Patent Application
20080198086
The field of the disclosure is that of planar antennas of the type that include at least one radiating element (also known as a “patch”, planar pattern, radiating pattern or printed pattern) separated from a ground plane by a dielectric.
Our era is currently experiencing a significant expansion in mobile networks, and, more generally, in all “wireless” networks. Since such systems bring attractive responses on many points, such as connection flexibility, mobility, redeployment or the possibilities of network extension, this expansion should continue to grow in a highly significant manner in the future.
In fact, in all these systems, the radiating elements are part of the key components, in respect of which the required specifications are increasingly restrictive. Clearly all areas of electrical performance in relation to these antennas need constantly to be optimised, but there is also a need to satisfy increasingly critical criteria, such as the space requirement, the weight or the cost of these components.
Antenna miniaturisation currently represents therefore a significant challenge and a great deal of work is being done in this area at an international level. This miniaturisation offers in fact a great many advantages, among which may be cited: the ease with which antennas can be built into on-board equipment (particularly, within mobiles), greater flexibility in networking these radiating elements (on account of their small size), a wider diagram aperture facilitating in particular the incorporation of wide beam steering systems etc.
Among the different technologies used to incorporate the antennas, planar solutions today seem particularly appropriate in order to meet all the required specifications. This planar approach in fact offers designers sufficient flexibility in the development of effective solutions with particularly small dimensions.
By an entirely classic misuse of language in the field of antennas, “planar antennas” (or antennas implemented using planar technology) are taken to be:
Planar antennas of the aforementioned second category (antennas that are not actually plane) are generally, but not compulsorily, made using a printed technology. This explains why, historically, the adjective “planar” has been selected in the expression “planar antenna”, to show an opposition with the traditional antenna structure based on a three-dimensional (3-D) waveguide. The present disclosure falls within this framework and relates more exactly to an original planar antenna solution in the aforementioned sense, and to a method of manufacture thereof, allowing the physical size of the basic printed pattern (in other words of the radiating element or elements, also known as patches) to be considerably reduced.
The reduction in the size of planar antennas is a major issue in making them easier to use and to incorporate in modem systems.
The basic principle of most of the solutions implemented hitherto consists in increasing the equivalent electrical length of the printed pattern, so that it can radiate at the required frequency, while reducing its physical dimensions (i.e. its surface or its volume).
To this end, the most commonly used structures correspond to:
It should be noted that these different concepts may also be combined within one and the same structure (see for example patent document WO 02/101874).
An embodiment of the invention uses a planar antenna of the type that comprises at least one radiating element separated from a ground plane by a dielectric. According to an embodiment of the invention, the antenna further comprises at least one assembly of conductive studs 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, in order to reduce at least one physical dimension of said at least one radiating element for a given resonant frequency.
The general principle of an embodiment of the invention therefore consists simply in arranging studs on the ground plane and/or on one or more radiating element(s) (patch(es)) of the planar antenna.
In the context of an embodiment of the present invention, the term stud is used in a generic sense, in that it is able to be broken down into different variants (and particularly but not exclusively, as set out in detail in the disclosure below, in the form of a projection, a hole or again a tab).
Dielectric is taken to mean the air or a solid material with characteristics close to those of air, such as for example materials of the plastic, or foam type etc.,
As explained in detail below, in relation to
Different assemblies of conductive studs are specified hereinafter. It is clear that there are many conceivable embodiments of the present invention, each corresponding to a different combination of one or more of these assemblies. It should also be noted that an embodiment of the present invention applies with an antenna structure that comprises a single radiating element or with an antenna structure that comprises a stack of several radiating elements.
To advantage, the antenna comprises a first assembly of conductive studs connected to the ground-plane and extending towards, without being connected to, said at least one radiating element.
In the event of the antenna being of the type that comprises a single radiating element, it comprises to advantage a second assembly of conductive studs connected to said single radiating element and extending towards, without being connected to, said ground plane.
In the event of the antenna being of the type that comprises a stack of at least two radiating elements separated from each other by a dielectric, the radiating element closest to the ground plane being known as the primary radiating element, the antenna comprises to advantage a third assembly of conductive studs connected to a first surface of said primary radiating element and extending towards, without being connected to, said ground plane.
In the event of the antenna being of the type that comprises a stack of at least two radiating elements separated from each other by a dielectric, the radiating element closest to the ground plane being known as the primary radiating element, the antenna comprises to advantage a fourth assembly of conductive studs connected to a second surface of said primary radiating element and extending towards, without being connected to, another of said radiating elements.
In the event of the antenna being of the type that comprises a stack of at least three radiating elements separated from each other by dielectrics, the radiating element closest to the ground plane being known as the primary radiating element, the radiating element furthest away from the ground plane being known as the upper radiating element, each radiating element other than the primary radiating element and the upper radiating element being known as an intermediate radiating element, the antenna comprises to advantage, for at least one of the intermediate radiating elements, a fifth assembly of conductive studs connected to a first surface of said intermediate radiating element and extending towards, without being connected to, another of said radiating elements which follows said intermediate radiating element along a direction of run of said stack of the primary radiating element towards the upper radiating element.
In the event of the antenna being of the type that comprises a stack of at least three radiating elements separated from each other by dielectrics, the radiating element closest to the ground plane being known as the primary radiating element, the radiating element furthest away from the ground plane being known as the upper radiating element, each radiating element other than said primary radiating element and said upper radiating element being known as an intermediate radiating element, the antenna comprises to advantage, for at least one of the intermediate radiating elements, a sixth assembly of conductive studs connected to a second surface of said intermediate radiating element and extending towards, without being connected to, another of said radiating elements which precedes said intermediate radiating element along a direction of run of said stack of the primary radiating element towards the upper radiating element.
In the event of the antenna being of the type that comprises a stack of at least two radiating elements separated from each other by a dielectric, the radiating element closest to the ground plane being known as the primary radiating element, the radiating element furthest away from the ground plane being known as the upper radiating element, each radiating element other than said primary radiating element and said upper radiating element being known as an intermediate radiating element, the antenna comprises to advantage a seventh assembly of conductive studs connected to a first surface of said upper radiating element and extending towards, without being connected to, another of said radiating elements which precedes said upper radiating element along a direction of run of said stack of the primary radiating element towards the upper radiating element.
To advantage, an assembly of conductive studs, extending from the ground plane of from one of the radiating elements respectively, interlaces with another assembly of conductive studs, extending from one of the radiating elements or from another of the radiating elements respectively.
To advantage, for each radiating element to which an assembly of conductive studs is connected, said radiating element is not connected to any conductive stud in an area where said radiating element is connected with power supply means.
To advantage, the conductive studs of one and the same assembly of conductive studs are distributed in a matrix.
According to one advantageous characteristic, at least one radiating element to which at least one assembly of conductive studs is connected is of the type that has symmetry along its two main axes, and in that said conductive studs are distributed in an arrangement that respects said symmetry.
In this way, it is perfectly possible to use the antenna of an embodiment of the invention in accordance with two crossed linear polarisations, or even in circular polarisation. The solution developed, based on conductive studs, is not therefore per se an obstacle to the use of the antenna for any type of required polarisation.
Preferentially, 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 inscribed slot radiating element type, planar antennas of the inverted-F radiating element type.
To advantage, the antenna belongs to the group comprising: plane antennas and antennas that are not plane on account of the non-planeness of the ground plane and/or of at least one of the radiating elements.
In a first particular embodiment of the invention, at least one of the conductive studs connected to the ground plane or to one of the radiating elements is a conductive projection formed in a first conductive component and extending from a principal body of said first conductive component, said principal body forming said ground plane or said radiating element.
In a second particular embodiment of the invention, at least one of the conductive studs connected to at least one of the radiating elements is a conductive tab, cut from at least one excentric part of a second conductive component, and folded back relative to a central part of the second conductive component, said central part forming said radiating element.
To advantage, the antenna further comprises at least one support element of said first or second conductive component, made of a dielectric material and allowing the ground plane to be positioned relative to at least one of the radiating elements or said radiating element to be positioned relative to the ground plane or at least one other of the radiating elements.
In a third particular embodiment of the invention, at least one of the conductive studs connected to the ground plane or to at least one of the radiating elements is a conductive hole extending from a first surface of a layer of dielectric material, said first surface carrying said ground plane or said at least one radiating element, said conductive hole extending from said first surface and not emerging on a second surface of said layer of dielectric material, the surface of said conductive hole being coated with a conductive material.
An embodiment of the invention also relates to a process for manufacturing a planar antenna of the type that comprises at least one radiating element separated from a ground plane by a dielectric. According to an embodiment of the invention, the method comprises a stage of implementing at least one assembly of conductive studs 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 given resonant frequency.
In a first particular embodiment of the invention, the method comprises the following stage, for the ground plane and/or at least one of the radiating elements to which an assembly of conductive studs is connected: a first conductive component is implemented comprising:
In a second particular embodiment of the invention, the process comprises the following stages, for at least one of the radiating elements to which an assembly of conductive studs is connected:
To advantage, the process further comprises a stage of positioning said first or second conductive component relative to another element of the antenna, using at least one support element made of a dielectric material.
In a third particular embodiment of the invention, the method comprises the following stages, for the ground plane and/or at least one of the radiating elements to which an assembly of conductive studs is connected:
Other characteristics and advantages will emerge from reading the following description of a preferential embodiment of the invention, which is given purely by way of example and in no way restrictively, and of the attended drawings, wherein:
In
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, and the radiating elements from each other. “Dielectric” is taken to mean air or a solid material possessing characteristics closer those of air, such as for example materials of the plastic, foam type etc.
The general principle of an embodiment of the invention consists in adding to a conventional planar antenna of this type a plurality of conductive studs connected to and extending from the ground plane and/or from one or more radiating elements, so as to reduce at least one physical dimension of the radiating element or elements for a given resonant frequency.
The studs are for example distributed in accordance with a spatial distribution, known as a matrix, as shown in
The upper part of
At the electrical level, the studs 4, positioned between the radiating pattern 1 and the ground plane 2, and solely connected to this radiating pattern 1, have the effect locally of modifying the electromagnetic field distribution, hence an increase in the equivalent capacitive effect (local capacitance C), returned to the different connection points of these studs 4 with the radiating pattern 1. Consequently, the signal phase velocity on the radiating pattern 1 diminishes, which allows at least one physical dimension (the length and/or the width) of the radiating pattern 1 to be reduced for a fixed resonant frequency (see below the reminder as to the mathematical reasoning which explains this). It should be noted that this reduction in length and/or width is directly dependent on the number of studs 4 under the radiating pattern 1, and on the positions and dimensions (length and diameter) thereof. Thus, for example, the greater the increase in the number and length of the studs, the greater the reduction in size becomes.
To clarify the above, it should be remembered that in respect of the radiating element, the phase velocity vω is a function of the local capacitance C and the local inductance L:
Consequently, an increase in C allows vω to be reduced.
Furthermore, at a given resonant frequency fres, the antenna must be equivalent to a given electrical length φ. For example, for a half-wave patch type antenna: φ=180°.
In fact, φ=β×lphysique, where β=(2πfres/vω) and lphysique is the physical length of the antenna. Therefore, φ=2πfres(lphysique/vω)
For given fres and φ, if vω diminishes, then lphysique also diminishes, hence the miniaturisation of the antenna. Furthermore, the more C increases, the more vφ diminishes and therefore the more lphysique diminishes.
It is not necessary to have a uniform stud assembly. It is perfectly conceivable to design studs different in form and dimension.
To supply power to a planar antenna according to an embodiment of the invention, all conventional excitation means are conceivable, whether by a straightforward line section connected to 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 “50Ω” point on the surface of the radiating element or by an excitation solution based on electromagnetic coupling.
In all cases, so as not to obstruct this connection with the signal processing circuits placed upstream of the antenna, it is sufficient, where necessary, not to add any studs under the area locally concerned by this interconnection between the radiating element and the power supply means.
On the other hand, in the example in
Another fundamental point, emphasising the full extent of the advantages offered by the technique of an embodiment of the invention, lies in the ease of implementation thereof in respect of any other type of planar antenna. Indeed, the principle of conductive studs under the radiating element can be adapted without no particular difficulty to very different planar antenna configurations and geometries, whether for planar patterns with ground return, for channelled out or annular patterns, for inscribed slot patterns or in a very general way, for any other type of planar structures known to the man skilled in the art.
To illustrate this point, two other examples of planar antennas with studs according to an embodiment of the invention are given in
As regards the material embodiment of planar antennas with studs according to an embodiment of the invention, several straightforward manufacturing methods are conceivable, this simplicity being a fundamental criterion for the reduction in particular of the cost of these components.
A first embodiment of the antenna manufacturing method according to the invention will now be presented in relation to
This component is then transferred to one or more support elements 8, allowing it to be positioned relative to the lower ground plane. A preferred solution consists in using at support level 8 a dielectric material the nature of which makes it close to air, in such a way that this support or these supports are as transparent as possible, from an electromagnetic point of view. The use is recommended, for example, of a material of the foam type for which the electrical characteristics are fully compliant with the required specifications (for example: polymeth acrylate imide foam ROHACELL HF71 from ROEHM: ∈r=1.11 and tgδ=7.10−4 to 5 GHz). In an embodiment variant, the dielectric material out of which the support elements or elements are made is a plastic material, easily shaped for example by one of the known techniques.
A second embodiment of the antenna manufacturing method according to the invention will now be presented in relation to
It involves boring directly into the support substrate 3 of the antenna (which may be foam, plastic material etc, in other words a layer of dielectric material other than air), non-emergent holes (via holes) and coating with a conductive material, in a selective way, the upper surface of this substrate (so as to form the radiating element 1), and the inside of the holes extending from this upper surface (so as to form the conductive studs 4). In other words the conductive studs 4 are here embodied in the form of conductive holes.
In a preferred embodiment, the conductive material coating consists of metal plating. This metal plating can be achieved in a straightforward way for example by deposition of conductive paint or by electrochemical deposition. It is a clear that any technique known to the man skilled in the art can be used to apply the conductive material coating.
At the electrical level, the conductive holes (via holes) 4 have a similar effect to that of the conductive studs in previous solutions (conductive projections), hence the reduction in the size of the radiating element 1.
This element (support substrate 3 the upper surface of which carries the radiating element 1 and has a plurality of metal-plated holes 4) is then brought into contact, via its lower surface, with a ground plane 2 to obtain the final antenna structure.
It should be noted that, for this second solution, it is also preferable to choose a substrate of the foam type, which, as specified previously, has electrical characteristics that are fully appropriate for the implementation of planar antennas and which, furthermore, lends itself very easily to a three-dimensional configuration according to the shape required. In an embodiment variant, the support substrate is a plastic material, easily shaped by one of the known moulding techniques.
A third embodiment of the antenna manufacturing method according to the invention will now be presented in relation to
The radiating element is positioned relative to the ground plane or vice-versa through the use of one or more supports which can be of the same style as those shown in
To validate miniature planar antennas according to an embodiment of the invention, a first antenna prototype, of the type of antenna shown in
It is perfectly-conceivable to have a design where the holes are of variable shape and dimension.
By way of comparison, the measurements of a straightforward conventional half-wave patch antenna, also printed on foam and with dimensions identical to the previous radiating element (50×50×100 mm3), are shown in
As can be seen in
To emphasise the general nature of the technique of an embodiment of the invention, a second miniature antenna prototype was made: this is a quarter-wave patch antenna, with ground return located on one of the support wafers. As in the previous case, it is the principle of holes (via holes) distributed in the foam material which was selected. This antenna was printed on a substrate of dimensions 25×25×10 mm3 and transferred to a ground plane of 100×100 mm2. The non-emergent holes still have a cylindrical geometry (Φ=2 mm and h=7.5 mm). The ground return is implemented by a 5 mm wide tab, printed on one of the wafers of the foam support substrate and connected at its end to the ground plane. Excitation is obtained by coaxial probe connected to a “50Ω” point.
These results can be compared to those from a conventional antenna of the quarter-wave patch type, completely similar in geometry to that of the second prototype, outside the presence of the non-emergent holes, and the performance of which is given in
As shown in
Furthermore, the general principle of an embodiment of the invention (adding studs under the surface of a radiating element in order to reduce at least one physical dimension thereof (length and/or width) for a fixed resonant frequency) can also be applied to planar antennas with a number of stacked elements.
It will be remembered that multi-element antennas of this kind are used for example for broadband applications or again multi-frequency applications.
By way of example,
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 being the radiating element closest to the ground plane. The upper radiating element is defined as being the radiating element furthest away from the ground plane.
In this example, the concept of miniaturisation according to an embodiment of the invention (addition of studs 124) is only applied to the primary radiating element 1. In other words, the upper radiating element 10 is not connected to any stud.
Generally speaking, the antenna may comprise any number of stacked radiating elements and the concept of an embodiment of the invention (adding conductive studs) may be applied to all the radiating elements in the stack or only to one or more thereof.
As already mentioned above, the concept of an embodiment of the invention (adding conductive studs) may also be applied to the ground plane (adding studs to the surface thereof located facing the radiating element or elements), independently or in combination with an application to one or more radiating elements. In other words, the following different situations are conceivable in the context of one or more embodiments of the present invention:
In this case, the electrical effect of the studs as described previously (in relation to
To validate this principle, a prototype of an antenna with studs connected to the radiating element and to the ground plane was made. This is a solution of the half-wave patch type, printed on a foam material of dimensions 50×50×10 mm3 and transferred to a ground plane of 100×100 mm2. Compared with a conventional half-wave patch (in other words without studs) of the same dimensions, the reduction in the resonant frequency is then very considerable: this frequency in fact drops from 2.634 GHz for the conventional antenna to 1.225 GHz for the antenna of an embodiment of the invention, giving a reduction of more than 53%. This therefore leads to possibilities for the ultra-miniaturisation of the basic printed pattern.
In the case of an antenna comprising a stack of several radiating elements, the concept of an embodiment of the invention (adding conductive studs) may also be applied simultaneously to both surfaces of one and the same radiating element (except for the last one in the stack, in other words the one that is furthest away from the ground plane). In other words, one and the same radiating element may comprise first studs which extend from its lower surface and second studs which extend from its upper surface.
An embodiment of the present invention applies to any type of planar antenna (in the general sense already discussed above), in other words just as well to planar antennas that are actually plane as to planar antennas that are not actually plane (on account of the fact that the ground plane and/or a least one radiating element is not plane but conformed according to a given three-dimensional shape).
The
Three examples of manufacturing techniques applied to the manufacture of a radiating element with conductive studs have been presented above in relation to
It should be noted that in the event of the studs being made in the form of conductive holes, one and the same layer of dielectric substrate may carry the ground plane (or a first radiating element) on its lower surface and a radiating element (or a second radiating element) on its upper surface. The studs 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 surface of the substrate layer and do not emerge on the upper surface of the substrate layer. The studs connected to the radiating element (or to the second radiating element) are made in the form of the second conductive holes which extend from the upper surface of the substrate layer and do not emerge on the lower surface of the substrate layer.
It should also be noted that the aforementioned manufacturing techniques can be combined. For example, for the ground plane or a radiating element, a conductive component can be implemented which comprises on the one hand conductive projections, forming first conductive studs and on the other hand folded back conductive tabs, forming second conductive studs.
Of course, the invention is not limited to the embodiment examples mentioned above. Other variants may be anticipated which allow the size of the antenna to be minimised still further by playing on the number, size, shape and arrangement of the studs.
The general principle of an embodiment of the present invention may be implemented in any field of application able to use a planar antenna (mobile applications, satellite communication applications, wireless RF applications etc) in very different frequency ranges (from a few hundred MHz to a few tens of GHz).
An embodiment of the invention provides a technique, which is quite different from those used hitherto to increase the equivalent electrical length of the printed pattern (radiating element or patch) of the antenna, so as to obtain a very compact planar antenna.
An embodiment of the invention provides such a technique, which is straightforward to implement and inexpensive.
An embodiment of the invention provides such a technique that can be applied to any kind of planar radiating structures, such as basic “half-wave patch” or “quarter-wave patch” antennas, “annular patch” antennas, “inscribed slot patch” antennas, PIFA (Planar Inverted-F Antenna) antennas etc.
An embodiment of the invention provides such a technique that can be applied just as well to a planar antenna with a single radiating element as to a planar antenna that comprises a stack of several radiating elements.
An embodiment of the invention provides a corresponding method for the manufacture of planar antennas, based on very straightforward integration technologies, which allows very low-cost solutions to be found, fully adapted to the expansion in consumer markets.
Although the present disclosure has been described with reference to various embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0404679 | Apr 2004 | FR | national |
| 0502130 | Mar 2005 | FR | national |
This Application is a Section 371 National Stage Application of International Application No. PCT/FR2005/000966, filed Apr. 19, 2005 and published as WO 2005/117208 on Dec. 8, 2005, not in English.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2005/000966 | 4/19/2005 | WO | 00 | 12/21/2007 |
