EP1245485B1 - Device for preventing the detection by radar of flat superstructures of ships - Google Patents

Abstract

The radar deflector for a marine vessel has a frusto-conical casing attached to the superstructure of the vessel to reflect the radar waves. The lower edge of the casing (6) has a gusset (7). The angled surfaces of the casing reflect the radar waves in a different direction from the incident angle. The height of the casing and gusset is less than the length of the missile well doors which they cover.

Description

The present invention relates to a radar detection device of a flattened ship superstructure.

We know that the armament of a combat ship, in addition or to the places the usual cannons and torpedoes, includes batteries of missiles anti-ships or anti-aircraft missiles. These missiles and their means of launch can be arranged in superstructure on the deck of the ship. However, for obvious reasons of radar detectability, it is preferable that said missile batteries are, at most, arranged inside said vessel.

In this case, said missiles can be placed in wells verticals arranged under the deck of said vessel and closed at their upper part, by pivoting doors which, in the closed position - i.e. at battery rest outside of a firing sequence-- protrude slightly with respect to said bridge.

At rest, the superstructure of said missile batteries comprises therefore said doors in the closed position. She can understand, plus, flue gas exhaust stacks missiles. In all cases, it is very flat on the deck, not exceeding that pretty little this one. As a result, the vessel's global radar signature mainly results from the other superstructures of it, such that hull, castle, gangway, masts, antennas, etc ...

However, although relatively weak, the radar signature of the superstructure of such a missile battery at rest, partially enclosed under the bridge, adversely affects the global radar signature of the ship.

The object of the present invention is therefore to make the part stealthy upper part of the superstructure of such missile batteries at rest, so that the overall radar signature of the ship is not affected.

• au moins sur chacun des côtés bâbord et tribord de ladite superstructure, au moins un écran plan incliné apte à réfléchir un faisceau incident d'ondes électromagnétiques dans une direction différente de celle dudit faisceau incident, lesdits écrans faisant saillie par rapport audit pont d'une hauteur supérieure à celle de ladite superstructure et l'inclinaison desdits écrans étant telle qu'ils se rapprochent de ladite superstructure en s'éloignant dudit pont ; et
• un filet, réfléchissant les ondes électromagnétiques et tendu au-dessus de ladite superstructure.

To this end, according to the invention, the device making it possible to make discrete to the electromagnetic waves a flattened superstructure carried by the deck of a ship, in particular the superstructure of a battery of missiles at rest which is embarked on board a ship and of which said missiles are contained in vertical shafts partially disposed under the deck of said ship and closed at their upper part by pivoting doors which, in the closed position, constitute at least partially said superstructure, is remarkable in that it comprises:

• at least on each of the port and starboard sides of said superstructure, at least one inclined plane screen capable of reflecting an incident beam of electromagnetic waves in a direction different from that of said incident beam, said screens projecting from said deck of a height greater than that of said superstructure and the inclination of said screens being such that they approach said superstructure away from said bridge; and
• a net, reflecting electromagnetic waves and stretched over said superstructure.

Thus, when a detection radar, positioned laterally relative to said vessel, sends an incident beam on said superstructure, it can receive the corresponding reflected beam only, said incident beam hits one of said flat screens or said protective net.

It will be noted that, thanks to the presence of said protective net stretched above the superstructure, the height of said screens can be relatively weak. Indeed, the incident radar beams passing over of said screens and striking said net are also reflected in a different direction.

Preferably, said protective net is stretched, between the edges free, opposite to said deck, of said inclined plane screens, so that the height of said net above deck is equal to that of said flat screens inclined.

Thus, said inclined plane screens and said net form a anti-radar protection enclosure enveloping said superstructure in the making it particularly discreet.

To further increase this protective effect by wrapping, it is advantageous that the device according to the present invention comprises, in addition to the port and starboard inclined flat screens, flat screens additional similar inclines forming, with said port screens and starboard, a polyhedron surrounding said superstructure, said protective net being stretched between the free edges of all of said inclined plane screens.

In an advantageous embodiment of this type, said device has four inclined plane screens - including a port screen and a screen starboard-- forming a trunk-pyramidal tetrahedron surrounding said superstructure.

Furthermore, to prevent such anti-detection protection from being an obstacle to firing missiles, we ensure that said height of inclined plane screens and said net is less than the length of the doors pivoting closure and that said protective net can be torn by each of said doors passing from the closed position to the position opened. So, by simply opening the doors, the net is torn and releases the passage opposite said wells, so that the missiles can be drawn instantly.

It will be noted that said net must, on the one hand, be able to be easily torn off by the doors of the wells when they opened, but, on the other hand, be strong enough to withstand wind and bundles of Wed. We found it possible to meet these conflicting requirements by making said net with steel wires, the diameter of which is at more equal to 0.4 cm.

We also know that detection radars emit electromagnetic wave beams whose frequency is included between 2 and 18 GHz. It follows that, so that said net can reflect these electromagnetic waves, the largest dimension of its meshes must not be more than 0.8 cm. Preferably, we choose a mesh square with sides at most equal to 0.8 cm.

Furthermore, to take into account the roll of the ship, as we will see below, the angle of inclination of the flat inclined screens relative to the deck of the ship is chosen at most equal to 60 °.

La figure 1 montre, en vue de dessus, la proue d'un navire équipé d'une batterie de missiles, protégée par le dispositif antidétection conforme à la présente invention.

La figure 2 est une vue en perspective du dessus, selon la flèche II de la figure 1, du dispositif antidétection de cette dernière figure.

La figure 3 est une vue schématique dudit dispositif antidétection semblable à celle de la figure 2, le filet de protection furtif étant supposé ôté.

Les figures 4 et 5 sont des vues schématiques en coupe, respectivement selon les lignes IV-IV et V-V de la figure 3.

La figure 6 illustre schématiquement l'ouverture d'une porte de puits de la batterie de missiles, entraínant la déchirure dudit filet de protection furtif.

La figure 7 est un schéma illustrant le fonctionnement dudit dispositif antidétection.

La figure 8 est un diagramme illustrant la variation de l'angle de réflexion d'un faisceau incident d'ondes électromagnétiques en fonction de l'angle d'incidence de ce faisceau.

La figure 9 est une vue agrandie partielle d'un exemple de réalisation du filet de protection furtif du dispositif de l'invention.

The figures of the appended drawing will make it clear how the invention can be implemented. In these figures, identical references designate similar elements.

Figure 1 shows, in top view, the bow of a ship equipped with a missile battery, protected by the anti-detection device according to the present invention.

Figure 2 is a perspective view from above, along arrow II of Figure 1, of the anti-detection device of this latter figure.

Figure 3 is a schematic view of said anti-detection device similar to that of Figure 2, the stealth protective net being assumed to be removed.

Figures 4 and 5 are schematic sectional views, respectively along lines IV-IV and VV of Figure 3.

Figure 6 schematically illustrates the opening of a well door of the missile battery, causing the tearing of said stealth protective net.

Figure 7 is a diagram illustrating the operation of said anti-detection device.

FIG. 8 is a diagram illustrating the variation of the angle of reflection of an incident beam of electromagnetic waves as a function of the angle of incidence of this beam.

Figure 9 is a partial enlarged view of an exemplary embodiment of the stealth protective net of the device of the invention.

Vessel 1, of longitudinal axis X-X, of which only the bow is represented in FIG. 1, has a bridge 2 and a castle 3, as well as a front artillery turret 4. Between the castle 3 and the turret 4, is planned a missile battery 5, surrounded by a frame 6 and covered by a net 7 (partially broken away in FIG. 1). Frame 6 and net 7 are shown on a larger scale in the perspective view of FIG. 2.

As can be seen in the sections of Figures 4 and 5, the battery missile 5, on board the ship, comprises a plurality of missiles 8, contained in vertical wells 9 arranged under deck 2.

Outside the firing sequences, the superstructure of the missiles 5, lying above deck 2, consists essentially a base plate 10, a plurality of closed doors 11 each of which of them closes the upper part of a well 9 and chimneys 12, intended for the evacuation of combustion gases from propellants (not shown) missiles 8 when fired. Each door 11 is articulated in rotation on the base plate 10 around an axis 13.

In the embodiment shown in Figures 1 to 8, the frame 6 consists of four inclined plane faces 14.1 to 14.4 forming a truncated pyramid with a rectangular base, projecting from the deck 2. The height H of the frame 6 above the deck 2 is greater than the corresponding height h of the superstructure 10, 11 and 12 (the doors 11 being closed, as shown in Figures 3, 4, 5). Box 6 is fixed to deck 2 and / or to base plate 10, by its large base using all known means, not shown. Furthermore, the length L of the doors 11 is greater than the height H of the frame 6.

Each face 14.1 to 14.4, for example made of steel, is capable of reflecting electromagnetic waves and forms a screen salient plane with respect to deck 2, forming an angle Φ with it. The inclination Φ of the plan screens 14.1 to 14.4 is such that each of these approaches the superstructure 10, 11 and 12 (and therefore the others screens to form the small base of the pyramid trunk) away from the deck 2.

As can be seen in Figure 1, the trunk-pyramid frame 6 is arranged so that the inclined plane screens 14.1 and 14.3 are respectively to starboard and to port, while the flat screens inclined 14.2 and 14.4 are transverse.

The small base of the trunk-pyramidal frame 6, formed by the free edges 15.1 to 15.4, opposite deck 2, inclined flat screens 14.1 to 14.4, is closed by the thread 7, fixed and stretched on said free edges of all known and unrepresented ways. Net 7, the height of which above of the deck 2 is therefore substantially equal to the height H of the frame 6, is metallic and is able to reflect electromagnetic waves.

The thread 7 has a sufficiently high mechanical resistance to be self-supporting, but weak enough to be able to be torn off partially by a door 11 passing in the open position, as this is illustrated schematically in FIG. 6.

Thus, when a missile 8 must be fired, the corresponding door 11 is open, which makes it possible to locally tear the net 7 opposite the corresponding well 9, since the length L of said door 11 is greater at the height H of the net 7. The missile is fired and it passes through the tear in the net 7, while the propellant combustion gases of the missile escape through the associated chimney 12, as is illustrated schematically by arrows in Figure 6.

In FIG. 7, diagram 2 shows the deck 2 of the ship 1 and a horizontal reference plane r-r.

• l'angle I d'incidence d'un faisceau d'ondes électromagnétiques latéral 19 frappant l'écran plan incliné 14.3 ;
• l'angle R de réflexion du faisceau d'ondes électromagnétiques 20, réfléchi correspondant ; et
• l'angle de roulis ρ du navire 1 autour de son axe X-X.

In relation to this horizontal reference plane rr, we have also indicated:

• the angle I of incidence of a lateral electromagnetic wave beam 19 striking the inclined plane screen 14.3;
• the angle R of reflection of the beam of electromagnetic waves 20, corresponding reflected; and
• the roll angle ρ of the ship 1 around its axis XX.

In addition, we have designated by Φ the angle of inclination of the screens plans 14.1 to 14.4 in relation to deck 2.

We can easily verify that the above quantities are linked by the relation:

To take into account the main backscatter lobe of the superstructure and to get rid of it, it is necessary to subtract from the angle R, determined by the relation (1), the value of 3/2 times the width LP at three dB of the lobe main screen backscatter 14.3. Expression (1) then becomes:

In an exemplary embodiment in which the angle of inclination Φ is chosen to be equal to 60 °, the maximum roll ρ of the vessel 1 being 5 ° and the width LP to three dB being equal to 5 °, the angle of reflection R is expressed according to: (3) R = 42.5 ° - I as shown in the diagram in Figure 8.

Expression (3) makes it clear that when the angle of incidence I increases, the angle of reflection R decreases. However, so that the reflected beam 20 does not return to the radar emitting the incident beam 19, that is to say so that the frame 6 is stealthy for this radar, it is necessary that the angle of reflection R remains constantly greater than the angle incidence I, a minimum safety margin.

So, as shown in the diagram in Figure 8, if the angle incidence I is between 0 ° and 20 °, the angle of reflection R remains greater at 22.5 °, which ensures a minimum safety margin of 2.5 °.

We thus see that with an angle of inclination Φ equal to 60 °, the superstructure 10, 11, 12 is discrete for the incident beam 19, up to angles of incidence I of 20 °.

If it is desirable that discretion be maintained for angles of incidence I greater than 20 °, it is then necessary to reduce the angle of inclination Φ, in accordance with relation (2).

To be stealthy, we know that the metal net 7 must have meshes the largest dimension of which must be less than half the length minimum waveform of the detection radar frequency band. Usually, this frequency band is delimited by the values extremes 2 and 18 GHz. It is therefore easy to deduce that the largest mesh size must be at most 8 mm.

In Figure 9, there is shown an embodiment of net 7 with square meshes, formed of warp threads 17 and weft threads 18 perpendicular. Of course, the dimension has sides of the square meshes is at most equal to 8 mm, as mentioned above.

The diameter of the steel wires 17 and 18 constituting the thread 7 can be of the order of 3 to 4 mm, in order to ensure a certain mechanical strength (for withstand the wind and sea packets), without this net 7 is too solid, since it must tear under the action of doors 11 passing in the open position.

Possibly, to facilitate the tearing of the net 7 by the doors 11, rigid spacers 16 can be provided between said net and said doors, as shown in Figure 4.

In FIG. 7, a lateral incident beam has also been illustrated. of electromagnetic waves 21 striking the net 7 and reflected according to the beam 22 by the latter. We can see that this reflected beam 22 cannot in any case return to the lateral detection radar having emitted the incident beam 21.

Claims (9)

1. A device enabling a flattened superstructure (10, 11, 12) carried by the deck (2) of a ship (1) to be rendered insusceptible to electromagnetic waves, in particular the superstructure of an idle battery (5) of missiles (8) onboard said ship and said missiles of which are contained in vertical shafts (9) disposed partially under the deck of said ship and occluded at their upper part by swiveling doors (11) which, in the closed position, constitute said superstructure at least in part,
   characterized in that it comprises:

   at least on each of the port and starboard sides of said superstructure at least one inclined plane screen (14.1, 14.3) able to reflect an incident beam (19) of electromagnetic waves in a different direction from that of said incident beam, said screens projecting with respect to said deck by a height (H) greater than that (h) of said superstructure and the inclination of said screens being such that they get closer to said superstructure as they get further from said deck; and

   a net (7), reflecting the electromagnetic waves and stretched above said superstructure.
2. The device as claimed in claim 1,
   characterized in that said protective net (7) is stretched between the free edges (15.1, 15.3), away from said deck, of said inclined plane screens (14.1, 14.3).
3. The device as claimed in claim 2,
   characterized in that it comprises, in addition to said port and starboard inclined plane screens (14.1, 14.3), other additional similar inclined plane screens (14.2, 14.4) forming, with said port and starboard screens, a polyhedron surrounding said superstructure, and in that said protective net (7) is stretched between the free edges (15.1 to 15.4) of all said inclined plane screens (14.1 to 14.4).
4. The device as claimed in claim 3,
   characterized in that it comprises four inclined plane screens (14.1 to 14.4) forming a frusto-pyramidal tetrahedron surrounding said superstructure.
5. The device as claimed in any one of claims 2 to 4,
   characterized in that said height (H) of the inclined plane screens and of said net (7) is less than the length (L) of said swiveling occluding doors (11) and in that said protective net (7) can be ripped by each of said doors (11) passing from the closed position to the open position.
6. The device as claimed in any one of claims 1 to 5,
   characterized in that the angle of inclination (Φ) of said inclined plane screens (14.1 to 14.4) with respect to said deck (2) is at most equal to 60°.
7. The device as claimed in any one of claims 1 to 6,
   characterized in that the largest dimension of the cells of said protective net (7) is at most equal to 0.8 cm.
8. The device as claimed in claim 7,
   characterized in that the cells of said protective net (7) are square with sides (a) at most equal to 0.8 cm.
9. The device as claimed in any one of claims 1 to 8,
   characterized in that said protective net (7) consists of criss-crossed steel wires (17, 18) having diameters at most equal to 0.4 cm.

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