Improvements in and relating to continuous wave radar systems

Abstract

Abstract 724,555. Radar. BRITISH THOMSONHOUSTON CO., Ltd. Feb. 19, 1953 [Feb. 19, 1952], No. 4678/53. Class 40 (7). A radar system radiates continuously a random signal (e.g. noise-spectrum signal) within a definite frequency band and compares the echo signals received with variably delayed transmitted signals to determine the delay required for delayed signals and echo signals to correspond; the delay being representative of target range. In one embodiment the random signal transmitter 1 is coupled to aerial A1 and also through attenuator 2 to mixer 3 wherein the signal is transposed to a lower frequency by being mixed with the output of local oscillator 4. Echo signals received on aerial A2 are similarly transposed by mixer 5 also fed by oscillator 4. The reference signals from mixer 3 are fed to mixer 6 where they are mixed with a signal from oscillator 11 of a frequency equal to the average frequency of the output signal from unit 3 so that a " video " signals output is produced. A similar output from the echo signal is produced in mixer 10 fed from units 5 and 11. The signal from mixer 6 is fed through variable delay circuit 7 to multiplier circuit 8 where the delayed video reference signal and the video echo signal from mixer 10 are multiplied together. The output of circuit 8 is fed to integrator 12 capable of integrating the product signal point.by point over a period corresponding to several cycles of the periodically varying delay introduced at unit 7 and the resultant signal fed to produce a deflection of cathode-ray tube indicator 13 in a direction at right angles to the scan direction. The scan itself is performed under the control of scan generator 14 which controls the periodic and preferably linear variation of the delay time introduced by unit 7. Owing to the random nature of the signal the output of multiplier 8 when integrated by unit 12 is only of significant amplitude when the echo time and the delay introduced by delay unit 7 are equal and the same signals are applied to the input. When this occurs a deflection is produced at a point along the trace corresponding to the instantaneous delay at 7 and the echo time. From the position of the deflection the range of the object causing the deflection can be determined. A suitable circuit for multiplier 8 is described with reference to Fig. 3 (not shown).

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