EP3669422A1

EP3669422A1 - Patch antenna having two different radiation modes with two separate working frequencies, device using such an antenna

Info

Publication number: EP3669422A1
Application number: EP18753199.1A
Authority: EP
Inventors: Cyril JOUANLANNE
Original assignee: Sigfox SA
Current assignee: Unabiz
Priority date: 2017-08-18
Filing date: 2018-08-17
Publication date: 2020-06-24
Anticipated expiration: 2038-08-17
Also published as: EP3669422B1; FR3070224B1; FR3070224A1; US11196162B2; WO2019034760A1; US20200227829A1; EP3669422C0

Abstract

The invention relates to an antenna (1) comprising a ground plane (11), a metal plate (10) arranged facing said ground plane (11), and a supply wire (12) for connecting the plate (10) to a generator (16) or a receiver, such that said antenna (1) has a first resonance frequency in a patch antenna mode. The antenna (1) further comprises a ground wire (13) connecting the plate (10) to the ground plane (11), and a capacitive element (15a, 15b, 15c) arranged in series with the ground wire (13) between the supply wire (12) and the ground plane (11), such that the antenna (1) also has a second resonance frequency in a wire-plate antenna mode.

Description

Plated antenna having two different radiation modes at two different working frequencies, device using such antenna

TECHNICAL AREA

The present invention belongs to the field of antennas. An antenna is a device for radiating (emitting) or capturing (receiving) electromagnetic waves. In particular, the invention relates to an antenna whose structure makes it possible to radiate or pick up radio waves at two different working frequencies according to two different radiation modes and with particularly advantageous performances. STATE OF THE ART

In the field of compact antennas used for telecommunications, antennas known to those skilled in the art are already known under the name of "plated antenna". These antennas are also known as "printed antenna", or under the Anglicism "antenna patch".

Such an antenna consists of a radiating element corresponding to a metal plate of any shape (rectangular, circular, or other more elaborate forms) 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 similar to that of the air, or be removed if the mechanical maintenance of the radiating element can be provided by other means. The antenna power is generally supplied 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, that is, to say to the plate.

A plated antenna, however, has the disadvantage of having relatively large dimensions, of the order of half the length of the desired working frequency. Indeed, it can be considered as a first approximation that an antenna plated with a rectangular plate behaves as a cavity whose various discrete resonant frequencies correspond to known modes depending on the dimensions of the plate. In particular, for a so-called "fundamental" mode, the antenna resonates at a frequency whose half of the wavelength corresponds to the length of the cavity. Thus, the lower the desired working frequencies, the greater the size 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, antennas known to those skilled in the art are also known under the name of "wire-plate antenna". With respect to a plated antenna, a wire-plate antenna has at least one additional lead connecting the plate to the ground plane. It is a return wire to the active mass and 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 implementing 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 occurs at a frequency lower than that of the cavity-like fundamental resonant frequency of a plated antenna. Thus, for given plate dimensions, a wire-plate antenna has a working frequency lower than a plated antenna.

It should be noted that the operation of a wire-plate antenna is very different from the operation of a plated antenna. Indeed, the resonance that we speak for a plated antenna is of 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 itself of electrical type: the resonant elements are localized, comparable to electrical components.

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

For this purpose, it is known to combine several antennas on a single structure. For example, it is known to overlay several antennas of the wire-plate type, or to superpose a plated-type antenna and a wire-plate type antenna, in order to obtain an antenna behavior that would be equivalent to that of several separate antennas. These solutions, however, have several drawbacks, in particular an obstruction 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. . STATEMENT OF THE INVENTION

The present invention aims to overcome all or part of the disadvantages of the prior art, including those described above.

For this purpose, and according to a first aspect, the present invention relates to an antenna comprising a ground plane, a metal plate arranged facing said ground plane, a feed wire for connecting said plate to a generator or a receiver, a ground return wire connecting the plate to the ground plane, and a capacitive element arranged in series with the wire back to ground between the power wire and the ground plane. The grounding wire is arranged substantially perpendicular to the plate and ground plane and is positioned substantially in the middle of the plate.

With such arrangements, the antenna not only has a plated antenna resonance (i.e., an electromagnetic type cavity resonance) at a first working frequency, but also a resonance in wire-plate antenna mode (i.e., electric-type resonance) at a second working frequency lower than the first working frequency. The return wire is a radiating element at the second working frequency. At each of these two resonances corresponds 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 adaptation in impedance 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 a maximum omnidirectional radiation in a plane. parallel to the ground plane.

In particular embodiments, the invention may further comprise one or more of the following features, taken separately or in any technically possible combination.

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

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

In particular embodiments, the capacitive component is of controllable capacitive value.

In particular embodiments, the capacitive element comprises two electrodes of which an electrode is formed by a metal plate located at one end of the grounding 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 grounding 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 of which an electrode is formed by a part of the antenna plate which is outside a periphery 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 and power supply son is a metal ribbon cut into the plate of the antenna.

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

According to a second aspect, the invention relates to a transmission device comprising an antenna according to any one of the preceding embodiments and a generator connected to the supply wire, adapted to form an electrical signal at the first working frequency and / or at the second working frequency.

According to a third aspect, the invention relates to a reception device comprising an antenna according to any one of the preceding embodiments and a receiver connected to the supply wire, adapted to receive an electrical signal at the first working frequency and / or at the second working frequency.

According to a fourth aspect, the invention relates to a transceiver device comprising an antenna according to any one of the preceding embodiments, configured to receive a signal at the first working frequency comprising geolocation information transmitted by a communication system. by satellite and for transmitting to a terrestrial wireless communication system a signal at the second working frequency comprising the geographical position of said device. PRESENTATION OF FIGURES

The invention will be better understood on reading the following description, given by way of non-limiting example, and with reference to FIGS. 1 to 15 which represent: FIG. 1: a schematic representation, in a perspective view, of a first embodiment of an antenna according to the invention,

FIG. 2: a schematic representation, in a sectional view in a vertical plane, of the first embodiment of the antenna,

FIG. 3: a schematic representation of the shape of the plate for the first embodiment of the antenna,

FIG. 4: a schematic representation of a variant of the first embodiment of the antenna,

FIG. 5: a schematic representation of the plate for a variant of the first embodiment of the antenna,

FIG. 6: a diagram representing the reflection coefficient at the input of the antenna for the first embodiment,

FIG. 7: a radiation diagram according to a vertical sectional plane for the first embodiment of the antenna and for a first working frequency,

FIG. 8: a radiation diagram according to a vertical sectional plane for the first embodiment of the antenna and for a second working frequency,

FIG. 9: a diagram representing the antenna input reflection coefficient for different values of a capacitive element, FIG. 10: a schematic representation, in a sectional view in a vertical plane, of a second embodiment of FIG. the antenna,

FIG. 11: a diagram representing the antenna input reflection coefficient for the second embodiment, FIG. 12: a radiation diagram according to a vertical section plane for the second embodiment of the antenna and for a first working frequency,

FIG. 13: a radiation diagram according to 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,

FIG. 15: a diagram representing the antenna input reflection coefficient for the third embodiment. In these figures, identical references from one figure to another designate identical or similar elements. For the sake of clarity, the elements shown are not to scale unless otherwise stated.

DETAILED DESCRIPTION OF EMBODIMENTS

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

In the remainder of the description, reference is made 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 navigation system (also referred to as the GNSS acronym for Global Navigation Satellite System), such as the Global Positioning System (GPS), to determine its geographical position, and to transmit it, possibly accompanied by other information, to another wireless communication system such as an Internet of Things type of access network, or loT (acronym for "Internet Of Things").

In order 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. For example, considering the GPS system, the working frequency, that is the frequency of the radio signals emitted by the GPS satellites, is about 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 (acronym for Right Hand Circular Polarization).

In order to transmit information to a loT-type wireless communication system, it is 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. at the roof of the vehicle. In fact, the base stations of an access network of such a wireless communication system are generally located on the sides with respect to the vehicle, and not vertically. In the remainder of the description, reference is made by way of example and in a nonlimiting manner in the case of an ultra-narrowband wireless communication system. By "Ultra Narrow Band" ("Ultra Narrow Band" or UNB in the Anglo-Saxon literature), it is meant that the instantaneous frequency spectrum of the radio signals emitted is of frequency width less than two kilohertz, or even less than one kilohertz. Such UNB wireless communication systems are particularly suitable for loT applications. For example, they can use the ISM ("Industrial, Scientific and Medical") frequency band around 868 MHz in Europe, or the ISM frequency band around 915 MHz in the United States. Straight polarization is generally used in such systems.

Thus, for the rest of the description, one places oneself 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.

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

The plate 10 is arranged facing a ground plane 1 1. In the Following the description, it is considered in a nonlimiting manner that the plate 10 is flat. Nothing, however, excludes, according to other examples, having a plate 10 not planar. In addition, it is considered that the plate 10 is disposed horizontally and substantially parallel to the ground plane January 1. According to other alternative examples, the plate 10 may be slightly inclined relative to the ground plane 11. The distance separating the plate 10 from 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 one tenth of the wavelength of the first working frequency. The two metal surfaces corresponding to the plate 10 and the ground plane 1 1 may for example be disposed on either side of a dielectric substrate 14 which then acts as a 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 maintenance of the plate 10 relative to the 1 1 ground plane is provided by other means. The dimensions of the ground plane 1 1 are generally greater than those of the plate 10. In the example in which the antenna is integrated in 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 size of the plate 10 and the ground plane 1 1 dimensions will be discussed later in the description.

The plate 10 and the ground plane 1 1 are connected via a wire 12 supply. The supply wire 12 may 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 comprises a wire 13 back to ground which connects the plate 10 to the ground plane January 1. As will be detailed hereinafter, this grounding wire 13 acts as a second radiating element at the second working frequency. Preferably, the feed wire 12 and / or the return wire 13 are arranged substantially perpendicular to the ground plane. In the case where the feed wire 12 and the wire 13 return to the both are perpendicular to the ground plane 1 1 and the plate 10, then they are further arranged substantially parallel between said ground plane 1 1 and said plate 10.

More generally, "wire" means a conductor of any section, not necessarily circular. In particular, the feed wire 12 and / or the return wire 13 could be a metal ribbon.

In transmission, the antenna 1 converts a voltage or an electric current existing in the feed wire 12 into an electromagnetic field. This power supply is for example provided by a generator 1 6 voltage or current.

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

In general, a passive antenna can be modeled by a component having a certain impedance seen at the input of the antenna. It is a complex impedance whose real part corresponds to the "active" part of the antenna, that is to say to a dissipation of the energy by ohmic losses and electromagnetic radiation, and whose part imaginary corresponds to the "reactive" part of the antenna, that is to say to a storage in the form of electrical energy (capacitive behavior) and magnetic (inductive behavior). If at a particular frequency, called the resonance frequency, the inductance and the capacity 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 a power source and an antenna, it is necessary to provide impedance matching. The adaptation makes it possible to cancel the reflection coefficient, conventionally noted Su, at the input of the antenna. The reflection coefficient is the ratio between the wave reflected at the input of the antenna and the incident wave. If the adaptation is not assured, some of the power is returned to the source. In practice, to ensure a good adaptation impedance, the antenna must have an impedance equal to that of the transmission line, generally 50 ohms.

In other words, to obtain an optimal behavior of the antenna 1 in terms of radiation, it must be ensured that it behaves, for the generator that feeds it and at a predetermined resonant frequency, as a load whose part real is close to a determined value, most often 50 ohms, and whose imaginary part is null or almost nil. To this end, it is common to insert between the generator 1 6 and the antenna 1 an impedance transformation electronic circuit, called "matching circuit" 17, which modifies the input impedance of the antenna 1 view from the source and ensures impedance matching. Such an adaptation circuit 17 may for example comprise passive elements such as filters based on inductances and capacitors or transmission lines.

The plate 10 and the ground plane 11 can be likened to a resonant cavity which can be considered, at low frequency, as a capacitance which stores charges and in which a uniform electric field is created between the ground plane 1 1 and the plate 10. As long as the distance separating the ground plane 1 1 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 1 1 . At high frequency, the distribution of the charges on the plate 10 is no longer uniform, and this is also the case for the distribution of the current and that of the electric field. A magnetic field also appears. It is then known that for particular frequencies, called cavity resonance frequencies, related to the dimensions of the cavity (that is to say related 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 _mtn 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 nonzero, which represent the cavity modes: expression in which:

- it is the speed of light in a vacuum

£ _r is the relative permittivity for the dielectric substrate 14

- L is the length of the plate 10

- / is the width of the plate 10

It then clearly appears 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 the ambient air), for a mode, said fundamental mode of cavity resonance, 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 with reference to FIG. 1, the length L and the width / 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 about 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 affect 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 8.5 cm square. At the first working frequency of 1575 MHz, the antenna 1 then has a behavior close to that of a plated antenna. The impedance matching of such an antenna is generally achieved when the feed wire 12 is positioned at one side of the plate 10 rather than at its central area.

On the other hand, the plate 10 and the wire 13 back to earth can act as two elements having a radiating behavior of the electric type. The antenna 1 then has a behavior close to that of a wire-plate antenna. The antenna 1 may in particular be the seat of a parallel type resonance implementing the wire 13 back to the ground and the capacitor formed by the plate 10 and the ground plane 1 1. This so-called parallel resonance caused by the ground return wire 13 takes place at a frequency lower than that of the cavity-type fundamental resonant frequency mentioned above.

If the shape of the plate 10 is not critical for this type of electric radiation, the value of its surface has an impact on the working frequency. In particular, the smaller the area of the plate 10, the higher the wire-plate resonance frequency. For a square plate, the wire-plate resonance frequency is generally such that one quarter of its wavelength is close to the length of one side of the plate 10, but again other parameters of the Antenna structure 1 can affect the resonance frequency. In the example considered for the first embodiment, an electric type of 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 decreasing the surface of the plate 10, for example by using a rectangular-shaped plate of length L fixed relative to the wavelength of the first working frequency, and advantageously choosing the width / plate to obtain the second desired 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, at a frequency of 1575 MHz, of a resonance of the electromagnetic type (resonance in plated antenna mode) corresponding to the resonance of a cavity formed by the ground plane 1 1, the plate 10 and the four imaginary "magnetic walls" connecting the four edges of the plate 10 to the ground plane January 1, and secondly, at a frequency of 868 MHz, a resonance of the electric type (resonance in antenna mode wire-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 1 1 and the plate 10 is comparable to a capacitance while the wire 13 of return to ground has an inductance). In the realization of such an antenna 1, a great difficulty lies in the possibility of adapting the impedance antenna 1 for the two operating modes corresponding to two different radiation modes.

Many parameters affect the impedance matching of the antenna 1, such as the position of the feed wire 1 2, that of the wire 13 back to ground, the distance between the wire 12 feed wire 13 back to the ground, their diameter, etc. It is therefore possible to play on these different parameters to obtain the best adaptation impedance possible.

It is also possible to play on the matching circuit 17 to improve this impedance matching. However, the performance of an antenna is generally better if it is adapted in impedance by its own structure rather than by an adaptation circuit inserted between the generator 1 6 and the antenna 1.

It is generally futile to be able to impedance 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 antenna. generator 16, while keeping reasonable antenna performance. This is why an additional capacitive element 15a is placed in series with the wire 13 of return to ground between the feed wire 12 and the ground plane January 1. As explained above, it is a question of making the antenna 1 behave, for the generator 16 which supplies it and at a predetermined resonant frequency, as a load whose real part is close to a determined value. , most often 50 ohms, and whose imaginary part is null or almost nil. The capacitive element 15a has an impedance which depends on its capacitive value and the frequency used. It thus modifies the impedance of the antenna 1 and can make it possible to obtain impedance matching at the two working frequencies considered. It can in particular compensate the inductance represented by the wire 13 back to the ground.

It should also be noted that in order to obtain electrical resonance at the second working frequency, it is important that inductive coupling exists between the supply wire 12 and the grounding wire 13. These two sons must therefore be close enough to one another. It turns out nevertheless that the impedance matching of the antenna 1 to the first working frequency is better if the feed wire 12 is positioned at one side of the plate 10 whereas the wire 13 of the back-to-ground must it should rather be positioned towards the central zone of the plate 10. Indeed, as will be detailed later with reference to FIG. 8, it is important for the wire 13 to return to ground to be positioned towards the middle of the plate 10 to optimize the monopolar type radiation with a linear polarization at the second working frequency. In addition, to obtain a cavity-type resonance at the first working frequency, it is important that the electric current flowing through the wire 13 back to earth at this frequency is as low as possible. This can be promoted by positioning the wire 13 back 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 low, or even almost zero, at the first working frequency. This is particularly the case in the middle of the plate 10.

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

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

FIG. 2 diagrammatically shows in a sectional view in a vertical plane the first embodiment of the antenna 1 described above with reference to FIG. 1. This sectional view makes it possible to observe that the feed wire 12 passes through the ground plane 1 1 to be connected to a generator 1 6 or to a receiver. It should be noted that the feed wire 12 must in this case be isolated from the ground plane January 1 where it passes through.

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 January 1 and the other side to the wire 13 back to ground.

Figure 2 also clarifies what is meant by the vertical direction 18. This is the upward direction perpendicular to the plane containing the ground plane 1 1 which is considered horizontal. An angle Θ formed between this vertical direction 18 and another direction can then be defined. This angle will be of interest in particular to define the radiation of the antenna 1 in the different directions of space.

FIG. 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 portion 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 a circular polarization, such as for example by exciting the antenna 1 with two sources out of phase by 90 °.

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

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

FIG. 5 is a schematic representation in perspective of the plate 10 of the antenna 1 for a variant of the embodiment described with reference to FIG. 4. In this variant, the feed wire 12 and the wire 13 return to FIG. the mass are two metal strips cut into the plate 10 and folded perpendicularly to the plate. The dimensions of the slots corresponding to the recesses due to the cuts in the plate 10 are sufficiently small (for example about 3 mm wide) to have no effect on the performance of the antenna. A particularly interesting aspect of this variant is to simplify the manufacture of the antenna since it is no longer necessary to connect wires to the plate 10. The metal ribbons play indeed the role of the wire 12 and the power supply. wire 13 back to the 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 January 1.

FIG. 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 FIGS. 1 to 4. In general, the reflection coefficient conventionally denoted Su 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 Su of the first embodiment of 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 # 2. Each resonance frequency corresponds to a minimum of the reflection coefficient Su. It takes a value close to -13 dB for resonance at 1575 MHz, and a value close to -1 6 dB for 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, for example, to have a reflection coefficient of less than -10 dB on the bandwidth of the antenna, that is to say on the frequency band for which the energy transfer from the power supply to the antenna (or antenna to the receiver) is maximum The curve 20 thus confirms that with the characteristics previously listed for the first embodiment described with reference to Figures 1 to 4, the antenna 1 is adapted impedance at the two working frequencies considered.

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

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

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

Figure 8 shows a radiation pattern in a vertical sectional plane for the first embodiment of the antenna 1 for the second 868 MHz working frequency.

The curve 21 corresponds in particular to the radiation of the antenna 1 at this frequency according to a rectilinear polarization along the vertical 18. It is significant of an omnidirectional radiation of the monopolar type (that is to say corresponding to the radiation of a monopole ). One can notably observe a symmetrical lobe of revolution. 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 about 5 dBi in the horizontal directions (Θ = 90 °). There is a loss of more than 3 dB gain compared to the maximum gain for angles Θ relative to the vertical 18 less than or equal to about 40 °. The position of the wire 13 back to the ground in the middle of the plate 10 advantageously allows to promote this omnidirectional radiation monopolar type with a linear polarization inscribed in a plane containing the wire 13 back 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 back to the ground, that is to say according to the vertical 18). The antenna 1 is thus particularly efficient in rectilinear polarization at the second working frequency of 868 MHz in predominantly horizontal directions. It is therefore entirely suitable for transmitting signals to a loT type access network operating around this frequency.

It should be noted that the radiation patterns of Figures 7 and 8 show radiation only in the space above the ground plane 1 1 of the antenna 1 (-90 ° <Θ <90 °). This is because the dimensions of the ground plane 11 are sufficiently large compared to the dimensions of the plate 10 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.

FIG. 9 represents the reflection coefficient Su at the input of the antenna 1 for different values of the capacitive component 15a.

Curve 23 represents the reflection coefficient Su for a first capacitance value of 21.3 pF for which an electric-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 under consideration). The triangular marker # 4 indicates a minimum value of Su less than -1 6 dB for this frequency.

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

Curve 25 represents the reflection coefficient Su for a third capacitance value of 13.8 pF for which an electric-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 in Japan for the loT network). The triangular marker # 1 indicates a minimum value of Su of the order of -14 dB for this frequency.

For these three values of the capacitive component 15a, a cavity-like fundamental resonant frequency is always obtained for the first working frequency of 1575 MHz. Triangular marker # 2 indicates a minimum value of Su of the order of -14 dB for this frequency.

Experience shows that it is possible, for example, to vary the capacitance value of the capacitive component 15a from 10 pF to 50 pF to obtain an electrical resonance for a second working frequency of between 800 MHz and 1 GHz. The larger the value of the capacitance, the lower the value of the second working frequency for which electrical 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 affected. For some capacitance component capacitance values 15a lower 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 suffices 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 conceivable to use a capacitive component 15a whose capacitive value is controllable, for example a variable capacitor, a varicap diode (of the English "variable capacitor", a component DTC (acronym for "Digitally Tunable Capacitor") or a switch to different capabilities, so that one and the same antenna 1 can operate in different geographical areas where different working frequencies of the loT type access network are used.

FIG. 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 of which one electrode 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 wire 13 back to earth between the feed wire 12 and the ground plane 1 January. In the example illustrated in FIG. 10 for this second embodiment, the plate 19 is placed at the end of the grounding wire 13 which is on the side of the plate 10, but nothing would prevent, according to a another example, to place at the other end of the wire 13 back to the ground which is on the side of the ground plane 1 1 (in this case, it is the ground plane 1 1, 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 PCB 31 (PCB in English for "Printed Circuit Board"), one side of which is entirely metallized to produce the plate 10, and a small surface area only of which Another face is metallized to make the bottom plate 19 of the capacitive element 15b. In particular, this makes it easier to manufacture of the antenna 1 because the wire 13 back to earth can then act as a 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 disc with a diameter of 10 mm and the distance between the plate 19 and the plate 10 is 0.1 mm.

In addition, in this second embodiment, the impedance matching of the antenna 1 is performed only by playing on the various parameters of the structure of said antenna. The adaptation circuit 17 of the first embodiment described with reference to FIGS. 1 to 4 is thus eliminated.

FIGS. 11, 12 and 13 respectively represent 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 FIG. 11 represents the reflection coefficient of antenna 1. In FIG. 12, the curve 27 represents its 1575 MHz radiation pattern according to an RHCP polarization while the curve 28 represents its LHCP polarization pattern. Curve 26 of FIG. 13 represents, for its part, the radiation pattern of antenna 1 at 988 MHz in a vertical rectilinear polarization.

It should be noted that, unlike the radiation patterns of FIGS. 7 and 8, the diagrams of FIGS. 12 and 13 show a radiation throughout the space, even under the horizontal plane containing the ground plane 1 1 of the antenna 1 (90 ° <Θ <270 °). This is because for the second embodiment, the dimensions of the ground plane 1 1 are not large enough to those of the plate 10 so that it completely reflects 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 mass plane, and the radiation observed would be exclusively in the space located at above the ground plane.

It appears from these different curves that even if the performance of the antenna 1 according to the second embodiment is a little less good as 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 a loT access network.

Indeed, at 1575 MHz the antenna has a coefficient Su of about -

18 dB and a gain close to 10 dBi in the vertical direction 18 (Θ = 0 °) for the RHCP polarization. In this direction, the gain is -2 dBi for the LHCP polarization. The discrimination of the polarization RHCP with respect to the polarization LHCP is therefore still possible even if the difference in gain between these two polarizations is less important than for the first embodiment. At 988 MHz, a Su coefficient of about -13 dB is observed and a gain close to 2 dBi in the horizontal directions (Θ close to 90 °).

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

Part (b) of FIG. 14 is an enlargement of the particular shape of the slot 30. In the example considered, the slot 30 is inscribed in a side square of 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 maximizes the value of the capacity for a given surface (sometimes referred to in this case as "interdigitated capacity"). 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 made 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 wire 13 back to ground between the feed wire 12 and the ground plane January 1. Thus, unlike prior art wire-plate antennas using slots, for the antenna 1 according to the third embodiment described with reference to FIG. 14 there is no direct electrical connection between the wire 12 supply and the wire 13 back to the ground because the slot 30 completely surrounds the point of connection between the wire 13 back to the ground and the plate 10.

FIG. 15 represents the reflection coefficient at the input of the antenna for this third embodiment. It contains the two resonance frequencies for which the antenna 1 is impedance matched. In particular, marker No. 1 indicates the second resonance frequency around 982 MHz and marker No. 2 indicates the first resonance frequency at 1575 MHz.

The invention also relates to a transmission device comprising an antenna 1 according to any of the embodiments described above and a generator 1 6 connected to the feed wire 12, adapted to form an electrical signal to the first working frequency and / or at the second working frequency. For example, the generator 1 6 applies a voltage or an electric current to the first working frequency and / or the second working frequency in the supply wire 12, thereby generating an electromagnetic field radiated by the antenna 1. According to other examples, the transmission device could also comprise 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 feed 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 feed wire 12 by the electric field of an electromagnetic wave picked up by the antenna 1.

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

These devices comprise, in a conventional manner, one or more microcontrollers, and / or programmable logic circuits (of the FPGA, PLD, etc. type), and / or specialized integrated circuits (ASIC), and / or a set of components. discrete electronics, and a set of means, considered as known to those skilled in the art to do 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 a matching 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 FIG. 10, it is possible to dispense with 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, by its different 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 a good impedance matching at each of the two working frequencies considered. In addition, the invention offers the possibility of easily adjusting to least 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 facilitates its manufacture and reduces its size compared to the solutions of the prior art. The manufacturing cost of 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 of return 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 from GPS satellites and to transmit information to a wireless communication system of the loT type, but it could have to 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 is configured to transmit and receive on each of the two working frequencies of the antenna.

Claims

Antenna (1) comprising a ground plane (1 1), a metal plate (10) arranged opposite said ground plane (1 1), a feed wire (12) for connecting said plate (10) to a generator (1 6) or a receiver, so that the antenna (1) has a resonant frequency in plated antenna mode, called "first working frequency", said antenna (1) being characterized in that it further comprises:

- a grounding wire (13) connecting the plate (10) to the ground plane (1 1), the ground wire (13) being arranged substantially perpendicular to the plate (10) and to the ground plane mass (1 1) and positioned substantially in the middle of the plate (10),

a capacitive element (15a, 15b, 15c) arranged in series with the grounding wire (13) between the supply wire (12) and the ground plane (1 1),

and in that the grounding wire (13) is a radiating element at a "second working frequency", lower than said first working frequency, so that the antenna (1) has a resonant frequency in wire-plate antenna mode at said second working frequency.

2. Antenna (1) according to claim 1 wherein the radiation of the antenna (1) at the first working frequency is maximum in a direction perpendicular to the plate (10), and the radiation of the antenna (1) at the second working frequency is maximum omnidirectional radiation in a plane parallel to the ground plane.

3. Antenna (1) according to one of claims 1 or 2 wherein the plate (10) is a rectangular plate whose two opposite angles of the same diagonal are truncated so that the antenna (1) has a circular polarization at said first working frequency.

4. Antenna (1) according to one of claims 1 to 3 wherein the capacitive element (15a) is a discrete electronic component.

5. Antenna (1) according to claim 4 wherein the capacitive component (15a) is of controllable capacitive value.

6. Antenna (1) according to one of claims 1 to 3 wherein the capacitive element (15b) comprises two electrodes, an electrode is formed by a plate (19) at one end of the metal wire (13) back to ground and arranged facing the plate (10) of the antenna (1) or the ground plane (1 1).

7. Antenna (1) according to claim 6 wherein said plate (19) of the metal capacitive element (15b) is located at the end of the wire (13) of ground return to the side of the plate (10) of the antenna (1), so that the other electrode is formed by the plate (10) of the antenna (1).

8. Antenna (1) according to one of claims 1 to 3 wherein a slot (30) is formed in the plate (10) so that said slot (30) completely surrounds the point of connection between the wire (13). ) to the ground and the plate (10), and the capacitive element (15c) comprises two electrodes of which an electrode is formed by a portion (10a) of the plate (10) which is outside a the periphery formed by the slot (30), and the other electrode is formed by another portion (10b) of the plate (10) which is inside said periphery formed by the slot (30).

9. Antenna (1) according to one of claims 1 to 8 wherein at least one of the son return to the ground (13) and supply (12) is a metal ribbon cut in the plate (10) .

10. Antenna (1) according to one of claims 1 to 9 wherein the distance between the wire (12) supply and the wire (13) back to the ground is greater than one-tenth of the wavelength of the second working frequency.

11. Transmission device comprising an antenna (1) according to one of claims 1 to 10 and a generator (1 6) connected to the wire (12) for supply, adapted to form an electrical signal at the first working frequency and / or at the second working frequency.

12. Reception device comprising an antenna (1) according to one of claims 1 to 10 and a receiver connected to the supply wire (12) adapted to receive an electrical signal at the first working frequency and / or the second working frequency.

13. Transceiver device comprising an antenna (1) according to one of claims 1 to 10 configured to receive a signal at the first working frequency comprising geolocation information transmitted by a satellite communication system and to transmit to a terrestrial wireless communication system a signal at the second working frequency comprising the geographical position of said device.