Abstract:
A device for conveying signals for a mobile antenna positioner is provided. The device comprises a waveguide with a conductive structure including a first end connected to the antenna, and a second end connected to the mount of the positioner, wherein the waveguide has a continuous structure, each of its ends being attached by means allowing a range of movement of the waveguide in order to limit the bending forces of said guide and to reduce the force applied to the attachment means during the movements of the positioner. The device applies notably to communication systems with mobile antennas, and more particularly to the production of antenna stations comprising antenna positioners with a wide range of movement in relative bearing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Patent Application No. PCT/EP2008/067650, filed on Dec. 16, 2008, which claims priority to foreign Patent Application No. FR 07 09053, filed on Dec. 21, 2007, the disclosures of which are incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to a device for conveying signals for a mobile antenna positioner. The invention applies notably to communication systems with mobile antennas, and more particularly to the production of antenna stations comprising antenna positioners with a wide range of movement in relative bearing. 
     BACKGROUND OF THE INVENTION 
     As an example, antenna systems used in two-way communications between two mobile carriers are usually provided with a pursuit function, the antenna of each of said carriers then having to cover a wide pointing surface area, so that the radio-electric axes of each antenna remain oriented facing one another, irrespective of the movements of the carriers. In order to orient the antenna in the desired directions, an antenna system comprises a positioner, that is to say a programmable controller comprising a mobile portion to which the antenna is attached. 
     A first category of positioners, called tower positioners, makes it possible to orient the antenna by making it pivot, on the one hand, about a vertical axis in order to modify the angle of relative bearing and, on the other hand, about a horizontal axis in order to modify the angle of elevation. The signals transmitted and/or received by the mobile antenna are transmitted to a fixed portion, for example to the mount of the positioner, via a waveguide. When the antenna system has a large range of movement in relative bearing, or even has infinite relative bearing—in other words, when it allows the antenna to pivot indefinitely about the vertical axis—, the use of rotating collectors and/or of rotating joints at the junction of the waveguide with the fixed portion is necessary in order to prevent subjecting the waveguide to torsional forces which would damage it. A drawback of such antenna systems is their high cost of production. 
     A second category of positioners, made on the principle of a Cardan suspension, makes it possible to dispense with collectors and rotating joints. Certain of these positioners benefit from an enhancement proposed in a patent application published under reference FR2769969 for the applicant “ACC ingénierie &amp; maintenance SA”. These enhanced positioners comprise a pointing device with no top dead center based on a pantograph mechanism; they will be qualified in what follows as “pantograph positioners”. In order to convey the electromagnetic signals between the antenna and the fixed mount of a pantograph positioner, waveguides that are sufficiently flexible and accept the torsional movements are used. 
     These waveguides consist of a discontinuous structure, often on the basis of interlocked scales which lead to reliability problems. Specifically, the structure of such a waveguide wears very quickly, and even breaks under the effect of the repeated torsional movements that are applied to it. Thus, the service life of the waveguide is short, which imposes regular preventive replacements. Moreover, considerable insertion losses and intermodulation products appear when this type of waveguide is used. In transmission, the powers are then severely limited. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to propose means making it possible to convey signals between the antenna and the mount of a positioner with a wide range of movement in relative bearing while limiting the insertion losses, the deterioration of the received signals and the problems of mechanical reliability. Accordingly, the subject of the invention is a device for conveying signals for a mobile antenna positioner with a wide range of movement in relative bearing comprising a waveguide with a conductive structure, a first end of which is connected to the antenna, a second end being connected to the mount of the positioner, said device being characterized in that the waveguide has a continuous structure, each of its ends being attached by means allowing a range of movement of the waveguide in order to limit the bending forces of said guide during the movements of the positioner. 
     According to one embodiment, the antenna positioner is an antenna positioner of the pantograph type. 
     According to one embodiment, the means for attaching the waveguide comprise at least one support, immobilization means and one or more swivel joint assemblies attached to said support, the end of the waveguide being kept substantially immobile relative to the support by the immobilization means, the waveguide being inserted in said swivel joint assemblies in order to stabilize the waveguide while conferring a range of movement thereon. 
     According to one embodiment, the device comprises at least one spring, the spring being held against the waveguide by cable ties. 
     According to one embodiment, the signals conveyed by the waveguide are microwave signals. 
     According to one embodiment, the waveguide is electroformed and made of an alloy comprising beryllium and copper, this material being well suited to the transmissions of microwave signals, and also being suitable for sustaining bends along its structure. 
     According to one embodiment, the waveguide has a bellows structure, the waveguide being able to be deformed alternately on a first axis of rotation and a second axis of rotation, the waveguide not being able to deform under the effect of a torsional movement. 
     Preferably, the inner wall of the waveguide is smooth and comprises no roughness or aperture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features will appear on reading the following detailed description given as an example and being non-limiting and made with respect to the appended drawings which represent: 
         FIGS. 1A and 1B , diagrams illustrating various positions taken by a pantograph positioner, 
         FIG. 2 , an overview of an embodiment of the device for conveying signals according to the invention, attached to a pantograph positioner, 
         FIG. 3 , a detail of the means for attaching the signal-conveying device to the top portion of the positioner, 
         FIG. 4 , a detail of the means for attaching the signal-conveying device to the bottom portion of the positioner, 
         FIG. 5 , another embodiment of the means for attaching the signal-conveying device to the bottom portion of the positioner, 
         FIG. 6 , an illustration of the structure of the waveguide used in the conveying device according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     For the purposes of clarity, the same reference numbers in different figures designate the same elements. 
       FIGS. 1A and 1B  illustrate a pantograph positioner  100  in various positions. 
       FIG. 1A  shows the pantograph positioner  100  orienting an antenna  101  vertically upward, and  FIG. 1B  shows the positioner  100  articulated so that the antenna  101  is oriented at a negative angle of elevation. A conveying device explained in detail hereafter comprises a waveguide  200  which connects the antenna  101  to the positioner  100 . 
       FIG. 2  shows an overview of an embodiment of the signal-conveying device according to the invention attached to the pantograph positioner  100 . The signal-conveying device comprises the waveguide  200  attached, on the one hand, to a mobile portion  300  of the positioner  100  supporting the antenna  101  ( FIG. 1 ), and, on the other hand, to a bottom and fixed portion  400  of the positioner. The first means  201  for attaching the waveguide  200  to said mobile portion  300  of the positioner  100  and the second means  202   a ,  202   b  for attachment to its bottom portion  400  are shown in detail respectively in  FIGS. 3 and 4 . 
     The mobile portion  300  of the positioner  100  moves about two axes of rotation X and Y, represented in dashed lines in  FIG. 2 . The top end  200   a  of the waveguide  200 , which is attached to the mobile portion  300  of the positioner  100  by virtue of the first attachment means  201 , is held substantially parallel with the second axis of rotation Y of the positioner, this second axis of rotation Y itself being subjected to a rotary movement about the first axis of rotation X. The bottom end  200   b  of the waveguide  200  is held in a fixed position by virtue of the second attachment means  202   a ,  202   b , said bottom end being held, in the example, substantially horizontal. Moreover, in the example, the second attachment means  202   a ,  202   b  comprise a first attachment point  202   a  allowing a freedom of movement to the waveguide  200 , and a second attachment point  202   b , placed beneath the first  202   a , making it possible to immobilize the bottom end  200   b  of the waveguide  200 . Therefore, in the example, the waveguide  200  is held by three attachment points  201 ,  202   a ,  202   b ; it forms substantially an S between its top end  200   a  and its bottom end  200   b , this S being deformed as a function of the movements of the mobile portion  300  of the positioner  100 , alternately in a movement about the first axis of rotation X and about the second axis of rotation Y. In the example, the top end  200   a  of the waveguide  200  is attached to the fork  203   a  of the positioner, while the bottom end  200   b  of the waveguide  200  is attached to the height extension  204  of the positioner  100 . 
     According to one embodiment, one or more springs (not shown in the figures) are attached to the waveguide  200  in order to prevent said guide  200  from collapsing on itself because of its own weight, and therefore to better distribute the mechanical stresses applied to the waveguide  200 . These springs may be distributed sporadically over the waveguide  200  or may extend over its whole length, the stiffness of a spring notably being chosen as a function of the weight of the waveguide  200 , of the dimension of the waveguide, and of the dimension of the positioner  100 . The springs are attached so as to be able to slide only along a plane of the guide through flexible fasteners, such as, for example, plastic cable ties. 
     The continuous character of the structure of the waveguide  200 —which makes it possible to obtain good performance in terms of signal transmission—makes it necessary to design specific attachment means in order to limit the mechanical forces that are applied to it when the positioner  100  moves. 
       FIG. 3  shows, for the embodiment of  FIG. 2 , a detail of the means  201  for attaching the signal-conveying device to the top and mobile portion  300  of the positioner. These attachment means  201  comprise a support  301  attached to the top and mobile portion  300  of the positioner which, in the example, is the fork  203   a . In the example, the support  301  is a rectangular rigid plate one wall of which is attached to the fork  203   a  of the positioner  100 , the support  301  thus forming a plane orthogonal to the first axis of rotation X. One or more brackets  302  are attached to the opposite wall of the support  301 , the two orthogonal planes  302   a ,  302   b  formed by the walls of each bracket  302  themselves being orthogonal to the plane formed by the two axes of rotation X and Y. The first wall  302   a  of each bracket  302  is joined to the support  301 , while the second wall  302   b  of the bracket  302  is orthogonal to the second axis of rotation Y. A flange  303  secured to the waveguide  200  is placed on the second wall of each bracket  302  so that the waveguide  200  is clamped by each of the flanges  303  along the support  301  and its top end  200   a  is held fixed relative to the mobile portion  300  of the positioner  100  in order to be connected to the antenna  101  ( FIGS. 1A and 1B ). 
     Since the top end  200   a  of the waveguide  200  is held fixed relative to the mobile portion  300  of the positioner  100  while the bottom portion  200   b  ( FIG. 4 ) of the waveguide  200  remains fixed, the waveguide  200  must support bending forces because of the movements of the positioner  100 , both about the first axis of rotation X and about the second axis of rotation Y. In order to limit these bending forces, the waveguide  200  is inserted into one or more swivel joint assemblies  304  placed in the extension of the brackets  302 , along the support  301 . In this manner, the waveguide  200  is held in place while having a range of movement that allows it to better withstand the flexing imposed by the movement of the positioner  100  and simultaneously to reduce the stresses applied to the flange  303 . The spacings between the swivel joint assemblies  304  can be adapted as a function notably of the length of the waveguide  200  and of its flexibility characteristics. 
       FIG. 4  shows, for the embodiment of  FIG. 2 , a detail of the means  202   a ,  202   b  for attaching the signal-conveying device to the bottom portion  400  of the positioner  100 . In the example of  FIG. 4 , the attachment means  202   a ,  202   b  comprise a first portion  202   a  situated substantially above a second portion  202   b.    
     The first portion  202   a  of the attachment means  202   a ,  202   b  comprises a swivel-joint assembly  304 ′ attached to a support  301 ′ and the second portion  202   b  comprises an attachment flange  303 ′ attached to a bracket  302 ′ which is attached to a support  301 ″. The waveguide  200  is held by the swivel joint assembly  304 ′ of the first portion  202   a  and the bottom end  200   b  of the waveguide  200  is attached to the second portion  202   b  via the attachment flange  303 ′ so that the waveguide  200  creates substantially a half-loop between the first portion  202   a  and the second portion  202   b.    
     According to another embodiment shown in  FIG. 5 , the means  202  for attaching the signal-conveying device to the bottom portion  400  of the positioner  100  are similar to those shown in  FIG. 3 . They also comprise one or more brackets  302 ″ substantially in line with a support  301 ″. In  FIG. 5 , the waveguide  200  is shown slightly set back from the bracket  302 ″. The bottom end  200   b  of the waveguide  200  is attached to the bracket  302 ″ by means of an attachment flange  303 ″. Preferably, the waveguide  200  is also stabilized with one or more swivel joint assemblies  304 ″ in order to give it a range of movement in order to limit the bending forces that are applied to it, as in  FIG. 3  and to reduce the force applied to the attachment flange  303 ″. 
       FIG. 6  illustrates the structure of the waveguide  200  with a cross section  6 A and a view in perspective  6 B. The waveguide  200  has a continuous structure, that is to say that, unlike a conventional structure formed by several linked elements, the waveguide  200  used in the signal-conveying device according to the invention is formed in a single piece, with no opening or roughness on its inner wall. In the example, the waveguide  200  comprises a bellows structure  202 , of rectangular section, with a conductive inner wall, in this instance made of an alloy comprising beryllium and copper. Advantageously, the waveguide is electroformed. 
     Unlike a waveguide with a discontinuous structure, the waveguide  200  used in the present invention cannot, because of its continuous character, sustain a torsional movement at one and the same point, that is to say sustain two orthogonal bends at one and the same point. Therefore, the waveguide  200 , in order nevertheless to adapt to the mechanical stresses imposed by the movement of the positioner  100 , is suitable for sustaining flexions in different directions in several successive locations, notably by virtue of the material used and its bellows structure  202 . 
     Unlike a waveguide with a discontinuous structure, the waveguide  200  used in the present invention cannot, because of its continuous character, sustain a torsional movement at one and the same point, that is to say sustain two orthogonal bends at one and the same point. Therefore, the waveguide  200 , in order nevertheless to adapt to the mechanical stresses imposed by the movement of the positioner  100 , is suitable for sustaining flexions in different directions in several successive locations, notably by virtue of the material used and its bellows structure. 
     Preferably, the length of the waveguide  200  should be chosen so as to minimize the flexing forces that are applied to it; therefore a waveguide  200  that is too short for example would risk causing mechanical breakages. 
     The use of a signal-conveying device according to the invention makes it possible to reduce the insertion losses, to insulate the waveguide over time and not to generate intermodulation products toward the outside of the waveguide particularly for high-power microwave signals. Moreover, by virtue of the attachment means employed, and despite the continuous character of the structure of the waveguide, the latter is not subjected to bending forces that are too great, thus ensuring good reliability of the device. The signal-conveying device according to the invention is particularly suited to pantograph antenna positioners and makes it possible to provide infinite rotational coverage of the range-of-movement zone of the positioner. Nevertheless, it can also be mounted on positioners of different types and notably positioners of the tower type with a wide range of movement in relative bearing.