GB1520371A - Airborne target acquisition systems - Google Patents

Abstract

1520371 Pulse radar VEGA PRECISION LABORATORIES Inc 26 April 1976 16848/76 Heading H4D In a radar target acquisition system the amplitude modulated video return signal is used for discrimination of moving target information from ground clutter to enable a track gate to identify and lock on to the target. An automatic gate circuit A2 sweeps out over the range and gates the video return into acquisition filter Al to determine when video from the target is being received, at which time radar track gate 4 is locked on the target. Circuit A2 is normally inhibited by inhibit timer 21; its operation is initiated by the activation by the pilot of a manual mode switch 3, to put the radar into the PLM mode or target acquisition mode, turning on a range gate one slot 10. Thereafter the normal tracking gate pulses provided by radar range gate circuit 2 are expanded in circuit 10 to define a period within which video return is gated to circuit Al, and thus define an envelope within which the amplitude modulated video return must exceed a predetermined threshold. When PLM circuit switch 3 is activated, turning on automatic gate A2, this locks out track gate 4 through gate control relay 6 and deactivates detector 5. When a signal of greater than threshold value is acquired in circuit Al, then relay 6 is triggered to return to its original position, via control flip-flop 19, turning on detector 5 and enabling track gate 4 to lock on target. In a conical scan radar embodiment, the video return from receiver 1 is applied to a log IF amplifier 7, amplified and detected at video amplifier 8 and applied through video gate 9 to video stretch circuit 11. The input to acquisition filter circuit 41 is applied to filter 16, rectifier 17 and compared in comparator 18 to an established threshold frequency. Filter 16 passes signals at the conical scan frequency. The output from comparator 18 is applied through reset circuit 20 to reset flip-flop 19 to return relay circuit 6 to its normal position and energize track gate 4. To overcome any counter-measures technique returning a false conical scan frequency, detection and comparison of the video return at its own pulse repetition frequency is used (filter 12, rectifier 13, comparator 14) and any positive acquisition signal applied, in conjunction with the output from comparator 18, through NAND gate 15 to reset flip-flop 19. Instead of a conical scan antenna, a beam switched antenna may be used in which case the known scan frequency is the beam switching frequency. In an alternative embodiment, the acquisition circuit may be located on a missile air frame, the range gate search and track functions being replaced by speedgate search and track functions. The automatic range sweep and track lock on circuits are replaced by automatic frequency sweep and velocity speedgate lock on circuits, whereby the speedgate is caused to lock on to video return of a specific frequency modulation in lieu of range. The detailed circuitry is described in Figs. 2A-2D.