EP2086053B1 - Printed antenna with a two-beam diagram - Google Patents

Description

The field of the invention is that of telecommunication antennas, and more particularly that of antennas for cellular networks of mobile communication.

The invention relates more precisely to an antenna made in printed technology, of the type comprising a ground plane, a substrate superimposed on the ground plane and a metal deposit made on the substrate to form a resonant pellet.

The urban antennas of GSM / DCS / UMTS base stations are designed to absorb the high traffic generated in high-traffic areas: shopping malls, shops, pedestrian streets, etc.

These antennas are also subject to landscape integration constraints.

In the case where the area to be covered is lengthened, in particular a corridor or a pedestrian street, the use of a directional antenna with a maximum gain in the direction perpendicular to the plane of the antenna is not optimal. This type of antenna actually promotes the environment close to the antenna, including the building just in front of the antenna, to the detriment of the areas at the ends of the corridor or the street.

• la pastille est carrée de côté sensiblement égal à k*λS où k est un entier strictement positif et λS représente la longueur d'onde dans le substrat,
• le point d'excitation est sensiblement situé au 3 /4 de l'un des côtés de la pastille.

The invention aims to overcome this drawback, and proposes for this purpose a printed antenna comprising a ground plane, a substrate superimposed on the ground plane, a metal deposit made on the substrate to form a resonant chip, and a means for supply for energizing the resonant pellet, characterized in that the pellet has dimensions adapted so that the wafer is likely to radiate in both upper electromagnetic modes TM ₀₂ and TM _20, and in that the supply means allows for exciting the pellet at an excitation point arranged in such a way that the pellet resonates in only one of said upper electromagnetic modes, thus inducing a two-beam radiation pattern with, in the same plane orthogonal to the pellet , two main lobes that are remote and symmetrical with respect to the normal to the pellet and in which:

• the pellet is square on the side substantially equal to k * λS where k is a strictly positive integer and λS represents the wavelength in the substrate,
• the excitation point is substantially located 3/4 of one of the sides of the pellet.

• le moyen d'alimentation alimente la pastille par couplage électromagnétique ;
• une fente de couplage est découpée dans le plan de masse ;
• le moyen d'alimentation alimente la pastille par contact ;
• le moyen d'alimentation est une ligne micro-ruban ;
• le moyen d'alimentation est une sonde coaxiale ;
• l'antenne comporte en outre des moyens de compensation capacitive visant à atténuer le comportement selfique de l'impédance d'entrée de l'antenne alimentée par sonde coaxiale ;
• les moyens de compensation capacitive prennent la forme d'une extension de la pastille autour du point d'excitation ;
• l'extension présente une surface sensiblement égale à celle d'un demi-disque de rayon Re=4*h où h désigne l'épaisseur du substrat ;
• l'extension est un demi-disque ;
• le point d'excitation est positionné à mi-chemin entre le côté de la pastille et le bord du demi-disque ;
• la pastille présente un premier et second points d'excitation sur des côtés orthogonaux de la pastille pour que la pastille puisse résonner dans un premier mode supérieur dans un premier plan orthogonal à la pastille lorsqu'elle est excitée depuis le premier point d'excitation et dans un deuxième mode supérieur dans un second plan orthogonal à la pastille et au premier plan lorsqu'elle est excitée depuis le second point d'excitation, les moyens d'alimentation étant configurés pour exciter alternativement la pastille depuis le premier et depuis le second points d'excitation ;
• la pastille présente quatre points d'excitation disposés chacun sur un côté de la pastille, les moyens d'alimentation étant configurés pour exciter la pastille en alimentant séquentiellement les points d'excitation, la pastille présentant de la sorte un diagramme de rayonnement conique ;
• l'antenne est optiquement transparente à la lumière visible.

Some preferred, but not limiting, aspects of this antenna are:

• the supply means supplies the pellet by electromagnetic coupling;
• a coupling slot is cut in the ground plane;
• the supply means feeds the tablet by contact;
• the feeding means is a micro-ribbon line;
• the supply means is a coaxial probe;
• the antenna further comprises capacitive compensation means for attenuating the inductive behavior of the input impedance of the antenna fed by coaxial probe;
• the capacitive compensation means takes the form of an extension of the chip around the excitation point;
• the extension has a surface substantially equal to that of a half-disk of radius Re = 4 * h where h denotes the thickness of the substrate;
• the extension is a half-disk;
• the excitation point is positioned midway between the side of the patch and the edge of the half-disc;
• the wafer has first and second excitation points on orthogonal sides of the wafer so that the wafer can resonate in a first higher mode in a first plane orthogonal to the wafer when it is excited from the first excitation point and in a second upper mode in a second plane orthogonal to the pellet and in the foreground when it is excited from the second excitation point, the supply means being configured to alternately excite the pellet from the first and second points of excitement;
• the pellet has four excitation points each arranged on one side of the pellet, the supply means being configured to excite the pellet by sequentially supplying the excitation points, the pellet thus having a conical radiation pattern;
• the antenna is optically transparent to visible light.

• la figure 1 illustre la couverture d'un espace confiné de type rue piétonne par l'antenne selon l'invention ;
• les figures 2 à 4 représentent respectivement une pastille carré excitée au milieu de l'un de ses côtés, sa distribution surfacique de courants et son diagramme de rayonnement ;
• les figures 5 à 7 représentent respectivement une pastille d'une antenne conforme à un mode de réalisation possible de l'invention, sa distribution surfacique de courants et son diagramme de rayonnement ;
• la figure 8 est un schéma illustrant le comportement selfique d'une alimentation de l'antenne par une sonde coaxiale ;
• la figure 9 est un schéma illustrant la mise en oeuvre d'une compensation capacitive au comportement selfique de l'alimentation de l'antenne par une sonde coaxiale ;
• la figure 10 illustre un mode de réalisation possible de la compensation capacitive ;
• la figure 11 représente une pastille à deux points d'excitation disposés le long de la pastille conformément à une mise en oeuvre de l'invention ;
• la figure 12 illustre l'obtention alternée d'un rayonnement bi-faisceaux dans le plan horizontal puis dans le plan vertical avec l'antenne de la figure 11;
• la figure 13 représente une pastille à quatre points d'excitation disposés le long de la pastille conformément à une mise en oeuvre de l'invention ;
• la figure 14 illustre l'obtention d'un diagramme de rayonnement conique en alimentant séquentiellement les points d'excitation de la pastille de la figure 13 ;
• les figures 15 et 16 sont des exemples d'antennes optiquement transparentes conformes à l'invention.

Other aspects, objects and advantages of the present invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and with reference to the appended drawings in which: :

• the figure 1 illustrates the coverage of a pedestrian-type confined space by the antenna according to the invention;
• the Figures 2 to 4 respectively represent a square pellet excited in the middle of one of its sides, its surface distribution of currents and its radiation pattern;
• the Figures 5 to 7 respectively represent a tablet of an antenna according to a possible embodiment of the invention, its surface current distribution and its radiation pattern;
• the figure 8 is a diagram illustrating the inductive behavior of a supply of the antenna by a coaxial probe;
• the figure 9 is a diagram illustrating the implementation of a capacitive compensation to the inductive behavior of the supply of the antenna by a coaxial probe;
• the figure 10 illustrates a possible embodiment of the capacitive compensation;
• the figure 11 represents a pellet with two excitation points arranged along the pellet in accordance with an implementation of the invention;
• the figure 12 illustrates the alternate obtaining of a dual-beam radiation in the horizontal plane and then in the vertical plane with the antenna of the figure 11 ;
• the figure 13 represents a pellet with four excitation points arranged along the pellet according to an implementation of the invention;
• the figure 14 illustrates obtaining a conical radiation pattern by sequentially feeding the excitation points of the pellet of the figure 13 ;
• the Figures 15 and 16 are examples of optically transparent antennas according to the invention.

The object of the invention is notably to propose a printed antenna which presents a bidirectional radiation pattern in the horizontal plane (plane view) able to compensate the losses induced by the path of the signals coming from or towards the mobile terminals at ends of the elongated area to be covered.

The figure 1 illustrates in this regard the coverage of a confined space E in the form of a corridor or pedestrian street that one seeks to obtain, with two preferred directions of radiation (see arrows F _R ) of the antenna A, these privileged directions being offset from the main axis of radiation perpendicular to the direction S of the corridor or the pedestrian street to better cover the ends of the space E.

The solution recommended by the invention is an antenna made in radiating printed technology according to a two-beam radiation pattern from a single resonant chip operating in a higher electromagnetic mode. The pellet is made more precisely by metal deposition on a substrate, which substrate rests on a ground plane.

In this regard, it is intended in the context of the invention to use a pellet having dimensions adapted so that the pellet is likely to resonate in the two higher modes TM ₀₂ and TM ₂₀ .

We have shown on the figure 2 a square pellet 1 having a side of dimension equal to the wavelength in the substrate λ _s (where typically the dimensions of a resonant pellet are of the order of half a wavelength).

The supply of the pellet at an excitation point 2 disposed in the middle of one side of the pellet 1 generates the excitation of two transverse modes and perpendicular to each other, TM02 and TM20.

The figure 3 represents the distribution of simulated surface currents by CAD software in the 1 pellet of the figure 2 , and the figure 4 represents the 3D simulated radiation pattern of the pellet 1 showing the operation of the two radiated modes by the presence of four main lobes. The theoretical gain raises it to -1 dBi.

The pellet 1 thus radiates, on opposite sides of each other, fields in phase opposition, inducing a bi-beam pattern for each plane orthogonal to the plane of the antenna (a two-beam diagram in the vertical plane, a two-beam diagram). -beams in the horizontal plane), that is to say a final four-beam radiation pattern.

Such a quad-beam diagram is however not desirable, since the two lobes lying in the vertical plane of the antenna are not useful. The energy found in these lobes does not actually provide the desired coverage function, these lobes not being directed in the length of the corridor or the street to cover.

It is proposed in the context of the invention to suppress one of the upper electromagnetic modes, to reduce the radiation behavior of the antenna in a single mode and thus produce a two-beam radiation pattern. For this purpose, it is within the scope of the invention to move the excitation point along the chip until one of the modes TM02 or TM 20 fades.

The original positioning of the power supply allows the antenna according to the invention to operate in a single higher mode, with a distribution of surface currents of the type of that shown in FIG. figure 6 (corresponding to lozenge 3 of the diagram of the figure 5 discussed below), inducing a two-beam radiation pattern of the type shown in the 3D simulation of the figure 7 with, in the same plane orthogonal to the pellet, two lobes remote and symmetrical with respect to the normal to the pellet.

According to one possible embodiment of the invention, the pellet is square on the side substantially equal to k * λ _s where k is a strictly positive integer and λ _s represents the wavelength in the substrate.

This is, for example, a 3-square patch with side λ _s , as shown in FIG. figure 5 .

In the context of this embodiment, the feeding means comes to excite the pellet at an excitation point 4 disposed ¾ of one side of the pellet.

The au excitation of one of the sides of the pellet makes it possible to inhibit the radiation of the undesired transverse mode (for example the TM ₂₀ mode), since it imposes the arrival of a maximum current where the field should cancel each other to allow the radiation of that mode.

It will be noted that the excitation at% of the side is indifferent on the left or right side of the pellet.

We note that the tablet 3 of the figure 5 has a theoretical gain of 2 dBi, which is 3 dB higher than the 1 figure 2 because of the focus of energy on two lobes instead of four.

Avec :

• ε_e : constante diélectrique effective du substrat
• λ_o: longueur d'onde dans le vide
• λ_s : longueur d'onde dans le substrat, λ_s = λ_o /√ε_e

The bi-beam diagram of an antenna according to the invention has, in a same plane orthogonal to the pellet, two main lobes that are remote and symmetrical with respect to the normal to the pellet. The deviation of the main axes of radiation from the normal to the pellet (represented by θ on the figure 7 ) is in particular dependent on the dielectric constant of the substrate, according to $$\mathrm{\theta }=\mathrm{arc\; sin}\left({\mathrm{\lambda }}_{\mathrm{o}}/\mathrm{2}\mathrm{d}\right)=\mathrm{bow}\sin \left({\mathrm{\surd \epsilon }}_{\mathrm{e}}/\mathrm{2}\right)$$

With:

• ε _e : effective dielectric constant of the substrate
• λ _o : wavelength in the vacuum
• λ _s : wavelength in the substrate, λ _s = λ _o / √ε _e

By way of example, for a Plexiglas type substrate (PPMA), used in a prototype developed by the inventors, ε _e = 2.7. An angle of inclination of the two lobes of θ = 55 ° is then obtained.

According to a possible embodiment of the invention, the supply means feeds the pellet by electromagnetic coupling. This coupling is for example achieved by means of a slot made in the ground plane facing the aforementioned excitation point.

According to another possible embodiment of the invention, the supply means feeds the tablet by contact.

The supply means is for example a micro-ribbon line coming into contact with the pellet at the aforementioned excitation point. It can also be a coaxial probe.

The input impedance of the antenna fed by coaxial probe may have a significant self-inductive behavior. This behavior is represented by an inductance L _s in series with the antenna (represented by a resonant circuit RLC) on the diagram of the figure 8 .

According to an advantageous variant of the invention, the antenna further comprises capacitive compensation means for attenuating the inductive behavior of the input impedance of the antenna fed by coaxial probe.

The capacitive compensation means (represented by a capacitance Ce on the figure 9 ) make it possible to compensate for the effect of the inductance L _s and consequently to adapt the input impedance of the antenna.

As shown on the figure 9 the capacitive compensation means may form part of the antenna body, for example taking the form of an extension of the half-disk type chip around the excitation point 4.

The radius R _e of the half-disk of the extension 5 is essentially dependent on the wavelength of the coaxial probe passing through the antenna and consequently on the thickness of the substrate. We will retain approximately Re = 4 * h where h denotes the thickness of the substrate.

In order to take full advantage of the capacitive effect of the extension, the position of the coaxial probe can be positioned midway between the side of the pellet and the edge of the half-disk as shown on the figure 10 .

The capacitive extension is not limited to a half-disk extension, but can take other geometric shapes. It should be noted that the total area of the extension should be approximately equal to that of the half-disk to produce a similar capacitive effect.

In the above, the antenna according to the invention had a single excitation point for feeding the pellet and the generation of a two-beam diagram in the same plane.

The invention is however not limited to this case, but also extends to variants in which the antenna has a plurality of excitation points arranged along the chip for each generate a two-beam diagram. in the same plane.

In the variant represented by the diagram of the figure 11 , the square pellet 7 comprises a first and second excitation points 8, 9 arranged on orthogonal sides of the pellet so that the pellet resonates in a first of the higher modes (for example TM20) in a first plane orthogonal to the pellet when it is excited from the first excitation point and in a second of the higher modes (TM02 in the example) in a second plane orthogonal to the pellet and in the foreground when it is excited from the second excitation point. As shown on the figure 12 the excitation of the pellet 7 at the point 8 makes it possible to induce a two-beam radiation pattern in the horizontal plane (H plane), while the excitation of the pellet at the point 9 allows to induce a bi-beam radiation pattern in the vertical plane (plane V). In the context of this variant, the supply means may be configured to alternately excite the chip from the first and second excitation points, so that the antenna alternately has a bi-beam pattern in the H plane. (horizontal diagram) and a diagram (called vertical diagram) orthogonal to the horizontal diagram.

This variant finds particular application for the design of a compact antenna for the detection of movement and speed by effect Doppler in Janus configuration in two axes (where current applications are configured in a single axis).

According to another variant embodiment illustrated by the diagram of the figure 13 , the square pellet 10 comprises four excitation points 11-14 each arranged on one side of the pellet according to the invention (here at ¾ on each side for a square pellet), the supply means being configured to excite the pastille by sequentially feeding the excitation points, such that the pellet has a conical radiation pattern.

As shown on the figure 13 the supply of each excitation point 11-14 is delayed by a phase of 90 ° with respect to the previous point. Such a variant makes it possible to obtain a conical configuration with a right or left circular polarized wave in the sequential feed direction.

This variant finds particular application for the design of a very compact satellite reception antenna embedded, especially on the roof of a car as shown on the figure 14 for receiving signals from geostationary satellites. Indeed, a geostationary satellite is at an angle to the ground of 35 ° (average for Europe). However, the fact of having an angle θ = 55 ° with respect to the vertical (in the case of a plexiglass substrate) makes it possible for the antenna to constitute a particularly interesting solution for satellite reception from a horizontal surface (such as than the roof of a car).

As mentioned in the introduction, urban antennas are also subject to landscape integration constraints. In order to meet these constraints, the invention provides according to a preferred embodiment an optically transparent antenna with a two-beam diagram.

For this purpose, the substrate of the antenna may be made of glass, or formed of any other optically transparent dielectric material, for example plexiglass.

It is specified here that the term "optically transparent" material, a material substantially transparent to visible light, allowing at least about 30% of this light, and preferably more than 60% of the light.

The ground plane and the resonant pad preferably side λ _s are each formed by depositing an optically transparent conductive material on a plastic film, for example on a polyester film. The optically transparent conductive material can also be directly deposited by etching processes. The optically transparent conductive material is preferably, but not limited to, indium tin oxide (ITO) or silver doped tin oxide (AgHT).

On the other hand, the ground plane and the resonant pad can be sandwiched between optically transparent dielectric layers, such as glass layers.

The Figures 15 and 16 are optically transparent antenna patterns given for illustrative purposes.

The figure 15 represents an optically transparent antenna according to the invention comprising a ground plane M, a substrate S and a resonant pellet P, in which the pellet is fed at an excitation point E arranged in accordance with the invention and fed with by a coaxial probe.

The figure 16 represents another optically transparent antenna according to the invention comprising a ground plane M, a substrate S and a resonant pellet P, in which the pellet P is fed at an excitation point E via a micro-ribbon line L also made

On these two Figures 15 and 16 , the ground plane M and the pellet P are sandwiched between two optically transparent layers V.

Claims (14)

1. A printed antenna comprising a ground plane (P), a substrate (S) stacked to the ground plane, a metal deposit made on the substrate in order to form therein a resonating patch (3, 6, 7, 10, P) , and a means of supplying to excite the resonating patch, characterized in that the patch has dimensions that are adapted so that the patch is able to radiate in both upper electromagnetic modes TM₀₂ and TM₂₀, and in that the means of supplying make it possible to excite the patch on an excitation point (4, 8, 9, 11-15, E) arranged in such a way that the patch resonates in a single of said upper electromagnetic modes, by inducing in this way a dual-beam radiation diagram with, in the same plane orthogonal to the patch, two main misaligned lobes that are symmetric in relation to the normal to the patch;
   wherein:

   - the patch is square of side substantially equal to k*λS where k is a strictly positive integer and λS shows the wavelength in the substrate,

   - the excitation point is substantially located at ¾ of one of the sides of the patch.
2. The antenna according to claim 1, wherein the means of supplying supplies the patch via coupling.
3. The antenna according to claim 2, wherein a coupling slot is cut in the ground plane.
4. The antenna according to claim 1, wherein the means of supplying supplies the patch by contact.
5. The antenna according to claim 4, wherein the means of supplying is a microstrip line.
6. The antenna according to claim 4, wherein the means of supplying is a coaxial probe.
7. The antenna according to claim 6, further comprising capacitive compensation means (5) aiming at lowering the self-inductive behaviour of the input impedance of the antenna supplied by coaxial probe.
8. The antenna according to claim 7, wherein the capacitive compensation means (5) take the form of an extension of the patch around the excitation point.
9. The antenna according to claim 8, wherein the extension (5) has a surface substantially equal to that of a half-disk of radius Re=4*h where h designates the thickness of the substrate.
10. The antenna according to claim 9, wherein the extension is a half-disk (5).
11. Antenna according to claim 10, wherein the excitation point (4) is positioned midway between the side of the patch (6) and the edge of the half-disk (5).
12. The antenna according to one of claims 1 to 11, wherein the patch (7) has a first (8) and second (9) excitation points on orthogonal sides of the patch so that the patch can resonate in a first upper mode in a first plane orthogonal to the patch when it is excited from the first excitation point and in a second upper mode in a second plane orthogonal to the patch and to the first plane when it is excited from the second excitation point, the means of supplying being configured to alternatively excite the patch from the first and from the second excitation points.
13. The antenna according to one of claims 1 to 11, wherein the patch (10) has four excitation points (11-15) arranged each on one side of the patch, the means of supplying being configured to excite the patch by sequentially supplying the excitation points, the patch having as such a conical radiation diagram.
14. The antenna according to one of claims 1 to 13, characterized in that it is optically transparent to visible light.

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