Patent GB-1082406-A (GB)
Title: Double sideband-suppressed carrier doppler distance measuring system
Inventor: CARTWRIGHT VICTOR F
IPC: G01S13/50
Filed: 1964-08-28
Abstract: 1,082,406. Radio-navigation. BABCOCKS ELECTRONICS CORPORATION. Aug. 28, 1964, No. 35418/64. Heading H4D. A Doppler radar system for measuring the miss distance between a target and a missile comprises, on the target, means for transmitting two signals of fixed small frequency difference towards the missile, means for detecting the reflections thereof and for detecting the resultant Doppler signals, means for determining the phase difference between the two Doppler signals, and telemetry means for transmitting said phase difference information to a monitoring station for display thereat as a recording of the variation of the distance between the target and missile. The transmitting means comprises a U.H.F. carrier source 10, Fig. 1, of frequency fc, and a sideband oscillator 12 of frequency fs, both feeding a balanced modulator 14 to produce two transmission signals, of frequencies f1= fc+fs and/2=/c -fs, which are fed to antenna 16. A local oscillator system comprises a balanced modulator 18, fed with the output of source 10 and the output of an offset oscillator 20 at a frequency fo in the IF range, to produce two sideband signals, and a filter 22 which selects the lower sideband at frequency fLO= fc - fo, and feeds it to a signal mixer 24. The reflected signals, containing Doppler signals, at frequencies f1+fd1 and f2 +fd2, are fed from antenna 16 to the signal mixer 24 via directional coupler 26, to produce, by combination with the local oscillator signal, two corresponding IF signals which are separated and amplified in IF amplifiers 28 and 30. The local oscillator signal is mixed, in injection mixer 32 with the two transmission signals, to produce two reference IF signals of frequencies F1 -fLO and f2 -fLo, which signals are separated by filters 34 and 36, respectively. The IF signal output of amplifier 28 at a frequency of f1 - f Lo +fd1 is fed to a balanced detector 38, together with the reference IF signal of frequency f1-fLo,to produce the Doppler signal fd1. The other Doppler signal fd2 is similarly produced by balanced detector 40. The two Doppler signals are amplified and limited in means 42 and 44, to produce corresponding square waves, which are used to control the output of a bi-stable multivibrator 46, the leading edge of each fd1 square wave triggering the multivibrator into an " on " state, and the leading edge of the next fd2 square wave triggering the multivibrator back into the " off " state. Since fdl and fd2 are different, the output of the multivibrator will consist of a succession of pulses of increasing duration, Fig. 2 (not shown), the duration of any pulse representing the difference in phase of the two Doppler signals and thus the distance between the target and missile. The integral of the output will likewise represent said distance. The output of the multivibrator is transmitted to a monitoring station, Fig. 3 (not shown) where it is integrated and the resulting distance indication displayed on a pen recorder. Due to inaccurracies near the region of least distance, fine range markings are produced on the record from the received multivibrator output. In the described embodiment, the maximum range is 200 ft., and each fine range marking represents an incremental range of 1 ft. On the target, the output of the multivibrator is also used to provide a distance indication whereby a camera is controlled to take a photograph of the missile when closest to the target.