EP0954055B1 - Dual-frequency radiocommunication antenna realised according to microstrip technique - Google Patents

Abstract

The same patch antenna produces a quarter wave resonance across one dimension and a half wave resonance across the second dimension.

Description

The present invention relates generally to radio communication devices, in particular portable radio telephones, and more particularly to antennas which are produced according to the microstrip technique to be included in such devices. Such an antenna comprises a patch which is typically formed by etching a metal layer. It is called in English by specialists "microstrip patch antenna" for "microstrip pellet antenna".

The microstrip technique is a planar technique that applies both to the realization of lines transmitting signals and to that of antennas coupling between such lines and radiated waves. It uses ribbons and / or conductive pads formed on the upper surface of a thin dielectric substrate which separates them from a conductive layer extending on the lower surface of this substrate and constituting a mass of the line or antenna . Such a pellet is typically wider than such ribbon and its shapes and dimensions are important features of the antenna. The shape of the substrate is typically that of a rectangular flat sheet of constant thickness and the pellet is also typically rectangular. But this is not an obligation. In particular, it is known that a variation in the thickness of the substrate, for example according to an exponential law, makes it possible to widen the bandwidth of such an antenna and that the shape of the wafer may in particular be circular. The electric field lines extend between the ribbon or pellet and the ground layer as they pass through the substrate.

This technique differs from various other techniques also using conductive elements on a thin substrate, and in particular that of coplanar lines in which the electric field is established on the upper surface of the substrate and symmetrically between a a central conductive ribbon and two conductive pads located on either side of the ribbon from which they are respectively separated by two slots. In the case of an antenna a pellet is surrounded by a continuous conducting pad from which it is separated by a slot.

Antennas made according to these techniques typically, although not necessarily, resonant structures capable of being the seat of standing waves for coupling with the radiated waves.

In a schematic way, a distinction can be made between various types of resonant structures that can be made according to the microstrip technique, these types respectively corresponding to various modes of resonance of these structures. A first type is the most common and can be called "half wave". Given that a dimension of the pellet constitutes a length and extends along a so-called longitudinal direction, this length is typically substantially equal to a half wave, ie to half the wavelength of a wave. electromagnetic propagation propagating in this direction in the line formed by the mass, the substrate and the pellet. The antenna is then called "half wave". This type of resonances can be defined in a general manner by the presence of an electrical current node at each of the two ends of this length which can also be equal to said half wave multiplied by an integer other than one. This number is typically odd. The coupling with the radiated waves is at the ends of this length, these ends being located in the regions where the amplitude of the electric field prevailing in the substrate is maximum.

A second type of resonant structure that can be produced using this same technique can be called "quarter wave". It differs from said half-wave type on the one hand by the fact that the pellet typically has a length substantially equal to a quarter wave, that is to say a quarter of a wavelength, this length of the pellet and this wavelength being defined as above, the antenna then being called "quarter wave". It differs on the other hand by the fact that a large short circuit is made at one end of this length between the mass and the chip so as to impose a resonance mode of a type called "quarter wave" . This type of resonance can be defined generally by the presence of an electric field node fixed by this short circuit at one end of the length of the chip and by an electrical current node at the other end. of this length. The latter can therefore also be equal to an integer number of half-waves adding to said quarter wave. The coupling with the radiated waves is at the other end of this length, this other end being located in the region where the amplitude of the electric field through the substrate is maximum.

• de la configuration des pastilles, ces dernières pouvant notamment présenter des fentes, éventuellement radiatives,
• de l'éventuelle présence et de la localisation de courts-circuits ainsi que des modèles électriques représentatifs de ces courts-circuits, ces derniers n'étant pas toujours assimilables, même approximativement, à des courts-circuits parfaits dont les impédances seraient nulles,
• et des dispositifs de couplage qui ont été inclus dans ces antennes pour permettre de coupler leurs structures résonantes à un organe de traitement de signal tel qu'un émetteur, ainsi que de la localisation de ces dispositifs.

Still other modes of resonance can be established in planar antennas. These modes depend in particular:

• the configuration of the pellets, the latter may in particular have slots, possibly radiative,
• the possible presence and location of short-circuits as well as electrical models representative of these short-circuits, the latter being not always comparable, even approximately, to perfect short circuits whose impedances would be zero,
• and coupling devices which have been included in these antennas to enable coupling of their resonant structures to a signal processor such as an emitter, as well as the location of these devices.

Moreover, for a given antenna configuration, several resonance modes may appear and allow the use of the multi-frequency antenna corresponding to these modes.

The present invention will notably be characterized by the choice of certain "resonance paths" which will be specified below. This is why the meaning given below to the expression "resonance path" will be defined as follows:

Each mode of resonance can be described as resulting from the superposition of two waves propagating in two opposite directions on the same path by reflecting alternately at both ends of this path. This path is imposed by the constituent elements of the antenna. It constitutes said "resonance path" for this resonance mode. It is rectilinear and longitudinal in the case of half-wave and quarter-wave antennas previously mentioned. But it can also conform to a curved radiative slot. In all cases, the resonance frequency is inversely proportional to the time during which a progressive wave considered above traverses this resonance path. The expression "resonance mode" will sometimes be replaced hereinafter by the term "resonance".

The coupling of an antenna to a signal processing element such as an emitter is typically done via a connection assembly comprising a coupling device included in this antenna, and a connection line external to this antenna and connecting the coupling device to the signal processing member.

In the case of a transmitting antenna with a resonant structure, the respective functions of the coupling device, the connection line and the antenna are as follows: the function of the connection line is to carry a radio frequency signal or microwave from the transmitter to the antenna terminals. Throughout such a line the signal propagates in the form of a progressive wave without undergoing, at least in principle, significant modification of its characteristics. The function of the coupling device is to transform the signal supplied by the connecting line so that this signal excites a resonance of the antenna, that is to say that the energy of the progressive wave carrying this signal is transferred to a standing wave established in the antenna with characteristics defined by the latter. This transfer is generally imperfect, that is to say that the coupling device reflects a portion of the energy to the connection line which gives rise in the latter to a parasitic standing wave. The corresponding stationary wave ratio varies according to the frequency and the diagram of this variation defines the bandwidth (s) of the antenna. As for the antenna, it transfers the energy of the useful standing wave to a radiated wave in space. The signal provided by the transmitter thus undergoes a first transformation to change from the shape of a progressive wave to that of a standing wave, then a second transformation which gives it the shape of a radiated wave. In the case of a receiving antenna the signal takes the same forms in the same organs but it takes them in reverse order.

The coupling device and the connecting line may be produced using a technique other than that of microstrips, for example in the form of coaxial or coplanar lines. Their natures and their dimensions are chosen so as to obtain a mutual adaptation of the impedances of the various organs traversed by the signals, this to limit parasitic reflections.

With reference to the case of transmitting antennas, the connection assembly of an antenna is often designated as constituting a supply line of this antenna.

The present invention relates to antennas suitable for inclusion in various types of apparatus. These devices include portable radiotelephones, base stations for the latter, automobiles and aircraft or air missiles. In the case of a portable radiotelephone, the continuous nature of the lower ground layer of an antenna made using the microstrip technique makes it possible to easily limit the radiation power intercepted by the body of the user of the apparatus. In the case of automobiles and especially in the case of aircraft or missiles whose outer surface is metallic and has a curved profile to obtain a low aerodynamic drag, the antenna can be conformed to this profile so as not to appear additional aerodynamic drag annoying.

• elle doit être bifréquence 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 fonctionnement d'un dispositif de radiocommunication 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 of this kind must have the following qualities:

• it must be dual frequency, ie it must be able to transmit and / or efficiently receive waves radiated on two frequencies separated by a large spectral difference,
• it must be capable of being connected to a signal processing unit by means of a single connecting line for all the operating frequencies of a radiocommunication device without giving rise in this line to a standing wave ratio troublesome parasites,
• and it must not be necessary for this purpose to use a frequency multiplexer or demultiplexer.

Many known dual-frequency antennas have been made or proposed in the context of the microstrip technique. They differ from each other by the means used to obtain several resonant frequencies. Four such antennas will be examined:

A first such known antenna is described in the document ORMISTON TD AND AL: "microstrip short-circuit patch design equations" microwave and optical technology letters, vol. 16, No. 1, September 1997, pages 12-14 , XP000198277 . The pellet of this antenna has a rectangular shape allowing this antenna to have a quarter-wave resonance along a resonance path extending between two opposite edges of the pellet. This antenna has the disadvantage of only having a single quarter wave resonance.

A second such known antenna is described in the patent document US-A-4,766,440 (Gan ). The patch 10 of this antenna has a generally rectangular shape allowing this antenna to present two half-wave resonances whose paths are established along a length and a width of this patch. Moreover, it has a U-shaped curved slot which is entirely internal to this pellet. This slot is radiative and shows an additional resonance mode established in another path. 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 circularly polarized wave through the combination of two modes having a same frequency and crossed linear polarizations. The coupling device has the form of a line which is made according to the microstrip technique but which is also said to be coplanar, because the microstrip extends in the plane of the pellet and penetrates between two notches of the latter. This device is provided with impedance transformation means to adapt it to the different input impedances respectively presented by the line at different resonance frequencies used as operating 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 second known antenna has the following drawbacks:

• The need to provide impedance transformation means complicates the implementation.
• Accurate adjustment of the resonance frequencies to desired values is difficult to achieve.

A third known antenna differs from the previous one by the use of a single resonance path. It is described in the patent document US-A-4,771,291 (LO et al ). Its pellet has punctual short circuits and slots extending in line segments respectively inner to the pellet. These slots and short circuits make it possible to reduce the difference between two frequencies corresponding to two resonances having said path in common but two mutually different respective modes which are designated by the digits (0,1) and (0,3). that is to say that this common path is occupied by a half wave or three half-waves depending on the mode considered. The ratio between these two frequencies can thus be lowered from 3 to 1.8. Punctual short circuits consist of conductors crossing the substrate.

• L'encombrement correspond à trois demi-ondes.
• L'incorporation des courts-circuits ponctuels complique la réalisation de l'antenne.
• Le dispositif de couplage de l'antenne sous la forme d'une ligne coaxiale nécessite un ajustage précis de la position de la structure coaxiale traversant le substrat, pour obtenir une bonne adaptation à une ligne d'alimentation ayant une impédance de 50 ohms, pour les deux fréquences de fonctionnement.

This third known antenna has the following drawbacks:

• The size corresponds to three half-waves.
• The incorporation of short-circuits punctuates the realization of the antenna.
• The coupling device of the antenna in the form of a coaxial line requires a precise adjustment of the position of the coaxial structure passing through the substrate, to obtain a good adaptation to a power supply line having an impedance of 50 ohms, for the two operating frequencies.

A fourth 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 DIGEST SYMPOSIUM, NEWPORT BEACH, JUNE 18-23, 1995, pp. 2124-2127 Boag et al "Dual Band Cavity-Backed Quarter-wave Patch Antenna A first resonance frequency is defined by the dimensions and characteristics of the substrate and the pellet of this antenna. substantially of the same type is obtained at a second frequency on the same resonance path through 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 fourth known antenna has the following drawbacks:

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

We also know of the document EP-A1-0 735 609 an antenna structure which is fed by a coaxial point which is arranged in a zero potential plane.

• permettre de réaliser simplement une antenne bifréquence en choisissant plus librement que précédemment le rapport de deux fréquences de résonance utiles de cette antenne, et plus particulièrement de réaliser une telle antenne pour que ce rapport soit compris entre 0,2 et 0,8 environ et notamment voisin de 0,5
• donner à cette antenne une bande passante suffisamment large autour de chacune de ces deux fréquences de résonance pour permettre de situer dans cette bande une fréquence d'émission et une fréquence de réception sans faire apparaître de diaphonie,
• 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 the following aims in particular:

• allow to simply realize a dual frequency antenna by choosing more freely than before the ratio of two useful resonant frequencies of this antenna, and more particularly to realize such an antenna so that this ratio is between 0.2 and about 0.8 and including neighbor of 0.5
• give this antenna a bandwidth sufficiently wide around each of these two resonant frequencies to allow to locate in this band a transmission frequency and a reception frequency without causing crosstalk,
• enable easy and precise adjustment of these two resonance frequencies,
• allow to use a single coupling device and easily adaptable impedance for each of these two resonant frequencies, and
• limit the dimensions of this antenna.

And for these purposes it relates in particular to a dual-frequency antenna according to claim 1. the fact that its coupling device has an asymmetry differentiating one of the lateral edges of the wafer relative to the other so as to allow this device to couple this antenna to said signal processing member not only for said resonance of the type quarter wave, but also for a half-wave type resonance established in this antenna with a resonance path extending between the two lateral edges of the pellet.

• un organe de traitement de signal adapté à être accordé au voisinage d'au moins deux fréquences prédéterminées pour émettre et/ou recevoir un signal électrique à chacune de ces deux fréquences, et
• une antenne raccordée à cet organe de traitement pour coupler ledit signal électrique à des ondes rayonnées. Ce dispositif est caractérisé par le fait que l'autre dite fréquence prédéterminée est une fréquence de résonance demi onde constituée par la fréquence d'une résonance du type demi onde s'établissant dans cette antenne avec un trajet de résonance s'étendant entre les deux dits bords latéraux. Les types de résonances considérés dans le cadre de cette invention ont été définis d'une manière générale ci-avant.

The present invention also relates to a dual-frequency radiocommunication device, this device comprising:

• a signal processor adapted to be tuned in the vicinity of at least two predetermined frequencies for transmitting and / or receiving an electrical signal at each of these two frequencies, and
• an antenna connected to this processing unit for coupling said electrical signal to radiated waves. This device is characterized in that the other said predetermined frequency is a half-wave resonance frequency constituted by the frequency of a half-wave type resonance established in this antenna with a resonance path extending between the two said side edges. The types of resonances considered in the context of this invention have been defined in a general manner above.

Whatever the nature of the antenna coupling device that will be used to allow this radiocommunication device to operate in the two spectral bands centered on the two quarter wave and half wave resonant frequencies, this invention has an advantage in the case where the ratio between two desired operating frequencies takes some thieves, and more particularly in the case where this ratio is between 0.2 and about 0.8 and in particular close to 0.5. This advantage is to allow to achieve this desired report in a way relatively simple and effective. It is obtained thanks to the combined use of two modes of resonance which are, one of a said quarter-wave type, the other of a said half-wave type, and which are established from progressive waves traveling the same area in two respective mutually crossed directions.

Various aspects of the present invention will be better understood with the aid of the following description and the accompanying diagrammatic figures. When the same element is represented in more than one of these figures, it is designated by the same numbers and / or letters of reference.

Figure 1 shows a perspective view of a radio communication device made according to this invention.

FIG. 2 represents a view from above of the antenna of the device of FIG. 1.

FIG. 3 represents a diagram of the variation of a reflection coefficient measured at the input of this same antenna and plotted on the ordinate, as a function of the frequency of a signal supplying this antenna, this frequency being plotted on the abscissa.

• Un substrat diélectrique 2 présentant deux surfaces principales mutuellement opposées s'étendant selon des directions définies dans cette antenne et constituant des directions horizontales DL et DT, ces directions pouvant dépendre de la zone considérée de l'antenne. Ce substrat peut présenter des formes diverses comme précédemment exposé. Ses deux surfaces principales constituent respectivement une surface inférieure S1 et une surface supérieure S2.
• 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 du type désigné mondialement par le mot anglais patch. De manière générale cette pastille a une longueur et une largeur s'étendant selon deux dites directions horizontales qui seront définies ci-après et qui constituent une direction longitudinale DL et une direction transversale DT, respectivement, et sa périphérie peut être considérée comme constituée par quatre bords s'étendant deux à deux sensiblement selon ces deux directions. Quoique les mots longueur et largeur s'appliquent usuellement aux deux dimensions mutuellement perpendiculaires d'un objet rectangulaire, la longueur étant plus grande que la largeur, il doit être compris que la pastille 6 pourrait s'écarter de la forme d'un rectangle sans sortir du cadre de cette invention. Plus particulièrement les directions DL et DT peuvent former un angle différent de 90 degrés, lesdits bords de cette pastille peuvent ne pas être rectilignes et ne pas être séparés par des sommets anguleux et la dite longueur de la pastille peut être plus courte que sa dite largeur. L'un de ces bords s'étend selon la direction transversale DT et constitue un bord arrière 10. Un bord avant 12 est opposé à ce bord arrière. Deux bords latéraux 14 et 16 joignent ce bord arrière à ce bord avant.
• Enfin un court circuit C2 raccordant électriquement la pastille 6 à la masse 4 à partir du bord arrière de cette pastille. Ce court-circuit est formé par une couche conductrice s'étendant sur une surface de tranche du substrat, surface qui est typiquement plane et constitue alors un plan de court-circuit. Il impose à une résonance de l'antenne de présenter un noeud de champ électrique sur le bord arrière 10 et d'être au moins approximativement du type quart d'onde. La fréquence de cette résonance sera appelée ci-après "fréquence de résonance quart d'onde". Les dits 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 est suffisamment étendu et a une impédance suffisamment basse pour imposer à l'antenne l'existence d'une résonance dudit type quart d'onde.

According to FIGS. 1 and 2 and in a manner known per se, an antenna according to the present invention comprises firstly a resonant structure which itself comprises the following elements:

• A dielectric substrate 2 having two mutually opposite main surfaces extending along defined directions in this antenna and constituting horizontal directions DL and DT, these directions being able to depend on the considered area of the antenna. This substrate may have various shapes as previously stated. Its two main surfaces respectively constitute a lower surface S1 and an upper surface S2.
• A lower conductive layer extending for example over the entire 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 of the type designated worldwide by the English word patch. In general, this pellet has a length and a width extending along two said horizontal directions which will be defined hereinafter and which constitute a longitudinal direction DL and a transverse direction DT, respectively, and its periphery can be considered as constituted by four edges extending two by two substantially in both directions. Although the words length and width usually apply to the two mutually perpendicular dimensions of a rectangular object, the length being greater than the width, it must be understood that the wafer 6 could deviate from the shape of a rectangle without depart from the scope of this invention. More particularly, the directions DL and DT may form an angle other than 90 degrees, said edges of this pellet may not be straight and not be separated by angular vertices and said length of the pellet may be shorter than its said width . One of these edges extends in the transverse direction DT and constitutes a rear edge 10. A front edge 12 is opposite this rear edge. Two lateral edges 14 and 16 join this rear edge to this front edge.
• Finally a short circuit C2 electrically connecting the chip 6 to the ground 4 from the rear edge of this chip. This short circuit is formed by a conductive layer extending on a wafer surface of the substrate, which surface is typically flat and then constitutes a short-circuit plane. It requires a resonance of the antenna to present an electric field node on the rear edge 10 and to be at least approximately of the quarter-wave type. The frequency of this resonance will be called hereinafter "quarter wave resonance frequency". Said rear, front and lateral 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 is sufficiently wide and has a impedance sufficiently low to impose on the antenna the existence of a resonance of said quarter wave type.

The antenna further comprises a coupling device. This device comprises on the one hand a main conductor constituted by a coupling strip C1 extending on the upper surface S2 of the substrate and connected to the chip 6 at an internal connection point 18. It also comprises a conductor mass formed by the layer 4. It constitutes all or part of a connection assembly which connects the resonant structure of the antenna to a signal processing element 22, for example to excite one or more resonances of the antenna from of this organ in the case where it is a transmitting antenna. In addition to this device the connection assembly typically includes a connection line which is external to the antenna. This line may in particular be of the coaxial type, of the microstrip type or of the coplanar type.

• un conducteur principal présentant la forme d'un ruban de raccordement C3 s'étendant sur la surface supérieure S2 du substrat 2 en continuité avec le ruban de couplage C1, et
• un conducteur de masse s'étendant sur la surface inférieure du substrat en continuité avec la masse de l'antenne. Ce conducteur est par exemple constitué comme cette masse par la couche conductrice inférieure 4.

In the context of the present invention, at least a fraction of a length of this connecting line is advantageously of the microstrip type and more particularly comprises:

• a main conductor in the form of a connecting strip C3 extending on the upper surface S2 of the substrate 2 in continuity with the coupling strip C1, and
• a ground conductor extending on the bottom surface of the substrate in continuity with the ground of the antenna. This conductor is for example constituted as this mass by the lower conductive layer 4.

In FIG. 1, the remaining fraction of the connecting line has been symbolically represented in the form of two conducting wires C4 and C5 respectively connecting the ground 4 and the ribbon C3 to the two terminals of the signal processing unit 22. It should be understood that this remaining fraction would in practice preferably be in the form of a microstrip line or a coaxial line.

The signal processing unit 22 is adapted to operate at predetermined operating frequencies which are at least close to useful resonant frequencies of the antenna, ie which are included in passbands centered on these frequencies of frequency. resonance. It can be composite and then have an element permanently assigned to each of these operating frequencies. It may also include a tunable element on the various operating frequencies. Said quarter-wave resonance frequency constitutes such a useful resonant frequency.

According to the present invention another said useful resonant frequency is a half-wave resonance frequency constituted by the frequency of a resonance of said half-wave type establishing itself in this antenna with a resonance path extending between the two lateral edges. 14 and 16.

To enable the radio communication device according to the invention to operate, the antenna coupling device must be able to perform its coupling function for each of the two quarter wave and half wave resonance frequencies. According to one embodiment of this invention, this aptitude is obtained by the fact that this device presents, relative to a longitudinal axis not shown of the antenna, an asymmetry which differentiates one of the two lateral edges of the pellet relative to the other. This dissymmetry of the coupling device can be obtained in various known ways. It can in particular affect the position, orientation and / or dimensions of all or part of this device. However, it appeared that the realization of the latter in the form of a coaxial line would be inappropriate, at least if this line was vertical. This device can advantageously be formed according to a planar technique at the level of the pellet and / or that of the mass of the antenna.

More particularly, the wafer 6 has the usual shape of a rectangle and the dissymmetry of the coupling device of the antenna can advantageously be achieved by the following provision: the wafer 6 has a coupling inlet slot 20 opening outwardly of this pellet through a first lateral edge 14 of this pellet and extending from this first lateral edge, for example in the transverse direction DT, to an end of this slot. A coupling tape C1 then extends over the upper surface of the substrate within this coupling inlet slot from this first side edge. It is connected to this chip at the end of this slot, this end constituting an internal connection point 18. The distances from this point to a first lateral edge 14 and the rear edge 10 respectively constitute a connection depth L3 and a dimension connection L4. The ground conductor of the antenna coupling device is constituted by the ground 4 of the antenna.

Preferably the L1 / L2 ratio of the length of the pellet to its width is between about 2.5 and 0.625.

Preferably, said connection depth L3 is between about 8% and 25% of the width L2 of the tablet 6.

Preferably, said connection dimension L4 is between approximately 25% and 75% of the length L1 of the pellet 6.

Preferably, the short circuit C2 extends over a segment only of said rear edge 10 and this segment has a length of between 10% and 90% of the width L2 of the chip 6.

• fréquence de résonance quart d'onde : F1 = 980 MHz,
• fréquence de résonance demi onde : F2 = 1900 MHz,
• impédance d'entrée : 50 Ohms,
• composition et épaisseur du substrat : résine époxy ayant une permittivité relative ε_r égale à 3 et un facteur de dissipation tgδ égal à 0,003,
• épaisseur du substrat : 2 mm,
• composition des couches conductrices : cuivre,
• épaisseur de ces couches : 17 microns
• longueur du substrat : 65 mm,
• largeur du substrat : 70 mm,
• longueur de la pastille : L1 = 60 mm,
• largeur de la pastille: L2= 60 mm,
• profondeur de raccordement L3 = 10 mm,
• cote de raccordement : L4 = 30 mm,
• largeur du conducteur C1 et du conducteur C3 : 5 mm,
• largeur de la fente 20 : 0,7 mm,
• largeur du conducteur de court-circuit C2 : 36 mm.

In the context of an embodiment of an antenna according to this invention, various compositions and values will be given hereinafter by way of example. The length and the width of the substrate are respectively indicated along the longitudinal DL and transverse directions DT.

• quarter-wave resonance frequency: F1 = 980 MHz,
• half-wave resonance frequency: F2 = 1900 MHz,
• input impedance: 50 Ohms,
• composition and thickness of the substrate: epoxy resin having a relative permittivity ε _r equal to 3 and a dissipation factor tgδ equal to 0.003,
• substrate thickness: 2 mm,
• composition of conductive layers: copper,
• thickness of these layers: 17 microns
• length of the substrate: 65 mm,
• width of the substrate: 70 mm,
• length of the pellet: L1 = 60 mm,
• width of the pellet: L2 = 60 mm,
• connection depth L3 = 10 mm,
• connection dimension: L4 = 30 mm,
• conductor width C1 and conductor C3: 5 mm,
• width of the slot 20: 0.7 mm,
• width of the short-circuit conductor C2: 36 mm.

The diagram of FIG. 3 has been plotted from measurements made on the antenna whose numerical characteristics have been indicated above. In this figure, the 0 dB level corresponds to the upper horizontal registration line. The difference between two horizontal registration lines is 3 dB. The extreme frequencies of the scale shown are 200 and 2000 MHz. The difference between two vertical registration lines represents 180 MHz. The resonance peaks presented by the diagram correspond to the quarter-wave resonant frequencies F1 and half wave F2 previously indicated.

• une fréquence d'émission haute située dans ladite bande fréquentielle haute,
• une fréquence de réception haute située dans cette bande fréquentielle haute,
• une fréquence d'émission basse située dans ladite bande fréquentielle basse, et
• une fréquence de réception basse située dans cette bande fréquentielle basse.

The present invention is particularly applicable with advantage to the realization of a radiotelephone system. It is known that such a system comprises base stations and portable terminals and that it can be realized in the context of a GSM standard using frequencies close to 900 MHz and / or in the context of a DCS standard. using frequencies close to 1800 MHz. In such a system, base stations or portable terminals may each include a radio communication device according to this invention. In such a device adapted for this purpose the antenna is able to operate in a high frequency band in the vicinity of said half-wave resonance frequency and in a band low frequency in the vicinity of said quarter wave resonance frequency. Said signal processing unit 22 is then tunable on four mutually distinct operating frequencies that constitute:

• a high transmission frequency located in said high frequency band,
• a high reception frequency located in this high frequency band,
• a low transmission frequency located in said low frequency band, and
• a low reception frequency located in this low frequency band.

It is able to transmit or receive a signal when it is tuned to a said transmission frequency or to a said reception frequency, respectively.

This invention makes it possible to give each of these two frequency bands a sufficient width, not only to avoid a crosstalk between the spectral transmit and receive channels located in this band, but also to make it possible to choose between several possible positions of these channels. in this band. The low frequency band corresponds to the GSM standard and the high frequency band to the DCS standard. Thus, base stations and / or dual mode terminals are produced economically, that is to say capable of operating in the context of any of these standards.

By way of example, in the case of the antenna whose digital characteristics have been given above, the high transmit and receive frequencies can be respectively 1750 and 1840 MHz and the transmit and receive frequencies Low reception frequencies can be respectively 890 and 940 MHz.

Claims (9)

1. - A dual frequency antenna made using the microstrip technique, the antenna comprising:

   a dielectric substrate (2) having two opposite main surfaces extending in

   directions defined in said antenna and constituting horizontal directions (DL and DT), the two surfaces respectively constituting a bottom surface (S1) and

   a top surface (S2),

   - a bottom conductive layer on said bottom surface and constituting a ground (4) of the antenna,

   - a top conductive surface on an area of said top surface over said ground and constituting said patch (6),

   - a patch (6) having a rear edge (10) provided with a short-circuit, this patch also having a front edge (12) opposite the rear edge and two lateral edges (14,16) joining the rear edge to the front edge, said short-circuit (C2) enabling a quarter-wave resonance to be established in said antenna with an electric field node fixed by the short-circuit and a resonance path extending between said rear edge and said front edge, and

   - an antenna coupling device enabling said antenna to be coupled to said signal processor unit (22),

   - said antenna coupling device (20,C1,4) presenting asymmetry that distinguishes one said lateral edge (14) of the patch from the other said lateral edge (16) of the patch in a manner that enables said device to couple said antenna to said signal processor unit (22) not only for said quarter-wave resonance, but also for a half-wave type resonance that becomes established in said antenna with a resonance path that extends between the two lateral edges of the patch, said antenna being characterized in that it further comprises:

   - said short-circuit (C2) electrically connecting said patch (6) to said ground (4) from said rear edge (10) of the patch, this edge extending in a horizontal direction constituting a transverse direction (DT), a length (L1) of the patch extending between the rear edge and said front edge (12) in a longitudinal direction (DL) which is one of said horizontal directions, said two lateral edges of said patch respectively constituting a first lateral edge (14) and a second lateral edge (16), a width (L2) of the patch extending between the two lateral edges, and

   - said antenna coupling device, itself comprising:

   - a main conductor (C1), and

   - a ground conductor (4) enabling said antenna to be coupled to a signal processor unit (22) via the device

   said patch (6) having a coupling input slot (20) opening to the exterior of the patch via said first lateral edge (14) of the patch (6) and extending from the first lateral edge substantially in said transverse direction as far as an end (18) of the slot, said main conductor (C1) of the antenna coupling device having the form of a coupling strip extending from said first lateral edge of the patch on said top surface of the substrate inside said coupling input slot, the strip being connected to the patch at said end of the slot, said ground conductor of the antenna coupling device consisting of said antenna ground (4).
2. - A dual frequency radiocommunication device, comprising: signal processor unit (22) being adapted to be tuned to at least two predetermined frequencies to transmit and/or receive an electric signal to each of said two frequencies, and

   - an antenna (1) according to claim 1 and connected to the signal processor unit to couple said electric signal to the radiated waves,

   the device being characterized in that the other of said predetermined frequencies is a half-wave resonant frequency constituted by the frequency of a half-wave type resonance that becomes established in the antenna with a resonance path extending between said two lateral edges (14,16).
3. - A radiocommunication device according to claim 2, characterized by the fact that said patch (6) has a coupling input slot (20) opening to the outside of the patch through said first lateral edge (14) of the patch (6) and extending from the first lateral edge substantially in said transverse direction to an end (18) of the slot, said main conductor (C1) of the antenna coupling device having the form of a coupling strip extending from said first lateral edge of the patch on said top surface of the substrate in said coupling input slot, the strip being connected to the patch at said end of the slot, this end constituting an internal connection point (18), the distances from this point to the first lateral edge (14) and said rear edge (10) respectively constituting a connecting depth (L3) and a connecting dimension (L4), said ground conductor of the antenna coupling device being constituted by said antenna ground (4).
4. - A radiocommunication device according to claim 3 the ratio (L1/L2) of said length of the patch to said width of the patch being in the range approximately 2.5 to approximately 0.625.
5. - A radiocommunication device according to claim 4, said connecting depth (L3) being in the range approximately 8% to approximately 25% of said width (L2) of the patch (6).
6. - A radiocommunication device according to claim 4, said connecting dimension (L4) being in the range approximately 25% to approximately 75% of said length (L1) of the patch (6).
7. - A radiocommunication device according to claim 4, said short-circuit (C2) occupying a segment of said rear edge (10) of the patch having a length in the range 10% to 90% of said width (L2) of the patch (6).
8. - A radiocommunication device according to claim 3 further including a connection line (C3, 4) extending to the exterior of said antenna for connecting said antenna coupling device to said signal processor unit, at least a portion of a length of the connection line including:

   - a main conductor having the form of a connecting strip (C3) on said top surface of the substrate (2) and continuous with said coupling strip (C1), and

   - a ground conductor (4) on said bottom surface of the substrate and continuous with said ground of the antenna.
9. - A radiocommunication device according to any one of claims 2 to 8, said antenna being adapted to operate in a high frequency band near said half-wave resonant frequency and a low frequency band near said quarter-wave resonant frequency, said signal processor unit (22) being adapted to be tuned to four different predetermined frequencies:

   - a high transmit frequency in said high frequency band,

   - a high receive frequency in said high frequency band,

   - a low transmit frequency in said low frequency band, and

   - a low receive frequency in said low frequency band,

   the processor unit being respectively adapted to transmit or receive a signal when it is tuned to one of said transmit frequencies or one of said receive frequencies.

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