EP0305286B1 - Medium frequency rotating joint for antenna - Google Patents

Description

The invention relates to rotary joints which are used to transmit signals at medium or intermediate frequency between a rotary antenna and its support which is fixed, in particular those used in radar antennas.

Many radars use rotating antennas which are intended to first transmit high power signals at very high frequency and then to receive the signals reflected by objects, said reflected signals being of very low power. Before their processing to remove the information they contain, these signals are first amplified at very high frequency before being transposed to an average or intermediate frequency of about sixty megahertz, frequency at which they are again amplified . These different amplification and frequency transposition operations are carried out on the antenna itself in a part of the radar called "high frequency head". To be transmitted from the "high frequency head", which is on a rotating support, to the signal processing device proper, which is located on a fixed support at a certain distance from the antenna, it is necessary to provide a seal turning point that realizes this transmission.

According to the characteristics of the radar and therefore of the radar antenna, the signals of several reception channels in parallel must be transmitted simultaneously without the channels interfering with each other, which means that they must be isolated by suitable shielding.

Schematically, a rotary joint of the prior art comprises two cylindrical parts which are arranged concentrically and are articulated by means of ball bearings so as to rotate with respect to each other. These two parts are separated over a certain length by an annular space which is designed to accommodate several pairs of tuned circuits each corresponding to a reception channel. Each couple of tuned circuits is constituted by two concentric annular flat rings, the small ring being integral with the inner cylindrical part and the large ring being integral with the outer cylindrical part. To make the coil of each tuned circuit, a metal tape is placed on the same side of each ring, following the inner and outer edges; this ribbon being configured so as to form an open electrical winding, the ends of which are provided to receive appropriate electrical connections. This is how one end is connected to ground via the metallic strip placed on the inner periphery of the small ring and on the outer periphery of the large ring while the other end is connected to a coaxial conductor. . By this mechanical and electrical arrangement, only the opposite parts of the metal strip of each ring each constitute a coil of the tuned circuit. The capacitors of the tuned circuits result from the distributed capacity of the windings and the addition of a capacitor of determined capacity.

The signal to be transmitted is applied to the ends of a tuned circuit of a torque ring and is transmitted by a mutual inductance effect to the ends of the tuned circuit of the other torque ring. As the rings are concentric, this transmission takes place whatever their respective angular positions.

To make several channels, several pairs of rings are stacked, separating them by shields also constituted by pairs of rings, the spacing between the rings of the pairs of tuned circuits and the rings of the shields being obtained by spacers. These spacers are metallic and are in contact, on the one hand, with the concentric cylindrical parts of the rotary joint and, on the other hand, with the internal periphery of the small ring and the external periphery of the large ring. These various contacts constitute the electrical ground connection, a connection which is reinforced by screws for fixing the spacers to the corresponding cylindrical parts of the rotary joint.

The rotary joint which has just been described has a certain number of drawbacks. First, the bandwidth of the channels is at most twenty megahertz at three decibels of attenuation and the insertion loss is approximately half a decibel. Such a limitation is incompatible with the characteristics which are required of modern speed cameras.

Furthermore, the stacking of a large number of spacers requires great precision in their production and assembly because it is important that the rings of a couple are not offset in position because this would result in a lower mutual inductance. . This problem is all the more difficult to solve as the number of channels is large, which is the case of modern radars where the rotating joint is sometimes provided for twelve channels in parallel. In addition, the thickness of the spacers is such that we end up with dimensions of the rotary joint close to one meter.

Also, the ground connection is poorly established because the metal strip is deposited on only one side of the ring and is therefore only in contact with the spacers on the same side, spacers which are, moreover, connected to the earth of the rotary joint by the fixing screws.

An object of the present invention is therefore to produce a rotary joint whose different channels have a bandwidth as large as possible and in particular greater than forty-five megahertz and a loss of insertion as low as possible.

Another object of the present invention is also to produce a rotary joint which has a space as small as possible while having a high number of channels.

Yet another object of the present invention is to provide a rotary joint which is simpler and easier to produce than the rotary joint of the prior art.

The invention relates to a rotating joint for transmitting signals between a rotating antenna and its fixed support comprising two concentric parts which are articulated so as to rotate with respect to each other and which are separated over a certain length by an annular space, said annular space being designed to contain a stack of pairs of tuned and coupled circuits which are separated from each other by spacers, said pairs of circuits each comprising two concentric annular rings and integral with each of one of the two parts characterized in that the peripheries of the rings of a couple which are opposite one another, have on their two faces open metallic ribbons open and electrically connected together to form an open coil winding and in that the edges of the rings which are not opposite present on their two faces of annular metallic ribbons closed and electrically connected together to form a closed winding serving as ground contact.

The electrical connection of the metal strips of the open coil winding is carried out by the edge of the ring in the form of a metal strip.

The edges of the rings which are not facing each other have annular metal strips on their two faces which are electrically connected by metallized holes so as to produce a closed winding which serves as a ground contact.

Each separation spacer between the tuned circuits has a radial extension in the form of an annular ring which constitutes a shielding screen.

Each separation spacer has a circular groove for housing a metal braid which serves as an electrical connection between the spacer and the associated concentric part.

• la figure 1 est une vue en coupe partielle schématique d'un joint tournant limité à deux circuits couplés et de leur blindage associé, réalisés selon des techniques de l'art antérieur ;
• la figure 2 est une vue de dessus des bobines de deux circuits couplés qui sont réalisées selon l'invention ;
• la figure 3 est une vue de dessous des bobines de deux circuits couplés qui sont réalisées selon l'invention ;
• la figure 4 est une vue en coupe partielle schématique d'un certaine longueur par un espace annulaire, ledit espace annulaire étant prévu pour accommoder un empilement de couples de bagues annulaires concentriques séparés par les couples d'entretoises de manière à définir une pluralité de couples de circuits accordés et couplés qui sont blindes l'un par rapport à l'autre, caractérisé en ce que les pourtours en regard des bagues d'un couple présentent sur leurs deux faces des rubans métalliques annulaires qui sont connectés électriquement de manière à réaliser un enroulement de bobine ouvert.

Other characteristics and advantages of the present invention will appear on reading the following description of a particular embodiment, said description being made in relation to the appended drawings in which:

• Figure 1 is a schematic partial sectional view of a rotary joint limited to two coupled circuits and their associated shielding, produced according to techniques of the prior art;
• Figure 2 is a top view of the coils of two coupled circuits which are produced according to the invention;
• Figure 3 is a bottom view of the coils of two coupled circuits which are produced according to the invention;
• Figure 4 is a schematic partial sectional view of a a certain length by an annular space, said annular space being provided to accommodate a stack of pairs of concentric annular rings separated by the pairs of spacers so as to define a plurality of pairs of tuned and coupled circuits which are shielded from each other to the other, characterized in that the contours facing the rings of a couple have on their two faces annular metallic ribbons which are electrically connected so as to produce an open coil winding.

The electrical connection of the metal strips of the open coil winding is carried out by the edge of the ring in the form of a metal strip.

The edges of the rings which are not facing each other have annular metal strips on their two faces which are electrically connected by metallized holes so as to produce a closed winding which serves as a ground contact.

Each separation spacer between the tuned circuits has a radial extension in the form of an annular ring which constitutes a shielding screen.

Each separation spacer has a circular groove for housing a metal braid which serves as an electrical connection between the spacer and the associated concentric part.

• la figure 1 est une vue en coupe partielle schématique d'un joint tournant limité à deux circuits couplés et de leur blindage associé, réalisés selon des techniques de l'art antérieur ;
• la figure 2 est une vue de dessus des bobines de deux circuits couplés qui sont réalisées selon l'invention ;
• la figure 3 est une vue de dessous des bobines de deux circuits couplés qui sont réalisées selon l'invention ;
• la figure 4 est une vue en coupe partielle schématique d'un joint tournant, limité à deux circuits couplés et leur blindage associé, qui sont réalisés conformément à l'invention, et
• la figure 5 est une vue en coupe d'un joint tournant selon l'invention qui est prévu pour transmettre douze voies.

Other characteristics and advantages of the present invention will appear on reading the following description of a particular embodiment, said description being made in relation to the appended drawings in which:

• Figure 1 is a schematic partial sectional view of a rotary joint limited to two coupled circuits and their associated shielding, produced according to techniques of the prior art;
• Figure 2 is a top view of the coils of two coupled circuits which are produced according to the invention;
• Figure 3 is a bottom view of the coils of two coupled circuits which are produced according to the invention;
• Figure 4 is a schematic partial sectional view of a rotary joint, limited to two coupled circuits and their associated shielding, which are produced in accordance with the invention, and
• Figure 5 is a sectional view of a rotary joint according to the invention which is intended to transmit twelve channels.

In FIG. 1, the coil of a first tuned circuit is constituted by a small flat circular ring 1 which carries, on one side only, a first metallic strip 2 arranged on its internal periphery and a second metallic ribbon 3 arranged on its periphery external. The coil of a second tuned circuit is constituted by a large ring 4 which carries, on the same side as that of the small coil, a first metal strip 5 disposed on its outer periphery and a second metallic ribbon 6 disposed on its internal periphery. The metal strips 2 and 5 are connected to the ground potential by spacers 7 and 8 which rest on said strips and which are fixed one to an internal cylindrical part 9 and the other to an external cylindrical part 10 by the screw intermediate 11. The facing metal strips 3 and 6 are respectively connected to coaxial conductors 12 and 13.

It should be noted, as will be described below in relation to FIGS. 2 and 3, that the metal strips 3 and 6 are open and that one of their ends is connected to the metal strip of mass 2 or 5 carried by the same ring so as to make the earth terminal of the coil. It is therefore the metal strips 3 and 6 which each produce a coil of each tuned circuit, the two coils, by virtue of their opposite position, achieving mutual coupling.

The spacers 7 and 8 support two concentric flat metal rings 14 and 15 which provide a first shielding. A second shield is produced by two other concentric flat metal rings 16 and 17 separated from the rings 1 and 4 by spacers 18 and 19 on which the latter rest.

As will be described in relation to FIG. 5, the internal cylindrical parts 9 and external 10 are concentric and are connected at the top and bottom by a device of the type with bearings balls so as to rotate with respect to each other so that the various external rings 4, 15 and 17 rotate around the internal rings 1, 14 and 16.

According to the present invention, it is proposed to modify the arrangement of the metal ribbons on the rings 1 and 4, the production of the spacers, the shielding rings 14 to 17 and of the ground contact of the spacers, and the passage of the coaxial conductors.

To improve the characteristics of the tuned circuits, the metal strips 25, 26, 27 and 28 which make the ground contact are arranged on the two faces 20 and 21 of the concentric flat rings 22 and 23 (Figures 2, 3 and 4) in resin epoxy and are connected to each other by metallized holes 24. The same is true of the metallic tapes 29, 30, 31 and 32 which produce the coils in mutual coupling but, in this case, the width of the metallic tapes 31 and 32 is less wide as the ribbons 29 and 30 and the electrical connection between the ribbons 29 and 31, on the one hand, 30 and 32 on the other hand, is produced by a metallic deposit on the edges 33 of the facing edges By way of example , the width of the ribbons 29 and 30 can be of the order of two millimeters while that of the ribbons 31 and 32 is of the order of half a millimeter. In the same example, the width of the mass ribbons 25 to 28 can be approximately five millimeters.

Furthermore, the ground contact is improved between the spacers and the cylindrical support parts by a metal braid 34 which is housed in a circular groove in the spacers 35 to 38. These spacers are provided to achieve, at the same time, the spacing between the support rings of the tuned circuits and the concentric metal screens 39 to 42. In this way, the number of parts to be assembled by stacking is reduced and their thickness adjustment to align the rings in the same plane is easier.

The top and bottom views of Figures 2 and 3, respectively, show the arrangement and appearance of the metallic ribbons that surround the rings so as to make the coils of the tuned circuits and ground contacts. In these figures, the ground ribbons 25 and 27 are connected to the ribbons 29 and 31 forming the external coil by arms 43 and 44. It is the same for the ground ribbons 26 and 28 which are connected to the ribbons 30 and 32 making the internal coil by arms 45 and 46. It is noted that the mass metal ribbons are closed while the coil ribbons are open at the location of arms 43 to 46 over a distance of a few millimeters. To make the various electrical connections, the metal strips extend radially by arms 47 to 50 which are connected from one face to the other by metallized holes. For these connections, metallized surfaces 51 to 54 are also provided which are connected from one face to the other by metallized holes. These metallized arms and surfaces are of course used for connecting the input and output coaxial conductors but also for connecting capacitors to obtain the agreement of the circuits at the chosen frequency.

Each of the internal and external rings is pierced with four holes 55 which serve for the passage of the coaxial conductors 59 and are four in number in the case of four reception channels. For twelve reception channels, twelve holes of this type would be required for the passage of the coaxial conductors, not only in the twenty-four rings but also in the metal shielding screens, holes which establish the resistance of the rings and the shielding effect of the screens. . However, these holes 55 can be maintained to ensure interchangeability with rotary joints installed according to the technique of the prior art.

To avoid the presence of these holes, the invention proposes to pass these coaxial conductors 59 through the walls 56 and 57 of the concentric cylindrical support parts by holes 58 (FIG. 5) drilled in the spacers and longitudinal grooves dug in the walls of the internal cylindrical parts 60 and external 61, respectively.

The sectional view of Figure 5 shows a rotating joint provided for twelve receiving channels. He understands, as we already have indicated, an internal cylindrical part 60 and an external cylindrical part 61 which define between their walls 62 and 63 between them an annular space 64 in which are housed the twelve pairs of concentric rings 83 which support the tuned circuits and the twelve pairs of rings concentric 84 and spacers 85 which constitute the shielding screens. These cylindrical parts 60 and 61 are concentric and rotate relative to each other thanks to a mounting with ball bearings 65 and 66, bearings which are arranged at the bottom and at the top of the annular space 64. For the passage coaxial conductors 67 to 70, the walls 62 and 63 have grooves 71 to 74 which open into the upper part of the rotary joint to connect to input pins 75 and 76 fixed on the internal cylindrical part 60 and to pins outlet 77 and 78 fixed on the external cylindrical part 61.

The rotary joint has a ground terminal 79 arranged on the external cylindrical part 61, this ground terminal being equipped with a charcoal and spring device 80, the charcoal of which comes into contact with a thick metal ring 81 electrically connected with the cylindrical part internal 60.

As already indicated, the mounting of the various rings in the annular space is effected by stacking and provision is made for grinding of the surfaces in contact with the spacers in order to align each pair of rings in the same plane.

The pairs of rings making the tuned circuits which are coupled together are produced for example according to the printed circuit technique from a single plate of epoxy glass on which the interval between the rings is cut by a milling machine internal and external, except where there will be no metallization. It is on this plate that the various operations are carried out to obtain the design of the metal ribbons shown in FIGS. 2 and 3. When these operations are completed, the final trimming operations are completed by internal cutting of the small coil and external cutting of the large coil.

With the various improvements made by the invention, it is possible to realize tuned and coupled circuits which have a bandwidth of at least forty-five megahertz at three decibels of attenuation, at least thirty megahertz at half a decibel and at least twenty megahertz at one tenth decibel when the insertion loss is less than three tenths of a decibel.

In addition, the manufacturing and mounting operations of the various elements which constitute the rotary joint are easier to perform while having greater precision. This allows the realization of a rotary joint having a large number of channels in a relatively small volume.

Claims (11)

1. A rotary joint for transmitting signals between a rotary aerial and its fixed support comprising two concentric portions (56, 57 or 60, 61) which are articulated so as to rotate relative to one another and which are separated over a certain length by an annular space, said annular space being designed to contain a stack of pairs of tuned, coupled circuits which are separated from one another by spacers (35 to 38), said pairs of circuits each comprising two concentric annular rings (20, 22), each integral with one of the two portions (56, 57 or 60, 61), characterised in that the periphery of the rings (20, 22) in a pair which face one another have, on both their faces, open annular metal strips (29 to 32) electrically connected to each other so as to form an open coil winding and in that the periphery of the rings (20, 22) which are not facing have, on both their faces, closed annular metal strips (25 to 28), electrically connected to each other to form a closed winding serving as an earth contact.
2. A rotary joint according to Claim 1, characterised in that the electrical connection between the annular metal strips (29, 31 and 30, 32) of a coil is produced by the sheared edge of the ring in the form of a metal strip (33).
3. A rotary joint according to Claim 1 or 2, characterised in that the electrical connection between the annular metal strips (25, 27 and 26, 28) with the earth contact is produced by metallised holes (24) made in the thickness of the ring.
4. A rotary joint according to any one of the preceding claims, characterised in that the width of one (29, 30) of the annular metal strips of the coil winding is around two millimetres whereas the other (31, 32) is half a millimetre.
5. A rotary joint according to any one of the preceding claims, characterised in that the width of the annular metal strips (25 to 28) of the earth contact is around five millimetres.
6. A rotary joint according to any one of the preceding claims, characterised in that the rings are made of an insulating material and in that the various metal strips (25 to 33) and the associated connections (43 to 50) are obtained by deposition.
7. A rotary joint according to any one of the preceding claims, characterised in that each spacer (35 to 38) is annular and has a radial extension (39 to 42), also annular, which constitutes a screen between the pairs of circuits.
8. A rotary joint according to Claim 7, characterised in that each spacer (35 to 38) has a circular groove for housing a metal braid (34 or 82) which produces the electrical contact between each spacer and the associated concentric portion (56, 57 or 60, 61).
9. A rotary joint according to any one of the preceding claims, characterised in that the annular rings (20, 22, 39 to 42) have openings through which connecting conductors can pass.
10. A rotary joint according to any one of the preceding claims, characterised in that each spacer (35) has at least one radial opening (58 or 86) through which a connecting conductor (59 or 67 to 70) can pass.
11. A rotary joint according to any one of the preceding claims, characterised in that the walls (62, 63) of the annular space have longitudinal grooves (71 to 74) through which connecting conductors (59 or 67 to 70) can pass.

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