EP3073569A1 - Compact butler matrix , planar bi-dimensional beam-former, and planar antenna with such a butler matrix - Google Patents

Abstract

The compact Butler matrix consists of a planar multilayer structure comprising N waveguides with parallel metal plates PPW stacked one above the other, two adjacent waveguides PPW having a common wall formed by one metal plates. The couplers, phase shifters and crossover devices of the Butler matrix are constituted by metasurfaces integrated into the metal plates. The planar two-dimensional beamformer may comprise a PPW waveguide Butler matrix associated with optical lenses integrated in each PPW waveguide. Alternatively, the planar two-dimensional beamformer may comprise an upper stage consisting of a Butler matrix with PPW waveguides, and a lower stage comprising PPW waveguides equipped with integrated reflectors, the two stages being connected in series. .

Description

The present invention relates to a compact Butler matrix, a planar two-dimensional beamformer and a multi-beam planar antenna comprising such a Butler matrix. It applies to any multibeam antenna, especially in the field of space applications such as satellite telecommunications, and more particularly to thin antennas.

The beamformers are used in multibeam antennas to develop output beams from input radio frequency signals. A conventional beamformer comprises N inputs In1 to InN, P outputs Out1 to OutP, and a plurality of radio frequency circuits 11, 12, 13 able to divide and recombine the input radio frequency signals according to a chosen phase and amplitude law. to form output beams. There are different beamformer technologies. On the figure 1 , the radio frequency circuits comprise a large number of individual waveguides 10 which intercross with each other so as to allow the combinations necessary for the formation of the different output beams by radiofrequency signal combiners 12. These beam formers are suitable for a limited number of radiating elements and to form a limited number of beams as they become very complex as the number of beams increases due to the necessary crossovers between the waveguides.

It is also known to form beams using a Butler matrix consisting of a symmetrical passive circuit with N input ports and N output ports, which drives radiating elements producing N different beams of equal amplitudes. The circuit is composed of junctions that connect the input ports to the output ports by N different transmission lines 18 and parallel to each other. There are several possible configurations of Butler matrix. On the diagram of the figure 2 the Butler matrix comprises couplers 15, of the 3 dB, 90 ° hybrid coupler type, making it possible to combine or divide the power of the waves input radio frequency, phase shifters 16 capable of applying a phase delay of 45 °, and crossing devices 17 for crossing two different transmission lines. In known manner, each crossing device 17 may consist of two 3 dB, 90 ° couplers connected in series. An example of a Butler matrix architecture with four input ports A, B, C, D and four output ports A ', B', C ', D' is shown in FIG. figure 2 . In this example, the Butler matrix has four 3 dB, 90 °, two 45 ° phase shifters and a crossover. This type of beamformer is well suited for forming a small number of beams but becomes too complex as the number of beams increases. In addition, it allows the formation of beams in only one direction of the space perpendicular to the transmission lines 18.

According to another technology, there are planar quasi-optical beamformers using electromagnetic propagation of radiofrequency waves originating from several input power sources, for example radiating horns, according to a propagation mode in general TEM between two plates. parallel metallic. The focusing and collimation of the beams can be performed by an optical lens as described for example in the documents US 3170158 and US 5936588 which illustrate the case of a Rotman lens, or alternatively by a reflector as described for example in the documents FR 2944153 and FR 2 986377 , the optical lens or the reflector respectively being inserted in the propagation path of the radio frequency waves, between the two parallel metal plates. Different types of optical lenses may be used, these optical lenses serving essentially as phase correctors and allowing in most cases to convert one or more cylindrical waves emitted by the sources into one or more plane waves propagating in the waveguide with parallel metal plates. The optical lens may comprise two opposite edges with parabolic profiles, respectively input and output. Alternatively, the optical lens may be a dielectric lens, or a right-sided index gradient lens, or any other type of optical lens. In the case of an optical lens quasi-optical beamformer, to obtain a plane antenna, it is sufficient to place elements radiating input around the input edge of the optical lens and attaching radio frequency probes to the output edge of the optical lens, and then connecting each radio frequency probe to a radiating output element via a line transmission, for example a coaxial cable. In the case of a pillbox beamformer, to obtain a planar antenna, input radiating elements are placed in front of the integrated parabolic reflector, and radiating output elements are placed in the path of the radiofrequency waves reflected by the parabolic reflector. . There are different solutions of pillbox beamformers, using one or more reflectors.

Since this technology uses parallel plate waveguides, as an alternative to the use of multiple discrete radiators aligned side by side, it is possible to use a continuous linear aperture radiating out of each plate waveguide parallel. These linear radiating apertures, which are not spatially quantized, have much higher performances compared to the linear arrays of several radiating elements, for the depointed beams, because of the absence of quantization, and in bandwidth because of the absence of resonant propagation modes.

A quasi-optical beamformer is much simpler than traditional waveguide beamformers because it does not have a coupler or a crossover device. However, all known planar beam formers are able to form beams only in one dimension of space, in a direction parallel to the plane of the metal plates. To form beams according to two dimensions of the space, in two directions, respectively parallel and orthogonal to the plane of the metal plates, it is necessary to combine orthogonally between them, two sets of beam forming, each beam forming assembly consisting of a stack of several layers of unidirectional beamformers. To orthogonally combine two sets of beam forming, it is further necessary to arrange connection interfaces, in particular input / output connectors, on each set of beam forming and then connect in pairs the different inputs and outputs. corresponding outputs from both beam forming assemblies by dedicated interconnection cables as shown for example in the document US 5,936,588 for lens bundle trainers. This architecture is satisfactory for the formation of a small number of beams, but becomes very complex and too much space when the number of beams increases.

To our knowledge, to date, there is no planar beam forming device for forming beams in two dimensions of space. Moreover, there are also no simple solutions for interconnecting two unidirectional beamformers to overcome connection interfaces and interconnection cables.

The object of the invention is to overcome the drawbacks of known beam formers and to realize a planar two-dimensional beamformer comprising continuous transmission lines and making it possible to form beams in two dimensions of space without any connection interface or no interconnecting cable.

Another object of the invention is to provide a new and particularly compact Butler matrix having a new parallel plate architecture compatible with quasi-optical beamformers.

For this purpose, the invention relates to a compact Butler matrix comprising N waveguides, where N is an integer greater than three and selected from the powers of two, couplers for coupling two adjacent waveguides, phase shifters and at least one crossing device capable of crossing two adjacent waveguides, the crossing device comprising two couplers connected in series. The Butler matrix consists of a planar multilayer structure comprising N + 1 metal plates parallel to each other, stacked one above the other, and regularly spaced from each other, each space between two consecutive metal plates forming a guide parallel plate wave having two opposite walls, respectively upper and lower, constituted by the two consecutive metal plates, two waveguides with adjacent metal plates having a common wall formed by one of the metal plates, and the couplers, the phase shifters and the crossing device are constituted by metasurfaces integrated in the respective walls of the waveguides to be coupled, crossed and out of phase.

Advantageously, the metasurfaces constituting each coupler and the crossing device between two adjacent waveguides may consist of a metallized support provided with a plurality of through holes regularly distributed in a coupling zone, respectively a crossing zone, of the wall common to the two adjacent adjacent waveguides, the crossing zone consisting of two coupling zones arranged in cascade one behind the other.

Advantageously, the metasurfaces constituting each phase shifter integrated in a waveguide may consist of corrugations arranged in a phase shift zone, on the two opposite walls of the corresponding waveguide.

Alternatively, according to a particular embodiment, each metal plate may consist of a metal coating deposited on a dielectric substrate and each coupler and crossing device between two adjacent waveguides may consist of a plurality of slots etched in the metal coating, the slots being regularly distributed throughout the coupling zone, respectively throughout the crossing zone, the crossing zone consisting of two coupling zones arranged in cascade one behind the other.

Alternatively, each phase-shifter may consist of a set of periodically photo-etched metal patches on the dielectric substrate of the two walls of a phase-shifted waveguide.

The invention also relates to a planar beamformer capable of synthesizing beams according to two dimensions of space, comprising at least one Butler matrix with N + 1 parallel plates.

Advantageously, the beamformer may comprise two different Butler matrices stacked one above the other and respectively dedicated to two different polarizations orthogonal to each other.

According to one embodiment, the beamformer may further comprise N respectively integrated optical lenses, at the output, or alternatively at the input, of the Butler matrix, in the N waveguides delimited by the N + 1 metal plates.

Advantageously, each optical lens may be a lens of constant thickness and index gradient.

According to another embodiment, the beamformer may comprise two stacked stages, respectively lower and upper, each stage comprising an identical number of parallel plate waveguides, the Butler matrix being located on the upper stage, each waveguide of the lower stage being connected in series to a waveguide of the upper stage by a respective intermediate waveguide comprising parallel metal plates arranged orthogonally to the XOY plane of the two lower and upper stages, the parallel metal plates constituting the walls of each intermediate waveguide forming a reflector integrated in the beamformer.

The invention also relates to a planar antenna comprising at least one Butler matrix with N + 1 parallel plates, the antenna further comprising M radiating feed horns connected at the input of each waveguide with parallel metal plates, ie MN radiating feed horns for the N metal plate waveguides, where M is greater than 2, and N output radiating horns respectively connected to the N metal plate waveguides.

Advantageously, each output radiating horn can be a longitudinal horn coupled to a linear radiating aperture extending transversely over the entire width of the corresponding parallel plate waveguide.

Advantageously, the linear radiating openings may be oriented in a direction perpendicular to the plane of the parallel plates of the corresponding parallel plate waveguide.

• figure 1 : un schéma synoptique d'un exemple de formateur de faisceaux traditionnel, selon l'art antérieur ;
• figure 2 : un exemple de schéma synoptique d'une matrice de Butler, selon l'art antérieur ;
• figures 3a et 3b : deux schémas, respectivement en perspective et en coupe longitudinale, d'un premier exemple de réalisation d'une matrice de Butler comportant un empilement de plusieurs guides d'onde à plaques parallèles, selon l'invention ;
• figures 4a et 4b : deux schémas, respectivement en coupe longitudinale et en vue de dessus, illustrant un exemple de zone de couplage insérée dans une plaque métallique commune entre deux guides d'onde à plaques métalliques, selon l'invention ;
• figure 5 : un schéma en coupe longitudinale, d'un deuxième exemple de réalisation d'une matrice de Butler comportant un empilement composite de plusieurs couches de substrats gravés et métallisés séparées par des espaceurs, selon l'invention ;
• figure 6 : un schéma en perspective, d'un premier exemple de formateur de faisceaux à deux dimensions, connecté à des ouvertures linéaires rayonnantes, et comportant une matrice de Butler, selon l'invention ;
• figure 7 : un schéma en perspective, d'un deuxième exemple de formateur de faisceaux à deux dimensions, connecté à des ouvertures linéaires rayonnantes, et comportant une matrice de Butler, selon l'invention ;
• figure 8a : un schéma en perspective d'un exemple de lentille diélectrique intégrée dans un guide d'onde à plaques parallèles ; selon l'invention ;
• figure 8b : un schéma en perspective d'un exemple de lentille d'épaisseur constante et à gradient d'indice intégrée dans un guide d'onde à plaques parallèles ; selon l'invention ;
• figure 9 : un schéma, en coupe longitudinale, d'un troisième exemple de formateur de faisceaux à deux dimensions comportant une matrice de Butler, selon l'invention ;
• figure 10a et 10b : un schéma, en vue de dessus, de deux étages, respectivement inférieur et supérieur, d'une antenne plane selon le mode de réalisation de la figure 9 ;
• figure 11 : un schéma en coupe longitudinale, d'un exemple de matrice de Butler bi-polarisation, 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 block diagram of an example of traditional beamformer, according to the prior art;
• figure 2 an example of a block diagram of a Butler matrix, according to the prior art;
• Figures 3a and 3b two diagrams, respectively in perspective and in longitudinal section, of a first exemplary embodiment of a Butler matrix comprising a stack of several parallel plate waveguides, according to the invention;
• Figures 4a and 4b two diagrams, respectively in longitudinal section and in plan view, illustrating an example of a coupling zone inserted in a metal plate common between two waveguides with metal plates, according to the invention;
• figure 5 : a longitudinal sectional diagram of a second embodiment of a Butler matrix comprising a composite stack of several layers of etched and metallized substrates separated by spacers, according to the invention;
• figure 6 : a perspective diagram of a first example of a two-dimensional beamformer connected to linear apertures radiating, and comprising a Butler matrix, according to the invention;
• figure 7 a perspective diagram of a second example of a two-dimensional beamformer connected to linear apertures radiating and having a Butler matrix according to the invention;
• figure 8a : a perspective diagram of an example of a dielectric lens integrated into a parallel plate waveguide; according to the invention;
• figure 8b : a perspective diagram of an example of a constant thickness, index gradient lens integrated into a parallel plate waveguide; according to the invention;
• figure 9 : a diagram, in longitudinal section, of a third example of a two-dimensional beamformer comprising a Butler matrix, according to the invention;
• figure 10a and 10b : a diagram, in plan view, of two floors, respectively lower and upper, of a planar antenna according to the embodiment of the figure 9 ;
• figure 11 : a longitudinal sectional diagram of an example of bi-polarization Butler matrix, according to the invention.

According to the invention, as shown in the diagrams of Figures 3a and 3b , the Butler matrix consists of a planar multilayer structure comprising N + 1 metal plates 20, parallel to each other, stacked one above the other, and regularly spaced from each other. The space 21 between two consecutive metal plates, consisting of air or dielectric, forms a waveguide with parallel plates PPW (in English: parallel plate waveguide) whose upper and lower walls are the two consecutive metal plates. In the various figures, the metal plates are parallel to the XOY plane, the X direction corresponding to the longitudinal direction of propagation of the radio frequency waves in each parallel plate waveguide. Two adjacent waveguides PPW1 and PPW2, PPW2 and PPW3, PPW3 and PPW4, comprise a common wall formed by one of the metal plates 20. The Butler matrix therefore comprises N parallel-plate waveguides stacked one above the other in the direction Z orthogonal to the plane XOY, where N is an integer greater than three and selected from the powers of two. The Butler matrix also comprises couplers, for example of the hybrid coupler type 3dB, 90 °, each coupler being intended to couple two waveguides adjacent to each other, 45 ° phase shifters and crossover devices (in English: crossover) intended to intersect with each other two adjacent waveguides. According to the invention, the couplers 15, the crossing devices 17 and the phase-shifters 16 are integrated locally into the metal plates forming the walls of the waveguides PPW1, PPW2, PPW3, PPW4 in respective coupling zones 22a, 22b, 22c, 22d, crossover 24 and phase shift 23a, 23b, located in the path of propagation of radiofrequency waves and extending transversely, parallel to the Y direction, over the entire width D of the corresponding metal plate 20.

To couple or cross two waveguides adjacent to each other, the metal plate forming the common wall between the two adjacent waveguides comprises coupling zones and crossing zones constituted by metasurfaces integrated locally in said common wall. A metasurface is a textured surface consisting of a dense planar distribution of small identical or non-identical elements, fixed, or printed, or engraved, on a very thin support. A metasurface is characterized by a surface impedance that locally modifies the longitudinal propagation of a guided wave in a waveguide. A metasurface has very interesting properties from an electromagnetic point of view because it allows to control the propagation of electromagnetic waves along its surface. According to the desired properties, the elements fixed, or printed or engraved may for example be metal studs or metal patches or holes, or slots, regularly distributed or of variable density, the distance between two consecutive elements being less than Central wavelength of operation. As shown on Figures 4a and 4b according to the invention, in each coupling zone 22a, 22b, 22c, 22d and in the crossing zone 24 which consists of two coupling zones arranged in cascade one behind the other, the metasurface is constituted a metallized support 26 provided with a plurality of through holes 25 regularly distributed throughout the coupling zone, respectively throughout the crossing zone. The distance separating two adjacent holes is much less than, at least a factor of three, at the wavelengths guided in the parallel plate guide. The metasurface has a high reactive surface impedance, for example 100 ohms, the value of which depends on the density of the holes and the length L of the coupling zone. By way of non-limiting example, at 25 GHz, a 90 ° 3dB coupler synthesized by a metasurface having a reactive surface impedance of 100 Ohms was obtained with holes regularly distributed over a length L equal to 35 mm. Two identical metasurfaces put end to end synthesize the crossing zone. It has been verified that these surface impedances are effective for radio waves having different angles of incidence.

To make a phase shift in a parallel plate waveguide, PPW1, PPW4, the two metal plates forming the upper and lower walls of the corresponding waveguide comprise phase shift zones 23a, 23b which may consist of corrugations arranged locally on the inner surface of the two corresponding metal plates and whose width is equal to the transverse width D of the corresponding metal plates. In the example of Figures 3a and 3b the number N of waveguides is four, and the number of metal plates 20 is five. Between the inputs I1, I2, I3, I4, and the outputs O1, O2, O3, O4, of the Butler matrix, a first coupling zone 22a is integrated in the second metal plate common to the first waveguide PPW1 and at the second waveguide PPW2 and a second coupling zone 22b is integrated in the fourth metal plate common to the third waveguide PPW3 and the fourth waveguide PPW4. Downstream of the two coupling zones 22a, 22b, the Butler matrix comprises a crossing zone 24 consisting of two hybrid couplers 3dB, 90 °, cascaded, one behind the other, in the third metal plate common to the second and third waveguides PPW2, PPW3, and two phase shift zones 23a, 23b respectively arranged in the upper and lower walls of the first and fourth waveguides PPW1, PPW4. Finally, downstream of the phase shift zones 23a, 23b and the zone of 24, a third and a fourth coupling zone 23c, 23d are respectively integrated in the second metal plate common to the first and second waveguides PPW1, PPW2 and in the fourth metal plate common to the third and fourth waveguides PPW3, PPW4. In operation, in the crossing zone 24 between two adjacent waveguides PPW2, PPW3, the radiofrequency signals propagating in the two adjacent waveguides intersect and mutually exchange their propagation waveguide, which allows to group two by two signals that propagate initially in non-adjacent waveguides to couple them. Thus, in this example, the radiofrequency signals propagating initially in the waveguides PPW2 and PPW3 are exchanged in the crossing zone 24 and then propagate, downstream of the crossing zone, respectively in the waveguides. PPW3 and PPW2. They can then be respectively coupled to radio frequency signals that propagate in waveguides PPW4 and PPW1. For the Butler matrix to work well for multiple transmitting radio frequency waves, in a TEM mode, in the parallel plate waveguides, it is necessary that the phase shift, coupling and crossover areas be compact and so that the surface impedances are high. The size of the phase shift, coupling and crossover areas is further reduced if the Butler matrix operates over a wider band and for higher radiofrequency waveforms.

Alternatively, as shown in the example of the figure 5 , the Butler matrix can be made using a printed circuit technology by using a multilayer composite structure comprising a stack of several layers consisting of etched and metallized substrates S1, S2, S3, S4, S5 possibly being separated by spacers E1, E2, E3, E4. Each layer forms a waveguide comprising two metallized walls parallel to each other, each wall consisting of a metal coating 33 deposited on a dielectric substrate 32, the spacer located between two metallized walls may consist of air or comprise a material transparent to radiofrequency waves, such as for example a honeycomb material, or a quartz material, or a material made of kevlar, or an expanded polymer foam. The role of a spacer is to reduce propagation losses, but this spacer is not essential. The metal coating 33 deposited on the substrate 32 is then equivalent to a metal plate 20. The coupling zones 22a, 22b, 22c, 22d and crossing 24 between two adjacent waveguides then consist of a plurality of etched slots in the metal coating, the slots being evenly distributed throughout the coupling zone, respectively throughout the crossing zone, the length of the crossing zone 24 being equal to twice the length of a coupling zone. The phase shift zones consist of metasurfaces, deposited on the metal coating, which modify the propagation delay of the radiofrequency waves. According to the invention, in the phase shift zone 23a, 23b of a waveguide, the metasurfaces may, for example, consist of a set of metal pads, or metal patches 30 periodically photogravated by photolithography on the face. internal of the dielectric substrate of the two walls of the corresponding waveguide. Although this is not essential, the metal patches may for example be short-circuited by connecting them to the metal coating of the wall of the corresponding waveguide, through a metallized through hole 31 arranged in the corresponding dielectric substrate. The distribution period of the metal patches, equal to the distance between two adjacent metal patches, is less than the propagation wavelength of the radiofrequency waves in the waveguide with parallel metallic walls.

The Butler matrix according to the invention constitutes a one-dimensional beamformer when used alone. According to the invention, the two-dimensional planar beamformer comprises a Butler matrix 41 having N parallel-stacked PPW waveguides stacked one above the other, where N is an integer greater than three and selected among the powers of two, for example, 4, 8, 16, 32 ..., and further comprises an optical device of the optical lens or reflective type. On the figures 6 and 7 , the number N of waveguides PPW1, PPW2, PPW3, PPW4, is equal to 4. The structure of the Butler matrix is identical to that represented on the Figures 3a and 3b . In addition, the beam trainer has N optical lenses 42 respectively integrated in the N waveguides delimited by the N + 1 parallel metal plates. On the figure 6 , the optical lenses 42 are arranged in the waveguides PPW, at the input of the Butler matrix 41, between the input feed horns 43 of each waveguide and the Butler matrix 41, whereas on the figure 7 , the optical lenses 42 are arranged in the waveguides PPW at the outlet of the Butler matrix 41, between the Butler matrix and exit horns 44. For example, each optical lens 42 may be a dielectric lens whose dielectric permittivity is different from that of the propagation medium of the parallel plate waveguides PPW1, PPW2, PPW3, PPW4 (which is equal to 1 if the waveguides PPW1,..., PPW4 are filled with air or equal to the permittivity of the substrate 32 in the case where the waveguides consist of a stack of layers of metallized and etched substrates). Each optical lens 42 integrated in a parallel plate waveguide may have parabolic edges as shown in the waveguide PPW of the figure 8a , or be a lens of variable thickness, or, to avoid shape discontinuities, be a straight-edged lens of constant thickness and refractive index gradient as shown in the waveguide PPW of the figure 8b , or any other type of optical lens with a variable refractive index which makes it possible to phase out the radiofrequency waves according to a predefined phase law.

The planar beam former thus produced makes it possible, with the Butler matrix 41, to synthesize beams in the XOZ plane perpendicular to the parallel plates and makes it possible, with the optical lens 42, to synthesize beams in the XOY plane parallel to the parallel plates without any discontinuity. propagation in the parallel plate waveguides and without using any interconnection or any connecting cable.

To obtain a planar antenna, M feed horns 43 aligned next to each other are connected at the input of each waveguide PPW, where M is greater than two, and at the output of the beamformer, each waveguide PPW wave can be connected to several radiating output elements or to a single longitudinal radiating horn 44 coupled to a linear aperture radiating. On the figures 6 , 7, 8a and 8b , the number M of feeding horns 43 is equal to 7 per waveguide, ie MN horns input total, equal to 28 for the four PPW waveguides. On the figures 6 and 7 a single longitudinal radiating horn 44 is used at the output of each waveguide PPW. Each linear aperture radiant coupled to the longitudinal radiating horn 44 output extends transversely over the entire width D of the corresponding waveguide. On the figures 6 and 7 each linear aperture radiating is oriented to radiate in a direction Z perpendicular to the plane XOY parallel plates but it is not essential, the linear openings could also be in the extension of the parallel plates. It should be noted that in figures 6 and 7 the plane of radiation of the longitudinal radiating horns is not an extension of the parallel plates, but is folded with respect to the parallel plates. Of course, this is not essential. It is also possible to arrange the radiating cornets in the extension of the parallel plates, but in this case, it may be necessary to add a transition between each horn and the corresponding waveguide when the width of the horns is greater than the thickness of the waveguides. A longitudinal horn has the advantage of radiating energy over the entire width of the opening of the parallel plate waveguide, which makes it possible to produce an antenna with a large bandwidth of operation and with a large beam misalignment capability. formed and makes it possible to get rid of network lobes.

The dimensions of the beamformer including optical lenses are strongly constrained by the focal length between each optical lens 42 and the input feed horns 43. The greater the focal length, the better the quality of the depointed beams. When the optical lenses are arranged at the outlet of the Butler matrix, as shown in FIG. figure 7 , the required focal distance between each optical lens and the feed horns is advantageously used by the Butler matrix, which makes it possible to reduce the dimensions of the beamformer which is then more compact. In this embodiment, radiofrequency waves propagating in the Butler matrix are no longer flat but cylindrical.

The figure 9 illustrates another embodiment of a two-dimensional planar beamformer having no discontinuity of spread. In this embodiment, the planar beam former comprises 2N + 1 parallel plates 20 constituting the respective walls of 2N parallel plate waveguides distributed over two floors, respectively lower 50 and upper 51. Each stage comprises N guide plates. wave in PPW technology, stacked one above the other, where N is greater than three. Each parallel plate waveguide PPW1, PPW2, PPW3, PPW4 of the lower stage is respectively connected in series with a parallel plate waveguide PPW8, PPW7, PPW6, PPW5 of the upper stage via of a respective intermediate waveguide, with parallel plates PPWP1, PPWP2, PPWP3, PPWP4, arranged orthogonally to the XOY plane of the two stages of the beamformer. The parallel metal plates forming the walls of each intermediate waveguide then form a reflector integrated in the beamformer, as in a pillbox-type beamformer. The parallel metal plates constituting the walls of the intermediate waveguides may comprise a chosen shape profile, which may for example be of straight shape as illustrated in FIG. figure 9 or curved shape, for example of parabolic shape, as illustrated on the Figures 10a and 10b , which represent two stages, lower and upper, of a planar antenna comprising such a beamformer. At the output of the reflector, the N waveguides PPW8, PPW7, PPW6, PPW5 of the upper stage are coupled together by a Butler matrix according to the invention and as described in connection with the Figures 3a and 3b .

To make a planar antenna, it is then sufficient to equip, each waveguide PPWP1, PPWP2, PPWP3, PPWP4 of the lower stage of the beamformer, several radiating horns 43 of feed and output of the matrix of Butler 41, to couple each waveguide PPW8, PPW7, PPW6, PPW5 of the upper stage to an output longitudinal horn 44 coupled to a linear radiating aperture extending transversely across the width D of the waveguide to corresponding metal plates, as shown on the Figures 10a and 10b .

For operation in double polarization, for example circular, the invention consists in using two identical Butler matrices, respectively dedicated to each polarization, and stacked one above the other as shown on the figure 11 wherein each Butler matrix comprises four waveguides A, B, C, D and A ', B', C ', D', in PPW parallel plate waveguide technology. Each Butler matrix being dedicated to one of the two polarizations, at the output of the beamformer, the PPW waveguides operating in the same polarization are adjacent to each other. However, to achieve a circular double polarization antenna, it is necessary to feed radiating output elements in circular double polarization by means of OMT orthomode transducers. It is therefore necessary, at the output of the Butler matrix, to group two by two, different polarization waveguides. For this purpose, at the output of the two Butler matrices, the invention also consists in successively crossing adjacent waveguides chosen to group two by two the waveguides of different polarizations. The crossings are made by metasurfaces integrated in the metal plates common to two adjacent waveguides to cross, as explained in connection with the figure 3b . So, in the example of the figure 11 a first crossing is made between the waveguides D and A 'by a metasurface integrated in the fifth metal plate 5. Then two successive crossings are respectively made between the waveguides D and C and between the waveguides B and C by corresponding metasurfaces integrated in the fourth and third metal plates 4, 3. Similarly symmetrically, two successive crossings are respectively made between the waveguides A 'and B' and B 'and C' by corresponding metasurfaces embedded in the plates 6, 7. The different crossings made allow, at the output of the two Butler matrices, to regroup the waveguides A and A ', the waveguides B and B', the waveguides C and C 'and the waveguides D and D'. The number of waveguides of each Butler matrix is not limited to four but must be equal to a power of two.

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 (14)

Compact butler matrix having N waveguides, where N is an integer greater than three and selected from the powers of two, couplers (22a, 22b, 22c, 22d) for coupling two adjacent waveguides, phase shifters (23a, 23b) and at least one crossing device (24) adapted to intersect two adjacent waveguides, the crossing device (24) having two couplers connected in series, the Butler matrix being characterized in that it consists of a planar multilayer structure comprising N + 1 metal plates (20) parallel to each other, stacked one above the other, and regularly spaced from each other, each space between two consecutive metal plates forming a guide parallel plate wave (PPW1, PPW2, PPW3, PPW4) having two opposite walls, respectively upper and lower, constituted by the two consecutive metal plates, two waveguides with metallic plates adjacent ones having a common wall formed by one of the metal plates, and in that the couplers (22a, 22b, 22c, 22d), the phase shifters (23a, 23b) and the crossover device (24) are constituted by metasurfaces integrated locally into the respective walls (20) of the waveguides to be coupled, crossed and out of phase. Butler matrix according to claim 1, characterized in that the metasurfaces constituting each coupler (22a, 22b, 22c, 22d) and the crossover device (24) between two adjacent waveguides (PPW1, PPW2), (PPW2, PPW3), (PPW3, PPW4) consist of a metallized support (26) provided with a plurality of through holes (25) regularly distributed in a coupling zone, respectively a crossing zone, of the wall common to the two guides corresponding adjacent wave, the crossing zone consisting of two coupling zones arranged in cascade one behind the other. Butler matrix according to claim 2, characterized in that the metasurfaces constituting each phase shifter (23a, 23b) integrated in a waveguide (PPW1), (PPW4) consist of corrugations arranged in a phase shift zone, on the two opposite walls of the corresponding waveguide. Butler matrix according to claim 1, characterized in that each metal plate consists of a metal coating (33) deposited on a dielectric substrate (32) and in that each coupler (22a, 22b, 22c, 22d) and the crossing device (24) between two adjacent waveguides consists of a plurality of slots etched in the metal coating, the slots being evenly distributed throughout the coupling area, respectively throughout the crossing zone, the crossing consisting of two coupling zones arranged in cascade one behind the other. Butler matrix according to claim 4, characterized in that each phase shifter consists of a set of metal patches (30) periodically photogravated on the dielectric substrate (32) of the two walls of a waveguide to be shifted. Planar beamformer characterized in that it comprises at least one Butler matrix (41) according to one of Claims 1 to 5. Planar beamformer according to claim 6, characterized in that it comprises two different Butler matrices stacked one above the other and respectively dedicated to two different polarizations orthogonal to each other. Planar beamformer according to claim 6, characterized in that it further comprises N integrated optical lenses (42), at the output of the Butler matrix (41), in the N waveguides delimited by the N + 1 parallel metal plates. Planar beamformer according to claim 6, characterized in that it further comprises N optical lenses (42) respectively integrated, at the input of the Butler matrix (41), in the N waveguides delimited by the N + 1 metal plates. Planar beamformer according to one of claims 8 or 9, characterized in that each optical lens (42) is a lens of constant thickness and gradient index. Planar beamformer according to claim 6, characterized in that it comprises two stacked stages, respectively lower (50) and upper (51), each stage comprising an identical number of parallel plate waveguides, the Butler matrix (41) being located at the upper stage (51), each parallel plate waveguide (PPW1, PPW2, PPW3, PPW4) of the lower stage (50) being connected in series with a waveguide with parallel plates (PPW5, PPW6, PPW7, PPW8) of the upper stage (51) by a respective intermediate waveguide (PPWP1, PPWP2, PPWP3, PPWP4) having parallel metal plates arranged orthogonally to the XOY plane of the two lower floors and upper, the parallel metal plates constituting the walls of each intermediate waveguide forming a reflector integrated in the beamformer. Planar antenna comprising at least one Butler matrix according to one of Claims 1 to 5, characterized in that it furthermore comprises M feed radiating horns (43) connected at the input of each parallel metal plate waveguide (20), ie MN power supply horns for the N parallel metal plate waveguides, where M is greater than 2, and N output radiating horns (44) respectively connected to the N metal plate waveguides parallel. Planar antenna according to claim 12, characterized in that each output horn (44) is a longitudinal horn coupled to a linear radiating aperture extending transversely across the width of the corresponding parallel plate waveguide. Planar antenna according to Claim 13, characterized in that the linear radiating openings are oriented in a direction perpendicular to the plane of the parallel plates (20) of the corresponding parallel plate waveguide.

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