EP2380235B1 - System for emitting electromagnetic beams, comprising a network of antennae - Google Patents

Description

The invention relates to a large-sized transmitting and / or receiving antennal system comprising an array of radiating elements.

The field of application of the invention is satellite antennas, radar antennas, aircraft antennas, generally ground or embedded antennas integrating networks of radiating elements.

In transmission, the radiating elements of the network antenna are powered by electromagnetic signals previously numerically weighted in phase and amplitude by excitation coefficients determined by calculation means. In reception, the electromagnetic signals received by the elements of the network antenna are then numerically weighted in phase and amplitude by excitation coefficients determined by these same calculation means. These excitation coefficients are used in reception to transform the signals received by the elements of the network antenna and coming from one or more directions into a useful coherent signal, and into transmission to transform a useful signal into different signals supplying the elements. of the network and constituting one or more given illumination beams, in both cases to respect a certain law of illumination desired for the network. Those skilled in the art will recognize in the digital generation excitation coefficients and the digital weighting of the signals of the elements of the network antenna a Digital Beamforming Network (DBFN).

One of the problems with large network antennas is the fact that the layout and orientation of network elements may vary over time.

For example, a satellite in orbit may be subject to sudden changes in temperature depending on whether it is illuminated by the sun or not.

This results in deformations of the antenna due to the existence of significant thermal gradients.

In general, the antenna can be subjected to significant thermal and mechanical stresses resulting in deformations of the latter.

These deformations disturb the law of illumination of the elements of the network.

Currently, to limit these deformations, we use mechanical support structures of the network antenna, the design of which must allow the rigidity, flatness and shape of the antenna to be maintained under very high thermal and mechanical stresses. severe. As a result, these mechanical support structures generally have a large mass, cost and bulk.

Currently, the calibration functions of network elements are generally performed using couplers inserted in the transmission circuit to take a part of the signal sent to the transmitting elements.

Another calibration solution is to perform remote measurements. For example, on a satellite in orbit, measurements are taken from a ground station.

These means are heavy and expensive to implement and corrections can not always be made in real time for logistics and / or profitability issues. In addition, many approximations are made during these measurements (mutual coupling between elements not taken into account, behavior of the radiating elements not taken into account, non-exhaustive tests, etc.). This is detrimental to optimum operation of the antennas because the environmental conditions in which they are located (gradients in high and fast temperatures for example for space antennas, winds for ground radar antennas, etc.) cause variations in the shape the network, the performance of the radiating elements and the radiation pattern resulting from the antenna. Antenna concepts with complex mechanical structures and often heavy and cumbersome ensue.

An object of the invention is to overcome these disadvantages by providing a network antenna system that allows as much as possible to respect a desired illumination law and radiation pattern.

Another object of the invention is to obtain a network antenna system which is less cumbersome to implement.

Another object of the invention is to allow a real-time control of each of the elements of the antenna and the far-field radiated diagram.

A first subject of the invention is an electromagnetic beam emission system according to claim 1.

Thanks to the invention, the law of illumination of the network is controlled in real time from local measurements of the near field radiated by the latter, thus allowing rapid reconfiguration of the beams. The system thus comprises on-board control means making it possible to check the radiation pattern of the network antenna in real time. This allows adjustment and compensation in real time of the radiation pattern of the antenna in case of deformation of the network or failure of one or more elements of the network. In real time, the emission or reception radiation diagrams of the antenna are corrected by varying the values of the excitation coefficients of each element of the network. The system makes it possible to take into account the mechanical and thermal deformations that the antenna could undergo, and which can be significant in the Ku-band or Ka-band wavelength for a satellite in orbit, for example.

This will subsequently relax certain manufacturing constraints of large network antennas and their support means, especially in the space environment, and reduce the weight and costs of antennas and the system. Thus, it will be possible to accept a certain possibility of deformation of the network antenna and its support means under the effect of external conditions, knowing that the embedded control of the law of illumination of the antenna and the calculations of correction of the excitation coefficients will make it possible to compensate this deformation in real time.

Thus, according to this embodiment, the radiating elements of the network are fixed to a first support, the second sensor array being fixed to a second support separate from the first support, the first support and the second support being fixed to a common base with a space between the first support and the second support allowing deformation of the first support.

• Le premier support comprend une plaque de support en commun des éléments rayonnants du réseau, et il est prévu un deuxième support pour chaque capteur, ce support pour chaque capteur comportant une tige de maintien dont une extrémité est fixée au capteur et dont l'autre extrémité est fixée à une embase, à laquelle le premier support est également fixé par l'intermédiaire d'entretoises, la plaque comportant des trous pour la traversée des tiges avec ledit espace présent entre le bord du trou et la tige.
• Les capteurs sont positionnés dans l'espace libre et répartis au dessus du plan du réseau d'éléments rayonnants.
• La hauteur entre les capteurs et les éléments rayonnants du réseau est supérieure à une fraction de la longueur d'onde de travail des éléments.
• Les coefficients d'excitation comprennent un déphasage et une amplitude, le système comporte pour chaque élément du réseau une voie associée de réception et/ou une voie associée d'émission, les moyens de calcul étant prévus pour calculer les ajustement en déphasage des coefficients d'excitation et les ajustements en amplitude des coefficients d'excitation pour que le diagramme de rayonnement mesuré à partir des capteurs soit le plus proche possible d'un diagramme de rayonnement d'une consigne.
• Le système comporte des moyens d'adressage des capteurs pour recueillir la mesure de champ proche localement à l'endroit de chaque capteur en utilisant la technique de diffusion modulée par exemple.

According to other embodiments of the invention:

• The first support comprises a support plate in common of the radiating elements of the network, and there is provided a second support for each sensor, this support for each sensor comprising a holding rod whose one end is fixed to the sensor and whose other end is fixed to a base, to which the first support is also fixed by means of spacers, the plate having holes for the passage of the rods with said space present between the edge of the hole and the rod.
• The sensors are positioned in the free space and distributed above the plane of the array of radiating elements.
• The height between the sensors and the radiating elements of the network is greater than a fraction of the working wavelength of the elements.
• The excitation coefficients comprise a phase shift and an amplitude, the system comprises, for each element of the network, an associated reception channel and / or an associated transmission channel, the calculation means being designed to calculate the phase shift adjustments of the transmission coefficients. excitation and amplitude adjustments of the excitation coefficients so that the radiation pattern measured from the sensors is as close as possible to a radiation pattern of a setpoint.
• The system includes means for addressing the sensors to collect the near-field measurement locally at the location of each sensor using the modulated scattering technique for example.

• la figure 1 représente un synoptique modulaire d'un exemple de système antennaire d'émission et de réception suivant l'invention,
• la figure 2 représente un synoptique modulaire d'une partie de régulation du système antennaire suivant la figure 1,
• la figure 3 représente une vue de côté d'un exemple de partie du réseau d'éléments du système antennaire suivant la figure 1,
• la figure 4 représente une vue de dessus d'un autre exemple de partie du réseau d'éléments du système antennaire suivant la figure 1.

The invention will be better understood on reading the description which follows, given solely by way of non-limiting example with reference to the accompanying drawings, in which:

• the figure 1 represents a modular block diagram of an example of an antenna transmission and reception system according to the invention,
• the figure 2 represents a modular synoptic of a regulation part of the antennal system following the figure 1 ,
• the figure 3 represents a side view of an example of a part of the array of antennal system elements following the figure 1 ,
• the figure 4 represents a view from above of another example of a part of the network of elements of the antennal system following the figure 1 .

The invention is described below in the example of a satellite network antenna, responsible for retransmitting to the earth a signal received from a terrestrial base station.

The transmission and reception system 1 comprises a network 2 of a plurality of radiating elements 2 ₁ , 2 ₂ ,..., 2 _i ,... 2 _N. This network 2 is for example arranged on a plane. Each element 2 _i is for example in the form of a horn or printed element having an opening oriented towards a direction DIR common to all the antennas 2 _i .

The antenna network 2 is connected to a computer 3 via one side of a reception circuit 4 and on the other hand by a transmission circuit 5. The separation between the reception and transmission channels is achieved by means of a set 7 of frequency diplexers placed near the radiating elements.

The reception circuit 4 comprises a reception channel 4i for processing each signal s _i received on each antenna 2 _i and bringing it to an input 6i of the computer 3. The processing of each reception channel 4i comprises, as is known , a frequency diplexing stage 7, a low noise amplification stage 8, a variable gain amplification stage 9, a baseband passing stage 10 and an analog / digital conversion stage 110.

The transmission circuit 5 comprises a transmission path 5i for each element 2 _i of the network 2 and makes it possible to route a signal s' _i to be transmitted by the elements 2 _i of the 2. The processing of each transmission channel 5i comprises, as is known, a digital / analog conversion stage 12, a carrier frequency passing stage 13, a distribution stage 14 through Buttler matrices, an amplification stage, a filtering stage 16, a stage 17 of recombination through Buttler matrices and a stage 18 of frequency diplexing.

The computer 3 comprises means 30a for calculating the complex excitation coefficients of the antennas 2 _i in reception and means 30b for calculating the complex excitation coefficients of the transmit antennas 2 _i .

There is therefore a complex excitation coefficient Ki for each antenna 2 _i in reception and a complex excitation coefficient Lk for each antenna 2 _i in transmission. The excitation coefficients Ki and Lk make it possible, respectively, to reconstruct, from the signals s _i received by the antennas 2 _i , a useful coherent signal S, and to send back this useful signal S in the form of the signal s' _k to each transmission path 5k forming the desired transmission beams. The excitation coefficients Ki and Lk provide a gain and a phase shift, that is to say a complex multiplying factor or a complex weighting, respectively to each reception channel 4i with respect to the other reception channels 4i, and to each 5k transmission channel compared to other 5k transmission channels. In a manner known to those skilled in the art, the complex values of the coefficients Ki in reception are optimized and calculated numerically by the computing means 35 of the computer 3 to maximize the coherent signal from the sum weighted by the coefficients Ki of the signals s _i received.

The means 35 of the calculation means 30a produce, as a function of the reception signals s _i of the antennas 2 _i, a signal S equal to the weighted sum of the signals s _i by the excitation coefficients K _i according to the equation: $$S={\displaystyle \underset{i=1}{\overset{\mathrm{NOT}}{\Sigma }}}\mathit{Ki}\cdot s_i$$

According to the invention, in the vicinity of the network 2 of radiating elements 2 _i , sensors 10 ₁ , 10 ₂ , ..., 10 _j , ... 10 _M measuring the near field radiated by the elements 2 _i M can be different from N and is generally greater than the number N of elements 2 _i .

The network of the sensors 10 is connected by means 11 for addressing, collection and reception to the computing means 30b of the computer 3.

The means 30b for calculating the emission excitation complex coefficients Lk are represented in FIG. figure 2 .

The calculation means 30b comprises a module 31 for determining the excitation coefficients Lk from the near field Epj measured by the sensors 10 _j .

Each sensor 10 _{j is} used to measure the near field Epj radiated by the network 2 of radiating elements 2 _i . Addressing, collecting and receiving means 11 between each sensor 10 _j and a far-field computing module 32 is provided. The module 32 calculates the existing far field El from the measured near field Ep _j by the sensors 10 _j . The module 32 has for example for this purpose advanced computation algorithms of the far field from near-planar field data, prerecorded value tables of the radiation pattern of the sensors 10 _j and elements 2 _i and / or other pre-recorded correspondence rules, a memory being provided for this purpose.

A comparator 33 compares this calculated existing elongated field E1 with a predetermined distance field Elc predetermined and prerecorded, for example in a module 34. The comparator 33 thus calculates an error Err signal in far field as a function of the difference between the field remote existing calculated El and the far field of setpoint Elc. The calculation module 31 determines, by means of advanced optimization algorithms, the excitation coefficients Lk of the elements 2 _i from this error signal Err in the far field. The signal S is sent from the module 35 of the part 30a when it is provided or from a signal generator S to be sent to the calculation module 31. The excitation coefficients Lk are applied to the signal S to be transmitted on the different transmission channels 5k by the module 31 to form the signals s'k. $${\mathrm{s\text{'}}}_{\mathrm{k}}\mathrm{=}{\mathrm{The}}_{\mathrm{k}}\mathrm{.}\mathrm{S}$$

The module 31 modifies the radiated field in emission by the elements 2 _i , which will be measured again by the sensors 10. Thus, the far field radiated by the elements 2 _i is optimized by acting on the coefficients Lk to get closer to the ideal field Elc or be equal to it. The far field radiated by the elements 2 _i is therefore regulated to approach or be equal to the ideal far field Elc.

Of course, there may be more or fewer radiating elements used in transmission with respect to reception, the number of transmitting elements used being different from the number of receiving elements used. Of course, the system could only work in transmission. In the above, the index i refers to the elements used in reception, less than or equal to the number N of elements of the network 2, and k refers to the elements used in transmission, less than or equal to the number N of elements of the network 2. In a satellite, the system operates in reception and transmission, that is to say in transponder, where the received signal is re-transmitted. If the system does not function as a satellite transponder, but mainly in transmission, as for example for a radar, in which the signal is emitted, we receive an echo signal which is processed separately, then the signal S comes from a signal generator and the block 30a becomes a digital signal source S.

To the figure 3 , the plurality of radiating elements 2 _i , symbolized by two lines at the figure 3 , is attached to the same first support 20, while the plurality of sensors 10 _j is fixed to another second support 100, different from the first support 20. The first support 20 is for example formed by a single flat plate. It is for example provided a second support 100 for each sensor 10. This support 100 is for example formed by a holding rod whose one end is fixed to the sensor 10 _j and whose other end is fixed to a base 40 and stable rigid which may be the platform of the satellite, to which the first support 20 is also fixed via spacers 21. The sensors 10 _j are positioned in the free space in front of the plane of the array of radiating elements 2 _i , for example by being located in the same geometrical plane parallel to the plane in which the elements 2 _i of the network 2 are arranged. The height H between the sensors 10 and the elements 2 _i , for example perpendicular to the plane on which the elements 2 _i are arranged, is for example greater than one fifth of the working wavelength λ of the elements 2 _i .

The figure 3 shows that the sensors 10 _i are provided next to and between elements 2 _i . There is a space 22 between the first support 20 of the elements 2 _i and each second support 100 of the sensors 10 _j . To the figure 3 the plate forming the first support 20 has holes 23 for the passage of the second supports 100 in it. Therefore, each second support 100 passes through a hole 23 of the plate forming the first support 20 with the space 22 present between the edge of the hole 23 and the support 100. The space 22 thus allows a clearance between the support 20 and the support 20. support 100. This clearance enabled by the spaces 22 allows the first support 20 to deform to a certain extent because of thermal or mechanical stresses, for example. The deformation of the support 20 will be taken into account by the sensors 10 _j because these sensors 10 _j will measure the near field Epj radiated by the elements 2 _i . Therefore, this deformation can be corrected in real time. It will therefore be possible to impose much less stringent requirements on the first support 20 and to accept to a certain extent a deformation thereof, which will lighten this support 20 and the means 21 of connection to the base 40.

The figure 4 shows that several sensors 10 _j may be provided around and between each radiating element 2 _i , such as for example the number of 6 by elements 2 _i in the hexagonal configuration shown. In addition, a sensor 10 _j may be provided above each element 2 _i , as is also shown in FIG. figure 4 . In this case, the support 100 of the sensor 10 situated above the element 2 _i passes as well through the first support 20 as this element 2 _i .

The sensors 10 are very discrete due to their small size and because they do not disturb the field radiated by the array antenna 2. Modulated scattering techniques can be applied to the sensors 10 to locally measure the near field radiated by the network antenna 2.

The figure 1 represents an embodiment of a sensor system 10 using the modulated scattering technique to perform the near field measurements Epj locally at the location of the sensors. For this purpose, the system comprises a bus 11j for addressing the sensors 10 _j from the computer 3 and another channel 19 for collecting the near-field measurements Epj from the sensors to a measurement reception module 36. Because to address one of the sensors 10 _j , the signal addressing message sent by the computer 3 on the bus 11j is modulated for this sensor 11j, with for example a different modulation from one sensor to another to identify the responses of the sensors to this modulation on the collection path 19. measurement signal Epj collected by the module 36 on the collection channel 19 and having the modulation sent to the sensor 11j will be that provided by the sensor 11j. After having been previously digitized, the module 36 will provide the various near-field measurements Epj by means 30b.

The sensors 10 may be calibrated by receiving a far-field calibration signal in the DIR direction, for example from the ground for a satellite. This calibration can be periodic, for example once a month or a week or other. In the case of a satellite, a terrestrial base station illuminates the satellite in a plane wave. By this means, the complex correction coefficients of each sensor 10 are determined so that the amplitude and phase responses of the sensors are uniform, and, likewise, that the radioelectric axes of each sensor are orthogonal by sensor. and parallel to each other.

Claims (10)

1. System for emitting electromagnetic beams, including a network (2) of elements for emitting far field electromagnetic beams, the signals stemming from and/or arriving at each of the elements being weighted by excitation coefficients digitally determined by computing means,
   comprising

   - a second distinct network of sensors (10) laid out in proximity to the network (2) of radiating elements in order to measure the existing near field (Epj) radiated by the elements,

   - means (32) for computing the far field (E1) radiated by the network (2) from the near field (Epj) actually measured by the sensors (10),

   - means (31) for computing corrections of the excitation coefficients of the elements (2) from the difference which exists between the far field (E1) computed from the measurement of the near field (Epj) and a pre-determined set far field (Elc),
   characterized in that the system includes:

   the radiating elements (2_i) of the network (2) being attached to a first support (20), each sensor (10) being attached to a second support (100) distinct from the first support (20), the first support (20) and the second support (100) being attached to a common base with a space (22) between the first support (20) and each second support (100), the first support (20) comprising a common plate supporting the radiating elements (2_i) of the network (2), the plate including holes (23) for the crossing of the second supports (100) with said space (22) present between the edge of the hole (23) and the second support (100), said space (22) allowing deformation of the first support (20).
2. System according to claim 1, characterized in that the second support (100) for each sensor (10) includes a holding rod, one end of which is attached to the sensor (10) and the other end of which is attached to the base (40), to which the first support (20) is also attached via spacers (21), the plate including holes (23) for letting through the rods, with said space (22) present between the edge of the hole (23) and the rod.
3. System according to any of the preceding claims, characterized in that the sensors are provided on the side and between elements (2_i) .
4. System according to any of claims 1 and 2, characterized in that several sensors are provided around and between each element (2_i).
5. System according to any of claims 1 and 2, characterized in that one of the sensors is provided above each element (2_i), the second support (100) of this sensor is provided above each element (2_i) crossing the first support (20) and said element (2_i).
6. System according to any of the preceding claims, characterized in that the sensors (10) are positioned in the free space and distributed above the plane of the network (2) of radiating elements (2_i).
7. System according to claim 6, characterized in that the height (H) between the sensors (10) and the radiating elements (2_i) of the network (2) is greater than a fraction of the working wavelength (A) of the elements (2_i).
8. System according to claim 7, characterized in that the height (H) between the sensors (10) and the radiating elements (2_i) of the network (2) is greater than one fifth of the working wavelength (A) of the elements (2_i).
9. System according to any of the preceding claims, characterized in that the excitation coefficients comprise a phase shift and an amplitude, the system includes for each element of the network an associated reception channel and/or an associated emission channel, the computing means being provided for computing the phase shift adjustments of the excitation coefficients and the amplitude adjustments of the excitation coefficients so that the measured radiation diagram from the sensors (10) is as close as possible to a radiation diagram of a set instruction.
10. System according to any of the preceding claims, characterized in that it includes means for addressing the sensors and for collecting the near field value (Epj) measured locally at the location of each sensor (10_j) by using the modulated broadcasting method.

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