GB2461591A

GB2461591A - Rotary joint for the transmission of hyperfrequency waves

Info

Publication number: GB2461591A
Application number: GB8327541A
Authority: GB
Inventors: Yves Poncel; Roger Breheret; Jean-Claude Geoffriault; Werner Haseneyer
Original assignee: Dassault Electronique SA; Electronique Serge Dassault SA
Current assignee: Thales SA
Priority date: 1982-10-15
Filing date: 1983-10-14
Publication date: 2010-01-13
Anticipated expiration: 2003-10-14
Also published as: GB8327541D0; FR2632456B1; DE3337116A1; FR2632456A1; GB2461591B; DE3337116C2

Abstract

A rotary joint (10) for coupling two waveguides (60, 80)comprises a cavity (28) defined by two cylindrical co-axial shells (12, 14), of which the open extremities are arranged in opposition and separated by an air gap (25), and their closed opposite ends (20, 22). Waveguides (60,80) communicate radially with the internal space defined by the shells via respective coupling slots (50, 56) in their annular lateral wal1S (16, 18). The two shells (12, 14) are mounted for rotation relatively to one another by way of a ball bearing joint comprising a circular groove (30) in the external face of the shell (14), an annulus (34) united with the second shell (20) and a tightening ring having a section in the form of a right angle (40).

Description

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Rotary joint for the transmission of hyperfrequency waves This invention concerns the transmission of hyper-frequency waves as regards the emission and the reception of electromagnetic radiation.

It is particularly directed to the realisation of rotary joints for effecting such a transmission bet- ween a first part and a second part movable one relativ-ely to the other according to a rotary movement about an axis. Such devices can, for example, be utilised in radars with scanning antennas. They are disposed between a generator and/or a receiver of hyperfrequency waves and an antenna which is to be subjected to the movements concerned without interrupting its function of emission or reception of electromagnetic radiation corresponding to the transmitted waves.

In the known devices the hyperfrequency energy can be transferred at the entrance and at the exit of the rotary joint by coaxial lines or waveguides, accord-ing to the type of construction. The propagation of the energy, at the interior of the rotary joint itself, can proceed according to the mode TEM (transverse electro-magnetic) in the constructions of rotary joint of the purely coaxial type. There can equally be adopted a resonant cavity formed in two parts capable of assuming a rotary movement one with respect to the other. In all these devices the entry and the exit of the hyper-frequency signals can proceed along the axis of the joint, along a direction perpendicular to this axis, or following combinations of these two possible forms of construction. One thus speaks of an I, U or L joint.

Whilst the actually known constructions permit * satisfactory results to be obtained in a relatively large range of hyperfrequency and when the space avail-able for the rotary joint is relatively large, there exist situations in which it is still difficult to utili-se a rotary joint in a reduced space.

The object of the present invention is to provide a construction of rotary joint capable of conveying hyperfrequency signals at relatively high power and in particular sufficient for their employment in certain radar applications, and to achieve this in a reduced space. Additionally, the invention enables such an object to be obtained by means of a very simple construc-tion both from the mechanical and electrical point of view.

The invention accordingly provides a rotary joint for the transmission of hyperfrequency waves between a first part and a second part mounted for rotation one with respect to the other about an axis and compris-ing a first waveguide portion and a second waveguide portion and a cavity providing for the transfer of hyper-frequency energy between these waveguide portions.

The rotary joint according to the invention is character-ised in that the cavity is defined by a first shell and a second shell each having an annular lateral wall clo3ed at one extremity and open at the other, these two shells being mount?d for rotation one relatively to the other about the axis of the said annular walls and the open extremities of these shells being adjacent in the region of a plane perpendicular to their axes of rotation, and in that the first waveguide portion and second waveguide portion are respectively united with the first shell and second shell and each communi-cate radially with the said cavity by way of an opening in the lateral wall of the respective shell.

The studies and experiments conducted by the Appli-cant have shown that the defined construction enables rotary joints to be obtained having a generally U shape with a very much reduced thickness, this dimension being defined by the distance between the closed ends of the shells.

According to a preferred embodiment, the communica-tion openings between the waveguide portions and the resonant cavity have dimensions smaller than the internal dimensions of portions of these waveguides. When the waveguide portions have rectangular sections, the said openings are advantageously in the form of slots which extend parallel to the greatest transverse dimension of the respective waveguide in a plane perpendicular to the axis of rotation of the shells.

The slots effect an electromagnetic coupling bet-ween the waveguides and the cavity bounded by the shells, which acts as a resonant cavity with a relatively low load Q-factor. In such a system the energy propagates in transverse electrical mode in the waveguides and in transverse magnetic mode in the resonant cavity bet- ween the mouths or slots communicating with the wave-guides. The Q-factor is so selected as to generate a mode of sufficiently strong revolution within the cavity that the transmission from one waveguide to the other does not depend upon the position of the shells around their axis of rotation, that is to say the angle between the two waveguide portions.

It will be seen that the frequency of resonance of the cavity depends only upon the diameter of the latter and not on its thickness. This has the result

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that the latter can be chosen with small values. The waveguide portions formed in the connection with the cavity can be accommodated in a space of width not above that of the cavity. There is thus obtained a flat. rotary joint mechanism which readily lends itself to the forma-tion of stacks of such rotary joints. These stacks permit several degrees of liberty to be given to an assembly between a fixed part and a movable part between which hyperfrequency energy is to be propagated.

Having regard to the conditions outlined above, the load Q-factor of the cavity is chosen to have a sufficiently small value to allow a relatively large pass-band with respect to the conditions of use. In the transverse direction, the diameter of the shells is determined as a function of the central frequency of the hyperfrequency band that is desired to be trans-mitted.

It has been ascertained that the-resonant cavity defined by the two shells operates under satisfactory conditions when a simple air gap is provided between the open ends of the two shells. Such can be formed by the opposite edges of the lateral walls of the two shells. One thus obtains a good coupling with the aid of an extremely compact device and, when the dimensions of the joint to be formed are very small, it is possible to avoid the requirement for connecting labyrinths bet- ween the fixed and movable parts of the joint for trap-ping the transmitted energy. Such transmission with the aid of trapping is classically adopted in the rotary

joints of the prior art. However, the dimension of

the labyrinths depends on the length of the waves to be transmitted. This condition renders them inapplicable in certain constructions of small size.

According to another embodiment, the air gap bet-

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ween the two shells can *be formed by arranging that, * on the side of its open end, the lateral wall of one of the shells presents an annular extension of which the external diameter is less than the internal diameter of the other shell and which is engaged in the latter in such a manner as to provide a cylindrical air gap between them.

It is likewise possible, according to yet a further embodiment, to electrically interconnect the shells whilst allowing for a sliding contact between their external edges.

In all cases, there is obtained a rotary joint of which the cavity is void of all mechanical systems.

This produces a very great simplicity of construction which is characterised by advantages as regar4s the level of cost of its construction, the reproducibility from one rotary joint to the next, and the diversifica-tion of its characteristics.

The displacement of the shells relatively to one another is effected in the region of the median plane of the cavity, that is to say in a zone where the elect-ric field is weak. This likewise contributes to the uniformity of the transmission of energy from one wave-guide to the other, whatever is the relative position of these waveguides.

As regards the mechanical construction, a preferred arrangement provides a connection with balls between the two shells in the region of their open ends. This can be advantageously achieved by a track of balls accom-modated in a circular groove in the external wall of the first shell, the second shell presenting an annulus adapted to form a support at the outside of the track of balls. A ring can be mounted in an adjustable manner on the said annulus in order to provide a second support * at the exterior of the track of balls of which the posi-tion relatively to the annulus can be adjusted in such a manner as to control the tightening of the balls bet-ween the first and second shell.

Such a ball joint of circular construction is disposed between the first and second waveguide portions respectively connected to the first and second shells.

There thus results at the exterior of the rotary joint a structure which is likewise very simple. Such a struc- ture can be easily effected by specialists in the struc-tures of ball type joints in a manner independent of the arrangement specific to the propagation of hyperfreq-uency energy.

One thus obtains a rotary joint providing an exce-llent performance from the mechanical point of view, and in particular with low friction and with resistance to vibration and to wear, whilst possessing satisfact-ory electromagnetic properties with an extremely reduced size. In this respect a rotary joint according to the invention is suitable for cooperation with so-called "reduced" waveguides, that is to say of smaller dimension than is conventional, whilst transmitting relatively high powers, particularly for feeding an antenna in radar applications.

Further explanation and description of one embodi-

ment of the invention are given below by way of non-limiting example with reference to the accompanying drawings, in which: Figure 1 is a sectional view taken across the dia-meter of a rotary joint according to the invention; Figure 2 is a transverse sectional view of the joint of Figure 1 on the line II -II of Figure 1; Figures 3 and 4 show in section in a diametral plane similar to that of Figure 1, variations of the construction of the interface between the shells of a rotary joint according to the invention.

A rotary joint 10 (Fig. 1) comprises two metallic shells 12 *and 14 mounted for rotation one relatively to the other about an axis 15. These shells respect-ively comprise coaxial lateral cylindrical walls 16 and 18 centred on the axis 15, and are closed at one of their ends by a circular end wall, respectively 20 and 22. At their opposite extremities, the shells 12 and 14 are open and disposed face to face in such a manner that the respective edges 24 and 26 of their lateral walls 16 and 18 are arranged opposite one another and separated by a radial air space 25. The internal diameters of the lateral walls 16 and 18 are equal, the interior of these shells defining the cavity 28 between the end walls 20 and 22.

In the region of its open extremity the shell 14 comprises in the external face of its lateral wall 18, a groove of V-shaped transverse section 30 which houses balls 32 around its circumference. At the side of its open extremity, the shell 12 comprises an annulus 34 which projects relatively to the external face of its lateral wall 16. The internal diameter of the annu-lus 34 is greater than the external diameter of the lateral wall 18 of the shell 14 in which is formed the groove 30. The annulus 34 projects with respect to the plane of the adjoining edge 24 of the shell 12 in such a manner that the open end of the shell 14 can be accommodated within this annulus to an extent that the interior bevelled or chamfered edge 36 of the annulus engages against the balls 32 located' in the groove 30.

The external cylindrical surface 38 of the annulus 34 presents a threading on which is screwed a ring 40 with a transverse section in the form of an L. The stem of the L is internally threaded. The foot of the L is directed radially towards the axis 15 and presents a bevelled end 44 adapted to engage against the balls 32 of the track of balls 30 in a direction which, with respect to the normal to the axis 15, is symmetrical to the direction of engagement of the annulus 34 with these balls. When the ring 40 is caused to approach the annulus 34 by screwing, the combined action of the chamfered edges 44 of the ring and 36 of the annulus exert a tightening force on the balls 32. The resultant of this force, directed in a substantially radial direc-tion, urges the balls against the walls of the V-shaped groove 30. One can thus, by an appropriate adjustment of the position of the ring 40 on the foot of the annulus 38, adjust the play of the ball type joint 32 forming the rotary connection between the shells 12 and 14 about the axis 15.

Before a final adjustment of the tightness, a slight wear of the contact faces can be arranged by rubbing the contact faces of the shells against the track of balls 32 by effecting a prolonged rotation thereof. It is likewise possible to machine away the internal faces of the groove 30 and the contact faces 36 and 44 to give them a slight concavity rendering such a rubbing action unnecessary.

The lateral wall 16 of the shell 12 is traversed by a slot 50 of which the axial dimension or size para-llel to the axis 15 is relatively small with respect to the corresponding dimension of the lateral wall 16.

This slot is visible in Figure 2. It is elongated in a transverse plane perpendicular to the axis 15 over a relatively significant length of arc in the lateral wall 16..

Around the opening 52 issuing from this slot in the external face 54 of the lateral wall 16 is disposed a waveguide 60 of rectangular transverse section which joins with the wall 16 following a contour bounded by two portions with generatrices 62 and 64 (Figure 2) and two circular arcs 66 and 68 at the interior of the waveguide. As has been indicated this contour has dimen-sions greater than that of the slot 50, both in the io axial direction and in the direction perpendicular there-to. The waveguide 60 has an axis 65 intersecting the axis 15. At its end 69 opposite to the shell 12 it has a rectangular flange 70 adjoining with an entry or exit structure not shown. Considered in a section perpendicular to its axis 65, the waveguide has a dimen-sion e parallel to the axis 15 (thickness) smaller than the dimension L in the direction perpendicular thereto (Figure 2). In the construction shown the internal faces 53 of the slot 50 are parallel with the axis 65 (Figure 2); however, they could be directed otherwise, for example radially.

Towards the front of the shell 12, the external face 72 of the waveguide 60 is applied against the rear face 35 of the annulus 34. The opposite external face 73 of the waveguide 60 is substantially in the plane of the external face of the closing wall 20. In order to assemble the waveguide 60 with the external lateral face of the shell 12, it is prolonged by an annular portion 75 which is threaded around the shell 12 and soldered to the latter (Figures 1 and 2).

In the same manner there is associated with the shell 14 a waveguide 80 terminated by a flange 81 at one end and issuing at its other end, connected with the external face 02 of the lateral wall 18, into a curved slot 56 providing a communication between the interior of this waveguide 80 and the interior of the shell 14. The relative dimensions of the slot 56 and of the waveguide 80 are identical to those described in relation to the slot 50 and the waveguide 60. The waveguide 80 is assembled with the exterior of the shell 14, via an annular extension 83, by soldering. The internal face 84 of the waveguide 80 is arranged at a sufficient distance from the groove 30 to allow the space required for the part 42 of the ring 40.

As a result of the mounting which has been descri-bed, the two waveguides 60 and 80 can take up any angular position relatively to one another about the axis 15 by simple rotation of the shell 14 around the shell 12. In order to simplify the explanation these two waveguides, or portions of waveguides have been shown in Figure 1 as being directed in the same direction.

When one of the two, for example the waveguide 80 (arrow 90) is supplied with hyperfrequency energy in the pass-band of the device, this energy propagates in the transverse electrical mode TE10 (the mode determ-ined by the rectangular shape of the waveguides. It reaches the coupling slot 56 at the entrance of the cavity 28 through which is effected a conversion of the energy propagation to the transverse magnetic mode TM010. The cavity 28 acts as a resonant cavity. Its dimensions are determined in such a manner that the mode of propagation at the interior of the space bounded by the internal faces of the shells 12, 14 should be substantially one of revolution. Under these conditions, whatever is the angular relative position of the slots 56 and 50, the energy admitted at the periphery of the shell 14 propagates towards the axis 15 and, from the latter towards the periphery of the shell 12 where it can be taken through the slot 50 which effects the coup- ling between the interior of the cavity 28 and the wave- guide 60. The latter transmits the waves in the clirec- tion indicated by the arrow 92 in the transverse electri-cal mode. There is indicated by a broken line 100 the envelope of the extremities of the vector electrical field at the interior of the cavity 28 (vectors 102).

It will be noted that the electrical field has a minimum value at the periphery of the cavity and thus at the level of the zone of the air gap 25 between the opposite edges of the shells 12 and 14. There thus results a zone of low potential difference, which is a favourable condition for the admission of high powers.

The construction which has been described is parti-cularly notable in that it allows the transmission of powers which can reach several hundreds of watts for frequencies between 10 and 20 GFIz with waveguides 60 and8O and shells 12 and 14 of reduced dimensions.

In this respect, one can for example transmit energy at a frequency in the band indicated with wave-guides of thickness or height e equal to 3 mm and of breadth L equal to 15 mm in contrast to standard dimen-sions of 8 x 16 mm. With these waveguide portions, the total thickness of the rotary joint 10 (the distance between the walls 20 and 22) can be less than 10 mm for a total diameter of the shells less than 22 mm.

It is relevant to note in particular that the frequency of resonance of the cavity 28 responsible for the propagation at the interior of the rotary joint does not depend upon the thickness thereof, which can therefore be made as small as possible. It depends on the other hand on the diameter of the cavity. The latter is then determined as a function of the frequen-cies to be transmitted.

In all cases, the described construction allows the formation of very flat rotary joints, of a great simplicity both from the mechanical and electrical point of view.

A ball bearing joint 32, 34 and 40 can be made with great precision. It forms a very simple means of rotary connection with a low coefficient of friction and hardly subject to vibration in a space which is compatible with the terms of use indicated above. The shells can advantageously be formed in a material such as bronze or beryllium covered with an anti-oxidation coating such as silver and/or gold. This material pos-sess a good electrical conductivity as well as being very durable, characteristics desirable for the formation of a ball bearing joint. The annular portions 75 and 83 of the waveguides are soldered onto the shells with tin.

The air gap 25 is sufficient to ensure the electri-cal closure between the shells. It allows a satisfactory function without it being necessary to utilise labyrinths for trapping the energy. Such labyrinths, at the frequ-encies under consideration, would be incompatible with the small thickness required of the device 10. The facing surfaces of the metallic shells 12 and 14 can be aug-mented at the level of their open ends, as shown in Figure 3, in which the same reference numerals have been retained for the same elements. The open end 14A of the shell 14 is extended axially by a portion in the form of a ring 110 which penetrates to the inside of the open end 12A of the shell 12, in such a manner as to provide between the internal face of the latter and the ring 110 an air gap 112 of annular shape centred on the axis 15, and which supplements the radial air space 114 between the opposite edges of the ends 12A and 14A of the shells.

According to another embodiment shown in Figure * 4, one or several contact strips 120 are soldered or connected by other means at 122 to the shell 14on the internal face of the latter at the side of its open end. The forward part 124 of the flexible strip 120 makes resilient sliding contact against the internal face 125 of the annular wall 16 of the shell 12 at the side of the open end of the latter. It could alterna-tively engage, according to another embodiment, in the air gap 114 on the wall 16 of the shell 12.

Claims

Claims 1. A rotary joint for the transmission of hyperfreq-ency waves between first and second parts mounted for rotation relatively to one another about an axis, and comprising first and second waveguide portions and a cavity providing for the transfer of hyperfrequency energy between the waveguide portions, wherein the said cavity is defined by a first and a second shell each having an annular lateral wall closed at one extre-mity and open at the other, the two shells being mounted for rotation relatively to one another about the axis of the said annular walls and the open ends of the shells being adjacent one another in the region of a plane perpendicular to the axis of rotation, and the first and second waveguide portions are respectively united with the first and second shells and each communicate radially with the said cavity via an opening in the lateral wall of the respective shell.
2. A rotary joint according to Claim 1, wherein each opening has transverse dimensions smaller than the inter-nal transverse dimensions of the respective waveguide portion.
3. A rotary joint according to Claim 2, wherein each waveguide portion has a rectangular section and the said opening has the shape of a slot extending parallel to the major transverse dimension of the waveguide in a plane perpendicular to the axis of rotation of the shells.
4. A rotary joint according to any one of the preced- ing Claims, wherein the two shells are mounted for rota-tion one relatively to the other by a ball bearing joint in the region of the open ends of said shells.
5. A rotary joint according to Claim 4, wherein the ball bearing joint comprises a track of balls in a circu-lar groove in the external wall of the first shell, an annulus united with the second shell and adapted to engage the balls and a ring associated with the said annulus in an adjustable manner in order to provide a second engagement support for the controllable tighten-ing of the second shell onto the balls.
6. A rotary joint according to Claim 5, wherein the said ring has a section in the shape of an L of which a radial limb bears on the balls with one of its ends and of which the other limb is coupled to the said annu-lus by screwing.
7. A rotary joint according to any one of the preced-ing Claims, wherein the edges of the open ends of the shells are oppositely disposed and separated by a radial air gap.
8. A rotary joint according to any one of Claims 1 to 6, wherein the first shell is extended axially by a cylindrical ring or sleeve penetrating into the part of the cavity defined by the second shell in such a manner as to provide a cylindrical air gap between this ring and the internal lateral surface of said second shell.
9. A rotary joint according to any one of Claims 1 to 6, wherein the shells are electrically connected to one another in the region of their open ends by at least one sliding contact.
10. A rotary joint according to any one of the preced-ing Claims, wherein each waveguide portion terminates in a ring mounted around the external lateral wall of
11. A rotary joint substantially as described herein with reference to the accompanying drawings. (-IAmendments to the claims have been filed as follows 1. A rotary joint for the transmission of microwaves between first and second parts mounted for rotation relatively to one another about an axis, and comprising first and second waveguide portions and a cavity pro-.viding for the transfer of microwave energy between the waveguide portions, wherein the said cavity is defined by a first and second shell each having an annular lateral wall closed at one extremity and open at the other, the two shells being mounted for rotation relatively to one another about the axis of the said annular walls, the axial length of each said annular wall being less than the internal diameter thereof, and the open ends of the shells being adjacent one another in the region of a plane perpendicular, to the axis of rotation, and the first and second waveguide portions are respectively united with the first and second shells and each communicate radially with the said cavity via an opening in the lateral wall of the respective shell.2. A rotary joint according to Claim 1, wherein each opening has transverse dimensions smaller than the inter-nal transverse dimensions of the respective waveguide portion.3. A rotary joint according to Claim 2, wherein each waveguide portion has a rectangular section and the said opening has the shape of a slot extending parallel to the major transverse dimension of the waveguide in a plane perpendicular to the axis of rotation of the shells.4. A rotary joint according to any one of the preced- ing Claims, wherein the two shells are mounted for rota-tion one relatively to the other by a ball bearing joint in the region of the open ends of said shells.5. A rotary joint according to Claim 4, wherein the ball bearing joint comprises a track of balls in a circu-lar groove in the external wall of the first shell, an annulus united with the second shell and adapted to engage the balls and a ring associated with the said anriulus in an adjustable manner in order to provide a second engagement support for the controllable tighten-ing of the second shell onto the balls.6. A rotary joint according to Claim 5, wherein the said ring has a section in the shape of an L of which a radial limb bears on the balls with one of its ends and of which the other limb is coupled to the said annu-lus by screwing.7. A rotary joint according to any one of the preced-ing Claims, wherein the edges of the open ends of the shells are oppositely disposed and separated by a radial air gap.8. A rotary joint according to any one of Claims 1 to 6, wherein the first shell is extended axially by a cylindrical ring or sleeve penetrating into the part of the cavity defined by the second shell in such a manner as to provide a cylindrical air gap between this ring and the internal lateral surface of said second shell.9. A rotary joint according to any one of Claims 1 to 6, wherein the shells are electrically connected to one another in the region of their open ends by at least one sliding contact.10. A rotary joint according to any one of the preced-ing Claims, wherein each waveguide portion terminates in a ring mounted around the external lateral wall of C' 11. A rotary joint substantially as described herein with reference to the accompanying drawings.