Patent GB-869277-A (GB)
Title: Improvements in target tracking systems
IPC: G01S13/66
Filed: 1957-07-08
Abstract: 869,277. Pulse radar. SOC. D' ELECTRONIQUE ET D'AUTOMATISME. July 8, 1957 [July 6, 1956], No. 21572/57. Class 40(7) Relates to a target tracking system operating in conjunction with an azimuth scanning pulse radar in which the present range Dp and bearing Gp of a target is predicted from corresponding data Da, Ga measured during a plurality of previous pulse recurrence periods. Any fresh range and bearing data Dv, Gv obtained during the. present recurrence period is compared with the predicted data and if the fresh data agrees with the data predicted for a particular target with range and bearing limits Œdn and Œgp (so called range and bearing incertitude parameters) then it is assumed that the fresh data relates to that target and the freshly acquired data is used in the prediction for the next period. The invention further relates to such a system in which the data is in electrical digital form, the tracking equipment comprising a prediction computer and a fresh data acquisition arrangement both associated with a common main store 6 through separate routing and selection means. The data relating to a particular target is stored in a respective section of the main store 6 and is identified by a target address number Ni. According to the present invention the fresh data acquiring arrangement comprises a fast access store having a plurality of locations corresponding to different ranges and the echoes received in any one pulse recurrence period are stored in appropriate ones of these locations. The predicted range data Dp and dp of targets whose predicted bearing Gp is equal to the instantaneous bearing Gv of the radar beam is sequentially extracted from the main store and applied to sequentially sample the range locations Gp, Gp+1, Gp-1... Gp+dp, Gp-dp in the fast access store. When an echo is found in a range location Dv within the limits GpŒdp then the corresponding range and bearing Dv, Gv is recorded in the main store at the address of the corresponding target. In order to reduce the'size of the main store 6, certain locations therein may be used for storing different types of data which are not required simultaneously. As shown each target address Ni in the main store 6 comprises a location for storing past range and bearing data Da, Ga, a single location for storing either the predicted bearing Gp and the bearing incertitude parameter gp of the present bearing Gv; a single location for storing the predicted range Dp or the present range Dv, a single location for storing the range incertitude parameter dp or a number n indicating the number of successive pulse recurrence periods during which an echo of range Dv has been detected, and three locations x, y, z whose content is either 1 or 0; x = 1 indicates that the predicted bearing Gp is equal to the instantaneous radar bearing Gv, y = 1 indicates that at least one echo of range Dv within the limits Dp Œdp has been detected and z = 1 indicates completion of data acquisition, i.e. no more echoes of range Dv are being received. The prediction computer comprises a source 1 of timing pulses, a control unit 2, an arithmetic unit 3 and an intermediate fast access store 4; it may be of the type disclosed in Specifications 860,789 and 867,856. The fresh data acquisition arrangementis shown below the main store 6 and its fast access store comprises a store 45 having range locations covering slightly more than the first half of the effective radar range and a store 46 having range locations covering slightly more than the second half of the radar range so that mid-range echoes will be recorded in both stores. Radar echo pulses are applied from a terminal 55 to the stores 45, 46 through respective input gates 53, 54 and outputs are derived from respective output gates 48, 49, the gates 53, 54, 48, 49 being controlled respectively by waveforms aUc, bVc, c # b and a # c, Fig. 2, derived from waveforms a, b, c, c. Fig. 2, produced by a generator 60 synchronised with the transmitter trigger pulses p, Fig. 2, applied at a terminal 56 so that writing and reading is effected alternately in the two stores 45, 46 during alternate half pulse recurrence periods. The symbol U represents the logical "or" and a U c is equivalent to a+c; the symbol # represents the logical "and" and c # b is equivalent to c. b. During the writing periods the input gates are connected sequentially to the different range locations of the stores 45, 46 by selector circuits 51, 52 actuated through gates 58, 59 (controlled by waveforms a Uc and b Uc) by the output from a distance counter 57 which on initiation by a transmitter trigger pulse p counts the timing pulses from the timing source 1. During the reading periods the locations in the stores 45, 46 to be sampled are determined by applying the output from a circuit 41 to the selector circuits 51, 52 through gates 47, 50 controlled by the waveforms c # b and a # c. Since the operation of the stores 45, 46 is very similar only the operation of the store 45 will be described in detail. At the commencement of each reading period the waveform c is applied:- (1) to actuate a comparator 16 which actuates a generator 17 to insert a digit 1 in the x location of the addresses of all targets in the main store 6 whose predicted bearing Gp is equal to the instantaneous value Gv of the varying bearing Gva of the radar beam applied at a terminal 100; and (2) through a delay 31 to actuate a sequence control member 32 which transfers the contents of a first set of m registers x, y, z in the main store 6 to registers 13, 14, 15 and then scans the registers 13, 14 and 15. When a signal x = 1 is encountered in the register 13 a logical circuit 33 produces an output signal having a component b x d; where d; = 1 when the range register 11 is empty. This signal operates to:- (1) actuate a control circuit 8 causing the corresponding data gp Dp, dp to be erased and transferred from the main store 6 to registers 10, 11, 39. (2) activate a counter 37 to which are applied timing pulses from the timing source 1. (3) activate a subtractor circuit 21 to subtract one unit from the value gp in the register 10; and (4) stop the scanning of the register 13. The predicted range value Dp is applied from the register 11 through a normally open gate 23 to the circuit 41 and the output from the counter 37 is also applied to the circuit 41 through a gate 40 which is opened by the mark x = 1 in the register 13, the circuit 41 being such that it produces sequentially the range values Dp, Dp+1, Dp-1 Dp+2, Dp-2 .... These range values are applied as sampling signals through the gate 47 to the selector circuit 51 of the store 45 and when a stored echo pulse is present in a range location Dv within the limits DpŒdp a "Yes" output signal is produced by a checking circuit 43 which (1) resets the counter 37 to zero (2) erases the mark x = 1 in the register 13 (3) writes a mark y = 1 in the register 14 (4) actuates a circuit 20 to record a digit 1 in an n register 12 (5) closes the gate 23 (6) opens a gate 22 thereby applying the present range Dv of the echo to the register 11 (7) after a delay produced by unit 36, actuates a control circuit 28 which transfers the data Dv, n = 1 and gp - 1 in the registers 11, 12 and 10 to the locations in the main store 6 previously occupied by the corresponding data Dp, dp and gp; and (8) after a further delay produced by unit 35, blocks a gate 29 thereby allowing the sequence control member 32 to continue scanning the registers 13 and 14. The only difference in the operation of the store 46 is that the effective component of the output signal from the logical circuit 33 is 0a x #de. An output from the counter 37 is also compared in a comparator 38 with the value dp in the register 39 so that if there is no echo stored in a range location Dv within the predicted range limits DpŒdp then the comparator 38 produces an output signal which performs the above specified operations (1), (2), (7) and (8) initiated by the "Yes" output signal from the checking circuit 43 when a stored echo is within the predicted range limits DpŒdp. In addition the output signals from the comparator 38 opens a normally closed gate 30 to transfer the content dp of the register 39 to the register 12 so that when the output signal from the comparator 38 clears the registers 10, 11, 12 the content dp of the register 12 is transferred back to the location "dp, n" in the main store 6. When the registers 13, 14, 15 have been completely scanned their contents are returned to the main store 6 and the marks x, y, z relating to the next set of m targets are transferred from the main store 6 to the registers 13, 14, 15 and the above process is repeated until the data relating to all the targets in the main store 6 has been checked against the echoes in the store 45. The above sequence of operations is repeated during the next radar pulse recurrence period but in this case for certain sets of data called from the main store 6 the mark x may be 0 and the mark y may be 1 indicating that an echo pulse corresponding to that particular data set was obtained during the previous pulse recurrence period. When the mark y = 1 is encountered during the scanning of the registers 13, 14, 15 the logical circuit 33 will produce an output signal having components b. y. d. and a. y.#d. and the subsequent operations will be similar to those described above except that (1) the data transferred from the main store 6 to the registers 10, 11, 39 is now gp-1, D v  and n=1 respectively and (2) the output from the counter 37 is not applied to the comparator 41 since the gate 40 is closed (x = 0) and consequently only one range location is sampled in the store 45 or 46 corresponding to the range D v  of the echo detected during the previous recurrence period. When this sampled range location does contain an echo pulse the checking circuit 45 produces an output "Yes" signal which initiates the operations described