EP0805512A1 - Compact printed antenna with little radiation in elevation - Google Patents

Abstract

The antenna has a conductive deposit (30) on one face of a dielectric sheet. The other face is covered by an earth plane. Four radial slots (31-34) are spaced at 90 degrees intervals around the circumference of the sheet to determine resonant frequency of a selected higher mode. The fundamental mode gives a radiation pattern with a maximum at right angles to the plane of the element. In the higher (TM21,TM01) mode, the current flow at right angles to the slots. The lengths (Lo) and widths (La) of the slots are preferably computed by finite element analysis software.

Description

The field of the invention is that of planar printed antennas for transmitting and / or receiving microwave signals.

More specifically, the invention relates to a planar antenna producing maximum radiation for low elevations.

The antenna of the invention has many applications. It can for example be used in a network placed on the roof of a private vehicle, in order to provide telecommunications by satellite. Indeed, some mobiles, and in particular those in connection with geostationary satellites in countries with medium or high latitude (Northern Europe for example), require flat antennas producing maximum radiation for low elevations.

Currently, for reasons of space and cost, use is made in mobiles of printed antennas of the "patch" type. Indeed, these have the particular advantage of being flat and inexpensive.

Generally, a printed antenna comprises a dielectric substrate plate, a ground plane (constituted by a first conductive deposit deposited on a first face of the dielectric substrate plate), a radiating element (constituted by a second conductive deposit deposited on a second face of the dielectric substrate plate) and means for feeding the antenna.

In their current operation, that is to say when they operate in their fundamental mode, these printed antennas generate a radiation diagram having a maximum in the direction perpendicular to the plane containing the antenna. For this type of current operation, the length of the radiating element is very close to the half-wavelength taking into account the permittivity of the dielectric substrate used.

To be able to generate a radiation having a maximum for low elevations, that is to say in directions distant from the axis perpendicular to the plane containing the antenna, the printed antennas must operate in a higher mode whose current distribution allows to create this type of radiation.

The major problem lies in the fact that the higher modes of interest appear for relatively high frequencies compared to those of fundamental mode. This means that in order to be able to use this type of mode (higher) for the desired frequency band (close to that corresponding to the fundamental mode), the antenna must be very oversized.

This oversizing makes it almost impossible to integrate such radiating elements into a network in order to obtain high gain antennas. This congestion problem is all the more crucial since, for a network having to generate radiation at low elevation, the radiating elements must be placed very close to one another in order to avoid large lobes of network which strongly deteriorate the antenna gain.

The invention particularly aims to overcome this major drawback of the state of the art.

More specifically, one of the objectives of the present invention is to provide a printed antenna making it possible to obtain radiation for low elevations while having a reduced bulk.

The invention also aims to provide such an antenna which retains all the advantages of printed antennas, and in particular a low manufacturing cost.

• une plaque de substrat diélectrique,
• un plan de masse constitué par un premier dépôt conducteur déposé sur une première face de ladite plaque de substrat diélectrique,
• un élément rayonnant constitué par un second dépôt conducteur déposé sur une seconde face de ladite plaque de substrat diélectrique,
• des moyens d'alimentation de ladite antenne,

• ladite antenne présentant un mode fondamental, dans lequel elle génère un diagramme de rayonnement ayant un maximum dans la direction perpendiculaire au plan contenant l'élément rayonnant, et au moins un mode supérieur, dans lequel elle génère un diagramme de rayonnement à faible élévation,
• ladite antenne étant caractérisée en ce que ledit élément rayonnant présente au moins une encoche permettant de contrôler la fréquence de résonance d'un mode supérieur choisi.

These various objectives, as well as others which will appear subsequently, are achieved according to the invention using a planar printed antenna for transmitting and / or receiving microwave signals, of the type comprising in particular:

• a dielectric substrate plate,
• a ground plane constituted by a first conductive deposit deposited on a first face of said dielectric substrate plate,
• a radiating element constituted by a second conductive deposit deposited on a second face of said dielectric substrate plate,
• means for supplying said antenna,

• said antenna having a fundamental mode, in which it generates a radiation diagram having a maximum in the direction perpendicular to the plane containing the radiating element, and at least one higher mode, in which it generates a radiation diagram at low elevation,
• said antenna being characterized in that said radiating element has at minus a notch for controlling the resonant frequency of a selected higher mode.

The higher mode chosen is the one in which the antenna is to be operated, so that the maximum radiation is generated for low elevations.

Thus, the general principle of the invention consists, for a given higher mode, in reducing the resonant frequency only by making notches on the radiating element, that is to say without modifying the overall size of the antenna. In other words, for operation in the same higher mode, the printed antenna of the invention has a smaller footprint than a conventional printed antenna.

Advantageously, the notch (s) are arranged substantially perpendicular to the streamlines of said selected upper mode.

In this way, the electrical length of these current lines is increased, and the resonance frequency of the chosen higher mode is therefore reduced.

Advantageously, the dimensions (length, width) of the notch (s) are determined from a calculation technique based on a finite element method.

• l'alimentation par sonde coaxiale ;
• l'alimentation par couplage par fente ;
• l'alimentation par couplage de proximité ;
• l'alimentation par ligne d'alimentation dans le plan de l'élément rayonnant.

Preferably, said supply means implement a supply technique belonging to the group comprising:

• feeding by coaxial probe;
• slot feed;
• power supply by proximity coupling;
• supply by supply line in the plane of the radiating element.

Preferably, said radiating element is in the form of a disc.

In a first preferred embodiment of the invention, said upper mode chosen is mode TM21, the streamlines of which form a pattern which is repeated in each quarter of said disc,
said radiating element having four radial notches, spaced two by two angularly by approximately 90 °, each of said notches being substantially perpendicular to the current lines in one of said quarters of the disc.

In a second preferred embodiment of the invention, said mode higher selected is the mode TM01, whose currents are arranged radially,
said radiating element having at least one circular notch, the one or more notches extending over at least part of the circumference of a circle contained in said disc and having the same center as the latter.

Advantageously, each notch cooperates with means for annihilating its effect, said antenna comprising means for activating / deactivating said annihilation means.

Preferably, said means for annihilating the effect of a notch comprise a diode connecting the two edges of said notch.

• lorsque tous les moyens d'annihilation sont activés, l'antenne fonctionne dans ledit mode fondamental,
• lorsque tous les moyens d'annihilation sont désactivés, l'antenne fonctionne dans ledit mode supérieur choisi.

In a first particular embodiment of the invention, said radiating element has a plurality of notches,
said activation / deactivation means acting simultaneously on all the annihilation means associated with said plurality of notches, so as to allow multimode operation such as:

• when all the annihilation means are activated, the antenna operates in said fundamental mode,
• when all the annihilation means are deactivated, the antenna operates in said selected upper mode.

This multimode operation makes it possible to cover a wide solid angle with a maximum of radiation. In fact, in the fundamental mode, there is a maximum of radiation in the direction perpendicular to the plane containing the antenna, and in the chosen upper mode, there is a maximum of radiation for a low elevation.

In a second particular embodiment of the invention, said radiating element has a plurality of notches,
said activation / deactivation means acting on a time-varying number of annihilation means associated with said plurality of notches, so as to allow multifrequency operation such that each distinct number of annihilation means activated at a given time corresponds to a particular resonant frequency of said selected upper mode.

This allows multi-frequency operation for the same type of mode superior.

The invention also relates to a dual-band antenna, characterized in that it comprises two superimposed antennas, called lower and upper antennas, of the type presented above, the radiating element of said lower antenna constituting the ground plane of said upper antenna.

• la figure 1 présente une vue de côté d'une antenne classique alimentée par sonde coaxiale ;
• la figure 2 présente une courbe de variation, en fonction de la fréquence, du rapport d'onde stationnaire (ROS) de l'antenne classique de la figure 1;
• la figure 3 présente une vue de dessus d'un mode de réalisation d'une première antenne selon l'invention ;
• la figure 4 présente de façon schématique les lignes de courant du mode TM21 pour la première antenne de la figure 3 ;
• la figure 5 présente une courbe de variation, en fonction de la fréquence, du ROS de la première antenne de la figure 3 ;
• la figure 6 présente le diagramme de rayonnement complet, pour la composante Etheta, de la première antenne de la figure 3 ;
• les figures 7 et 8 présentent chacune une vue en coupe, pour phi = 0° et 90° respectivement, du diagramme de rayonnement de la figure 6 ;
• la figure 9 présente le diagramme de rayonnement complet, pour la composante Ephi, de la première antenne de la figure 3 ;
• les figures 10 et 11 présentent chacune une vue en coupe, pour phi = 45° et 135° respectivement, du diagramme de rayonnement de la figure 9 ;
• la figure 12 présente une vue de dessus d'un mode de réalisation d'une seconde antenne selon l'invention ;
• la figure 13 présente de façon schématique les lignes de courant du mode TM01 pour la seconde antenne de la figure 12 ;
• la figure 14 présente une courbe de variation, en fonction de la fréquence, du ROS de la seconde antenne de la figure 12 ;
• la figure 15 présente le diagramme de rayonnement complet, pour la composante Etheta, de la seconde antenne de la figure 12 ;
• les figures 16 et 17 présentent chacune une vue en coupe, pour phi = 0° et 90° respectivement, du diagramme de rayonnement de la figure 15 ;
• la figure 18 présente le diagramme de rayonnement complet, pour la composante Ephi, de la seconde antenne de la figure 12 ;
• les figures 19 et 20 présentent chacune une vue en coupe, pour phi = 0° et 90° respectivement, du diagramme de rayonnement de la figure 18 ;
• les figures 21 et 22 présentent chacune une vue, respectivement de côté et de dessus, d'une antenne selon l'invention alimentée par fente ;
• la figure 23 présente une vue de dessus d'un mode de réalisation particulier d'une antenne selon l'invention comprenant des moyens d'annihilation de l'effet de chaque encoche ; et
• les figures 24 et 25 présentent chacune une vue, respectivement de côté et de dessus, d'un mode de réalisation particulier d'une antenne bibande selon l'invention.

Other characteristics and advantages of the invention will appear on reading the following description of several preferred embodiments of the invention, given by way of indicative and nonlimiting examples, and of the appended drawings, in which:

• Figure 1 shows a side view of a conventional antenna supplied by coaxial probe;
• FIG. 2 shows a variation curve, as a function of frequency, of the standing wave ratio (ROS) of the conventional antenna of FIG. 1;
• Figure 3 shows a top view of an embodiment of a first antenna according to the invention;
• Figure 4 schematically shows the current lines of TM21 mode for the first antenna of Figure 3;
• FIG. 5 shows a variation curve, as a function of the frequency, of the ROS of the first antenna of FIG. 3;
• FIG. 6 shows the complete radiation diagram, for the Etheta component, of the first antenna in FIG. 3;
• Figures 7 and 8 each show a sectional view, for phi = 0 ° and 90 ° respectively, of the radiation diagram of Figure 6;
• FIG. 9 shows the complete radiation diagram, for the Ephi component, of the first antenna in FIG. 3;
• Figures 10 and 11 each show a sectional view, for phi = 45 ° and 135 ° respectively, of the radiation diagram of Figure 9;
• Figure 12 shows a top view of an embodiment of a second antenna according to the invention;
• Figure 13 schematically shows the current lines of TM01 mode for the second antenna of Figure 12;
• FIG. 14 shows a variation curve, as a function of the frequency, of the ROS of the second antenna of FIG. 12;
• FIG. 15 shows the complete radiation diagram, for the Etheta component, of the second antenna of FIG. 12;
• Figures 16 and 17 each show a sectional view, for phi = 0 ° and 90 ° respectively, of the radiation diagram of Figure 15;
• FIG. 18 shows the complete radiation diagram, for the Ephi component, of the second antenna of FIG. 12;
• Figures 19 and 20 each show a sectional view, for phi = 0 ° and 90 ° respectively, of the radiation diagram of Figure 18;
• Figures 21 and 22 each show a view, respectively from the side and from above, of an antenna according to the invention fed by slot;
• FIG. 23 presents a top view of a particular embodiment of an antenna according to the invention comprising means for annihilating the effect of each notch; and
• Figures 24 and 25 each show a view, respectively from the side and from above, of a particular embodiment of a dual-band antenna according to the invention.

The invention therefore relates to a flat printed antenna for transmitting and / or receiving microwave signals.

• une plaque de substrat diélectrique 1, d'épaisseur H = 2,28 mm et de permittivité relative ε_r = 2,2 par exemple ;
• un plan de masse 2 constitué par un premier dépôt conducteur, par exemple de cuivre, déposé sur une première face de la plaque de substrat diélectrique 1;
• un élément rayonnant 3 constitué par un second dépôt conducteur, par exemple un disque de cuivre de 73,5 mm de diamètre, déposé sur une seconde face de la plaque de substrat diélectrique 1 ; et
• une sonde coaxiale 4 permettant d'alimenter l'antenne et comprenant un conducteur externe 5 soudé au plan de masse 2 et un conducteur interne 6 soudé à l'élément rayonnant 3. Le positionnement de cette sonde coaxiale 4 permet d'obtenir l'adaptation de l'antenne.

Figure 1 shows a side view of a conventional antenna powered by a coaxial probe. The antenna includes:

• a dielectric substrate plate 1, of thickness H = 2.28 mm and of relative permittivity ε _r = 2.2 for example;
• a ground plane 2 consisting of a first conductive deposit, for example of copper, deposited on a first face of the dielectric substrate plate 1;
• a radiating element 3 constituted by a second conductive deposit, for example a copper disc 73.5 mm in diameter, deposited on a second face of the dielectric substrate plate 1; and
• a coaxial probe 4 for supplying the antenna and comprising an external conductor 5 welded to the ground plane 2 and an internal conductor 6 welded to the radiating element 3. The positioning of this coaxial probe 4 makes it possible to obtain the adaptation of the antenna.

The antenna has a fundamental mode, in which it generates a radiation diagram having a maximum in the direction perpendicular to the plane containing the radiating element, and at least one higher mode, in which it generates a radiation diagram at low elevation.

• une fréquence de résonance F1 = 1,57 GHz pour le mode fondamental TM11;
• une fréquence de résonance F2 = 2,63 GHz pour le mode supérieur TM21;
• une fréquence de résonance F3 = 3,26 GHz pour le mode supérieur TM01.

With the dimensions indicated above for the different elements 1, 2, 3 of the antenna, we obtain:

• a resonance frequency F1 = 1.57 GHz for the fundamental mode TM11;
• a resonance frequency F2 = 2.63 GHz for the higher mode TM21;
• a resonant frequency F3 = 3.26 GHz for the higher mode TM01.

FIG. 2 shows a curve of variation, as a function of frequency, of the standing wave ratio (ROS) of the conventional antenna of FIG. 1. This curve clearly shows the resonance frequencies F1 and F2.

• en relation avec les figures 3 à 11, une première antenne selon l'invention, pour laquelle le mode supérieur choisi est le mode TM21 ;
• en relation avec les figures 12 à 20, une seconde antenne selon l'invention, pour laquelle le mode supérieur choisi est le mode TM01.

According to the invention, the radiating element 3 (that is to say the copper disc in this example) is not solid but has one or more notches making it possible to control the resonance frequency of a chosen higher mode . In the following description, we present in particular:

• in relation to FIGS. 3 to 11, a first antenna according to the invention, for which the upper mode chosen is the TM21 mode;
• in relation to FIGS. 12 to 20, a second antenna according to the invention, for which the upper mode chosen is the TM01 mode.

Figure 3 shows a top view of the first antenna according to the invention. The radiating element 30 has four radial notches 31 to 34, spaced two by two angularly by about 90 °. As shown in Figure 4, for the first antenna of the invention, the current lines of the TM21 mode form a pattern which is repeated according to the quarter of the disc (the currents being represented in dotted lines). The notches 31 to 34 are placed in order to obtain maximum interception of the currents on the radiating element 30. In other words, each notch is substantially perpendicular to the current lines in one of the quarters of the disc 30.

In this example, the length of the notches is Lo = 18.375 mm and the width La = 7.35 mm. For the purpose of optimization, these values are preferably obtained using a calculation technique (implemented by software) based on a finite element method.

The purpose of the first antenna is to decrease the resonant frequency of the upper mode TM21. FIG. 5 presents a variation curve, as a function of the frequency, of the ROS of the first antenna of the invention. This FIG. 5 clearly shows that, using the notches 31 to 34, the resonance frequency of the upper mode TM21 is reduced from F2 = 2.63 GHz to F2 '= 1.662 GHz. We also note that the frequency of the fundamental mode is now located at F1 '= 1.325 GHz (instead of 1.57 GHz without the notches).

The invention therefore makes it possible to considerably reduce the size of the structure compared to a conventional antenna. In fact, to obtain a TM21 mode working at the frequency of 1.662 GHz, a solid disk would have to be had approximately a diameter of 119 mm instead of the diameter of 73.5 mm of the first antenna of the invention. Thus, in this specific example, the invention allows a reduction in the size of the antenna of approximately 40%.

FIGS. 6 and 9 each present the complete radiation diagram, for the components Etheta and Ephi respectively, of the first antenna of the invention. Figures 7 and 8 each show a sectional view, for phi = 0 ° and 90 ° respectively, of the radiation diagram of the Etheta component (Figure 6). Figures 10 and 11 each show a sectional view, for phi = 45 ° and 135 ° respectively, of the radiation pattern of the Ephi component (Figure 9).

The radiation patterns were measured at the TM21 mode resonant frequency. In order to be very meaningful, the results are presented for the two Etheta and Ephi components (with phi = 0 corresponding to the X axis of the antenna (see fig. 3), the Z axis corresponding to the normal to the plane of the antenna.

The radiation patterns are in the form of "petals" with a maximum located around theta = 45 °, with a spatial rotation phi = 45 ° between the two radiation patterns associated with the two components. The directivity is 5.56 dB. These radiation patterns correspond perfectly to those of a TM21 mode.

Figure 12 shows a top view of the second antenna according to the invention. The radiating element 40 has four circular notches 41 to 44, placed parallel to the circumference of the disc 40. As appears in FIG. 13, for the second antenna of the invention, the current lines of the TM01 mode are circular (the currents, shown in dotted lines, being arranged radially). The notches 41 to 44 are placed in order to obtain maximum interception of the currents on the radiating element 40. In other words, each notch is substantially perpendicular to the current lines in one of the quarters of the disc 40.

In this example, the internal radius of the notches is Ri = 23.52 mm, the external radius Re = 25.72 mm and the angular movement Da = 70 °. For the purpose of optimization, these values are preferably obtained using the abovementioned calculation technique based on a finite element method.

The purpose of the second antenna is to decrease the resonance frequency of the upper mode TM01. FIG. 14 shows a variation curve, as a function of the frequency, of the ROS of the second antenna of the invention. This FIG. 14 clearly shows that, using the notches 41 to 44, the resonance frequency of the upper mode TM01 is reduced from F3 = 3.26 GHz to F3 '= 2.104 GHz.

The invention therefore makes it possible to considerably reduce the size of the structure compared to a conventional antenna. In fact, to obtain a TM01 mode working at the frequency of 2.104 GHz, a solid disk would have to be obtained with an approximate diameter of 117 mm instead of the diameter of 73.5 mm of the second antenna of the invention. Thus, in this specific example, the invention again allows a reduction in the size of the antenna of approximately 40%.

Figures 15 and 18 each show the complete radiation pattern, for the Etheta and Ephi components respectively, of the second antenna of the invention. Figures 16 and 17 each show a sectional view, for phi = 0 ° and 90 ° respectively, of the radiation diagram of the Etheta component (Figure 15). Figures 19 and 20 each show a sectional view, for phi = 0 ° and 90 ° respectively, of the radiation pattern of the Ephi component (Figure 18). The radiation patterns were measured at the resonance frequency of the TM01 mode. The radiation patterns are presented in the same way as those in Figures 6 and 9.

We note that the Etheta component is in the form of a torus with a maximum located around theta = 45 °. The directivity obtained for this antenna is 6.31 dB. These radiation patterns correspond perfectly to those of a TM01 mode.

• un élément rayonnant 50 du type de celui présenté sur la figure 3 (avec quatre encoches radiales) et de diamètre W ;
• une première couche de substrat 51, de hauteur H1 et de permittivité relative ε_r1 ;
• un premier plan de masse 52 comportant une fente de couplage 53 ;
• une seconde couche de substrat 54, de hauteur H2 et de permittivité relative ε_r2 ;
• une ligne d'alimentation 55, dont l'extrémité qui s'étend au-delà de la fente 53 constitue un stub d'adaptation de longueur Lstub ;
• une troisième couche de substrat 56, de hauteur H3 et de permittivité relative ε_r3 ;
• un second plan de masse 57.

Figures 21 and 22 each show a view, respectively from the side and from above, of an antenna according to the invention fed by slot. This antenna includes the following superimposed elements:

• a radiating element 50 of the type presented in FIG. 3 (with four radial notches) and of diameter W;
• a first layer of substrate 51, of height H1 and of relative permittivity ε _r1 ;
• a first ground plane 52 comprising a coupling slot 53;
• a second layer of substrate 54, of height H2 and of relative permittivity ε _r2 ;
• a supply line 55, the end of which extends beyond the slot 53 constitutes an adaptation stub of length Lstub;
• a third substrate layer 56, of height H3 and of relative permittivity ε _r3 ;
• a second ground plane 57.

Two types of power supply have been presented above, namely by coaxial probe and by slot coupling. It is clear however that the invention is not limited to these two types of supply but can be used by any type of conventional supply (proximity coupling, supply line in the plane of the radiating element, etc.).

FIG. 23 presents a top view of a particular embodiment of an antenna according to the invention, in which each notch cooperates with means 61 for annihilating its effect. The antenna also includes means for activating / deactivating these means 61 of annihilation. These activation / deactivation means (not shown) are for example an electronic control device. In the example presented, the means for annihilating the effect of a notch comprise a varactor diode 61 connecting the two edges of this notch.

Thus, with these additional means, it is possible to envisage other types of operation of the antenna of the invention, and in particular multimode operation and multifrequency operation.

• lorsque toutes les diodes sont activées, l'antenne fonctionne dans le mode fondamental (ayant un maximum de rayonnement perpendiculaire à l'antenne),
• lorsque toutes les diodes sont désactivées, l'antenne fonctionne dans un mode supérieur choisi (ayant un maximum de rayonnement pour une faible élévation).

In multimode operation, the activation / deactivation means act simultaneously on all the diodes, so that:

• when all the diodes are activated, the antenna operates in the fundamental mode (having a maximum of radiation perpendicular to the antenna),
• when all the diodes are deactivated, the antenna operates in a selected higher mode (having a maximum of radiation for a low elevation).

In multifrequency operation for a chosen higher mode, the activation / deactivation means act on a time-varying number of diodes, so that each distinct number of diodes activated at a given instant corresponds to a particular resonant frequency of the higher mode selected.

Figures 24 and 25 each show a view, respectively from the side and from above, of a particular embodiment of a dual-band antenna according to the invention.

This dual band antenna comprises two antennas (lower 70 and upper 71) superimposed. The radiating element (for example a disk) 72 of the lower antenna 71 constitutes the ground plane of the upper antenna 71.

The lower antenna 70 comprises a ground plane 73, a substrate plate (not shown), a radiating element 72 and a first coaxial supply 74. The upper antenna 71 comprises a ground plane (constituted by the radiating element 72 of the lower antenna 70), a substrate plate (not shown) , a radiating element 75 and a second coaxial supply 76.

Each antenna 70, 71 operates independently. The two discs 72, 75 are offset so that the attack of the upper disc 75 passes through the lower disc 72 in the middle, so as to minimize the disturbance thus provided.

Claims (12)

Flat printed antenna for transmitting and / or receiving microwave signals, of the type comprising in particular: - a dielectric substrate plate (1), a ground plane (2) constituted by a first conductive deposit deposited on a first face of said dielectric substrate plate, - a radiating element (30; 40; 50) consisting of a second conductive deposit deposited on a second face of said dielectric substrate plate, - means (4) for supplying said antenna, said antenna having a fundamental mode (TM11), in which it generates a radiation diagram having a maximum in the direction perpendicular to the plane containing the radiating element, and at least one higher mode (TM21, TM01), in which it generates a low elevation radiation pattern,
characterized in that said radiating element has at least one notch (31 to 34; 41 to 44) making it possible to control the resonance frequency of a chosen higher mode. Antenna according to claim 1, characterized in that the notch (s) (31 to 34; 41 to 44) are arranged substantially perpendicular to the streamlines of said selected upper mode. Antenna according to any one of claims 1 and 2, characterized in that the dimensions of the notch (s) (31 to 34; 41 to 44) are determined using a calculation technique based on a finite element method . Antenna according to any one of claims 1 to 3, characterized in that said supply means employ a supply technique belonging to the group comprising: - feeding by coaxial probe (4); - supply by slot coupling (53); - power supply by proximity coupling; - supply by supply line in the plane of the radiating element. An antenna according to any one of claims 1 to 4, characterized in that said radiating element (30; 40; 50) is in the form of a disc. Antenna according to claim 5, characterized in that the said upper selected mode is the TM21 mode, the streamlines of which form a pattern which is repeated in each quarter of the said disc,
and in that said radiating element (30) has four radial notches (31 to 34), spaced two by two angularly by approximately 90 °, each of said notches being substantially perpendicular to the current lines in one of said quarters of the disc. Antenna according to claim 5, characterized in that the said upper selected mode is the TM01 mode, the currents of which are arranged radially,
and in that said radiating element (40) has at least one circular notch (41 to 44), the one or more notches extending over at least part of the circumference of a circle contained in said disc and having the same center as this one. Antenna according to any one of claims 1 to 7, characterized in that each notch cooperates with means (61) for annihilating its effect,
and in that it comprises means for activating / deactivating said means of annihilation. Antenna according to claim 8, characterized in that said means for annihilating the effect of a notch comprise a diode (61) connecting the two edges of said notch. Antenna according to any one of claims 8 and 9, characterized in that said radiating element has a plurality of notches,
and in that said activation / deactivation means act simultaneously on all the annihilation means (61) associated with said plurality of notches, so as to allow multimode operation such as: - when all the annihilation means are activated, the antenna operates in said fundamental mode, - when all the annihilation means are deactivated, the antenna operates in said selected upper mode. Antenna according to any one of claims 8 and 9, characterized in that said radiating element has a plurality of notches,
and in that said activation / deactivation means act on a time-varying number of annihilation means (61) associated with said plurality of notches, so as to allow multifrequency operation such that each distinct number of means d annihilation activated at a given instant corresponds to a particular resonant frequency of said chosen upper mode. Dual band antenna, characterized in that it comprises two superposed antennas, called lower (70) and upper (71) antennas, according to any one of claims 1 to 11, the radiating element (72) of said lower antenna constituting the ground plane of said upper antenna.

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