GB604672A - Improvements in or relating to radar systems - Google Patents

Abstract

604,672. Pulse circuits; radiolocation. ELLIOTT, W. S., JOHNSON, C. A., and WEBLEY, R. S. March 7, 1945, No. 5726. [Classes 40 (vi) and 40 (vii)] [Also in Group XL (a)] In a pulse radar system, echo signals which are amplitude modulated at Doppler frequency due to movement of the object producing them, are detected by storing the signals as a charge pattern on the target of an electronic storage tube and comparing the stored signals with undelayed signals to produce a differential output. In the arrangement of Fig. 1, transmitter 16 and receiver 17 are associated with an oscillator 18 which provides the heterodyning oscillation, preferably at I.F., to produce the Doppler beat frequencies as described in Specifications 596,650 and 596,657, and are coupled to a common aerial system by unit 19. The video signals from unit 20 are fed to the modulator electrode 3 of the storage tube 1 comprising cathode 2, anodes 4, 5, 6, two pairs of deflector plates 7 mounted between screens 8 and 9 and decelerating rings 11, 12, 13 connected to points of decreasing positive potential. The target 10 may be a mosaic, but preferably comprises a mica sheet backed by a conducting signal plate. Time-base unit 21, synchronized by the transmitter 16 produces a spiral scan in an annular space on the target, the remaining surface of which is covered by a conductive coating to prevent the target surface not under the scanning beam accumulating a charge. During recording scans, the switching unit 29, synchronized to the transmitter pulse recurrence frequency, controls the tube power supply unit 15 so that the tube operates above the first cross-over point of the secondary emission characteristic of the target and the signals are recorded as a positive charge pattern. During alternate pulse recurrence periods the video signals from receiver 17 are fed via a switch unit 24 to a cancelling unit 25 and the tube operating potentials are arranged under control of switch unit 29, so that the target is stabilized to cathode potential by the reproducing scan. The reproduced signals from the signal plate are fed via amplifier 23 and switch unit 24 to the cancelling unit 25 where they are in opposite polarity and nominally of equal amplitude to the unstored signals direct from the receiver. The resultant output which corresponds to signals containing a Doppler beat is fed through the full wave rectifier 26, giving a positive output, to the cathode-ray tube display unit 27 such as a P.P.I., the time-base 28 of which is synchronized by the transmitter. In an alternative method of operating the tube in which recording and reproduction are effected by low velocity beams, the target is first stabilized to cathode potential which is set at about 50 volts positive to earth and signals are then stored as negative-going charges by reducing the cathode potential to zero and scanning with a low velocity modulated beam. Signals are reproduced in reverse by stabilizing the target to zero with an intense unmodulated beam and finally charging the target to above 50 volts by scanning with a medium velocity beam preparatory to stabilizing to +50 volts. In order to obtain the differential signals corresponding to Doppler beats during each transmitter recurrence period, two storage tubes may be employed, each storing the signals of every alternate recurrence period while the unstored signals are fed continuously to a cancelling unit which is also fed with the output of the two tubes alternately. Alternatively, a single tube with a double-sided mosaic target and two electron guns may be employed, Fig. 2 (not shown). Two double-sided targets composed of ruled sputtered metal coatings on glass, Fig. 3 (not shown), with a common signal plate are employed and the recording beam, which is modulated continuously with the received signals, scans each target to produce positive charge patterns while the reproducing beam is arranged to stabilize each target to cathode potential. The two scanning beams are operative on the two targets alternately, but out of phase, the switching from target to target being performed by deflector coils controlled by a switching unit synchronized with the transmitter. A voltage from the timebase is fed to blackout the flyback of each scan, which occurs when the beams are being deflected from one target to the other and are crossing the common signal plate. The comparison of the signals of successive recurrences is effected actually by the signal plate which provides only the differential output which after full-wave rectification may be fed to a suitable display unit. Specification 594,483 also is referred to.