GB2280734A

GB2280734A - Proximity fuze and method of fuzing

Info

Publication number: GB2280734A
Application number: GB8609478A
Authority: GB
Inventors: James William Mcilroy
Original assignee: SHORTS MISSILE SYST Ltd; Thales Air Defence Ltd
Current assignee: SHORTS MISSILE SYST Ltd; Thales Air Defence Ltd
Priority date: 1985-04-19
Filing date: 1986-04-18
Publication date: 1995-02-08
Anticipated expiration: 2006-04-18
Also published as: GB8609478D0; GB2280734B; GB8510124D0

Abstract

A proximity fuze generates a focussed beam 18 of pulsed laser radiation. Reflected pulses are examined by a range gate 26 and by a comparator 36 which allows firing only if the pattern of reflected pulses matches one of a number of stored target profiles. The range gate 26 passes only those pulses from targets 19 within a required range bracket. An integrator 31 passes only pulses which are of long enough duration to be consistent with reflection from a desired target. <IMAGE>

Description

PROXIMITY FUZE AND METHOD OF FUZING This invention relates to a method of fuzing a warhead and to a proximity fuze for generating a firing pulse to detonate a warhead.

It has previously been proposed to use radar proximity fuzes, but high cost millimetric techniques are needed if a desirable narrow beam width is to be achieved.

The fuzes are also vulnerable to countermeasures.

It has been proposed to use passive infra-red or millimetric fuzes which, while been attractive for their narrow beam width and zero fuze signature, present difficulties with regard to range measurement and cut-off. If interferometric methods were to be employed to determine range, the optics and geometry would be likely to be complex and expensive. Besides, such fuzes might be very vulnerable to infra-red countermeasures, battlefield fires and extraneous millimetric radiations.

Although capacitance fuzes can give a relatively sharp range cut-off and represent a low cost system, they do not provide a narrow angle beam.

It is an object of the present invention to ameliorate the above-mentioned difficulties.

According to a first aspect of the present invention there is provided a method of fuzing a warhead comprising the steps of generating a focussed beam of pulsed laser radiation, detecting reflected pulses of the laser radiation, analysing the reflected radiation to discriminate between pulses deriving from reflections from objects within a preselected range of distances from the fuze (herein, allowed pulses) and pulses from objects at other distances (herein, rejected pulses), comparing the pattern of each burst of allowed pulses with stored profiles characteristic of different targets and when the pattern matches one of the stored profiles outputting the allowed pulses for actuation of an arming unit of the warhead.

According to a secondaspect of the present invention there is provided a proximity fuze for generating a firing pulse to detonate a warhead, the fuze comprising a generator of a focussed beam of pulsed laser radiation, a reflected beam detector, a range gate under the control of the beam generator to discriminate between pulses deriving from reflections from objects within a preselected range of distances from the fuze (herein, allowed pulses) and pulses from objects at other distances (herein rejected pulses), a comparator for comparing the pattern of bursts of allowed pulses with stored profiles characteristic of different targets and means for using allowed pulses in a pattern which matches one of the stored profiles to actuate an arming unit of the warhead.

A fuze in accordance with the present invention provides the desired narrow beam width (which would be directed downwardly when the warhead is in a guided aerial missile) with relatively cheap and simple optics. Range is determined by measurement of the propogation delay of the reflected pulses from potential target objects. The range gate permits a sharp range cut-off at a predetermined distance such as 1.5 metres. Consequently, the risk of triggering by spurious objects outside the fuzing distance range is virtually nil.

Fuzes in accordance with the invention have a high intrinsic immunity to countermeasures, weather effects, brush wood, camouflage, and clutter. Comparison of the allowed pulses with a prescribed target signature, to distinguish real targets from spurious objects at the target range from the fuze, is relatively simple.

Laser diodes to generate the beam, and photodiodes to detect the reflected beam, are relatively cheap components.

For a better understanding of the invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawing, which is a schematic diagram of the components of a fuze in accordance with the invention.

As may be seen from the schematic diagram, a 1MHz pulsed radio frequency (PRF) generator 10 triggers 11 a short pulse generator 12 (pulse duration 7 nanosecs approx) to produce firing pulses 13 to a drive circuit 14 of a gallium arsenide double hetro structure laser diode 15, operating on a wavelength of 850 nm. The optical output 16 of the laser diode is focussed by a simple lens system 17 to give a narrow beam 18 of 2-3 degrees width directed downwards onto a target 19 which may be a battle tank.

An optical receiver comprising a lens 20, optical bandpass filter 21 (850 nm), silicon PIN photodiode detector 22 and post detection pulse amplifier 23 also points downwards with a 2-3 degree field of view to encompass the beam 24 reflected by the target 19.

The output 25 of the receiver amplifier 23 is applied to a range gate 26 which is controlled 27 via a pulse delay circuit 28 driven from the short pulse generator 12.

In air, a light wave travels almost exactly at 30 cms/nanosecond. Thus, with a target at a range of 1.5 metres, the time taken for the optical pulse 18 to travel from the transmitter 15 to the target 19 and the reflected beam 24 back to the receiver 22 will be 10 nanoseconds. Making suitable allowance for propogation delay in the amplifier 23, the pulse delay circuit 28 can be arranged to open the range gate 26 to pass reflected pulses 24 from targets 19 within the required range bracket, and reject reflections from objects just outside the maximum desired range.

The fuze is housed in an aerial missile which has a warhead to be detonated. As the missile passes over the target 19 (within the required range bracket) the output 30 of the range gate will be a burst of 7 nsec pulses spaced 1 Fsec apart. The burst duration will be related to the missile velocity and the target size, e.g. a target 1 metre long and a missile velocity of 200 metres/sec would cause a burst duration of 5 msecs.

To ensure that the fuze does not trigger on small objects, such as brushwood, etc., and to arrange that the warhead beam is optimally placed over the target, the pulse burst 30 is caused to pump up an integrator 31 for a suitable period. Since this period is a variable, related to missile velocity, it is arranged that the integrator has a time constant which is continuously adjusted 32 during flight by a ramp generator 33 initiated at the commencement of flight e.g. by a start signal 34 initiated by the closure of a switch on deployment of a wing of the missile upon launch of the missile. The ramp profile follows the predicted average missile velocity/time curve.

When the integrator output 35 achieves the desired level it triggers a voltage comparator circuit 36 and then 37, in turn, a firing pulse circuit 38.

Essentially, the pattern of reflected pulses is compared in the comparator 36 with profiles stored in the comparator 36 and characteristic of particular targets. It is arranged that no output 37 issues from the comparator 36 unless the pattern of reflected pulses 24 matches one of the stored profiles. The firing pulse turns on a bipolar transistor switch 39 which parallels a crush fuze circuit of a safety and arming unit 40 of the warhead and thus detonates the warhead.

Claims

1. A method of fuzing a warhead comprising the steps of generating a focussed beam of pulsed laser radiation, detecting reflected pulses of the laser radiation, analysing the reflected radiation to discriminate between pulses deriving from reflections from objects within a preselected range of distances from the fuze (herein, allowed pulses) and pulses from objects at other distances (herein, rejected pulses), comparing the pattern of each burst of allowed pulses with stored profiles characteristic of different targets and when the pattern matches one of the stored profiles outputting the allowed pulses for actuation of an arming unit of the warhead.

2. A method according to claim 1, including the step of passing only those bursts of allowed pulses which, relative to a time constant indicative of warhead velocity, are of long enough duration to be consistent with reflection from a desired target.

3. A method of fuzing a warhead substantially as hereinbefore described with reference to the accompanying drawings.

4. A proximity fuze for generating a firing pulse to detonate a warhead, the fuze comprising means to generate a focussed beam of pulsed laser radiation, a reflected beam detector, a range gate under the control of the beam generating means to discriminate between pulses deriving from reflections from objects within a preselected range of distances from the fuze (herein, allowed pulses) and pulses from objects at other distances (herein rejected pulses), a comparator for comparing the pattern of bursts of allowed pulses with stored profiles characteristic of different targets, and means for using allowed pulses in a pattern which matches one of the stored profiles to actuate an arming unit of the warhead.

5. A proximity fuze as claimed in claim 4 including an integrator with a time constant related to warhead velocity effective to pass towards the arming unit only those pulses which are of long enough duration to be consistent with reflection from a desired target.

6. A proximity fuze substantially as hereinbefore described with reference to, and as shown in, the accompanying drawing.