FR2579374A1 - Device for supporting and/or reinforcing a surface element, in particular the convex rear face of an antenna reflector - Google Patents

Abstract

Device for supporting an antenna and/or for reinforcing a surface element, in particular the convex rear face 20 of a microwave frequency transmission antenna reflector 10, comprising a set of independent, coaxial compartments 141, 142, 143 which can be fitted into one another and can be adjusted in relative position along the axial direction X-X in order to follow the curvature of the surface element, the number of compartments being chosen as a function of the dimensions of the surface element, each compartment 141, 142, 143 being made fast, on the one hand to the surface element 10 and, on the other hand, to the immediately adjacent compartment(s).

Description

Device for supporting and / or reinforcing a surface element, in particular the convex rear surface of an antenna reflector.

The present invention relates to a device for supporting and / or reinforcing a surface element, planar or non-planar.

It applies more particularly, but not exclusively, to the support and / or reinforcement of the convex rear face of an antenna reflector for transmitting microwave waves. Such antennas are intended more particularly for radio-relay systems as well as for links between the earth and telecommunications satellites.

The main components of such an antenna include a reflector, a source and a support structure. The reflector is most often parabolic, although it can more generally have a quadric shape and even a shape with a so-called conformed meridian, that is to say a corrected quadric shape.

The concave front face of the reflector constitutes a reflective face with respect to microwave waves, while the convex rear face, which plays no role with respect to microwave waves, is most often connected to the support structure.

The reflector can be of revolution (antenna with centered reflector) or not of revolution (antenna with off-center reflector). In addition, for the same diameter of radioelectric beams, the reflector can have a greater or lesser depth according to the f / D ratio defined for each antenna, f being the focal length and D the diameter. This ratio is generally between 0.3 and 0.45.

The reflective face of the reflector is usually made either of a metal sheet of steel or of light alloy, or of a composite material comprising a reinforcement of glass fibers, kevlar or carbon and a binder of organic resin. In the latter case, the concave face of the reflector must be covered with a projected metallic film, or deposited by another process, to allow reflection of the waves.

Most antennas operate in a free atmosphere and therefore undergo static stresses due to the effects of gravity and dynamic stresses due to wind. To avoid that the reflector of an antenna undergoes too large deformations which could affect its proper functioning, this reflector is generally linked to a support structure which is produced, in most cases, from metal or similar profiles which form radiating assemblies from the rear central part of the antenna, these sections being braced by concentric circular belts and diagonal elements. This structure is sometimes in the form of a box made either of a sheet or thin wall of metal alloy, formed, repelled or molded, or of a plastic composite produced like the reflector.

The support and / or reinforcement devices, in particular those intended to equip the antennas for transmitting microwave waves, are of a relatively complex and therefore expensive construction. In addition, they do not always make it possible to ensure perfect rigidity of the reflector, especially when the latter has large dimensions.

In addition, it is necessary, for each type of reflector, to provide a particular support and / or reinforcement device which takes account of the characteristics of the shapes and dimensions of this reflector.

One of the aims of the invention is to remedy the drawbacks of the support and / or reinforcement devices of the prior art.

Another object of the invention is to provide such a device, applicable in particular to antennas for transmitting microwave waves, which is of a particularly simple construction and which however makes it possible to ensure perfect rigidity of the surface element on which he rode.

Another object of the invention is to provide such a device which can be used for elements of curvature surface and of different dimensions, in particular for different types of reflectors, without it being necessary to provide each time with a particular device. .

The device for supporting and / or reinforcing a surface element, in particular the convex rear face of a microwave reflector antenna, according to the invention, essentially comprises a set of independent coaxial boxes , nestable in each other and adjustable in relative position in the axial direction to match the curvature of the surface element, the number of boxes being chosen according to the dimensions of the surface element, each box being made integral, on the one hand, the surface element and, on the other hand, the box or boxes immediately adjacent.

The assembly formed by the device of the invention and the surface element, in particular the convex rear face of an antenna reflector, on which it is mounted, is particularly rigid. This constitutes an important advantage with regard to the stiffness of the assembly, both in terms of resistance to the non-axi-symmetrical effects of the wind and in terms of internal stresses which tend to give a buckling deformation.

The modular construction of the device of the invention makes it possible, from standard boxes, to support and reinforce the reflector of any type of antenna with diameters ranging from 0.5 meters 10 meters and even more, in ranges of 2, 3 or 4 meters, or even more, regardless of the curvature of the rear face of the reflector.

In a preferred embodiment of the invention, the boxes have a L-shaped half-section which comprises a first branch constituting a generator substantially parallel to the axial direction, the free end of which is intended to be secured to the element surface, and a second branch, the free end of which is directed radially inward and is designed to be secured to the second branch of the smaller box, which is immediately adjacent to it.

Advantageously, the boxes have an undercut shape which allows them to nest during storage or transport.
This set of boxes is adaptable to all types of surface elements and in particular to all types of antenna reflectors, whether they are revolution antennas or eccentric antennas. In the case of antennas of revolution, the boxes have the shape of a crown or a circular ring. In the case of eccentric antennas, they have an elliptical shape.

 They can also be deduced from closed curves, the largest of which follows the effective contour of the antenna reflector and the others of which are deduced therefrom by homothety.

In a first variant of the invention, the boxes are open boxes intended to be secured to each other and to the surface element.

In another variant, the boxes are closed boxes which are previously secured to an annular portion, for example to a portion in the form of a circular or elliptical ring, forming part of the surface element.

When this second variant is applied to the case of an antenna reflector, a modular constitution of the complete reflector is obtained by means of coaxial elements each formed of a box and part of the reflector. This characteristic is particularly important in the case where it is desired to manufacture reflectors of the same curvature, but having changing diameters.

In this way, it is possible a priori to constitute a family of reflectors which all have the same curvature, but which differ in their diameters. It is also possible to change the diameter of the reflector which has become too small after a first use, this by adding one or more closed boxes at the periphery of the existing reflector.

According to yet another characteristic of the invention, the boxes, once made integral with one another and integral with the surface element, are sealed from the outside. The invention also provides in this case to provide communication openings between the boxes to allow the circulation of a hot fluid, for example hot air, in particular to prevent icing of the reflector and possibly its rear part.

In the detailed description which follows, given by way of example, reference is made to the appended drawing, in which: FIG. 1 is a view in axial section of a microwave transmission antenna with which the reflector is equipped with 'a device according to the invention; - Figure 2 is an enlarged partial view of Figure 1 showing the possibilities for adjusting the positions of two adjacent boxes; - Figure 3 is a perspective view of the rear part of the antenna shown in Figure 1; and - Figure 4 is a perspective view of a radome or a dome formed from a device according to the invention.

The microwave transmission antenna, as shown in FIG. 1, comprises a reflector 10 of general parabolic shape of revolution around an axis XX, an insert 12 serving to support a source of emission of microwave waves (not shown) and a support and / or reinforcement device 14 according to the invention.

The reflector can receive, at several points on its surface, fasteners intended to receive source supports or auxiliary reflectors, for example of the cassegrain type.

The reflector 10 can be made of a metal sheet of steel or of light alloy, in which case the convex front face 16 of the reflector directly constitutes a reflective face with respect to microwave waves.

The reflector 16 can also be made from a synthetic material, in particular from a composite material comprising a fiber reinforcement and an organic resin binder. In the latter case, the concave face 16 is overlapped. of a metallic film projected or deposited by another process, to allow reflection of microwave waves.

The insert 12 is extended by a peripheral flange 18 which has a concave annular surface.

This surface is bonded to the central part of the convex rear face 20 of the reflector 10. Thus, as is well known in this technique, the insert 12 faces a central opening 21 of the reflector to allow the maintenance of an appropriate source in the region of the focus of the reflector 10.

The device 14 comprises a set of boxes, in this particular case three boxes 141, 142 and 143, which are coaxial, independent, nestable one inside the other: and adjustable in relative position along the axial direction XX to match the curvature of the convex rear face 20 of reflector 10.

In this particular example where the reflector 10 has a symmetry of revolution relative to the axis
XX, the three boxes are elements in the form of circular rings or rings arranged concentrically around the axis XX. The box 141 is placed around the insert 12, the box 142 around the box 141 and the box 143 around the box 142.

The boxes have a half section in the general shape of
L which comprises a first branch, respectively 221, 222 and 223, constituting a generator substantially parallel to the axial direction XX, the free end of which 24î, 242 and 243 respectively is intended to be secured to the rear face 20. This half-section in L also includes a second branch, respectively 261, 262 and 263, the free end of which, respectively 281, 282 and 283 is directed radially inwards, that is to say in the direction of the axis
XX, and is intended to be secured to the second branch of the smaller box, which is immediately adjacent to it.

The angle formed between the two branches of the L-shaped half-section is greater than or equal to 90 ". In the example shown, the angle of the two branches of the box 141 is substantially equal to 900, while the angle formed between the two branches of the other two boxes is greater than 900, as shown in Figure 1.

The box 141 constitutes a particular box insofar as, on the one hand, it fits around the insert 12 and, on the other hand, it constitutes a hanging box. Indeed, the profile of the box 141 is modified so that the branch 261 is extended by a part 27 defining a frustoconical part and by an annular part 29 which ends in the aforementioned free end 281.

The internal annular edge of the box 141 which corresponds to the free end 281 is intended to be attached to an element 30 in the form of a collar which is applied around the insert 12.

The element is advantageously constituted by a strip of plastic material which is glued to the rear face 20, to the flange 18 and to the cylindrical external surface of the insert 12.

On the other hand, the rear annular face 32 of the box 141 supports four flanges 341 342 '343 and 344 (Figure 3) intended to allow the attachment of the antenna on a particular support not shown.

it is preferable that at least one of the boxes, in this case the box 141, includes local reinforcements 36 (Figure 1). These local reinforcements can be obtained by folding or ribbing of the material of the box and make the cross section of the box non-deformable.

They can also be obtained by added elements, for example spacers, arranged at regular intervals.

To set up the device 14 on the rear face 20 of the reflector 10, we first begin by placing the attachment box 141 by sliding it axially around the insert 12 so that the annular edge corresponding to the end 241 comes to bear against the rear face 20. When the box is in the correct position, the annular edges corresponding respectively to the free ends 241 and 281 are secured respectively to the rear face 20 and to the flange 30 around the insert 12.

 This joining can be carried out by bolting or riveting, in the case of metallic materials, or by applying a strip of glued plastic fabric, in the case of composite materials.

In the latter case, the box 141 is joined to the rear face 20 by means of a glued strip forming a flange 381 which perfectly matches the curvature of the rear face 20.

The same box is joined to the flange 30 by means of a glued strip forming a flange 391 applied on the one hand to the annular part 29 of the box and, on the other hand, to the flange 30.

After setting up the box 141, the box 142 is placed which is made to slide axially with respect to the box 141 until its annular edge corresponding to the free end 242 also comes to bear against the rear face 20 .

FIG. 2 shows how the box 142 is secured to the rear face 20 by a strip of glued plastic fabric forming a flange 382 and to the box 141 by a strip of glued plastic fabric forming a flange 392. This figure also shows the possibilities of travel axial of box 143 which correspond to a fitting tolerance T.

The box 143 is also secured to the rear face 20 by a strip of plastic fabric bonded forming a collar 383 and to the box 142 by a strip of plastic fabric bonded forming a collar 393 (Figure 1).

In this exemplary embodiment ,. the boxes are joined together by strips of plastic fabric forming the collars 391 392 and 393 above. However, if the boxes are made of a metallic material, they are preferably joined together by mechanical means, such as bolts or rivets.

The strips of glued plastic fabric usable for the implementation of the invention can be, for example, formed from a glass fiber fabric impregnated with a polymerizable material, such as an epoxy resin.

The boxes 141, 142 and 143, once made integral with each other and with the rear face 20 of the reflector, are sealed vis-à-vis the outside.

Communication openings 40 and 42 are provided between the boxes to allow the circulation of hot fluid, for example hot air.

For this purpose, any suitable heating means can be used, in order to maintain the temperature of the reflective front face 16 above a critical value preventing the formation of frost and allowing the melting of the snow and the ice.

One can use for this purpose a resistive circuit incorporated in the thickness of the reflector 10, glued or linked to the front face 16 or rear 20 of the latter, or introduced into the volume of air trapped in each box. In another variant, it is possible to use a generator of hot air or any other hot fluid, making it possible to convey heat through the various boxes.

To improve the heat exchange towards the reflector 10, more particularly towards the reflecting surface 16, the boxes can be coated with an insulating material, more particularly on their internal face.

It will also be noted that the circulation of hot air is usable not only for the purpose of defrosting the reflective part, but also for defrosting the boxes in order to reduce the weight of ice, of ice attached and also in order to maintain a homoge temperature rise of all the elements of the reflector. This property of circulation of a fluid can also be used to homogenize all the elements of the antenna under the effects of sunshine and maintain the thermal equilibrium in difficult conditions of cold or hot, whatever
whatever the climatic conditions and mainly
sunshine, to avoid gradient effects
thermal and keep perfectly the shapes and yard
initial bures of the antenna reflector.

By design, the invention offers an appreciable advantage under certain conditions because the surface offered to frost is considerably reduced.

Given the possibilities of mutual adjustment of the boxes by relative-axial displacement, the same set of boxes can be used for a whole range of reflectors, which makes it possible to reduce the number of tools necessary for the manufacture of the boxes.

In the case of boxes in the form of circular rings, the diameters of these boxes will stagger in a regular manner, that is to say that the difference in diameter between two adjacent boxes will always be the same.

Thus, in the case of a set of n caissons, the smallest diameter D1 will be equal to ZR and the largest diameter Dn equal to 2R + 2a (nl), the value 2a corresponding to the variation in diameter between two adjacent caissons .

However, depending on the applications, the extension of the diameters may no longer be modular and follow rules dictated by the application of the laws of the resistance of materials, purely economic criteria or any other requirement imposed by the requirement.

Thus, with n tools corresponding respectively to the manufacture of n boxes, it will be possible to produce all the rear structures of reflectors, whatever their curvatures, the diameters of which range from 0 to Dn
For large reflectors, whose diameter exceeds 3 meters and whose transport poses problems with regard to the legislation concerning the respect of road gauges, large diameter boxes, that is to say of diameter greater than 3 meters, will be manufactured according to the same principles and cut into several parts in order to easily allow their transport. These sections will then be assembled together on the installation site using appropriate connecting means, for example joint covers, flanges, clips, by gluing, etc.

 Such cutting can be applied both to open boxes and to closed boxes as defined above. In the latter case, the annular portion of the surface element, for example of the reflector, must also be cut to allow the transport of the closed box section.

As shown in Figure 3, the shape of the rear face of the device 14 approaches the ideal aerodynamic shape, so that it allows a significant reduction in operation of the phenomena of turbulence, local drag and any harmful climatic stress the reliability of the transmissions and receptions of signals for which these reflectors are intended.

On the other hand, the constitution, in the sense of the resistance of materials, from coaxial boxes, gives the reflectors the first very high natural vibration modes, which constitutes an interesting factor in certain applications.

The high rigidity offered by the device of the invention allows a very great reduction in weight with equal performance compared to the solutions traditionally used. On the other hand, the device of the invention makes it possible, from a quasi-unique study, to constitute a whole family of reflectors and, consequently, to reduce the calculations intended for the establishment of the files of each type of antenna. In addition, by its very design, the device of the invention allows automation and therefore industrialization of manufacturing which results in a significant reduction in costs.

Another advantage to be noted results from the "stripped" shape of the boxes which can fit into each other and allow storage or transport at a lower cost, which allows to completely dissociate the manufacturing and assembly phases. /assembly.

It should also be noted that the very design of the device of the invention lends itself to domestic use and more particularly to assembly in a kit.

Although the device of the invention has been described with particular reference to an antenna reflector, it should be noted that it can be applied to the supports and / or the reinforcements of any flat or arbitrary surface. Among other possible applications, mention may be made, for example, of reinforcing mirrors for telecommunications, of vertical, or horizontal plane walls such as slabs, walls, curtains, or even the creation of arches or spheres of all sizes.

The boxes can have not only circular or elliptical shapes, but also polygonal shapes, in particular triangular, square, rectangular, hexagonal shapes.

 FIG. 4 shows an example of a radome or dome 44 formed from three boxes 441 ′ 442 and 443 each provided with reinforcing ribs such as 461J 462 and 463, and resting on a surface element 48.

The boxes can be formed from any material capable of giving them the desired resistance properties. In the particular case where these boxes are intended for antenna reflectors, they are advantageously made of the same material as the reflectors, for example in a thin sheet or wall of metal or metal alloy or in a formed plastic composite material. fibers united by an organic resin binder.

As a result, the material of the reflector and that of the boxes then have the same coefficient of thermal expansion.

Claims (16)

Claims. 1. Device for supporting and / or reinforcing a surface element, in particular of the convex rear face (20) of a reflector (10) of microwave transmission antenna, characterized in that it comprises a set of coaxial boxes (141, 142, 143), independent, nestable one inside the other and adjustable in relative position in the axial direction (XX) to match the curvature of the surface element (10), the number of boxes being chosen according to the dimensions of the surface element, and in that each box (141, 142, 143) is made integral, on the one hand, with the surface element (10) and, on the other part, of the immediately adjacent box (es). 2. Device according to claim 1, characterized in that the boxes (141, 1421 143) have a L-shaped half-section which comprises a first branch (221, 222, 223) constituting a generator substantially parallel to the axial direction, the free end (241 242, 243) is intended to be secured to the surface element (10), and a second branch (261, 262, 263) whose free end (281, 282, 283) is directed radially towards the interior and is designed to be secured to the second branch of the smaller dimension box immediately adjacent. 3. Device according to claim 2, characterized in that the angle formed between the two branches of the L-shaped half-section is greater than or equal to 900. 4. Device according to one of claims 1 to 3, characterized in that at least one of the boxes (141) comprises local reinforcements (36). 5. Device according to claim 4, characterized in that the local reinforcements (36) are obtained by folding or ribbing of the material of the box. 6. Device according to one of claims 1 to 5, characterized in that the boxes (141 142, 143) are made integral with one another and with the surface element (10) by bolting or riveting. 7. Device according to one of claims 1 to 5, characterized in that the boxes (141, 142, 143) are made integral with each other and the surface element (10) by application of a strip of plastic fabric glued. 8. Device according to claim 7, characterized in that the strip of glued plastic fabric constitutes a flange ensuring the attachment of the box to the surface element (10) or to an adjacent box. 9. Device according to one of claims 1 to 8, characterized in that the boxes (14î, 142, 143) are open boxes provided to be secured to each other and to the surface element (10). 10. Device according to one of claims 1 to 8, characterized in that the boxes are closed boxes previously secured to an annular portion, for example in the form of a circular or elliptical ring, forming part of the surface element. 11. Device according to one of claims 1 to 10, characterized in that the boxes (14î, 142, 143), once made integral with each other and the surface element (10), are tight vis-à-vis screw from the outside. 12. Device according to claim 11, characterized in that communication openings (40, 42) are provided between the boxes (141, 142, 143) to allow the circulation of hot fluid and in particular to prevent icing of the reflector (10) or the entire antenna.  13. Device according to one of claims 11 and 12, characterized in the boxes (141, 142, 143) are coated with an insulating material ~, preferably on the inner side. 14. Device according to one of claims 1 to 13, characterized in that the boxes of a dimension greater than the authorized road gauge are optionally cut into several parts. 15. Device according to one of claims 1 to 14, characterized in that at least one of the boxes (141) comprises attachment means (341 342, 343ess 344) to a support. 16. Surface element, in particular antenna reflector, equipped with a device according to one of claims 1 to 15.