Patent GB-933782-A (GB)
Title: Improvements relating to radar systems
Inventor: BATTY NEVILLE GEORGE
IPC: G01S13/72
Filed: 1960-07-05
Abstract: 933,782. Pulse radar. A. C. COSSOR Ltd. July 4, 1961 [July 5, 1960], No. 23543/60. Class 40 (7). In a directional pulse radar scanning in a single plane in which the echo from a moving target is displayed on a main C.R.T. display and also by intensity modulation on an auxiliary C.R.T. having a rectangular range-angle raster corresponding to an annular segment in said plane, the scale of the auxiliary display being greater than that of the main display, a marker is controlled manually to follow the movement of the displayed echo and the instants of initiation of the range and angle timebases of the auxiliary display raster are automatically controlled by a digital computer coupled to the marker and adapted to compute the predicted position of the target during the next aerial sweep from the positions of the marker during a plurality of preceding aerial sweeps so that during the next aerial sweep the predicted position of the echo lies within said display raster. Alternatively the auxiliary C.R.T. display may be replaced by a storage C.R.T. and associated display C.R.T., the writing raster of the storage tube being then controlled by the computer. As described, the invention is applied to an azimuth-scanning surveillance radar comprising a main P.P.I. display and a plurality of type B auxiliary displays each separately tracking a corresponding target but alternatively it may be applied to an elevation-scanning system comprising a main range-elevation polar-co-ordinate display and an auxiliary range-elevation rectangular co-ordinate display (i.e. type E). If the auxiliary raster is controlled continuously by the computer so that the centre of the raster represents the predicted target position, the target echo should remain in the centre of the raster but if the echo appears off-centre the operator moves the marker to cover the echo thereby applying a correction signal to the computer; alternatively the auxiliary raster may be changed only when the echo approaches the edges of the raster. The auxiliary rasters may be set initially by corresponding markers on the main P.P.I. display. The plurality of auxiliary type-B display tubes may be replaced by a plurality of corresponding storage tubes, the outputs from the storage tubes being applied selectively to a single display tube which may have (1) short persistence or (2) storage properties, the radar information from the storage tube being written with high beam current giving long persistence and the marker being written with a lower beam current giving short persistence. In the Figure the circuits individual to one of the plurality of auxiliary type-B displays are shown in the dot-dash enclosure E, the other components shownbeing common to all the auxiliarydisplays. The predicted ranges X and bearings # of all the targets to be displayed are computed in the digital computer 10 and stored in binary form in respective stores 14. The transmitter TX pulse triggers a bistable circuit 19 to open a gate 18 which applies range clock pulses from an oscillator 20 to a range counter 17 to which the predicted range X is applied through a gate 16 also opened by the TX pulse. When the number of clock pulses counted corresponds to a distance X -x/2, where x is the distance range covered by the type B display, the counter 17 triggers (1) the range timebase generator 21 which may operate by integration of the range clock pulses, and (2) a monostable circuit 22 producing a range gate pulse. Bearing pulses of recurrence frequency proportional to the rate of rotation of the aerial are produced by a digitizer 26 and applied to a bearing counter 25 to which the predicted bearing # is applied through a gate 24 when the aerial is directed in a reference direction, e.g. north, and when the number of pulses counted corresponds to a bearing # - #/2, where # is the angular range covered by the type-B display, the counter 25 triggers a bistable circuit 27 to initiate a bearing gate pulse which opens a gate 28 to apply pulses from the digitizer 26 to an integrator 29 producing a stepped bearing timebase which is terminated by a trigger 30 resetting the bi-stable circuit 27 when the amplitude of the bearing timebase corresponds to 0. The stepped timebase may be smoothed; alternatively any step occurring during a range time base period may be prevented by delaying any bearing pulse occurring during a range timebase period. The radar echoes are applied to the type-B display through a coincidence gate controlled by the range and bearing gate pulses. The computer may also comprise means for automatically controlling the bearing timebase in accordance with the target range so that the indicated bearing of a displayed echo is equal to the bearing of the target at the time at which the echo started to return from the target.