Patent GB-1305181-A (GB)
IPC: G01S13/72
Filed: 1968-04-24
Abstract: 1305181 Track-while scan radar HUGHES AIRCRAFT CO 24 April 1968 19513/68 Heading H4D A track-while-scan radar system includes an automatic detector which converts signals from each target into target position information (a plot) such as range (R) and azimuth (#). A tracking computer has a main memory and a plot correlator which associates each received plot with updated target positions developed by, and stored in the main memory of, the computer. The updated positions are the predicted positions at the particular point in time. If the plot correlates with the updated position of one of the targets, it is used by the computer to generate a new updated position which is stored in the main memory. If the plot does not correlate with any updated target position, thereby indicating it is not a plot of one of the targets already tracked, it is compared with plots previously stored in a temporary memory. If the plot is found not to associate with any of the plots in the temporary memory, it is stored in that memory for correlation with plots received on subsequent scans. If the received plot correlates with one of the plots in the temporary memory, it is assumed that the correlated received and stored plots are of a target, moving in a predictable pattern, which should be tracked. Thus, the plots are transferred to the tracking computer for target prediction on subsequent scans. Any plots in the temporary memory which do not correlate with any received plot during a selected number of succeeding scans, are cleared from that memory. In a prior art track-while-scan system (Fig. 1) a radar transmitter 12 transmits pulses at a given pulse rate frequency (PRF); a radar receiver 14 is assumed to generate noise and receive signals from a scanning antenna 16, the signals containing target information and clutter. Outputs from a processor 18 are supplied to a data processor 20 comprising track memory 21, control unit 22 and track correlator 23 associated with track correlation gates 24. The processor 20 tracks one or more operator-selected targets by means of a tracking logic unit 25 which automatically updates the position of each target correlated by the correlator 23. Where a received plot is found to correlate with a plot stored in memory 21, correlator 23 provides range and azimuth (#R) and (##) difference signals which represent differences between the corresponding signals of the plot and predicted track co-ordinates with which it correlates. #R and ## are stored in memory 21 for future prediction purposes. Initial determination to track a target is made by an operator viewing a display console 30, and initiation of tracking by the computer is then effected. The invention (Fig. 3) provides for automatic initiation of target tracking so that the operator merely monitors the proceedings via the console. The output of the processor 18 is supplied to a data processor 40 which, in addition to the elements described in the prior art processor 20 includes a temporary memory 41, a plot correlator 43 and an initiation correlation gate 44. The processor 40 operates in a manner similar to that already described for the prior art processor 20. In the latter, any plot not correlating with any track of the memory 21 is discarded. However, in the processor 40, such a plot is transferred to the plot correlator 43 where it is correlated with any plots stored in temporary memory 41. If the new plot does not so correlate, it is itself stored in the memory since it could be a plot of a potential new target to be tracked. If the new plot does so correlate, this is an indication that the two plots are of the same target and as a result the stored plot and the difference signals #R, ## are transferred to tracking logic unit 25 so that an initial track of the new target can be entered in the main memory 21 for use in updating succeeding plots. Any temporarily stored plot in memory 41 which does not correlate during a predetermined number of suceeding scans, usually 2¢ scans, with any new input plots, is automatically erased from memory 41. For improved accuracy, a new plot has to sequentially correlate, once in an initiation gate and twice in a tracking gate before it is accepted as a system track; any misses in this sequence that occur for 2¢ scans in succession automatically result in track elimination. Thus, any noise or random clutter plots are eliminated. New plots, in addition to comprising R and # signals, may comprise selective identification signals which are useful when the new plot correlates with tracks of different targets, so that the code signals enable the proper association of the new plot and its rightful target. Also, when two closely-spaced targets cannot be distinguished, the system can inhibit the use of the new plot in updating the position of any tracked target, to prevent updating the position of the wrong target.