EP3669422B1 - Patch antenna having two different radiation modes with two separate working frequencies, device using such an antenna - Google Patents

Description

TECHNICAL AREA

The present invention belongs to the field of antennas. An antenna is a device used to radiate (transmitter) or capture (receiver) electromagnetic waves. In particular, the invention relates to an antenna whose structure makes it possible to radiate or capture radio waves at two distinct working frequencies in two different radiation modes and with particularly advantageous performances.

STATE OF THE TECHNIQUE

In the field of compact antennas used for telecommunications, we already know the antennas known to those skilled in the art under the name of “plated antenna”. These antennas are also known under the name “printed antenna”, or by the English term “ patch antenna” .

Such an antenna consists of a radiating element corresponding to a metal plate of any shape (rectangular, circular, or other more elaborate shapes) generally deposited on the surface of a dielectric substrate which has on the other side a conductive plane, or plane massive. The dielectric substrate, which essentially plays a role of mechanical support of the radiating element, can be replaced by a honeycomb structure whose behavior is close to that of air, or even be eliminated if the mechanical maintenance of the radiating element can be provided by other means. The antenna is generally fed via a feed wire consisting of a coaxial probe which passes through the ground plane and the substrate and is connected to the radiating element, i.e. i.e. at the plate.

A plated antenna, however, has the disadvantage of having relatively large dimensions, of the order of half the length wave of the desired working frequency. Indeed, we can consider as a first approximation that an antenna plated with a rectangular plate behaves like a cavity whose various discrete resonance frequencies correspond to known modes depending on the dimensions of the plate. In particular, for a so-called “fundamental” mode, the antenna enters into resonance at a frequency of which half the wavelength corresponds to the length of the cavity. Thus, the lower the desired working frequencies, the larger the dimensions of the radiating element must be so that at least one of the resonant frequencies of the cavity coincides with the working frequency.

To overcome this problem and reduce the size of the antennas, we also know antennas known to those skilled in the art under the name of “wire-plate antenna”. Compared to a plated antenna, a wire-plate antenna has at least one additional conductive wire connecting the plate to the ground plane. This is an active ground return wire radiating at the working frequency considered.

Such a wire-plate antenna is the seat of two resonance phenomena, one relating to a series type resonance implementing all the constituent elements of the structure of the antenna, and the other relating to a resonance parallel type using the only elements due to the ground wire and the capacitor formed by the plate (also sometimes called “capacitive roof”) and the ground plane. This is why we sometimes speak of “double resonance” for wire-plate antennas. The so-called parallel resonance caused by the ground return wire of a wire-plate antenna takes place at a frequency lower than the fundamental cavity-type resonance frequency of a plate antenna. Thus, for given plate dimensions, a wire-plate antenna has a lower working frequency than a plated antenna.

It should be noted that the operation of a wire-patch antenna is very different from the operation of a plated antenna. Indeed, the resonance we are talking about for a plated antenna is of the electromagnetic type: resonance of a cavity formed by the ground plane, the plate and the four imaginary “magnetic walls” connecting the four edges of the plate to the plane of mass. The resonance of a wire-plate antenna is of the electrical type: the resonant elements are localized, comparable to electrical components.

However, it is sometimes desirable to have an antenna which is capable of operating at several distinct working frequencies, and with different radiation modes, in order to respond to different functions. These distinct working frequencies can for example belong to discontinuous frequency bands sometimes separated by several hundred megahertz from each other.

For this purpose, it is known to combine several antennas on a single structure. For example, it is known to superimpose several wire-plate type antennas, or to superimpose a plated type antenna and a wire-plate type antenna, in order to obtain an antenna behavior which would be equivalent to that of several distinct antennae. These solutions, however, have several disadvantages, in particular the size of the antenna, a mechanical complexity which increases its manufacturing cost, as well as difficulties in adapting the antenna to the different working frequencies, which leads to degraded performance of the antenna. . The document US 2009 167617 A1 discloses a patch antenna that includes a ground plane, and a circuit that includes switches and capacitors connected between the patch and the ground plane.

STATEMENT OF THE INVENTION

The present invention aims to remedy all or part of the drawbacks of the prior art, in particular those set out above.

To this end, and according to a first aspect, the present invention relates to an antenna according to claim 1.

With such arrangements, the antenna not only presents a resonance in plated antenna mode (that is to say an electromagnetic type cavity resonance) at a first working frequency, but also a resonance in wire-plate antenna mode (i.e. an electrical type resonance) at a second working frequency lower than the first working frequency. The ground return wire is a radiating element at the second working frequency. Each of these two resonances corresponds to a particular mode of radiation. The capacitive element makes it possible in particular to optimize the radiation power of the antenna as well as its impedance adaptation to the two working frequencies considered.

In particular embodiments, the radiation of the antenna at the first working frequency is maximum in a direction perpendicular to the plate, and the radiation of the antenna at the second working frequency is maximum omnidirectional radiation in a plane parallel to the ground plane.

In particular embodiments, the invention may also include one or more of the following characteristics, taken individually or in all technically possible combinations.

In particular embodiments, the antenna plate is a rectangular plate of which two opposite angles of the same diagonal are truncated so that the antenna has circular polarization at the first working frequency.

In particular embodiments, the capacitive element is a discrete electronic component.

In particular embodiments, the capacitive component has a controllable capacitive value.

In particular embodiments, the capacitive element comprises two electrodes, one electrode of which is formed by a metal plate located at one end of the ground return wire and arranged facing the antenna plate or the ground plane .

In particular embodiments, the metal plate of the capacitive element is located at the end of the ground return wire on the side of the antenna plate, so that the other electrode is formed by the plate of the antenna.

In particular embodiments, a slot is made in the antenna plate, so that said slot completely surrounds the point connection between the ground return wire and the plate, and the capacitive element comprises two electrodes, one electrode of which is formed by a part of the plate of the antenna which is outside a perimeter formed by the slot, and the other electrode is formed by another part of the antenna plate which is inside said periphery formed by the slot.

In particular embodiments, at least one of the ground return and power supply wires is a metal strip cut from the antenna plate.

In particular embodiments, the distance between the power supply wire and the ground return wire is greater than a tenth of the wavelength of the second working frequency.

In a particular embodiment, a transmission device comprises the antenna according to the invention and a generator connected to the power wire, adapted to form an electrical signal at the first working frequency and/or at the second working frequency. work.

In a particular embodiment, a receiving device comprises the antenna according to the invention and a receiver connected to the power wire, adapted to receive an electrical signal at the first working frequency and/or at the second working frequency .

In a particular embodiment, a transceiver device comprises the antenna according to the invention and is configured to receive a signal at the first working frequency comprising geolocation information transmitted by a satellite communication system and to transmit at a terrestrial wireless communication system a signal at the second working frequency comprising the geographical position of said device.

PRESENTATION OF FIGURES

• Figure 1 : une représentation schématique, selon une vue en perspective, d'un premier mode de réalisation d'une antenne selon l'invention,
• Figure 2 : une représentation schématique, selon une vue en coupe dans un plan vertical, du premier mode de réalisation de l'antenne,
• Figure 3 : une représentation schématique de la forme de la plaque pour le premier mode de réalisation de l'antenne,
• Figure 4: une représentation schématique d'une variante du premier mode de réalisation de l'antenne,
• Figure 5 : une représentation schématique de la plaque pour une variante du premier mode de réalisation de l'antenne,
• Figure 6 : un diagramme représentant le coefficient de réflexion en entrée de l'antenne pour le premier mode de réalisation,
• Figure 7 : un diagramme de rayonnement selon un plan de coupe vertical pour le premier mode de réalisation de l'antenne et pour une première fréquence de travail,
• Figure 8 : un diagramme de rayonnement selon un plan de coupe vertical pour le premier mode de réalisation de l'antenne et pour une deuxième fréquence de travail,
• Figure 9 : un diagramme représentant le coefficient de réflexion en entrée de l'antenne pour différentes valeurs d'un élément capacitif,
• Figure 10 : une représentation schématique, selon une vue en coupe dans un plan vertical, d'un deuxième mode de réalisation de l'antenne,
• Figure 11 : un diagramme représentant le coefficient de réflexion en entrée de l'antenne pour le deuxième mode de réalisation,
• Figure 12 : un diagramme de rayonnement selon un plan de coupe vertical pour le deuxième mode de réalisation de l'antenne et pour une première fréquence de travail,
• Figure 13 : un diagramme de rayonnement selon un plan de coupe vertical pour le deuxième mode de réalisation de l'antenne et pour une deuxième fréquence de travail,
• Figure 14 : une représentation schématique de la plaque de l'antenne pour un troisième mode de réalisation,
• Figure 15 : un diagramme représentant le coefficient de réflexion en entrée de l'antenne pour le troisième mode de réalisation,

The invention will be better understood on reading the following description, given by way of non-limiting example, and made with reference to the figures 1 at 15 that represent :

• Figure 1 : a schematic representation, in a perspective view, of a first embodiment of an antenna according to the invention,
• Figure 2 : a schematic representation, in a sectional view in a vertical plane, of the first embodiment of the antenna,
• Figure 3 : a schematic representation of the shape of the plate for the first embodiment of the antenna,
• Figure 4 : a schematic representation of a variant of the first embodiment of the antenna,
• Figure 5 : a schematic representation of the plate for a variant of the first embodiment of the antenna,
• Figure 6 : a diagram representing the reflection coefficient at the input of the antenna for the first embodiment,
• Figure 7 : a radiation diagram along a vertical section plane for the first embodiment of the antenna and for a first working frequency,
• Figure 8 : a radiation diagram along a vertical section plane for the first embodiment of the antenna and for a second working frequency,
• Figure 9 : a diagram representing the reflection coefficient at the antenna input for different values of a capacitive element,
• Figure 10 : a schematic representation, in a sectional view in a vertical plane, of a second embodiment of the antenna,
• Figure 11 : a diagram representing the reflection coefficient at the input of the antenna for the second embodiment,
• Figure 12 : a radiation diagram along a vertical section plane for the second embodiment of the antenna and for a first working frequency,
• Figure 13 : a radiation diagram along a vertical section plane for the second embodiment of the antenna and for a second working frequency,
• Figure 14 : a schematic representation of the antenna plate for a third embodiment,
• Figure 15 : a diagram representing the reflection coefficient at the input of the antenna for the third embodiment,

In these figures, identical references from one figure to another designate identical or similar elements. For reasons of clarity, items shown are not to scale unless otherwise noted.

DETAILED DESCRIPTION OF EMBODIMENTS

As indicated previously, the present invention relates to an antenna 1 whose structure makes it possible to radiate or capture electromagnetic waves at two distinct working frequencies according to two different radiation modes and with particularly advantageous performances.

In the remainder of the description, we place ourselves by way of example and in no way limiting, in the case where such an antenna 1 is integrated into a connected object intended to be placed for example on the roof of a motor vehicle and configured to receive a signal from a satellite geolocation system (also referred to in English by the acronym GNSS for Global Navigation Satellite System ), such as for example the GPS system ( Global Positioning System ), in order to determine its geographical position, and to transmit it, possibly accompanied by other information, to another wireless communication system such as for example an “Internet of Things” type access network, or loT (English acronym for “ Internet Of Things” ).

To receive a signal from a satellite geolocation system, the antenna 1 must preferably have a high gain in a vertical direction 18 and upwards relative to the roof of the vehicle at the working frequency of said geolocation system. If we consider, for example, the GPS system, the working frequency, that is to say the frequency of the radio signals emitted by the GPS satellites, is approximately 1575 MHz. Also, the polarization used by the GPS system, that is to say the polarization of the electric field of the wave emitted by an antenna of a GPS satellite, is a right circular polarization, called RHCP (English acronym for Right Hand Circular Polarization).

To transmit information to a wireless communication system of the loT type, it is on the other hand advantageous for the antenna 1 to present, at the working frequency of said communication system, an omnidirectional gain which is maximum in a substantially parallel horizontal plane to the roof of the vehicle. Indeed, the base stations of an access network of such a wireless communication system are generally located on the sides in relation to the vehicle, and not vertically. In the remainder of the description, we place ourselves by way of example and in a non-limiting manner in the case of an ultra-narrow band wireless communication system. By “ultra narrow band” (“ Ultra Narrow Band ” or UNB in the Anglo-Saxon literature), we mean that the instantaneous frequency spectrum of the radio signals transmitted has a frequency width of less than two kilohertz, or even less than one kilohertz. Such UNB wireless communication systems are particularly suitable for loT type applications. They can, for example, use the ISM frequency band (acronym for “Industrial, Scientific and Medical”) located around 868 MHz in Europe, or the ISM frequency band located around 915 MHz in the United States. Rectilinear polarization is generally used in such systems.

Thus, for the remainder of the description, we place ourselves in the case where the antenna 1 according to the invention operates at two distinct working frequencies: a first working frequency close to 1575 MHz corresponding to the frequency of the GPS system, and a second working frequency located in an ISM band supported by the loT type wireless communication network considered, for example the 868 MHz band or the 915 MHz band.

There figure 1 schematically represents, in a perspective view, a first embodiment of such an antenna. In the example illustrated by figure 1 , the antenna 1 comprises a first radiating element in the form of a square metal plate 10. According to other examples, the plate 10 could be rectangular, hexagonal, circular, or of any other shape.

The plate 10 is placed facing a ground plane 11. In the Following the description, we consider in a non-limiting manner that the plate 10 is flat. However, according to other examples, nothing excludes having a non-flat plate 10. Furthermore, it is considered that the plate 10 is arranged horizontally and substantially parallel to the ground plane 11. According to other alternative examples, the plate 10 can be slightly inclined relative to the ground plane 11. The distance separating the plate 10 of the ground plane 11 is much smaller than the dimensions of the plate 10 and the wavelengths of the working frequencies of the antenna. For example, this distance is at least less than a tenth of the wavelength of the first working frequency. The two metal surfaces corresponding to the plate 10 and the ground plane 11 can for example be arranged on either side of a dielectric substrate 14 which then plays the role of mechanical support. In other examples, the dielectric substrate 14 can be replaced by a honeycomb structure whose behavior is close to that of air, or it can be eliminated if the mechanical retention of the plate 10 relative to the ground plane 11 is ensured by other means. The dimensions of the ground plane 11 are generally greater than those of the plate 10. In the example considered where the antenna is integrated into a connected object intended to be placed on the roof of a motor vehicle, the metal roof of the vehicle can also play the role of a ground plane whose dimensions are very large compared to the dimensions of the plate 10. The importance of the dimensions of the plate 10 and the ground plane 11 will be discussed later in the description.

The plate 10 and the ground plane 11 are connected via a power wire 12. The power supply wire 12 can for example be, in a conventional manner, a coaxial probe which passes through the ground plane 11 and the dielectric substrate 14 and is connected to the plate 10.

In addition, the antenna 1 includes a ground return wire 13 which connects the plate 10 to the ground plane 11. As will be detailed later, this ground return wire 13 plays the role of a second radiating element at the second working frequency. Preferably, the power supply wire 12 and/or the ground return wire 13 are arranged substantially perpendicular to the ground plane. In the case where the power supply wire 12 and the return wire 13 mass are both perpendicular to the ground plane 11 and to the plate 10, then they are also arranged substantially parallel between said ground plane 11 and said plate 10.

More generally, by “wire” we mean a conductor with any section, not necessarily circular. In particular, the power supply wire 12 and/or the ground return wire 13 could be a metal ribbon.

In transmission, the antenna 1 converts a voltage or an electric current existing in the supply wire 12 into an electromagnetic field. This electrical supply is for example provided by a voltage or current generator 16.

Conversely, on reception, an electromagnetic field received by the antenna 1 is converted into an electrical signal which can then be amplified.

Generally speaking, a passive antenna can be modeled by a component having a certain impedance seen at the antenna input. It is a complex impedance whose real part corresponds to the “active” part of the antenna, that is to say a dissipation of energy by ohmic losses and electromagnetic radiation, and whose part imaginary corresponds to the “reactive” part of the antenna, that is to say to storage in the form of electrical energy (capacitive behavior) and magnetic (inductive behavior). If at a particular frequency, called resonant frequency, the inductance and capacitance of the antenna are such that their effects cancel each other out, then the antenna is equivalent to a pure resistance, and if the ohmic losses are negligible the power supplied to the antenna is almost entirely radiated. Such behavior is observed if the imaginary part of the antenna is zero.

On the other hand, to ensure maximum power transfer between an electrical power source and an antenna, it is necessary to ensure impedance matching. The adaptation makes it possible to cancel the reflection coefficient, conventionally denoted S ₁₁ , at the antenna input. The reflection coefficient is the ratio between the wave reflected at the antenna input and the incident wave. If adaptation is not ensured, part of the power is returned to the source. In practice, to ensure good adaptation impedance, the antenna must have an impedance equal to that of the transmission line, generally 50 ohms.

In other words, to obtain optimal behavior of the antenna 1 in terms of radiation, it must be ensured that it behaves, for the generator which supplies it and at a predetermined resonance frequency, like a load whose part real is close to a determined value, most often 50 ohms, and whose imaginary part is zero or almost zero. To this end, it is common to insert between the generator 16 and the antenna 1 an electronic impedance transformation circuit, called an “adaptation circuit” 17, which modifies the input impedance of the antenna 1 seen from the source and ensures impedance matching. Such an adaptation circuit 17 can for example include passive elements such as filters based on inductances and capacitances or transmission lines.

expression dans laquelle :

• c est la vitesse la lumière dans le vide
• ε_r est la permittivité relative pour le substrat diélectrique 14
• L est la longueur de la plaque 10
• l est la largeur de la plaque 10

Il apparaît alors clairement que si on considère que la permittivité relative est proche de 1 (par exemple dans le cas où le substrat diélectrique 14 est remplacé par l'air ambiant), pour un mode, dit mode fondamental de résonance de cavité, pour lequel m vaut 1 et n vaut 0, la fréquence de résonance est telle que la moitié de sa longueur d'onde correspond à la longueur L de la plaque. Il convient de noter que pour l'exemple considéré décrit en référence la figure 1, la longueur L et la largeur l sont toutes deux égales à la longueur d'un côté de la plaque 10 qui est de forme carrée.The plate 10 and the ground plane 11 can be compared to a resonant cavity which can be considered, at low frequency, as a capacitor which stores charges and in which a uniform electric field is created between the ground plane 11 and the plate 10. As long as the distance separating the ground plane 11 and the plate 10 is small compared to the wavelength of the frequencies considered, the electric field is oriented along an axis perpendicular to the horizontal plane containing the ground plane 11. At high frequency , the distribution of charges on plate 10 is no longer uniform, and this is also the case for the distribution of current and that of the electric field. A magnetic field also appears. It is then known that for particular frequencies, called cavity resonance frequencies, linked to the dimensions of the cavity (that is to say linked to the dimensions of the plate 10), the distribution of the electric field is such that the radiation of the antenna is optimized. Such frequencies F _m,n are defined according to the expression below by pairs ( m , n ) where m and n are integers greater than or equal to 0, at least one of m or n being non-zero, which represent the cavity modes: $$F_{m,\mathrm{not}}=\frac{\mathrm{vs}}{2\pi \sqrt{{\epsilon }_{\mathrm{<figure-callout\; id="2"\; label="r\; m\pi \; L"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">r</figure-callout>}}}}\sqrt{{\left(\frac{\mathit{m\pi }}{L}\right)}^{}}\sqrt{{\left(\frac{}{}\right)}^2+{\left(\frac{\mathit{<figure-callout\; id="2"\; label="n\pi \; L"\; filenames="imgf0003.png,imgf0005.png"\; state="\{\{state\}\}">n\pi </figure-callout>}}{L}\right)}^2}$$

expression in which:

• This is the speed of light in a vacuum
• ε _r is the relative permittivity for the dielectric substrate 14
• L is the length of plate 10
• l is the width of the plate 10

It then appears clearly that if we consider that the relative permittivity is close to 1 (for example in the case where the dielectric substrate 14 is replaced by ambient air), for a mode, called the fundamental cavity resonance mode, for which m is 1 and n is 0, the resonance frequency is such that half of its wavelength corresponds to the length L of the plate. It should be noted that for the example considered described in reference the figure 1 , the length L and the width l are both equal to the length of one side of the plate 10 which is square in shape.

Thus, radiation with an electromagnetic type cavity resonance can for example be obtained for a first working frequency of 1575 MHz using a length of one side of the plate 10 close to 9 cm, or approximately half the length wave corresponding to this frequency. Other parameters such as for example the distance separating the plate 10 from the ground plane 11 or the value of the permittivity of the dielectric substrate 14 can however influence the length of the plate 10 for which a cavity resonance is obtained. In the example considered for the first embodiment, the plate 10 is a square with a side of 8.5 cm. At the first working frequency of 1575 MHz, antenna 1 then behaves close to that of a plated antenna. The impedance matching of such an antenna is generally obtained when the feed wire 12 is positioned at one side of the plate 10 rather than towards its central zone.

On the other hand, the plate 10 and the ground return wire 13 can play the role of two elements having an electrical type radiating behavior. Antenna 1 then has a behavior close to that of a wire-plate antenna. The antenna 1 can in particular be the seat of a parallel type resonance using the ground return wire 13 and the capacitor formed by the plate 10 and the ground plane 11. This so-called parallel resonance caused by the ground return wire 13 takes place at a frequency lower than that of the aforementioned cavity-type fundamental resonance frequency.

If the shape of the plate 10 is not decisive for this electrical type radiation, the value of its surface has an impact on the working frequency. In particular, the smaller the surface of the plate 10, the higher the wire-plate type resonance frequency. For a square plate 10, the wire-plate type resonance frequency is generally such that a quarter of its wavelength is close to the length of one side of the plate 10, but again other parameters of the structure of the antenna 1 can influence the resonant frequency. In the example considered for the first embodiment, electrical type radiation is obtained for a second working frequency of 868 MHz.

It should be noted that it would be possible to obtain a second higher working frequency by reducing the surface of the plate 10, for example by using a rectangular plate of length L fixed in relation to the wavelength of the first working frequency, and advantageously choosing the width l of the plate to obtain the desired second working frequency.

It should be noted that the two operating modes of the antenna 1 described above are fundamentally different. Indeed, it is a question on the one hand, at a frequency of 1575 MHz, of an electromagnetic type resonance (resonance in plated antenna mode) corresponding to the resonance of a cavity formed by the ground plane 11, the plate 10 and the four imaginary “magnetic walls” connecting the four edges of the plate 10 to the ground plane 11, and on the other hand, at a frequency of 868 MHz, an electrical type resonance (resonance in wire antenna mode- plate), that is to say a resonance for which the resonant elements are localized, comparable to electrical components (in particular, the assembly formed by the ground plane 11 and the plate 10 is comparable to a capacitor while the wire 13 returning to ground has an inductance). In the production of such an antenna 1, a great difficulty lies in the possibility of adapting the antenna 1 in impedance for the two operating modes corresponding to two different radiation modes.

Many parameters influence the impedance matching of the antenna 1, such as for example the position of the power wire 12, that of the return-to-ground wire 13, the distance separating the power wire 12 from the wire 13 back to mass, their diameter, etc. It is therefore possible to play on these different parameters to obtain the best possible impedance adaptation.

It is also possible to play on the adaptation circuit 17 to improve this impedance adaptation. However, the performance of an antenna is generally better if it is matched in impedance by its own structure rather than by an adaptation circuit inserted between the generator 16 and the antenna 1.

It generally proves futile to be able to impedance adapt the antenna 1 described above for the two working frequencies considered using only the aforementioned parameters and/or by placing an adaptation circuit 17 between the antenna 1 and the generator 16, while maintaining reasonable performance of the antenna. This is why an additional capacitive element 15a is placed in series with the ground return wire 13 between the power supply wire 12 and the ground plane 11. As explained previously, this involves ensuring that the The antenna 1 behaves, for the generator 16 which supplies it and at a predetermined resonance frequency, like a load whose real part is close to a determined value, most often 50 ohms, and whose imaginary part is zero or almost zero. The capacitive element 15a has an impedance which depends on its capacitive value and the frequency used. It thus modifies the impedance of antenna 1 and can make it possible to obtain an impedance adaptation at the two working frequencies considered. It can in particular compensate for the inductance represented by the wire 13 returning to ground.

It should also be noted that to obtain an electrical type resonance at the second working frequency, it is important that an inductive coupling exists between the power supply wire 12 and the return to ground wire 13. These two wires must therefore be sufficiently close to each other. It nevertheless turns out that the impedance adaptation of the antenna 1 to the first working frequency is better if the power supply wire 12 is positioned at one side of the plate 10 while the wire 13 returning to ground must as rather be positioned towards the central zone of the plate 10. Indeed, as will be detailed later with reference to the figure 8 , it is important that the ground return wire 13 is positioned towards the middle of the plate 10 to optimize monopolar type radiation with rectilinear polarization at the second working frequency. Furthermore, to obtain a cavity type resonance at the first working frequency, it is important that the electric current flowing through the wire 13 returning to ground at this frequency is as low as possible. This can be favored by positioning the wire 13 returning to ground at a point corresponding to an electric field node at the first working frequency, that is to say at a point where the electric field is particularly weak, or even almost zero, at the first working frequency. This is particularly the case in the middle of plate 10.

This relatively large distance between the power supply wire 12 and the ground return wire 13 is one of the elements which distinguishes the antenna 1 according to the invention from conventional wire-plate antennas for which this distance must generally be less than a tenth of the wavelength of the working frequency considered, which is not the case for the antenna 1 according to the invention.

Preferably, the ground return wire 13 has a diameter at least four times greater than the diameter of the power supply wire 12.

There figure 2 schematically represents in a sectional view in a vertical plane the first embodiment of the antenna 1 described above with reference to the figure 1 . This sectional view allows us to see in particular that the power supply wire 12 crosses the ground plane 11 to be connected to a generator 16 or to a receiver. It should be noted that the power supply wire 12 must in this case be insulated from the ground plane 11 at the point where it crosses it.

The capacitive element 15a used in this first embodiment is a discrete electronic component, for example a capacitor, connected on one side to the ground plane 11 and on the other side to the wire 13 returning to ground.

There figure 2 also helps to clarify what is meant by the vertical direction 18. This is the upward direction perpendicular to the plane containing the ground plane 11 which is considered horizontal. We can then define an angle Θ formed between this vertical direction 18 and another direction. This angle will be of particular interest for defining the radiation of antenna 1 in the different directions of space.

There Figure 3 is a schematic representation of the shape of the plate 10 for a particular embodiment of the antenna 1. As indicated previously, the polarization of the electric field of the wave emitted by an antenna of a GPS satellite is a right circular polarization (RHCP). To obtain such a polarization for the electromagnetic wave radiated by the antenna 1 at the first working frequency, two opposite angles of the same diagonal of the plate 10 are truncated. In the example considered for the first embodiment, the truncated part at each of said angles is an isosceles right triangle whose hypotenuse has a length of 25 mm.

It should be noted, however, that there are other means of obtaining circular polarization, such as for example by exciting antenna 1 with two sources phase shifted by 90°.

There Figure 4 is a schematic representation of a variant of the first embodiment described with reference to figures 1 to 3 for which the ground return wire 13 crosses the ground plane 11. In this case, the ground return wire 13 must be isolated from the ground plane 11 at the point where it crosses it. The capacitive component 15a is then connected on one side to ground and on the other side to the end of the wire 13 returning to ground which has passed through the ground plane 11. Advantageously, the wire 13 returning to ground ground and/or the power wire 12 can then serve as mechanical support for the plate 10 relative to the ground plane 11.

The main characteristics of the first embodiment of the antenna 1 described above with reference to the figures 1 to 4 are given below by way of non-limiting example. Plate 10 is a square with a side of 8.5 cm. The distance separating the ground plane 11 from the plate 10 is 10 mm. The dimensions of the ground plane 11 are not decisive, but in the example considered they are of the order of three to four times those of the plate 10. The power wire 12 has a diameter of 1 mm and it is positioned at level of the middle of one of the sides of the plate 10, at a distance equal to 10 mm from said side. The ground return wire 13 has a diameter of 4 mm and is positioned in the center of the plate 10. The distance separating the power supply wire 12 from the ground return wire 13 is therefore approximately 32.5 mm. The value of the capacitive component 15a is 21.3 pF. The adaptation circuit 17 is a conventional series/parallel circuit (so-called “L” circuit) involving an inductance of 12.6 nH and a capacitor of 2 pF.

There figure 5 is a schematic perspective representation of the plate 10 of the antenna 1 for a variant of the embodiment described with reference to Figure 4 . In this variant, the power supply wire 12 and the ground return wire 13 are two metal ribbons cut from the plate 10 and folded perpendicular to the plate. The dimensions of the slots corresponding to the recesses due to the cutouts in the plate 10 are sufficiently small (for example approximately 3 mm wide) to have no impact on the performance of the antenna. A particularly interesting aspect of this variant is to simplify the manufacture of the antenna since it is then no longer necessary to connect wires to the plate 10. The metal ribbons in fact play the role of the power wire 12 and the wire 13 returns to ground and they are integral with the plate 10. The metal ribbons, since they are rigid by nature, can also play the role of mechanical support for the plate 10 relative to the ground plane 11.

There Figure 6 is a diagram which represents the reflection coefficient at the input of the antenna 1 for the first embodiment described above with reference to the figures 1 to 4 . Generally speaking, the reflection coefficient, conventionally denoted S ₁₁ and expressed in dB, is the ratio between the wave reflected at the input of an antenna and the incident wave. It depends on the input impedance of the antenna and the impedance of the transmission line that connects the generator to the antenna.

Curve 20 represents the evolution of the reflection coefficient S ₁₁ of the first embodiment of the antenna 1 as a function of frequency. A resonance frequency corresponding to the first working frequency of 1575 MHz is indicated by triangular marker No. 3. Another resonant frequency corresponding to the second working frequency of 868 MHz is indicated by triangular marker no. 2. Each resonance frequency corresponds to a minimum of the reflection coefficient S ₁₁ . It takes a value close to -13 dB for the resonance at 1575 MHz, and a value close to -16 dB for the resonance at 868 MHz. A minimum value of the reflection coefficient generally corresponds to a frequency for which the antenna is impedance matched. A typical criterion is to have for example a reflection coefficient less than -10dB on the antenna passband, that is to say on the frequency band for which the transfer of energy from the power supply to the antenna (or from the antenna to the receiver) is maximum. Curve 20 therefore makes it possible to confirm that with the characteristics previously listed for the first embodiment described with reference to the figures 1 to 4 , the antenna 1 is matched in impedance to the two working frequencies considered.

There Figure 7 represents a radiation pattern along a vertical section plane for the first embodiment of the antenna 1 for the first working frequency of 1575 MHz. It represents the variations in the power radiated by the antenna 1 in different directions in space. It indicates in particular the directions of space in which the radiated power is maximum.

Curve 22a corresponds to radiation according to right circular polarization (RHCP). It has a single lobe whose main direction is oriented along vertical 18 (Θ = 0°) upwards. It is in this direction that the energy emitted or received by the antenna is maximum. The maximum gain is approximately 10 dBi, and an opening angle at 3 dB of approximately 60° is observed.

Curve 22b corresponds to radiation according to left circular polarization (LHCP). It has a lobe in the vertical direction 18 upwards and another lobe in a direction 60° from the vertical 18 (Θ = 60°). For these two directions, the maximum gain is only about -10 dBi. Thus, there is approximately 20 dB of gain difference between the RHCP polarization and the LHCP polarization in the vertical direction 18 upwards. These values make it possible to obtain good discrimination of the two types of circular polarizations in this direction. Antenna 1 is thus particularly efficient in RHCP polarization at the first working frequency of 1575 MHz in this vertical direction 18 and upwards. It is therefore entirely suitable for receiving signals from satellites of the GPS system.

There figure 8 represents a radiation pattern along a vertical section plane for the first embodiment of the antenna 1 for the second working frequency of 868 MHz.

Curve 21 corresponds in particular to the radiation of antenna 1 at this frequency according to a rectilinear polarization along the vertical 18. It is significant of omnidirectional radiation of monopolar type (that is to say corresponding to the radiation of a monopole ). In particular, we can observe a lobe with rotational symmetry. The radiation is maximum horizontally, that is to say parallel to the ground plane ( Θ = 90°), and it is zero vertically, that is to say perpendicular to the latter ( Θ = 0°). The antenna has a gain of approximately 5 dBi in the horizontal directions ( Θ = 90°). We observe a loss of more than 3 dB of gain compared to the maximum gain for angles Θ relative to the vertical 18 less than or equal to approximately 40°. The position of the wire 13 returning to ground in the middle of the plate 10 advantageously makes it possible to promote this omnidirectional radiation of the monopolar type with a rectilinear polarization inscribed in a plane containing the wire 13 returning to ground (the electric field of the electromagnetic wave radiated or received by the antenna keeps a fixed direction along the axis of the wire 13 returning to ground, that is to say along the vertical 18). Antenna 1 is thus particularly efficient in rectilinear polarization at the second working frequency of 868 MHz in mainly horizontal directions. It is therefore entirely suitable for transmitting signals to an loT type access network operating around this frequency.

It should be noted that the radiation patterns of figures 7 and 8 only present radiation in the space located above the ground plane 11 of the antenna 1 (-90° ≤ Θ ≤ 90°). This comes from the fact that the dimensions of the ground plane 11 are large enough compared to the dimensions of the plate 10 for it to reflect the waves emitted by the antenna upwards. For example, the dimensions of the ground plane 11 are at least ten times greater than those of the plate 10, this is particularly the case when the roof of the motor vehicle plays the role of ground plane.

There Figure 9 represents the reflection coefficient S ₁₁ at the input of the antenna 1 for different values of the capacitive component 15a.

Curve 23 represents the reflection coefficient S ₁₁ for a first capacitance value of 21.3 pF for which an electrical type resonance is obtained for a second working frequency close to 868 MHz (which belongs for example to an ISM frequency band in Europe for the loT network considered). Triangular marker #4 indicates a minimum value of S ₁₁ less than -16 dB for this frequency.

Curve 24 represents the reflection coefficient S ₁₁ for a second capacitance value of 17 pF for which an electrical type resonance is obtained for a second working frequency close to 893 MHz (which belongs for example to an ISM frequency band at United States for the loT network considered). Triangular marker No. 3 indicates a minimum value of S ₁₁ of the order of -15 dB for this frequency.

Curve 25 represents the reflection coefficient S ₁₁ for a third capacitance value of 13.8 pF for which an electrical type resonance is obtained for a second working frequency close to 923 MHz (which belongs for example to an ISM frequency band in Australia or Japan for the loT network considered). Triangular marker No. 1 indicates a minimum value of S ₁₁ of the order of -14 dB for this frequency.

For these three values of the capacitive component 15a, we always obtain a fundamental cavity-type resonance frequency for the first working frequency of 1575 MHz. Triangular marker No. 2 indicates a minimum value of S ₁₁ of the order of -14 dB for this frequency.

Experience shows that it is possible, for example, to vary the value of the capacitance of the capacitive component 15a from 10 pF to 50 pF to obtain an electrical type resonance for a second working frequency varying between 800 MHz and 1 GHz. The greater the value of the capacitance, the lower the value of the second working frequency for which an electric type resonance is obtained. For this range of values of the capacitance of the capacitive component 15a between 10 pF and 50 pF, the operation of the antenna 1 at the first working frequency is not impacted. For some values of the capacitance of the capacitive component 15a less than 10 pF or greater than 50 pF, it no longer seems possible to adapt the antenna 1 for the two desired radiation modes.

Thus, it is very easy to adapt the manufacture of an antenna 1 according to the geographical area in which it is intended to operate. It is sufficient to change the capacitive value of the capacitive component 15a to obtain a value of the second working frequency corresponding to the operating frequency of the loT type access network for the geographical area considered. It is also possible to use a capacitive component 15a whose capacitive value is controllable, for example a variable capacitor, a varicap diode (from the English " variable capacitor", a DTC component (English acronym for " Digitally Tunable Capacitor ") , or a switch to different capacities, so that a single and same antenna 1 can operate in different geographical areas where different working frequencies of the loT type access network are used.

There Figure 10 is a schematic representation, in a sectional view in a vertical plane, of a second embodiment of the antenna 1.

In this second particular embodiment, the capacitive element 15b comprises two electrodes, one electrode of which is a metal plate 19 placed opposite the plate 10 which corresponds to the other electrode. The capacitive element 15b is therefore again placed in series with the ground return wire 13 between the power supply wire 12 and the ground plane 11. In the example illustrated in Figure 10 for this second embodiment, the plate 19 is placed at the end of the wire 13 returning to ground which is on the side of the plate 10, but nothing would prevent, according to another example, from placing it at the other the end of the wire 13 returning to ground which is on the side of the ground plane 11 (in this case, it is the ground plane 11, and not the plate 10, which corresponds to the other electrode of the capacitive element 15b).

In this second embodiment, it is possible for example to use a printed circuit 31 (PCB in English for " Printed Circuit Board "), one side of which is entirely metallized to produce the plate 10, and of which only a small surface of The other face is metallized to produce the lower plate 19 of the capacitive element 15b. This makes it possible in particular to facilitate the manufacturing the antenna 1 because the ground return wire 13 can then play the role of mechanical support for the printed circuit 31 which includes both the plate 10 and the capacitive element 15b. In the example considered for this second embodiment, the plate 19 is a disk with a diameter of 10 mm and the distance between the plate 19 and the plate 10 is 0.1 mm.

Furthermore, in this second embodiment, the impedance adaptation of the antenna 1 is carried out solely by adjusting the different parameters of the structure of said antenna. The adaptation circuit 17 of the first embodiment described with reference to the figures 1 to 4 is thus deleted.

THE figures 11, 12 and 13 represent respectively the reflection coefficient and the radiation patterns of the antenna 1 according to this second embodiment at a first working frequency of 1575 MHz and at a second working frequency close to 988 MHz.

Curve 25 of the Figure 11 represents the reflection coefficient of antenna 1. At the Figure 12 , curve 27 represents its radiation pattern at 1575 MHz according to RHCP polarization while curve 28 represents its radiation pattern according to LHCP polarization. Curve 26 of the Figure 13 represents the radiation pattern of antenna 1 at 988 MHz according to vertical rectilinear polarization.

It should be noted that, unlike the radiation diagrams of figures 7 and 8 , the diagrams of figures 12 and 13 present radiation throughout the space, even under the horizontal plane containing the ground plane 11 of the antenna 1 (90° < Θ < 270°). This comes from the fact that for the second embodiment, the dimensions of the ground plane 11 are not sufficiently large compared to those of the plate 10 for it to completely reflect the waves emitted by the antenna upwards. On the other hand, if we considered that the antenna was placed on the roof of a motor vehicle, then the roof of the vehicle would play the role of an infinite ground plane, and the observed radiation would be exclusively in the space located above. above the ground plane.

It appears from these different curves that even if the performances of the antenna 1 according to the second embodiment are a little less good than those of the antenna 1 according to the first embodiment, they remain very satisfactory for the expected operating modes, namely the reception of GPS signals and the transmission of messages on an loT access network.

Indeed, at 1575 MHz the antenna has a coefficient S ₁₁ of approximately - 18 dB and a gain close to 10 dBi in the vertical direction 18 ( Θ = 0°) for RHCP polarization. In this direction, the gain is -2 dBi for LHCP polarization. Discrimination of the RHCP polarization relative to the LHCP polarization is therefore always possible even if the difference in gain between these two polarizations is less significant than for the first embodiment. At 988 MHz, we observe an S ₁₁ coefficient of around -13 dB and a gain close to 2 dBi in the horizontal directions ( Θ close to 90°).

There Figure 14 presents a third embodiment of the antenna 1. In particular, part a) of the Figure 14 is a schematic representation of the plate 10 of the antenna 1 for this third embodiment. In this third embodiment, a slot 30 is made in the plate 10 such that it completely surrounds the connection point between the ground return wire 13 and the plate 10. A capacitive element 15c then appears: a of its electrodes is formed by part 10a of plate 10 which is outside the periphery formed by slot 30, and its other electrode is formed by part 10b of plate 10 which is inside said periphery formed by the slot 30. Thus, instead of using a discrete electronic component 15a or a metal plate 19, the capacitive element 15c is produced from a slot 30 in the plate 10 at the end of the wire 13 returns to ground which is in contact with plate 10.

Part b) of the Figure 14 is an enlargement of the particular shape of the slot 30. In the example considered, the slot 30 is inscribed in a square of side length L equal to 10.2 mm, and the thickness of the slot 30 is 0.2 mm. The particular shape of the slot 30 makes it possible to maximize the value of the capacitance for a given surface (we sometimes speak in this case of “interdigitated capacitance”). The dimensions of the slot 30 could vary depending on the dielectric substrate 14 used. Also, it is possible to vary the shape of the slot 30 to obtain different capacitance values.

It is important to note that the capacitive element 15c produced from the slot 30 in this third embodiment distinguishes the antenna 1 from certain wire-plate antennas of the prior art for which slots are also made in the plate . Indeed, the slot 30 corresponds to a capacitive element 15c placed in series with the ground return wire 13 between the power supply wire 12 and the ground plane 11. Thus, unlike the wire-plate antennas of the art prior using slots, for the antenna 1 according to the third embodiment described with reference to the Figure 14 there is no direct electrical connection between the power supply wire 12 and the ground return wire 13 because the slot 30 completely surrounds the connection point between the ground return wire 13 and the plate 10.

There Figure 15 represents the reflection coefficient at the input of the antenna for this third embodiment. We clearly see the two resonant frequencies for which the antenna 1 is adapted in impedance. Notably, marker no. 1 indicates the second resonant frequency around 982 MHz and marker no. 2 indicates the first resonant frequency at 1575 MHz.

The invention also relates to a transmission device comprising an antenna 1 according to any one of the embodiments described above and a generator 16 connected to the power supply wire 12, adapted to form an electrical signal at the first frequency working frequency and/or at the second working frequency. For example, the generator 16 applies a voltage or an electric current to the power supply wire 12 at the first working frequency and/or at the second working frequency, thus generating an electromagnetic field radiated by the antenna 1. According to other examples, the transmission device could also include two generators connected to the antenna 1, for example via a duplexer.

The invention also relates to a receiving device comprising an antenna 1 according to any one of the embodiments described above and a receiver connected to the power supply wire 12, adapted to receive an electrical signal at the first working frequency and/or at the second working frequency. For example, the receiver extracts a signal at the first working frequency and/or at the second working frequency from variations of a voltage or an electric current induced in the power supply wire 12 by the electric field of an electromagnetic wave captured by the antenna 1.

More particularly, the invention relates to a transceiver device comprising an antenna 1 according to any one of the embodiments described above and making it possible to receive, at the first working frequency of the antenna 1, a radio signal comprising geolocation information transmitted by a satellite communication system, and to transmit to a terrestrial wireless communication system, at the second working frequency of the antenna 1, a radio signal comprising the geographical position of said device possibly accompanied other information.

These devices include, in a conventional manner, one or more microcontrollers, and/or programmable logic circuits (of the FPGA, PLD type, etc.), and/or specialized integrated circuits (ASIC), and/or a set of components discrete electronics, and a set of means, considered to be known to those skilled in the art for carrying out signal processing (analog or digital filter, amplifier, analog/digital converter, sampler, modulator, demodulator, oscillator, mixer, etc. .).

Depending on the embodiment of the antenna 1 chosen, these devices may or may not include an adaptation circuit 17 between the transmission line carrying the radio frequency signal and the antenna. In particular, for the second embodiment of the antenna 1 described above with reference to the Figure 10 , it is possible to do without such an adaptation circuit because the antenna 1, by its very structure, is perfectly matched in impedance to the two working frequencies considered.

The above description clearly illustrates that, through its various characteristics and their advantages, the present invention achieves the objectives set. In particular, the antenna 1 according to the invention allows operation at two distinct frequencies according to two different radiation modes and with very satisfactory performance obtained thanks to good impedance adaptation at each of the two working frequencies considered. Furthermore, the invention offers the possibility of easily adjusting to the minus one of the working frequencies by varying the value of the capacitive element (15a, 15b, 15c). Finally, the mechanical structure of the antenna 1 according to the invention makes it easier to manufacture and reduces its bulk compared to the solutions of the prior art. The cost of manufacturing such an antenna 1 is also reduced.

More generally, it should be noted that the embodiments considered above have been described by way of non-limiting examples, and that other variants are therefore possible. In particular, different working frequencies can be obtained by varying certain parameters of the antenna such as for example the dimensions of the plate 10, the diameter and/or the position of the feed wire 12 and the wire 13 returning to the mass, the value of the dielectric substrate 14, the distance between the plate 10 and the ground plane 11, the value of the capacitive element 15a, 15b, 15c, etc.

It should be noted, finally, that the invention finds a particularly advantageous application for a device intended to receive signals coming from GPS satellites and to transmit information to a wireless communication system of the loT type, but it could have other applications, for example for communication systems using other frequency bands. Also, nothing would prevent a device using an antenna 1 according to the invention from being configured to transmit and receive on each of the two working frequencies of the antenna.

Claims (12)

1. Antenna (1) comprising a ground plane (11), a metal plate (10) arranged facing said ground plane (11), a power supply wire (12) allowing to connect said plate (10) to a generator (16) or a receiver, so that the antenna (1) has a resonance frequency in patch antenna mode, called "first working frequency", said antenna (1) being characterised in that it further comprises:

   - a ground-return wire (13) connecting the plate (10) to the ground plane (11), the ground-return wire (13) being arranged substantially perpendicularly to the plate (10) and to the ground plane (11) and positioned substantially in the middle of the plate (10),

   - a capacitive element (15a, 15b, 15c) arranged in series with the ground-return wire (13) between the power supply wire (12) and the ground plane (11),

   and in that the ground-return wire (13) is an element radiating at a "second working frequency", lower than said first working frequency, so that the antenna (1) has a resonance frequency in wire-plate antenna mode at said second working frequency.
2. Antenna (1) according to claim 1, wherein the plate (10) is a rectangular plate, two opposite angles of the same diagonal of which are truncated so that the antenna (1) has a circular polarisation at said first working frequency.
3. Antenna (1) according to one of claims 1 to 2, wherein the capacitive element (15a) is a discrete electronic component.
4. Antenna (1) according to clai3 4, wherein the capacitive component (15a) has a controllable capacitive value.
5. Antenna (1) according to one of claims 1 to 2, wherein the capacitive element (15b) comprises two electrodes, including one electrode that is formed by a metal plate (19) located at an end of the ground-return wire (13) and arranged facing the plate (10) of the antenna (1) or the ground plane (11).
6. Antenna (1) according to claim 5, wherein said metal plate (19) of the capacitive element (15b) is located at the end of the ground-return wire (13) near the plate (10) of the antenna (1), so that the other electrode is formed by the plate (10) of the antenna (1).
7. Antenna (1) according to one of claims 1 to 2, wherein a slot (30) is made in the plate (10) so that said slot (30) completely surrounds the point of connection between the ground-return wire (13) and the plate (10), and the capacitive element (15c) comprises two electrodes, including one electrode that is formed by a part (10a) of the plate (10) that is outside of the contour formed by the slot (30), and the other electrode is formed by another part (10b) of the plate (10) that is inside said contour formed by the slot (30).
8. Antenna (1) according to one of claims 1 to 7, wherein at least one of the ground-return (13) and power supply (12) wires is a metal strip cut out of the plate (10).
9. Antenna (1) according to one of claims 1 to 8, wherein the distance between the power supply wire (12) and the ground-return wire (13) is greater than one tenth of the wavelength of the second working frequency.
10. Emission device comprising an antenna (1) according to one of claims 1 to 9 and a generator (16) connected to the power supply wire (12), adapted to forming an electric signal at the first working frequency and/or at the second working frequency.
11. Reception device comprising an antenna (1) according to one of claims 1 to 9 and a receiver connected to the power supply wire (12), adapted to receiving an electric signal at the first working frequency and/or at the second working frequency.
12. Transceiver device comprising an antenna (1) according to one of claims 1 to 9, configured to receive a signal at the first working frequency comprising geolocation information emitted by a satellite communication system and to emit to a terrestrial wireless communication system a signal at the second working frequency comprising the geographic position of said device.

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