EP0617480A1 - Radiating structure with variable directivity - Google Patents

Abstract

The invention relates to a radiating structure with microstrip technology for an array antenna, comprising a plurality of unconnected and not necessarily identical radiating elements, distributed over an insulating surface and comprising electromagnetic means for exciting these radiating elements. These elements are excited by distribution of the electromagnetic excitation energy, and the structure of the invention is characterized in that the distribution is performed by coupling of the magnetic currents generated by each element when it is excited. According to one advantageous embodiment, the elements are arranged in such a way as to obtain a phase and amplitude condition on the surface; in effect, the best directivity is obtained when the illumination is equi-phase and equi-amplitude on the surface. The invention also relates to an antenna including the radiating structure, when installed on a planar surface or a surface shaped in three dimensions. <IMAGE>

Description

The field of the invention is that of array antennas, and more specifically printed array antennas, the radiating elements of which are produced by the microstrip technique. Such antennas are produced by etching 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.

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 fields, in view of 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.

The main characteristics of the simple devices which are the round or square printed tablets are described in the paper by Keith Carver and Joseph Mink, published by - IEEE - A.P., vol. 29 (no.1), January 1981.

From these simple structures, radio electricians have therefore made improvements by building more elaborate solutions. The improvement of the bandwidth of the elementary radiator can be obtained by inserting additional resonance poles on the structure. Many means are possible such as the superposition of pellets; double or multi-resonance structures, or the insertion of these poles in the supply circuit, either by coupling devices, or by equivalent RLC circuits.

These techniques, already widely practiced in the field, make it possible to obtain bandwidths of several tens of percent and generally have a favorable impact on the radiation patterns, since they symmetrical the co-polar signals and significantly lower the crossed polarization components. .

On the other hand, the directivity of the antenna remains partitioned between 5dB at 8 or 9 dB, depending on the embodiment technology, and it is hardly possible to change this parameter by known techniques.

Obtaining antennas or directive elements therefore goes almost inevitably through the sub-networks of elementary radiators. This method, known under the English name "sub-arraying", poses a certain number of difficulties and has its limits. The main difficulty relates to the necessary production of a distribution device or distributor, whose function is to distribute an excitation signal among the elements of each sub-network. Several technologies can be used, to choose according to the application. Some examples: radial mode cavity and multiple couplings; candlestick distributor semi-resonant or progressive distributor.

The design, development and technological definition of the distributor together constitute a major increase in complexity in the creation of a network or sub-network of elementary antennas. In addition, with current designs, problems remain because there are desirable performances, in terms of directivity and / or quality of radiation which cannot be obtained.

An important limitation of this technique is the discretization of achievable directivity situations which are incremented due to 10 log₁₀ (N) (N being the number of individual sources participating in the network); which means that from a radiating element concept only discrete directivity values can be obtained:

• les pertes du répartiteur, dues principalement à la technologie utilisée pour réaliser celui-ci.
• l'efficacité de l'échantillonnage en surface des radiateurs rapportés à la maille choisie pour la mise en réseau.

Another quantity limits the performance that can be obtained, the capacity of large sub-networks appears as the effective gain achieved by the directive antenna and translates the power yield of the solution. The gain will be limited by two main factors:

• losses of the dispatcher, mainly due to the technology used to make it.
• the efficiency of the surface sampling of radiators compared to the mesh chosen for networking.

The invention aims to overcome these drawbacks of the prior art: the design and implementation difficulties of the distributor and its associated losses, the discretization of the directivity, and the gain cap.

The new embodiment of a planar or shaped antenna according to the invention allows effective management of the directivity of the radiator and therefore gives planar or shaped solutions the flexibility and sizing capacity as they exist in the context of more conventional solutions with horns or with radiating openings.

For these purposes, the invention provides a radiating structure with microstrip technology for array antenna, this structure comprising a plurality of radiating elements distributed over an insulating surface, these elements being excited by a distribution of the electromagnetic excitation energy between said elements, characterized in that said distribution is carried out by coupling the magnetic currents generated by each element during its excitation.

This structure is a sub-network of radiating elements, comparable to a sub-network of the prior art, except that there is no distributor; the distribution is made by coupling the magnetic currents of the radiating elements together.

The structure according to the invention is produced by "splitting" the printed patch into several small disjointed conductive patches which are not necessarily identical, and by placing them on an insulating surface so as to optimize the couplings between the small patches for the purpose of the antenna.

The basic operation of an antenna according to the invention consists in exciting by an appropriate means currents (electric and magnetic) on a metallic pad (the printed "patch") whose precise geometric definition depends on the required application. According to different variants of the invention, the initial current distribution can be obtained by an excitation conveyed by a coaxial, microstrip, or stripline transmission line, or even by electromagnetic coupling, these techniques being known to those skilled in the art. .

Advantageously, by another technique known from the prior art, the simple radiator can be placed in an environment having electrical conditions particular, for example it can be surrounded by an electric or magnetic wall so as to secure its networking. Such an approach developed by the Applicant is described in French patent no. 89.11829 of September 11, 1989 of Dusseux, Raguenet et al. which forms an integral part of the present application for its description of the prior art.

• la figure 1 montre schématiquement et en coupe partielle un élément rayonnant imprimé de l'art antérieur, comprenant un premier résonateur qui consiste en un patch conducteur disposé au fond d'une cavité métallique ;
• la figure 2 montre schématiquement et en coupe partielle un élément rayonnant imprimé de l'art antérieur, comprenant un premier résonateur qui consiste en un patch conducteur disposé au fond d'une cavité métallique, ainsi qu'un second résonateur disposé devant le premier résonateur (dans le sens du rayonnement) ;
• la figure 3 montre schématiquement et en vue de dessus, un élément rayonnant imprimé de l'art antérieur, conforme à la géométrie commune aux figures 1 et 2 ;
• la figure 4 montre un exemple d'un élément rayonnant selon l'invention, dont le deuxième résonateur a une structure fragmentée multi-éléments ;
• la figure 5 montre schématiquement un modèle théorique du rayonnement d'un patch rectangulaire simple selon l'art antérieur, comme étant engendré par des courants magnétiques ;
• la figure 6 montre une vue schématique d'un élément rayonnant selon l'invention montré sur la figure 4, montrant les courants magnétiques équivalents principaux ;
• la figure 7 montre un exemple des mesures de diagramme de rayonnement effectuées sur un élément rayonnant selon l'art antérieur telle que montrée sur la figure 2 ;
• la figure 8 montre un exemple des mesures de diagramme de rayonnement effectuées sur un élément rayonnant selon l'invention, qui consiste en quatre patches carrés de 31x31mm² avec une séparation de 10 mm entre patches adjacents ;
• la figure 9 montre un exemple des mesures de diagramme de rayonnement effectuées sur un élément rayonnant selon l'invention, qui consiste en quatre patches carrés de 39x39mm² avec une séparation de 32 mm entre patches adjacents ;
• la figure 10 montre un exemple des mesures de diagramme de rayonnement effectuées sur un élément rayonnant selon l'invention, qui consiste en quatre patches carrés de 40x40mm².

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 following description, as well as its accompanying drawings, including:

• Figure 1 shows schematically and in partial section a radiating element printed from the prior art, comprising a first resonator which consists of a conductive patch disposed at the bottom of a metal cavity;
• FIG. 2 shows schematically and in partial section a radiating element printed from the prior art, comprising a first resonator which consists of a conductive patch placed at the bottom of a metal cavity, as well as a second resonator placed in front of the first resonator ( in the direction of the radiation);
• Figure 3 shows schematically and in top view, a printed radiating element of the prior art, conforming to the common geometry in Figures 1 and 2;
• FIG. 4 shows an example of a radiating element according to the invention, the second resonator of which has a fragmented multi-element structure;
• FIG. 5 schematically shows a theoretical model of the radiation of a simple rectangular patch according to the prior art, as being generated by magnetic currents;
• Figure 6 shows a schematic view of a radiating element according to the invention shown in Figure 4, showing the main equivalent magnetic currents;
• FIG. 7 shows an example of the radiation diagram measurements carried out on a radiating element according to the prior art as shown in FIG. 2;
• FIG. 8 shows an example of the radiation diagram measurements carried out on a radiating element according to the invention, which consists of four square patches of 31 × 31 mm² with a separation of 10 mm between adjacent patches;
• FIG. 9 shows an example of the radiation diagram measurements carried out on a radiating element according to the invention, which consists of four square patches of 39x39mm² with a separation of 32 mm between adjacent patches;
• FIG. 10 shows an example of the radiation diagram measurements carried out on a radiating element according to the invention, which consists of four square patches of 40 × 40 mm².

Thus the thin radiators of the prior art are often presented as structures as shown schematically in Figures 1, 2 and 3, and described in more detail in French patent application no. 92 13744 of November 16, 1992 in the name of the Claimant.

In Figure 1, we see an embodiment of a radiating element according to the prior art. By way of example, it is assumed that this element comprises an etched conductive patch 2 on a dielectric substrate 1 covered on its rear face by a ground plane 6. The patch 2 is powered by the microstrip 4b, which is an etched conductive track , usually of the same material as the patch. According to this example, the patch 2 is placed at the bottom of a closed system which consists for example of a cavity 7 defined by conductive walls 8 delimiting the radial extent of the cavity 7 around the patch 2. The dimensions of this cavity 7 determine its radioelectric characteristics according to rules known to those skilled in the art; as a result, these dimensions can be chosen by the designer in order to provide the desired bandwidth at the operating frequency of the radiating element, and this without increasing the thickness of dielectric 1 behind patch 2. The dimensioning of such structures is well known and the main parameters are conditioned by the criteria of the central operating frequency and the bandwidth around this central frequency.

A second example of an antenna embodiment using a very wide band element according to the prior art is shown in FIG. 2. FIG. 2 illustrates the method of this embodiment, which consists in adding to a basic patch 2 radiator, a second resonator 12 positioned above the first resonator 2. The configuration is therefore that of FIG. 2, except that the resonant cavity 7 is partially closed on its front face by a second resonator 12 which may for example be a printed patch on a dielectric support 11. In this specific case, the second element is implanted flush with the cavity 7, but it could be placed, by means of more elaborate constructions, either at a greater height or at a height smaller than the height of the conducting walls 8 of the cavity 7.

The approach, however, which consists of making the interpatch distance and the height of the cavity identical, makes technological realization very simple. The second resonator 12 can be etched on a carrier substrate 11 of small thickness and mass and its mounting can be done by simple bonding or screwing.

In FIG. 3, we see the geometry common to FIGS. 1 and 2, of a circular patch 2 printed on a substrate 1, and surrounded by a metallic mass 8 to form a resonant cavity 7, so as to widen the strip of operation. Patch 2 is excited via a supply line 4b.

The approach developed to produce a device with variable directivity according to the invention consists in fragmenting the radiating element into a multitude of small disjointed and not necessarily identical sub-elements as shown in FIG. 4.

In FIG. 4, which is to be compared with FIG. 3 already described, the printed patch (item 2 of FIG. 3) is divided into several sub-elements (21, 22, 23, 24, 25, 26, 27, 28) . Patch 2 of the prior art can be considered according to the model of magnetic currents, as generator of currents on its periphery 20. The sub-elements of the invention, on the other hand, generate equivalent magnetic currents on all the peripheries of all the elements. These currents generate couplings between the elements, which have the effect of increasing the equivalent sensing surface of the radiating element. The supply of the sub-elements is carried out as in the prior art for a simple resonator, and the distribution is carried out passively thanks to the couplings between the elements, so there is no need for a distributor.

We will describe the operating principle in the simple case of a single-level structure, using Figure 5.

In FIG. 5, we see in the upper part a rectangular printed patch 1 on an insulating substrate 2, with an instantaneous view of the electric fields generated on the periphery of the patch when it is excited by a signal carried on a non-transmissible transmission line. -shown. We see on the part in the middle of the figure that these electric fields are equivalent to those which would be excited in a rectangular slot 33 formed by a rectangular conductive patch 32 surrounded by a ground plane 31 extended around the patch 32, when the latter is excited by the same signal as before. The lower part of Figure 5 shows the magnetic currents equivalent to electric fields in the other two parts, according to Maxwell's equations for electromagnetic propagation.

We can assimilate the radiation behavior of a patch (see internal report of the University of Louvain October 1988 - UDC -421.394.47) to that of two magnetic surface currents corresponding to the steep terminations of the microstrip line. The geometry of the patch is advantageously of dimensions of λ _ε / 2 approximately so that the two main magnetic currents radiate in phase (see FIG. 5). The resonant side of such a device is therefore derived from the previous condition: $${\text{a = q λ}}_{\text{ε}}\text{with q ≅ 0.49}$$

Thus the dimensions of the patch, to function correctly, are fixed by this resonance condition. And for an element operating in circular polarization, there is no way to change the sensing surface, so the directivity is frozen in turn.

The operation of the fragmented structure offers an extension of the available parameters so as to make it possible, on the one hand, to control the central operating frequency, and on the other hand to develop the "equivalent" radiating surface of the whole, as well as the distribution on the different pellets and, by the same, the radiated diagram.

To better understand how these effects are obtained, we can consider the device of the invention as a set of microstrip lines fixed and coupled together. Thus, the initial exciter device (probe, coupling slot, patch at a lower level), directly induces currents on each pellet according to an initial distribution. In a first rough approximation these currents can be considered without interactions. According to a more detailed analysis, which reveals the principle of the invention, the relative arrangement of the different patterns printed with respect to each other modifies this initial distribution of currents due strong interactive couplings. We can thus proceed to the realization of many possible possibilities within the framework of a simple structure.

An object of the invention is to manage the fragmentation of the radiating element so as to increase the equivalent radiating surface of the assembly compared to a structure with a solid pellet and not fragmented.

In this case, we can consider that, in its radiation, each fragmented patch is equivalent to 2 magnetic current lines (see Figure 6) for an antenna in linear polarization. The radiation behavior of each of these equivalent slits is dependent on the one hand on the initial excitation induced by the excitation supply system, and on the other hand on the influence of the set of mutual couplings of all the slots, relative to each other.

Because of the new mechanisms brought into play in the device according to the invention, the structure must be correctly dimensioned and arranged according to a geometry (which includes the sizes of the pellets, their spacing, their shape and their relative arrangement ....), designed to ensure the phasing of all current sources. The phasing of the sources creates a maximum radiation normal to the plane of the elementary slits. The second condition to be satisfied in order to maximize the directivity of the surface consists in achieving an equi-amplitude distribution of the current sources. Obtaining the equi-phase and the equi-amplitude over an entire surface, ensures the maximum yield with respect to this.

Producing a variable directivity element according to the invention therefore consists in managing coupled multi-pattern geometries fulfilling the above conditions, the equivalent area of which will be varied. All other conditions being equal, the fact of modifying the equivalent sensing surface results in a simultaneous evolution of the directivity. This is how variable directivity is obtained by the invention. Thus, the bringing into play of new parameters therefore makes possible solutions which cannot be proposed using conventional devices.

• à l'aide d'un premier résonateur de type patch couplé à la structure multi-motif fragmentée,
• à l'aide d'une fente couplée, celle-ci pouvant être linéaire ou circulaire,
• ou même directement à l'aide d'une sonde connectée à l'un des motifs.

The proposed invention therefore relates to the use of a terminal radiation surface composed of a multitude of metallic printed patterns, not necessarily identical, which patterns being arranged so that when they are lit by an electromagnetic wave, they couple between them so as to create a current distribution in amplitude and phase contributing to the radiation of the structure. The excitation of the overall pattern thus developed is not in itself a major difficulty and we can consider that the primary illumination can be done in a very classic way, for example:

• using a first patch type resonator coupled to the fragmented multi-pattern structure,
• using a coupled slot, which can be linear or circular,
• or even directly using a probe connected to one of the patterns.

The above techniques are widely known and mastered in the field of feeding printed or planar antennas.

Examples of realizations

The fundamental principle of coupled fragmentation has been applied to a series of radiators whose radiation patterns have been measured in radiation. Thus from a reference embodiment according to the prior art, is it possible to assess the impact of the fragmentation according to the invention on the directivity.

The reference antenna is a double resonator structure as described in the aforementioned French patent of DUSSEUX, RAGUENET et al. : planar antenna , N ° 89 11 829.

The second resonator is a full circular patch of diameter ⌀ = 80mm. The excitation is carried out using a first circular patch resonator of diameter ⌀ = 63mm implanted in a cylindrical cavity of 100mm in diameter, making an annular slot with a width of about 19mm.

The distance between the two resonators is typically 13 to 14mm. The radiation pattern of this reference structure is presented in Figure 7.

The integrated directivity is 8.6dB / 8.7dB according to the different section plans studied. The results are shown in the following table MAXIMUM AMPLITUDE (dB / ISO) MERIDIEN (Azimuth) POLARIZATION 8.6 .00 VERTICAL -11.4 .00 HORIZONTAL 8.7 90.00 VERTICAL -15.4 90.00 HORIZONTAL 8.7 45.00 VERTICAL -10.6 45.00 HORIZONTAL 8.7 135.00 VERTICAL -11.2 135.00 HORIZONTAL 8.6 22.50 VERTICAL -11.3 22.50 HORIZONTAL

A first exemplary embodiment was measured according to the invention. A simple fragmentation of the second resonator has been carried out and consists of bursting into 4 equal square parts said upper resonator. Thus, the geometry was changed parametrically in size and in relative position so as to produce structures with variable directivity. The radiator considered is therefore always a thin assembly constantly retaining its excitation device by a first supply resonator. The invention relates, in essence, to the terminal surface which, thanks to the fragmentation of the second resonator into multiple elements, offers numerous possibilities to the designer, in view of the increase in the number of degrees of freedom available for the design in view of 'a desired result.

The radiant structure works on the principle of interposed couplings, it takes all the skill of man art to optimize the increase in the directivity of the device as well as its impedance adaptation.

• d'obtenir une excellente adaptation d'impédance dans la même bande de fonctionnement que l'antenne de référence.
• d'engager le processus d'augmentation de surface rayonnante équivalente donc d'évolution de directivité qui passe de 8.6/8.7 dB sur l'antenne de référence d'un diamètre ⌀ = 80mm, à 9.10 dB sur l'antenne à quatre patches carrés de 31x31mm². Les résultats sont portés sur le tableau suivant :

AMPLITUDE MAXIMUM (dB/ISO) MERIDIEN (Azimut) POLARISATION 9.1 .00 VERTICALE -10.3 .00 HORIZONTALE 9.1 45.00 VERTICALE -9.8 45.00 HORIZONTALE 9.1 90.00 VERTICALE 19.1 90.00 HORIZONTALE 9.1 135.00 VERTICALE -11.5 135.00 HORIZONTALE Figure 8 presents the radiation diagram of a fragmented structure with four square patches of size 31x31mm², separated by a distance of 10mm between adjacent patches. These four square patches therefore replace the circular patch of 80mm diameter of the reference antenna according to the prior art. A good arrangement of the upper blocks divided with respect to the lower coupling device allows:

• to obtain an excellent impedance matching in the same operating band as the reference antenna.
• to initiate the process of increasing the equivalent radiating surface, therefore the change in directivity, which goes from 8.6 / 8.7 dB on the reference antenna with a diameter ⌀ = 80mm, to 9.10 dB on the antenna with four square patches of 31x31mm². The results are shown in the following table:

MAXIMUM AMPLITUDE (dB / ISO) MERIDIEN (Azimuth) POLARIZATION 9.1 .00 VERTICAL -10.3 .00 HORIZONTAL 9.1 45.00 VERTICAL -9.8 45.00 HORIZONTAL 9.1 90.00 VERTICAL 19.1 90.00 HORIZONTAL 9.1 135.00 VERTICAL -11.5 135.00 HORIZONTAL

Figure 9 presents the radiation diagram of a structure identical to the previous one, except for the fragmentation of the second radiator into four blocks of 39x39mm², separated by 32mm. The results of the measurements are shown in the following table:

Figure 10 shows the measurement results for a structure fragmented into four square patches of 40x40mm². The measured values are shown in the following table: MAXIMUM AMPLITUDE (dB / ISO) MERIDIEN (Azimuth) POLARIZATION 10.1 .00 VERTICAL -11.0 .00 HORIZONTAL 10.3 90.00 VERTICAL -23.2 90.00 HORIZONTAL 10.2 45.00 VERTICAL -9.2 45.00 HORIZONTAL 10.3 135.00 VERTICAL -8.9 135.00 HORIZONTAL 10.3 22.50 VERTICAL -9.2 22.50 HORIZONTAL

The following table summarizes the different directivity situations for the cases studied experimentally. all values: dB Reference antenna Fragmented 4x31x31mm² Fragmented 4x39x39mm² Fragmented 4x40x40mm² Directivity 8.60 9.10 10.0 10.30 am reference deviation - +.50 +1.40 +1.70

Between these four configurations, the only modification relates to the production of the second final resonator which is therefore a conventional solid patch in the case of the reference antenna according to the prior art, and which takes on a fragmented geometry in the other cases which illustrate examples of embodiments according to the invention.

This technique makes it possible to increase the directivity measured experimentally by almost 2 dB on all of the models produced and described.

Many applications of the invention can be proposed, without departing from the scope of the invention which has been described above. We can cite a few non-limiting examples among all the imaginable variants.

A variant of the invention relates to the use of the fragmentation technique in order to obtain a given radiation pattern. For example, one may wish to obtain particular characteristics in radiation: quality of the side lobes, width of main lobe at 3dB, level of diffuse. By repeating the representation of FIG. 6, it can be considered that a network of elementary sources has been produced with regard to the representation of the pellets as equivalent magnetic currents.

Due to the creation of these multiple sources, it is possible to manage the couplings as well as the geometries of these elements so as to create a given primary current distribution. It is obvious that the condition equi-phase and equi-amplitude on the set of the elementary sources is only one particular case of the possibilities of the fragmented approach.

It is therefore not illusory to think of distributions of radiation sources, with a high degree of purity, or with perfect symmetry, etc.

These new capacities are a result of the fragmentation technique of the second resonator according to the invention.

A second variant concerns the use of the fragmentation technique according to the invention in order to obtain multiple resonances.

• a) soit des comportements multifréquences
• b) soit une réponse large bande.

The pads can have shapes and geometries whose variants are limited only by the imagination of the designer. Another variant of the invention consists in exploiting the geometric aspects of the coupled resonators so as to obtain:

• a) either multi-frequency behaviors
• b) or a broadband response.

Such a capacity is immediate because of the principles of coupled structures released by the approach of the invention.

Another variant concerns the use of single- or multi-frequency (s) or broadband antennas exploiting the principles set out above, in the configuration of networks or sub-networks of fragmented elements according to the invention.

An important variant concerns the use of this type of antenna on surfaces that are not flat or shaped in 3 dimensions. It is understood that the arrangement of the fragmented elements on a shaped surface will further introduce new parameters which will lend themselves to optimization by the designer, with a view to the mission of the antenna.

Another variant concerns the use of the geometry of the fragmented patches so as to generate polarized waves. For example, one can use a rectilinear geometry , made of coupled bars, to obtain linear polarization. Another possibility would be the use of fault geometry , which then acts as a polarizing pattern for circularly polarized waves.

A final variant proposed relates to the use of the invention for producing a dichroic surface with variable directivity.

According to this idea, a fragmented assembly according to the invention is arranged so as to absorb incident radiation at a certain frequency, while radiation of any other frequency will be reflected.

Claims (13)

Radiant structure with microstrip technology for array antenna, this structure comprising a plurality of radiating elements (21, 22, 23, 24, 25, 26, 27, 28) distributed on an insulating surface (1) and electromagnetic excitation means of these radiating elements, these elements being excited by a distribution of the electromagnetic excitation energy between said elements, characterized in that said distribution is carried out by coupling magnetic currents [J $\genfrac{}{}{0ex}{}{\text{m}}{\text{1}}$

, J $\genfrac{}{}{0ex}{}{\text{m}}{\text{2}}$

, J $\genfrac{}{}{0ex}{}{\text{m}}{\text{3}}$

, J $\genfrac{}{}{0ex}{}{\text{m}}{\text{4}}$

] generated by each element (21, 22, 23, 24, 25, 26, 27, 28) during its excitation. Radiant structure according to claim 1, characterized in that said plurality of radiating elements consists of several small printed conductive patches (21, 22, 23, 24, 25, 26, 27, 28), separate and not necessarily identical, arranged on an insulating surface (1) so as to optimize the couplings between said patches. Radiant structure according to claim 1 or 2, characterized in that it does not comprise specific means for distributing the electromagnetic excitation energy between said elements, this distribution being effected only by coupling magnetic currents [J $\genfrac{}{}{0ex}{}{\text{m}}{\text{1}}$

, J $\genfrac{}{}{0ex}{}{\text{m}}{\text{2}}$

, J $\genfrac{}{}{0ex}{}{\text{m}}{\text{3}}$

, J $\genfrac{}{}{0ex}{}{\text{m}}{\text{4}}$

] generated by each element during its excitation. Radiating structure according to any one of Claims 1 to 3, characterized in that the said radiating elements are arranged so as to obtain their phasing over the whole of the said insulating surface. Radiating structure according to any one of Claims 1 to 4, characterized in that the said radiating elements are arranged so as to obtain an equi-amplitude distribution of said magnetic currents [J $\genfrac{}{}{0ex}{}{\text{m}}{\text{1}}$

, J $\genfrac{}{}{0ex}{}{\text{m}}{\text{2}}$

, J $\genfrac{}{}{0ex}{}{\text{m}}{\text{3}}$

, J $\genfrac{}{}{0ex}{}{\text{m}}{\text{4}}$

] on said insulating surface. Radiating structure according to any one of Claims 1 to 5, characterized in that the said structure further comprises means around the said plurality of radiating elements for imposing particular electrical and magnetic conditions. Radiant structure according to any one of Claims 1 to 6, characterized in that the said excitation means are supplied by a transmission line. Radiant structure according to any one of Claims 1 to 7, characterized in that the said excitation of the said radiating elements is carried out using a first patch type resonator coupled to the multi-element structure (21, 22, 23, 24, 25, 26, 27, 28). Radiating structure according to any one of Claims 1 to 8, characterized in that the said excitation of the said radiating elements is carried out using a coupled, linear or circular slot. Radiating structure according to any one of Claims 1 to 9, characterized in that the said excitation of the said radiating elements is carried out using a probe connected to one of the said radiating elements. Radiant structure according to any one of Claims 1 to 10, characterized in that the said insulating surface is substantially planar. Radiant structure according to any one of Claims 1 to 11, characterized in that the said insulating surface is 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 12.

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