Patent GB-841854-A (GB)
Title: Automatic lock-on circuit for target-tracking radar systems
IPC: G01S13/70
Filed: 1956-08-30
Abstract: 841,854. Pulse radar. STANDARD TELEPHONES & CABLES Ltd. (International Telephone & Telegraph Corporation). Aug. 30, 1956, No. 26519/56. Class 40(7). Relates to a radar system comprising a master precision manual range-tracking pulse radar capable of tracking a target in the presence of noise and a plurality of less precise auxiliary range-tracking radars each adapted to automatically track a particular target selected by the master radar. According to the present invention the pulse recurrence frequencies of all the radars are synchronized and when a target for any one auxiliary radar is being selected by the master radar the range gate of said auxiliary radar is automatically brought into coincidence with the range gate of the master radar by means of an automatic lock-on circuit which is then automatically disconnected from the auxiliary radar, the lock-on circuit being such that after coincidence is achieved the rate of displacement of the auxiliary range gate is equal to the rate of displacement of the master range gate immediately prior to coincidence. As described, in each auxiliary radar, 10 Fig. 2, a range gate pulse from a generator 15 is applied together with echo pulses from the receiver 12 to a time discriminator 16 and the error output therefrom is integrated twice at 18 and 19 to give a range voltage which controls the delay produced by a time modulator 13 such that when the range gate has been set on a target echo it is automatically maintained coincident therewith, the first and second integrators 18 and 19 cause the automatic range control to have velocity and position memory respectively. Inputs to the first and second integrators 18 and 19 are also applied from the automatic lock-on circuit 20 by means of a switching arrangement 32 comprising a manuallyoperated multipole Track- Reset switch 48, Fig. 3, and the contacts of relays 53, 59 which are in the anode circuits of gas discharge tubes 61, 60 (37, 38, Fig. 2) whose trigger electrodes are coupled through short and long delay networks 65-67, 62-64 (35, 36, Fig. 2) to the anode of the normally conducting section 57b of a bistable trigger circuit 57 (34, Fig. 2) such that the tubes 60, 61 are normally cut-off and the relays 53, 59 are de-energized, the positions of the associated contacts being then as shown. The range gate pulse, Fig. 4A, from the precision radar is applied via an amplitier 25, Fig. 2 (V40, Fig. 3) to trigger a monostable multivibrator 26 (V41, Fig. 3) whose output, Fig. 4B, is applied through a cathode follower 27 (V44, Fig. 3) to a double-diode balanced modulator 28 (V46, Fig. 3) together with a pulse P, Fig. 4C, coincident with the auxiliary radar gate pulse and derived therefrom by an amplifier 29 (V49, Fig. 3) and a blocking oscillator 30 (V50, Fig. 3). The output from the balanced modulator 28 comprises a D.C. error voltage of amplitude and polarity dependent on the magnitude and sense of any displacement of the pulse P from the position P3 shown in Fig. 4C and this error voltage is applied to a cathode follower 31 (V51, Fig. 3), an output of like polarity from the suppressor grid thereof being applied through the potentiometer 52, Fig. 3, and closed relay contact 53a to the second integrator 19, Fig. 2, such that the auxiliary gate pulse is displaced towards coincidence with the step in the output wave, Fig. 4B, from the multivibrator 26. If the initial position P1 of the pulse P, Fig. 4C, precedes the precision gate pulse then the error voltage from the cathode follower 51, Fig. 3, applied to the second integrator 19 will be negative and it will change to positive as the pulse P passes through the position P3, Fig. 4C. This positive swing is applied from the cathode load resistor 52a of cathode follower 51 to a D.C. amplifier 54 and the resultant negative swing at the anode thereof is applied through a diode 55b to the grid of the conductive section 57b of the trigger valve 57 thereby triggering the circuit and sequentially firing the gas tubes 61 and 60. When the tube 61 fires, relay 53 energizes thereby (1) opening contact 53a to break the connection between the suppressor grid of cathode follower 51 and the second integrator 19 and (2) closing contact 53b thereby applying a negative voltage swing from a potentiometer 58 in the anode circuit of the D.C. amplifier 54 to the first integrator 18 via the closed contact 59a of relay 59 to establish the required rate control of the auxiliary range gate. After a short interval determined by the difference in the delay times of delay networks 62-64 and 65-67, the tube 60 fires and energizes relay 59 thereby breaking the input to the first integrator 18 and lighting a lamp 69 to indicate that the lock-on process has been completed.