EP2264830A1 - Reflector antenna with variable coverage and operating frequencies and a satellite with such antenna - Google Patents

Abstract

The antenna has a reversible reflector (10) with two separate reflecting surfaces (R1, R2) shaped geometrically to respectively cover different geographical zones. Two independent radiofrequency signal sources (S1, S2) are arranged in a fixed configuration and connected to separate radio-frequency supply chains (2, 3) defining different and predefined operating frequency planes (F1, F2). The reflector occupies two deployment positions in which focal points of the surfaces are located at a phase center (5) and another phase center of the sources by two motors (M1, M2), respectively.

Description

The present invention relates to a reflector antenna with coverage and frequency flexibility and a satellite having such an antenna. It applies in particular to the field of satellite telecommunication antennas.

The increasing lifespan of telecommunications satellites and the evolution of the requirements associated with the various missions that may be entrusted to them, requires that the payloads, and in particular the antennas, of future generations of satellites be flexible. This flexibility can be achieved at the geographical coverage area of the antenna and / or at the level of the polarization and / or at the level of the frequency band of operation. This flexibility is not intended to cover all geographical coverage areas at the same time but to have the choice of several geographic coverage that can be generated by the same antenna and to be able to modify, in orbit, the mission of the satellite.

Antennas on board satellites typically have a geometrically shaped, single-source reflector for covering a coverage area pointed at the Earth. A satellite typically includes a transmitting and receiving antenna, or a transmitting antenna and receiving antenna, per coverage area. The geometric shape of the reflector may optionally be defined to be optimized for several orbital positions of the satellite but generally to cover a single geographical coverage.

Frequency flexibility over a broadband spectrum, for example the Ku, Ku + frequency plan covering frequencies between 10.7GHz and 18.4GHz and a single coverage area, can not be obtained with a single source because no source is currently sufficiently broadband. In addition, there is a critical point concerning the diplexing between the transmit and receive tapes and it is necessary to maintain a margin of the order of 250 MHz between the high frequency of the transmission band and the low frequency of the transmission band. reception band.

A first known solution is to use two separate antennas to cover the same geographical area, but this solution causes problems of mass, size and cost.

A second known solution is to place two sources side by side in front of an oversized reflector so as to minimize the defocusing of the two sources. The phase centers of the two sources are placed in the focal plane of the reflector and their axes of radiation are parallel. The two sources are positioned as close to the focus of the reflector to reduce the defocusing of the sources and the resulting directivity losses of the antenna. However, this solution is not optimal.

For example, the French patent application referenced under the publication number FR2648278 discloses an antenna device comprising two sources and a pivotable auxiliary reflector and provided with two reflective surfaces. On the one hand, this device suffers from the aforementioned disadvantages of defocusing, which degrades the performance of the antenna, on the other hand, the number of degrees of freedom accessible on an auxiliary reflector is quite low, which amounts to limiting the possibilities of deformation of the coverage obtained by beam of the antenna.

Another possibility is to use a single source placed at the focus of a reflector, the source being connected to a complex electrical architecture combining two radio frequency chains, the first channel operating in a first frequency plane, the second channel operating in a second plane of frequencies. However, this architecture induces a complexity generating non-negligible ohmic losses and a significant cost of implementation.

Moreover, to achieve two distinct coverage areas, the current solutions require the use of two separate and independent antennas each having a deployable reflector, the reflector to be associated with two different sources to fully cover a chosen frequency band, which imposes thus four sources in total, placed on a lateral face of a satellite and a double system of stacking to deploy or store the two reflectors of the two antennas.

The patent US 6,859,188 discloses another alternative of using a returnable reflector having two reflective surfaces covering two different coverage areas the reflector being associated with a single source. The positioning of one of the reflective surfaces in front of the source makes it possible to select one of the coverage areas, however this solution has no frequency flexibility and does not allow operation in a broadband frequency plan.

The object of the invention is to provide an optimal antenna to meet the need for flexibility in coverage and frequency, to eliminate the aberrations and losses due to defocusing, simple to implement, and whose geometry does not result no compromise in performance and reduces the ohmic losses compared to previous solutions.

For this purpose, the invention relates to a reflector antenna with a coverage and frequency flexibility comprising a returnable reflector having two distinct reflective surfaces geometrically formed so as to cover respectively a first and a second different geographical area and of predetermined shapes, characterized in that that the two reflective surfaces are fixed back-to-back on a common support, and in that the antenna further comprises at least two independent sources arranged in a fixed configuration and connected to separate radiofrequency power supply channels defining frequency planes different and predetermined operation, the reflector having a first deployment position in which the focus of the first reflective surface is placed in the center of phase of the first source S1 and a second deployment position in which the focus of the second the reflective surface is placed in the center of phase of the second source S2.

Thus, whatever the configuration in which the antenna according to the invention is used, the active source, S1 or S2, is focused because its phase center is positioned at the focus of the reflector.

Advantageously, the antenna comprises reflector deployment means comprising at least a first motor and reflector reversing means comprising at least a second motor, the two motors having axes of rotation perpendicular to each other, the second motor actuating the reversal of the reflector from the first position to the second position by a rotation of a predetermined angle of the common support.

Advantageously, the reflector comprises a third deployment position in which the focus of the first reflecting surface is placed at the phase center of the second source and a fourth deployment position in which the focus of the second reflecting surface is placed in the center of phase. from the first source.

Advantageously, the antenna further comprises translational means of the reflector comprising a third motor connected to the first motor and the second motor by lever arms, the third motor having an axis of rotation parallel to the axis of rotation of the first motor the first and third motors actuating the translational reflector to change the focus position of the first reflective surface, respectively the second reflective surface, from the first source to the second source. The antenna according to the invention thus benefits from a specific kinematics, thanks in particular to the three judiciously placed motors, and makes it possible to achieve optimal RF performance on two distinct covers and on two different frequency planes.

According to one embodiment, the antenna comprises a single reflector, this reflector being the returnable reflector. A large number of different covers can thus be produced (although, ultimately, only two covers are accessible on the reflector), for example highly distorted geographical covers, very elongated.

According to another embodiment, the antenna comprises a main reflector associated with an auxiliary reflector (for example an antenna with a Cassegrain type mounting). In this case, it is preferably the main reflector which has two returnable reflective surfaces, so as to benefit from a maximum of degrees of freedom in the production of covers.

Advantageously, the sources can be attached side by side or one above the other.

The invention also relates to a telecommunications satellite comprising such an antenna.

• figure 1 a : un schéma en perspective d'un exemple d'antenne à réflecteur à flexibilité de couverture, montée sur la plate-forme d'un satellite, le réflecteur étant dans une position stockée, selon l'invention;
• figure 1b : un schéma en perspective du réflecteur en position déployée montrant les deux surfaces réfléchissantes du réflecteur montées sur un support commun, selon l'invention ;
• figures 2a, 2b: deux schémas de la même antenne pour deux directions de pointage différentes, selon l'invention ;
• figures 3a, 3b : deux schémas de la même antenne dans une deuxième et une troisième positions selon lesquelles la source S1, respectivement la source S2, est au foyer du réflecteur pointé dans une même direction, selon l'invention ;

Other features and advantages of the invention will become clear in the following description given by way of purely illustrative and non-limiting example, with reference to the attached schematic drawings which represent:

• figure 1 a: a perspective diagram of an example of a reflector antenna with flexibility of coverage, mounted on the platform of a satellite, the reflector being in a stored position, according to the invention;
• figure 1b : a perspective diagram of the reflector in the deployed position showing the two reflecting surfaces of the reflector mounted on a common support, according to the invention;
• Figures 2a , 2b : two diagrams of the same antenna for two different pointing directions, according to the invention;
• figures 3a , 3b : two diagrams of the same antenna in a second and a third positions according to which the source S1, respectively the source S2, is at the focus of the reflector pointed in the same direction, according to the invention;

In the example shown on the figure 1a the passive simple offset antenna comprises a reflector 10 in the stored position on the platform 11 of a satellite, for example on a lateral face parallel to a plane YZ, and two independent sources S1, S2 of radio frequency signals. A deployment mechanism 12 visible in the following figures, deploys the reflector 10 so that in an extended position, the two sources S1, S2 are arranged in front of the reflector in its focal plane. The reflector 10 comprises two distinct and differently shaped reflective surfaces R1, R2 fixed back-to-back on a common support 15, as represented for example on the figure 1 b. Each reflective surface is geometrically shaped and optimized for a given mission so as to illuminate a ground coverage area having predetermined dimensions when only one source is placed in the home. This shape looks like a parabola and differs only slightly. The sources S1, S2, for example of the horn type, are fixed on an inclined plane 16 arranged on the platform 11 and are arranged in a predetermined fixed configuration for example one next to the other. The sources S1 and S2 may in some cases be placed one above the other or in any other configuration.

In the deployed position, one of the reflecting surfaces R1, R2 is positioned facing the two sources S1, S2 and is oriented in a predetermined pointing direction 17. The reflector 10 is returnable relative to the plane of the support 15 by a rotation of the assembly consisting of the support 15 and the two reflecting surfaces R1, R2, which allows to change reflective surface and therefore desired coverage area. The invention therefore consists in positioning the two reflecting surfaces R1, R2 on the common support 15 so that in a first position of the reflector 10 corresponding to a first mission of the satellite, the phase center of the source S1 is placed at the focus of the first reflecting surface R1 and so that in a second position of the reflector obtained by a rotation of the reflector and corresponding to a second mission of the satellite, the phase center of the second source S2 is placed at the focus of the second reflecting surface R2. The rotation allowing the reversal of the reflector from the first position to the second position is performed around an axis 22 parallel to the plane of the support 15 and at a predetermined angle depending on the relative positioning of the reflecting surfaces R1, R2 on the support 15. A As a non-limiting example, the angle of rotation for the reversal of the reflector is adjustable within a predetermined range of values, for example between 175 ° and 195 °.

The reflector deployment mechanism comprises for example a motor M1 having an axis of rotation parallel to the plane YZ and a deployment arm 13 which can be actuated in rotation by the motor M1 between a position in which the reflector 10 is stored against the wall of the platform 11 parallel to the YZ plane of the satellite and a deployment position. The reversal mechanism of the reflector 10 comprises, for example, a second motor M2 axis perpendicular to the axis of the motor M1 and connected to the deployment arm 13 and the reflector 10. The second motor M2 actuates the reversal of the reflector 10 from the first position to the second position by a rotation of a predetermined angle of the common support 15.

The two sources S1, S2 are fed respectively via two different channels 2, 3 for supplying radiofrequency RF signals preferably integrated in a box 14. Each RF channel 2, 3 being dedicated to telecommunication functions, the two sources S1, S2 may be fed in different frequency planes F1 and F2, each frequency plan may include one or more frequency subbands on transmission and / or reception.

On the figure 2a the phase center 5 of the source S1 is positioned at the focus of the first reflecting surface R1 which points in a first pointing direction 17 located on a first land cover area corresponding to a first predetermined mission. On the figure 2b , the phase center 6 of the source S2 is positioned at the focus of the second reflecting surface R2 which points in a second pointing direction 18 located on a second land cover area different from the first coverage area and corresponding to a second mission predetermined. The transition from the first mission to the second mission is performed by rotating a predetermined angle of the returnable reflector 10, for example 180 °, relative to the plane of the support 15. The rotational drive of the reflector 10 is performed at second motor M2. The desired change of pointing direction between mission 1 and mission 2 determines the relative position of the two reflecting surfaces R1, R2 relative to each other on support 15.

In addition to the flexibility of coverage obtained by the reversal of the reflector 10, it is possible to obtain a frequency flexibility over the same coverage area and therefore for the same position and the same pointing direction of the reflector, without losses or aberrations due to a defocus. For this, the invention consists in selecting one of the sources S1 or S2 as a function of the desired frequency and then moving and orienting the reflector 10 so that the selected source is positioned in the focus of the reflector and that the reflector illuminates the selected coverage area.

In the initial configuration shown on the figure 3a , the phase center of the source S1 is positioned at the focus of the first reflective surface R1 of the reflector 10 which points in a pointing direction 17 located for example on the Earth's equator. If the source S1 is for example supplied in a frequency plane F1 via a first RF channel and the source S2 is connected to a second RF channel optimized to operate in a frequency plane F2, to go from the frequency F1 at the frequency plane F2 without changing the pointing of the antenna, the invention consists in switching the power supply from the source S1 to the source S2 and moving the reflector in translation from the source S1 to the source S2 to position the focus of the first reflective surface R1 at the center of phase 6 of the source S2, as shown in FIG. figure 3b . The displacement and orientation of the reflector 10 in front of the source S2 without changing the pointing direction 17 of the antenna can be achieved for example by means of two motors M1, M3, the motor M3 being connected to the motor M1 and the motor M2 by means of corresponding lever arms 20, 21. The two motors M1, M3 have axes of rotation parallel, or almost parallel, between them and almost parallel to the plane YZ of the lateral face of the platform 11 of the satellite which supports the reflector 10. The actuation of the motor M1 in rotation in the opposite direction of the clockwise and at a rotation angle depending on the spacing between the sources S1 and S2, causes the first lever arm 20 to rotate in the same direction which has the effect of moving and to bring the motor M3 and the reflector 10 closer to the platform 11 of the satellite, as shown in FIG. figure 3b and thus move the reflector of the source S1 to the source S2. Actuating the motor M3 in rotation in the clockwise direction at the same angle of rotation as the motor M1, then makes it possible, by means of the lever arm 21, to tilt the reflector 10 in rotation in the direction of rotation. other direction until it is in a position parallel to its initial position and that the center of phase 6 of the source S2 is thus positioned at the focus of the reflector 10 and illuminates the same coverage area on the Earth. The successive rotations of the various motors M1 and M3 thus make a translation to the reflector 10 such that the focal point of the reflecting surface R1 passes from the source S1 to the source S2. Using a number of sources greater than two, the same operations may be reproduced with one or more additional sources, for example to perform one or more other missions in other frequency plans if each additional source is connected to an RF channel dedicated and optimized for another frequency plan than that of sources S1 and S2.

With a single antenna comprising two interchangeable reflective surfaces, three motors and two sources S1, S2, it is thus possible to deploy the antenna in orbit, to position it so as to fulfill one of four possible missions. The two reflective surfaces being interchangeable and mechanically joined together, the four different missions are fulfilled using a single mechanical structure of support and deployment. The first mission is carried out by placing the focus of the reflecting surface R1 on the center of phase 5 of the first source S1, for the second mission, the reflector is translated and the center of phase 6 of the second source S2 is at the focus of the reflective surface R1, for the third mission, the reflector is rotated by a predetermined adjustable angle, for example between 175 ° and 195 ° in the exemplary embodiments, and the first source S1 is at the focus of the reflecting surface R2 and for the fourth mission, the second source S2 is at the focus of the reflecting surface R2.

Thanks to the three motors, it is thus possible to focus the sources S1 or S2 at the focus of one of the reflective surfaces R1, R2 of the reflector 10 which allows to obtain optimum performance over the entire frequency plan. By adding additional sources, additional missions in different frequency schemes also become possible.

Although the invention has been described in connection with particular embodiments, it is obvious that it is not limited thereto and that it includes all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims (6)

A reflective antenna with a coverage and frequency flexibility comprising a returnable reflector (10) having two distinct reflecting surfaces (R1, R2) geometrically shaped so as to respectively cover first and second different geographical areas and predetermined shapes, characterized in that that the two reflecting surfaces (R1, R2) are fixed back-to-back on a common support (15) and that the antenna further comprises at least two independent sources (S1, S2) arranged in a fixed configuration and connected to distinct radiofrequency power supply chains (2, 3) defining different and predefined operating frequency planes (F1, F2), the reflector (10) having a first deployment position in which the focal point of the first reflecting surface (R1 ) is placed at the phase center (5) of the first source (S1) and a second deployment position according to the which focus of the second reflecting surface (R2) is placed at the phase center (6) of the second source (S2). Antenna according to claim 1, characterized in that it comprises means for deploying the reflector (10) comprising at least a first motor (M1) and means for turning the reflector (10) comprising at least one second motor (M2). , the two motors (M1, M2) having axes of rotation perpendicular to each other, the second motor (M2) actuating the reversal of the reflector (10) from the first position to the second position by a rotation of a predetermined angle of the support common (15). Antenna according to one of claims 1 or 2, characterized in that the reflector (10) has a third deployment position in which the focus of the first reflecting surface (R1) is placed in the center of phase (5) of the second source (S2) and a fourth deployment position according to which the focus of the second surface reflective (R2) is placed at the phase center (5) of the first source (S1). Antenna according to claim 3, characterized in that it further comprises translational means of the reflector (10) comprising a third motor (M3) connected to the first motor (M1) and the second motor (M2) by lever arms (20, 21), the third motor (M3) having an axis of rotation parallel to the axis of rotation of the first motor (M1), the first and the third motor (M1, M3) actuating the reflector (10) in translation allowing a change of the focus position of the first reflective surface (R1), respectively the second reflective surface (R2), the first source (S1) to the second source (S2). Antenna according to any one of the preceding claims, characterized in that the sources (S1, S2) are fixed side by side or one above the other. Telecommunication satellite, characterized in that it comprises at least one antenna according to any one of the preceding claims.

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