizes maximal length pseudo-random sequences as described, for example, on pages 20-18 to -20 of "Radar Handbook" by M. I. Skolnik (1970). The invention provides at least one of the said stations commutation switch means having two inputs connected to the PN code generator, and a single output connected to the correlating means, and a commutation switch signal generator operatively connected to the commutation switch means, whereby the PN modulated received signals are successively and alternately correlated with the successive PN codes locally generated at the station. As described, a first station, which may be carried by a satellite, comprises an ultra-stable oscillator 10, Fig. 1, directly connected to one input each of distance measuring circuitry 83, and Doppler measuring circuitry 84. It is also connected through a frequency divider 11a to a reference code generator 13, and through a frequency multiplier 11 to a modulator 12. The generator 13 supplies pseudo-noise repetitive sequences of (2<SP>n</SP>-1) terms each of + 1 and - 1 signals to the modulator 12, and to another input of the distance measuring circuitry 83. The output side of the modulator 12 is connected to a transmitter 15, which radiates signals from an aerial 16. A second station, which may be carried by a radio beacon, comprises a receiving aerial 21, Fig. 2, from which the signals received from the first station are fed to a first input of a high frequency correlation member 23, which has a second input from a modulator 27 and the output of which is connected to a phase-lock receiver 25. The modulating input to the modulator 27 is derived by alternate connection to the (n)th. and [n-1)th. ranks 29, 31 of pseudo-noise code generator 32 by means of a switch 33 under the control of a swiching signal generator 38. The modulator 27 also receives input from an oscillator 52 through a frequency multiplier. A second switch 41 controlled by the switching signal generator 38 connects the output of a coherent demodulator or detector 43, which follows the receiver 25, alternately to the + and - inputs of an active filter 47, whose output controls the frequency of a clock 48, which steps the code generator 32. A modulator 51 is fed by the oscillator 52 through a frequency multiplier 53, and by the code generator 32, and provides output to a transmitter 55, which radiates signals from an aerial 56. These signals are received at the first station on an aerial 61, Fig. 1, and are applied as one input to an H.F. correlation member 63, The second input of the member 63 is the modulated output from the modulator 65, modulating input for which is obtained from a switch 70, controlled by a switching signal generator 92, and alternately connecting the outputs from the (n)th. and (n-1)th. ranks 67, 68 of an n-rank pseudo-noise code generator 69 to said modulator. A second switch 76 controlled by the generator 92 connects the output of a coherent demodulator or detector 74, which follows the member 63, alternately to the + and - inputs of an active filter 79, whose output controls the frequency of a clock 82, which steps the code generator 69. Said code generator 69 provides a third input to the distance measuring circuitry 83.