EP0252779B1 - Aerial element with a suspended stripeline between two self-supporting ground planes provided with superimposed radiating slots, and processes for its manufacture - Google Patents

Description

The invention relates to a flat microwave antenna as indicated in the introduction to the main claim. Such an antenna is known from European patent application EP-A-0123350.

It is known that the market for microwave antennas, in particular operating in S or X band, is bound to develop significantly, due among other things to the numerous projects for broadcasting television programs by satellite. However, until now, the network antennas capable of being used for the reception of such broadcasts have been designed on criteria of maximum efficiency, using sophisticated embodiments which are hardly compatible with mass production at reduced cost.

Thus, the antenna described in patent application EP-A-064313 relates to an antenna of the "stripline" type intended to operate in circular polarization, and has the drawback of involving the use of an expensive solid dielectric material.

On the other hand, in the case where it is desired to operate in double polarization, the prior device described proposes to produce two separate supply lines located in the same plane. However, such a supply system is only possible when the planar network consists only of a small number of elements. There is in fact a geometric incompatibility in making such a network when, for example, it must consist of sixteen elements out of sixteen, owing to the fact that some of the lines must cross.

The system described is therefore relatively expensive and incapable of serving as a principle for the realization of a network for DBS satellite (direct telecommunications satellite for radio or television broadcasting), which commonly comprises systems of 200 to 1000 elements.

In addition, for a number of reasons, notably related to the multiplicity of parameters and the complexity of the phenomena involved in the development of network antennas, specialists in these antennas have so far systematically imposed very strict tolerance conditions for the shaping and mounting of the various elements of network antennas (conductive circuits, ground plates, dielectric materials, waveguides, etc.). This caution, or more precisely this prejudice, was particularly widespread with regard to the creation of an antenna with a suspended microstrip conductor, as evidenced by the article "multiconductor guides" in the book "The Techniques of the Engineer" (E621 -10). A recent attempt to overcome the constraints of tolerance is exposed in the European patent application EP-A-0123350 which describes a microstrip suspended by positioning pads between two metal plates. These metal plates are machined so as to form waveguides coupled to terminations of the central conductor. However, the embodiments described in this prior patent application always involve a machining operation in a very thick metal plate (of the order of 7 to 10 mm, at 12 GHz).

Another similar recent attempt is set out in European patent application EP-A-0228742. This document relates to the state of the art referred to in Article 54 (3) EPC and proposes the use of thin sheets as a support for the production of screen-printed studs associated with external waveguides acting as elements radiant. These elements are square waveguides.

To summarize the state of mind of a person skilled in the art with regard to microwave antennas, it seemed unthinkable until today to produce a microwave network antenna by suspending a conductive circuit between two stamped sheets as described below. after. However, against all expectations, the efficiency and the yield of an apparently so rudimentary antenna are not only surprising, but also not very sensitive to the inaccuracies of shaping and mounting inherent in a mass production process.

Consequently, the present invention proposes to produce a network antenna making it possible in particular to remedy the drawbacks mentioned above of the known devices.

To this end, a first object of the invention is to provide a network antenna of simple construction, thanks to the original arrangement. supply lines, and with low tolerance requirements.

A second object of the invention is to produce the radiating elements integrated into the structure of the supply lines, also for reasons of simplicity of construction.

Another object of the invention is to produce such a network antenna which operates over a wide band, by virtue of the grouping, in pairs (or in greater number), of radiating slits electromagnetically coupled to the supply leagues.

A complementary object of the invention is to provide a highly efficient antenna (thanks to a low-loss feed system), which can also operate in double circular polarization.

The present invention also discloses several variants of a simple and inexpensive method of manufacturing such antennas involving shaping and assembly processes with mild tolerance adapted to mass production.

Another object of the invention is to provide such manufacturing methods allowing maximum standardization of the constituent elements of each antenna.

An additional object of the invention is to provide methods of manufacturing and assembling several standardized antenna modules, with the aim of producing large radiating surfaces at low cost price.

These objectives, as well as others which will appear subsequently, are achieved by means of a flat microwave antenna comprising a central conductor interposed between two ground planes, said central conductor being a microstrip conductor carried by a dielectric support sheet suspended between the upper and lower ground planes, and radiating elements which cooperate with terminations of the conductor in electromagnetic coupling, the spacing between the dielectric sheet supporting the central conductor and the metal plates being maintained by means of spaced positioning pads, characterized in that that the radiating elements are radiating slots formed in the ground planes and aligned in pairs and in that said ground planes are produced by thin self-supporting metallic plates forming a thin triple structure with said dielectric support sheet. These radiating slots can be circular.

This structure characterizing the antenna according to the invention then makes it possible to obtain operation over a wide band, in particular if the two recesses of the same pair do not have quite the same diameter, and if the triplate structure is overcome by '' an additional plate also hollowed out.

In any event, due to the use of air as a dielectric and the spacing of the positioning pads, the support sheet for the microstrip can be produced in an inexpensive dielectric without drawbacks. The positioning pads can be made of dielectric material.

Advantageously, the triplate structure A, formed of said support sheet of the supply circuit and of the two metal plates is completed by a reflective lower plate, said reflective lower plate being separated from the triplate structure A by a distance equivalent to approximately a quarter. wavelength.

Advantageously, the antenna also comprises closed rear cavities and / or open front cavities, in alignment with at least some of the pairs of radiating slots, said cavities being produced by low tolerance shaping methods.

According to another essential characteristic, the adjacent input modules of a modular antenna assembly according to the invention cooperate with common inputs / outputs of the signal in the form of low loss waveguides.

The objectives of the invention are also achieved using a method of manufacturing the antennas characterized in that the shaping of each of said ground plates is carried out by a stamping / stamping operation on the one hand pierce said radiating slots and on the other hand push spacing stops on the face of the plates facing the dielectric sheet supporting the central conductor, in that said antenna is assembled by simply resting non-conductive areas of the support sheet dielectric of the conductor printed against the repellents facing the plates of lower and upper mass so as to protrude the terminations of the conductive circuit between pairs of aligned slots, and by overlapping said triplate thus produced above a plate metallic background located at the rear of the antenna, and in that one immobilizes with respect to the other and solidaris e the bottom metal plate and the elements of said triplate thus assembled by fixing means.

According to an important characteristic of the invention, the method includes a step of manufacturing cavities, and a step of assembling each cavity to the rear of the antenna in correspondence with a pair of radiating slots.

Advantageously, said cavities are produced in particular by a stamping / stamping operation of a metal plate, or by construction of a grid formed by an interlacing of blades on the field defining between them rectangular cells closed by the bottom plate , or by mounting cylinder trunks on the bottom plate, or finally by fitting a metal lining against the walls of cells formed in a block of non-metallic material.

These different manufacturing processes constitute variants which are easy to implement, inexpensive, and which surprisingly confer acceptable formatting and mounting precision.

According to an advantageous embodiment of the method according to the invention, the means for fixing the elements of the antenna ensuring their relative immobilization and their joining consist of a set of tightening bolts of the assembly, or also of a housing reception of the superimposed elements of the antenna, the raised edges of which are integral with the base plate of the antenna.

According to another advantageous characteristic of the invention, the method includes a step of manufacturing an additional coupling ring consisting of bottomless cavities produced in particular in a similar manner to the closed cavities situated at the rear of the antenna, and a step assembly of said crown on the radiating face of the antenna, so as to align each bottomless cavity with a pair of radiating slots.

The method according to the invention also includes a step of assembling several antenna modules manufactured according to one of the preceding methods, in which several elements of plate plates are juxtaposed mass, and possibly several elements of rear cavities and / or front crowns in coupling with a single conductive circuit. This manufacturing process, by reducing the size of the metal elements to be shaped, and allowing their standardization, makes it possible to further reduce the cost price of the antenna. In this regard, the modularity of the antenna is particularly advantageous for applications for reception of television broadcasts by satellite, for which the receiving surface is for example around 0.3 m² (individual antenna), as presented below.

According to another principle of modular antenna according to the invention, each module consists of an independent conductive circuit cooperating with ground plates, rear cavities and specific front rings. The method of coupling the modules is then for example characterized in that the input / output of the antenna is carried out by waveguide, either by coupling the conductive circuits of at least two modules by "T" link with single termination on common waveguide, either by separately performing the input / output of each module on independent waveguides coupled by power divider (s) in waveguide (s).

Standardization of manufacturing of modular conductive circuits is advantageously obtained when the antenna manufacturing process consists in using support plates of the identical conductive circuit for each module, the support plates being alternately turned front and back when they are inserted between the plates. stamped mass from adjacent modules.

• la Fig.1 représente une vue éclatée de la version de base de l'antenne suivant l'invention ;
• la Fig.2 représente une vue détaillée en coupe et en perspective de deux éléments rayonnants de l'antenne ;
• la Fig.3 représente un diviseur en T de la ligne d'alimentation de l'antenne suivant l'invention ;
• les Figs.4a, 4b et 5 représentent le tracé théorique de l'impédance et des pertes de l'antenne suivant l'invention en fonction de la distance entre les plaques contenant les fentes rayonnantes et qui forment les plans de masse de la ligne d'alimentation, et en fonction du centrage du circuit d'alimentation dans le cas d'un fonctionnement typique en bande S et/ou en bande X du prototype de la Fig.22.
• la Fig.6 représente un second mode de réalisation de l'antenne suivant l'invention permettant une double polarisation linéaire.
• les Figs. 7 et 8 schématisent deux versions de l'antenne suivant l'invention comportant respectivement un patch additionnel de couplage électromagnétique, et une fente additionnelle de couplage électromagnétique ;
• la Fig. 9 représente un mode de réalisation de l'antenne suivant l'invention dont le circuit d'alimentation est formé d'un circuit imprimé inversé.
• La figure 10 est une section schématique transversale d'une portion d'un module d'antenne suivant l'invention, avec plaques de masse, cavités arrière et couronnes avant embouties;
• La figure 11 représente une vue éclatée d'un module d'antenne suivant l'invention dont toutes les plaques sont réalisées par emboutissage;
• La figure 11 bis illustre une variante de réalisation des cavités sous forme de cabochons emboutis;
• La figure 12 représente un module d'antenne suivant l'invention avec cavités à anneaux;
• Les figures 13a et 13b représentent un module d'antenne suivant l'invention, à cavités définies par une grille d'entrecroisement de lames sur champ;
• La figure 14 schématise un module d'antenne selon l'invention avec blocs non métalliques percés de cavités intérieurement métallisées;
• La figure 15 représente un assemblage de plusieurs modules de plaques de couplage suivant l'invention avec un circuit conducteur unique;
• Les figures 16, 17 et 18 représentent des exemples de réalisation du circuit conducteur dans le cas du circuit unique de la figure 15 (figure 16) et dans le cas de la juxtaposition de deux circuits conducteurs de deux modules adjacents (figures 17 et 18);
• Les figures 19, 20, 21 représentent trois procédés de recombinaison du signal de sortie (ou encore de division du signal d'entrée), dans des guides d'onde, pour deux modules d'antennes adjacents;
• La figure 22 représente un élément d'antenne suivant l'invention réalisé pour en tester les conditions de fonctionnement;
• Les figures 23a, et 23b représentent les résultats de mesure effectués sur les éléments d'antenne de la figure 22, et correspondent respectivement à la mesure du TOS, et du diagramme de rayonnement à 10 GHz dans le plan H, en polarisation nominale et en polarisation croisée;
• La figure 24 représente la géométrie typique du circuit conducteur d'un module d'antenne à 16 éléments suivant l'invention réalisé pour effectuer les tests de fonctionnement;
• Les figures 25a, 25b et 25c représentent les résultats de mesure de tests effectués sur le module d'antenne à 16 éléments correspondant au dessin du conducteur central de la figure 24, et correspondent respectivement aux mesures de gains, de TOS et à la détermination du diagramme de rayonnement en polarisation nominale et en polarisation croisée dans le plan H à 11 GHz;
     Comme représenté en figures 1, 2 et 10, l'antenne selon l'invention est du type à ligne à microruban suspendu, constituée d'un conducteur central 22 porté par une feuille support diélectrique 12 suspendue entre deux plaques métalliques supérieure 11 et inférieure 13. Les plaques 11, 13 sont chacune munies d'évidements 20a, 20b alignés par paires au niveau de terminaisons saillantes 30 du conducteur 22. La structure d'antenne est également complétée par une plaque de fond métallique 14 réfléchissante.

Other characteristics and advantages of the invention will appear on reading the following description of preferred embodiments of the invention, given by way of illustration and not limitation, and of the appended drawings in which:

• Fig.1 shows an exploded view of the basic version of the antenna according to the invention;
• Fig.2 shows a detailed sectional and perspective view of two radiating elements of the antenna;
• Fig.3 shows a T-divider of the antenna feed line according to the invention;
• Figs. 4a, 4b and 5 represent the theoretical plot of the impedance and losses of the antenna according to the invention as a function of the distance between the plates containing the radiating slots and which form the ground planes of the line d 'supply, and depending on the centering of the supply circuit in the case of a typical S-band and / or X-band operation of the prototype of Fig. 22.
• Fig.6 shows a second embodiment of the antenna according to the invention allowing a double linear polarization.
• Figs. 7 and 8 show diagrammatically two versions of the antenna according to the invention respectively comprising an additional electromagnetic coupling patch, and an additional electromagnetic coupling slot;
• Fig. 9 shows an embodiment of the antenna according to the invention, the feed circuit of which is formed by an inverted printed circuit.
• Figure 10 is a schematic cross section of a portion of an antenna module according to the invention, with ground plates, rear cavities and stamped front crowns;
• FIG. 11 represents an exploded view of an antenna module according to the invention, all the plates of which are produced by stamping;
• FIG. 11 bis illustrates an alternative embodiment of the cavities in the form of stamped cabochons;
• FIG. 12 represents an antenna module according to the invention with ring cavities;
• FIGS. 13a and 13b represent an antenna module according to the invention, with cavities defined by a grid of interlacing of blades on the field;
• Figure 14 shows schematically an antenna module according to the invention with non-metallic blocks pierced with internally metallized cavities;
• FIG. 15 represents an assembly of several modules of coupling plates according to the invention with a single conductive circuit;
• Figures 16, 17 and 18 show exemplary embodiments of the conductive circuit in the case of the single circuit of Figure 15 (Figure 16) and in the case of the juxtaposition of two conductive circuits of two adjacent modules (Figures 17 and 18) ;
• Figures 19, 20, 21 show three methods of recombining the output signal (or even dividing the input signal), in waveguides, for two adjacent antenna modules;
• FIG. 22 represents an antenna element according to the invention produced to test its operating conditions;
• FIGS. 23a, and 23b represent the measurement results carried out on the antenna elements of FIG. 22, and correspond respectively to the measurement of the TOS, and of the radiation diagram at 10 GHz in the H plane, in nominal polarization and in cross polarization;
• FIG. 24 represents the typical geometry of the conductive circuit of an antenna module with 16 elements according to the invention produced for carrying out the functional tests;
• FIGS. 25a, 25b and 25c represent the measurement results of tests carried out on the 16-element antenna module corresponding to the drawing of the central conductor of FIG. 24, and correspond respectively to the measurements of gains, of TOS and to the determination of the radiation pattern in nominal polarization and in cross polarization in the H plane at 11 GHz;
  As shown in Figures 1, 2 and 10, the antenna according to the invention is of the suspended microstrip line type, consisting of a central conductor 22 carried by a dielectric support sheet 12 suspended between two upper metal plates 11 and lower 13 The plates 11, 13 are each provided with recesses 20a, 20b aligned in pairs at the projecting endings 30 of the conductor 22. The antenna structure is also completed by a reflective metal base plate 14.

The relative positioning of the planes 11, 12, 13, 14, the dimensioning of the recesses 20a, 20b, and the length 1 of the projecting termination 30 of the conductor 22 are chosen so that the recesses 20a, 20b play the role of coupled radiating slots electromagnetically, for a relatively wide operating frequency band.

The recesses 20a, 20b of the same pair have their centers aligned on a vertical axis, and may have an equal diameter. However, it is preferable that the diameters of the recesses of the same pair are slightly different to improve the bandwidth.

In fact, the operating frequency of each recess depends essentially on its dimensions, and if the two recesses of the same pair have a slightly different central operating frequency, the total bandwidth is increased. The diameter of the recesses is of the order of 0.3 to 0.7 wavelength.

Advantageously, the spacing between two consecutive recesses on a row or a column can be equal to 0.7 to 0.9 wavelength.

The bottom reflecting plate 14 makes it possible to give a direction to the radiated energy, and is located at a distance from the triplate structure A of the order of a quarter wavelength. The distance between this bottom reflecting plate and the structure of the triplate is very important since it gives the possibility of optimizing the operation in conjunction with the dimensions of the supply line 22.

FIG. 10 represents another embodiment of an antenna mode according to the present invention, consisting of the successive stacking of a stamped bottom plate 14 forming closed cavities 26, of a bottom ground plate 13 stamped , of a support plate 12 of the conductive circuit 22 and of a stamped upper ground sheet 11 and of a stamped upper crown 25 forming open cavities 27.

It will be noted that this embodiment of the antenna exclusively involves a metal sheet stamping technology for the manufacture of the four plates 11, 13, 14, 25. The stamping operation makes it possible on the one hand to release the recesses 20a, 20b forming each radiating pair, and forming bulges or stops 31 forming positioning pads. These bulges 31 come to bear on the dielectric intermediate plate 12, and define the spacing between the three plates of the structure A. A supply circuit of the "suspended" type is thus obtained, while producing the radiating elements themselves . This type of antenna is therefore particularly suitable for mass production, at reduced cost price.

Note also that the stamped sheet 25 can also be placed upside down (upside down), relative to its position in fig.10).

Figure 10 does not in any way account for the proportion of spacings and thicknesses of the plates. Indeed the distances Hu and Hl in particular have been considerably oversized for reasons of clarity.

Of course, the two problems which arise with regard to an antenna with a fully suspended printed circuit of this type, are on the one hand the conditions allowing a good adaptation of each element to the working frequencies and on the other hand the conditions guaranteeing good efficiency of the antenna, that is to say an acceptable value of the gain per unit area.

Surprisingly, the technology used makes it possible to obtain satisfactory values for these two parameters without difficulty.

If we consider a radiating element of the antenna, constituted and a conductive termination 30 linked to a pair of slots 20a, 20b and to a closed lower cavity 26, the adaptation of this element is a function of the length 1 of penetration of the termination 30 between the slots 20a, 20b, of the distance d _f between the triplate 11, 12, 13 and the bottom of the cavity 26, of the diameter D _C of the cavity, of the diameter D _e of the slots 20a, 20b, and the impedance Z _O of the supply conductor. In turn Z _O depends on the width w of the central conductor, on the thickness H of the dielectric plate 12, and on the distances H _U and H _L separating the electrical support plate 12 and the upper mass plate 11 and lower 13 respectively, as well as the dielectric constant ε _R of the support plate 12.

These different factors influencing the adaptation of the antenna are of unequal relative importance. In particular, the distance d _f separating the triplate of the bottom plate (or of the bottom of the closed cavity 26), as well as the relative positioning of the conductor 22 between the ground plates 11, 13, have a certain range of variations within which the adaptation is little affected. Thus, FIG. 5 represents the calculations carried out on a line of the antenna (by the CAD program "Supercompact"), in which the central conductor has been moved between the two ground plates, keeping constant the distance b separating the ground plates. The dimensional characteristics of the radiating element studied are as follows (with reference to the notations in FIG. 10):
w = 1.2 mm
H _U + H _L + 1.6 mm
H = 0.075 mm
εR = 2.2
f = 12.1 GHz.

It can be seen that the variation in the impedance Z _O obtained varies only within a range of approximately 10% when the conductive circuit is moved in an interval centered between the ground planes 11, 13 and corresponding to a third of the spacing b between the two ground planes. This curve is one of the elements demonstrating the low sensitivity of the claimed antenna to manufacturing and mounting inaccuracies, and therefore the perfect feasibility of the invention.

These theoretical results are corroborated by the experimental measurements carried out on the prototype.

As can be seen in FIGS. 4a and 4b, the distance b between the ground planes 11 and 13 is not very critical either for the resulting impedance of the system, whether for the S band or the X band.

The second important parameter is the efficiency of the antenna, that is to say its gain per unit area. Surprisingly, and as confirmed by the measurements made on a prototype and presented below, the antenna claimed has an almost constant gain over a very large bandwidth (12.5% on the 4x4 element prototype). However, satellite reception antennas usable in Europe will only be asked for a bandwidth of around 7% (from 11.7 to 12.5 GHz). Consequently, there is a comfortable margin for adaptation of the antenna, which easily tolerates inaccuracies in shaping and mounting due to the rusticity of the manufacturing technologies employed for the invention.

The efficiency of the antenna is further increased by limiting the losses in each radiating element.

The claimed technology lends itself perfectly to optimization in this area. Indeed, the fact of using air as a dielectric between the support plate 12 and the two ground planes 11, 13 makes it possible to reduce the losses in comparison with an equivalent antenna of the "stripline" or "microstrip" type, where the central conductor is separated from two ground planes or from a single ground plane respectively, by an expensive dielectric solid material. According to the invention, the dielectric of the support plate 12 can be as thin as possible without affecting its mechanical stability. For example, it has been found that a thickness of 25 to 75 microns is perfectly suitable. The losses as presented in FIGS. 4a and 4b for operation in S-band (2.0 GHz) and in X-band (12.1 GHz) are completely reduced because there is no radiation interference thanks to the isolation of circuit 22. (The loss graphs in FIGS. 4a, 4b correspond to the use of a dielectric with a low tangent of losses (tan d = 0.0009)).

The concentration of several elements on the same surface, in order to increase the gain of the antenna, is achievable within the limit where the coupling occurring between each adjacent line does not exceed some detrimental limit. However, the use of radiating slots on the one hand, and the care given to the geometric designs of the driver on the other hand, give the invention good performance from this point of view.

The use of pairs of radiating slits 20a, 20b has the effect of concentrating the radiant energy in a zone lower than for example that obtained in embodiments where each conductive termination 30 is only coupled to cavities forming waveguide .

Indeed, the width of a waveguide D _L is greater than the width D _e of the radiating slits. Due to the location of the radiating effect caused by the radiating slits, the distance between two adjacent elements (for example element A and element B of the antenna module of FIG. 10) can be reduced for a value tolerable minimum decoupling between lines.

In addition, to limit the influence of the positioning pads 10, 31 on the adjacent elements or lines, it is possible to reduce their number to a minimum and place them in planes offset from the slots as shown in FIG. 1.

The geometry of the lines is also of paramount importance. An exemplary embodiment of the supply circuit 22 is shown in FIG. 3.

The impedance of the supply circuit 22 depends on the width that it has in each of its conductive portions, for a distance b given between the plates 11 and 13.

The power dividers of circuit 22, as shown in FIG. 3, can be easily produced so as to obtain that the two decoupled outputs 41, 43 are adapted. This is achieved if the power ratio released by the two outputs 41, 43 is equal to or close to unity. It is therefore not necessary to provide a fourth output (for example in the form of a Wilkinson resistor bridged between the two decoupled outputs).

The power divider of FIG. 3 is for example of the type with two adapted output sections 44, 45, of a quarter wavelength, with a width W of the doors producing an impedance Zo and a width W 'of said sections having a characteristic impedance equal to 2 ^1/2 Z _O.

Figures 16, 17, 18 show optimized embodiments for modules of 16 x 16 elements (two adjacent modules are shown in each figure). Each of the embodiments shown is particularly advantageous insofar as each of the 512 elements of the antenna is located at exactly the same electrical distance from the input / output of the antenna, and the resulting drawing emerges, on the support plate of the conductor, non-conductive areas 90 where the pushed-in positioning studs 31 of the ground planes can rest without inconvenience.

The addition of a closed rear cavity 26, and possibly an open front cavity 27, to an element of the antenna makes it possible to recover the maximum of radiated energy in the direction of transmission / reception of the antenna.

The polarization of the antenna according to the invention depends on the polarization of each of the radiating elements.

In the case where a single excitation line is used, the polarization is linear with an electric field E parallel to the excitation lines.

Circular polarization can be obtained by using a printed plane polarizer (for example a meandering line polarizer) placed above the triplate.

Another method of obtaining a circular polarization consists in exciting two perpendicular linear polarizations in each of the radiating elements.

FIG. 6 represents an embodiment of the invention, in which the two independent supply lines serving to excite each of the radiating elements of the network are at two different levels 51, 52.

The structure A of the antenna therefore consists of five superimposed plates, namely three metallized plates 53, 54, 55 pierced with aligned recesses 20A, 20B, 20C, between which the two dielectric sheets 51, 52 carrying the supply circuits 56, 57.

The excitation in "vertical" polarization is for example provided by the circuit 56, and the "horizontal" polarization is provided by the circuit 57.

However, although this structure with five plates is justified in the case of a network with many radiating elements, it is also possible to form the two circuits 56, 57 on the same dielectric plate, between only two metallized plates with recesses.

In the embodiment of FIG. 6, the middle ground plate 54 is used by the two circuits 56, 57. Preferably, the two external recesses 20a, 20c have the same diameter.

The adaptation of each excitation line is obtained by adjusting the length of their termination advancing opposite said recesses, and the distance to the reflective bottom plate 58. By conferring a phase shift at + 90 ° or -90 ° , at the excitation lines, one can obtain a right or left circular polarization. If a hybrid - 3dB is used to combine the signals from the two outputs linear polarization, we can obtain a double circular polarization.

The embodiments shown in FIGS. 7 and 8 present variants of the antenna shown in FIG. 1.

The suspended triplate A, in FIG. 7, is surmounted by an additional coupling element 60. In the case of FIG. 8, the triplate A is surmounted by an additional plate 70 provided with a recess 71 substantially in alignment with the recesses 20a, 20b.

In the latter case, the additional plate 70 can also be stamped, and separated from the triplate A by dielectric spacers 72 or stops formed by stamping.

These two embodiments of FIGS. 7 and 8 make it possible to increase the bandwidth, that of FIG. 8 being probably better from an electrical point of view.

It should be noted that for all the embodiments shown, it is possible to increase the mechanical rigidity of the entire antenna, for example by replacing the dielectric formed by the air between the plates of the structure A, or between this structure A and the bottom plate B, by means of a honeycomb dielectric inserted between the plates.

For reasons of compactness and simplicity of structure, it is also possible that the dielectric plate 12 carrying the supply circuit 22 is not located between the two metallized plates 11, 13. This embodiment is produced in FIG. 9. The array antenna then consists of a succession of plates in a different order from that of FIG. 1, the upper plate 11 and the lower plate 13 being separated by a spacer 80. The dielectric plate 12 carrying the circuit 22 is next to the outside of the double plate thus formed, on the side of the plate bottom 14. Advantageously, the supply circuit 22 is in the form of an inverted printed circuit. In any event, the dielectric plate 12 prevents any contact between the circuit 22 and the metallized plate 13.

Figures 11, 12, 13, 14 illustrate four technologies for manufacturing the front and rear cavities, for a ground plane antenna module 11, 13.

More specifically, FIG. 11 is an exploded view of a module with 4 x 4 elements of an antenna of the type shown in FIG. 10. The module simply consists of the stack of stamped sheets 14, 13, 11, 25, in the middle of which is placed the support plate 12 of the conductive circuit 22.

Advantageously, by adding, by stamping, positioning pads in the plate 14 and in the plate 25, positioned upside down, the plates 11 and 13 can be eliminated.

The stack thus produced can be held in place either by means of bolts 26 passing through all the plates (FIG. 2), or by producing the bottom plate 14 in the form of a housing. The stack can either be placed on the housing, or introduced at least partially inside the housing. In all cases, a predetermined spacing d _f must be obtained between the triplate and the bottom of the housing. The housing can be stamped, or machined by any other means, or even produced by metallization of a non-metallic housing. The assembly and the locking of the assembly are carried out by screwing, gluing, welding or other.

Of course, the embodiment of the invention shown in FIG. 11 can, if necessary, be produced with a flat bottom plate 14, possibly forming a support housing, and kept at a distance from the triplate 11, 12, 13. The crown 25 with open cavities 27 is optional. In the event that uses closed rear cavities, a non-metallic support box B (for example: plastic) can be used.

The closed rear cavities 26 can also be in the form of individual stamped cabochons 72 (FIG. 11a) and attached by soldering, bonding or other points to the lower mass plate 13, facing the pairs of radiating slots.

FIG. 12 represents another embodiment of an antenna module according to the invention in which the rear closed cavities 26, and the front cavities 27 are produced by metal rings 150, mounted by any means on the bottom plate full 14, and an added plate 151 respectively. Advantageously, the fixing of the rings 150 on the metal bottom plate 14 is carried out by welding, gluing or the like. The added plate 151 may be metallic or non-metallic, and the rings 150 may also be glued or the like on the plates 14,151.

In an embodiment slightly different from that of FIG. 12, but still using metal rings, the housing B serves as a housing for a set of cylindrical metal rings 150 on which the triplate 11, 12, 13 will come to rest. 14 and 25 have become useless. The rings 150 are mounted by any means on the bottom plate of the housing and / or on the lower ground plate 13.

Advantageously, the fixing of the rings 150 on the metal or metallized plate of the bottom of the housing and / or on the ground plate 13 is carried out by welding, gluing or the like.

In the embodiment of FIGS. 13a, 13b, the housing B serves as a housing for a set of intercrossed blades 160 placed on the field, and forming a grid on which the triplate 11, 12 will come to rest, 13. Advantageously, the grid is formed of blades provided with notches 161, and intended to fit into one another as shown in FIG. 13b.

The intersection of the blades defines cavities 162 each corresponding to one of the radiating elements of the triplate. It may be noted in this regard that the shape of the cavities of the antenna module is not a limiting characteristic of the invention, as is the shape of the radiating slots 20a, 20b. Circular, square, elliptical, rectangular, polygonal sections as required may be suitable. In this regard, it may be noted that in certain cases, the rectangular openings are advantageous for freeing up more space for the passage of the conductor 22.

FIG. 14 illustrates a fourth embodiment of the invention, according to which the closed rear cavities 26 are produced by placing a metal covering on the non-opening recess walls 170 formed in a non-metallic bottom block 171. By way of FIG. 'nonlimiting example, the bottom block can be made of plastic, and the metallization of the cavities can be performed using aluminum foil. In the case of a non-opening bottom block, the support box B of FIG. 14 can be omitted. The bottom block can also be replaced by a juxtaposition of elementary blocks, each having one or more cavities. In the case where the recesses are through, the metal bottom plate closes the cavities.

It is understood that the embodiments of FIGS. 11 to 14 can be combined and in particular that the antenna modules of FIGS. 13 and 14 can be provided with a front crown of the type with stamped plates, or with rings 150. The adding open front cavities 27 increases the gain of the antenna. The cavity height is preferably greater than 0.1 times the emission wavelength. For example, a height of the open cavities of 5 mm to 10 mm would give an increase in gain of the order of 2 dB depending on the geometry, for an operating frequency of 12 GHz.

Whatever the means used for the relative immobilization and the joining of the plates of the various embodiments, of the antenna module according to the invention (tightening bolts, housing B or the like), the modules can then be coated with an electromagnetically neutral material of the type of an expanded or molded plastic, for example expanded polyurethane. This coating has the particular advantage of protecting the module against bad weather when the antenna is to be used outside.

Advantageously, an antenna can be produced by combining several modules. In the case of antennas of relatively large dimensions, this technique has the advantage of reducing the manufacturing cost, by reducing the size of the tools used. In the embossed plate embodiment, the savings made can be significant; furthermore, the reduction in the size of the tools makes it possible to better control the precision of shaping of the stamped plates.

In addition, the advantage is even greater if each antenna is produced by adding several identical modules, as presented below.

FIG. 15 shows a first embodiment of a modular antenna, in which the single conductor circuit 80 covers two modules 81, 82 produced according to any one of the embodiments described above. More specifically, the left part of the support plate 80 is inserted for example between an upper mass plate 11a, and a mass plate lower 13a mounted in a housing Ba as regards the first module 81, and between corresponding components 11b, 13b, B _b as regards the second module 82.

The conductive circuit 80 is for example of the type shown in FIG. 16.

This embodiment is relatively satisfactory, but has the drawback that the input / output section 83 of the antenna conductor runs along the intersection of the modules. To avoid possible unfavorable effects caused by the cracking effect caused by an approximate junction of the module plates, due to the technology chosen, the junction gap can be closed with a thin sheet of metal, for example copper self-adhesive or others.

However, it is more satisfactory, to overcome this possible drawback, to make the conductive circuit itself in two parts. Advantageous embodiments of the two-part conductive circuit are shown in FIG. 17 (vertical polarization) and 18 (horizontal polarization). It will be noted that, in the two embodiments, the two adjacent circuits are identical and allow standardization of their production.

In these Figures 17 and 18, the conductor 83 is therefore produced in the form of two decoupled parallel lines, on either side of the junction plane of two adjacent antenna modules. In these embodiments, each antenna element is at an identical electrical distance from the entry / exit point of the conductive circuit.

In Figure 18, the two modules have identical conductive circuits oriented in the same direction (without having symmetry with respect to the junction line). Advantageously (not shown), the supply sections 110 run along the entire edge concerned support plates 22a, 22b, in order to standardize their manufacture; in this case, the parasitic half-sections are disconnected by notch over their entire width, preferably at 45 °, at their connection with the vertical lines.

The input / output of the adjacent modules is preferably carried out in waveguides as shown in FIG. 19 or 20. The use of an output directly in waveguide is advantageous compared to the use of a coaxial which constitutes a more expensive solution.

FIG. 19 illustrates an input / output waveguide in the case where the two adjacent conductive circuits are electrically connected by T-divider to present a single termination 120. To this end, openings 121a, 121b, 122a, 122b are made on the joining edges of the upper plates 11a and 11b and lower 13a, 13b of the adjacent modules. The pair of openings thus produced after joining the modules is completed by an upper cover 123 forming a closed waveguide element, and returning to an input / output waveguide 124 located on the other side of the triplate .

The upper reflective cover 123 is made for example of metallized plastic, or of a stamped metal sheet. Its height is for example of the order of a quarter wavelength.

In order to limit the effect of the junction slot, and to improve the electrical junction of the adjacent plates 11a, 11b and 13a, 13b respectively, it is possible to place a thin sheet of metal 125, 126 around each opening 121a, 121b , 122a, 122b, by gluing or other.

The input / output waveguide 124 can for example be screwed, glued or the like onto the lower metal ground plates 13a, 13b.

This embodiment is suitable both for a single printed circuit cooperating with two modules (case of FIG. 15) as for two separate modules, the respective conductive circuits of which are only subsequently electrically connected to a termination. unique.

The electrical connection of the two conductors can for example be carried out as shown in FIG. 21, or the two support plates 12a, 12b of the adjacent modules overlap at their junction, so as to overlap the input / output termination of their respective conducting circuit 22a, 22b.

In an advantageous embodiment of the invention, and as shown in FIG. 17, the conductive circuits 22a, 22b of two adjacent modules are produced from two identical printed support plates, one of which is used on the front, and the other on the back. In this case, the printed circuit of one of the support plates is on the upper face, while the other printed circuit is on the lower face. The slight offset which results therefrom does not, however, present any drawback, since the low sensitivity of the impedance Z _O of the antenna according to the invention has been noted above, and therefore of its adaptation to small variations in the position of the printed circuit. between the two ground planes. However, the dielectric material support plate which carries the printed conductive circuit 22a, 22b can be very thin, for example of the order of 50 microns.

In the case where the two adjacent circuits are reversed with respect to each other, the electrical connection of FIG. 21 can be carried out by drilling right through the support plates 12 _a , 12 _b at the terminations of input / output 140a, 140b of circuits corresponding conductors, then soldering of the circuits through said holes.

FIG. 20 shows another embodiment of the combined input / output device of the conductive circuits of two adjacent modules. In this case, no electrical connection is made, and the combination is made through a power divider 130, in an angled waveguide, so as to return the signal along the bottom of the antenna.

Each adjacent triplate is then provided with a pair of outlet slots (131a, 131b), to which is attached a double closed cover 132.

Advantageously, the double cover 132, as well as the single cover 123 in FIG. 19 can be produced at least partially by stamping the upper plates 11a, 11b of the adjacent modules of the antenna.

Finally, it is always possible to stabilize the support plates 12a, 12b of the two adjacent modules by applying an adhesive tape, preferably non-metallic, to the edges of the support plates which adjoin each other, in particular along their free conductor half-depth. central.

Parasitic coupling of the two adjacent modules can also be effectively avoided by providing between the modules an interval greater than the wavelength between the radiating elements (84, 85) adjacent to each other (81, 82) . This free interval advantageously allows the passage of the central supply conductors, eliminating the risks of coupling and without affecting the radiation pattern too much.

EXAMPLE OF IMPLEMENTATION

Tests were carried out on an antenna module formed from a single element as shown in FIG. 22 in order to determine the bandwidth obtained with the implementation of the invention.

The test element is formed by two aluminum plates 0.8 mm thick, forming the ground plates 11, 13. Each of the plates has a radiating opening of 16.5 mm. The distance between the earth plates 11, 13 is 1.7 mm. A 75 micron thick "Kapton" sheet supports the printed central conductor 22. The width of the central conductor corresponds to an impedance of lines of Z _O = 50 ohms for the spacing of the earth plates 11, 13 of 1 , 7 mm.

The excitation termination 30 of the conductor penetrates 5.0 mm between the slots 20a, 20b. Finally, a closed cylindrical cavity 21 with a diameter of 20 mm and a height of 9.2 mm has been aligned under the pair of radiating slots 20a, 20b.

This demonstration element is optimized to operate around frequencies around 11 GHz.

The manufacturing tolerances for this item have been intentionally kept very rough. To this end, three successive tests were carried out.

For the first test, on the one hand, the TOS was measured on the band 10.4 GHz-12.4 GHz for a standard conductor produced by lithography. FIG. 23a reproduces the measurements obtained, which demonstrate a remarkable behavior of the element having a TOS less than 1.4 over a bandwidth greater than 20%.

On the other hand, Figure 23b shows that the measured cross polarization is very low (less than -30 dB) in the direction perpendicular to the plane of the elementary antenna. The useful radiation of the element takes place in linear polarization with an electric field parallel to the excitation line.

The second test carried out on the element consisted in replacing the excitation conductor 22 manufactured by lithography, by a conductor cut by hand (with a scalpel) for an impedance of 75 ohms from a line of 50 ohms. The TOS measurement did not show any difference compared to the standard line produced by lithography.

In the third test carried out on the radiating element of FIG. 22, the cylindrical cavities 26 were replaced by a cavity produced by hand in kitchen aluminum foil. The tests performed did not show a significant increase in the TOS.

The antenna specialists of the Dutch laboratory C.H.L. who carried out these measurements expressed their surprise at the quality of the test results obtained, when they were used to working with precision on the order of a micron.

A second series of tests was carried out on an antenna module with 16 elements, with a drawing of the conducting circuits as shown in FIG. 24.

As it was not economical to carry out the test model by stamping, trunks of glued cylinders were used to form the closed rear cavities. The spacing pads 10, 31 were not formed by stamping, but by bonding sheet metal pads to the ground plates 11, 13.

The test measurements were also carried out in the anechoic chamber of the CHL laboratory. These measurements confirm the good results already observed during the test of the single antenna element, and are moreover more reliable than the previous tests of the fact that a module of 16 elements is less sensitive to measurement conditions than a single item.

Graph 25a indicates that the maximum gain obtained is 20 dB, and that the gain is greater than 19 dB on a frequency band greater than 10% (from 10.25 to 11.5 GHz).

The measured TOS is less than 2 on a frequency band wider than 2 GHz (Figure 25b).

Finally, the 11 GHz radiation diagram in Figure 25c confirms the absence of cross polarization in the main direction of radiation. The first cross polarization lobes are approximately -25 dB from the maximum main radiation.

Consequently, the antenna modules according to the invention make it possible to obtain excellent performance with low tolerance manufacturing methods corresponding to mass production at low cost price.

As a preferred application, the invention can be used to manufacture antennas for receiving television broadcasts by satellite, in the X band. Advantageously, these antennas consist of two adjacent modules each formed from 16 x 16 elements . This preferential application corresponds to the drawings of the conductive circuit shown in FIGS. 16, 17, 18. In the most frequent case where the polarization of the emission is circular, it is possible either to lace an adequate printed plane polarizer above the antenna, or to superimpose on the antenna an additional stage with excitation terminations perpendicular to the terminations 30 of the base stage, as illustrated in FIG. 6.

The operating frequency band can for example be the X band (3 cm), the S band (1500 to 5200 MHz), or the L band (390 to 1550 MHz). Although the antenna according to the invention can also in principle operate in higher frequency bands, its structure makes it more advantageous for use at frequencies of the X band and lower, due to the even less demanding tolerance constraints which make it even easier manufacturing.

Claims (25)

1. Microwave planar antenna comprising a central conductor (22) interposed between two earth planes (11, 13), the said central conductor being a microstrip conductor carried by a dielectric support sheet (12) suspended between the upper (11) and lower (13) earth planes, and radiating elements which interact, by electromagnetic coupling, with terminations of the conductor, the spacing between the dielectric sheet (12) supporting the central conductor and the metal plates (11, 13) being maintained by means of spaced-apart positioning hubs (31, 10), characterised in that the radiating elements are radiating slots made in the earth planes (11, 13) and aligned in pairs (20a, 20b) and in that the said earth planes (11, 13) are produced by self-supporting thin metal plates forming a thin triplet structure (A) with the said dielectric support sheet (12).
2. Planar antenna according to Claim 1, characterised in that the radiating slots are circular.
3. Planar antenna according to Claim 1, characterised in that the said positioning hubs are produced by embossments (31) formed by deep drawing in the said metal plates (11, 13).
4. Planar antenna according to Claim 1, characterised in that the said positioning hubs (10) are made of dielectric material.
5. Planar antenna according to Claim 1, characterised in that the triplet structure (A) is supplemented by a reflective lower plate (14), the said reflective lower plate (14) being separated from the triplet structure (A) by a distance approximately equivalent to a quarter of a wavelength.
6. Planar antenna according to Claim 1, characterised in that the said slots (20a, 20b) of a same pair have identical or slightly different dimensions.
7. Planar antenna according to Claim 2, characterised in that the said slots (20) made in each metal plate (11, 13) are aligned in rows and columns, the diameter of the said slots being of the order of approximately 0.3 to 0.7 of a wavelength and the distance separating two adjacent slots of the same row or column being approximately 0.7 to 0.9 of a wavelength.
8. Planar antenna according to Claim 1, characterised in that, in order to produce an excitation of the antenna in double linear polarisation, the said support sheet (12) carries two independent supply circuits.
9. Planar antenna according to Claim 1, characterised in that, in order to produce an excitation of the antenna in double linear polarisation, two triplet structures (A) are superimposed so as to form a structure having five plates (51, 52, 53, 54, 55), which is formed by three metal plates (53, 54, 55) pierced with aligned slots (20a, 20b, 20c), between which are inserted two dielectric support sheets (51, 52) each carrying an independent supply line (56, 57), the said lines (56, 57) exciting the radiating antenna with two perpendicular polarisations.
10. Planar antenna according to Claim 1, characterised in that the said triplet structure (A) is surmounted by an additional electromagnetic-coupling plate (60).
11. Planar antenna according to Claim 1, characterised in that the said triplet structure (A) is surmounted by an additional plate (70) provided with recesses (71) in alignment with each of the pairs of slots (20a, 20b).
12. Planar antenna according to Claim 1, characterised in that the triplet structure (A) is supplemented by a reflective lower plate (14) and in that the said support sheet (12) is attached to the outer face of one of the two metal plates (11, 13), the said supply circuit (22) being located on that face of the said support sheet (12) which faces the said bottom plate (14).
13. Planar antenna according to any one of the preceding claims, characterised in that it also comprises closed cavities (26) aligned at the rear of at least some of the said pairs of radiating slots (20a, 20b).
14. Planar antenna according to Claim 13, characterised in that the said cavities (26) are constituted by a deep-drawn metal sheet (14, 25).
15. Planar antenna according to Claim 13, characterised in that the said cavities (26) are constituted by a grid formed by an edgewise interlacing of strips (160) defining between them rectangular cells closed by a bottom plate (14).
16. Planar antenna according to Claim 13, characterised in that the said cavities (26) are constituted by truncated metal cylinders (150) joined onto the earth plate (13) or onto a solid metal bottom plate, respectively.
17. Planar antenna according to Claim 13, characterised in that the said cavities (26) are constituted by cells (170) hollowed out in at least one block (171) of non-metallic material, the walls of the said cells (170) being coated with a metal lining.
18. Planar antenna according to any one of the preceding claims, and intended to interact with at least one second planar antenna, characterised in that the contiguous edges of the earth plates (11a, 13a; 11b, 13b) and of the adjacent modules are each provided with a radiating aperture (121a, 122a; 121b, 122b) which are intended to interact in order to form a pair of input/output slots in the region of a common termination (120) of the conductors of the modules and in that the said pair of slots (121a, 122a; 121b, 122b) thus constituted also interacts with a reflective cover (123) and an input/output waveguide (124).
19. Planar antenna according to any one of Claims 1 to 17, intended to interact with at least one other planar antenna, characterised in that an output slot (131a, 132a; 131b, 132b) is produced in the vicinity of the junction edge of each of the earth plates of the modules so as to form two pairs of adjacent input/output slots each interacting with the input/output end (133a, 133b) of the respective conducting circuits of the modules, the said pairs of slots of the adjacent modules interacting, on the one hand, with a common reflective double cover (132) at one of their ends and, on the other hand, with a waveguide power divider (130) at the opposite end.
20. Planar antenna according to either of Claims 18 and 19, characterised in that the said covers (123, 132) are produced by deep drawing of the upper earth plate (11a, 11b) of the adjacent antenna modules.
21. Planar antenna according to any one of Claims 1 to 17, intended to interact with at least one other planar antenna, characterised in that a single excitation-conductor (22) support sheet (12) is coupled to a plurality of sets of earth plates (11, 13), each set corresponding to a separate antenna element.
22. Planar antenna according to any one of Claims 1 to 17, intended to interact with at least one second planar antenna, characterised in that the conducting circuits (22) of two adjacent antennas are identical and turned over with respect to each other so that the printed circuit (22a) of a first antenna lies on the recto of the corresponding support sheet (12a) and the conducting circuit (22b) of the second antenna lies on the verso of the support sheet (12b).
23. Planar antenna according to any one of Claims 13 to 17, characterised in that the stack of the triplet structure (11, 12, 13) is housed in a case (B), the bottom of which includes closed rear cavities (26).
24. Planar antenna according to any one of Claims 1 to 13, characterised in that the spacings between each of the plates (11, 12, 13, 14; 51, 52, 53, 54, 55; A, 60; A, 70) are partially or completely filled with a solid dielectric stiffening material.
25. Method of manufacturing a wideband array antenna module according to any one of Claims 1 to 24, characterised in that each of the said earth plates (11, 13) of the antennas is shaped by a die-stamping/deep-drawing operation in order, on the one hand, to pierce the said radiating slots (20a, 20b) and, on the other hand, to embossment the spacing stops (31) on that face of the plates (11, 13) which is turned towards the dielectric support sheet supporting the central conductor, in that the said antenna is assembled simply by resting the non-conducting zones of the dielectric support sheet (12) of the excitation conductor (22) against the embossments (31) facing the lower (13) and upper (11) earth plates so that the terminations (30) of the conducting circuit (22) penetrate between the pairs of aligned slots (20a, 20b), and in that the said triplet structure (11, 12, 13) thus produced is superposed with rear closed cavities (26).

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