Patent GB-604671-A (GB)
Title: Improvements in or relating to radar systems
IPC: G01S13/64
Filed: 1945-03-07
Abstract: 604,671. Pulse circuits; radiolocation. ELLIOTT, W. S., BAILEY, A. E., and WEBLEY, R. S. March 7, 1945, No. 5725. [Classes 40 (vi) and 40 (vii)] [Also in Group XL (a)] Doppler beats in the output of a pulse radar system produced by moving objects are detected by storing the output signals in an electronic storage tube, sets of signals corresponding to single pulses being recorded as charge patterns along adjacent tracks on the target electrode of the tube, and the signals being reproduced by scanning perpendicularly to the tracks. Signals in the output of the radar receiver 3, which when produced by moving objects are caused to vary in amplitude at the Doppler frequency by beating in the receiver with signals from fixed objects or locally generated oscillations from a unit 2 as described in Specifications 596,650 or 596,657, are fed via switch 15 to the modulator 6 of the storage tube 4. The tube comprises a cathode 5, anode 7, wall anode 8 and means for producing an axial focusing magnetic field. Deflection in one direction is obtained by plates 11 situated between screens 13, 14 and in the transverse direction by a coil 12. The target 9 consists of a mica sheet backed by a signal plate and surrounded by a metallised border and decelerating ring 10 which are connected to the signal plate. During recording, a pulse recurrence frequency sweep from time-base 24 which is synchronized from the transmitter 1 is fed to the deflecting coil through switch 17, while a lower speed framing sweep from generator 23 is fed to the deflector plates through switch 16, and the signal plate and decelerating ring are connected via switch 18 to a source 22 of potential between the first cross-over point of the secondary emission characteristic of the target and the potential of the wall anode. The target is thus charged positively in proportion to the signals applied to the modulator electrode 6. The rotary switches 15-18 remain in the recording position for a time interval sufficient to permit a sufficient number of recurrences to be recorded to obtain several cycles of the lowest Doppler beat frequency required. When switches 15-18 pass to the reproducing condition the modulator electrode 6 is connected to earth and a heavy beam is produced, the signal plate which is also earthed through the resistance 28 being stabilized to cathode potential by the beam. A fast sweep from generator 19 is applied to the deflector plates 11 while a slow frame sweep is applied from generator 20 to the deflecting coil 12 to cause the high-speed reproducing scan to be moved transversely (i.e. in the direction of the recording range scans) by one spot diameter for each successive scan. During each highspeed scan all the recorded signals of the same range will be reproduced across the resistance 28 and any Doppler beat present in the recorded signals will have its frequency effectively increased in the reproduction by the higher speed of the reproducing scan. The signals are fed to a filter 21 which is arranged to pass frequencies in the range corresponding to the desired limits of velocity to be detected, and the output of the filter is amplified at 25 and caused to produce an indication on a display unit 26 such as a P.P.I., the range time-base of which is operated in synchronism with the slow speed reproducing scan. In an alternative arrangement, Fig. 2 (not shown), the storage tube comprises' separate recording and reproducing beams operating on opposite sides of a double-sided mosaic target. Recording and reproduction are carried out simultaneously on alternate halves of the mosaic, the tube being operated so that the mosaic assumes potentials approximating to the second cross-over point of the secondary emission characteristic. The output signals are obtained from a collecting electrode maintained at a potential above the second crossover point.