A proximity fuse

Abstract: A proximity fuse for a launchable unit, for example a missile, which includes transmitters (10¹-13⁴) for emitting optical radiation in a plurality of narrow lobes (10¹³), and receivers for receiving optical radiation reflected from a target illuminated by transmitters (10¹-13⁴) onto which the unit is homing. The receivers are capable to distinguish reflected radiation from each respective lobe relative to the radiation emitted and reflected from the other lobes. The radiation signal received from each respective lobe is individually processed in the receiver.

Description: TECHNICAL FIELD The present invention relates to a proximity fuse for a unit in the form of a missile, projectile or corresponding unit. Such a unit may include a warhead and a sensing device which detonates the warhead when the unit hits its target. The purpose of the proximity fuse is to detonate the warhead on target passage in those cases where no direct hit is obtained. SUMMARY OF THE INVENTION The proximity fuse includes means for emitting electromagnetic radiation, and means for receiving such reflected radiation from the target when this is bypassed. In addition, the proximity fuse includes means for signal processing of the signal initiated by the received radiation. The signal processing may include filtration and other measures to highlight, as far as is possible, the signal reflected by the target in relation to background noise and monkey chatter, and also testing in relation to predetermined criteria. If the signal satifies these criteria, the warhead is detonated. The criteria are selected such that the probability of detonation by background noise and monkey chatter will be as slight as possible, and the probability of detonation by radiation reflected from the target will be as high as possible. In the present invention, it is assumed that such signal processing and criteria assessment are effected in accordance with known methods. BACKGROUND ART In this art, it is desirable that the proximity fuse does not detonate the warhead in cases which offer a direct hit on the target. Consequently, prior-art proposals have been put forward to give one and the same lobe for the emitted electromagnetic radiation the configuration of a planar disc with the normal directed in the flight path of the unit or alternatively the form of the circumferential surface of a cone. It is further desirable in this art to employ short wave electromagnetic radiation - preferably within the IR range - such that unwieldy antenna clusters will be thus avoided. The drawback inherent in the prior-art IR radiation is that it is greatly reflected by the water droplets and ice crystals which are present in cloud and in precipitation. The conditions will become particularly unfavourable for proximity fuses of the above-mentioned disc or conical ray lobe under these circumstances. On target by-pass, or "near miss", but a minor faction of the radiation lobe will impinge upon the target, which entails that the emitted radiation must be given a high efficiency level in order that a reflected signal of sufficient strength be received. On passage through cloud or precipitation, the entire radiation lobe will be subject to "window effect" from the reflection of water droplets or ice crystals. As a result of the extent of the radiation lobe about the circumference of the launchable unit, and the high emitted effect, the reflected effect, ie the return dispersion, will be very high indeed. According to another prior-art proposal known from US-A-4 306 500, a plurality of transmitter and receiver lobes are present. In order to reduce the backscatter and improve the signal-to-noise ratio, two receivers that are associated with each transmitter are angularly displaced from the transmitter. The proximity fuse according to the invention provides for return dispersion or backscatter in quite a different way. OBJECT OF THE PRESENT INVENTION The object of the present invention is to obviate the above-mentioned drawbacks. In addition to the fact that sensitivity to cloud, mist, fog and precipitation may be reduced considerably, the present intention also makes for an improved detection of a target in that it is possible, with the assistance of the reflected radiation in the part lobes, to present a rough picture of the configuration of the target. Using this aid, it is possible, in turn, to realize an optimum detonation delay in the unit such that the unit may be detonated adjacent a vulnerability centre on the target. The present invention is based on a division of the conical or disc-shaped transmitter and receiver lobes into part lobes, and that which may be considered as characterizing the present invention is that the transmitter and receiver means are operative to work with narrow part lobes distributed about the circumference of the unit which part lobes to the number are so great and to the width are so narrow that there is room for a separate lob in its entirety upon a minimal target to be detected even when it is located at a maximum detecting distance from the unit; and that said receiver means are operative to discern the reflected and received radiation of each respective part lobe for individual processing in said signal processing means. In one preferred embodiment of the present invention, the large number of part lobes will be obtained with a relatively small cluster of components. For each part lobe, there is provided a transmitter of simple construction which is intermittently activated in the form of brief pulses. Furthermore, there is provided a number of receivers (n) which are arranged such that each receiver device is common to a number of transmitters (m). The transmitters may be grouped in two different ways. When the transmitters are divided in accordance with the first method, it applies that these transmitters, in one and the same group, are pulsed simultaneously from one and the same pulse assembly or from a plurality of synchronous such assemblies, and that each one of these transmitter units is provided with its receiver unit. When the transmitter units are divided up according to the second method, it further applies according to the invention that the transmitter units within one and the same group utilize one and the same receiver unit; and that each of these transmitter units are pulsed from their respective pulse unit, and that the different transmitter units are pulsed at non-coincidental points in time, In a first embodiment of the present invention, activation of the transmitter unit is effected electrically, laser diodes or other pulsable sources of radiation being used in the transmitter means. In an alternative embodiment, transmission between the drive means and transmitter means may be effected fibre optically, in which event the radiation sources are integrally built with the pulse assemblies. The receiver units are each coupled to their subsequent signal processing units. Each respective receiver unit is allocated its second transmitter means group, the transmitter and receiver units within these groups being directed in substantially the same direction. By utilizing a matrix sensing function, it is possible to establish, at any given moment, the part lobe association for each respective received optical radiation. The number of transmitters (m x n) substantially exceeds the number of receiver units. The number of drive units (m) preferably corresponds to the number of receiver units (n). As a result of the above-proposed construction of the proximity fuse, it is possible to obtain a function in-which the return dispersion is considerably reduced. The employment of a plurality of narrow part lobes and the separate signal processing of the signal from each part lobe prevents the return dispersion in the part lobes of each respective sector from being accumulated. The present invention may be employed together with prior-art range finding principles and per se known subsequent signal processing which utilizes the range information from the different part lobes to effectuate a rough picture of the target and calculate therefrom the optimum triggering delay for the unit. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS A currently proposed embodiment of a proximity fuse displaying the significative characterizing features of the present invention will be described in greater detail below with the reference to the accompanying drawings. In the accompanying drawings: Fig. 1 shows the fundamental siting of the proximity fuse on a missile or the like and the position of the missile in relation to the target; Fig. 2 shows, in schematic diagram form, transmitter units included in the transmitter of the proximity fuse, and drive units for these transmitters; Fig. 3 shows an alternative embodiment of the transmitter according to Fig. 2; and Fig. 4 shows receiver units included in the receiver and signal processing stages operative subsequent to these units. DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawings, Fig. 1 shows part of a missile indicated by reference numeral 1. The missile includes a proximity fuse section 2 which is housed in the missile in a per se known manner. The missile is provided with activation circuits 3 actuable by the proximity fuse, by means of which circuits the warhead 4 of the missile may be triggered or detonated. In Fig. 1, the transmitters of the proximity fuse are symbolized by a number of output openings 5 by the intermediary of which a plurality of narrow lobes 6 of optic radiation may be transmitted. The receiver of the proximity fuse is symbolized by a number of input openings 7 which may be exposed to optic radiation 8 deriving from the optical radiation emitted in part lobe form and reflected on a target 9. In accordance with the disclosures presented below, the number of transmitter devices is greater than the number of receiver devices, and one and the same input opening 7 constitutes the receiver input for the radiation from a plurality of output openings 5. The transmitter 10 according to Fig. 2 shows a number of transmitter devices for optic radiation and are designated 10¹ ... 10⁴; 11¹ ... 11⁴; 12¹ ... 12⁴; and 13¹ ... 13 4. Each respective transmitter device includes a per se known laser diode 10¹¹ with associated collecting lens 10¹². From each respective transmitter device, there departs a narrow part lobe 10¹³. The proximity fuse is an all-round sensor, which entails that the part lobes together cover the entire circumference of the proximity fuse (the missile). In the general case, there should be provided a plurality (m x n) of transmitters. In the illustrated embodiment, the transmitter devices are 16 in number. The transmitter devices may be divided into groups in two different manners, hereinafter designated first and second groups. Both the first and second groups are four in number. However, the number of groups may be varied. The transmitter devices 10¹, 11¹, 12¹, 13¹ form a first group. The transmitter devices 10², 11², 12², 13² form a second first group. The transmitter devices 10³, 11³, 12³, 13³; and 10⁴, 11⁴, 12⁴ and 13⁴ form the third and fourth first groups. The transmitter devices 10¹, 10², 10³, 11⁴ form a first second group. The transmitter devices 11¹, 11², 11³, 11⁴ form a second second group. The transmitter devices 12¹, 12², 12³, 12⁴; and 13¹, 13², 13³, 13⁴ form a third and fourth second group, respectively. The transmitter devices in each respective first group are energized from their drive unit 14, 15, 16 and 17, respectively. Energization from the drive unit 14 of the first first group is effected by the intermediary of electric lines 18. The drive units 15, 16 and 17 correspondingly energize their first groups by the intermediary of electric lines 19, 20 and 21. The transmitter devices included in each respective second group each cover their sector 22, 23, 24 and 25. The above-mentioned drive units 14-17 are controlled by a clock generator 26 which emits four parallel pulse trains for controlling each respective drive unit. In accordance with the figure, the pulses/pulse trains are offset in relation to one another, such that the transmitter units within each respective second group are actuated in series from their respective drive unit. Activation from the drive units is, in this instance, such that the activation of one transmitter device in question within the group is initiated and terminated before activation is effected of subsequent transmitter devices, and so on. As a result of the illustrated construction, activation will be effected simultaneously of one transmitter device in each respective group. The simultaneously activated transmitter devices are, in this instance, directed substantially away from one another and, in the illustrated embodiment, all activated transmitter devices are arranged at 90° in relation to one another. The drive units may be constructed in a per se known manner by digital technology (flipflops, gates, etc.). The clock generator 26 may also consist of a per se known digital generator. The pulses in the pulse train from the clock generator are of the same amplitude and the mutual offset between the pulse trains may be arranged by previously known frequency distribution circuits in the clock generator. In one embodiment, the pulse frequency is at most but a few kHz and the pulse time in each respective pulse train is shorter than 1 microsecond. Power supply is obtained in a per se known manner from a power source in the unit/missile. As a result of the illustrated arrangement, full-circle scanning may be obtained at the same time as return dispersion can be kept at a low level despite the relatively high total transmission power which is necessary to give the desired triggering effect on reflection of emitted radiation on the target. By the series, or successive, activation of the transmitter devices within each respective second group, cumulative effects of the return dispersion will be avoided. The number (m) of drive units is selected in dependence upon the number of first and second groups, respectively, and is preferably equal to the latter in number. In Fig. 2, a sensing circuit 27 is also connected to outputs on the drive units. The sensing circuit is intended to give an indication of that drive unit of the above-mentioned drive units which is activated at any given time. Fig. 3 shows an alternative embodiment of the transmitter. In this case, use is made of fibre optic leads 18', 19', 20' and 21', instead of the electric leads 18, 19, 20 and 21 in Fig. 2. Electronic drive units 14', 15', 16' and 17' are also included in this particular embodiment and are driven by a digital clock generator 26' in a manner corresponding to that according to the embodiment of Fig. 2. The drive units 14'-17' are connected to LEDs or laser diodes 28, 29, 30 and 31, respectively. The ends of the fibre optic leads facing away from the above-mentioned transmitter units 28-31 are disposed at collecting lenses 32 of the same type as in the previously-described embodiment. The group arrangement and departing part lobes are disposed in a manner corresponding to that described in conjunction with the embodiment according to Fig. 2. Each respective now departing part lobe passes its associated opening 5 on the missile according to Fig. 1. The lens of the part lobe is disposed at each respective opening. Fig. 4 shows the receiver unit in the proximity fuse seen in a cross-sectional plane through the missile or the like. In the figures, the sectors disclosed in Fig. 2 have also been included, having there been given the designations 22', 23', 24' and 25', respectively. The receiver comprises four receiver units 33, 34, 35 and 36 which each cover their sector of the incoming reflected radiation. Each respective receiver device displays a collimator lens 33¹ and a photodetector 33². The receiver devices 33-36 are arranged so as to cooperate with transmitter devices in each respective second group. Hence, the receiver device 33 may react to radiation transmitted by the transmitter devices 10¹, 10², 10³, 10⁴ and reflected on actual target. Correspondingly, the receiver device 34 may react to transmitted radiation from the transmitter devices 11¹, 11², 11³, 11⁴ and reflected on the target, and so on. In Fig. 4, the radiation from each respective part lobe has been indicated. Thus, the received lobe 37 represents reflected radiation from the part lobe of the transmitter device 10¹. The incoming radiation 38, 39 and 40, respectively represents reflected radiation from the part lobes of the transmitter devices 10², 10³ and 10⁴. This incoming radiation 37-40 occurs successively in time sequence after one another. The lenses of the receivers are disposed at the openings 7 on the missile according to Fig. 1. The photodetectors in each respective receiver 33-36 are each connected to their amplifier 41-44. The outputs of the amplifiers are connected to a signal processing circuit 45 which processes received information in a per se known manner. The outputs of the amplifier circuits 41-44 are connected to sensing means 46. The sensors 27 of the transmitter devices and the sensors 46 of the receivers may, in one embodiment, be connected to a sensing matrix 47 to whose columns the outputs of the sensing circuit 27 are connected and to whose lines the outputs of the sensing circuit 46 are connected. Further sensing devices 48 are connected to the interstices in the matrix and, from the illustrated matrix sensing, it is possible to obtain, in the circuit 48, information as to that part lobe from which received radiation derives on each occasion. Together with the range information A1, it is possible, using the calculator circuits 45, to obtain a rough outline image of the target and derive therefrom optimum warhead triggering delay. Thus, it is possible, from the signal processing circuits, to obtain on one output, for instance output 45', a signal/signals for activating the triggering circuits 3 (see Fig. 1) in the missile. The lobe angles are selected to be so narrow that an individual lobe will, in its entirety, be accommodated on a smallest target which could be detectable even when the target is at the maximum detection range. The distribution angles between the different lobes are selected to be so small that one lobe always impinges upon the smallest target which it is possible to detect when it is at the maximum detection range. The lobe angles are suitably selected within the order of magnitude of between 5 and 45°, preferably within the range of between 5 and 30°. The transmitter and receiver devices may be disposed such that the lobes mutually overlap or not. As a result of the above-disclosed construction, the radiation of each respective part lobe reflected on the target and received in the missile may be identified and individually treated in relation to the radiation deriving from other part lobes.

Claims: A proximity fuse for a unit in the form of a missile (1), projectile or the like and comprising transmitter means (10¹-13⁴) for emitting electromagnetic radiation in a plurality of part lobes (10¹³), receiver means (33-36) for receiving the radiation which is reflected on a proximally adjacent target, and signal processing means for processing of an electric signal initiated by the received radiation, charactarized in that said transmitter and receiver means are operative to work with narrow part lobes distributed about the circumference of the unit which part lobes to the number are so great and to the width are so narrow that there is room for a separate lobe in its entirety upon a minimal target to be detected even when it is located at a maximum detecting distance from the unit; and that said receiver means are operative to discern the reflected and received radiation of each respective part lobe for individual processing in said signal processing means. The proximity fuse as claimed in Claim 1, characterized in that said transmitter means (10¹-13⁴) are disposed in a full-circle emitting lobe system in which said transmitter means are divided into first transmitter means groups which are drivable each by their drive unit (14-17); and that said transmitter means within each first group are divided, preferably symmetrically, about the circumference of the proximity fuse. The proximity fuse as claimed in claim 2, characterized in that said drive units (14-17) feed their respective first transmitter means groups with short time-offset pulses such that transmitter means forming mutually adjacent groups and other transmitter means groups which, with their part lobes, cover a sector (22-25) of the full-circle sensing of said proximity fuse seen in a cross-sectional plane through the unit, effectuate a series-pulsed emission of their part lobes. The proximity fuse as claimed in Claim 2 or 3, characterized in that said drive units (14-17) actuate their respective first transmitter means groups by the intermediary of electrically (18-21) and/or optically (18'-21') operating transmission lines. The proximity fuse as claimed in any one of the preceding Claims, characterized in that said receiver means are disposed in a full-circle sensing system in which said receiver means are divided in a plurality of receiver means which are each coupled to their signal processing circuit (41-44) or to a common signal processing circuit (45); and that the receiver means are distributed, preferably symmetrically, about the circumference of said proximity fuse. The proximity fuse as claimed in Claim 3, 4 or 5, characterized in that each respective receiver means is allocated its second transmitter means group; and that each respective receiver means is directed in the same direction as the transmitter means in the associated second transmitter means group. The proximity fuse as claimed in any one of Claims 3-6, characterized in that said sensing means (27, 46, 47, 48) are operative to determine, by sensing/comparison of the time offset of said transmitter means and the activation of receiver means by received reflected radiation, that part lobe among all part lobes which may be related to the radiation received on the immediate occasion in the considered receiver means. The proximity fuse as claimed in Claim 7, characterized in that first sensing means (48) are connected to interstices in a matrix (47) to whose columns said drive units (14-17) are connected, and to whose lines said receiver means are connected, or vice versa. The proximity fuse as claimed in any one of the preceding Claims, characterized in that the number of transmitter means substantially exceeds the number of receiver means or drive means.

Inventors: SKAGERLUND LARS-ERIK, SKAGERLUND, LARS-ERIK
Applicants: BOFORS AB, AB BOFORS
Application year: 1988
Main classification: F42C13
IPC codes: G01S7, F42C13