EP0204367A1 - Proximity fuse for an artillery projectile with base bleed reducing means - Google Patents

Abstract

A radar device (1,2,3,4) provides a beat signal Se to a first chain to activate the trigger (9) after a time τ 1 after Se has exceeded a certain threshold. According to the invention, the rocket comprises an additional chain, to counteract the effect of drag, which has blocking (32) amplification (33) and threshold crossing (35, 36) characteristics comparable to those of the first. chain, the output signal of which is transmitted to inhibition means (47, 48, 49, 41, 39 and 44, 38 and 43) and which comprises first and second delay means (34). Application: artillery projectile of the type with reduction of the aerodynamic drag of base.

Description

The invention relates to a proximity rocket for an artillery projectile of the type for reduction of the aerodynamic drag of the base comprising a radar device for providing at the output of a mixer a subtractive beat signal Se between the emitted wave and the reflected wave. a part in a first processing chain intended to activate the trigger of the ignition circuit of said rocket after a time _'1 , variable, of the order of a tenth of a second, after said amplified beat signal and filtered has exceeded a certain number of times a certain threshold, on the other hand to a second anti-jamming chain having band-pass characteristics different from those of the first chain.

In order to increase the range of the shells, a very effective means consists in carrying out a reduction in the base drag (RDTC), which is formed in flight at the base of the shell, especially at the start of the trajectory. This reduction in drag can be obtained by emitting a gas jet at the base, called "Base Bleed" in English, the principle of which is recalled below. The invention applies precisely to a proximity rocket for this type of artillery projectile.

Known proximity rockets include an electronic circuit sensitive to signals included in predetermined frequency bands. This circuit responds either to signals transmitted from the designated target or to reflected signals, initially transmitted from the fired projectile such as, in particular Doppler signals, the latter case being more particularly targeted by the invention which relates to shells whose preferred target is the soil.

The major technical problem which arises for proximity rockets of this type is the risk of being influenced by parasitic signals which can cause a untimely triggering in general far from the target. To counteract these parasitic signals, a known means consists in adding to a first processing chain a second chain which has the essential function of inhibiting the first chain in the presence of parasitic signals, as described for example in French patent 2,175,810 and its addition 2 223 658.

The spurious signals which justify the presence of a second chain may be due to particular atmospheric conditions or to voluntary or involuntary interference and their frequency bands are essentially outside the Doppler frequency band to which must be sensitive the proximity fuse in normal operation. For RDTC type projectiles, on the other hand, the additional interference induced by the emission of ionized gases at the base has two characteristics which make it very troublesome for correct operation of the rocket: approximately half of the additional parasitic radioelectric energy is located in the Doppler frequency band to be considered and the amplitude of these additional spurious signals is comparable to that of the Doppler signals. Against such parasitic signals the second anti-jamming chain mentioned above is inoperative.

The object of the invention is to adapt the sensitivity of the signal processing module of the proximity rocket of an artillery projectile with reduction of aerodynamic base drag.

Another object is to provide a proximity rocket adaptable to different types of artillery projectiles, whether or not these are of the RDTC type.

These aims are achieved thanks to the fact that the proximity rocket defined in the preamble is remarkable in that it further comprises an additional chain intended to counteract the parasitic effect caused in said first chain by the electromagnetic disturbances due to the reduction of the aerodynamic base drag, that said additional chain has characteristics of bandpass filtering, amplification and threshold crossing by said beat signal comparable to those of said first chain, that the output signal of the additional chain is transmitted to inhibition means for partially or totally inhibit, via said first chain or said initiation circuit, the firing of the rocket, and that said additional chain comprises first delay means which delay the appearance of said output signal, relative to the input signal, of a time T ₁ greater than the maximum value of τ1 and of the second delay means for maintaining said output signal of the additional chain for a time T ₂ of the order of a few seconds after said amplified and filtered beat signal stopped exceeding the threshold of the additional channel.

Since the additional chain processes signals whose amplitude and frequency is comparable to that of useful signals, that is to say target Doppler signals, the delay T ₁ makes it possible to avoid that the additional chain n 'inhibits the first chain in the most frequent case where the shell arrives on the ground after the RDTC effect has ceased, which allows the first chain to trigger the explosion as expected in nominal fashion. For short-range shooting, which remains interesting with RDTC type projectiles because of their increased speed, provision can be made to only partially inhibit the first chain, ground arrival being able to occur while one is still in RDTC phase.

It will be noted that the establishment of the delay time T ₁ is made possible thanks to the property that the disturbing signal RDTC has of existing from the start of the shot, that is to say during the initial phase in which any explosion of the projectile is made impossible as a safety measure for the gunner. Furthermore, the presence of the additional chain is compatible with that of the second chain of the prior art described above.

According to a preferred embodiment of the invention, said proximity rocket comprises in cascade a first and a second timing circuit of the priming circuit, the first chain comprises in cascade following said mixer a bandpass filter, an amplifier , a threshold circuit and a pulse counter with continuous progressive reset and said trigger, and the additional chain comprises in cascade a bandpass filter, an amplifier, said first and second delay means, a threshold circuit and a decision circuit which supplies said output signal.

An advantageous embodiment of the proximity rocket according to which the pulse counter of the first chain, constituted by a charge transfer circuit between a first and a second capacitor, is partially inhibited, is remarkable in that said signal output of the additional chain acts, by means of inhibition, on said first capacitor, to reduce the charge transfer of the latter on the occasion of each threshold crossing in the threshold circuit of the first chain.

According to this last embodiment, if the arrival of the projectile on the target, in this case the ground, occurs during the phase of reduction of the pellet drag, the rocket still operates in proximity at a reduced height compared to the nominal height provided.

The following description with reference to the accompanying drawings, all given by way of example, will make it clear how the invention can be implemented.

• Figure 1 is an overall block diagram of the proximity rocket according to the invention.
• FIG. 2a represents the shape of the beat signal to be processed as a function of time and FIGS. 2b to 2d are time diagrams explaining the operation of the proximity rocket according to the invention.
• FIG. 3 represents a first embodiment of the invention in the form of a partial synoptic electronic diagram.
• FIG. 4 represents a second embodiment of the invention in the form of a partial synoptic electronic diagram.
• FIG. 5 is an electronic diagram of part of the first processing chain as well as part of the additional chain for a third embodiment of the invention.

In the figures, the same references designate the same elements with the same functions.

The RDTC device is a relatively recent achievement. The principle consists in providing the rear of the shell projectile with an appendage open towards the rear and which contains combustible material; the combustible material is ignited at the start of the projectile which results in the presence of ignited gases in the wake of the shell and by an increase in pressure which causes a reduction in the drag of the base which can reach 80%. Although the projectile then functions like a rocket engine, the emission of ignited gases takes place at subsonic speed and no additional propelling force is provided, thanks to which the accuracy of the firing is in no way affected by this device. The RDTC phase is planned to last during the fastest part of the trajectory of the shell for which the efficiency of the device is maximum, that is to say during the first 20 to 30 seconds counted from the start of the shot referenced to. For shots with a high emission angle, close to 45 degrees with respect to the horizontal, the RDTC phase is much less than the total time of the trajectory of the shell; on the other hand, for shots with a low emission angle, the arrival on the ground can occur during the RDTC phase. The reminders given above on the operation of RDTC type projectiles are useful for a good understanding of the invention.

A known proximity rocket for artillery projectile can comprise, as indicated in FIG. 1, a radar device constituted for example by an oscillator 1 coupled to a transmitting antenna 2 to emit a continuous wave. The wave reflected by the target, normally the ground, is picked up by a receiving antenna 3 assumed for example to be separate from the transmitting antenna. The antennas 2 and 3 are assumed to be omnidirectional. A mixer circuit 4 forms the subtractive beat signal between the signal supplied by the receiving antenna 3 and the signal supplied by a coupler 5 which takes a fraction of the signal from the oscillator 1. After removal of the DC component by means of 'a resistor 6 and a capacitor 7, this beat signal is supplied as signal Se to a terminal 8. In a known manner terminal 8 is connected to a first signal processing chain Se intended to activate the trigger 9 the rocket's ignition circuit 11 after a variable time τ †, as described in more detail below. The first chain comprises in cascade between terminal 8 and a terminal 10 a bandpass filter 12, an amplifier 13, a terminal 14, a threshold circuit 15, a pulse counter 16 and the trigger 9. The filter 12 and the amplifier 13 are for example constituted by operational amplifiers. The filter 12 allows signals of frequencies typically between 50 Hz and 300 Hz to pass, to fix ideas, that is to say the range of Doppler frequencies expected for the shell on its arrival on the ground, depending on its speed and its angle d incidence for a given given frequency of the transmitted wave. The threshold circuit 15 can be produced by means of a transistor or an operational amplifier. The pulse counter 16 which has the essential function of establishing the time _T1 is for example an analog counter as described below in detail with reference to FIG. 5. The trigger 9 can be a Zener diode. The priming circuit 11 shown inside a broken line comprises, between a terminal of ali electrical mentation 17 and ground a first time delay circuit constituted by the series connection of a resistor Rn and of a capacitor Cn which define a charging time Tn = RnCn. The common point 18 with the elements Rn and Cn is connected to a trigger circuit 19, for example a suitably biased transistor, which in turn supplies a second timing circuit only when a predetermined voltage threshold is reached at point 18. The second time delay circuit consists of the series connection of a resistor Ra of a connection point 22, and of a capacitor Ca connected to ground via the primer AM. Furthermore, point 22 is connected to ground by the parallel connection of the cathode anode path of a thyristor Q, the trigger of which is connected to terminal 10 and of an electromechanical target switch 24. The power supply on the terminal 17 and at other points of the circuit is carried out in a known manner not shown, for example by means of a battery whose electrolyte is released under the effect of the shock from the shell. After a time Tn of the order of 9 seconds, fixed by the values of Rn and Cn, the capacitor Ca in turn charges through the resistor Ra and the voltage at point 22 rises to a value such as a sudden discharge of the capacitor C _A , at this voltage value, through the primer AM alone would suffice to ignite the latter, voltage value which is obtained after a time Ta, from order of a second, which is added to the time Tn. In summary, the ignition of the primer AM can only be obtained after a time Tn + Ta of the order of 10 seconds after the departure of the shell either by triggering of the thyristor Q by the first chain, or by closing of the switch 24 obtained by percussion on the ground.

The operating principle of the counter 16, in its analog version is as follows: between two threshold overruns in the form of a pulse of the filtered and amplified signal Se, in the threshold circuit 15, a first capacitor of low capacity is charged under a constant tension across a resistance, during the time the threshold is exceeded by the pulse; the charge of the first capacitor is transferred to a second capacitor of high capacity. Furthermore, the second capacitor is shunted by a reset resistor which provides continuous progressive reset of the second capacitor. In FIG. 1, this continuous progressive reset is symbolically represented by an automatic reset circuit 25. For threshold crossing pulses sufficiently close in time, the charge in discrete form of the second capacitor prevails over its continuous discharge and it is possible to size the elements of the pulse counter 16 so that a second voltage threshold capable of making the thyristor Q conductive is obtained after a predetermined number N of Doppler pulses exceeding in amplitude a first threshold, at 15, the Doppler pulses taken into account and for example the number of N = 5 being close enough that the charge of the second capacitor clearly outweighs its discharge. The time _T i previously defined can therefore be expressed in the form:
_T1 ⁼ N _T
τ designating the period of the signal at the Doppler frequency for the shot considered. To fix the ideas, the period _T typically corresponds to an altitude difference of 1 m on the final trajectory part of the projectile. Since the amplitude of the echo signal increases very strongly upon arrival on the ground, this results in an envelope of substantially hyperbolic shape of the beat signal in the last twenty or thirty meters of the trajectory. The threshold circuit 15 is for example adjusted so that the threshold is exceeded, for the target signal, from an altitude of 15 m at time tio. From the above, it follows that the launching of the rocket will take place five meters lower, that is to say at the nominal altitude of 10 m, at time t ₁₁ (τ ₁ = t ₁₁ - tio = 0.1 s).

Still under the known prior art, the proximity rocket shown in FIG. 1 may include a second anti-jamming chain which receives the signal present on terminal 8. This second chain comprises for example a bandpass filter 27, an amplifier 28 and a threshold circuit 29. The output of circuit 29 is connected to an input 31 of the pulse counter 16 to shunt, in the latter, the reset resistance to cause a sudden reset of the second capacitor, this which causes inhibition of the triggering of thyristor 10. The circuits 27, 28 and 29 can be of the same structure as the homologous circuits 12, 13 and 15 of the first chain but their settings are different and the band (s) bandwidth (s) of filter 27 must be separated from the bandwidth of filter 12 in order to avoid inhibition of the triggering of thyristor Q on arrival at the ground of the projectile.

According to the invention, an additional chain, which receives the signal Se on terminal 8 in the same way as the first and second chains, has the function of specifically counteracting the radio interference produced by the operation of the RDTC device when the projectile is fired. This additional chain comprises in cascade a bandpass filter 32, an amplifier 33, first and second delay means 34, a threshold circuit 35 and a decision circuit 36 whose output 37 is provided for controlling one or more elements of the first chain or starting circuit 11 of the rocket. The pass band of the filter 32 includes that of the filter 12 and has substantially the same lower terminal as the latter. This bandwidth is for example 50 to 1500 Hz, half of the energy being concentrated at the lowest frequencies which are also the Doppler frequencies, ie between 50 and 350 Hz. The amplification rate of the amplifier 33 is comparable to that of amplifier 13. The first and second delay means which bring a delay T ₁ to the appearance and a delay T ₂ to the disappearance of the signal RDTC are represented ted in Figure 1 symbolically by a resistor and capacitor network, the durations T ₁ of the order of 2 s and Tz, of the order of a few seconds and fairly widely variable depending on the type of projectile, which must be able to be set independently of each other. According to the arrangement of FIG. 1, the time Ti is established by the series connection, from the output of the amplifier 33, of a diode 35 in the passing direction, of a resistor Ri and of a capacitor Ci of which an armature is connected to ground. Furthermore, a resistor Rj is connected between the point common to the diode 35 and to the resistor Ri and the ground, so that the capacitor Ci discharges through the series connection of the resistors Ri and Rj, this circuit being isolated, upstream, by the diode 35. The precise function fulfilled by the implementation of the delays T ₁ and T ₂ is explained below with reference to FIG. 2. For example, the threshold circuit 35 is produced by a Zener diode whose reverse conduction voltage sets the desired voltage threshold and the decision circuit 36 by a transistor which is turned on when this reverse voltage is exceeded, so as to connect, in substance, the output conductor 37 to ground , situation in which the output signal S _d on the conductor 37, said in the logic state "1", activates at least one element of the ignition circuit 11 of the rocket or at least one element of the first chain to inhibit totally or partially the firing of the pr rocket approximation. Total inhibition is indicated, in FIG. 1, by dashed lines 38, 39, 41, 42 which respectively connect the conductor 37 to a voltage-controlled switch 43 or to a voltage-controlled switch 44, or to the trigger 9, or even at input 31 of the pulse counter 16 either directly or, in the presence of a second chain, via an OR logic gate circuit 45, another input of which is connected to the output of the threshold circuit 29 when there is a second anti-jamming processing chain. Voltage-controlled switch 43 is connected between point 18 and mass. The state 1 of the signal S _d can thus cause the closing of the switch 43 which inhibits the operation of the first time-delay circuit by preventing the charging of the capacitor Cn. Similarly, the voltage-controlled switch 44 is connected between ground and terminal 22 with a series resistance of high value 46, so as to inhibit the operation of the second time delay circuit by closing the switch 44 when the signal S _d is in state 1. The line 41 symbolizes for example the fact of directly connecting the terminal 10, that is to say the trigger of the thyristor Q to maintain the latter in the non-conducting state and the line 42 a, on the counting circuit 16 , the same authoritative reset effect as the second channel, when the latter exists. In FIG. 1, the partial inhibition of the triggering of the proximity rocket is indicated by dashed lines 47, 48, 49 which respectively connect the conductor 37 to the amplifier 13, to the threshold circuit 15 or to the counter d pulses 16. When the signal S _d is in state 1, it is thus possible to reduce the gain of the amplifier 13 or to increase the level of the threshold in the circuit 15, in a manner known per se, or to modify the count in the pulse counter 16 as described below with reference to FIG. 5.

In Figure 2 there is shown at a the signal Se present on terminal 8 of Figure 1 for which there are, in chronological order, four phases identified on the time axis of Figure 2b: the main phase of RDTC between instants to and t ₃ and which lasts from 20 to 40 seconds; the so-called re-ignition phase between t ₃ and t ₄ which is that during which the RDTC device, theoretically extinguished by disappearance of the combustible material, can still possibly function sporadically; the phase between t ₄ and t ₁₀ during which the RDTC device no longer works and the target signal is not yet noticeable; then the final phase between t ₁₀ and t ₁₁ already described above during which the target signal is taken into account by the pulse counter 16.

FIG. 2c characterizes the operation of the proximity rocket in so-called percussive emergency mode. Between the instants to and t ₂ , t ₂ being before t ₃ the two timing circuits of the priming circuit 11 prevent any explosion, the capacitor C _A not yet being sufficiently charged, which is symbolized in FIG. 2c by a logical level "0". After the instant t ₂ , the percussion on the ground of the projectile causes the explosion by triggering of the electromechanical target switch 24, which is symbolized by the logic level 1.

In FIG. 2d, we find the phase of total inhibition between to and t ₂ , reinforced if necessary by the total or partial inhibition provided by the additional chain between the instants t ₁ and t ₂ , the instant t ₁ prior to t ₂ being that for which the signal S _d goes from state 0 to state 1, with: t ₁ - to = T _l . The phase between t ₂ and t ₄ is that during which the signal S _d is in state 1, the inhibition due to the timing circuits being lifted, which is symbolized by logic level 1, this phase ending with the re-ignition phase from t ₃ to t ₄ whose duration t ₄ - t _{3 is} identified with the delay T ₂ insofar as it is possible to accurately estimate the duration t ₄ - t ₃ which is linked to the type of projectile considered. For safety, one can choose the duration T ₂ greater than the estimated duration t ₄ - t ₃ , this being true especially for projectiles whose shooting angle is high. On the other hand, for projectiles whose re-ignition phase is short and / or for which the firing angles are small, the delay T _{2 should be set} at a low value, to increase the probability of the projectile reaching the ground after l 'instant t ₄ i.e. at an instant when the additional chain no longer inhibits the operation of the first chain and when the operation of the rocket proximity is nominal, which is symbolized by a logic level 0 in FIG. 2d. The duration T ₂ is for example between 3 s and 10 s.

FIG. 3 represents a particular embodiment of the invention according to which is used, in addition to the first chain, a first auxiliary processing chain, constituted, like the first chain, by the cascading of a bandpass filter 52 , an amplifier 53, a threshold circuit 55, a pulse counter 56 and a trip device 59. The first chain and the first auxiliary chain are connected to terminals 8 and 10 by means of two-position switches 60 and 61 of so that when the signal S _d on the conductor 37 is in state 1, the first auxiliary chain is connected to terminals 8 and 10, the first chain not being connected, as shown in the figure, the position of the switches 60 and 61 being inverted when the signal S _d is in state 0. The first auxiliary chain can have a structure identical to that of the first chain but its organs are adjusted so as to be less sensitive to a signal at Doppler frequency than those of e the first chain. In particular, the filter 52 can be more selective than its homogoque 12 so as to improve the signal to noise ratio; amplifier 53 may have a lower gain than that of amplifier 13; the threshold voltage can be higher at 55 than at 15, the greater counting at 56 than at 16. The switches 60 and 61 can be produced simply by means of transistors. Furthermore, it is clear that it is not essential to switch entirely from the first chain to a first complete auxiliary chain, only one organ or a group of organs from the first chain can also be switched to homologous organs whose settings are different.

FIG. 4 shows how it is possible to use certain members in common for the first processing chain and the additional chain. These organs are the bandpass filter 62 and the amplifier 63. It will be noted that if the gain of the amplifier 63 is not optimal either for the first processing chain or for the additional chain, it is always possible to compensate for this slight defect by an adequate adjustment of the organs located downstream in one or the other of these two chains. In the embodiment shown in FIG. 4, the additional chain acts on the first processing chain by modifying the count in the pulse counter 16 as explained in more detail below with reference to FIG. 5.

en négligeant le courant de fuite de C₂ à travers R₃. La présence de 1a résistance R₂ à la place d'une diode permet d'obtenir des accroissements de charge de C₂ sensiblement égaux, à chaque impulsion, au lieu d'une variation en progression exponentielle, de façon qu'après un nombre prédéterminé N d'accroissements de charge, c'est-à-dire d'impulsions de dépassement de seuil en 14, la tension de conduction en inverse de la diode D₁ soit dépassée, ce qui a pour effet de débloquer le thyristor Q. Ce nombre N est par exemple choisi égal à 5. Il est possible de faire varier légèrement la valeur de N en modifiant légèrement un ou plusieurs parmi les paramètres suivants : valeur de C₁, C₂, R₂, R₃ et tension inverse de D₁. Le signal de sortie du circuit à seuil 29 de la deuxième chaine de traitement est fourni à la base de T₃ pour rendre conducteur ce transistor et provoquer ainsi la décharge quasi instantanée du condensateur C₂. En présence de signaux parasites pour lesquels les dépassements de seuil sont irréguliers et en moyenne nettement plus espacés dans le temps que ceux qui sont dus au signal de cible, la décharge de C₂ à travers R₃ l'emporte sur la charge et le seuil de tension inverse de D₁ ne peut en général pas être atteint. Pour des signaux parasites de type RDTC, par contre, la fréquence des impulsions de dépassement de seuil, en 14, peut être suffisante pour que, la charge de C₂ l'emportant sur sa décharge, la tension inverse de D₁ soit atteinte, au bout d'un nombre indéterminé de dépassements de seuil en 14, ce qui provoquerait un déclenchement intempestif de la fusée de proximité. Pour éviter ce défaut, on a prévu qu'un tel signal RDTC parasite provoque l'augmentation du comptage N. A cet effet, la chaîne supplémentaire comporte, en aval 4e l'amplificateur 33, ou 63 à partir d'une borne 66, un circuit comparable à celui qui est décrit ci-dessus pour la première chaîne, soit un condensateur C₂₀ de suppression de la composante de tension continue, un amplificateur différentiel AD qui remplit une fonction analogue à celle du transistor T₁ et dont l'entrée inverseuse qui constitue un seuil est convenablement polarisée au moyen de résistances Rs et R₆, des condensateurs C₁₁ et C₁₂, des résistances R₁₂ et R₁₃, un transistor T₁₂ et une diode Zener D₁₁ homologues respectivement des compostants C₁, C₂, R₂, R₃, T₂ et D₁. Cependant, la fonction assurée par ce dernier circuit est différente et ne consiste pas à proprement parler en un comptage mais en l'établissement d'un signal, au-delà d'un certain seuil, ayant un retard T₁ à l'apparition et un retard T₂ à la disparition. Le retard T₁ est obtenu au moyen de la pompe à transistor T₁₂ et résistance R₁₂ par transfert de charges entre C₁₁ et C₁₂, la fonction de seuil est assurée par la diode Zener D₁₁ dont l'anode est reliée à la base du transistor T₄ et à la masse par l'intermédiaire d'une résistance R₁₅. La décharge de C₁₂ à travers D₁₁ et R₁₅ définit le retard T₂. Ce dernier circuit est réglé de façon telle que le signal RDTC provoque le déblocage du transistor T₄, ce qui a pour effet de faire baisser la tension du point A, à l'état bloqué du transistor T₁, de la valeur Vo à la valeur R₄ R₁ + R₄ Vo, par Vo exemple la valeur 2 = 15 volts si les valeurs de Ri et R₄ sont égales. Ceci entraîne qu'à chaque transfert de charge de Ci à C₂, la quantité d'électricité transmise est plus faible, par exemple dans un rapport de 1 à 0,5 en comparaison du fonctionnement précédemment décrit. Pour le signal de cible, ceci se traduit par une valeur de N doublée. Physiquement, ceci signifie, pour une arrivée au sol du projectile en phase RDTC, qu'au lieu d'un comptage d'impulsions Doppler compris entre 15 m et 10 m au-dessus du sol avec explosion à la hauteur nominale de 10 m du projectile on obtient dès lors un comptage d'impulsions Doppler compris entre 15 m et 5 m avec explosion à la hauteur réduite de 5 m, à raison d'une période Doppler par mètre de dénivelé. On notera que dans cette hypothèse de présence simultanée de signal de cible et de signal parasite RDTC, des impulsions parasites de dépassement de seuil peuvent se glisser entre des impulsions de dépassement de seuil dues au signal de cible, ce qui réduit d'autant le temps de déclenchement de la fusée, compté à partir de l'instant t₁₀ marquant la première impulsion comptabilisée due à la cible, et donc qui rapproche d'autant le fonctionnement comportant une action de la chaîne supplémentaire, du fonctionnement nominal de la première chaîne seule. Par exemple, pour 3 impulsions parasites interdigitées parmi 7 impulsions de cible et qui seraient toutes trois prises en compte, l'explosion en proximité pendant la phase RDTC se produirait à : 15 - 7 = 8 m au-dessus du sol et on peut faire en sorte qu'une telle fréquence d'impulsions parasites soit insuffisante pour provoquer à elle seule l'explosion, en augmentant suffisamment la valeur de la résistance R₃.FIG. 5 represents the part of the first processing chain and the part of the additional chain located downstream of the filter 12 (respectively 32, 62) and of the amplifier 13 (respectively 33, 63). Terminal 14 is connected to the base of an NPN transistor T ₁ via a capacitor C ₁₀ which has the function of removing the DC component of the voltage signal on terminal 14. The base of transistor T ₁ is connected to the supply terminal 65 at the positive voltage Vo, for example equal to 30 volts, by a bias resistor of adjustable value R ₁₀ . The transmitter of T ₁ is connected to ground and its collector at a point A which is itself connected on the one hand to the supply terminal 65 by means of a resistor R ₁ on the other hand to a capacitor Ci, the other armature of which is connected to terminal 65 via a resistor R ₂ and to the emitter of a PNP transistor T ₂ , the base of which is connected to terminal 65. The collector of T ₂ is connected on the one hand to ground by the parallel connection of a capacitor C ₂ , a resistor R ₃ and the collector-emitter path of an NPN transistor T ₃ , on the other hand to the cathode of a Zener diode D ₁ . Furthermore, point A is connected, via a resistor R ₄ to the collector-emitter path of a transistor T ₄ which is supposed to be blocked at first. The circuit consisting essentially of the elements Ti, R ₁ , C ₁ , R ₂ , T ₂ , C ₂ , is a charge transfer circuit, known under the name of transistor and diode pump, unlike close that in this assembly the diode is replaced by resistor R ₂ . As long as a predetermined negative voltage threshold on terminal 14 is not exceeded, the transistor T ₁ is conductive and the capacitor Ci is charged at the voltage Vo through the resistor R ₂ , the charge of the capacitor C ₂ being zero , and the transistor T ₂ is blocked. When the threshold is exceeded for the first time and for the entire duration of the electrical angle of the overshoot pulse beyond the threshold, the transistor T ₁ is blocked, there is a voltage offset equal to Vo on the two armatures of C ₁ , T ₂ becomes conductive and the charge from C ₁ is transferred to C ₂ , so that the voltage on the armature of C ₂ connected to the collector of T ₂ goes from the zero value to the value:
Ci Vo VS ₂ Ci and C ₂ also designating the respective capacities
of the capacitors C ₁ and C ₂ and being in a ratio of the order of 1 to 10. Between two successive pulses of threshold crossing C ₁ is charged again and C ₂ is discharged through R ₃ , which constitutes the discount at continuous progressive zero of the pulse counter 16. The operating cycle described above is repeated for each pulse exceeding the threshold and the states of charge of C ₂ , for sufficiently close pulses such as those due to the target signal are substantially equal to:

neglecting the leakage current of C ₂ through R ₃ . The presence of the resistor R ₂ in place of a diode makes it possible to obtain substantially equal increases in charge of C ₂ , with each pulse, instead of a variation in exponential progression, so that after a predetermined number N of charge increases, that is to say of threshold crossing pulses at 14, the reverse conduction voltage of the diode D ₁ is exceeded, which has for the purpose of unblocking the thyristor Q. This number N is for example chosen equal to 5. It is possible to vary the value of N slightly by slightly modifying one or more among the following parameters: value of C ₁ , C ₂ , R ₂ , R ₃ and reverse voltage of D ₁ . The output signal of the threshold circuit 29 of the second processing chain is supplied to the base of T ₃ to make this transistor conductive and thus cause the almost instantaneous discharge of the capacitor C ₂ . In the presence of spurious signals for which the threshold overshoots are irregular and on average significantly more spaced in time than those due to the target signal, the discharge of C ₂ through R ₃ outweighs the charge and the threshold the reverse voltage of D ₁ cannot generally be reached. For parasitic signals of RDTC type, on the other hand, the frequency of the threshold-crossing pulses, at 14, may be sufficient so that, the charge of C ₂ prevailing over its discharge, the reverse voltage of D ₁ is reached, after an indefinite number of threshold overruns in 14, which would cause an unwanted triggering of the proximity rocket. To avoid this fault, provision has been made for such a parasitic RDTC signal to cause the counting N to increase. For this purpose, the additional chain comprises, downstream of the amplifier 33, or 63 from a terminal 66, a circuit comparable to that described above for the first chain, namely a capacitor C ₂₀ for removing the DC voltage component, a differential amplifier AD which performs a function similar to that of transistor T ₁ and whose input inverter which constitutes a threshold is suitably polarized by means of resistors Rs and R ₆ , capacitors C ₁₁ and C ₁₂ , resistors R ₁₂ and R ₁₃ , a transistor T ₁₂ and a Zener diode D ₁₁ homologous respectively of the compostants C ₁ , C ₂ , R ₂ , R ₃ , T ₂ and D ₁ . However, the function provided by this latter circuit is different and does not strictly speaking consist of counting but of establishing a signal, beyond a certain threshold, having a delay T ₁ on the appearance and a delay T ₂ at disappearance. The delay T ₁ is obtained by means of the transistor pump T ₁₂ and resistance R ₁₂ by transfer of charges between C ₁₁ and C ₁₂ , the threshold function is provided by the Zener diode D ₁₁ whose anode is connected to the base of transistor T ₄ and to ground via a resistor R ₁₅ . The discharge of C ₁₂ through D ₁₁ and R ₁₅ defines the delay T ₂ . The latter circuit is adjusted so that the RDTC signal causes the transistor T _{4 to be} unblocked, which has the effect of lowering the voltage of point A, in the blocked state of transistor T ₁ , from the value Vo to the value R ₄ R ₁ + R ₄ Vo, for example Vo the value 2 = 15 volts if the values of Ri and R ₄ are equal. This results in each charge transfer from Ci to C ₂ , the quantity of electricity transmitted is lower, for example in a ratio of 1 to 0.5 in comparison with the previously described operation. For the target signal, this results in a doubled value of N. Physically, this means, for an arrival on the ground of the projectile in RDTC phase, that instead of a Doppler pulse count between 15 m and 10 m above the ground with explosion at the nominal height of 10 m from projectile we then obtain a Doppler pulse count between 15 m and 5 m with explosion at the reduced height of 5 m, at the rate of a Doppler period per vertical drop. It will be noted that in this hypothesis of simultaneous presence of target signal and parasitic signal RDTC, parasitic pulses of threshold crossing can slip between pulses of threshold crossing due to the target signal, which reduces the time accordingly triggering of the rocket, counted from time t ₁₀ marking the first recorded pulse due to the target, and therefore which brings the operation comprising an action of the additional chain all the closer to the nominal operation of the first chain only . For example, for 3 parasitic pulses your interdigitated among 7 target pulses and which would all be taken into account, the explosion in proximity during the RDTC phase would occur at: 15 - 7 = 8 m above the ground and we can make such that the frequency of parasitic pulses is insufficient to cause the explosion alone, by sufficiently increasing the value of the resistance R ₃ .

The values of certain components of FIG. 5 are for example the following:

It will be noted that the ratio C ₁₂ C ₁₁ , of the order of 200, is much higher than the ratio C ₂ C ₁ , of the order of 10. This corresponds to the fact that two hundred RDTC pulses are necessary for the establishment of the delay T ₁ of the order of 2 s whereas the time τ ₁ of counting from five to ten pulses of exceeding the threshold at 14 takes place in approximately 0.1 s.

It will be noted that the differential amplifier AD is not essential and that terminal 66 could be connected directly to the capacitor C ₁₁ , with slight modifications to the part of the circuit located downstream to compensate for the fact that the load of C ₁₁ does not then takes place more under constant tension. It is also possible to replace the resistor 12 with a diode. Furthermore, the differential amplifier AD could be replaced by a transistor and the transistor T ₁ by a differential amplifier.

The invention is not limited to an analog embodiment because the different channels can also perform digital processing of the signal Se, in particular for counting N and establishing the delay times Tt and T ₂ .

Claims (8)

1. Proximity rocket for artillery projectiles of the aerodynamic base drag reduction type comprising a radar device for providing at the output of a mixer a subtractive beat signal Se between emitted wave and reflected wave on the one hand a first processing chain intended to activate the trigger of the ignition circuit of said rocket after a time _'1 , variable, of the order of a tenth of a second, after said amplified and filtered beat signal has exceeded a certain number of times a certain threshold, on the other hand to a second anti-jamming chain having band pass characteristics different from those of the first chain, characterized in that it also comprises an additional chain intended to counteract the effect caused in said first chain by the electromagnetic disturbances due to the reduction in the aerodynamic drag of the base, that said additional chain has filtering characteristics bandpass, amplification and threshold crossing by said beat signal comparable to those of said first chain, that the output signal of the additional chain is transmitted to inhibition means to partially or totally inhibit, by l intermediary of said first chain or of said priming circuit, the triggering of the rocket, and that said additional chain comprises first delay means which delay the appearance of said output signal, relative to the input signal, a time τ † as well as second delay means for maintaining said output signal from the additional chain for a time T ₂ of the order of a few seconds after said beat signal Se amplified and filtered has ceased to exceed the threshold of the extra chain. 2. Proximity rocket for artillery projectile comprising in cascade first and second timing circuits of the priming circuit and the first chain of which, in cascade following said mixer, comprises a bandpass filter, an amplifier, a circuit with threshold and a counter of continuous progressive reset pulses and said trigger according to claim 1. 3. Proximity rocket for artillery projectile according to claim 2, characterized in that said additional chain comprises in cascade a bandpass filter, an amplifier, said first and second delay means, a threshold circuit and a decision. 4. proximity fuse for artillery projectile according to claim 3, characterized in that said bandpass filter and said amplifier of the additional chain are identified respectively with the bandpass filter and with the amplifier of said first chain. 5. Proximity rocket for artillery projectile according to claim 2 or 3, characterized in that said inhibition means control, in order to totally inhibit it, at least one of the following organs: first timing circuit, second timing circuit, trip unit, pulse counter. 6. Proximity rocket for artillery projectile according to claim 2 or 3, characterized in that said inhibition means control, in order to partially inhibit it, at least one of the following organs: amplifier, threshold circuit , pulse counter. 7. Proximity fuse for artillery projectile with partial inhibition of the pulse counter by the additional chain, in which said pulse counter consists of a charge transfer circuit between a first and a second capacitor, according to claim 6, characterized in that said output signal from the additional chain acts as inhibition means, on said first capacitor, to reduce the charge transfer of the latter on the occasion of each threshold crossing in the circuit at the threshold of the first chain. 8. Proximity fuse for artillery projectile according to one of claims 1 to 3, characterized in that it further comprises a first auxiliary chain or a part of first auxiliary processing chain less sensitive to said beat signal than said first chain, and that said inhibition means are constituted by two electronic switches which make it possible to substitute for said first chains said first auxiliary chain.

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