FR2672435A1 - Device for mounting and removing the source of an antenna - Google Patents

Abstract

Device for mounting and removing the source of an antenna on a reflector of this antenna, the source including an electromagnetic excitation assembly situated at the end of an assembly for guiding the electromagnetic waves, the device comprising: - a support for the source traversed by the guidance assembly in such a way that the excitation assembly is turned towards the concave face, called front face, of the reflector when the support has been installed in an aperture formed for this purpose in the reflector, - intermediate means for fixing the support, equipped with the source, onto the reflector, the intermediate means being fixed onto the convex face, called rear face, of the reflector, - means for radio frequency matching of the source to the reflector, centred on the reflector and situated on its concave face, characterised in that the intermediate means (7) are arranged to be fixed onto the rear face (8) of the reflector (9), in order to accommodate the support (4) coming through the front face (11) and to be removed with the support (4) through the rear face (8). Such a device may particularly be used on the reflector of a parabolic antenna.

Description

Device for mounting and dismounting the source of an antenna
The present invention relates to a device for mounting and dismounting the source, also called excitation, of an antenna. It is more particularly interested in mono and bipolar sources supplied either by means of waveguides or by means of coaxial cables, and used in microwave antennas with parabolic reflector.

 For the sake of clarity, we will only be concerned in the following with a parabolic reflector antenna whose bipolar source is supplied by waveguides. However, this restriction for the sake of simplification is obviously not limiting.

 Several elements are necessary for the installation of such sources on a parabolic reflector - a generally circular plate, called vertex plate, support of the waveguides and constituting the interface between the paraboloid and the source: it is installed in a corresponding central opening of the reflector previously cut for this purpose, so that the source is on the concave side (called the front face) and at the focal point of the parabolic reflector, part of the waveguides emerging from the convex side (or face rear) of the latter - an adapter plate: it has an important radioelectric role.

Indeed, in the parabolic antennas illuminated at the focus, there is a reaction of the reflector on the adaptation characteristics of the source. All rays from the opening diameter of the source are returned by the reflector to the source. This reflected energy therefore modifies the adaptation of the source. To remedy this, there is a flat metal plate called the adapter plate at the top of the reflector, the dimensions of which are defined in such a way that they make it possible to cancel the previous reflection while disturbing at least the radiation characteristics of the antenna, - a housing ring, fixed on the rear face of the reflector and intended to receive the vertex plate, - shrouds which are stretched between the excitation and the reflector, in order to take up part of the forces supported by the guides waves.

 Two types of source installation devices, comprising these various elements, are conventionally used.

 In a first type of device, the light alloy housing ring is installed at the rear of the reflector. We then fix, by means of screws and nuts, an adapter ring on the front face of the reflector. The adapter ring is then secured to the housing ring and can allow the brass vertex plate to pass. Finally, the vertex plate secured to the source is brought through the front of the reflector, passes through it and is fixed in a shoulder provided for this purpose in the housing ring. A stop segment coming to lodge beforehand in this shoulder and coated with an anti-corrosion grease has the role both to position and to center the vertex plate, and to separate the light alloy ring (based on aluminum) of the brass vertex plate to prevent electrochemical corrosion between these two elements. Finally, clamps, for example, hold the vertex plate to the housing ring.

 Several problems are posed by this type of device.

 Indeed, once the antenna is installed, at the top of a pylon in general (some can reach 200m in height), maintenance operations (replacement of the source, inspection, repair) are more convenient to perform from the rear of the reflector. With this type of device, it is possible to remove certain sources from the rear, then replace them by bringing the new vertex plate also from the rear. During this operation, care must be taken not to drop any of the numerous elements of the device.

In addition, it is not possible to remove the adapter plate from the rear. Consequently, if you want to change the type of source and therefore the adapter plate, you must have access to the front of the reflector. Consequently, the operations are very complex.

 Furthermore, some antennas operating at low frequencies (typically less than approximately 60 Hz) use very bulky sources. Such sources cannot be replaced from the rear in the type of device described above.

 In addition, the space filled with anti-corrosion grease is small (1 to 1.5mm) and the product quickly consumed, which leads to short-term electrochemical corrosion.

 In summary, these devices - are of complex use (the installation of a source requires, as we have seen, many operations and many parts), - do not systematically allow maintenance from the rear of the reflector , - are expensive because of the numerous metal parts to be machined which they comprise, - do not provide good protection against electrochemical corrosion.

 We can then use a second type of device that solves some of these problems. These devices include a housing ring fixed to the rear face of the reflector, and a vertex plate also sometimes serving as an adapter plate (it is flat) or as a support for the circular adapter plates fitted with screws, the diameter of the plate never being greater than the diameter of the vertex plate. To install the source, simply bring the vertex plate through the rear of the reflector, place it against the housing ring, which has a retaining shoulder for this purpose, then fix it with screws, nuts and clamps. This device is therefore much simpler than the previous one since the number of operations is considerably reduced.

 In addition, it allows systematic maintenance from the rear of the reflector.

 In addition, it has several standard sizes of vertex plates (around four) adapted to the size of the sources and the adaptation diameter. These vertex plates can be fixed from the rear to the housing ring, and there is for this a housing ring adapted to each size.

 However, such a device still has three major drawbacks.

 First, the shoulder of the housing ring prevents the initial installation of the source from the front of the reflector. This is very annoying because, during this installation, the reflector is on the ground. Given the length of the waveguides, it must be kept vertical in order to bring the source from the rear.

This position of the reflector is unstable and therefore requires the use of supports. In addition, some reflectors can reach 4m in diameter, the installer must use a ladder to tension the guy wires from the top.

 In addition, the waveguides, made of brass, are held at the level of the light alloy vertex plate (aluminum based in general) by two light alloy flanges coming into contact with them over a length of about 5cm. However, copper and aluminum have very different electrochemical potentials. Contacting them therefore results in an electrochemical corrosion effect. To overcome this, the device plans to insert, between the waveguides and the flanges, stainless steel strips around the entire periphery of the contact surface. However, these very thin strips (a few tenths of a millimeter thick) provide only limited and short-term protection.

 Finally, as there are several sizes of vertex plates depending on the size and adaptation of the source, there are also several sizes of corresponding housing rings; such devices are therefore expensive due to the multiplicity of parts specific to each type of source.

 The object of the present invention is then to produce a device for mounting and dismounting the source, simple, inexpensive, usable whatever the size of the source, allowing the initial installation of the source from the front. and rear maintenance, and avoiding the problems of electrochemical corrosion due to the proximity between copper alloys and light alloys.

 The present invention provides for this purpose a device for mounting and dismounting the source of an antenna on the reflector of said antenna, said source comprising an electromagnetic excitation assembly located at the end of a waveguiding assembly electromagnetic, said device comprising - a support of said source traversed by said guide assembly so that said excitation assembly is turned towards the concave face, said front face, of said reflector when said support has been installed in an opening made in this effect in said reflector, - intermediate means for fixing said support provided with said source on said reflector, said intermediate means being fixed on the convex face, said rear face, of said reflector, - radioelectric adaptation means from said source to said reflector, centered on said reflector and situated on its concave face, characterized in that lesdi ts intermediate means are arranged to be fixed on said rear face of said reflector, to receive said support coming from said front face and to be disassembled with said support by said rear face.

 Advantageously, the reflector further comprises a removable part called a blanking plate and located in contact with the support when the latter is installed; this closure plate is removable from the rear of the reflector so as to allow access to the front face and the passage of bulky sources.

 According to an important characteristic, when the material constituting the support and the material constituting the guide assembly have distant electrochemical potentials, the device according to the invention may also comprise means for protecting the support against electrochemical corrosion consisting of elements in a metallic material such that its electrochemical potential prevents it from reacting with the material constituting the support, and with the material constituting the guide assembly, brazed around the guide assembly and installed in the support without introducing discontinuity by relative to its initial surface, so as to leave a sufficient space of non-reactive material between the guide assembly and the support.

 In addition, the support may consist of a circular perimeter plate which is received in the corresponding opening of the reflector; the intermediate fixing means then comprise a housing ring having a shoulder against which the support is fixed.

 When the excitation frequency of the source is greater than 6 GHz, the adaptation means are integrated into the support and the support then has a planar part facing the excitation assembly. On the other hand, when the excitation frequency is less than 6 GHz (the source is then bulky), the adaptation means are two flat plates which are fixed on the front face, over the support, so as to present a sufficient flat surface for radio adaptation.

 In addition, the device according to the invention can be used on the reflector of an antenna with a monopolar or bipolar source.

 Furthermore, the reflector may be of parabolic shape.

 The support is for example made of a light alloy material based on aluminum.

 Finally, when the source is bipolar and supplied by waveguides, the brazed elements for protection against possible electrochemical corrosion are two flat stainless steel discs each brazed on a waveguide.

 Other characteristics and advantages of the present invention will appear during the following description of a device according to the invention, given by way of illustration and in no way limitative.

 In the following figures - Figure 1 shows, once installed, a device according to the invention, - Figure 2 is a section along line II-II of Figure 1, - Figure 3 is a section along line III -III of Figure 2 with enlargement, - Figure 4 is a front view of a variant of the device of Figures 1, 2 and 3.

 In all these figures, the common elements are referenced with the same numbers.

 In FIG. 1, a source l supplied by two brass waveguides 2 and 3 bent by bending, emits electromagnetic waves with orthogonal polarizations between them. Near the opposite end to the source 1 of each of the waveguides 2 and 3 are respectively two solid flat discs 5 and 6 made of stainless steel intended in part to secure the waveguides to a vertex plate 4 in light aluminum-based alloy, for example. They are bolted to the vertex plate 4 and brazed to the waveguides 2 and 3; they have a thickness less than that of the vertex plate 4.

 A housing ring 7 is fixed to the rear face 8 of a reflector 9 (2 m in diameter) by a series of screws 10, the heads of which are flush with the front face 11 of the reflector 9 (see FIGS. 2 and 3). Nuts 12 integral with each of the screws 10 and located against the rear face 8 of the reflector 9 (see FIG. 3) make it possible to immobilize the screws 10 to facilitate subsequent disassembly of the ring 7. When the vertex plate 4 comes lodge in a shoulder 13 of the ring 7 provided for this purpose, its surface extends the surface of the reflector 9. The ring 7 is threaded on the screws 10 and bears against the rear face 8 of the reflector 9. Nuts 14 fix the ring 7. The vertex plate 4 is then fixed to the ring 7 by screws 15, the heads of which are also flush with the front face 11 of the reflector 9, and which are each held at the rear by nuts 16.

 In addition, a quasi-rectangular plate 17, called a shutter, has been cut from the reflector 9 (length L = 26 cm and width 1 = 11 cm) directly above the opening intended to receive the vertex plate 4. The plate 17 is fixed to the reflector 9 by means of joint covers 18, 19 and 20 (which prevent radio leaks) to which it is attached by rivets 21. These joint covers 18, 19 and 20 are themselves fixed to the reflector 9 by means of screws 22, the heads of which are flush with the rear face 8 of the reflector 9.

 In this way, the plate 17 can be removed, together with the joint covers 18, 19 and 20, by the rear of the reflector 9.

 We will now endeavor to describe in detail the sequence of operations to be carried out to proceed with the initial installation of a source, its disassembly and the reassembly of this source or another on the parabolic reflector.

 On leaving the manufacturing plant, the parabolic reflector 9 is already provided with its housing ring 7. The plate 17 is fixed to the reflector.

 The source is it, integral with its vertex plate 4. In fact, each source has its own vertex plate, in which the stainless steel discs 5 and 6 have a diameter such that the space they provide between the guides waves and the vertex plate itself is sufficient to avoid any risk of corrosion (their diameter is therefore adapted to the size of the waveguides). On the other hand, the outside diameter D (D = 27cm) of the vertex plate is standard, that is to say that any source can be mounted in the ring 7, which is also of standard size.

 To install the source, bring the front of the reflector, aiming at the zenith resting on the ground and placed on its rear structure (not shown), the vertex plate 4 provided with the source 1, and insert the screws 15 in the locations 23 provided for this purpose in the ring 7. These locations are such that they allow a rotation of plus or minus 50 of the vertex plate 4 to ensure correct polarization and centering of the source.

 Once these operations have been carried out, access is obtained at the rear to tighten the nuts 16. Finally, the guy wires 24 are tensioned (see FIG. 1) between the source 1 and the attachment points on the front face of the reflector 9 (not shown). .

 Until then the operations are identical, whether the source is bulky (excitation frequency less than 6 GHz approximately) or not (excitation frequency greater than 6 0Hz approximately).

 For space-saving sources, such as that of FIG. 1, the width E of the source-bent waveguide assembly is less than the diameter D of the opening 25 (see FIG. 2) of the reflector 9 receiving the vertex plate 4 .

 In addition, the shape of the vertex plate 4 allows the latter to play the role of adaptation plate at the same time. Indeed, on an outer ring 26 of variable width depending on the frequency of the antenna, the surface of the vertex plate 4 is a portion of a parabola extending the reflector 9. Beyond this ring and towards the center of the vertex plate ( in particular the part containing the discs 5 and 6), the surface 27 of this plate is flat so as to fulfill the adaptation function explained above.

 For bulky sources, the width E is greater than the diameter D. In addition, it is not possible to have a plane surface of sufficient adaptation according to the principle used for the bulky sources because the standard diameter D of the plate vertex 4 is not enough to provide the necessary flat surface. We then use two flat semi-hexagonal plates 28 (see FIG. 4) which are just fixed by means of screws 29 in locations 30 provided for this purpose on the vertex plate 4. The heads of the screws are flush with the face front 11 of the reflector 9 and the corresponding nuts (not shown) are tightened at the rear at the same time as the nuts 16.

 The installation of sources from the front using the device according to the invention is therefore simple to carry out, whatever the source to be installed. The machining of the vertex plate, also serving as an adaptation plate, is inexpensive. Similarly, the semi-hexagonal adapter plates are very simple to machine (it suffices to shear a metal plate). They are much easier to machine than semi-circular or annular plates that are conventionally found in interior art.

 In addition, the stainless steel discs ensure good separation between the light alloy constituting the vertex plate and the brass constituting the waveguides. It is also simple to solder them on the waveguides.

 To remove space-saving sources, simply unscrew the nuts 16 and pull the ring 7 - vertex plate 4 assembly backwards. Indeed, like ECD, the bending of the waveguides 2 and 3 does not prevent passage through the opening 25. The guys 24 are then detached from the source 1, taking care to leave them accessible from the rear face 8 of the reflector 9. Thanks to the nuts 12 the screws 10 cannot fall.

 To dismantle bulky sources, the plate 17 is first removed. Then the nuts of the adapter plates 28 are unscrewed on the rear face of the reflector. Then pass the arm through the opening 31 left by the plate 17 to catch the two adapter plates 28. The screws 29 integral with these plates have been made captive by O-rings (not shown) threaded on these screws behind the adapter plates. One can then proceed in the same way as for dismantling a space-saving source, the waveguides being able to pass into the empty space formed by the openings 25 and 31.

 To reassemble a new source (identical or different from the previous one), the operations described above are carried out in reverse order.

 It is therefore understood that the assembly and disassembly, from the front or the rear, of any sources require extremely simple operations. The screw-nut system used each time allows easy maneuvering in both directions. In addition, the use of a standard vertex plate size (and therefore a standard size of housing ring) is less complicated than the solution advocating different sizes, since it allows more flexible use of the reflector. Indeed, when using several sizes of vertex plates, it is necessary to know a priori how often the reflector will be adapted in order to practice a sufficient opening there, which will no longer be adapted if the source is changed (therefore vertex plate).

 We therefore produced a device for mounting and dismounting the source of a parabolic antenna which is simple to use, making it possible to initially install the source from the front of the parabolic reflector and to ensure on-site maintenance from the rear of the reflector. This device also facilitates the use of standard parts whose manufacturing and cost price can be quickly amortized; thus, any type of source can be mounted and dismounted using this device. Finally, the use of stainless steel separation discs between the brass waveguides and the aluminum alloy vertex plate avoids the effect of electrochemical corrosion.

 Of course, the present invention is not limited to the devices and modes of operation which have just been described.

 It is indeed obvious that the device according to the invention has been described in particular for a parabolic reflector antenna, but that it can be used in general with any reflector.

 Furthermore, all the dimensions and shapes given are for information only.

 In addition, any source other than a bipolar source with supply waveguides can be adapted to the device according to the invention. One can for example use this device with a monopolar source supplied by coaxial cables supported by a mast. In this case, the mast may not be made of copper alloy, and the corrosion problems are then different and sometimes nonexistent.

 Furthermore, the vertex plate, the housing ring and the possible adaptation plates can be made of any metallic material. It will then be necessary to take care with the possible effects of electrochemical corrosion between these various elements.

 The adapter plates need not be semi-hexagonal even if such a shape results in the least costly machining. They can for example be semi-circular or rectangular.

 The shape of the hatch is also not critical. I1 suffices that it allows the passage of the most bulky source adaptable to the antenna considered.

 The reflector and the vertex plate can be made of any light alloy having the required radioelectric characteristics.

 The separation discs can be made of stainless steel or any other metallic material (because it reflects electromagnetic radiation) which cannot react with the metals composing the vertex plate and the waveguides.

 Finally, it is obviously possible to replace any means with equivalent means without departing from the scope of the invention.

Claims (11)

1 / Device for mounting and dismounting the source of an antenna on the reflector of said antenna, said source comprising an electromagnetic excitation assembly situated at the end of an assembly for guiding electromagnetic waves, said device comprising - a support of said source traversed by said guide assembly so that said excitation assembly is turned towards the concave face, said front face, of said reflector when said support has been installed in an opening made for this purpose in said reflector, - intermediate means for fixing said support provided with said source on said reflector, said intermediate means being fixed on the convex face, said rear face, of said reflector, - radioelectric adaptation means from said source to said reflector, centered on said reflector and located on its concave face, characterized in that said intermediate means are arranged for r be fixed on said rear face of said reflector, to receive said support coming from said front face and to be disassembled with said support by said rear face. 2 / Device according to claim 1, characterized in that said reflector further comprises a removable part called shutter plate and located in contact with said support when the latter is installed. 3 / Device according to one of claim 2, characterized in that said closure plate is removable from the rear of said reflector. 4 / Device according to one of claims 1 to 3, characterized in that when the material constituting said support and the material constituting said guide assembly have distant electrochemical potentials, said device further comprises means for protecting said support against electrochemical corrosion consisting of elements made of a metallic material such that its electrochemical potential prevents it from reacting with the material constituting said support, and with the material constituting said guide assembly, brazed around said guide assembly and installed in said support without introducing discontinuity with respect to its initial surface, so as to leave a sufficient space of non-reactive material between said assembly and said support. 5 / Device according to one of claims 1 to 4, characterized in that said support is a circular perimeter plate which is received in said corresponding opening of said reflector. 6 / Device according to one of claims 1 to 5, characterized in that said intermediate fixing means comprise a housing ring having a shoulder against which is fixed said support. 7 / Device according to one of claims 1 to 6, characterized in that said adaptation means are integrated into said support, said support then having a planar portion facing said excitation assembly.  8 / Device according to one of claims 1 to 6, characterized in that said adaptation means are two flat plates coming to be fixed on said front face, over said support, so as to present a sufficient flat surface to the radio adaptation. 9 / Device according to one of claims 1 to 8, characterized in that said source is chosen from a monopolar source and a bipolar source. 10 / Device according to one of claims 1 to 9, characterized in that said reflector is parabolic. 11 / Device according to claim 4, characterized in that, when said source is a bipolar source supplied by waveguides, said brazed elements consist of two flat stainless steel discs each brazed on a waveguide.