EP1225655A1 - Dual-band planar antenna and apparatus including such an antenna device - Google Patents

Abstract

The antenna (1) of this device is produced using the microstrip technique. Its patch (6) is provided with a short circuit (S) allowing the establishment of resonance modes of the quarter wave type. A slot (17) penetrates into this patch from its periphery in the vicinity of this short circuit and it separates there a first pad (31) from a second pad (33) which remains however connected to this first pad by a passage (32). Two resonance modes extend one over this first range and the other over this first range, this passage and this second range. They can be energized from the same connection line (C1). According to the invention the central frequencies and the bandwidths of these two modes are adjusted using a reactive element such as a capacitor (CR) which couples the first range to the second range in the vicinity of the origin ( 40) from the slot. The invention applies in particular to the production of a dual mode radiotelephony system using the two GSM and DCS standards. <IMAGE>

Description

The present invention relates generally to radio devices transmission, in particular portable radiotelephones, and it concerns more particularly the antennas which are produced according to the technique of microstrips to be included in such devices.

Such an antenna includes a patch which is typically constituted by etching of a metallic layer. It is called in English by "microstrip patch antenna" specialists for "pellet type antenna microstrip ".

The microstrip technique is a planar technique that applies to the both for the realization of lines transmitting signals and that of antennas realizing a coupling between such lines and radiated waves. She uses conductive tapes and / or pads formed on the upper surface of a thin dielectric substrate. A conductive layer extends over the surface bottom of this substrate and constitutes a mass of the line or the antenna. Such a patch is typically wider than such a ribbon and its shapes and dimensions are important features of the antenna. The form of the substrate is typically that of a flat rectangular sheet of thickness constant and the patch is also typically rectangular. But one varying the thickness of the substrate can widen the bandwidth of such antenna and its patch can take various forms and for example be circular. The electric field lines extend between the ribbon or the pellet and the mass layer crossing the substrate.

The antennas produced according to these techniques typically constitute, although not necessarily, resonant structures capable of being the seat standing waves allowing coupling with radiated waves in space.

Various types of resonant structures can be produced depending on the microstrip technique and can be the seat of various modes of resonance, such modes being more briefly called below "Resonances". Schematically each such resonance can be described as a standing wave formed by the superposition of two progressive waves propagating in two opposite directions on the same path, these two waves resulting from the alternative reflection of the same wave progressive electromagnetic at both ends of this path. As part from such a description, it is considered that this last wave propagates in an electromagnetic line which would be constituted by the mass, the substrate and the patch and which would define a linear path devoid of width. Actually a such wave has wave surfaces which extend transversely across the entire section offered to them by the antenna so this description simplifies the reality in a sometimes excessive way. As far as it can be considered linear, this path can be straight or curved. He will be hereinafter referred to as the "resonance path". The frequency of resonance is inversely proportional to the time taken by the traveling wave considered above to travel this route.

A first type of resonance can be called "half wave". In this type the length of the resonance path is typically substantially equal to one half wavelength i.e. half the wavelength of the wave progressive considered above. The antenna is then called "half-wave". This guy of resonance can be defined generally by the presence of a electric current node at each of the two ends of such a path including the length can therefore also be equal to said half-wavelength multiplied by an integer other than one. This number is typically odd. The coupling with the radiated waves takes place at at least one of the two ends of this path, these ends being located in regions where the amplitude of the electric field prevailing in the substrate is maximum.

A second type of resonance which can be obtained within the framework of this same technique can be called "quarter wave". It differs from said half-wave type on the one hand by the fact that the resonance path typically has a length substantially equal to a quarter wave, i.e. a quarter of the wavelength defined above. For this, the resonant structure must have a short circuit at one end of this path, the word short circuit designating a connection connecting the ground and the patch. In addition this short circuit must have an impedance small enough to be able to impose such resonance. This type of resonance can be generally defined by the presence of an electric field node fixed by such a short circuit to the near an edge of the patch and by an electric current node located the other end of the resonance path. The length of the latter can therefore also be equal to a whole number of half-wavelengths added to said quarter wavelength. The coupling with the radiated waves in the space is made on an edge of the patch in a region where the amplitude of the electric field through the substrate is large enough.

Resonances of other more or less complex types can be established in antennas of this kind, each resonance being characterized by a distribution of electric and magnetic fields which oscillate in an area of space including the antenna and its immediate vicinity. They depend in particular on the configuration of the pellets, the latter possibly in particular present slots, possibly radiative. They depend also of the possible presence and location of short circuits as well as electrical models representative of these short circuits when these are imperfect short circuits, i.e. when they are not similar, even approximately, to perfect short-circuits whose impedances would be zero.

The present invention finds application in various types of devices such as portable radios, base stations for mobile phones, automobiles and airplanes or air missiles. In the case of a portable radiotelephone, the continuous nature of the lower mass layer of an antenna produced using the microstrip technique limits the power of radiation which is intercepted by the body of the user of the device when the latter is operating in transmission. In the case of automobiles and especially in that of airplanes or missiles whose outer surface is metallic and has a curved profile to obtain a low drag aerodynamic, the antenna can be conformed to this profile so as not to bring up annoying additional aerodynamic drag.

• elle doit être bi-fréquence c'est à dire qu'elle doit pouvoir émettre et/ou recevoir efficacement des ondes rayonnées sur deux fréquences séparées par un écart spectral important,
• elle doit pouvoir être raccordée à un organe de traitement de signal à l'aide d'une seule ligne de raccordement pour l'ensemble des fréquences de travail d'un dispositif de transmission sans donner naissance dans cette ligne à un taux d'ondes stationnaires parasites gênant,
• et il ne doit pas être nécessaire pour cela d'utiliser un multiplexeur ou démultiplexeur en fréquence.

This invention relates more particularly to the case where an antenna produced using the microstrip technique must have the following qualities:

• it must be dual-frequency, that is to say that it must be able to efficiently transmit and / or receive radiated waves on two frequencies separated by a significant spectral difference,
• it must be possible to be connected to a signal processor using a single connection line for all the working frequencies of a transmission device without giving rise in this line to a standing wave rate annoying parasites,
• and it should not be necessary for this to use a frequency multiplexer or demultiplexer.

Many known antennas have been produced or proposed in the framework of the microstrip technique so as to present these three qualities. They differ from each other in the means used to obtain several resonant frequencies. Three such antennas will be examined:

A first such known antenna is described in the patent document US-A 4,766,440 (Gegan). The patch 10 of this antenna has a shape general rectangular allowing this antenna to present two half wave resonances whose paths are established along a length and a width of this patch. Furthermore it has a curved slit in the shape of U which is entirely internal to this patch. This slit is radiative and brings up an additional mode of resonance established according to a other route. It also allows, by a suitable choice of its shape and its dimensions, to bring the frequencies of the resonance modes to desired values which gives the possibility of emitting a polarized wave circular thanks to the association of two modes having the same frequency and linear polarizations crossed and phase shifted by 90 °. The device coupling has the form of a line which is produced according to the technique of microstrips but which is also said to be coplanar, this because the microstrip extends in the plane of the patch and enters between two notches of the latter. This device is provided with transformation means impedance to adapt it to the different input impedances respectively presented by the line at the different resonance frequencies used as working frequencies.

• La nécessité de prévoir des moyens de transformation d'impédance complique la réalisation.
• L'ajustement précis des fréquences de résonance à des valeurs souhaitées est difficile à réaliser.

This first known antenna has the following disadvantages in particular:

• The need to provide means for impedance transformation complicates the implementation.
• It is difficult to precisely adjust the resonant frequencies to desired values.

A second known antenna is described in the patent document USA 4,692,769 (Gegan). In a first embodiment, the tablet of this antenna has the shape of a circular disc 10 allowing this antenna to present two half wave resonances. The coupling system presents the form of a line 16 constituting a quarter wave transformer and is connecting at an interior point to the area of the patch so as to give the real part of the antenna input impedance values substantially equal for these two resonances. Line 16 is made using the technique microstrips. Two slits are formed in the conductive layer of this pastille and enter the area thereof from its periphery to delimit between them the ribbon of a terminal segment of this line. One of these two slits is continued by an extension which constitutes a slit impedance matching 28.

• La réalisation des moyens de transformation d'impédance est délicate.
• L'ajustement précis des fréquences de résonance à des valeurs souhaitées est difficile à réaliser.

This second known antenna has the following disadvantages in particular:

• The realization of the means of impedance transformation is delicate.
• It is difficult to precisely adjust the resonant frequencies to desired values.

A third known dual-frequency antenna differs from the previous ones by the use of a quarter wave resonance. It is described in an article: IEEE ANTENNAS AND PROPAGATION SOCIETY INTERNATIONAL SYMPOSIUM DIGEST, NEWPORT BEACH, JUNE 18-23, 1995, pages 2124-2127 Boag et al "Dual Band Cavity-Backed Quarter-wave Patch Antenna". A first resonant frequency is defined by the dimensions and characteristics of the substrate and the patch of this antenna. A resonance substantially the same type is obtained at a second frequency on the same resonance path thanks to the use of an adaptation system.

• L'écart entre les deux fréquences de résonance est trop petit dans certains cas d'application.
• La nécessité d'utiliser un système d'adaptation complique la réalisation de l'antenne.
• Il peut en être de même de la réalisation du dispositif de couplage de l'antenne sous la forme d'une ligne coaxiale.

This third known antenna has the following disadvantages in particular:

• The difference between the two resonant frequencies is too small in certain application cases.
• The need to use an adaptation system complicates the creation of the antenna.
• It can be the same for the realization of the antenna coupling device in the form of a coaxial line.

• permettre de réaliser simplement une antenne bi-fréquence,
• permettre de choisir plus librement que précédemment le rapport des fréquences centrales de deux bandes de travail d'un dispositif de transmission, et plus particulièrement de réaliser pour ce dispositif une antenne telle que le rapport de deux fréquences de résonance utiles de cette antenne soit compris entre 1,25 et 5 environ et notamment voisin de 2,
• donner à cette antenne une bande passante suffisamment large autour de chacune de ces deux fréquences de résonance pour permettre de situer dans chacune de ces deux bandes une fréquence d'émission et une fréquence de réception de ce dispositif,
• permettre un ajustement facile et précis de ces deux fréquences de résonance,
• permettre d'utiliser un dispositif de couplage unique et facilement adaptable en impédance pour chacune de ces deux fréquences de résonance, et
• limiter les dimensions de cette antenne.

The present invention has in particular the following aims:

• allow the simple realization of a dual-frequency antenna,
• allow to choose more freely than previously the ratio of the central frequencies of two working bands of a transmission device, and more particularly to produce for this device an antenna such that the ratio of two useful resonant frequencies of this antenna is between 1.25 and 5 approximately and in particular close to 2,
• give this antenna a sufficiently wide bandwidth around each of these two resonant frequencies to make it possible to locate in each of these two bands a transmission frequency and a reception frequency of this device,
• allow easy and precise adjustment of these two resonance frequencies,
• allow the use of a single coupling device which is easily adaptable in impedance for each of these two resonant frequencies, and
• limit the dimensions of this antenna.

• une masse conductrice
• un substrat diélectrique formé sur cette masse, et
• une pastille formée sur ce substrat. Cette pastille a une aire et une périphérie. Elle présente une fente séparatrice ayant de préférence une origine située sur cette périphérie et un fond situé dans cette aire, ce fond laissant un passage entre lui et cette périphérie. Cette fente pénètre dans cette aire à partir de cette origine et coopère avec cette périphérie pour délimiter dans cette aire une première plage et une deuxième plage, ces deux plages étant conductrices et étant électriquement mutuellement séparées par cette fente et raccordées par ce passage.

For these purposes it notably has a planar antenna. This antenna includes mutually superimposed layers constituting respectively:

• a conductive mass
• a dielectric substrate formed on this mass, and
• a pellet formed on this substrate. This patch has an area and a periphery. It has a separating slot preferably having an origin located on this periphery and a bottom located in this area, this bottom leaving a passage between it and this periphery. This slot enters this area from this origin and cooperates with this periphery to delimit in this area a first area and a second area, these two areas being conductive and being electrically separated by this slot and connected by this passage.

• une couche diélectrique formée sur cette pastille, et
• une armature conductrice formée sur cette couche diélectrique.

According to this invention, this antenna also includes a reactive element which mutually couples these two conductive pads, and this element is preferably flat, for example of the type known as “Surface Mounted Component”, so as not to form a sensitive projection on the planar structure of the antenna. It is for example constituted by a capacitor having an area less than each of said areas of the first and second ranges. This area is inside the area of the patch and it extends continuously over the first area, over the separating slot at a distance from the bottom thereof, and over the second area. This capacitor is formed by said mutually superimposed layers cooperating with said pellet and constituting respectively:

• a dielectric layer formed on this patch, and
• a conductive armature formed on this dielectric layer.

A flat reactive element may, however, have another shape for perform a coupling according to this invention. It can for example be constituted by an interdigitated capacity integrated in the layout of the separating slot thanks to an adequate cutting of the edges opposite the two areas of the pellet.

Preferably, this antenna also includes a short circuit connecting electrically the first conductive ground to earth in the vicinity of the origin of the separating slit.

More preferably, the area of the capacitor is between 1% and 25% of that of the pastille.

Preferably finally the origin of the separating slit is close to the short circuit so as to give the two resonances two resonance paths respective both extending from this short circuit, one of these two paths extending only in the first range and the other extending in this first range and in the second range.

Various aspects of the present invention will be better understood using the description below and attached schematic figures. When elements are represented in several of these figures, they are designated by the same reference numbers and / or letters.

FIG. 1 represents a perspective view of a device for transmission made according to this invention.

FIG. 2 represents a top view of an antenna produced according to this invention and analogous to that of the device of FIG. 1.

FIG. 3 represents a partial view in vertical section of the antenna of Figure 2.

Figure 4 reproduces the view of Figure 2 to designate different dimensions of the same antenna.

• Un substrat diélectrique 2 présentant deux surfaces principales mutuellement opposées s'étendant selon des directions horizontales constituant une direction longitudinale DL et une direction transversale DT. Ce substrat peut présenter des formes diverses comme précédemment exposé. Ses deux surfaces principales constituent respectivement une surface inférieure et une surface supérieure.
• Une couche conductrice inférieure s'étendant par exemple sur la totalité de cette surface inférieure et constituant une masse 4 de cette antenne.
• Une couche conductrice supérieure s'étendant sur une aire de cette surface supérieure au-dessus de la masse 4 de manière à constituer une pastille 6. De manière générale cette pastille a une longueur et une largeur s'étendant respectivement selon les directions DL et DT, et sa périphérie peut être considérée comme constituée par quatre bords. L'un de ces bords s'étend de manière générale selon la direction DT et constitue un bord arrière incluant deux segments 10 et 11. Un bord avant 12 est opposé à ce bord arrière. Un premier et un deuxième bords latéraux 14 et 16 s'étendent de manière générale selon la direction DL et joignent ce bord arrière à ce bord avant.
• Enfin un court-circuit raccordant électriquement la pastille 6 à la masse 4 à partir du segment 10 du bord arrière de cette pastille. Dans le mode représenté de mise en oeuvre de cette invention, ce court-circuit est formé par une couche conductrice S s'étendant sur une surface de tranche du substrat 2, surface qui est typiquement plane et constitue alors un plan de court-circuit. Il impose à au moins une résonance de l'antenne de présenter au moins approximativement un noeud de champ électrique au voisinage du segment 10 de manière à être sensiblement du type quart d'onde. Les bords arrière, avant et latéraux et les directions longitudinale et transversale sont définis par la position d'un tel court-circuit dans la mesure où ce court-circuit est suffisamment important, c'est à dire notamment où son impédance est suffisamment basse pour imposer à l'antenne l'existence d'une résonance présentant un tel noeud de champ électrique.

In accordance with FIGS. 1 to 3 and in a manner known per se, the resonant structure of an antenna according to this invention comprises the following elements:

• A dielectric substrate 2 having two mutually opposite main surfaces extending in horizontal directions constituting a longitudinal direction DL and a transverse direction DT. This substrate can have various shapes as previously exposed. Its two main surfaces respectively constitute a lower surface and an upper surface.
• A lower conductive layer extending for example over the whole of this lower surface and constituting a mass 4 of this antenna.
• An upper conductive layer extending over an area of this upper surface above the mass 4 so as to constitute a patch 6. In general, this patch has a length and a width extending respectively in the directions DL and DT , and its periphery can be considered as constituted by four edges. One of these edges generally extends in the direction DT and constitutes a rear edge including two segments 10 and 11. A front edge 12 is opposite this rear edge. First and second lateral edges 14 and 16 extend generally in the direction DL and join this rear edge to this front edge.
• Finally a short circuit electrically connecting the patch 6 to ground 4 from segment 10 of the rear edge of this patch. In the illustrated embodiment of this invention, this short circuit is formed by a conductive layer S extending over a wafer surface of the substrate 2, a surface which is typically planar and then constitutes a short circuit plane. It requires at least one resonance of the antenna to present at least approximately an electric field node in the vicinity of segment 10 so as to be substantially of the quarter wave type. The rear, front and side edges and the longitudinal and transverse directions are defined by the position of such a short circuit insofar as this short circuit is sufficiently large, that is to say in particular where its impedance is sufficiently low to impose on the antenna the existence of a resonance having such an electric field node.

The antenna further includes a coupling system. This system has the form of a microstrip line. This line includes on the one hand a main conductor consisting of a C1 coupling strip extending over the upper surface of the substrate. This ribbon is connected to the patch 6 at a point connection 18 which can for example be located on the first lateral edge 14. The distance from the rear edge 10 to this point constitutes a dimension of connection L4. This line also has a ground conductor constituted by layer 4. In FIG. 1, it is only to simplify the drawing that the substrate 2 is not represented under the ribbon C1 and that this line is shown with a very small length. This system is part of a connection assembly which connects the resonant structure of the antenna to a signal processing device T, for example for driving one or more resonances of the antenna from this organ in case it is a transmitting antenna. In addition to this system, the connection set typically comprises a connection line which is external to the antenna. This line can in particular be of the coaxial type, of the microstrip type or of the coplanar type. In Figure 1 it has been symbolically represented under the form of two conductive wires C2 and C3 respectively connecting the ground 4 and the ribbon C1 at the two terminals of the signal processing member T. But it must be understood that this line would in practice be preferably carried out under the shape of a microstrip line or a coaxial line.

The signal processor T is adapted to operate at predetermined working frequencies which are at least close to frequencies useful of the antenna, i.e. which are included in bandwidths centered on such useful frequencies, these frequencies being those of certain at least antenna resonance modes. It can be composite and then have an element permanently tuned to each of these working frequencies. It can also include a tunable element on the various working frequencies.

A separating slit 17 enters the area of the patch 6 from a origin 40 separating two segments 10 and 11 from the rear edge thereof. extends to a bottom 15 located at a distance from the lateral edges 14 and 16 and from the front edge 12. It partially separates from each other a first and a second ranges 31 and 33 which are connected beyond this bottom by a passage 32. It comprises for example three straight segments of length neighbors, a first segment extending from the origin 40 towards the edge front 12 approaching the second lateral edge 16, a second segment extending parallel to this front edge towards this lateral edge, and a third segment extending parallel to this first segment up to background 15. The distances from this background to these two edges are respectively less than half the length and width of the patch. A width of this slit is defined at each point of its length. She is by example, although not necessarily, uniform.

The presence of this slot reveals two modes of resonance constituting respectively a primary resonance having a frequency of primary resonance and a secondary resonance having a frequency of secondary resonance. The primary resonance extends over the entire patch 6. It is approximately of the quarter wave type, its path of resonance extending from short circuit S to segment 11 of the rear edge. His coupling with radiated waves is mainly done from this segment and the adjacent part of the second lateral edge 16. The resonance secondary extends only on the range 31. It is also approximately quarter-wave type, its resonance path extending from short circuit S to front edge 12. Its coupling with radiated waves is mainly done from this edge and from the adjacent part of the first lateral edge 14.

As shown in FIG. 1 only, the first area 31 can have a protrusion 34 extending in the plane of the patch 6, projection on the first lateral edge 14, in the vicinity of the front edge 12. It has Indeed, it was found that such a projection could facilitate the adjustment of the resonant frequencies of the antenna.

• une couche diélectrique CD formée sur cette pastille, et
• une armature conductrice CA formée sur cette couche diélectrique.

In the context of this invention, the antenna 1 further includes a reactive coupling element which is preferably flat and which is for example constituted by a capacitor CR. This capacitor has an area less than each of the areas of the first and second areas 31 and 33, this area being inside the area of the patch 6 and extending continuously over this first area, on the separating slot. 17 away from the bottom 15 and on this second beach. As shown in FIG. 3, it is formed by mutually superimposed layers cooperating with the patch 6 and constituting respectively:

• a dielectric layer CD formed on this patch, and
• a conductive armature CA formed on this dielectric layer.

The area of this capacitor is for example rectangular and close to 5% of that of this pastille. It preferably extends to contact or immediate vicinity of the periphery of this patch.

• Lors de la réalisation de l'antenne, il est facile d'ajuster la longueur et la largeur du condensateur, ce qui permet d'ajuster ce couplage et d'agir ainsi sur les paramètres électriques de l'antenne.
• La présence de ce condensateur allonge les longueurs électriques de l'antenne. C'est à dire qu'elle permet de diminuer l'encombrement de l'antenne tout en conservant des valeurs souhaitées pour les fréquences de résonance.
• Elle élargit les bandes passantes des deux résonances sans augmenter sensiblement les taux d'ondes stationnaires.

The coupling reactive element constituted by the capacitor CR creates a coupling between the first and second conductive pads 31 and 33, which provides the following three advantages:

• When making the antenna, it is easy to adjust the length and the width of the capacitor, which makes it possible to adjust this coupling and thus act on the electrical parameters of the antenna.
• The presence of this capacitor lengthens the electrical lengths of the antenna. That is to say that it makes it possible to reduce the bulk of the antenna while retaining desired values for the resonance frequencies.
• It widens the bandwidths of the two resonances without significantly increasing the standing wave rates.

• La masse de l'antenne recouvre la face inférieure du substrat.
• Le court-circuit S occupe toute la largeur du segment 10 qui constitue un bord arrière de la première plage 31.
• Composition du substrat 2: mousse ayant une permittivité relative de 1,07 et un facteur de dissipation de 0,0002,
• Epaisseur de ce substrat : H1 = 7 mm,
• Composition des couches conductrices : cuivre,
• Epaisseur de ces couches : 17 microns,
• Largeur du conducteur C1 : 5 mm,
• Cote de raccordement : L4 = 10 mm,
• Longueur de la pastille : L1 = 35 mm,
• Largeur de la pastille : W1 = 24 mm,
• Largeur du segment 11: W5 = 16 mm,
• Largeur de la fente 17: 0,75 mm,
• Tracé de cette fente : L5 = 13.mm, W2 = 9 mm, W3 = 8 mm, L2 = 6.mm, W4 = 3 mm,
• Permittivité relative de la couche CD du condensateur CR égale à 2,2,
• Epaisseur de cette couche: H2 = 0,1 mm,
• Longueur de ce condensateur: L3 = 6 mm,
• Largeur de ce condensateur: W6 = 7 mm,
• Impédance d'entrée : 50 ohms,
• Fréquence de résonance primaire : F1 = 965 MHz,
• Fréquence de résonance secondaire : F2 = 1860 MHz,
• Largeurs des bandes passantes autour des fréquences primaire et secondaire : 9,1% et 19% de ces fréquences, respectivement, ces largeurs étant mesurées à - 6 dB.

In the context of the embodiment shown in FIG. 2, various arrangements, compositions and values will be indicated below by way of examples:

• The mass of the antenna covers the underside of the substrate.
• The short-circuit S occupies the entire width of the segment 10 which constitutes a rear edge of the first area 31.
• Composition of substrate 2: foam having a relative permittivity of 1.07 and a dissipation factor of 0.0002,
• Thickness of this substrate: H1 = 7 mm,
• Composition of conductive layers: copper,
• Thickness of these layers: 17 microns,
• Conductor width C1: 5 mm,
• Connection dimension: L4 = 10 mm,
• Pellet length: L1 = 35 mm,
• Pellet width: W1 = 24 mm,
• Width of segment 11: W5 = 16 mm,
• Width of slot 17: 0.75 mm,
• Plot of this slot: L5 = 13.mm, W2 = 9 mm, W3 = 8 mm, L2 = 6.mm, W4 = 3 mm,
• Relative permittivity of the CD layer of the CR capacitor equal to 2.2,
• Thickness of this layer: H2 = 0.1 mm,
• Length of this capacitor: L3 = 6 mm,
• Width of this capacitor: W6 = 7 mm,
• Input impedance: 50 ohms,
• Primary resonance frequency: F1 = 965 MHz,
• Secondary resonance frequency: F2 = 1860 MHz,
• Bandwidths around the primary and secondary frequencies: 9.1% and 19% of these frequencies, respectively, these widths being measured at - 6 dB.

In the absence of the capacitor CR, these resonant frequencies and these bandwidths would have been, respectively, F1 = 1120 MHz, F2 = 2270 MHz, 16% and 10%.

Claims (9)

Planar antenna, this antenna including mutually superimposed layers constituting respectively: a conductive mass (4), a dielectric substrate (2) formed on this mass, and a tablet (6) formed on this substrate, this tablet having an area and a periphery (10,12,14,16), this tablet having a separating slot (17) having an origin (40) situated on this periphery and a bottom (15) located in this area, this bottom leaving a passage (32) between it and this periphery, this slot penetrating into this area from this origin and cooperating with this periphery to delimit in this area a first area (31) and a second area (33), these two areas being conductive and being electrically mutually separated by this slot and connected by this passage, these areas having respective areas, this antenna being characterized in that it also includes a flat reactive element (CR) mutually coupling the two said conductive pads (31, 33). Antenna according to claim 1, this antenna being characterized in that said flat reactive element is a capacitor (CR) having an area less than each of said areas of the first and second ranges, this area being inside said area of the pad (6) and extending continuously over said first area (31), over said separating slot (17) at a distance from said bottom (15) and over said second area (33), this capacitor being formed by said mutually superimposed layers cooperating with said patch (6) and constituting respectively: a dielectric layer (CD) formed on this patch, and a conductive armature (CA) formed on this dielectric layer. Antenna according to claim 2, this antenna being characterized in that said area of the capacitor (CR) is between 1% and 25% of said area of the patch (6). Antenna according to claim 1, this antenna being characterized in that said flat reactive element (CR) is located in the vicinity of said origin (40) of the separating slot (17). Antenna according to claim 4, this antenna being characterized in that it further includes a short circuit (S) electrically connecting said first conductive pad (31) to said ground (4) in the vicinity of said origin (40) of the separating slot (17). Dual-band transmission device, this device comprising: a signal processing device (T) adapted to be tuned in frequency in two working bands extending respectively around two predetermined center frequencies to transmit and / or receive an electrical signal in each of these two bands, an antenna (1) including a patch (6) and a mass (4) according to the microstrip technique, and an antenna connection assembly including electrical conductors (C1, 4, C2, C3) connecting this processing member to this antenna to couple said electrical signal to waves radiated around each of the two said center frequencies, some of these conductors (C1,4) being connected directly to this antenna, a separating slot (17) at least partially isolating two conductive pads (31, 33) in said patch (6) so as to give this antenna two resonances differing from one another by areas occupied respectively by these two resonances in this patch, these two resonances being respectively centered in the two said working bands,
this transmission device being characterized in that it further includes a reactive element (CR) external to said antenna connection assembly and mutually coupling the two said conductive pads (31, 33) of the antenna. Transmission device according to claim 6, said antenna including mutually superimposed layers constituting respectively: said mass (4), a dielectric substrate (2) formed on this mass, and said patch (6) formed on this substrate, this patch having an area and a periphery (10,12,14,16), this patch having said separating slot (17), this slot having an origin (40) located on this periphery and a bottom (15) located in this area, this bottom leaving a passage (32) between it and this periphery, this slot penetrating into this area from this origin and cooperating with this periphery to delimit in this area a first so-called range (31) and a second said area (33), these two areas being conductive and being electrically mutually separated by this slot and connected by this passage, these areas having respective areas, this antenna further including a short circuit (S) formed in said first area on said periphery of the patch (6), this short circuit and said separating slot allowing two resonances to be established in this antenna, one in the month of these two resonances being of the quarter wave type with an electric field node at least virtual fixed by this short-circuit, one of these two resonances constituting a primary resonance and having a primary frequency (F1) substantially equal at one of the two said central frequencies, the other of these two resonances constituting a secondary resonance having a secondary frequency (F2) substantially equal to the other of these two central frequencies, said connection assembly coupling said antenna to said member signal processing (T) around each of the two said central frequencies,
said transmission device being characterized in that said reactive element (CR) is a flat element extending substantially in the plane of said pellet (6). Transmission device according to claim 7, this device being characterized in that said flat reactive element is a capacitor (CR), this capacitor having an area less than each of said areas of the first and second ranges, this area being inside said area of the patch (6) and extending continuously over said first area (31), over said separating slot (17) at a distance from said bottom (15) and over said second area (33), capacitor being formed by said mutually superimposed layers cooperating with said pad (6) and constituting respectively: a dielectric layer (CD) formed on this patch, and a conductive armature (CA) formed on this dielectric layer. Transmission device according to claim 7, said conductors (C1,4) included in the antenna connection assembly and connected directly to the antenna being only: a strip (C1) formed in the same conductive layer as said patch (6), and a mass formed in the same conductive layer (4) as said mass of the antenna so as to constitute with this ribbon a line of the microstrip type.

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