EP1170823A1 - Telecommunications antenna for covering a large terrestrial zone - Google Patents

Abstract

The invention relates to a receive (or send) antenna for a geosynchronous satellite of a telecommunications system intended to cover a territory divided into areas, the beam intended for each area being defined by a plurality of radiating elements, or sources, disposed in the vicinity of the focal plane of a reflector. The antenna includes at least one first matrix each input of which is connected to a radiating element and each output (or input) of which is connected to a corresponding input of an inverse Butler matrix by an amplifier and a phase-shifter. The phase-shifters move the areas or correct pointing errors.

Description

The invention relates to an antenna telecommunications installed in a geostationary satellite and intended to relay communications over a large area.

To ensure communications on a territory extended, for example the size of North America, we uses a geostationary satellite including an antenna transmitting and receiving antenna each of which has a reflector associated with a multiplicity of radiating elements or sources. In order to be able to reuse resources in communication, including frequency sub-bands, territory to be covered is divided into zones and these resources are assigned to the various areas in such a way that when to an area a resource is assigned, adjacent areas are assigned different resources.

Each zone, for example, with a diameter of the order of several hundred kilometers, is of such an extent that it must be covered by several radiating elements in order ensure a high gain and sufficient homogeneity of the radiation from the antenna in the area.

Thus in Figure 1, there is shown a territory 10 covered by an antenna on board a geostationary satellite and n zones 12 ₁ , 12 ₂ , ..., 12 _n . In this example, 4 sub-bands of frequencies f1, f2, f3, f4 are used.

Zone 12 _i is divided into several sub-zones 14 ₁ , 14 ₂ , etc. each of which corresponds to a radiating element of the antenna. FIG. 1 shows that with certain radiating elements, for example that of reference 14 ₃ in the center of the zone 12 _i , corresponds only one sub-band of frequencies f4, while others, such as those being at the periphery of the zone 12 _i are associated with several sub-bands, those which are assigned to the adjacent zones.

FIG. 2 represents an antenna for receiving a type known for such a telecommunications system.

This antenna comprises a reflector 20 and a plurality of radiating elements 22 ₁ , ..., 22 _N located near the focal plane of the reflector. The signal received by each radiating element, for example that of element 22 _N , first passes through a filter 24 _N intended in particular for eliminating the transmission frequency (powerful) then a low noise amplifier 26 _N. At the output of the low noise amplifier 26 _N , the signal is, thanks to a divider 30 _N , divided into several parts, possibly with coefficients which may differ from one part to another; the purpose of this division is to allow a radiating element to participate in the formation of several beams. It can thus be seen that an output 32 ₁ of the divider 30 _N is assigned to a zone 34 _p , while another output 32 _i of the divider 30 _N is assigned to another zone 34 _q .

The dividers 30 ₁ , ..., 30 _{N as} well as the summers 34 _p , ..., 34 _q intended to reconstitute the zones form part of a device 40 called a beam forming network or brushes.

In the beam forming network 40 shown in FIG. 2, there is provided for each output of each divider 30 _i , an assembly comprising a phase shifter 42 and an attenuator 44. The phase shifters 42 and attenuators 44 allow the radiation diagram to be modified either for correct it, if the satellite has undergone an unwanted move, that is to give a different distribution to the terrestrial areas.

Furthermore, each low noise amplifier 26 _N is associated with another low noise amplifier 26 ′ _N , which is identical to it and whose purpose is to replace the amplifier 26 _N in the event of the latter failing. To this end, two switches 46 _N and 48 _{N are provided} for replacement. It is therefore necessary to provide telemetry means (not shown) to detect the failure and remote control means (also not shown) to ensure replacement.

It can be seen that in an antenna system of the type of that shown in FIG. 2, the number of amplifiers to low noise and the number of phase shifters and attenuators are important. A high number of components in a satellite is an annoying drawback due to the mass. Additionally the number high of phase shifters 42 and attenuators 44 is not favorable to reliability.

The invention makes it possible to reduce in a proportion important the number of low noise amplifiers and the number phase shifters and attenuators.

• au moins une première matrice de type Butler dont chaque entrée reçoit le signal d'un élément rayonnant et à chaque sortie de laquelle est associé un amplificateur à faible bruit en série avec un déphaseur et, de préférence, un atténuateur,
• une seconde matrice de type Butler inverse de la première comportant un nombre d'entrées égal au nombre de sorties de la première et un nombre de sorties égal au nombre d'entrées de la première matrice de type Butler, les sorties de la seconde matrice étant recombinées pour former les faisceaux des zones, et
• des moyens de commandes des déphaseurs et, le cas échéant, des atténuateurs, pour corriger, ou modifier, les faisceaux.

To this end, a reception antenna according to the invention comprises:

• at least a first Butler type matrix, each input of which receives the signal from a radiating element and each output of which is associated a low noise amplifier in series with a phase shifter and, preferably, an attenuator,
• a second inverse Butler type matrix of the first comprising a number of inputs equal to the number of outputs of the first and a number of outputs equal to the number of inputs of the first Butler type matrix, the outputs of the second matrix being recombined to form the zone beams, and
• means for controlling the phase shifters and, if necessary, attenuators, for correcting or modifying the beams.

In a Butler type matrix, which is formed of 3dB couplers, the signal on each output is a combination signals on all inputs, but signals from of the various inputs have a determined phase, distinct from a entry to another, which allows, after passing through the matrix reverse Butler type, to fully reconstruct the signals inputs, after amplification and phase shift, and attenuation optionally.

The number of outputs of the first Butler matrix is preferably equal to its number of entries. In these conditions, the number of low noise amplifiers is equal to number of radiating elements while in the realization anterior, such as that shown in Figure 2, the number of low noise amplifiers is double the number of radiant elements. In addition, the number of phase shifters is also equal to the number of radiating elements while with the prior art this number of phase shifters and attenuators is significantly higher since the output signal of a radiating element is divided and that the phase shift and attenuation 42, 44 are assigned to each channel of the training network of beam.

To correct or modify the beams in an antenna according to the invention, the command to be applied to phase shifters in series with low noise amplifiers is particularly simple.

Thanks to the use of Butler-type matrices, when a low noise amplifier fails, the signal is reduced uniformly on all outputs.

To reduce the effect of an amplifier failure on the output signals, in one embodiment the low noise amplifier that is associated with each output of the first matrix of the Butler type, comprises a plurality, by example a pair of amplifiers in parallel thanks, by example, to couplers. Under these conditions, the effect of failure of only one of the two amplifiers of a pair results in a degradation at least half as much as with just one amplifier associated with each output.

We can show that if we use matrices of Butler of order 8 and a pair of amplifiers in parallel associated with each output, the degradation is -0.56 dB, and with butler matrices of order 16 - also with a pair of amplifiers associated with each output of the first matrix Butler type - the degradation is -0.28 dB.

In one embodiment, use is made of a plurality of associated two-dimensional matrices, for example in different planes, so that each signal received by a radiating element be distributed over nxn low amplifiers noise, n being the order of each two-dimensional matrix. In an example, n = 8 and, under these conditions, each signal received by a radiating element is distributed over 64 low amplifiers noise. In this example, a failure of an amplifier does not a loss of -0.14 dB if only one amplifier is associated with every exit.

The invention also applies to an antenna of emission with an analogous structure. In this case, the inputs of the first Butler type matrix receive the signals to emit, while these are the outputs of the second matrix of Butler type which are connected to the radiating elements. Well of course, instead of low noise amplifiers, for such transmitting antennas, amplifiers of power.

In an embodiment which applies both to the broadcast that upon receipt, one of Butler's matrices and the beam forming network constitutes a unique device.

It is true that it is already known to use a structure with two Butler arrays for transmitting antennas in order to distribute the transmission power over all power amplifiers but in these known antennas the correction or reconfiguration of beams was obtained as described in relation to FIG. 2 for the antennas of reception. Thus, for transmitting antennas, the invention reduces the number of phase shifters, and attenuators' possibly, and also simplifies the ordering of the latter. Furthermore, for reception antennas, the invention, as above, reduced (compared to receiving antennas known) the number of low noise amplifiers.

Each pair of Butler matrices corresponds, from preferably several zones. It is even possible to predict a single Butler matrix for all of the zones. However, for reasons of simplicity of implementation, it is preferable to provide several Butler matrices. In this case, some radiant elements can be assigned to two matrices of Butler different. In this hypothesis, a breakdown of a amplifier associated with a Butler matrix of a pair of such matrices leads to degradation of signals for the set of beams associated with the Butler matrix corresponding. On the other hand if there is no breakdown amplifier for the Butler matrix of the same pair, it turns will then produce an attenuation for the corresponding subzones to the first matrix of the pair while there will be no attenuation for the subzones of the second matrix of the pair.

To remedy this drawback, the invention provides, in one embodiment, to control the attenuators associated with a Butler matrix adjacent to a matrix for which at least one amplifier has failed so that standardize the transmit or receive powers.

Thus, the invention relates to a reception antenna (or transmission) for a geostationary satellite of a telecommunications intended to cover a territory divided into zones, the beam for each zone being defined from several radiating elements, or sources, arranged in the vicinity of the focal plane of a reflector, the antenna comprising means to change zone locations or to correct a antenna pointing fault. This antenna is characterized in that it comprises at least a first matrix of the type Butler, each input (or output) of which is connected to an element radiating and each output (or input) is connected to a . corresponding entry of an inverse Butler type matrix by through an amplifier and a phase shifter, the outputs (or inputs) inverse Butler type matrices being associated to a beam forming network, and in that the phase shifters are ordered to move areas or correct faults in pointing, the first matrix and the Butler type matrix inverse allowing to distribute the energy received by each element radiating across all amplifiers so that a breakdown of one of these has an evenly distributed effect on all the output signals.

Preferably, an attenuator is in series with each amplifier and each phase shifter to allow equalization the amplifiers gains.

In one embodiment, the antenna comprises at least two Butler type matrices with inputs (or outputs) connected to radiating elements, at least one of the radiating elements being connected both to an input of the first matrix and to a input of the second Butler type matrix.

In this case, it is preferable that the radiating element associated with two Butler type matrices be connected to the inputs (or outputs) of these two matrices via a 3dB coupler and that an analog coupler is provided at the outputs (or the entries) corresponding to Butler type matrices inverses.

We can also arrange in series with each amplifier and phase shifter, an attenuator which, in the event of a fault of an amplifier associated with a matrix, attenuates the signals of outputs of the other Butler type matrix, in order to homogenize the output signals of these two matrices.

According to one embodiment, between each output (entry) of the first Butler type matrix and each entry (output) corresponding to the inverse Butler type matrix, we provides amplifiers in parallel, for example associated by 90 ° couplers.

To correct an angular deviation and repoin simultaneously all the beams, preferably the phase shifters are ordered to modify the slope of the phase front of output signals of the first Butler type matrix.

The inverse Butler type matrix and the training network bundles advantageously form a single set.

When providing an attenuator in series with each amplifier, it preferably has a dynamic less than 3dB.

Butler's matrices are, for example, of order eight or sixteen.

In one embodiment, the antenna comprises a first series of first Butler matrices arranged in planes parallels and a second series of first Butler matrices also arranged in planes parallel to a direction different from the first series, for example orthogonal, so as to allow the zones to be moved, or pointing error corrections in two directions different and thus in all directions of the area covered by the antenna.

• la figure 1, déjà décrite, montre un territoire divisé en zones qui est couvert par une antenne à bord d'un satellite géostationnaire,
• la figure 2, également déjà décrite, représente une antenne de réception de l'état antérieur de la technique,
• les figures 3 et 4 sont des schémas montrant des parties d'antennes de réception conformes à l'invention,
• la figure 5 est un schéma d'une variante d'une partie d'antenne selon l'invention,
• la figure 6 représente une matrice de Butler d'ordre 64,
• la figure 7 est un schéma d'une matrice de Butler d'ordre 4,
• la figure 8 est un schéma d'une matrice de Butler d'ordre 16,et
• la figure 9 est un schéma d'une antenne de réception montrant d'autres dispositions de l'invention.

Other characteristics and advantages of the invention will appear with the description of some of its embodiments, this being carried out with reference to the attached drawings in which:

• FIG. 1, already described, shows a territory divided into zones which is covered by an antenna on board a geostationary satellite,
• FIG. 2, also already described, represents a reception antenna of the prior art,
• FIGS. 3 and 4 are diagrams showing parts of reception antennas in accordance with the invention,
• FIG. 5 is a diagram of a variant of an antenna part according to the invention,
• FIG. 6 represents a Butler matrix of order 64,
• FIG. 7 is a diagram of a Butler matrix of order 4,
• FIG. 8 is a diagram of a Butler matrix of order 16, and
• FIG. 9 is a diagram of a reception antenna showing other arrangements of the invention.

The receiving antenna shown in Figure 3 includes, like the antenna shown in Figure 2, a reflector (not shown in Figure 3) and a plurality of radiating elements 22 ₁ , .., 22 _N arranged in the vicinity of the focal area of the receiver.

In the example of FIG. 3, the reception antenna comprises several Butler matrices 50 ₁ , ..., 50 _d , ..., 50 _p . These matrices are all identical, with a number of inputs equal to the number of outputs.

Each input receives the signal from a radiating element. Thus the Butler matrix 50 _j has eight inputs 52 ₁ to 52 ₈ and the input 52 ₁ receives the signal from the radiating element 22 _{k + 1} while the input 52 ₈ receives the signal from the radiating element 22 _{k +8} . The radiating elements 22 _{k + 1} to 22 _{k + 8} are, in one embodiment, all assigned to the same zone, that is to say to the same beam. However, as indicated above, some of these radiating elements also contribute to the formation of other beams for adjacent zones.

Each output of the Butler matrix 50 _j is connected to a corresponding input of a reverse Butler matrix 54 _i via a filter and a low noise amplifier. In FIG. 3, only the low noise amplifiers and the filters are represented which correspond, on the one hand, to the first output 56 _{k + 1} of the matrix 50 _j and, on the other hand, to the last output 56 _{k + 8} of this matrix 50 _j . Thus the output 56 _{k + 1} of the matrix 50 _j is connected to the input 58 _{k + 1} of the matrix 54j via a filter 60 _{k + 1} and a low noise amplifier 62 _{k + 1} arranged in series. The purpose of the 60 _{k + 1} filter is to eliminate the emission signals. This filter can be part of the matrix 50 _j , in particular if this is carried out in waveguide technology.

The Butler matrix 54 _j has an inverse transfer function to that of the matrix 50 _j . It has a number of inputs equal to the number, of outputs from the matrix 50 _d and a number of outputs equal to the number of inputs of the matrix 50 _d .

The outputs of the various inverse Butler matrices 54 _j are connected to the beam outputs 64 ₁ , ..., 64 _S via a beam forming network 66.

We know that a Butler matrix, which is, as we will see later, formed from 3dB couplers, is such that a signal applied to an input is distributed over all the outputs with phases shifted by one output to another of 2π / M, M being the number of outputs. The matrix 54 _j having an inverse function of the matrix 50 _j , a signal of a determined input of the matrix 50 _j is found, with a filtering and an amplification near, on the corresponding output of the matrix 54 _j .

Each output 56 of the matrix 50 _j delivers a signal representing all of the input signals of this same matrix. Under these conditions, a failure of one or more of the low noise amplifiers 62 will not cause a defect in the homogeneity of the reconstituted beam for the corresponding area, but a homogeneous decrease in power over the entire area or zones corresponding to the radiating elements 22 _{k + 1} to 22 _{k + 8} .

We can show that in case of failure of an amplifier, the signal on all the outputs of the matrix 54 _j is reduced by a factor 20log (1-1 / M) in dB, M being the order of the matrix of Butler concerned, i.e. eight in the example. However the degradation of the parameter G / T of the antenna has a value half, that is to say 10log (1-1 / M), because the loss in the loads of the matrix 54 _j is negligible. Indeed, the predominant noise is that collected at the output of low noise amplifiers and since a faulty amplifier no longer contributes to the noise, the total noise power is reduced by a factor 1-1 / M.

Under these conditions, for matrices of order eight, the failure of a low noise amplifier leads to degradation of G / T equal to -0.56 dB and if M = 16 the degradation is -0.28 dB. These figures correspond to the assumption that each amplifier consists of a pair of amplifiers, such as described further with Figure 5 and where by "failure of a amplifier ”means the failure of a single amplifier of a pair.

Failure of a low noise amplifier results also a degradation of the insulation between the signals of exits. Thus, if before the failure the input signals are perfectly isolated, and therefore the output signals too perfectly isolated, after the failure of an amplifier the insulation between two outputs is 20log (M-1) or 17 dB if G = 8 and 23.5 dB if G = 16.

The values indicated above are values theoretical from classical calculations. However, if we do use of appropriate technologies, for example the technique compact waveguide distributors, losses and errors are small and the results practically match to those indicated by the calculations.

In one embodiment, the inverse matrices 54 _j and the beam forming network 66 constitute a single multilayer circuit. This realization is made possible, because the reverse matrices and the network 66 are preferably formed using planar multilayer circuits using the same technology and can thus be arranged in the same housing. The losses caused by the circuits located downstream of the low noise amplifiers being less critical than upstream, it is possible to use circuits of the microstrip or triplate type rather than waveguide circuits because these microstrip or triplate circuits are more compact, but cause losses slightly higher than the waveguide circuits, which is not a problem, as indicated above.

FIG. 4 represents a preferred embodiment of the invention in which the use of matrices is exploited from Butler to simplify the correction command or the modification of beams. In this figure, we have represented in mixed lines the correct direction of radiation 70 relative to antenna, and, in dashed lines 72, the direction of the radiation that is viewed incorrectly by the antenna, by example due to satellite instability.

The energy of radiation 70 corresponds to diagram 74 shown in solid lines, and the energy of radiation 72 corresponds to diagram 76 shown in broken lines. We therefore sees that an incorrect orientation of the antenna corresponds to an offset of the radiation in the focal plane, and the element radiant designed to capture the most energy from a given direction receives the latter only with strong mitigation. Thus, the shift results in a significant loss of gain and alteration of the insulation.

To repoint the antenna, i.e. correct its orientation, as described above in relation to FIG. 2, the previous solution is to assign to each element radiating, a phase shifter 42 and an attenuator 44, and to be controlled the phase shifters 42 individually. In addition, attenuators have a strong dynamic because they must be able “Turn off” or “turn on” certain sources. This constraint entails the need for low noise amplifiers to have a big gain. In addition, it is necessary that the number of radiating elements, or sources, assigned to an area either more important as the number of subzones. For example, if seven radiating elements provide the nominal diagram, for allow repointing you need at least one crown around the septet formed by these radiating elements. It will therefore be necessary provide 19 sources (instead of 7) for each access to an area. In the case where the zones form a square mesh and if one provides four active sources per zone, the number of accesses for an area will be 16.

The invention allows a correction of pointing or a displacement of the zones on the ground of a greater simplicity than the solution represented on figure 2. It takes advantage of the presence of the dies of Butler 50 _j . We start from the observation that at the output of the matrix 50 _j , the phase front 80 _{k + 1} is simply inclined relative to the desired phase front 82 _{k + 1} . Indeed, the signal of each beam is distributed over all the outputs of the corresponding matrix 50 _j with a given phase slope; the slopes corresponding to each entry are separated by a fixed value, constant for a given order matrix. Under these conditions, to carry out the repointing, that is to say the desired correction, it suffices to rectify the slope by providing a phase shifter associated with each output of the matrix 50 _j .

In FIG. 4, the lines 80 _{k + 1} and 82 _{k + 1 show} the distribution of the phases on the outputs 56 _{k + 1} to 56 _{k + 8} for the signals coming from the radiating element 22 _{k + 1} . The lines 80 _{k + 3} and 82 _{k + 3} correspond to the phase distributions on the outputs for the signal coming from the radiating element 22 _{k + 3} while the lines 80 _{k + 7} and 82 _{k + 7} correspond to the phases on all the outputs for the signals supplied by the 22 _{k + 7} radiating element. On these diagrams, the distance between the output 56 _{k + 1} and the intersection P _{k + 1} of the line 82 _{k + 1} with the line D _{k + 1} linked to the output 56 _{k + 1} represents, by convention, the phase for this signal output from the radiating element 22 _{k + 1} . Similarly, the intersections of this line 82 _{k + 1} with the corresponding lines D _{k + 2} , etc., will provide the phases of the signals on the other outputs always for the signal corresponding to the radiating element 22 _{k + 1} .

Thus, for example for the output 56 _{k + 1} , to correct the phase front from 80 to 82, of the signal coming from a radiating element 22 _i , it will be necessary to apply a phase correction δ _{k + 1} , δ _{k + 2} ..., δ _{k + 8} . But we note that the values of δ _{k + 1} , δ _{k + 2} , δ _{k + 3} , etc., are the same. It therefore suffices with a simple phase shifter 84 _{k + 1} , etc., to correct this common value δ _{k + 1} , δ _{k + 2} , etc.

It should be noted that the correction which is carried out by the Butler matrix 50j is only carried out in one plane, that of the figure. To make a real correction, you must predict Butler matrices in another plane, for example perpendicular, as shown in Figure 6 which will described later.

In the example, such a phase shifter 84 is provided downstream of the low noise amplifier 52. Thus, the phase shifter 84 _{k + 1} in FIG. 4 is connected to the output of the amplifier 62 _{k + 1} by through an attenuator 86 _{k + 1} and the output of the phase shifter 84 _{k + 1} is connected to the corresponding input of the inverse matrix 54 _j .

In this embodiment, the attenuators controllable 86 allow equalization of the gain of amplifiers 62. They also allow compensation in failure of one (or more) weak amplifier (s) noise connected to a matrix coupled to the 50j matrix, as we will see it later.

In this example, high-pass filters are provided in the Butler 50 _j matrices to prevent the transmission frequencies from disturbing the reception frequencies. These are, for example, waveguides whose cutoff frequency is between the receive band and the transmit band.

In this example, it is also possible, as described in relation to FIG. 3, to provide for the inverse Butler matrices 54 _{j to} be integrated into the beam forming network 66.

In the variant shown in FIG. 5, the low noise amplifiers 62 are associated in pairs by means of 90 ° couplers. More precisely, the amplifier 62 _{k + 1} is associated with the amplifier 62 _{k + 2} , so that a 90 ° coupler, 88, connects the inputs of the amplifiers and a 90 ° coupler connects the outputs of these amplifiers. In this way, in the event of an amplifier failure, a 0.28 dB loss is obtained with an Butler matrix of order 8, which corresponds, in the absence of the arrangement shown in FIG. 5, to the loss when the Butler matrices are of order 16. Indeed, the arrangement, which consists in making each amplifier associated with an output of a Butler matrix, using a pair of amplifiers, reduced by half the power loss in the event of failure of only one amplifier in the pair since the other amplifier in this pair is still in operation. In other words, this arrangement has the same effect as doubling the order of Butler matrices

More generally, also with the aim of reducing the effect of an amplifier failure, we can associate with each outputs a plurality of amplifiers in parallel. In that case, the number of amplifiers associated with each output is one power of 2 to facilitate the division then the recombination.

Although in the examples described so far, several matrices 50 _j have been provided, it is possible to provide a single Butler matrix of order M, M being the number of radiating elements. However, the space constraints on board a satellite prevent such a Butler matrix from being produced in a single plane as soon as the number of radiating elements becomes large. In this case, it is necessary to use a two-dimensional Butler matrix as shown in FIG. 6. The latter shows a matrix of order 64 produced with a first layer of 8 Butler matrices 90 ₁ to 90 ₈ and a second layer of Butler dies 92 ₁ to 92 ₈ arranged perpendicular to the dies 90.

Such a two-dimensional matrix is of realization complex; it may also present losses detrimental to the antenna noise temperature. But, it allows a simultaneous repointing in two orthogonal planes and it reduces the impact of a breakdown by coupling a higher number between them low noise amplifiers.

In general, it is not essential for ability to correct in two different planes than the dies 90 and 92 are in two perpendicular planes. They just need to be in two directions different, sufficiently separated. In one example, directions are spaced 60 ° apart for easy connection to a network whose centers of adjacent sources form equilateral triangles.

Butler matrices of order 8 and order 16 are made from order 4 Butler matrices.

A Butler matrix of order 4 is represented on the figure 7. It has six 3dB couplers with two couplers entry 94, 96, two. output couplers 100, 104 and two intermediate couplers 98 and 100. In a variant (not shown), instead of intermediate couplers 98 and 100, we provides for crossings; however these crosses are difficult to achieve in waveguide technology.

à la sortie 104₃ et le signal

sur la sortie 104₄. A un signal S' appliqué sur l'entrée 104₂ correspond un signal

sur la sortie 104₄ et

sur la sortie 104₃.Recall that a 3dB coupler, for example the input coupler 104, has two inputs 104 ₁ and 104 ₂ and two outputs 104 ₃ and 104 ₄ and is such that a signal applied to an output, for example the reference one 104 ₁ , sees its power distributed over the two outputs 104 ₃ , 104 ₄ with a phase shift of π / 2 between the two output signals. Thus, as shown in FIG. 7, the signal S at the input 104 ₁ becomes the signal

at output 104 ₃ and the signal

on exit 104 ₄ . A signal S 'applied to input 104 ₂ corresponds to a signal

on exit 104 ₄ and

on exit 104 ₃ .

The signal on input 104 ₁ is found on the four outputs of the Butler matrix of order 4, namely outputs 94 ₃ , 94 ₄ and 96 ₃ , 96 ₄ of couplers 94 and 96 respectively. On output 94 ₃ we obtain the signal j S / 2, on output 94 ₄ , the signal - S / 2, on output 96 ₃ the signal - j S / 2 e ^{-j _ψ} , and on output 96 ₄ the signal S / 2 e ^{- j _ψ} . The constant phase ϕ is introduced by a phase shifter 105 between the couplers 98 and 100. This phase shifter is adjusted to compensate for the differences between guide lengths in the central channels and the end channels; thus, the matrix provides a regular slope to the phases of the signals on the outputs.

We note that with a 4th order Butler matrix, the phases of the output signals vary in 90 ° increments. With an Butler matrix of order 8, the increment is 45 °.

To make such a Butler matrix of order eight, 120 or 130 (FIG. 8), two matrices of order four, respectively 122 and 124, are used, and the outputs of these two matrices of order four are combined using with four 3dB couplers: 126 ₁ , 126 ₂ , 126 ₃ , 126 ₄ .

For the production of a Butler matrix of order 16 (figure 8), two matrices, 120 and 130, of order 8 are used, and the outputs of matrices 120 and 130 are combined using eight 3dB couplers: 132 ₁ to 132 ₈ .

It should be noted that, in known manner, the line crossings of the order 16 matrix which are shown in Figure 8, can be replaced by head-to-tail couplers similar to couplers 98 and 100 of the order 4 matrix shown in Figure 7.

The Butler 50 matrices are, in the example, realized in technology “compact distributor in guide of waves ”. In this case it is possible to integrate into these matrices filtering preventing low noise amplifiers from are delineated by out-of-band spurious signals. he in particular, filtering allowing the rejection of transmission frequencies which, due to the very high power are necessarily reinjected into the antennas of reception arranged nearby.

It is preferable to make each Butler matrix 50 _d in such a way that it corresponds to one or more zones and that the other matrices do not intervene for the zone (s) associated with the matrix. Butler 50 _d . However, it is not always possible to satisfy this condition since each source generally contributes to the formation of several adjacent zones. Under these conditions, a source 22 _q (FIG. 9) which must be associated with two adjacent matrices 50 ₁ , 50 ₂ is connected to the inputs, respectively 140 ₁ and 140 ₂ , of matrices 50 ₁ and 50 ₂ by means of a 3 dB coupler 142. An identical coupler 144 makes it possible to recombine the corresponding outputs of the inverse matrices 50 ′ ₁ and 50 ′ ₂ .

The couplers 142, 144 also make it possible to limit the degradation of the signal coming from a source shared between two matrices, in the event of a low noise amplifier failure associated either with the matrices 50 ₁ , 50 ′ ₁ or with the matrices 50 ₂ , 50 ' ₂ . Indeed, the signal picked up by such a source is distributed in equal parts over two matrices. Thus, only the part affected by a breakdown intervenes.

Although these couplers make it possible to reduce (by half) the imbalance caused by a failure in a matrix, the imbalance which remains in the event of failure is generally not acceptable. This is why instead of the couplers 142, 144, or in addition to the latter, in the event of a breakdown of a low noise amplifier associated with one of the matrices, for example that of reference 50 ₁ , the output signals of the other matrix 50 ₂ by an amount which makes it possible to balance the signals of the outputs of the matrices 50 ₁ and 50 ₂ . This attenuation command is carried out using the attenuators 86 shown in FIG. 4. This attenuation must be 20log (1-1 / M) for inputs or outputs not using a 3dB coupler and 10log (1 -1 / M) for the outputs connected to 3dB 144 couplers.

Mitigation is performed automatically after detection of a fault. Failure detection on each low noise amplifier is, for example, achieved by control of its supply current or using a diode detector placed downstream of each amplifier low noise.

It should be noted that the attenuators 86 (FIG. 4) have, in the example, a weak dynamic, less than 3dB. In effect, their dynamics are mainly determined by their gain equalization function of the various amplifiers at low noise when installing the antenna. For this equalization, the dynamic range is at most 2.5 dB. Through elsewhere, the compensation to be brought to rebalance the outputs of a matrix when the adjacent matrix has a amplifier down, is 0.28 dB.

Although only an antenna of reception, it goes without saying that the invention also applies to a transmitting antenna with a similar structure but in the opposite direction, power amplifiers being used in place of low noise amplifiers.

Claims (14)

Receiving (or transmitting) antenna for geostationary satellite of a telecommunication system intended to cover a territory divided into zones, the beam intended for each zone being defined from several radiating elements, or sources, arranged in the vicinity of the plane focal length of a reflector, the antenna comprising means for modifying the locations of zones or for correcting a pointing error of the antenna, characterized in that it comprises at least a first matrix (50 _i ) of the Butler type, each input (or output) of which is connected to a radiating element (22 _{k + 1} , ..., 22 _{k + 8} ) and each output of which (or input) (56 _{k + 1} , ..., 56 _{k + 8} ) is connected to a corresponding input of a matrix (54 _i ) of reverse Butler type via an amplifier (62 _{k + 1} ) and a phase shifter (84 _{k + 1} ), the outputs (or inputs) of the inverse Butler type matrices being associated with a beam forming network, and, in that the phase shifters are controlled to move the zones or correct the pointing errors, the first matrix and the inverse Butler type matrix making it possible to distribute the energy received by each radiating element over all of the amplifiers so that a failure of one of these amplifiers has a uniformly distributed effect on all the output signals . Antenna according to claim 1 characterized in that each Butler type matrix has a number of inputs equal to its number of outputs. Antenna according to claim 1 or 2 characterized in that an attenuator (86 _{k + 1} ) is in series with each amplifier and each phase shifter so as to allow the gains of the amplifiers to be equalized. Antenna according to any one of claims 1 to 3 characterized in that it comprises at least two Butler type arrays (M ₁ , M ₂ ) with inputs (or outputs) connected to the radiating elements, at least one (22 _q ) radiating elements being connected both to an input of the first matrix (M ₁ ) and to an input of the second matrix (M ₂ ) of the Butler type. Antenna according to claim 4 characterized in that the radiating element associated with two Butler type arrays is connected to the inputs (or outputs) of these two arrays via a 3dB coupler (14 ₂ ) and in that an analog coupler (144) is provided at the corresponding outputs (or inputs) of inverse Butler type dies. Antenna according to claim 4 or 5 characterized in that it comprises, in series with each amplifier and phase shifter, an attenuator (86 _{k + 1} ) which, in the event of an amplifier associated with a matrix failure, attenuates the output signals of the other Butler type matrix, in order to homogenize the output signals of these two matrices. Antenna according to any one of the preceding claims, characterized in that amplifiers are provided in parallel between each output (input) of the first Butler type matrix and each corresponding input (output) of the reverse Butler type matrix (62 _{k + 1} , 62 ' _{k + 1} ), for example associated by 90 ° couplers (88, 90). Antenna according to any one of the preceding claims, characterized in that to correct an angular deviation and simultaneously repoint all the beams; the phase shifters are controlled to modify the slope of the phase front of the output signals of the first Butler type matrix. Antenna according to any one of the preceding claims, characterized in that being intended for reception, the first Butler type matrix comprises filtering means for eliminating the transmission frequency bands. An antenna according to any one of the preceding claims, characterized in that the inverse Butler type matrix and the beam forming network form a single unit. Antenna according to claim 3 or 6 characterized in that the attenuator in series with each amplifier has a dynamic range less than 3dB. Antenna according to any one of the preceding claims, characterized in that the Butler matrices are of order eight or sixteen. Antenna according to any one of the preceding claims, characterized in that it comprises a first series of first Butler arrays arranged in parallel planes and a second series of first Butler arrays also arranged in planes parallel to a direction different from that of the first series, so as to allow the displacement of the zones, or corrections of pointing errors in two different directions and, thus, in all the directions of the zone covered by the antenna. Antenna according to claim 13 characterized in that the directions of the two series of first Butler matrices are orthogonal.

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