EP0083280B1 - Decoy means for electromagnetic detectors - Google Patents

Abstract

A rope is pulled between an end member such as a parachute forming a sail with regard to the wind and a main floating anchor located at the other end. This rope is connected at chosen intervals to captive-balloons, each associated with secondary floating anchors. The captive-balloons are chosen to be sensitive to the wind in order to incline themselves with respect to the floating anchor and to respectively support decoys formed by sets of retroreflective trihedrons. Advantageously, the decoys are individually connected in their lower part to floating bodies such as slightly inflated and loaded balloons. The invention has application, in particular, to the simulation of large surface ships.

Description

The present invention relates to electromechanical decoys.

Missile weapon systems are often equipped with active electromagnetic detector guidance, such as radar or laser. The same is true for fire lines, which can also be controlled from information obtained by detectors of the same kind. In such a case, the main defense consists in developing a decoy likely to deceive the electromagnetic detector, in order to remove it from the real objective, of which it must completely lose track.

The main type of electromagnetic lure used so far is based on metallized glass fiber flakes of selected length, often referred to as "chaffs". These flakes form a reflector for a wavelength which is linked to their size. They also have the property of remaining suspended in the air for a long time, being very light. Therefore, by creating a fairly dense cloud of glitter of this type, of various lengths chosen, we manage to create a strong electromagnetic echo, which makes it possible to simulate a target, and consequently to remove the threat from the real target. Although this type of lure has proven to be very useful, it presents problems in application. Indeed, the active electromagnetic detection means tend to become increasingly fine, and therefore to be capable of at least embryonic recognition. It is then very difficult with glitter clouds to obtain a desired shape, and above all to maintain it over time. The object of the present invention is in particular to provide a new solution to this problem, which is essentially a problem of credibility, accompanied by other technical problems which will be mentioned below.

Basically, the present invention provides a method for decoying active electromagnetic detectors, which method can be used in particular for the protection of surface ships at sea and comprises the implementation of at least one set of retro-reflective trihedra, this set of trihedrons comprising a network of contiguous trihedrons mounted head to tail.

The use, for decoying an active electromagnetic detector, of a decoy comprising at least one panel of honeycomb structure defining a network of identical, adjoining retro-reflective trihedra, arranged head to tail in adjacent rows, has already been recommended in US-A-4,096,479 which describes three lures thus formed; however, these three known lures have drawbacks.

Two of these known lures, illustrated in FIGS. 1 and 3 of US Pat. No. 4,096,479, have the form of a panel on which the retro-reflective trihedra are defined by cells all oriented in the same direction, that is to say that is to say towards the rear of the panel as illustrated, so that this panel is not reversible in the sense that it does not have the same geometry of its cells on its two faces and, therefore does not present the same image to detection means according to its face turned towards the latter; moreover, the simulation of a surface ship at sea means that this panel must be given large dimensions, which poses major problems of storage on board and of implementation, even when the panel can be rolled up like this. is the case for one of these two lures.

The third of these known lures, illustrated in FIG. 2 of US-A-4,096,479, has the form of a rigid polyhedral assembly of panels on which the retro-reflective trihedra are also defined by cells all oriented in the same sense, that is to say towards the interior of the assembly so that each panel in itself is not reversible; this third known lure can only present the same image to detection means regardless of the face it presents to them because of its polyhedral shape, placing the panels back to back, that is to say at the cost of 'A volume that must be large if we want to credibly simulate a surface ship at sea, with the difficulties of storage on board and implementation resulting.

The present invention also overcomes the drawbacks of the decoys described by US-A-4,096,479 in that it proposes a decoy for an active electromagnetic detector, comprising at least one panel of cellular structure defining a network of identical retro-reflective trihedra. , contiguous, arranged head to tail in adjacent rows,

characterized in that the contiguous retro-reflecting trihedra are oriented alternately towards the front and towards the rear of the panel in each row and from one row to another, and in that said rows are articulated mutually around axes of relative pivoting, so that the rows of retro-reflecting trihedrons can be folded over one another with mutual interlocking of the retro-reflecting trihedrons from one row to the other. This possibility of folding with interlocking of the lines of trihedrons on each other makes it possible to store them in very compact form, inside a launch munition, as will be seen below.

We already know the retro-reflecting properties of trihedra for electromagnetic radiation. The trihedrons, also known as "cube corners", are used in particular in telemetry. In optics, the most common embodiment is based on glass. Indeed, an extremely precise surfacing is necessary, surfacing which was accompanied by the obtaining of sharp edges.

Quite unexpectedly, the Applicant has observed that the trihedra also function satisfactorily when the edges of the trihedrons are not sharp but rounded. This feature facilitates the practical realization of the sets of aforementioned retro-reflective trihedra.

The electromagnetic decoy has a reversible honeycomb structure, at least part of the hollow cells being provided with a reflective coating in the shape of a trihedron.

The structure is advantageously made of plastic material injected or cast under pressure, or alternatively of stamped light alloy sheet.

Another embodiment, also very advantageous, of said structure, consists of pouring an epoxy resin under vacuum onto a fiberglass fabric placed between two optical surfacing molds, the molds further comprising a reflective coating which is transferred. on the resin after molding.

The present invention also provides a method for decoying active electromagnetic detectors, characterized in that it uses at least one decoy according to the invention.

The present invention provides in particular a method for defending surface ships, a method which therefore applies at sea, and which consists in deploying at least one lure of the aforementioned type at an altitude of between 3 and 20 meters approximately. For their part, the elementary trihedra, which are preferably identical, have an edge which measures between 2 and 20 cm.

With a lure, you can simulate a small vessel.

Another aspect of the invention proposes an improved method, capable of simulating a large vessel, and according to which a substantially horizontal alignment of interconnected lures is developed. At least one of the lures comprises two substantially perpendicular panels. A practically isotropic retro-reflection property is thus obtained, with however small areas of shadow which in themselves are interesting: they indeed allow, when the two panels rotate together on themselves, to present variations. This prevents the lure from being recognizable by the fact that it reflects emissive electromagnetic radiation too perfectly.

In a particular embodiment of this method, the lure (s) are suspended from respective captive balloons.

It can be a pendulum suspension, the captive balloon being connected on its side to a floating anchor. These balloons are preferably chosen shaped to link their aerostatic thrust to an aerodynamic lift in the wind encountered.

One can also provide, in an interesting variant, means for urging the lures downwards, these means possibly advantageously comprising a member capable of dragging on the water, of the slightly inflated balloon type. The connection between the captive balloon carrier and the lower balloon, or simply the pendulum suspension of the lure to its captive balloon carrier, are in both cases arranged so that the lures can turn on themselves.

To simulate a large surface vessel, the suspensions of a certain number of lures are interconnected, using a rope, mounted between a towing member, which may be a device of the sail type, parachute for example, or even a gas generator, and a retaining member, which is a floating anchor which will be called main, because it is more important than the floating anchors connected to the individual carrying balloon.

In practice, three to ten lures thus aligned will be used, the ends advantageously comprising a single panel of trihedra, while the intermediaries comprise two, perpendicular.

• - la figure 1 est une illustration schématique d'un panneau de trièdres selon la présente invention;
• - les figures 2A et 2B sont des vues en coupe montrant comment les trièdres dudit panneau peuvent se replier les uns sur les autres pour former, en position de stockage, une structure compacte;
• - la figure 3 est une vue schématique en perspective montrant la mise en oeuvre d'un ensemble de leurres pour la simulation d'un bâtiment de surface;
• - les figures 4A à 4D montrent comment peut se faire le déploiement du leurre selon la présente invention à partir d'une roquette; et
• - les figures 5 et 6 montrent schématiquement l'implantation des différents éléments du leurre à l'intérieur d'un corps de roquette.

Other characteristics and advantages of the invention will appear on reading the detailed description which follows, given with reference to the appended drawings, given to illustrate without limitation a preferred embodiment of the present invention, and in which:

• - Figure 1 is a schematic illustration of a trihedral panel according to the present invention;
• - Figures 2A and 2B are sectional views showing how the trihedra of said panel can fold over each other to form, in the storage position, a compact structure;
• - Figure 3 is a schematic perspective view showing the implementation of a set of lures for the simulation of a surface building;
• - Figures 4A to 4D show how can be made the deployment of the lure according to the present invention from a rocket; and
• - Figures 5 and 6 schematically show the location of the different elements of the lure inside a rocket body.

FIG. 1 illustrates in the form of a shaded front view a panel of trihedra according to the invention. The panel is here composed of seven rows or lines of trihedra, denoted R1 to R7. Row R1 has three forward-facing trihedrons, supplemented by two rear-facing trihedrons. The first trihedron at the top and left, noted as a whole T1, consists of three orthogonal faces T11, T12 and T13, separated from each other by the edges A11, A12 and A13. This structure will be repeated for all the other trihedra. It will also be noted that the essential part of the trihedron in electromagnetic retroreflection, delimited by the equilateral triangle whose sides are C11, C12 and C13, is undeformable. Immediately adjacent to row R1 is the second row R2, which is composed of three rear-facing trihedrons interspersed with two forward-facing trihedrons. Row R3 takes up the structure of row R1, then row R4 that of row R2, and so on alternately until the row R7. We noted T2 and T3 the first trihedrons to the left of rows R2 and R3, T2 being oriented towards the rear and T3 towards the front. In the illustration of FIG. 1, the lower face of the trihedron T1 is presented in continuity with the upper face of the trihedron T2, which can in practice be achieved. However, according to the present invention, it is considered to be clearly preferable to provide pivot axes such as PA1, PA2 and PA3 between the different rows of trihedra, which makes it possible to fold them over one another, the cubes such as T1 , T2 and T3 fitting together as illustrated in FIGS. 2A and 2B. This will give an extremely compact structure. Of course, depending on the size of the trihedrons as well as the geometry of the available volume, it is possible to provide the pivot axis not between each of the rows, but between the rows taken two by two, or three by three, for example.

We can immediately see that the panel in Figure 1 has the reversible honeycomb structure already mentioned, of which at least part of the hollow cells is provided with a reflective coating in the shape of a trihedron.

As previously indicated, such trihedrons have already been used as retroreflectors in the context of optical measurements. For such applications, they are naturally given a very neat optical surfacing, the flatness being quite significant, as well as very sharp edges A11, A12 and A13. Under these conditions, whatever its orientation, the cube returns the incident electromagnetic radiation in the direction from which it comes.

One of the starting points of the present invention is the observation that the trihedra continue to function in a satisfactory manner for the production of electromagnetic lures, even if their edges A11, A12 and A13 are rounded. This allows first of all, under reasonable economic conditions, to manufacture trihedral panels of the type of that of FIG. 1.

Although the phenomenon has not yet been fully explained, it even seems that rounded edges contribute to the proper functioning of the device as a lure, by producing irregularities in the response of the lure according to its orientation, as well as in its response. to incident electromagnetic waves of any polarization.

It will naturally be possible to produce the lure panel of FIG. 1 from a structure made of injected plastic or die-cast, or even from a stamped light alloy sheet. To obtain a reflective coating of optical quality, the panel is metallized by an operation of the electroplating type, varnish with electrostatic aluminum deposition, or even vacuum metallization.

• - à l'intersection entre les trièdres T1 et T2, le point d'articulation est à gauche ;
• - à l'intersection entre les trièdres T2 et T3, le point d'articulation est à droite.

In the case of a light alloy sheet structure, the pivot axes such as PA1, ... may be produced by thin hinges of the piano hinge type. One will take care, according to the thickness of the material, as well as the shape of its cutout at the level of the hinges, to realize the points of articulation in a way allowing to ensure the proper folding. It will be noted that in the particular case of FIG. 2A, the point of articulation is alternately on one side then on the other:

• - at the intersection between the trihedrons T1 and T2, the articulation point is on the left;
• - at the intersection between the trihedrons T2 and T3, the point of articulation is on the right.

For a plastic structure injected or cast under pressure, the articulation can be produced in the same way, or even by insertion of a deformable material between the two blocks of plastic material.

In another embodiment, currently considered to be particularly advantageous, the structure is made of epoxy resin on fiberglass fabric.

More specifically, two homologous molds are provided, made of optical surfacing glass, the shapes of which correspond to the two sides of the panel in FIG. 1. The optical surfaces of these molds are previously provided with a suitable reflective coating, which is held in place. using medium strength glue. Between the two molds, we will make a fiberglass fabric, preferably using three interlaced bands. The first strip of fiberglass will pass over the faces such as T11 and T12, and will therefore follow the general direction of the rows R1, R2, ..., in the direction of the arrow F1. The second fiberglass strip will follow the faces such as T11 and T13, therefore taking the direction of the orientation diagonal F2 in FIG. 1. Finally, the third fiberglass strip will follow the faces such as T12 and T13, then taking the direction of arrow F3. We can immediately see that each face of the trihedron is defined by superposition of two parts of the aforementioned fiberglass strips. The strips are preferably cut to follow each time the staircase profile corresponding to the width of the individual trihedron. After having put in place between the two molds the fiberglass fabric thus defined, an epoxy resin is poured under vacuum between the molds. After polymerization, the epoxy resin retains the reflective coating, which adheres more to it than to the glass mold. Since the exterior surface of this coating has been defined by the optical surface of the mold, a reflective coating of optical quality is thus obtained directly on a structure molded in epoxy resin, which is also very solid given its fiber reinforcement. of glass.

The molding unit may have a size which depends on the position of the pivot axes. If a pivot axis is desired between each row of trihedrons, a mold will then be provided for a single row of trihedrons, which makes it possible to leave the area of the hinge point PA1 uncoated by the epoxy resin. We then obtain easily a hinge pin, which is based on the flexibility of uncoated fiberglass. We then start again, inverting the molds, for row R2, and so on. If on the contrary one wishes axes of articulation every two rows of molds, one will then have a mold of shape corresponding to the block of rows R1 and R2, with the homologous mold on the other side, the assembly being moved by simple translation. If the rigid base unit has three rows of trihedrons, the mold will be of corresponding shape. Again, you will have to reverse the molds each time.

We have seen, with reference to FIG. 1, that the most active part of a trihedron is delimited by the equilateral triangle C11, C12 and C13. In the context of the aforementioned molding, it is possible to limit the coating fixed beforehand on the mold to what corresponds to this useful part of the trihedron to be obtained. Similarly, one can also, before or after molding, wear on the retroreflective coating any design or modification which could be useful for the good realization of a lure, in particular with regard to the retroreflection of circularly polarized waves.

As a particular example of a structure made of injected or pressure-cast plastic, it is possible to use the materials known under the brands PLEXIGLAS or ALTUGLAS, equipped with a non-wetting reflective coating. Polycarbonates such as MAKROLON can also be used.

As an example of a light alloy sheet, aluminum may be used, optionally provided with a retroreflective coating, if necessary.

As an example of an epoxy resin, products of the kind known under the name of ARALDITE (registered trademark) can be used.

After describing the basic electromagnetic decoy, we will now move on to its implementation process. Although this process may, ultimately, use rigid trihedron panels, which may be different from each other, it will be assumed in the remainder of this description that each set of trihedra comprises at least one panel of adjacent lines of trihedrons articulated to pivoting on each other.

Furthermore, although the trihedra are susceptible of other applications, where they may possibly take network shapes other than the shapes of a panel, we will now assume that it is a surface ship defense in sea.

In its elementary version, the method for decoying active electromagnetic detectors consists in deploying at least one set of trihedra at an altitude of between 3 and 20 meters approximately.

Referring to FIG. 3, a set of trihedrons can be deployed using a captive balloon BC1, connected by wire to a floating anchor AFS1, and supporting the set of trihedra LT1, which is preferably biased downwards by a floating body BF1, which is advantageously a slightly inflated loaded balloon. The captive balloon BC1 preferably has a shape obtained by the intersection of two discs, which allows it to link the aerostatic thrust to an aerodynamic lift linked to the wind encountered. In this way, there will be traction of the captive balloon on the floating anchor, which allows the inclination of the rope, therefore the support of the LT1 lure without it coming to mix with the rope of the floating anchor. In the presence of the floating ball BF1, the LT1 lure is pulled down, and therefore it will be subjected essentially to pivoting movements on itself, movement whose angular speed is relatively random, being in particular related to the wind. In the presence of incident electromagnetic radiation, the intensity of the retroreflected radiation will be directly linked to the angle at which the incident radiation is seen by each of the trihedra. It therefore results from the aforementioned pivoting movement a component of random fluctuation in amplitude in response which is currently considered particularly important for obtaining a good lure. Indeed, the radar echo for example of a surface ship also has a fairly strong random component, at least for some of the areas of the ship.

In the case in particular of a captive balloon carrying in the wind, and which therefore strongly pulls on the rope which connects it to its floating anchor, one can envisage the elimination of the balloon BF1, in which case the lure LT1 is subjected not only to a pivoting on itself, but also on pendulum movements which still contribute to give a realistic character to the retroreflected signal.

In the hypothesis where a single set of trihedrons is used, it is in most cases desirable to use not a single panel such as LT1, but two panels inclined one on the other, as this is illustrated in LT2. Very advantageously, the two panels are substantially perpendicular, although a different inclination can be used in certain cases.

It has been observed that two substantially perpendicular panels, and connected by one of their long side, have a substantially isotropic reflection characteristic, with however small fluctuations, which seem to be due in particular to the fact that the edges of the elementary trihedra are rounded. Another advantage of using two trihedral panels at right angles is that the response in retro-reflection nevertheless varies with the angle, it being observed that one of the trihedral panels will more or less mask the active surface of the other. for certain orientations, when the incident radiation arrives via the concave side formed by the decoy.

In practical realization, starting from the panel of FIG. 1, it suffices to complete on one of the sides at least of the panel the gaps left between

the different rows of trihedrons so as to make a continuous line, which is practically the equivalent of the lines forming a pivot axis of the type PA1. And two panels of trihedra are then connected to each other, the panels being able to be produced at the same time by the molding process already mentioned, in which case the shape of the molds will take into account not only the pivot axes such as PA1, PA2, ..., but also with a pivot axis perpendicular in the vertical direction. The two panels thus interconnected will normally be stored flat, folded as shown in Figures 2A and 2B. During deployment, an automatic development device will separate the two panels, to bring them to the desired angle, while at the same time defining a means of suspension in line with the center of gravity of the lure, taking into account the angle between these two panels. This can be obtained in particular by a means of the spring-actuated compass type, or the like.

If we now consider it as a whole, Figure 3 develops a substantially horizontal alignment of interconnected set of trihedra. We recognize indeed the captive balloons BC1, BC2, BC3, BC4, the suspension ropes of which are interconnected by a main horizontal rope F substantially horizontal, connected on one side to a traction member OT which can be a sail, or a device gas discharge, or even more simply the parachute which will be used to lower the lure after its release. At its other end, the main rope F is connected to a main floating anchor AFP. Each balloon BC1 to BC4 is connected to its secondary floating anchor AFS1 to AFS4. Each of the balloons also receives a lure LT1 to LT4, a lure which is preferably biased downward either by a mass incorporated therein, or even by a floating balloon such as BF1 to BF4 of the type already mentioned.

Preferably, lures with one panel are provided at the ends, as shown here in LT1 and LT4, while at all intermediate levels, lures with two perpendicular panels are provided such as LT2 and LT3.

It has been observed that this arrangement reproduces in a very "credible" manner the "signature" of a large surface ship in electromagnetic radiation. We can naturally modulate this appearance by acting on the formats, distances and altitudes of the games of lures.

The fact that the lures used according to the present invention are endowed with an excellent retroreflection gives them a large "radar equivalent surface", which makes it possible to simulate, with devices of small real surface, suitably arranged in relation to one another, a ship whose physical dimensions are much larger. As previously indicated, the fact of using lures with two panels such as LT2 and LT3 at the intermediate levels makes it possible to increase the average level and to simulate the peaks of the signature of a building, these "peaks" being in themselves- same known in advance, while obtaining, as already indicated, a component of random fluctuation around these peaks.

On the contrary, it has been observed that the ends of a ship have a much more fluctuating radar echo, which is advantageously defined here by a single panel, the pivoting of which on itself will produce a fluctuation identifiable with that of the ship.

The presence of the rope F between the various suspended lures provides them on the one hand with a spacing which can be chosen optimally taking into account the "peaks" to be produced and the size of the resolution cells and of the active electromagnetic detectors. In addition, this line also ensures a certain correlation in the vertical positioning of the various suspended lures. Finally, the rope still provides a certain coupling between the movement of the lure and the movement of the sea surface, by the existence of the floating anchors AFS1 to AFS4.

According to another aspect of the invention, this component sensitive to the movement of the sea is greatly increased by the use of floating bodies such as slightly inflated balloons BF1 to BF4, which ensure a much more direct coupling between the level of the surface marine and lures LT1 to LT4. This may be desirable, at least for certain vessel sizes.

Apart from the case of a single lure, the minimum combination to define a vessel will preferably include two end lures such as LT1 to LT4 framing at least one two-panel lure such as LT2.

For the simulation of a large vessel, we can go up to 7 to 10 suspended lures, the end lures are again simple lures, while the intermediate lures, or at least most of them , are two-panel lures.

In the foregoing, it has been indicated that lures with two perpendicular panels are desirable because of their ability to respond in all directions, but with varying intensity depending on the angle. In cases where a more regular omnidirectionality is desired, one can use lures with three panels regularly distributed in star, or with four perpendicular panels, and so on.

A mode of implementation of the lure according to the invention will now be described with reference to FIGS. 4A to 4D.

As shown in FIG. 4A, the lure can be carried to the desired location by a rocket, which can be the SAGAIE rocket manufactured by the plaintiff, or by any other launching vehicle, such as those which are incorporated in the DAGAIE suitcases also manufactured by the plaintiff.

At the end of the trajectory, the launching vehicle releases an assembly constituted at the head of the floating anchor main AFP, suitably ballasted to start first and pull all the modules M4 to M1, followed finally by the rearward traction unit OT, which consists for example of a parachute capable of forming a sail (FIG. 4B ). Figure 4C shows the assembly in the landed position.

Each module such as M1 includes a captive balloon such as BC1, a floating anchor AFS1, and the folded lure such as LT1, possibly with the floating balloon BF1. The module is also completed with a connection sleeve between the APS1 floating anchor and the BC1 balloon, a sleeve which can also provide the mechanical connection between these two elements. The floating anchors can consist of bags capable of filling with water, and the secondary anchors such as AFS1 also comprise a chemical composition such as calcium hydride, capable of decomposing on contact with water to produce hydrogen, hydrogen which is transferred by said sleeve to the tethered balloon, which then inflates. We immediately understand that all the captive balloons will be thus inflated, and mounted together, thus lifting the rope, and thereby the lures. For its part, the OT parachute gains height, and ensures the final traction of the rope, if necessary. Initially folded, the lures unfold either by the fact that a mass has been added to them at the bottom, or under the action of the traction exerted by the cable which connects them to the floating body such as BF1. We then obtain the arrangement shown in Figure 4D, and which is similar to that of Figure 3, except the absence of floating bodies such as BF1, as well as the simplification of the intermediate lures. Advantageously, provision is made for a rolling of the gases which will be produced in each of the secondary floating anchors, before sending these gases to the balloon, so as to ensure sufficient cooling thereof. The reaction rate of calcium hydride with seawater can also be adjusted as desired to obtain characteristics of frank and progressive ascents of the captive balloons in the air.

In some cases, it will be possible to dispense with the main floating anchor AFP, in which case it is replaced by a simple drive mass to ensure the descent as shown in FIG. 4B.

Finally, the lure can be easily made self-destructing, by incorporating in each of the captive balloons a suitable delay charge, which will ensure the initiation of a reaction between the hydrogen of the balloons and the air, and consequently the explosion of these, the lure then falling back into the water as a whole, and becoming very difficult to detect.

It will also be observed that the non-wetting side of the surfaces of the reflecting trihedra makes them practically insensitive to the presence of sea water, as regards their retroreflection characteristics, at least for a sufficiently short time compared to their instant. of implementation.

The modules M1 to M4 can be contained in suitable envelopes, loose enough to be able to be broken when releasing the captive balloons.

Figure 5 shows how you can store the different modules side by side, alternately connecting the bottom of one with the top of the other, one end being connected to the parachute, and the other to the floating anchor .

Finally, FIG. 6 shows how the modules thus coupled can be introduced inside the body of a rocket, the different modules M1 to M4 occupying the respective sectors of the cross section of the rocket, while the parachute OT and the AFP floating anchor occupies the two ends of the rocket, possibly passing partly in the central zone of the latter.

It should be noted that the foldable side of the proposed electromagnetic decoys is important for their placement in the relatively narrow volume which is available inside a launch vehicle such as a rocket.

In the above, it was considered that the decoys were retroreflectors for electromagnetic radiation emitted by active detectors. These detectors can be of different types, radar, laser.

Of course, it is possible to adapt the characteristics of the reflective coatings as well as the geometry of the different trihedrons as required, and of the frequency bands concerned.

Of course, the present invention is not limited to the embodiment described, but extends to any variant in accordance with its spirit.

In certain cases, it may in particular be envisaged to deploy decoys not only in a main horizontal direction defined by the rope F, but also in the transverse direction. It will also be possible to provide sources forming infrared decoys complementary to the electromagnetic decoy obtained, so as to perfect the simulation. These sources can in particular be incorporated into the secondary floating anchors AFS1 to AFS4, or even to the floating bodies such as BF1 to BF4.

Claims (24)

1. Decoy for an active electromagnetic detector, comprising at least one panel of alveolar structure defining a system of contiguous, identical retro-reflective trihedrons (T1 to T3), arranged head to tail in adjacent rows (R1 to R7), characterised in that the contiguous retro-reflective trihedrons (T1 to T3) are orientated alternately towards the front and towards the rear of the panel in each row (R1 to R7) and from one row to the other and in that the said rows (R1 to R7) are pivoted mutually about relative pivot axes (P1 to P3), so that the rows (R1 to R7) of retroreflective trihedrons (T1 to T3) may be folded over one on the other with mutual nesting of the retroreflective trihedrons (T1 to T3) from one row (R1 to R7) to the other.

2. Decoy according to Claim 1, characterised by the fact that the edges (A11 to A13) of the trihedrons (T1 to T3) are rounded.

3. Decoy according to one of Claims 1 and 2, characterised by the fact that the edge (A11 to A13) of one trihedron (T1 to T3) measures between 2 and 20 cm.

4. Decoy according to one of Claims 1 to 3, characterised by the fact that the structure consists of plastics material injected or moulded under pressure.

5. Decoy according to one of Claims 1 to 3, characterised by the fact that the structure consists of a sheet of stamped alloy.

6. Decoy according to one of Claims 1 to 5, characterised by the fact that the retro-reflective trihedrons (T1 to T3) are metallized.

7. Decoy according to one of Claims 1 to 3, characterised by the fact that the structure consists of epoxy resin moulded under vacuum on a glass fibre fabric between two moulds having optical surfacing and a reflective coating transferred to the resin during moulding.

8. Decoy according to one of Claims 1 to 7, characterised by the fact that it comprises two of the said panels pivoted mutually about an axis in order to be able to be superposed flat or inclined one on the other and an automatic opening device forming a suspension in line with the centre of gravity.

9. Decoy according to one of Claims 1 to 8, characterised by the fact that it is incorporated in the folded state, with lift means comprising a captive balloon (BC1 to BC4), with launching ammunition/vehicle (R).

10. Method for providing decoys for active electromagnetic detectors, characterised by the fact that it uses at least one decoy (LT1 to LT4) according to one of Claims 1 to 9.

11. Method according to Claim 10, applicable at sea, characterised by the fact that it consists of deploying at least one decoy (LT1 to LT4) at an altitude comprised between approximately 3 and 20 metres.

12. Method according to Claim 11, characterised by the fact that a substantially horizontal alignment of interconnected decoys (LT1 to LT4) is opened out.

13. Method according to Claim 12, characterised by the fact that from 3 to 10 aligned decoys (LT1 to LT4) are provided, the ends comprising only one panel of trihedrons.

14. Method according to one of Claims 12 and 13, characterised by the fact that the formats, distances and altitudes of the decoys (LT1 to LT4) are chosen in order to imitate the signature of a ship.

15. Method according to one of Claims 11 to 14, characterised by the fact that the or each decoy (LT1 to LT4) is suspended from a respective captive balloon (BC1 to BC4).

16. Method according to Claim 15, characterised by the fact that the or each decoy (LT1 to LT4) is suspended to swing and that the or each captive balloon (BC1 to BC4) is connected to a floating anchor (AFS1 to AFS4).

17. Method according to one of Claims 15 and 16, characterised by the fact that the or each balloon (BC1 to BC4) is self-inflatable, preferably by the reaction of calcium hydride on sea water and the throttling of the gases produced towards the inside of the balloon.

18. Method according to one of Claims 15 to 17, characterised by the fact that the or each balloon (BC1 to BC4) is chosen with a conformation for linking its aerostatic thrust with an aerodynamic lift in connection with the wind encountered.

19. Method according to one of Claims 15 to 18, characterised by the fact that the suspensions of several decoys (LT1 to LT4) are interconnected to each other and between a pulling member (OT) and a main retaining floating anchor (AFP).

20. Method according to Claim 19, characterised by the fact that the pulling member (OT) comprises a device of the sail type or gas generator type.

21. Method according to one of Claims 15 to 20, characterised by the fact that means (BF1 to BF4) are provided for pulling the or each decoy (LT1 to LT4) downwards.

22. Method according to one of Claims 15 to 21, characterised by the fact that the or each decoy (LT1 to LT4) is connected in its lower part to a member (BF1 to BF4) able to drag on the water, such as a slighly inflated, loaded balloon.

23. Method according to one of Claims 15 to 22, characterised by the fact that the deployment operation comprises the firing of ammunition (R) housing several folded balloon/decoy groups (M1 to M4), as well as a member (OT) for holding them in the wind after release such as a parachute and an entrainment mass comprising the possible main floating anchor (AFP).

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