Patent GB-867856-A (GB)
Title: Target tracking system
IPC: G01S13/72
Filed: 1957-07-04
Abstract: 867,856. Radar. SOC. D'ELECTRONIQUE ET D'AUTOMATISME. July 4, 1957 [July 5, 1956], No. 21203/57. Class 40(7) Relates to an electrical digital target tracking system operating in conjunction with a scanning pulse radar in which values Da and Ga of the range and bearing of targets detected during a preceding period are stored in coded digital form in one section 2 of a main store 1, 2, 3. The data is classified into target tracks each of which is identified by a corresponding identification number Ni and the future values Dp, Gp of the range and bearing of each target are computed by a prediction computer and stored with the corresponding identification number Ni in another section 1 of the main store 1, 2, 3; "incertitude parameters", i.e. limits dp and gp defining the possible deviations of the actual future co-ordinates from the predicted values Dp, Gp are also stored with the corresponding identification number Ni in section 1 of the main store 1, 2, 3. During each pulse recurrence period the actual co-ordinates Dv, Gv of the targets detected are compared in an acquisition computer with the predicted values Dp, Gp and if the actual co-ordinates of a detected target are within the zone defined by the predicted co-ordinates Dp, Gp and the incertitude parameters dp, gp of a track Ni then the actual range Dv and the average bearing Gm are inserted in section 3 of the main store 1, 2, 3 in a location corresponding to the track number Ni in place of the corresponding co-ordinates obtained during the preceding pulse recurrence period which are transferred to section 2 of the main store 1, 2, 3. According to the present invention the main store 1, 2, 3 and a source 6 of timing pulses are common to both the prediction and acquisition computers and the acquisition computer comprises:- (1) a first temporary store 26 in which is recorded during the first phase of each pulse recurrence period (a) all echo pulses corresponding to the predicted zones and (b) the corresponding track numbers Ni, (2) a second temporary store 50 in which is recorded the actual range Dv and bearing Gv of said echo pulses, (3) means for (a) selecting from the second temporary store 50 all pairs of values Dv, Gv falling within the prediction zone of the first track number Ni recorded in the first temporary store 26, (b) computing the average value Gm of the selected Gv values and (c) storing the corresponding Ni, Dv and Gm values in a third temporary store 10, (4) means for repeating operation (3) for all the track numbers recorded in the first temporary store 26, (5) means for transferring the contents of the third temporary store 10 to section 3 of the main store. The prediction computer may comprise a control unit 5, an arithmetical unit 4 and fast access stores as described in Specification 860,789. Detailed operation As shown the transmitter trigger pulse and echo pulses are applied at terminals 30 and 40 respectively and a continuously varying digital code defining the instantaneous bearing of the aerial is applied at terminal 12. The aerial bearing code is applied to:- (1) a register 36 and decoder 39 which produces a corresponding analogue voltage, (2) a control unit 14 which actuates a selector circuit 15 to transfer to a fast access store 9 the contents of section 1 of the main store 1, 2, 3 corresponding to a predetermined sector which includes the instantaneous aerial bearing. During the first phase of each radar pulse recurrence period the transmitter trigger pulse actuates a bi-stable flip-flop 29 which opens a gate 28 to pass the timing pulses from the pulse source 6 to range counters 16 and 45. When the output from the counter 16 corresponds to a predicted range value Dp in the store 9, the corresponding values Ni, Gp, gp and dp are transferred to one work stores 17, 18, 19 and 20 respectively. The content Ni of the store 17 is applied directly to the first line of the upper half of a fast access store 26 and the contents Gp, gp of the stores 18, 19 are converted in a decoder 34 into an analogue voltage defining the angular width of the predicted zone which is applied to a comparator 35 together with the aerial bearing voltage from the decoder 39. If the aerial bearing is within said zone width then the output from the comparator 35 opens gates 37 and 38 to which are applied the timing pulses and the echo pulses respectively. The timing pulses passed by the gate 37 are applied to a counter 22 and when the output from the counter 22 corresponds to the range limit dp in the store 20 a comparator 42 operates to close the gates 37 and 38. Any echo pulses passed by the gate 38 during the period corresponding to the range interval bounded by the limits Dp and Dp+dp are stored in the upper half of the store 26 in the location containing the corresponding identity number Ni and also open gates 47 and 46 to apply the corresponding instantaneous range and bearing values Dv, Gv from the range counter 45 and bearing register 36 to the store 50. If more than one echo pulse is received during the range interval Dp-(Dp+dp) these pulses are superimposed in the store 26 but the corresponding values of Dv and Gv in the store 50 are recorded in different locations since the associated selecting circuit 51 is stepped on by each echo pulse applied thereto through a normally open gate 48. When the output from the range counter 16 corresponds to the next highest predicted range value Dp corresponding to another track the above process is repeated, the new value of Ni from the store 17 being applied to clear the counter 22 and to actuate the selector control 24, 25 of the store 26 so that the new value of Ni is stored in the next line of the store 26. Thus during the first phase of each radar pulse recurrence period all the track numbers Ni in the store 9 will be recorded in the store 26 but only echoes whose instantaneous range Dv and bearing Gv are within the prediction zones of these tracks will be recorded in the store 26 with the track numbers and the instantaneous range Dv and bearing Gv of all these echoes will be recorded in separate locations in the store 26. When the output from the range counter 16 corresponds to the maximum range of the system it produces an output pulse which resets the counter 16, terminates the bi-stable flip-flop 29 and actuates the control unit 14 to initiate the second phase of operation which lasts until transmission of the next radar pulse. During this second phase the contents of the store 26 are sequentially erased and transferred to a one word register 61 which checks the presence or absence of an echo pulse. If no echo pulse is associated with the transferred track number the control unit 14 records the corresponding track number in the store 10 together with a series of zeroes. If however an echo pulse is associated with the transferred track number, the control unit 14 records the corresponding track number in the store 10 and reads out from the store 9 (1) the corresponding range prediction data Dp, dp to a computer 65 which computes the value Dp+dp and applies the values Dp and Dp+dp to a comparator 68 and (2) the corresponding bearing prediction data Gp, gp to a computer 66 which computes the value Gp+gp. The control unit 14 then sequentially applies the values Dv in the store 50 to the comparator 68 via a read-out circuit 67 and when an output Dv is within the limits Dp and Dp+dp the comparator 68 opens a gate 69 which thereby applies the corresponding bearing value Gv from the store 50 to a computer 70 which stores this value Gv. When the store 50 has been completely searched, all bearing values Gvi ... Gvj corresponding to the same range value Dv will be stored in the computer 70 which then computes the average value Gm and if this value is within the limits Gp and Gp+ gp as determined by the computer 66 then the values Dv and Gm are applied through gates 73 and 74 to the store 10 and recorded with the corresponding track number Ni. The above operations are repeated until the store 26 is empty and the control unit then transfers the data in the store 10 to section 3 of the main store 1, 2, 3. An alternative mode of operation may be effected by using an additional store 55 similar to the store 50 and a lower portion of the store 26 similar to the upper portion thereof, the stores 50, 55 and 26 being controlled by a flip-flop 51 actuated by the transmitter trigger pulses so that during one radar pulse recurrence period the store 50 and upper portion of the store 26 operate as in the first phase described above and the store 55 and lower portion of store 26 operate as in the second phase, the modes of operation being reversed in the next pulse recurrence period. New target tracks may be initiated manually by visual observation of a P.P.I. display.