EP0627783A1 - Radiating multi-layer structure with variable directivity - Google Patents

Abstract

The antenna of the invention comprises radiating sources having a multi-layer dielectric/conductor structure and a multiplicity of coupled elements distributed over the interfaces between the successive dielectric layers, fed by a single radiating block situated on the lower level of the antenna. The geometric parameters of the conducting patches and of their distributions on successive layers confer great flexibility in the antenna design, especially as far as the simultaneous optimisation of antenna parameters are concerned, such as: directivity, pass band, efficiency (by minimising distribution loses), the purity of the polarisation, and the symmetry of the radiating diagram. These advantages of the invention stem principally from the possibility for increasing the radiating aperture of a source without increasing the complexity of the passive distributors for distributing the radiated signals. This is achieved by the coupling of the elements between levels, and by the production of a geometry which makes it possible to increase the equivalent radiating surface at each successive level. <IMAGE>

Description

The field of the invention is that of network antennas, and more specifically that of multi-layer and multi-element printed network antennas, the radiating elements of which are produced by the microstrip technique. Such antennas are produced by etching or lithography of conductive tracks and blocks on dielectric substrates, which are generally but not exclusively planar. More elaborate configurations exist with several dielectric substrates, ground planes, resonator cavities, et cetera, some examples of which will be described in more detail below. In the case under consideration, several layers of dielectric, each of which comprises a pattern of conductive tracks and / or blocks, are stacked.

These flat or thin antennas have been widely used in many forms for the past fifteen years. They have even imposed themselves widely in a number of areas, given their intrinsic qualities: mass, volume, low cost of production.

It is widely known to those skilled in the art that the simplest embodiments of radiating elements, namely the microstrip track etched on a substrate, suffer from fundamental radioelectric limitations, and in particular in terms of bandwidth, the directivity and the quality of radiation. The latter presents, on the one hand, significant asymmetries for an element operating in linear polarization according to the different section planes, and on the other hand, crossed polarization levels very often incompatible with the specifications of space missions.

It is known from French patent application No. 93 03502 in the name of the Applicant, a multi-element system which makes it possible to increase the directivity of a printed antenna by using a sub-network composed of a multiplicity of elements electromagnetically coupled together, and distributed on a flat or shaped surface.

It is also known from French application n ° 89 111829 of 11.09.1989 in the name of the Applicant, to use metal cavities to increase the bandwidth of a printed radiating element. This configuration also allows control of radiation and inter-element coupling in a network created of such elements.

Compared to conventional solutions such as horns or dipoles, solutions using printed elements have the advantages of less weight and size, but nevertheless with lower performance on certain operating parameters of the antenna. In particular, it proves difficult to simultaneously obtain an acceptable bandwidth with a determined directivity, and a polarization purity compatible with telecommunications applications.

Indeed, to date the printed radiating elements have directivities conventionally between 5 and 10 dBi approximately depending on the geometrical characteristics of the antenna (height of substrate, dimensions of the radiating blocks and cavities if they exist) and of the materials used (dielectric constant of substrates).

These directivity values are moreover intrinsically linked to the resonant dimensions (of the order of the guided half-wavelength) of this type of radiating elements which limit their radiating surfaces and therefore the maximum directivity available.

The classic solution for obtaining more directivity from a printed antenna is the networking of radiating elements. This generally leads to the design of a supply network intended to generate the supply law necessary for the formation of the desired radiation template. These feeding systems are in particular necessary for apodiser the law of illumination of the radiating opening, thus making it possible to avoid the appearance of lobes secondary, often undesirable in telecommunications or radar antenna systems.

• 1) la complexité d'un tel système croît avec le nombre d'éléments à alimenter ; la complexité est encore plus grande dans le cas d'une antenne fonctionnant avec la polarisation circulaire.
• 2) la discontinuité ou la discrétisation de l'apodisation, due à l'échantillonnage de la surface rayonnante par les éléments rayonnants élémentaires discrets.
• 3) le couplage entre les éléments est difficilement pris en compte, et il est vu en général comme un phénomène tendant à dégrader les performances de l'antenne.
• 4) la connectique est complexe, tendant à diminuer la fiabilité de l'antenne.
• 5) les pertes dans le répartiteur d'énergie peuvent être importantes, ce qui grève l'utilisation d'une telle solution pour les fréquences très élevées ou pour des antennes passives ayant plusieurs dizaines d'éléments, les pertes résistives étant trop pénalisantes dans ces cas.

The design of such supply systems presents a certain number of problems, described in more detail in French application No. 93 03502. Among these problems, we can briefly mention:

• 1) the complexity of such a system increases with the number of elements to be supplied; the complexity is even greater in the case of an antenna operating with circular polarization.
• 2) the discontinuity or the discretization of the apodization, due to the sampling of the radiating surface by the discrete elementary radiating elements.
• 3) the coupling between the elements is hardly taken into account, and it is generally seen as a phenomenon tending to degrade the performance of the antenna.
• 4) the connection is complex, tending to reduce the reliability of the antenna.
• 5) the losses in the energy distributor can be significant, which strikes the use of such a solution for very high frequencies or for passive antennas having several tens of elements, the resistive losses being too penalizing in these case.

These problems are known to those skilled in the art and have been the subject of numerous attempts at improvement and of numerous publications, a synthesis of which is given in the "Handbook of Microstrip Antennas", by JAMES, J.R.; HALL, P.S; and WOOD, C., published in IEE Electromagnetic Waves series, N ° 12, Published by: P. Périgrinus Ltd, Stevenage, U.K. This publication is an integral part of this request for its description of the prior art.

However, the solutions proposed in the prior art involve compromises, since it is found that other antenna performances are limited in return for improvements in directivity. For example, the article by RQ LEE, R. ACOSTA, and KF LEE: "Radiation characteristics of microstrip arrays with parasitic elements" published in Electronics Letters Vol. 23, pp. 835-837, (1987) describes a device which gives 11 dBi of directivity, but with a bandwidth of less than 1%, a very high total height of the substrate of the order of 0.4 λ, and all this without control of neither the polarization nor the symmetry of the radiation diagram.

Two other solutions propose enlarging the radiating surface to improve the directivity, either by coupling radiating elements in the same plane as the exciter paver, or by fragmenting the upper resonant paver in the case of a structure with two superimposed pavers. The first solution is described by R.Q. LEE and K.F. LEE in "Experimental study of the two layer electromagnetically coupled rectangular patch antenna :, IEEE Transactions Antennas and Propagation, (1990), Vol. AP-38 no. 8, pp. 1298 - 1302; the second solution is described in the request for French patent n ° 93 03502.

The improvements in directivity presented by these known solutions however remain modest due to an insufficient coupling in the first case cited, and due to a still insufficient radiating surface for the second solution.

The invention aims to overcome these performance limitations of antennas of the prior art, and in particular aims to simultaneously provide a high gain, a very wide bandwidth, the control of the polarization purity, and the control of the template. of radiation.

For these purposes, the invention provides a radiating structure with variable directivity, this structure comprising a plurality of radiating elements and means of electromagnetic excitation of these radiating elements, characterized in that said radiating elements are distributed at the interfaces of a plurality of dielectric spacers stacked on successive levels in a multilayer radiating structure, this structure radiant multilayer being itself disposed on said excitation means.

According to an advantageous embodiment, said multilayer radiating structure comprises a plurality of dielectric interfaces, each dielectric interface comprising one or more radiating elements, said structure being composed so that each successive interface comprises a coupled radiating surface larger than the surface of the radiating elements of the previous level, starting from a first level containing said excitation means.

According to a particularly advantageous variant, the radiating elements of different levels are coupled by electromagnetic coupling so as to obviate the need for a specific structure for distributing electromagnetic energy.

According to a preferred embodiment, the lower level comprises a single radiating block, which will be excited by said excitation means, and which in turn will excite the radiating elements of the next level, and so on.

According to another characteristic, the first radiating block, which is located on the first level of the multilayer structure, is supplied so as to radiate the desired polarization. The polarization of this exciting radiating block will then be controlled and improved during coupling to the different radiating structures of higher levels by the use of radiating structures and elements of suitable shape.

According to another preferred characteristic, the radiating elements of a higher level partially cover the radiating elements of an immediately lower level when seen in projection in the direction of stacking of the levels, and the coupling between the elements of the contiguous levels is managed by the percentage of overlap of these elements in the current zones magnetic, as well as the thickness and dielectric qualities of the separators.

According to a preferred embodiment, a particular polarization can be obtained by the use of excitations by sequential rotation in coupled structure. According to a variant, the radiating structure can be equipped with a polarizing grid.

• la figure 1 montre schématiquement et en plan un élément rayonnant imprimé de l'art antérieur, comprenant un premier élément d'excitation E qui consiste en un pavé conducteur (connu de l'homme de l'art par son nom anglais "patch") disposé sur une face d'un substrat diélectrique D1 plan ou conformé ;
• la figure 2 montre schématiquement et en coupe l'élément rayonnant imprimé de l'art antérieur selon la figure 1 ;
• la figure 3 montre schématiquement et en vue de dessus, un élément rayonnant imprimé de l'art antérieur, comprenant un premier élément "patch" d'excitation E conforme à la géométrie commune aux figures 1 et 2, ainsi qu'un second élément patch résonateur R disposé devant le premier élément d'excitation E (dans le sens du rayonnement) sur un deuxième substrat diélectrique D2 ;
• la figure 4 montre schématiquement et en coupe l'exemple d'un élément rayonnant selon la figure 3 ;
• la figure 5 montre schématiquement et en vue de dessus un exemple d'une structure rayonnante imprimée selon l'art antérieur, dont le deuxième élément résonateur à une structure multi-éléments ;
• la figure 6 montre schématiquement et en coupe l'exemple d'une structure rayonnante imprimée selon la figure 5 ;
• la figure 7 montre schématiquement et en plan un autre exemple d'une structure rayonnante imprimée, qui consiste en un premier patch excitateur E sur un premier niveau inférieur, et une grille de polarisation formée d'une multiplicité de patches disposés sur un deuxième niveau de diélectrique D2 selon une géométrie particulière;
• la figure 8 montre schématiquement et en coupe l'exemple d'une structure rayonnante imprimée selon la figure 7 ;
• la figure 9 montre schématiquement et en plan un exemple d'une structure rayonnante imprimée selon l'invention, qui consiste en un premier patch excitateur E sur un premier substrat diélectrique D1, et un deuxième élément résonateur ayant une structure multi-éléments (R1...R6) disposée sur un deuxième substrat diélectrique D2, et un troisième élément résonateur multi-éléments (R21, R22, ... R26) disposé sur un troisième substrat diélectrique D3, qui est superposé à une configuration comme celle de la figure 5 ;
• la figure 10 montre schématiquement et en coupe l'exemple d'une structure rayonnante imprimée selon la figure 9 ;
• la figure 11 montre schématiquement et en vue de dessus un autre exemple d'une structure rayonnante imprimée selon l'invention, dont le deuxième élément résonateur à une structure multi-éléments, et dont un troisième élément résonateur multi-éléments, superposé à la configuration de la figure 5, à la forme et la fonction d'une grille de polarisation ;
• la figure 12 montre schématiquement et en coupe l'exemple d'une structure rayonnante imprimée selon la figure 11 ;
• la figure 13 montre les résultats de mesures effectuées sur la structure rayonnante montrée dans les figures 11 et 12.

The principles of the invention, as well as some embodiments and the advantages acquired by the use of the invention will be understood in more detail by the description which follows, as well as its attached drawings, including:

• Figure 1 shows schematically and in plan a radiating element printed from the prior art, comprising a first excitation element E which consists of a conductive pad (known to those skilled in the art by its English name "patch") disposed on one face of a dielectric substrate D1 plane or shaped;
• Figure 2 shows schematically and in section the radiating element printed from the prior art according to Figure 1;
• Figure 3 shows schematically and in top view, a printed radiating element of the prior art, comprising a first "patch" excitation element E conforming to the geometry common to FIGS. 1 and 2, as well as a second patch element resonator R placed in front of the first excitation element E (in the direction of the radiation) on a second dielectric substrate D2;
• Figure 4 shows schematically and in section the example of a radiating element according to Figure 3;
• FIG. 5 schematically shows a top view of an example of a radiating structure printed according to the prior art, the second resonator element of which has a multi-element structure;
• Figure 6 shows schematically and in section the example of a radiating structure printed according to Figure 5;
• Figure 7 shows schematically and in plan another example of a printed radiating structure, which consists of a first excitation patch E on a first lower level, and a polarization grid formed of a multiplicity of patches arranged on a second level of dielectric D2 according to a particular geometry;
• Figure 8 shows schematically and in section the example of a radiating structure printed according to Figure 7;
• FIG. 9 shows schematically and in plan an example of a radiating structure printed according to the invention, which consists of a first excitation patch E on a first dielectric substrate D1, and a second resonator element having a multi-element structure (R1. ..R6) disposed on a second dielectric substrate D2, and a third multi-element resonator element (R21, R22, ... R26) disposed on a third dielectric substrate D3, which is superimposed on a configuration like that of FIG. 5 ;
• Figure 10 shows schematically and in section the example of a radiating structure printed according to Figure 9;
• Figure 11 shows schematically and in top view another example of a radiating structure printed according to the invention, of which the second resonator element has a multi-element structure, and of which a third multi-element resonator element, superimposed on the configuration of Figure 5, the shape and function of a polarization grid;
• Figure 12 shows schematically and in section the example of a radiating structure printed according to Figure 11;
• FIG. 13 shows the results of measurements carried out on the radiating structure shown in FIGS. 11 and 12.

In all the figures, the same references refer to the same elements, the description of which will not be repeated each time for each figure.

In FIGS. 1 and 2, we have the simplest example of a radiating element of the "patch" type according to the prior art, shown in plan and in section respectively. The excitation element E is a block of conductive material, printed or etched on one face of a dielectric substrate D1. The other face of this dielectric is covered with a conductive layer M which forms a ground plane. In the present example, the exciter patch E is supplied via coaxial connectors C, but one can imagine any other supply technology instead, for example: triplate, microstrip, slot coupling, and so on.

It should be mentioned here that all the examples in FIGS. 1 to 12 are shown on flat substrates, however, the invention, as well as the devices of the prior art, can be adapted on shaped surfaces, and the examples given are not not intended to be limiting in this regard.

In FIGS. 3 and 4, we have a second example of a printed radiating element of the prior art, comprising a first excitation patch element E disposed on a first dielectric substrate D1 conforming to the geometry common to FIGS. 1 and 2 , as well as a second resonator patch element R placed on a second dielectric substrate D2 placed in front of the first excitation element E (in the direction of the radiation). For reasons of ease of manufacture and mechanical stability, these substrates are contiguous in practical embodiments, and they are most often made of the same dielectric material.

In the example of FIGS. 3 and 4, the height H2 of the second dielectric substrate D2 is greater than the height H1 of the dielectric substrate D1, to form a resonant cavity between the excitation patch E and the patch resonator R at the operating frequency. This configuration makes it possible to manage the coupling between elements, and by the same, the bandwidth of the device. The diameter of the resonator patch R is less than the diameter of the exciter patch E. These parameters can be manipulated to optimize the gain and directivity, or the bandwidth of the single element.

In the example of Figures 5 and 6, we see another simple embodiment of a radiating structure according to the prior art. As in the example according to FIGS. 3 and 4, we have an exciter patch E on one side of a first dielectric substrate D1, the other side of which carries a conductive layer M which forms a ground plane.

As in the previous figures, a resonator patch R is placed on a second dielectric substrate D2, placed on the first substrate D1. The diameter of the resonator patch R is less than the diameter of the exciter patch E. According to the example of FIGS. 5 and 6, the simple patch R is completed by a plurality of radiating elements (R1 ... R6, ...) distributed on an insulating surface (D2) stacked on said excitation means (C, E, M, D1) in a multilayer structure. The secondary resonator patches (R1 ... R6) are arranged around the central resonator patch R, to form a multi-element resonator so as to cover the exciter patch E in a current area of the latter, that is to say say on its periphery.

The second insulating surface D2 thus comprises a total surface of resonator patch elements (R1, ... R6, R) clearly greater than the surface of the excitation patch E alone, or of the resonator patch R of FIG. 3. The effective opening of the antenna is increased in proportion, allowing a gain in directivity. An example of a device according to this principle is described in more detail in French application No. 93 03502.

In FIGS. 7 and 8, we see in plan and in section respectively an example of another embodiment of a radiating element, in which a polarization grid is formed by a particular geometry of the patch resonator elements (P1, ... P12) arranged in a star on the surface of a dielectric substrate D2 of height H2.

The arrangement of Figure 7 is particularly suitable for radiation in circular polarization. The excitation means (C) of the exciter patch E are supplied so as to excite a circular polarization at the level of this first patch E, which in turn excites the multi-element resonator (P1 ... P12) by electromagnetic coupling. The magnetic currents on the periphery of the exciter element E excite currents in the elements P1 to P12. Because circular polarization generates a rotating electric field vector, a pair of collinear elements (P1, P7 for example) will be preferentially excited at a given time, depending on the orientation of the electric field at that time, with an excitation of lower amplitude on the neighboring pairs (P12, P6; P2, P8) and zero excitation of the orthogonal pair (P4, P10 for example). A pair of excited dipoles with a 180 ° phase shift (phase opposition) compensates for the 180 ° spatial phase shift between these elements. This allows a summation of the co-polar component and a difference of the counter-polar component.

In this way, the desired polarization is controlled and reinforced by the multi-element resonator (P1, ... P12), which gives a very high purity of polarization at the same time as an increased directivity, thanks to a larger radiating opening. , as well as an optimized yield.

In FIGS. 9 and 10, we see in plan and in section respectively an example of an embodiment of a radiating structure printed according to the invention, in which there are two upper levels each comprising a dielectric substrate (D2; D3) on which a resonator multi-elements (R1, ... R6; R21, ... R26) is deposited by lithography or by engraving.

As in the previous figures, a first excitation patch E on the upper face of a first dielectric substrate D1 having a ground plane M on its opposite face, is excited by excitation means which include, in this example, connectors coaxial C. The excitation of the element E generates magnetic currents on its periphery, which, by electromagnetic coupling, in turn excite currents in the resonator elements R1, ... R6 of the neighboring level.

The excitation of these level D2 resonator elements by patch E generates magnetic currents on the periphery of each block R1, ... R6, which, by electromagnetic coupling, in turn excite the resonator elements (R21, ... R26) of the next level of the radiating structure, which are arranged on the dielectric substrate D3.

The coupling between the elements of a level results from the geometry of the different patches, and the relative geometry of their arrangement, as described in French application n ° 93 03502 in the name of the Applicant. The coupling between the elements of different levels will depend on the overlap of the elements of neighboring levels (as it appears on figure 9), and on the dielectric height (H1, H2) which separates the elements, as well as on the dielectric constant of each substrate (D1, D2, D3, ...).

In FIGS. 11 and 12, we see in section and in plan respectively an example of an embodiment according to the invention, which comprises a plurality of levels (D2, D3) each comprising a multiplicity of radiating elements (R1, .. .R6; P1, ... P1 respectively). The embodiment of Figures 11 and 12 includes the features of Figures 7.8 and 9.10. In the example presented here, the elements P1, ... P6 have a particular shape and arrangement, those of a polarization grid, to improve and control the polarization emitted as in FIGS. 7 and 8.

The lower level of the radiating structure, disposed on a dielectric substrate D1, comprises the excitation means (not shown) of an excitation patch E as well as a ground plane (M); the plurality of substrates stacked on top (D2, D3) comprises multi-element resonators whose area of grip on each substrate increases according to the position of the substrate in the structure, according to the normal direction of radiation of the antenna.

The geometry of the patches and their relative arrangement, as well as the relative heights H1 / H2 / H3 of the dielectric substrates are important parameters which make it possible to obtain a variable directivity and a desired frequency response, according to rules within the reach of the skilled in the art. The dielectric constant is a coupling control parameter and therefore affects all the performance of the antenna. The dielectric constants of the different levels can all be identical, or on the contrary, chosen to reduce the thickness of dielectric between two patches located on adjoining levels.

The examples of the preceding figures are based on simple geometries in each level of multi-element resonators, and on three levels of planar substrates. The invention can be used on curved or shaped substrates, with geometries of patches and their relative arrangement more or less complicated, depending on the design of the radiating element for a given mission. The invention can also use four or even five or more substrates for the development of a radiating structure with an even wider radiating opening. However, the total thickness of the structure should preferably remain relatively modest, in order to meet the needs of the targeted fields of application, in particular space.

Comparative measurements have been made for some of the radiating structures presented in the previous figures, and the results are given in the table below.

The results of the measurements carried out on the structure of FIGS. 11 and 12 are given by the curves plotted in FIG. 13 and summarized in the following table. In this figure, the different curves represent the directivity for the different azimuth angles, that is to say the amplitude measured, relative to an isotropic antenna (in dB / ISO), as a function of the angle d elevation which is given on the abscissa. The levels in cross polarization according to the elevation are plotted in dotted lines. The secondary lobes are absent from these curves because they are smaller than the scale of these graphics. VALUES TRACKED IN FIGURE 13 MAXIMUM AMPLITUDE (dB / ISO) MERIDIEN (Azimuth) CIRCULAR POLARIZATION 13.7 0.00 LEFT 1.5 0.00 RIGHT 13.8 90.00 LEFT - 1.4 90.00 RIGHT 13.8 45.00 LEFT 1.2 45.00 RIGHT 13.7 135.00 LEFT 0.3 135.00 RIGHT

It emerges from these curves and these tables that in addition to a significant increase in the directivity of the antenna according to the invention, the apodization is effective, because the secondary lobes are almost nonexistent. The polarization purity obtained by the addition of the polarization grid excited in sequential rotation by the coupled structure is excellent, as shown by the curves of FIG. 13.

Even the bandwidth has been improved in this device according to the invention by the addition of a level of multi-element resonators. And the ellipticity rate, a relevant parameter for circular polarization, has also been improved.

In addition to the performance advantages, the radiating structure according to the invention provides significant advantages in terms of the design and construction of the antennas, in particular by eliminating the need for complex distribution structures between the members of 'a sub-network of radiating elements. In the present invention, the radiating elements are powered only by the electromagnetic coupling, and it is the parameters of this coupling which determines the law of illumination. The directivity can thus take intermediate values between the discrete values obtained by conventional distribution techniques.

The examples of embodiments and the measurements carried out are given by way of non-limiting examples to illustrate the principles of the invention. Other examples of embodiments will be easily imagined by those skilled in the art, without departing from the scope of the invention.

Claims (12)

Multilayer radiating structure with microstrip technology for network antenna, this structure comprising: - a plurality of levels including a lower level and at least one upper level included in an upper part, a plurality of radiating elements (R1, R2, R3, R4, R5, R6; R21, R22, R23, R24, R25, R26) arranged in the upper part, - And means of electromagnetic excitation of these radiating elements (E, D1, C, M), arranged in said lower level;
These radiating elements being excited by a distribution of the electromagnetic excitation energy between said elements, said distribution being effected by an electromagnetic coupling between said elements, said upper part comprising at least two upper levels, said radiating elements being distributed over a plurality dielectric substrates (D2, D3, ...) stacked by successive levels in a multilayer radiating structure, this multilayer radiating structure being itself disposed on said excitation means disposed in said lower level, characterized in that
each dielectric substrate of said upper part (D2, D3, ...) comprises several radiating elements (R1, ... R6; R21, ... R26), and in that said structure is composed so that each successive dielectric substrate comprises radiating elements on a surface larger than the surface occupied by the radiating elements of the previous level, starting from a first lower level containing said excitation means (E, D1, C, M). Radiant structure according to claim 1, characterized in that it does not include means specific distribution of the excitation electromagnetic energy between said elements, this distribution being effected only by coupling the magnetic currents generated by each element. Radiant structure according to claim 2, characterized in that it does not comprise specific means for coupling the electromagnetic excitation energy between said levels, this excitation being carried out only by coupling the magnetic currents generated by the elements of the level immediately below which excite the elements of the immediately higher level. Radiant structure according to any one of claims 1 to 3, characterized in that said lower level comprises a single radiating block (E), which will be excited by said excitation means (C), and which in turn will excite the elements radiant (R1, ... R6) of the next level, and so on. Radiant structure according to any one of Claims 1 to 4, characterized in that said first radiating block (E), which is located on said lower level of the multilayer structure, is supplied so as to radiate the desired polarization. Radiating structure according to claim 5, characterized in that said radiating elements of at least one of said upper levels are arranged so as to form a radiating structure capable of reinforcing and refining the polarization of the radiation emitted. Radiating structure according to any one of Claims 1 to 6, characterized in that the radiating elements (R21, ... R26) of a higher level partially cover the radiating elements (R1, ... R6) of a level immediately lower when viewed in projection according to the stacking direction of the levels, and in that the coupling between the elements of the contiguous levels is managed by the percentage of overlap of these elements in the magnetic current zones, as well as by the thickness and the dielectric qualities of the separators. Radiant structure according to any one of Claims 5 to 6, characterized in that the said polarization is circular, and in that it is obtained by the use of excitation by sequential rotation in coupled structure. Radiant structure according to any one of claims 5 to 6 or 8, characterized in that it is equipped with a polarizing grid. Radiant structure according to any one of Claims 1 to 9, characterized in that the said dielectric substrates (D1, D2, D3, ...) are substantially planar. Radiant structure according to any one of Claims 1 to 9, characterized in that the said dielectric substrates (D1, D2, D3, ...) are shaped in 3 dimensions. Electromagnetic antenna with variable directivity comprising at least a plurality of radiating elements organized in a radiating structure according to any one of claims 1 to 11.

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