EP1751820B1 - Planar antenna provided with conductive studs above a ground plane and/or with at least one radiator element, and corresponding production method - Google Patents

Abstract

The disclosure relates to a planar antenna comprising at least one radiator element separated from a ground plane by a dielectric. The antenna also comprises an assembly of conductive studs which is connected to and extends from at least one element of a group of elements comprising the ground plane and at least one radiator element in such a way that at least one physical dimension of said at least one radiator element for a determined resonance frequency is reduced.

Description

1. Field of the invention

The field of the invention is that of planar antennas, of the type comprising at least one radiating element (also called "patch", planar pattern, radiating pattern or printed pattern) separated from a ground plane by a dielectric.

Our era is currently experiencing a considerable expansion of mobile networks and, more generally, of all wireless networks. Since these systems offer attractive answers on many points, such as connection flexibility, mobility, redeployment or network expansion possibilities, this growth should continue to increase significantly in the future.

However, in all these systems, radiating elements are among the key components, for which the specifications requested are increasingly binding. It must of course constantly optimize all the electrical performance of these antennas, but also satisfy criteria increasingly critical, such as the size, weight or cost of these components.

The miniaturization of the antennas thus constitutes today an important challenge and is the subject of numerous works on the international level. This miniaturization offers indeed many advantages, among which we can mention: ease of integration of antennas in embedded hardware (in particular, within laptops), greater flexibility of networking of these radiating elements (of by their small size), a larger diagram opening facilitating in particular the integration of wide beam scanning systems ...

Among the various technologies used to integrate antennas, planar solutions appear today as particularly appropriate to meet all the specifications requested. This planar approach offers developers enough flexibility to develop efficient solutions with particularly small dimensions.

• aussi bien les antennes réellement planes, c'est-à-dire celles dont le plan de masse et le ou les éléments rayonnants sont plans,
• que les antennes non réellement planes, c'est-à-dire celles dont le plan de masse et/ou au moins un des éléments rayonnants n'est (ne sont) pas plan(s) mais conformé(s) selon une forme tridimensionnelle (3D) déterminée, de manière à épouser la forme d'un support.

In accordance with an abuse of language quite conventional in the field of antennas, the term "planar antennas" (or antennas made according to the planar technology):

• both really flat antennas, that is to say those whose plane of mass and the radiating elements are planes,
• that the antennas not really planar, that is to say those whose plane of mass and / or at least one of the radiating elements is (are) not plane (s) but conformed (s) in a three-dimensional form (3D) determined, so as to follow the shape of a support.

The planar antennas of the aforementioned second category (antennas that are not actually flat) are generally, but not necessarily, produced using a printed technology. This explains why, historically, the adjective "planar" has been chosen in the expression "planar antenna", to show an opposition with the traditional antenna structure based on three-dimensional waveguide (3D). is in this context and relates more specifically to an original planar antenna solution in the above sense, as well as a corresponding manufacturing process, to greatly reduce the physical dimension of the basic printed pattern (ie say the radiating element or elements, also called patches).

2. Prior Art

Reducing the size of planar antennas is a major challenge to facilitate their use and integration into modern systems.

The basic principle of most of the solutions implemented to date is to increase the equivalent electrical length of the printed pattern, so that it can radiate at the desired frequency, while reducing its physical dimensions (ie its surface or its volume ).

• des solutions de type patchs à fentes inscrites, ces fentes permettant d'allonger le chemin électrique du signal sur le motif planaire (voir par exemple les documents de brevet WO 01/31739 et WO 01/17063 ), ou
• des solutions pour lesquelles le motif rayonnant est replié de manière à gagner en compacité (voir par exemple les documents de brevet WO 02/052680 , WO 01/63695 et US 6,483,462 B2 ).

For this purpose, the most commonly used structures correspond to:

• patch-type solutions with inscribed slots, these slots making it possible to extend the electrical path of the signal on the planar pattern (see, for example, patent documents WO 01/31739 and WO 01/17063 ), or
• solutions for which the radiating pattern is folded in order to gain compactness (see for example the patent documents WO 02/052680 , WO 01/63695 and US 6,483,462 B2 ).

It should be noted that these different concepts can also be combined within the same structure (see for example the patent document WO 02/01874 ).

3. Objectives of the invention

The invention particularly aims to provide a technique other than those used until today to increase the equivalent electrical length of the printed pattern (radiating element or patch) of the antenna, so as to obtain a very planar antenna compact.

A complementary objective of the invention is to provide such a technique which is simple to implement and inexpensive.

The invention also aims to provide such a technique that can be applied to any type of planar radiating structures, such as the basic antennas "half-wave patches" or "quarter-wave patches", the antennas "ring patches" , antennas "slotted patches", antennas PIFA (Planar Inverted-F Antenna) ...

Another object of the invention is to provide such a technique that can be applied to both a planar antenna with a single radiating element and a planar antenna comprising a superposition of several radiating elements.

Yet another object of the invention is to provide a planar antenna manufacturing method corresponding, based on very simple integration technologies, which leads to very low cost solutions, quite suitable for development consumer markets.

4. Summary of the invention

These various objectives, as well as others which will appear later, are achieved according to the invention using a planar antenna of the type comprising at least one radiating element separated from a ground plane by a dielectric. According to the invention, the antenna further comprises at least one set of conductive pads connected to and extending from at least one of the elements belonging to the group comprising the ground plane and the said at least one radiating element, in order to reduce at least one physical dimension of said at least one radiating element for a determined resonant frequency.

The general principle of the invention is therefore simply to have the pads on the ground plane and / or on one or more element (s) radiating (s) (patch (s)) of the planar antenna.

In the context of the present invention, the term pad is used in a generic sense, which can be broken down into different variants (and in particular but not exclusively, as detailed in the description below, in the form of a projection, a hole or tongue).

Dielectric means air or a solid material with characteristics close to those of air, such as for example materials of plastic type, foam, etc.

As explained in detail later, in relation to the figure 3 these pads locally come to modify the distribution of the electromagnetic field, and make it possible to reduce at least one dimension (the length and / or the width) of the physical element (s) radiating (s) for a fixed resonant frequency.

Different sets of conductive pads are specified below. It is clear that many embodiments of the present invention may be contemplated, each corresponding to a different combination of one or more of these sets. It should also be noted that the present invention applies with an antenna structure comprising a single radiating element or with an antenna structure comprising a superposition of several radiating elements.

Advantageously, the antenna comprises a first set of conductive pads connected to the ground plane and extending towards, without being connected to, said at least one radiating element.

In the case where the antenna is of the type comprising a single radiating element, it advantageously comprises a second set of conductive pads connected to said single radiating element and extending towards, without being connected to, said ground plane.

In the case where the antenna is of the type comprising a superposition of at least two radiating elements separated from each other by a dielectric, the radiating element closest to the ground plane being called primary radiating element, the antenna advantageously comprises a third set of conductive pads connected to a first face of said primary radiating element and extending towards, without being connected to, said ground plane.

In the case where the antenna is of the type comprising a superposition of at least two radiating elements separated from each other by a dielectric, the element radiating the closer to the ground plane being called the primary radiating element, the antenna advantageously comprises a fourth set of conductive pads connected to a second face of said primary radiating element and extending towards, without being connected to, another of said radiating elements.

In the case where the antenna is of the type comprising a superposition of at least three radiating elements separated from each other by dielectrics, the radiating element closest to the ground plane is called the primary radiating element, the radiating element the most away from the ground plane being called upper radiating element, each radiating element other than the primary radiating element and the upper radiating element being called intermediate radiating element, the antenna advantageously comprises, for at least one of the intermediate radiating elements, a fifth set of conductive pads connected to a first face of said intermediate radiating element and extending towards, without being connected to, another of said radiating elements which follows said intermediate radiating element in a direction of travel of said superposition of the primary radiating element towards the upper radiating element.

In the case where the antenna is of the type comprising a superposition of at least three radiating elements separated from each other by dielectrics, the radiating element closest to the ground plane is called the primary radiating element, the radiating element the most away from the ground plane being called the upper radiating element, each radiating element other than said primary radiating element and said upper radiating element being called intermediate radiating element, the antenna advantageously comprises, for at least one of the intermediate radiating elements, a sixth set of conductive pads connected to a second face of said intermediate radiating element and extending towards, without being connected to, another one of said radiating elements which precedes said intermediate radiating element in a direction of travel of said superposition of the primary radiating element towards the upper radiating element.

In the case where the antenna is of the type comprising a superposition of at least two radiating elements separated from each other by a dielectric, the radiating element closest to the ground plane being called primary radiating element, the element radiating the farthest from the ground plane being called upper radiating element, each radiating element other than said primary radiating element and said upper radiating element being called intermediate radiating element, the antenna advantageously comprises a seventh set of conductive pads connected to a first face said upper radiating element and extending towards, without being connected to, another of said radiating elements which precedes said upper radiating element in a direction of travel of said superposition of the primary radiating element towards the upper radiating element.

Advantageously, a set of conductive pads, extending from the ground plane or respectively one of the radiating elements, intertwine with another set of conductive pads, extending from one of the radiating elements. or respectively another of the radiating elements.

Advantageously, for each radiating element to which is connected a set of conductive pads, said radiating element is not connected to any conductive pad in an area where said radiating element is connected with supply means.

Advantageously, the conductive pads of the same set of conductive pads are distributed in a matrix.

According to an advantageous characteristic, at least one radiating element to which is connected at least one set of conductive pads is of the type having a symmetry along its two main axes, and in that said conductive pads are distributed in a disposition respecting said symmetry.

Thus, it is entirely possible to exploit the antenna of the invention according to two crossed linear polarizations, or even in circular polarization. The solution developed, based on conductive pads, is not in itself an obstacle to the use of the antenna for any desired type of polarization.

Preferably, the antenna belongs to the group comprising: planar antennas of the half-wave radiating element type, planar antennas of the quarter-wave radiating element type, planar antennas of the annular radiating element type, planar antennas of the radiating element type with slots written, planar antennas of type radiating element in F-inverted.

Advantageously, the antenna belongs to the group comprising: planar antennas and non-planar antennas due to non-flatness of the ground plane and / or at least one of the radiating elements.

In a first particular embodiment of the invention, at least one of the conductive pads connected to the ground plane or to one of the radiating elements is a conductive projection formed in a first conductive part and extending from a main body. said first conductive part, said main body forming said ground plane or said radiating element.

In a second particular embodiment of the invention, at least one of the conductive pads connected to at least one of the radiating elements is a conductive tab, cut in at least an eccentric part of a second conductive part and folded relative to a central part of the second conductive part, said central part forming said radiating element.

Advantageously, the antenna further comprises at least one support element of said first or second conductive part, made of a dielectric material and for positioning the ground plane with respect to at least one of the radiating elements or for positioning said radiating element with respect to the ground plane or at least one other radiating element.

In a third particular embodiment of the invention, at least one of the conductive pads connected to the ground plane or to at least one of the radiating elements is a conductive hole extending from a first face of a layer of dielectric material, said first face carrying said ground plane or said at least one radiating element, said conductive hole extending from said first face and not opening onto a second face of said dielectric material layer, the surface of said hole conductor being covered with a conductive material.

The invention also relates to a method of manufacturing a planar antenna of the type comprising at least one radiating element separated from a ground plane by a dielectric. According to the invention, the method comprises a step of producing at least one set of conductive pads connected to and extending from at least one of the elements belonging to the group comprising the ground plane and said at least one radiating element, so as to reduce at least one physical dimension of said at least one radiating element for a determined resonant frequency.

• un corps principal formant ledit plan de masse ou ledit élément rayonnant ; et
• au moins une saillie conductrice s'étendant à partir dudit corps principal, de façon à former un des plots conducteurs connectés au plan de masse ou à un des éléments rayonnants.

In a first particular embodiment of the invention, the method comprises the following step, for the ground plane and / or at least one of the radiating elements to which is connected a set of conductive pads: a first conductive part comprising :

• a main body forming said ground plane or said radiating element; and
• at least one conductive projection extending from said main body, so as to form one of the conductive pads connected to the ground plane or to one of the radiating elements.

• on réalise une seconde pièce conductrice comprenant une partie centrale formant ledit élément rayonnant ;
• on découpe au moins une languette conductrice dans une partie excentrique de ladite seconde pièce conductrice ;
• on replie ladite au moins une languette conductrice par rapport à la partie centrale, de façon à former un des plots conducteurs connectés à un des éléments rayonnants.

In a second particular embodiment of the invention, the method comprises the following steps, for at least one of the radiating elements to which is connected a set of conductive pads:

• a second conductive part is made comprising a central part forming said radiating element;
• at least one conductive tongue is cut in an eccentric portion of said second conductive part;
• said at least one conductive tab is folded with respect to the central portion so as to form one of the conductive pads connected to one of the radiating elements.

Advantageously, the method further comprises a step of positioning said first or second conductive part relative to another element of the antenna, using at least one support element made of a dielectric material.

• on réalise au moins un trou dans une couche de matériau diélectrique, ledit au moins un trou s'étendant à partir d'une première face de ladite couche et ne débouchant pas sur une seconde face de ladite couche ;
• on recouvre sélectivement, avec un matériau conducteur :
  • * au moins une partie de ladite première face, de façon à former ledit plan de masse ou ledit élément rayonnant ; et
  • * la surface dudit au moins un trou, de façon à obtenir un trou conducteur formant un des plots conducteurs connectés au plan de masse ou à un des éléments rayonnants.

In a third particular embodiment of the invention, the method comprises the following steps, for the ground plane and / or at least one of the radiating elements to which is connected a set of conductive pads:

• at least one hole is made in a layer of dielectric material, said at least one hole extending from a first face of said layer and not opening onto a second face of said layer;
• selectively covering, with a conductive material:
  • at least a portion of said first face, so as to form said ground plane or said radiating element; and
  • the surface of said at least one hole, so as to obtain a conductive hole forming one of the conductive pads connected to the ground plane or to one of the radiating elements.

5. List of figures

• la figure 1 présente une vue en perspective d'un exemple d'antenne planaire de type patch demi-onde selon l'invention, avec des plots distribués sous l'élément rayonnant ;
• la figure 2 est une vue en coupe de l'antenne de la figure 1 suivant l'axe B-B' ;
• la partie haute de la figure 3 est une vue en coupe de l'antenne de la figure 1 suivant l'axe A-A', permettant d'interpréter l'effet des plots positionnés sous l'élément rayonnant, et la partie basse de la figure 3 est une modélisation électrique de l'effet des plots ;
• la figure 4 présente un exemple d'une antenne planaire de type patch quart-d'onde selon l'invention, avec des plots distribués sous l'élément rayonnant ;
• la figure 5 présente un exemple d'une antenne planaire de type patch annulaire selon l'invention, avec des plots distribués sous l'élément rayonnant ;
• la figure 6 présente un exemple d'antenne obtenue avec un premier mode de réalisation du procédé de fabrication d'antenne selon l'invention, basé sur l'utilisation d'une pièce métallique tridimensionnelle (3D) et de supports de positionnement ;
• la figure 7 présente un exemple d'antenne obtenue avec un second mode de réalisation du procédé de fabrication d'antenne selon l'invention, basé sur l'utilisation d'une couche de substrat diélectrique présentant des trous métallisés non débouchants ;
• la figure 8 illustre des résultats expérimentaux d'une antenne planaire de type patch demi-onde selon l'invention, obtenue avec le second mode de réalisation du procédé de fabrication d'antenne selon l'invention ;
• la figure 9 illustre des résultats expérimentaux d'une antenne planaire de type patch demi-onde classique, et de dimensions identiques à celle de l'antenne selon l'invention dont les résultats sont illustrés sur la figure 8 ;
• la figure 10 illustre des résultats expérimentaux d'une antenne planaire de type patch quart-d'onde selon l'invention, obtenue avec le second mode de réalisation du procédé de fabrication d'antenne selon l'invention ;
• la figure 11 illustre des résultats expérimentaux d'une antenne planaire de type patch quart-d'onde classique, et de dimensions identiques à celle de l'antenne selon l'invention dont les résultats sont illustrés sur la figure 10 ;
• la figure 12 est une vue en coupe d'une configuration d'antenne à deux éléments rayonnants empilés, selon l'invention ;
• la figure 13 est une vue en coupe d'une variante d'antenne à un élément rayonnant selon l'invention, dans laquelle le plan de masse et la face inférieure de l'unique élément rayonnant présentent des plots conducteurs ;
• la figure 14 est une vue en coupe d'une variante d'antenne à deux éléments rayonnants selon l'invention, dans laquelle le plan de masse et les deux faces de l'élément rayonnant primaire présentent des plots conducteurs ;
• la figure 15 est une vue en coupe d'une autre variante d'antenne à un élément rayonnant selon l'invention, dans laquelle le plan de masse est plat et l'unique élément rayonnant est conformé ;
• la figure 16 est une vue en coupe d'une autre variante d'antenne à deux éléments rayonnants selon l'invention, dans laquelle le plan de masse et les deux éléments rayonnants sont conformés ;
• la figure 17 présente une vue en perspective d'une autre variante d'antenne à un élément rayonnant selon l'invention, avec des plots réalisés sous la forme de languettes réparties sur la périphérie de l'élément rayonnant ; et
• la figure 18 est une vue en coupe d'une autre variante d'antenne à trois éléments rayonnants selon l'invention, dans laquelle une face de l'élément rayonnant primaire et les deux faces de l'élément rayonnant intermédiaire présentent des plots conducteurs.

Other features and advantages of the invention will appear on reading the following description of a preferred embodiment of the invention, given by way of indicative and nonlimiting example, and the appended drawings, in which:

• the figure 1 shows a perspective view of an example of a half-wave patch planar antenna according to the invention, with studs distributed under the radiating element;
• the figure 2 is a sectional view of the antenna of the figure 1 along the BB 'axis;
• the upper part of the figure 3 is a sectional view of the antenna of the figure 1 along the axis A-A ', making it possible to interpret the effect of the pads positioned under the radiating element, and the lower part of the figure 3 is an electrical modeling of the effect of the pads;
• the figure 4 shows an example of a planar antenna of quarter-wave patch type according to the invention, with studs distributed under the radiating element;
• the figure 5 shows an example of a planar ring-type antenna according to the invention, with studs distributed under the radiating element;
• the figure 6 shows an example of an antenna obtained with a first embodiment of the antenna manufacturing method according to the invention, based on the use of a three-dimensional metal part (3D) and positioning supports;
• the figure 7 shows an example of an antenna obtained with a second embodiment of the antenna manufacturing method according to the invention, based on the use of a dielectric substrate layer having non-emerging metallized holes;
• the figure 8 illustrates experimental results of a planar antenna of half-wave patch type according to the invention, obtained with the second embodiment of the antenna manufacturing method according to the invention;
• the figure 9 illustrates experimental results of a planar antenna of the conventional half-wave patch type, and of dimensions identical to that of the antenna according to the invention, the results of which are illustrated on FIG. figure 8 ;
• the figure 10 illustrates experimental results of a planar antenna of quarter-wave patch type according to the invention, obtained with the second embodiment of the antenna manufacturing method according to the invention;
• the figure 11 illustrates experimental results of a conventional quarter-wave-type planar antenna of identical dimensions to that of the antenna according to the invention, the results of which are illustrated in FIG. figure 10 ;
• the figure 12 is a sectional view of an antenna configuration with two stacked radiating elements, according to the invention;
• the figure 13 is a sectional view of an antenna variant to a radiating element according to the invention, wherein the ground plane and the lower face of the single radiating element have conductive pads;
• the figure 14 is a sectional view of an antenna variant with two radiating elements according to the invention, wherein the ground plane and the two faces of the primary radiating element have conductive pads;
• the figure 15 is a sectional view of another antenna variant to a radiating element according to the invention, wherein the ground plane is flat and the single radiating element is shaped;
• the figure 16 is a sectional view of another variant of antenna with two radiating elements according to the invention, wherein the ground plane and the two radiating elements are shaped;
• the figure 17 shows a perspective view of another antenna variant to a radiating element according to the invention, with pads made in the form of tabs distributed over the periphery of the radiating element; and
• the figure 18 is a sectional view of another variant of antenna with three radiating elements according to the invention, in which a face of the radiating element primary and the two faces of the intermediate radiating element have conductive pads.

6. Detailed description

On the Figures 1 to 7 , 12 and 17 the same element retains the same numerical reference from one figure to the other (in particular 1 for the radiating element, 2 for the ground plane, 3 for the dielectric between the radiating element and the ground plane, and 4 for conductive pads).

A conventional planar antenna comprises at least one radiating element and a ground plane. At least one dielectric separates the radiating element closest to the ground plane and the ground plane itself, as well as the radiating elements between them. "Dielectric" is understood to mean air or a solid material having characteristics close to those of air, such as, for example, materials of plastic type, foam, etc.

The general principle of the invention is to add to such a conventional planar antenna a plurality of conductive pads connected to and extending from the ground plane and / or one or more radiating elements, so as to reduce minus a physical dimension of the radiating element (s) for a determined resonant frequency.

The figure 1 shows a perspective view of an example of a half-wave patch planar antenna according to the invention, with studs distributed only under the radiating element. These pads 4 are connected to the radiating element 1 and extend towards the ground plane 2 without being connected thereto. In this example, the antenna is modeled by two radiating slots 5, located at the two ends separated by the half-wave length ( figure 3 ).

The pads are for example distributed according to a spatial distribution, called matrix, as illustrated in FIG. figure 2 , which is a sectional view of the antenna of the figure 1 along the axis B-B '. This distribution may be uniform or not. In general, any type of arrangement of the pads may be considered, without departing from the scope of the present invention.

The upper part of the figure 3 is a sectional view of the antenna of the figure 1 along the axis A-A ', making it possible to interpret the effect of the studs positioned under the element beaming. The distribution of the electric field between the radiating element 1 and the ground plane 2 is represented by dashed arrows. The lower part of the figure 3 is an electrical modeling of the effect of the pads 4 positioned under the radiating element 1.

At the electrical level, the pads 4, positioned between the radiating pattern 1 and the ground plane 2, and only connected to this radiating pattern 1, locally change the distribution of the electromagnetic field, resulting in an increase in the equivalent capacitive effect (local capacitance C), brought back to the different connection points of these pads 4 with the radiating pattern 1. As a result, the phase velocity of the signal on the radiating pattern 1 decreases, which makes it possible to reduce at least one dimension (the length and / or the physical width of the radiating pattern 1 for a fixed resonant frequency (see hereinafter the reminder of the mathematical reasoning which explains this). It should be noted that this decrease in length and / or width depends directly on the number of pads 4 under the radiating pattern 1, as well as their positions and their dimensions (length and diameter). Thus, for example, the more the number and the length of the studs increase, the more the reduction in size becomes important.

In order to explain the above, it is recalled that on the radiating element, the phase velocity v _φ is a function of the local capacitance C and the local inductance L: $$v_{\phi }=\frac{1}{\sqrt{\mathit{LxC}}}$$

Consequently, an increase of C makes it possible to decrease v _φ .

In addition, at a given resonance frequency f _res , the antenna must be equivalent to a given electrical length φ. For example, for a half-wave patch antenna: φ = 180 °.

Now, φ = _physical β xl, where β = (2πf _res / v _φ ) and _physical is the physical length of the antenna. So, φ = 2πf _res (l _physics / v _φ )

For f _res and φ data, if v _φ decreases, then the _physics also decreases, hence the miniaturization of the antenna. In addition, the more one increases C, the more v _φ decreases and therefore the more _physical decreases.

It is not necessary to have a set of uniform pads. It is quite conceivable to design studs of different shapes and sizes.

To feed a planar antenna according to the invention, all conventional excitation means can be envisaged, whether by a simple line section connected on one of the edges of the radiating element and acting as an impedance transformer to correctly adapt the antenna, by a probe connected directly to an equivalent point "50Ω" on the surface of the radiating element or by an excitation solution based on electromagnetic coupling.

In any case, in order not to impede this connection with the signal processing circuits placed upstream of the antenna, it suffices, if necessary, not to add pads under the zone locally concerned by this interconnection between the element. radiating and feeding means.

On the other hand, on the example of figure 1 , the symmetry along the two main axes (X, Y on the figure 2 ) of the radiating element 1 is respected. In other words, the studs are distributed according to a provision respecting this symmetry. It is therefore entirely possible to exploit the antenna according to two crossed linear polarizations, or even circular polarization. The developed solution, based on pads, is not in itself an obstacle to the use of the antenna for any desired type of polarization.

Another fundamental point, underlining all the interest presented by the technique of the invention, corresponds to its easy implementation for any other type of planar antenna. Indeed, the principle of conductive pads under the radiating element can adapt without any particular difficulty to configurations and very different planar antenna geometries, whether for planar patterns with mass return, for recessed patterns or annular, for reasons with inscribed slots or, very generally, for any type of planar structures known to those skilled in the art.

To illustrate this point, two other examples of planar antennas with studs according to the invention are given on the Figures 4 and 5 : it is a planar antenna of the quarter-wave patch type, with mass return (referenced 6) located on one of the slices of the support 3 ( figure 4 ), as well as a planar ring-type antenna ( figure 5 ).

Concerning the concrete realization of the planar antennas with pads according to the invention, several simple manufacturing processes can be envisaged, this simplicity being a fundamental criterion to reduce in particular the cost of these components.

We present now, in relation to the figure 6 , a first embodiment of the antenna manufacturing method according to the invention. In this first embodiment, the radiating element (patch) 1 and the pads 4 are produced in a single conductive part 7 (for example a metal part), obtained by machining, stamping or any other method of manufacturing metal parts. dimensional. In other words, the main body of the conductive part 7 forms the radiating element 1, and the conductive pads 4 are conductive projections formed in the conductive part and which extend from the main body of this part.

This piece is then transferred to one or more support elements 8, to position it relative to the lower ground plane. A preferred solution is to use at the support 8 a dielectric material whose nature makes it close to the air, so that this or these media are the most transparent possible, from an electromagnetic point of view. It is, for example, recommended to use a foam-type material for which the electrical characteristics are entirely in accordance with the required requirements (eg ROHACELL HF71 polymethacrylate imide foam from ROEHM: εr = 1.1 1 and tgδ = 7.10 ^-4 at 5GHz). In an alternative embodiment, the dielectric material in which the support element or elements is produced is a plastic material, easily shaped for example by one of the known molding techniques.

The figure 6 shows an example of an antenna obtained with this first embodiment of the antenna manufacturing method according to the invention, based on the use of a three-dimensional metal part 7 (integrating the radiating element 1 and the pads 4) and The dielectric 3 included in the space between the radiating element 1, on which the conductive pads 4 are connected, and the ground plane 2 is for example air.

We present now, in relation to the figure 7 , a second embodiment of the antenna manufacturing method according to the invention. This second solution is much more consistent with the techniques of making standard printed circuits.

It involves drilling directly into the support substrate 3 of the antenna (which may be of foam, plastic material ..., that is to say a layer of dielectric material other than air), holes (vias) non-emerging and to cover selectively with a conductive material, the upper face of this substrate (so as to form the radiating element 1), as well as the inside of the holes extending from this upper face (so as to form the conductive pads 4). In other words, the conductive pads 4 are here made in the form of conductive holes.

In a preferred embodiment, the coating with a conductive material consists of a metallization. This metallization can be carried out simply for example by conductive paint deposition or by electrochemical deposition. It is clear, however, that any technique known to those skilled in the art can be used to perform the coating with a conductive material.

Electrically, the conductive holes (vias) 4 have an effect similar to that of the conductive pads of the preceding solutions (conductive projections), hence the reduction in the size of the radiating element 1.

This element (support substrate 3 whose upper face carries the radiating element 1 and has a plurality of metallized holes 4) is then brought into contact, by its lower face, with a ground plane 2 to obtain the final structure of the antenna.

It should be noted that, for this second solution, it is also preferable to choose a foam-type substrate, which, as specified above, has electrical characteristics quite suitable for the production of planar antennas and which, moreover, very easily lends itself to a three-dimensional conformation according to the desired shape. In an alternative embodiment, the support substrate is a plastic material, easily shaped by one of the known molding techniques.

The figure 7 shows an example of an antenna obtained with this second embodiment of the antenna manufacturing method according to the invention, based on the use of a dielectric substrate 3 whose upper face carries the radiating element 1 and has a plurality of metallized holes forming conductive pads 4.

• on réalise une pièce conductrice 171 (par exemple une feuille métallique) comprenant une partie centrale formant l'élément rayonnant 1 ;
• on découpe une pluralité de languettes conductrices sur le pourtour de cette pièce conductrice (c'est-à-dire dans des parties excentriques de cette pièce, adjacentes à la partie centrale) ;
• on replie les languettes conductrices, par rapport à la partie centrale, de façon à former des plots conducteurs 4 connectés à l'élément rayonnant 1. Une fois repliées (par exemple orthogonalement à la partie centrale formant l'élément rayonnant), les languettes conductrices 4 sont par exemple positionnées sur les tranches d'un substrat formant un élément de support 170.

We present now, in relation to the figure 17 , a third embodiment of the antenna manufacturing method according to the invention. In this third embodiment, the radiating element (patch) and the pads are produced in the following manner:

• a conductive part 171 (for example a metal foil) is formed comprising a central part forming the radiating element 1;
• a plurality of conductive tongues are cut on the periphery of this conductive part (ie in eccentric parts of this part, adjacent to the central part);
• the conductive tabs are folded, with respect to the central part, so as to form conductive pads 4 connected to the radiating element 1. Once folded (for example orthogonally to the central part forming the radiating element), the conductive tabs 4 are for example positioned on the edges of a substrate forming a support member 170.

The figure 17 shows an example of antenna obtained with this third embodiment of the antenna manufacturing method according to the invention, based on the realization of folded conductive tabs, which form conductive pads 4.

The positioning of the radiating element relative to the ground plane or vice versa is carried out using one or more supports that may be of the same style as those presented in FIG. figure 6 . In a preferred embodiment, the support member is other than a dielectric substrate wafer 170 whose height is slightly greater than the height of the tongues to prevent contact between the tongues and the ground plane.

To validate miniature planar antennas according to the invention, a first antenna prototype according to the invention, of the type, of the antenna presented on the figure 7 , Have been realised. This is a half-wave patch solution, printed on a foam material of dimensions 50x50x10mm ³ and reported on a ground plane of 100x100mm ² . In this substrate, non-emerging vias of cylindrical geometry (diameter Φ = 2mm and height h = 7.5mm) were drilled evenly over the entire upper surface of the foam block. In the present case, the metallization of this upper surface and the interior of the vias is carried out by direct deposition of a conductive silver-based paint (reference: Spraylat 599B3730). At the polarization level, it has been chosen to integrate a single linear polarization antenna, which does not then require only one point of excitation. This is done by using a coaxial probe, connected at its end at an equivalent point "50Ω" on the upper surface of the radiating element.

One can quite consider a design where holes vary in shape and size.

The figure 8 illustrates experimental results of this first planar antenna prototype according to the invention. The antenna has been characterized in adaptation and transmission along the preferred axis of radiation. The transmission measurement is based on the implementation of a simple link budget between the developed prototype and a reference antenna (in this case, a printed dipole). It should be noted that, since this link budget is not carried out in an anechoic chamber, the result presented only makes it possible to illustrate the radiation qualitatively.

By comparison, the measurements of a simple classical half-wave patch antenna, also printed on foam and of dimensions identical to the previous radiating element (50x50x10mm ³ ), are illustrated on the figure 9 . To allow this comparison between the two antennas, the measurement of the link budget was performed under conditions quite similar to the previous one.

As can be noted on the Figures 8 and 9 , the resonant frequency of the antenna according to the invention (with vias non-emerging) is much lower than that of the conventional antenna. A 25% reduction effect is observed in the value of this resonance frequency (that is to say .DELTA.f = _{665MHz. Minia} f _r = 1.969GHz instead of _classi f _r = _2.634GHz.). Apart from this significant frequency shift, the levels of adaptation, bandwidth and radiation remain fundamentally correct, as shown by the responses measured on both antennas. The technique of the invention (addition of conductive pads 4) thus leads to significant possibilities of miniaturization of the printed pattern (radiating element).

To underline the general character of the technique of the invention, a second miniature antenna prototype has been made: it is a quarter-wave patch antenna, with mass return located on one of the slices. of the support. As in the previous case, it is the principle of the holes (vias) distributed in the foam material which has been retained. This antenna was printed on a substrate of dimensions 25x25x10mm ³ and reported on a ground plane of 100x100mm ² . Non-through vias always have a cylindrical geometry (Φ = 2mm and h = 7.5mm). The mass return is performed by a tab of 5mm width, printed on one of the slices of the foam support substrate and connected at its end to the ground plane. The excitation is obtained by coaxial probe connected at a point "50Ω".

The figure 10 illustrates experimental results of this second planar antenna prototype according to the invention. This second prototype has also been characterized in adaptation and transmission.

These results can be compared to those of a conventional quarter-wave patch antenna, with a geometry quite similar to that of the second prototype, except for the presence of non-emerging vias, and whose performances are given on the figure 11 .

As illustrated by these figures 10 and 11 , there is again a clear shift towards low frequencies for the antenna according to the invention (with vias non-emerging), resulting in significant opportunities for reducing the size of the radiating element (basic printed pattern). In this case, the resonance frequency was reduced by approximately 20% (.DELTA.f = _{265MHz. Minia} f _r = 1.210GHz instead of f _r = 1.475GHz _{classification.),} Other antenna performance does not seem to priori disturbed.

Furthermore, the general principle of the invention (adding pads under the surface of a radiating element in order to reduce at least one dimension (length and / or width) physically for a fixed resonant frequency) can also be used. apply for planar antennas with several stacked elements.

It is recalled that such multi-element antennas are used for example for broadband applications or multifrequency applications.

For example, the figure 12 shows a sectional view of an antenna configuration with two stacked radiating elements, according to the invention.

This antenna comprises a primary radiating element 1, separated from the ground plane 2 by a first dielectric 3, and an upper radiating element 10, separated from the primary radiating element 1 by a second dielectric 9.

The primary radiating element is defined as the radiating element closest to the ground plane. The upper radiating element is defined as the radiating element furthest from the ground plane.

In this example, the concept of miniaturization according to the invention (addition of pads 124) is applied only to the primary radiating element 1. In other words, the upper radiating element 10 is not connected to any stud .

In general, the antenna may comprise any number of superimposed radiating elements and the concept of the invention (addition of conductive pads) may be applied to all the radiating elements of the superposition or to only one or more 'between them.

• seul le plan de masse présente des plots conducteurs ;
• seul(s) un ou plusieurs élément(s) rayonnant(s) présente(nt) des plots conducteurs ;
• le plan de masse et un ou plusieurs élément(s) rayonnant(s) présentent des plots conducteurs. Cette configuration permet de réduire encore plus la taille finale du ou des élément(s) rayonnant(s).

As already mentioned above, the concept of the invention (addition of conductive pads) can also be applied to the ground plane (addition of pads on its face located on the side of the radiating element or elements), independently or in combination with an application to one or more radiating elements. In other words, the following different cases can be envisaged in the context of the present invention:

• only the ground plane has conductive pads;
• only one or more radiating element (s) present conductive studs;
• the ground plane and one or more element (s) radiating (s) have conductive pads. This configuration further reduces the final size of the element (s) radiating (s).

The figure 13 is a sectional view of an antenna variant to a radiating element according to the invention. The ground plane 132 has conductive pads 135. The lower face of the single radiating element 131 also has conductive pads 134. There is then an array of first pads 134 distributed under the radiating element 131 and connected only to the latter , and an array of second pads 135 distributed on the ground plane and connected only to this plane. These two matrices are located in the area between the upper radiating element and the lower ground plane. To avoid contact between the pads of the two matrices, the first pads are interlaced with the second pads.

In this case, the electrical effect of the pads as described previously (in relation to the figure 3 ) is accentuated, which further reduces the physical dimension (length and / or width) of the radiating element for a fixed resonant frequency.

To validate this principle, an antenna prototype with pads connected to the radiating element and to the ground plane has been realized. This is a half-wave patch type solution, printed on a 50x50x10mm3 foam material and reported on a 100x100mm2 ground plane. In comparison with a conventional half-wave patch (that is to say without a pad) of the same dimensions, the reduction of the resonant frequency is then very significant: this frequency passes in effect from 2.634GHz for the conventional antenna to 1.225GHz for the antenna of the invention, resulting in a decrease of more than 53%. This therefore leads to possibilities of ultra miniaturization of the basic printed pattern.

In the case of an antenna comprising a superposition of several radiating elements, the concept of the invention (addition of conductive pads) can also be applied simultaneously to the two faces of the same radiating element (except for the last of the superposition, that is to say the one farthest from the ground plane). In other words, the same radiating element may comprise first pads which extend from its lower face and second pads which extend from its upper face.

The figure 14 is a sectional view of an antenna variant according to the invention, comprising a ground plane 142 and two radiating elements 141, 147. The ground plane 142 has conductive pads 144. The upper radiating element 147 does not present no plot. The primary radiating element 141 has first conductive pads 146 on its lower face and second conductive pads 145 on its upper face.

The figure 18 is a sectional view of another antenna variant according to the invention, comprising a ground plane 180 and three radiating elements: a primary radiating element 181 (see definition above), an upper radiating element 183 (see definition above) and an intermediate radiating element 182. An intermediate radiating element is defined as a radiating element placed between the element radiating primary and the upper radiating element. The ground plane 180 and the upper radiating element 183 do not have a stud. The primary radiating element 181 has conductive pads 184 on its underside. The intermediate radiating element 182 has first conductive pads 185 on its lower face and second conductive pads 186 on its upper face. In general, the fact that the same radiating element has conductive pads on its two faces allows to further miniaturize the antenna. In the same antenna, one can of course have several radiating elements having conductive pads on their two faces.

The present invention applies to any type of planar antenna (in the general sense already discussed above), that is to say both planar planar antennas actually flat planar antennas not actually planar (because the ground plane and / or at least one radiating element is not plane but shaped according to a determined three-dimensional shape).

The figure 15 is a sectional view of another antenna variant according to the invention, comprising a flat ground plane 152 and a radiating element 151 which has conductive pads 154 and is shaped (i.e. three-dimensional non-planar).

The figure 16 is a sectional view of another antenna variant according to the invention, comprising: a ground plane 162 which has conductive pads 164 and is shaped; and two radiating elements 161, 167, which each have conductive pads 165, 166 and which are shaped. The radiating element referenced 161, between the upper radiating element 167 and the ground plane 162, is called primary radiating element.

We have presented above, in relation with the Figures 6, 7 and 17 , three examples of manufacturing techniques applied to the manufacture of a radiating element having conductive pads. In the first technique, the conductive pads are conductive projections ( figure 6 ). In the second technique, the conductive pads are conductive holes ( figure 7 ). In the third technique, the conductive pads are conductive tabs ( figure 17 ). The first and second techniques can be used to make a ground plane with pads. On the other hand, because the ground plane has a dimension always greater than that of the radiating element, the third technique (tabs) can not be applied to the manufacture of a ground plane comprising conductive pads.

It should be noted that in the case where the pads are made in the form of conductive holes, a same layer of dielectric substrate may carry the ground plane (or a first radiating element) on its lower face and a radiating element (or a second radiating element) on its upper face. The pads connected to the ground plane (or to the first radiating element) are made in the form of first conductive holes which extend from the lower face of the substrate layer and do not open on the upper face of the ground layer. substrate. The pads connected to the radiating element (or the second radiating element) are made in the form of second conductive holes which extend from the upper face of the substrate layer and do not open on the underside of the layer. of substrate.

It should also be noted that the aforementioned manufacturing techniques can be combined. For example, for the ground plane or a radiating element, it is possible to produce a conductive part which comprises, on the one hand, conductive projections forming first conductive pads and, on the other hand, folded conductive tabs forming second conductive pads.

Of course, the invention is not limited to the embodiments mentioned above. There may be other variants that further minimize the size of the antenna by varying the number, size, shape and layout of the pads.

The general principle of the present invention can be implemented in any field of application that can use a planar antenna (mobile applications, satellite communications applications, wireless RF applications, etc.) in very different frequency ranges (from a few hundred MHz to a few tens of GHz).

Claims (24)

1. Planar antenna of the type comprising a radiating element (1) separated from a flat base element (2) by an insulator (3), characterised in that it additionally comprises at least one series of conductive studs (4; 124; 134; 145; 146; 154; 165; 166; 184 to 186) belonging to the group comprising:

   - a series of conductive studs connected to a given radiating element and extending towards, without being connected to, one face of the flat base element, with each conductive stud having a length that is strictly less than the minimum distance between, on the one hand, the end of the stud connected to the radiating element indicated above and, on the other, the said face of the flat base element;

   - a series of conductive studs connected to a given radiating element and extending towards, without being connected to, one face of another radiating element, with each conductive stud having a length that is strictly less that the minimum distance between, on the one hand, the end of the stud connected to the radiating element indicated above and, on the other, the said face of the other radiating element.
2. Antenna in accordance with claim 1 above, characterised in that it comprises at least one series of conductive studs (135; 144; 164) connected to the flat base element and extending towards, without being connected to, one face of a given radiating element, with each conductive plot having a length that is strictly less than the minimum distance between, on the one hand, the end of the stud connected to the flat base element and, on the other, the said face of the radiating element indicated above.
3. Antenna in accordance with either claim 1 or 2 above, of the type comprising a single radiating element, characterised in that it comprises a second series of conductive studs (4; 134; 154) connected to the said single radiating element and extending towards, but not connected to, the said flat base element.
4. Antenna in accordance with either claim 1 or 2 above, of the type comprising a superposition of at least two radiating elements separated by an insulator, with the radiating element that is closest to the flat base element being known as the primary radiating element, characterised in that it comprises a third series of conductive studs (124; 146; 165; 184) connected to a first face of the said primary radiating element and extending towards, but not connected to the said flat base element.
5. Antenna in accordance with any of the above claims 1 to 4, with the exception of claim 3, of the type comprising a superposition of at least two radiating elements separated by an insulator, with the radiating element that is closest to the flat base element being known as the primary radiating element, characterised in that it comprises a fourth series of conductive studs (145) connected to a second face of the said primary radiating element and extending towards, but not connected to another of the said radiating elements.
6. Antenna in accordance with any of the above claims 1 to 5, with the exception of claim 3, of the type comprising a superposition of at least three radiating elements separated by insulators, with the radiating element that is closest to the flat base element being known as the primary radiating element, and the radiating element that is furthest from the flat base element being known as the upper radiating element, with each radiating element other than the primary radiating element and the upper radiating element being known as the intermediary radiating element, characterised in that it comprises, for at least one of the intermediary radiating elements, a fifth series of conductive studs (186) connected to a first face of the said intermediary radiating element and extending towards, but not connected to, another of the said radiating elements, which follows the said intermediary radiating element along a direction of travel of the said superposition of the primary radiating element towards the upper radiating element.
7. Antenna in accordance with any of the above claims 1 to 6, with the exception of claim 3, of the type comprising a superposition of at least three radiating elements separated by insulators, with the radiating element that is closest to the flat base element being known as the primary radiating element and the radiating element that is furthest from the flat base element being known as the upper radiating element, with each radiating element other than the said primary radiating element and the said upper radiating element, being known as the intermediary radiating element, characterised in that it comprises, for least one of the intermediary radiating elements, a sixth series of conductive studs (185) connected to a second face of the said intermediary radiating element and extending towards, but not connected to, one of the other said radiating elements preceding the said intermediary radiating element along a direction of travel of the said superposition of the primary radiating element towards the upper radiating element.
8. Antenna in accordance with any of claims 1 t5o 7 above, with the exception of claim 3, of the type comprising a superposition of at least two radiating elements separated by insulators, with the radiating element that is closest to the flat base element being known as the primary radiating element and the radiating element that is furthest from the flat base element being known as the upper radiating element, with each radiating element other than the said primary radiating element and the said upper radiating element, being known as the intermediary radiating element, characterised in that it comprises, for least one of the intermediary radiating elements, a seventh series of conductive studs (166) connected to a second face of the said intermediary radiating element and extending towards, but not connected to, one of the other said radiating elements preceding the said intermediary radiating element along a direction of travel of the said superposition of the primary radiating element towards the upper radiating element.
9. Antenna in accordance with any of the above claims 1 to 8 above, characterised in that a series of conductive studs, extending from the flat base element or respectively from one of the radiating elements, is interlaced with another series of conductive studs, extending from one of the radiating elements or respectively from one of the other radiating elements.
10. Antenna in accordance with any of the above claims 1 to 9, characterised in that for each radiating element to which is connected a series of conductive studs, the said radiating element is not connected to any conductive stud in a zone in which the said radiating element is connected to the power supply source.
11. Antenna in accordance with any of the above claims 1 to 10, characterised in that the conductive studs of an individual series of conductive studs are arranged in the manner of a matrix.
12. Antenna in accordance with any of the above claims 1 to 11, characterised in that at least one radiating element to which is connected at least one series of conductive studs is of the type having a symmetry along its two principal axes and in that the said conductive studs are arranged in a manner that respects this symmetry.
13. Antenna in accordance with any of the above claims 1 to 12, characterised in that it belongs to the group comprising: antennae of the half-wave radiating element type, antennae of the quarter wave radiating element type, antennae of the annular radiating element type, antennae of the inscribed slot radiating element type and antennae of the inverted F radiating element type.
14. Antenna in accordance with any of the above claims 1 to 13, characterised in that it belongs to the group comprising: planar antennae and non-planar antennae by virtue of the lack of inherent flatness of the flat base element and/or of at least one of the radiating elements.
15. Antenna in accordance with any of the above claims 1 to 14, characterised in that at least one of the conductive studs connected to the flat base element or to one of the radiating elements is a conductive projection in the form of a first conductive piece (7) extending from a principal body of the said first conductive piece, this principal body forming the said flat base element or the said radiating element.
16. Antenna in accordance with any of the above claims 1 to 15, characterised in that at least one of the conductive studs connected to at least one of the radiating elements is in the form of a conductive strip, cut into at least one eccentric part of a second conductive piece (171) and folded in relation to a central part of the second conductive piece, the said central piece constituting the radiating element.
17. Antenna in accordance with the above claims 15 and 16, characterised in that it also comprises at least one supporting element (8; 170) of the said first (7) or second (171) conductive piece, formed from an insulating material and allowing the flat base element to be positioned in relation to at least one of the radiating elements or allowing the said radiating element to be positioned in relation to the flat base element or at least one of the other radiating elements.
18. Antenna in accordance with any of the above claims 1 to 17, characterised in that at least one of the conductive studs connected to the flat base element or to at least one of the radiating elements is conductor aperture extending from a first face of a layer of dielectric material, the said first face bearing the said flat base element or the said at least one radiating element, the said conductor aperture extending from the said first face and not opening out onto a second face of the said layer of dielectric material, the surface of the said conductor aperture being coated with a conductive material.
19. Process for the manufacture of a planar antenna of the type comprising at least one radiating element (1) separated from a flat base element (2) by a dielectric element (3), characterised in that it comprises a manufacturing stage of at least one series of conductive studs (4) belonging to the group comprising:

    - a series of conductive studs connected to a given radiating element and extending towards, but not connected to, one face of the flat base element, with each conductive stud having a length strictly less than the distance between on the one hand the end of the stud connected to the given radiating element and, on the other, to the said face of the flat base element;

    - a series of conductive studs connected to a given radiating element and extending towards, but not connected to, one face of another radiating element, with each conductive stud having a length strictly less than the minimum distance between, on the one hand, the end of the stud connected to the given radiating element and, on the other hand, the said face of the other radiating element.
20. Process in accordance with claim 19 above, characterised in that it comprises a stage for the manufacture of at least one series of conductive studs (135; 144; 164) connected to the flat base element and extending towards, but not connected to, one face of a given radiating element, with each conductive stud having a length strictly less than the minimum distance between on the one hand the end of the stud connected to the flat base element and, on the other, to the face of the said radiating element.
21. Process in accordance with either of the claims 19 and 20 above, characterised in that it comprises the following stage for the flat base element and/or at least one of the radiating elements to which is connected a series of conductive studs: a first conductive piece is produced comprising:

    - a principal body constituting the said flat base element or the said radiating element; and

    - at least one conductive projection extending from the said principal body, in such a way as to form one of the conductive studs connected to the flat base element or to one of the radiating elements.
22. Process in accordance with any of the claims 19 to 21 above, characterised in that it comprises the following stages for at least one of the radiating elements to which is connected a series of conductive studs:

    - a second conductive piece is produced comprising a central part constituting the said radiating element;

    - at least one small conductive strip is cut into an eccentric part of the second conductive piece;

    - at least one conductive strip is folded in relation to the central part, in such a way as to form one of the conductive strips connected to one of the radiating elements.
23. Process in accordance with one of the above claims 21 and 22, characterised in that it also comprises a stage by which the first or second conductive piece is positioned in relation to another element of the antenna by means of at least one supporting element made of an insulating material.
24. Process in accordance with any of the claims 21 to 23 above, characterised in that it comprises the following stages for the flat base element and/or at least one of the radiating elements to which is connected a series of conductive studs:

    - at least, one aperture is made in a layer of dielectric material, with the said at least one aperture extending from a first face of the said layer and not opening out onto a second face of the said layer;

    - using a conductive material, the following is then selectively covered:

    • at least a part of the said first face, in such a way as to form the said flat base element or the said radiating element, and

    • the surface of the said at least one aperture in such a way as to obtain a conductive aperture forming one of the conductive studs connected to the flat base layer or to one of the radiating elements.

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