ANTENNA. WITH LONG FOCAL LENGTH THAT IS COMPACT, ROBUST AND CAN BE TESTED ON THE GROUND, MOUNTED ON A SATELLITE
The present invention relates to an antenna with long focal length that is compact, robust and can be tested on the ground, mounted on a satellite, and as a non-limiting example, on satellites at a height that is less than the focal length of the antenna.
Certain spacecraft, and telecommunication satellites in particular, must be furnished with antennae with long focal length (for example more than 3.5 m) which makes it possible to optimize their performance.
By their design, "simple offset" antennae with a large-diameter reflector (for example of at least 2 m) require a considerable focal length (more than or equal to 1.5 times the diameter of the reflector) in order to prevent problems of cross-polarization. The result of this is that, depending on the height of the platform carrying such an antenna, its integration onto this platform may be very difficult, which would make it necessary to choose a complex and heavy solution, and sometimes this integration may be impossible, making it necessary to choose another type of antenna that is heavier and more expensive.
In greater detail, the solutions of the prior art are as follows:
Raising the height of the antenna source: requires a source-carrying structure that is heavy and expensive, and "the field of vision of the source interferes with the platform and its appendices. Moreover, the face of the satellite facing the Earth is encumbered by the structure supporting the source, which limits the arrangement of the other antennae of the platform.
Use of a deployment mechanism comprising three axes of which two deployment axes are placed on either side of the arm of the antenna reflector (one on the side of the platform and one on the side of the reflector) . In this solution, the arm and the fittings are specific and complex, the reflector turns over (cannot be tested on the ground) during its deployment.
Gregorian antenna: it has considerable weight and cost because it requires two reflectors and dedicated structures for supporting the source and the secondary reflector; the heat control of the source is critical because this source is encased in order to limit the space requirement towards the outside of the satellite, and the face turned towards the Earth is encumbered by the structure carrying the secondary reflector, which limits the arrangement possibilities of the other antennae. Two-grid antenna: this type of antenna has the advantage of not requiring much focal length - its focal length/diameter ratio is of the order of 1 -and it is therefore possible to manage to arrange considerable diameters on platforms of reduced height. However, the space requirement in the stored configuration, due to the height of the peripheral stiffener between its two shells, poses compatibility problems with the nose cones of standard-sized launch vehicles.
The subject of the present invention is an antenna with long focal length that is compact, robust and can be tested on the ground, mounted on a satellite, and, as a non-limiting example, on satellites at a height that is less than the focal length of the antenna, this antenna being lighter, more robust and less expensive than the existing solutions, easy to test and not interfering with the other equipment of the carrying satellite,
whether it be in the stored position or in the deployed position of the antenna.
The antenna according to the invention is characterized in that it comprises a reflector which, in the stored position of the antenna, has its active face oriented away from the supporting structure of the antenna, the stem for connecting the reflector with the deployment arm then being directed towards the top of the supporting structure, the articulation of this stem with the arm having a degree of rotational freedom, the arm for deployment of the reflector being connected to the carrying structure of the antenna via an articulation having at least one degree of rotational freedom attached to this structure, this arm being positioned between the reflector and the structure in the stored position of the antenna, the reflector then being pressed against this structure.
The concepts of "top" and "bottom" of the elements in question relate in this instance to elements used on board a satellite travelling in space, the "top" being the portion of these elements facing the Earth.
The present invention will be better understood on reading the detailed description of an embodiment, taken as a non-limiting example and illustrated by the appended drawing in which:
Figures 1 to 3 are schematic views in profile of one embodiment of the arrangement of the antenna according to the invention in various phases of deployment, and
Figure 4 is a three-quarter view in perspective of the configuration of Figure 3.
In the figures of the drawing, all that is depicted are the essential elements of the antenna of the invention
and of its supporting structure that are necessary to the understanding of the invention. The arrow 1, directed towards the top of the drawing, indicates the direction of the Earth, the carrying satellite being assumed to be in space. Figures 1 to 3 correspond respectively to the stored state, an intermediate state of deployment of the antenna and the deployed state of the antenna, Figure 4 being a view in perspective of the configuration of Figure '3, as specified above.
The antenna 2 of the invention is attached to the lateral face 3A of a supporting structure 3 supporting other devices not shown. The source 4 of the antenna is attached to the upper portion of the structure 3. The paraboloid reflector 5 of the antenna comprises, on its rear face, a radial attachment stem 6 secured to the rear face of the reflector (shell and/or any other rear structure) . The stem 6 is connected via a motorized articulation 7 (motorized with the aid of a leaf spring or a stepper motor) with a degree of rotational freedom at one end of the arm 8 itself for deployment of the reflector. The other end of the arm 8 is connected via an articulation 9 to a secondary support 10, itself attached to the structure 3. The articulation 9 has at least one degree of rotational freedom. As a variant, the articulation 9 is motorized and comprises one or two electric stepper motors, or else a leaf spring (for only one degree of rotational freedom).
As shown in Figure 1, in the stored state (antenna not yet in service) , the arm 8 is folded and is substantially parallel to the face 3A of the structure 3, the articulation 7 being pressed against the upper portion of the face 3A. The stem 6 and the reflector 5 are also pressed against this face 3A. In this position, the reflector 5 practically does not protrude beyond the sides of the face 3A.
As shown in Figure 2, during the intermediate phase of deployment of the antenna 2, the motorization provided by a spring (mechanical) or by a stepper motor (electrical) - of the articulation 9 moves the arm 8 away from the face 3A, while that of the articulation 7 turns the stem 6 which turns about the axis of the articulation 7 (in Figure 2, the stem 6 is represented after having rotated approximately 90°). The stem 6 turns from its folded position (Figure 1) to the position of normal use of the reflector 5 (see Figures 3 and 4) through an angle of approximately 280°, while the arm 8 makes a rotation of' approximately 170°. For this position of normal use of the reflector 5, the latter is oriented towards the Earth, while naturally being positioned correctly relative to the source 4. The rotations of the arm 8 and of the stem 6 may be synchronized, sequenced or simultaneous.

CLAIMS
1. Antenna with long focal length, that is compact, robust and can be tested on the ground, mounted on a satellite, characterized in that it comprises a reflector (5) which, in the stored position of the antenna (Figure 1), has its active face oriented away from the supporting structure of the antenna (3), the stem (6) for connecting the' reflector with the arm (8) for deployment of the reflector then being directed towards the top of the supporting structure, the articulation (7) of this stem' with the arm having a degree of rotational freedom, the deployment arm being connected to the carrying structure of the antenna via an articulation (9) having at least one degree of rotational freedom attached to this structure (3) (10), this arm being positioned between the reflector and the structure in the stored position of the antenna, the reflector then being pressed against this structure.
2. Antenna with long focal length on a satellite according to Claim 1, characterized in that the articulation (7) between the stem (6) for connecting the reflector with the arm (8) for deployment of the reflector is motorized by a leaf spring.
3. Antenna with long focal length on a satellite according to Claim 1, characterized in that the articulation (7) between the stem (6) for connecting the reflector with the arm (8) for deployment of the reflector is motorized by an electric stepper motor.
4. Antenna with long focal length on a satellite according to Claim 1, characterized in that the articulation (9) connecting the arm (8) for deployment of the reflector to the carrying structure of the antenna (3) (10) is of the type with a degree of rotational freedom.
5. Antenna with long focal length on a satellite
according to Claim 4, characterized in that the
articulation (9) is motorized by a leaf spring.
6. Antenna with long focal length on a satellite
according to Claim 4, characterized in that the
articulation (9) is motorized by an electric stepper
motor.
7. Antenna with long focal length on a satellite according to Claim 1, characterized in that the articulation (9) connecting the" arm (8) for deployment of the reflector to the carrying structure of the antenna (3) (10) is of the type with two degrees of rotational freedom.
8. Antenna with long focal length on a satellite according to Claim 7, characterized in that the articulation (9) is motorized by two electric stepper motors.
9. Antenna with long focal length on a satellite
according to Claim 8, characterized in that, in the
normal position of use of the reflector (5) (see
Figures 3 and 4), one of the two axes of rotation is
, perpendicular to the arrangement face of the antenna (3A) .