EP0030895B1 - Method of correcting the cross-defocusing of a paraboloid and matching device for correcting a parabolic antenna - Google Patents

Abstract

A correction method for transverse defocussing of paraboloid oriented relative to the source initially aligned with the focus consists of securing said paraboloid to first platform, articulating said first platform through hinge means jointed to second platform, itself articulated through further hinge means jointed to a stationary part, and then orienting said hinge means to said focus, while providing moving means for said platforms, said moving means being servocontrolled responsive to pointing error detector thereby to hold permanently said focus close to the source. Provision is also made of a parabolic antenna comprising means for carrying out said method. The system is applied to radio and TV broadcast apparatus aboard satellites.

Description

The orientation of a beam of satellite dishes and a satellite dish in general can be obtained in different ways.

When the source is rigidly linked to the paraboloid, the assembly can be pivoted around the reference axes.

This can be the case of satellite dishes mounted on satellite where the whole body of the satellite is then stabilized according to a determined pointing direction.

It is also possible to constitute the source-paraboloid assembly in a base and to orient this base in relation to its support.

This solution is commonly used on surveillance radars for example.

We can finally orient the paraboloid with respect to the source but in this case appears a defocusing phenomenon which is both axial and transverse and which results from the fact that the pivot point no longer makes it possible to subject the focal point of the paraboloid to the source.

This last case is however the only one which can be retained when, for example, on a radio-broadcasting satellite on which the power losses on the emission have to be reduced, it is important to subject the horn containing the source directly to the body of the satellite.

Thus, this satellite is roughly stabilized on the orientation axis while a fine pointing system brings the focus of the dish in the intended direction.

Such systems are well known in themselves.

According to these systems, the antenna is linked to a platform that can be oriented relative to the satellite and the orientation device essentially consists of a particular electromagnetic system which has the advantage of eliminating friction generating disturbing torques and which has been described in another European patent application of the Applicant EP-A-0 015 829 entitled "Electromagnetic method for adjusting the orientation of a platform".

However, if such systems solve the problems of friction by absence of mechanisms, they do not avoid the aforementioned defocusing phenomenon, which remains inherent in the fact that the virtual point of rotation of the paraboloid is located behind this paraboloid, therefore far behind the foyer.

One could envisage a device making it possible to attenuate this defocusing starting from a tripod or tetrapod system, of the kind such as that described in the patent of the United States of America No. 3 871 778 for example.

According to such a conception, the source-paraboloid assembly can be symbolically represented by a truncated pyramid with a triangular (or square) base in which the fixed source would be at the top of said pyramid and the director of the paraboloid perpendicular to the plane of the truncated part; the base being for its part subject to a fixed part.

In this way, the truncated part being linked to this base by axially deformable elements oriented along the edges, it is possible to obtain, by rotation of the connection points, a displacement of the sides of said truncated part which then takes place substantially in the plane of the lateral faces of said pyramid thus bringing a minimum difference between the focus and the source.

Unfortunately for such a device, the axial torsional stiffness remains very low, which requires, for example, additional means with parallelograms such as those described in the United States patent mentioned above.

In addition, when the system is tripod, it is necessary to combine the detection of pointing errors for the control of the orientation motors, which requires coupling of the axes in X and in Y.

Finally, the adaptation of electromagnetic techniques revealed by the Applicant in its European patent application EP-A-0015829 above-mentioned, would be hardly compatible with such tripod or tetrapod systems due to the large axial deflection resulting which decreases correspondingly the efficiency of the installation due to the large air gaps required.

Consequently, the invention proposes a method for correcting the transverse defocusing of a paraboloid which does not have any of the drawbacks described above.

According to the invention, the paraboloid is supported on a first platform articulated transversely according to a deformable trapezoid and said first platform is itself articulated orthogonally on a second platform articulated according to a deformable trapezium linked to the fixed base.

In this way and under the action of suitable servomotor means acting independently on the transverse movements of the platforms, the focal point of the paraboloid can remain appreciably mistaken for the source, except for a second degree error, negligible in practice but which will nevertheless be explained later in this text.

The invention will be, in any case, well understood in the remainder of the present text which gives, by way of example and in support of the attached drawings, a preferred embodiment of said invention for a parabolic antenna reflector for satellite.

• la figure 1 est un schéma en coupe représentant une source liée à un paraboloïde, l'ensemble étant assujetti au corps proprement dit;
• la figure 2 est un schéma en coupe représentant une source liée au paraboloïde, l'ensemble étant pivoté sur le corps proprement dit;
• la figure 3 est un schéma en coupe représentant une source non liée au paraboloïde qui est lui-même orientable par rapport au corps proprement dit;
• la figure 4 est une vue schématique en perspective montrant les moyens mis en oeuvre dans l'invention pour corriger la défocalisation transversale d'un paraboloïde;
• la figure 5 est un schéma géométrique montrant comment la correction de défocalisation transversale est obtenue dans une première conception selon l'invention;
• la figure 6 est un schéma géométrique montrant comment la correction de défocalisation transversale est obtenue dans une seconde conception selon l'invention;
• la figure 7 est un schéma géométrique montrant comment la correction de défocalisation transversale est obtenue dans une troisième conception l'invention; et
• la figure 8 est une schématique en perspective montrant des moyens électromagnétiques connus de déplacement des plates-formes.

In the drawings:

• Figure 1 is a sectional diagram showing a source linked to a paraboloid, the assembly being subject to the body itself;
• Figure 2 is a sectional diagram showing a source linked to the paraboloid, the assembly being pivoted on the body itself;
• Figure 3 is a sectional diagram showing both a source not linked to the paraboloid which is itself orientable with respect to the body proper;
• Figure 4 is a schematic perspective view showing the means used in the invention to correct the transverse defocusing of a paraboloid;
• FIG. 5 is a geometric diagram showing how the correction of transverse defocusing is obtained in a first design according to the invention;
• FIG. 6 is a geometric diagram showing how the correction of transverse defocusing is obtained in a second design according to the invention;
• FIG. 7 is a geometrical diagram showing how the correction of transverse defocusing is obtained in a third design of the invention; and
• Figure 8 is a perspective diagram showing known electromagnetic means for moving the platforms.

In FIG. 1, the paraboloid 1 is linked by the frame 3 to the source S of the horn 2 located at the focal point F and the director Z is oriented by pivoting of the body 4 around the axes XX 'and / or YY'.

In Figure 2, the dish is linked by the frame 3 'to the source S of the horn 2' located at the focal point F and the director Z is oriented by pivoting of the ball 5 around the axes XX 'and / or YY' .

By cons and if we refer to Figure 3, we see that when the dish 1 "must be oriented along 6 in X and Y relative to the frame 3" linked to the source S of the horn 2 ", problems appear essentially at the level of transverse defocusing.

By neglecting the axial defocus which remains relatively low, we can analyze the importance of this transverse defocus by referring to the study by M. Leo Thourel made in "The Engineering Techniques" ref. E 3086, page 11: »If the horn (containing the source S) is displaced along a line perpendicular to the axis of symmetry and passing through the focal point (F), the corresponding phase variation is an odd function and it appears a deviation in direction of maximum radiation.

If the phase center is in S, the direction SO making with OZ an angle 0, it follows a phase variation Φ (y) on the aperture AB which causes a deviation of the beam ... and an asymmetry in the radiation pattern ..., an important secondary lobe appears on the side opposite the deviation (coma lobe).

Defocusing always results in losses on the gain of the antenna because the beams widen because the rays reflected by the reflector are no longer parallel. "

In certain space applications, according to FIG. 3, the body 4 "of the satellite is oriented along OZ by its own attitude correction means while the pointing which, according to OZ, is obtained using appropriate means by correction around axes XX 'and / or YY' according to the articulation point 0 located at 6, which shows the above-mentioned transverse defocus defect.

Thus, for the INTELSAT 5 satellite for example, a value of <x = 5 ° has been accepted.

On the other hand, on broadcasting satellites for which very strict regulations narrowly limit the size of the transmitted beam, an a value of 1 ° is tolerated to within ± 0.02 °, which corresponds practically to approximately ± 1 mm of defocusing. transverse between focus and source and which cannot be ensured by current known means.

To this end, the invention proposes a method for correcting the transverse defocusing of a parabolic antenna which does not have the aforementioned drawbacks.

According to the invention, the focal point F of the paraboloid is maintained in the immediate vicinity of the source S by the fact that the point 0 is moved transversely to the pointing axis SZ, using a device shown diagrammatically on the FIG. 4 and the principle of which is set out in FIG. 5 or as a variant in FIGS. 6 and 7.

In FIG. 4, the paraboloid 10 with a focal point F centered in S is connected by a pylon 9 to a first platform 18 in a trapezoid articulated around the axes XX ′ according to A, B, C and D of FIG. 5.

The sides AB and CD are arranged at rest in the direction of the confused points F and S.

The first platform is articulated on a second trapezoid platform 19 articulated on the base 12 around the axes Y - Y 'along A, B, C and D, FIG. 5.

The sides AB and CD are also arranged at rest in the direction of the confused points F and S.

It is easy to note so that, when the articulated trapezium, formed by the platform 18 or the platform 19, is moved by pivoting around the axes of articulation X1, X1'-X3, X3 'and X2 , X2'-X4, X4 'for platform 18 and Y1, Y1'-Y3, Y3' and Y2, Y2'-Y4, Y4 'for platform 19, the focal point F of dish 10 will be found moved to F 'as shown in Figure 5.

According to this FIG. 5, the rotation of the straight line BC around the point F is obtained by deformation of the articulated trapezium ABCD and this deformation A · B '. C'D makes it possible to combine rotation and translation of the line BC so that the displacements of the point F on the perpendicular bisector of BC remain very small during the movement.

Thus by a rotation of BC around E only, the point F would move from d≃EFα.

In the present case, this point F will move in F 'by a quantity d≃kα ² , that is to say by a 2nd order term in α if, of course, AB and DC initially converge all two towards this point F.

According to Figure 6, in a design similar to Figure 5, the base BC is this time fixed while the base AD is deformable along A'D '. Here again, F will move in F 'by a quantity d≃kα ² , that is to say a term of the 2nd order in α if, of course, AB and DC converge initially towards F.

Figures 5 and 6 show the cases where BC and AD are initially parallel.

It is possible to conceive of other cases where they would no longer be parallel, as shown for example in FIG. 7, but nevertheless the initial convergence of AB and DC in F should be preserved.

Of course, the line of sight F - S Z remains in all cases initially perpendicular to the line BC, that is to say E = θ0 °.

The displacement of the focal point F in F 'follows from conventional geometric laws which will not be explained here.

Only can be taken into account the fact that this displacement results from a second order term which always remains within the limits acceptable in practice. Thus, one can achieve, with a suitable choice of parameters, a defocusing <1 mm for an angle of around 1 °, which is suitable on a broadcasting satellite antenna.

It should be noted that a slight convergence anomaly of AB and CD in front or behind FS is not prohibitive with regard to the application of the method according to the invention, only the search for the minimization of defocus F - F 'must guide the choice of the adaptation of the parameters.

In this spirit, it could likewise be envisaged, for particular applications, a different choice of point of convergence for one platform compared to the other.

Returning to FIG. 4, it can be seen that the platforms 18 and 19 are moved orthogonally using electromagnetic devices slaved to a deflection detector, which allows great torsional stiffness of the assembly.

These electromagnetic devices can be of the type such as those described in the aforementioned patent application EP-A-0015829, identified 16-17 in FIG. 4 and shown on a larger scale in FIG. 8 and for which the operating principle is recalled below.

Each platform 18 or 19 therefore carries a flat winding situated in its plane and the strands of which are in the direction of movement. These coils 21 and 22 are connected to a servo unit 23 connected to a deflection detector 7 (not shown).

The order commands being thus decoupled, each winding sees the direction of current flow established according to, for example, the arrows in FIG. 8.

Each coil is overlapped by a pair of magnets 24-25, of reverse polarity, which are fixed to the fixed base 12 by a support 26. The arrangement of the magnets and the coils can be reversed without changing the result.

Depending on the direction of current flow and its intensity, each platform 18 or 19 will therefore move in the magnetic field in the direction of arrows f1 or f2 with more or less amplitude and this in accordance with the law of LAPLACE .

In this way, the direction and the value of the current sent to each coil will depend on the direction and the magnitude of the displacement of each platform.

Of course, the translation of the platforms not being rigorously exercised in a plane, it is important to provide a clearance space (arrows e1, e2, e3, e4) for each platform.

It is of course possible to provide two devices per platform without the principle being thereby modified, each of said devices being electrically coupled in parallel on the box 23 (or in redundancy).

It should also be noted that for the paraboloids used in the electromagnetic field of microwaves, the source of emission and / or reception is, according to the known manner, a horn in waveguide 8 with progressively increasing section, secured to the fixed base.

The paraboloid constitutes the reflector of a parabolic antenna which can be implemented, through the invention, in all the fields where it is usually used from the moment when the source S is not subject to the director passing through foyer F.

Thus, the application given for a broadcasting satellite is not a restrictive case of the application of the method according to the invention, but on the contrary is only a simple example.

In this spirit, all the adaptations which would be made of the invention would remain within its scope, which is defined in the claims which follow.

Claims (8)

1. A method of correcting cross-defocusing of a paraboloid when it is to be oriented in respect to the source, characterized in that it consists of:

- fixing said paraboloid (10) to a first platform (18) perpendicular to the symmetry axis (Z) passing through the focus (F) and articulated laterally and in parallel to two first double hinges (X3-X3', X4-X4') themselves articulated in parallel (X1--X1', X2-X2') to a second platform (19),

- articulating said second platform (19) on its lateral sides and orthogonally of both of the first double hinges to two second double hinges (Y3-Y3', Y4-Y4'), themselves articulated in parallel (Y1 -Y1', Y2-Y2') to the fixed part (12),

- orienting the arms (AB-DC) of said double hinges substantially and conjointly in the direction of the focus (F) of the paraboloid initially aligned with the source (S),

- providing means (16, 17) for moving said platforms (18,19),

- servo-controlling said moving means by a depointing sensor (7),

- said actions having the effect of permanently correcting cross-defocusing of the paraboloid (10) by constantly maintaining its focus (F) in the immediate neighbourhood of the source (S).

2. A method of correcting cross-defocusing of a paraboloid according to claim 1, characterized in that it consists of differently orienting (AB-DC) the double hinges on the symmetry axis (Z) of the paraboloid (10) substantially in the direction of the focus (F) which is initially aligned with the source (S).

3. A method of correcting cross-defocusing of a paraboloid according to claims 1 and 2, characterized in that it consists of disposing the platforms (18,19) between the source (S) and the fixed part (12).

4. A method of correcting cross-defocusing of a paraboloid according to claims 1 and 2, characterized in that it consists of disposing the platforms (18, 19) rearwardly of the fixed part (12) in respect to the source (S).

5. A method of correcting cross-defocusing of a paraboloid according to claims 1, 2 and 3, characterized in that it consists of off-centering the symmetry axis (Z) of the paraboloid (10) with respect to the middle of the platforms (18,19).

6. A parabolic antenna corrected according to the method defined in any one of claims 1 to 4, characterized in that it comprises:

- a first platform (18) perpendicular to the symmetry axis (Z) passing through the focus (F) of the paraboloid (10) to which it is fixed,

- a first set of two double hinges (X3-X3', X4-X4') articulated in parallel to two sides of said first platform (18), on the one hand, and on the other hand, articulated (X1 -X1', X2 - X2') in parallel to two sides of a second platform (19),

- a second platform (19) articulated to said two double hinges, on the one hand, and on the other hand, orthogonally, to two other double hinges (Y3-Y3', Y4-Y4'),

- a second set of two double hinges articulated (Y3-Y3', Y4-Y4') in parallel to two sides of said second platform (19), on the one hand, and on the other hand, articulated (Y1-Y1', Y2-Y2') in parallel to the fixed part (12),

- electro-magnetic means (16, 17) for moving said platforms (18,19),

- and, means (23) for servo-controlling said electro-magnetic means by a depointing sensor (7).

7. A parabolic antenna according to claim 6, characterized in that the moving means comprise:

- at least one flat winding (21 or 22) on the side of each platform (18, 19), the wires of which are perpendicular to the direction of movement (f1 or f2) of said platform,

- a pair of magnets (24, 25) connected to the fixed part (12) or the movable part that should move in respect to the winding, spanning each winding (21, 22) and being disposed in such way that the magnetic field intersects the winding conductors to produce through Laplace forces the amplitude of the movement in one or the other direction, depending on the direction of flow of the current in said winding conductors,

- a servo-control box (23) for receiving signals from the depointing sensor (7) and supplying windings (21, 22) with current proportional thereto.

8. A utilization in a radiobroadcasting and/or television-broadcasting satellite of a parabolic antenna according to one of claims 6 or 7 wherein the cross-defocusing is lower than 1 mm for a depointing angle of about 1°.

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