EP4066315B1 - Radiating element and associated antenna and manufacturing method - Google Patents

Description

The field of the invention is that of microwave devices, such as array antennas.

Such devices can be used in various applications such as radar applications in avionics and aerospace, high-speed communication, space technologies.

An array antenna is formed from a two-dimensional array of radiating elements.

The present invention relates to a radiating element and an antenna comprising such a radiating element.

Many types of antennas exist, varying according to the intended applications, for example according to the wavelength and the power, or even the spectral characteristics of the emission sought. In particular, many types of antennas include a set of radiating elements, also called elementary antennas. The radiating elements make it possible, by controlling their arrangement, their conformation or the electrical signal which supplies each of them, to improve the gain of the antenna or to control its directivity or the shape of the beam emitted.

However, existing antennas have relatively large dimensions, of the order of several centimeters to several tens of centimeters depending on the frequency and the power required by the intended application, and therefore a large volume and weight. The large dimensions are inconvenient for certain applications, for example for mobile devices, since an increase in the volume and/or the weight of the devices results therefrom. In addition, devices containing large antennas are more difficult to transport. The integration of antennas in devices whose geometry is fixed with a view to functions other than communication is, moreover, made difficult.

US 2009/251371 A1 describes a communication solution to or from a nanodevice, ensured by an antenna based on a nanostructure, this for eliminate the need to provide a physical communication connection to the nanodevice.

US 2009/251267 A1 describes an inductor comprising a conductive line comprising a material in which an electrical resistance varies depending on an electric field applied to the material and/or first and second electrodes electrically connected to the first and second end portions of the conductive line.

CN 105 914 201 A describes a sheet of graphene passing through an adjustable inductor. The graphene sheet includes a grapheme coil layer, an insulating medium layer, an electrode driving layer and a substrate.

US 2005/116861 A1 proposes a small antenna with high frequency band response characteristic, comprising a radiator made of a carbon nanotube.

Brun C et al., “Monopole antenna based on carbon nanotubes”, IEEE - MTTS International Microwave symposium digest, US, June 2, 2013, pages 1-4 , relates to a millimeter-wave monopole antenna, with size reduction by using the quantum effects of the carbon nanotube.

US 3,453,618 A provides an antenna for mobile communication use, in combination with an antenna mounting unit and further providing impedance matching coupling of the antenna.

There is therefore a need for a radiating element having a smaller footprint than the radiating elements of the state of the art.

To this end, a radiating element is proposed for an antenna comprising a set of at least one wire nanostructure, each wire nanostructure extending in the same direction, called the common direction, between a first end and a second end. The radiating element also comprises an inductor connected to each first end of said at least one wire nanostructure, the inductor being made from a first conductive material, the inductor extending in a plane normal to the common direction. According to the invention, the first conductive material has an electrical conductivity varying under the effect of a variation of an electric field applied within the first conductive material.

Advantageously, the inductance is configured so as to present an inductance value that can be tuned with a capacitance of the set of at least one wire nanostructure.

Advantageously, the first conductive material comprises a semimetal.

The first material is, for example, graphene, or a transition metal dihalogenide.

Advantageously, at least one wire nanostructure is a carbon nanotube.

Advantageously, the set of at least one wire nanostructure comprises several wire nanostructures.

Advantageously, each wire nanostructure has an aspect ratio greater than 20.

Advantageously, the inductance has a spiral shape.

Advantageously, the set of at least one wire nanostructure comprises several wire nanostructures.

Advantageously, in the latter case, the inductance is configured so as to present an inductance value tunable with a capacitance of the set of wire nanostructures.

The invention also relates to an elementary antenna comprising a first radiating element according to the invention. The antenna also comprises a transmission line comprising a zone made of a second conductive material and two ground planes, the transmission line extending in the same plane as the inductor and the zone being connected to the inductor, each ground plane being made of a third conductive material, the zone being arranged between the two ground planes. According to the invention, the antenna comprises a variable DC voltage generator capable of applying the electric field within the first conductive material.

As the DC voltage generator is a variable DC voltage generator, the DC voltage generator is capable of applying a variable electric field within the first conductive material.

Advantageously, the elementary antenna comprises an electrode in physical contact with the inductance, the voltage generator applying the electric field within the first conductive material via the electrode.

The invention also relates to an array antenna. It comprises a network of several radiating elements according to the invention. In other words, it comprises several elementary antennas according to the invention arranged so that the radiating elements of the various elementary antennas form an array of radiating elements.

Advantageously, the inductors of the radiating elements are coplanar or able to be coplanar.

The array antenna comprises, for example, several radiating elements including a first radiating element according to the invention and a second radiating element according to the invention, the first radiating element and the second radiating element having sets of at least one wired nanostructure with different abilities.

• [fig.1] la figure 1 est un schéma d'une antenne comprenant un ensemble d'éléments rayonnants et un ensemble de lignes de transmission,
• [fig.2] la figure 2 est une vue en coupe d'un élément rayonnant de l'invention et d'une ligne de transmission de la figure 1, l'élément rayonnant comprenant un faisceau de nanostructures,
• [fig.3] la figure 3 est une vue de dessus d'un faisceau de nanostructures,
• [fig.4] la figure 4 est une vue de dessus de l'élément rayonnant et de la ligne de transmission de la figure 2,
• [fig.5] la figure 5 représente schématiquement d'une courbe de valeurs de l'inductance cinétique d'une inductance formée d'une pluralité de couches monoatomiques de graphène en fonction d'une tension appliquée aux bornes de l'inductance,
• [fig.6] la figure 6 est une représentation schématique d'un élément rayonnant selon l'invention associé à un générateur de tension continue réglable, l'élément rayonnant comprenant un faisceau de nanostructures,
• [fig.7] la figure 7 est une représentation schématique de courbes de valeurs réelle (en trait plein) et imaginaire (en traits pointillés) d'une impédance d'entrée d'une antenne en fonction de la fréquence,
• [fig.8] la figure 8 représente une courbe représentant la réactance d'un faisceau de nanostructures nanofilaires en fonction de la fréquence,
• [fig.9] la figure 9 représente un premier mode de réalisation d'une antenne réseau comprenant un réseau monodimensionnel d'éléments rayonnants selon le deuxième mode de réalisation.
• [fig.10] la figure 10 représente un premier mode de réalisation d'une antenne réseau comprenant un réseau monodimensionnel d'éléments rayonnants selon le deuxième mode de réalisation.
• [fig.11] la figure 11 est un ordinogramme des étapes d'un procédé de fabrication d'un élément rayonnant.

Characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings, in which:

• [ fig.1 ] there figure 1 is a diagram of an antenna comprising a set of radiating elements and a set of transmission lines,
• [ fig.2 ] there figure 2 is a sectional view of a radiating element of the invention and of a transmission line of the figure 1 , the radiating element comprising a bundle of nanostructures,
• [ fig.3 ] there picture 3 is a top view of a bundle of nanostructures,
• [ fig.4 ] there figure 4 is a top view of the radiating element and the transmission line of the figure 2 ,
• [ fig.5 ] there figure 5 schematically represents a curve of values of the kinetic inductance of an inductor formed of a plurality of monatomic layers of graphene as a function of a voltage applied to the terminals of the inductor,
• [ fig.6 ] there figure 6 is a schematic representation of a radiating element according to the invention associated with an adjustable DC voltage generator, the radiating element comprising a beam of nanostructures,
• [ fig.7 ] there figure 7 is a schematic representation of curves of real (solid line) and imaginary (dotted line) values of an antenna input impedance as a function of frequency,
• [ fig.8 ] there figure 8 represents a curve representing the reactance of a beam of nanofilar nanostructures as a function of frequency,
• [ fig.9 ] there figure 9 represents a first embodiment of an array antenna comprising a one-dimensional array of radiating elements according to the second embodiment.
• [ fig.10 ] there figure 10 represents a first embodiment of an array antenna comprising a one-dimensional array of radiating elements according to the second embodiment.
• [ fig.11 ] there figure 11 is a flowchart of the steps of a manufacturing process for a radiating element.

From one figure to another, the same elements are identified by the same references.

An antenna 10 is shown on the figure 1 .

Antenna 10 is configured to transmit and/or receive a set of electromagnetic waves. For example, the antenna 10 is configured to transmit and to receive a set of electromagnetic waves.

The electromagnetic wave has a frequency between 3 kilohertz (KHz) and 300 gigahertz (GHz). It should be noted that the frequency of the electromagnetic wave is liable to vary according to the applications envisaged for the antenna 10.

The antenna 10 comprises a substrate 15, radiating elements 20 and transmission lines 25.

According to the example of figure 1 , the antenna 10 comprises a transmission line 25 for each radiating element 20.

Alternatively, the antenna 10 comprises a single radiating element 20 and a single transmission line 25.

Antenna 10 further comprises an electrical ground such as a metal frame. Alternatively, the electrical ground is an electrical circuit connected to ground.

The substrate 15 is provided to support the radiating elements 20 and the transmission lines 25.

The substrate 15 has a support face 30.

The support face 30 is flat.

A normal direction Z is defined as being the direction perpendicular to the support face 30. The axis Z defined by the direction Z and oriented in the direction of the substrate towards the radiating elements is also defined.

The substrate 15 comprises a support plate 35 and a buffer layer 40.

The support plate 35 is configured to serve as a support for the buffer layer 40, the radiating elements 20 and the transmission lines 25.

The support plate 35 is, for example, made of silicon. According to a variant, the support plate 35 is made of alumina.

The support plate 35 has, for example, a thickness of between 200 micrometers (μm) and 500 μm.

The support plate 35 is made of a material having electrical resistivity. The electrical resistivity is, for example, greater than or equal to 10,000 Ohm.centimeter. Such an electrical resistivity makes it possible to limit the radio frequency losses in the support plate 35.

It should be noted that a material other than silicon is likely to be used to produce the support plate 35. The buffer layer 40 is interposed between, on one side, the support plate 35 and, on the other side, the radiating elements 20 and the transmission lines 25.

The buffer layer 40 is delimited along the normal direction Z by the support plate 35 and by the support face 30.

The buffer layer 40 is made of an electrically insulating material. The buffer layer 40 is, for example, made of silicon oxide.

The buffer layer 40 has a thickness, along the normal direction Z, of between 500 nanometers and 5 micrometers. For example, the thickness of the buffer layer 40 is equal to 2 micrometers.

A sectional view of a radiating element 20 in a plane parallel to the normal direction Z is represented on the figure 2 .

Each radiating element 20 is configured to emit and/or receive an electromagnetic wave.

Each radiating element 20 comprises a beam F of nanostructures 45 and an inductor 50.

The bundle or bundle F comprises at least ten nanostructures 45.

The bundle comprises for example thousands or millions of nanostructures 45.

Alternatively, the radiating element 20 comprises a single nanostructure 45.

The term “nanostructure” is understood to mean a structure having at least one nanometric dimension.

A dimension of an object, measured along a direction, is the distance between the two points of the object furthest from each other along said direction. A nanometric dimension is a dimension strictly less than 1 micrometer, preferably strictly less than 100 nanometers.

A direction D is defined for each nanostructure 45. This means that each nanostructure 45 extends along the direction D defined for the nanostructure 45 considered.

The direction D of each nanostructure 45 is parallel to the normal direction Z.

Each nanostructure 45 has a first end 55 and a second end 60. Each nanostructure 45 extends between the first end 55 and the second end 60.

The direction D is, for example, parallel to the normal direction Z.

The direction D is common to all the nanostructures 45 of the same radiating element 20.

A diameter measured in a plane perpendicular to the direction D is defined for each nanostructure 45,
The diameter of each nanostructure 45 is between 2 nanometers (nm) and 10 nm.

The length of each nanostructure 45 is between 300 μm and 1 millimeter (mm). In particular, the length of each nanostructure 45 is greater than or equal to 500 μm.

The length of each nanostructure 45 is measured along the common direction D.

Each nanostructure 45 is a wire nanostructure. A wire structure is a structure having a length strictly greater than 10 times the diameter. The ratio between, in the numerator, the length and, in the denominator, the diameter, is called “aspect ratio” also called aspect ratio.

Advantageously, each nanostructure 45 is such that the aspect ratio is strictly greater than 20.

Nanotubes are examples of wireframe nanostructures 45. Nanotubes are hollow wireframe structures with a diameter of less than 100 nanometers.

In other words, a nanotube is a hollow wire nanostructure.

“Beam” is understood to mean a set of nanostructures 45 in which the nanostructures 45 are separated from each other by a distance less than or equal to the length of the nanostructures 45. The distance between the nanostructures 45 is measured in a plane perpendicular to the common direction D.

According to particular cases, the distance is less than or equal to half the length, for example less than or equal to one fifth of the length, in particular less than or equal to one tenth of the length.

According to one embodiment, a median value is defined for the length of the nanostructures 45 of the same beam F. The median value is a value such that half of the nanostructures 45 of the beam F considered have a length greater than or equal to the value median, the other half having a length less than or equal to the median value.

The lengths of the nanostructures 45 of the bundle considered vary between 50 percent (%) and 150% of the median value.

The median value is, for example, greater than or equal to five hundred micrometers.

A total length is defined for the beam F. The total length is, for example, defined as being the length of the longest nanostructure 45 among all the nanostructures 45 belonging to the beam F.

The total length is, for example, identical for each beam F.

According to one embodiment, the total lengths of at least two beams F are different from each other.

The beam has an envelope common to all the nanostructures. The term “envelope” is understood to mean a surface enveloping the nanostructures 45 and tangent to the nanostructures 45 which delimit the beam F in a plane perpendicular to the common direction D.

A maximum side dimension is defined for the envelope. The maximum lateral dimension is the largest dimension of the envelope in a plane perpendicular to the common direction D. The maximum lateral dimension is between 10 μm (or 20 μm) and 1 mm.

An aspect ratio equal to the ratio between, in the numerator, the total length of the beam F and, in the denominator, the maximum lateral dimension, is defined for the beam F.

The aspect ratio of the beam F is, for example, between 5 and 15. According to one embodiment, the aspect ratio of the beam F is less than or equal to 10. It is, for example, between 9 and 10.

The bundle F typically has a total length comprised between 100 micrometers and 1 mm and a diameter comprised between 10 micrometers and 100 micrometers.

The aspect ratio depends on the target transmission or reception frequency, that is to say according to the target resonance frequency.

In radio frequency applications, the beam or bundle F is advantageously configured to resonate at a frequency between 1 GHz and 100 GHz.

The beam F is represented seen according to the common direction D on the picture 3 .

The envelope has a cross section in the common direction D of circular shape.

It should be noted that shapes other than the circular shape can be envisaged for the section of the beam F. For example, the section of the beam F has a circular shape, or even a polygonal shape such as a rectangular or cross shape.

The nanostructures 45 are all made of the same material. In particular, each nanostructure 45 is a carbon nanotube.

On the picture 3 , each nanostructure 45 is a double-layered carbon nanotube. It should be noted that the carbon nanotubes are likely to be single-wall carbon nanotubes, multi-wall carbon nanotubes or MWCNT in reference to the Anglo-Saxon expression "multi-wall carbon nanotubes" or even a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes. It should be noted that other types of wire nanostructures 45 are likely to be used instead of carbon nanotubes.

The carbon nanotubes are advantageously aligned vertically. In other words, the carbon nanotubes extend longitudinally in the same direction D.

It should be noted that other types of wire nanostructures 45 are likely to be used instead of carbon nanotubes.

For example, the nanostructures 45 are nanowires, for example silicon nanowires or another semiconductor material.

According to another variant, the nanostructures 45 are made of an electrically conductive material such as a metallic material.

The inductor 50 of each radiating element 20 extends in a plane normal to the common direction D. Each inductor 50 is, for example, made in the form of a conductive layer carried by the substrate 15. For example, each inductance 50 is perpendicular to normal direction Z and to common direction D. In particular, inductance 50 is carried by buffer layer 40.

Inductor 50 is made from a first conductive material.

According to the example of figure 4 , each inductance 50 comprises a first portion 65 and a second portion 70.

The first portion 65 extends in a plane perpendicular to the normal direction Z.

The first portion 65 is interposed between the bundle F of nanostructures 45 and the substrate 15. The first portion 65 is connected to the first end 55 of each nanostructure 45.

The first portion 65 has a triangular shape in a plane normal to the common direction D.

It should be noted that shapes other than triangular shapes can be envisaged for the first portion 65. For example, the first portion 65 has a circular or square shape. The second portion 70 extends in a plane perpendicular to the normal direction Z.

A maximum dimension is defined for the second portion 70. The maximum dimension is measured in a plane perpendicular to the normal direction Z between the two points of the second portion 70 furthest apart from each other.

The maximum dimension 70 is between 100 µm and 1 mm. For example, the maximum dimension 70 is between 200 µm and 500 µm. It should be noted that the maximum dimension 70 is likely to vary.

The second portion 70 has a spiral shape in a plane perpendicular to the normal direction Z.

The second portion 70 surrounds the first portion 65 in a plane perpendicular to the normal direction Z.

According to one embodiment, the second portion 70 is formed by a succession of line segments. For example, each line segment is perpendicular to the line segments to which it is contiguous.

As a variant, a curved part of the second portion 70 is interposed between two contiguous straight line segments.

According to another variant, the second portion 70 is formed by a single curve wound on itself.

It should be noted that a second portion 70 having a shape other than a spiral can also be envisaged.

The second portion 70 has a third end 75 and a fourth end 80. The second portion 70 extends in a spiral from the third end 75 to the fourth end 80.

The third end 75 is the end of the second portion 70 which is located on the periphery of the second portion 70 in a plane perpendicular to the normal direction Z.

The fourth end 80 is the end of the second portion 70 which is located on the periphery of the first portion 65 in a plane perpendicular to the normal direction Z. The fourth end 80 is therefore surrounded by the rest of the second portion 70 in a plane perpendicular to the Z normal direction.

The fourth end 80 is connected to the first portion 65.

Transmission line 25 extends in the same plane as inductor 50. In particular, transmission line 25 is made in the form of a layer carried by substrate 15.

The transmission line 25 comprises a conductive zone 85 and at least one ground plane 90. In particular, the transmission line 25 represented on the figure 4 has two ground planes 90.

The conductive zone 85 is connected to the inductor 50. For example, the conductive zone 85 is connected to the third end 75 of the inductor 50.

The conductive zone 85 is configured to receive an electric current from the inductor 50. Such a current is notably generated by the inductance 50 following the reception of an electromagnetic wave.

The conductive zone 85 is furthermore configured to receive an electric current from an electric source external to the antenna 10 and to supply the inductor 50 with said electric current. The conductive zone 85 has, for example, a rectangular shape.

The conductive zone 85 has a thickness measured along the normal direction Z. The thickness of the conductive zone 85 is between 100 nanometers and 1 micrometer. For example, the thickness of conductive zone 85 is equal to 600 nanometers.

Conductive zone 85 is made of a second conductive material.

The second conductive material is, for example, a metallic material. The second conductive material is for example molybdenum.

According to one embodiment, the second conductive material is the same material as the first conductive material.

It should be noted that other conductive materials can be envisaged for the conductive zone 85.

Each ground plane 90 is connected to the ground of the antenna 10.

Each ground plane 90 has a thickness measured along the normal direction Z. The thickness of each ground plane 90 is between 100 nanometers and 1 micrometer.

For example, the thickness of each ground plane 90 is equal to 600 nanometers.

Each ground plane 90 is made of a third conductive material.

The third conductive material is, for example, a metallic material. The third conductive material is, for example, molydbdenum.

According to one embodiment, the third conductive material is the same material as the first conductive material.

It should be noted that other conductive materials are possible for each ground plane 90.

According to one embodiment, the conductive zone 85 is arranged between the two ground planes 90.

A distance, in a plane perpendicular to the normal direction Z, between the conductive zone 85 and the ground plane 90 closest to the conductive zone 85 is between 50 μm and 250 μm.

According to the example proposed, the conductive zone 85 is equidistant from the two ground planes 90.

In the example shown in the figure 4 , the inductor 50 is at least partially interposed between the two ground planes 90.

A distance between the inductor 50 and the ground plane(s) 90 is between 20 μm and 300 μm.

According to one embodiment, each ground plane 90 has an “L” shape. Each ground plane 90 then has a first branch and a second branch, the two branches being perpendicular to each other.

The first branch of each ground plane 90 extends in the direction of the other ground plane 90 belonging to the same transmission line 25. For example, the first two branches of the same transmission line 25 are aligned with each other.

The conductive zone 85 of each transmission line 25 is, for example, interposed between the first two branches of the transmission line 25 in question.

The two first branches of the same transmission line 25 are, for example, interposed between the two corresponding second branches. Each inductor 50 is, for example, interposed between the two second branches of the ground planes 90 between which the inductor 50 is interposed. For example, the inductance 50 is housed in a rectangular zone delimited on a first side of the rectangular zone by the two first branches, on a second side of the rectangular zone by one of the second branches and on a third side of the rectangular zone by the other second branch, the first side being perpendicular to the second side and to the third side.

The operation of antenna 10 will now be described.

In transmission, at least one transmission line 25 receives a first electric current. In particular, the first electric current is transmitted, from a device external to the antenna 10, to the conductive zone 85.

The conductive zone 85 transmits the first electric current to the inductor 50 of the radiating element 20 connected to the transmission line 25 in question.

In response to the reception of the first electric current by the inductance 50, a first electromagnetic wave is emitted by the radiating element 20.

In reception, a second electromagnetic wave is received by at least one radiating element 20.

Following the reception of the second electromagnetic wave, a second electric current appears in the inductance 50 of the radiating element 20 considered. The second electric current is transmitted by the inductor 50 to the conductive zone 85 connected to the inductor 50.

The second electric current is then transmitted, by the transmission line 25 considered, to a device external to the antenna 10.

The radiating element 20 has very small dimensions. In particular, the dimensions of the radiating element 20 are smaller than the dimensions of the radiating elements of the state of the art. The antenna 10 therefore has a lower volume and weight than the antennas of the state of the art.

In particular, the combination of the nanostructure(s) 45 and the inductor 50 makes it possible to minimize the length of the nanostructures 45 with respect to a radiating element 20 not comprising an inductor 50.

An aspect ratio, for the beam F, of between 5 and 15 typically has good mechanical strength while allowing good efficiency in converting the electric current into an electromagnetic wave and vice versa. An aspect ratio of between 9 and 10 is an example of an aspect ratio that is particularly advantageous for obtaining good mechanical strength and good conversion efficiency.

Furthermore, the length of the nanostructures 45 and the inductance value of the inductor 50, which varies according to the dimensions of the inductor 50, make it possible to easily adapt the radiating element 20 to different frequency values. In In particular, antennas 10 having a wide transmission and/or reception band are obtained when total lengths or different inductance values are used for certain radiating elements 20.

Nanostructures 45 having a median value of length greater than or equal to 500 nanometers make it possible to obtain good conversion efficiency.

The spiral shape is a shape making it possible to obtain a particularly compact inductance 50, and therefore a radiating element 20 of particularly small dimensions.

The use of a buffer layer 40 made of an electrically insulating material makes it possible to limit the radiofrequency losses during the use of the radiating element 20.

An antenna 10 in which each inductor 50 is interposed at least partially between the two corresponding ground planes 90 is also particularly compact.

As a reminder, inductor 50 is made from a first conductive material.

According to the invention, the first conductive material is chosen so as to have an electrical conductivity varying under the effect of a variation of an electric field applied within the first conductive material, that is to say within the inductor 50.

In other words, the first material has an electrically controllable electrical conductivity.

The inductance has an inductance value L which varies under the effect of the electrical conductivity of the first material and therefore under the effect of the variation of the electric field applied to the first conductive material.

Thus, the inductance value varies under the effect of a variation of a voltage U1 applied between two terminals of the first material. It is the voltage U1 which generates an electric field within the inductor 50.

The first conductive material is distinct from a metal. Metals have a fixed electrical conductivity.

The first conductive material is advantageously a semimetal.

According to a particular embodiment, the first conductive material is graphene.

The inductor 50 comprises, for example, a plurality of layers of a first conductive material or a single layer of graphene.

Advantageously, each graphene layer is an atomic monolayer. In other words, it has a monatomic thickness.

Inductance 50 may comprise only the first conductive material or comprise the first material and at least one other material.

The inductance 50 comprises, for example, an alternation of layers of graphene and layers of another material.

The other material advantageously has a lower electrical conductivity than that of graphene.

The other material is, for example, graphene oxide.

It should be noted that the inductance of an element made of a predefined material comprises a magnetic inductance essentially defined by the geometric characteristics of the element and a kinetic inductance due to the movement of electrons within the material under voltage. By varying the voltage applied between two terminals of the element, the speed of movement of the electrons within the material is varied and therefore its kinetic inductance while its magnetic inductance does not vary.

It should be noted that the inductance of graphene exhibits a remarkable property. The kinetic inductance of graphene is very much greater than its magnetic inductance, which distinguishes it from metals whose kinetic inductance is negligible.

In figure 5 , the kinetic inductance L _k defined in Hm ⁻¹ of a graphene inductance 50 has been represented. This kinetic inductance decreases as a function of voltage U1 applied between two faces of inductance 50.

Other materials having a variable electrical conductivity as a function of the electrical voltage at the terminals of the first material can of course be envisaged.

Two-dimensional materials can be used. The first material may be a transition metal dichalide or TMD, an acronym for the English expression "transition metal dichalcogenide".

Alternatively, the first conductive material is based on a semimetal or several semimetals.

It is possible, for example, to propose a first topological semi-metal comprising the Dirac semi-metal (Cd3As2, Na3Bi) and the Weyl semi-metal (TaAs, NbAs).

Each inductor 50 has a thickness measured along the normal direction Z. The thickness of the inductor 50 is between 100 nanometers and 1 micrometer. For example, the thickness of the inductor 50 is equal to 600 nanometers.

Each inductor 50 has an adjustable inductance value by adjusting an electric field applied within the inductor, that is to say by adjusting a voltage applied between two terminals of the inductor 50.

The antenna according to the invention advantageously comprises, as shown in figure 6 , a variable DC voltage generator G for applying a DC voltage U1 between two terminals FI, FS of the inductance so as to apply an electric field E within the first conductive material 50.

The DC voltage U1 is applied so that a substantially uniform electric field E of variable value is applied within the first conductive material.

The electrical conductivity of the first conductive electrical material varying according to the electric field to which it is subjected, the electrical conductivity is adjustable by adjusting the electric field.

However, the inductance value L of the inductor 50 varying according to the electrical conductivity of the first conductive electrical material, the inductance value L varies under the effect of a variation of the voltage U1, that is i.e. the electric field E.

The antenna advantageously comprises, as visible in figure 6 , an electrically conductive EL electrode in direct physical contact with the inductor 50.

The variable DC voltage generator G is capable of applying a potential difference between the conductive electrode EL and a mass M so that the first conductive material is subjected to a substantially uniform electric field.

This electric field E extends for example along the Z axis as in the embodiment of the figure 2 .

The inductor 50 extends, along the axis Z, from a lower face FI in direct physical contact with the substrate 15 and more particularly with the support face 30, up to an upper face FS.

Substrate 15 is attached to a lower conductive plate PC connected to electrical ground. The substrate 15 is interposed, along the Z axis, between the conductive plate PC and the inductor 50.

The EL electrode is electrically conductive, it is for example metallic.

In the embodiment shown in figure 6 , the electrode EL is deposited on the upper face FS of the inductor 50. The inductor 50 is interposed, along the axis Z, between the substrate 15 and the lower face FI of the inductor 50.

The variable DC voltage generator is able to apply a variable DC voltage U between the electrode EL and the lower conductive plate PC so that a voltage U1 is applied between the upper face FS and the lower face DI of the inductance 50 .

When a voltage U1 is applied between the upper face FS and the lower face DI, the first conductive material is subjected to an electric field E extending along the axis Z.

As a variant, the variable DC voltage generator is intended to apply a voltage between two coplanar terminals of the inductor 50 so that the first conductive material is subjected to an electric field extending in a plane perpendicular to the axis Z. An electrode and a mass are then provided coplanar extending in the same transverse plane perpendicular to the axis Z as the inductor 50. The inductor is interposed between the electrode and the mass in this transverse plane according to a direction of the transverse plane. The generator is designed to apply a DC voltage between the coplanar electrode and ground.

It should be noted that the resonant mode of the radiating element 20 is mainly capacitive for the bundle F of wire nanostructures and inductive for the inductor. A wire nanostructure has a high resistance when it is alone whereas a bundle F of wire nanostructures has a very low resistance which can reach 50 Ohms. It therefore becomes essentially capacitive. The wire nanostructures arranged in a bundle form an element equivalent to a capacitance C. This distributed capacitance C depends on the number of wire nanostructures, on their diameter, on the form factor.

The addition of an inductance in series with the bundle F, (for example of the spiral type as seen in figure 4 ) makes it possible to obtain a radiating element resonating at a desired frequency.

The fact of providing an inductor 50 having an inductance value varying according to the electric field to which it is subjected, makes it possible to match the inductance value L of the inductor 50 with the capacitance C of the bundle F of wire nanostructures 45 , at a predetermined frequency, and thus to guarantee the correct operation of the antenna at this frequency.

By matching the inductance value L of the inductance 50 to the capacitance C of the bundle of wire nanostructures 45 at the frequency f ₀ , we mean choosing the inductance value L so that the radiating element 20 is resonant at the frequency f ₀ .

When the radiating element is in resonant mode, the resonance inductance value L is linked to the frequency f ₀ and to the capacitance C of the wire nanostructure F by the following formula:

It should be noted that a transmitting antenna is a resonant electronic circuit of the RLC type: resistive (R)-inductive (L)-capacitive (C) series or parallel, at a resonance frequency f ₀ . This circuit delivers an impedance Z _RLC adapted at the output to the air impedance (ie 377 Ohms and at the input a reference impedance Z ₀ (usually 50 Ohms). When these conditions are respected, it is then possible to transmit the energy of the input signal by this circuit which is then described by an impedance brought back to its input demonstrating this resonance visible on its real part (close to Z ₀ ) and part imaginary (zero value at f ₀ ).

avec $${\mathrm{Z}}_{\mathrm{RLC}}=\mathrm{R}+\mathrm{j}\left(\mathrm{L}\mathrm{\omega }-\frac{1}{\mathrm{C\omega }}\right)$$

où ω = 2*π*f et R est la résistance ou partie réelle de l'impédance du circuit RLC et f est la fréquence, L est l'inductance du circuit RLC et C est la capacité du circuit RLC.The input impedance Z _in of the antenna is linked to the impedance Z _RLC of the RLC circuit and to the impedance of the air Z _air by the following formula
$${\mathrm{Z}}_{\mathrm{in}}=\left({\mathrm{Z}}_{\mathrm{RLC}}+{\mathrm{Z}}_{\mathrm{air}}\right)$$

with $${\mathrm{Z}}_{\mathrm{RLC}}=\mathrm{R}+\mathrm{I}\left(\mathrm{L}\mathrm{\omega }-\frac{1}{\mathrm{C\omega }}\right)$$

where ω = 2*π*f and R is the resistance or real part of the impedance of the RLC circuit and f is the frequency, L is the inductance of the RLC circuit and C is the capacitance of the RLC circuit.

As seen in figure 7 , representing the real part of the input impedance of an antenna and the imaginary part of the imaginary part of the antenna input impedance in dotted lines, at the resonant frequency the imaginary part of the input impedance is zero and its real part is maximum.

When the real part of the input impedance is equal to 50 Ohms at the resonance frequency f ₀ , this real part is suitable for radiofrequency emission from an input signal usually having a real part of this value . Its zero imaginary part is suitable for transmission from the input signal usually having a zero imaginary part.

The possibility of varying the inductance value of the inductor 50 makes it possible to obtain the resonance of the radiating element 20 even when the bundle F has, after its growth, a capacitance C which differs slightly from the desired capacitance. This solution therefore makes it possible to optimize the gain of the antenna by applying a voltage to the inductor 50, the value of which makes it possible to match the inductance value L of the inductor with the capacitance C of the bundle F.

The electric field ensuring the agreement is advantageously applied during operation of the antenna, that is to say during the transmission or reception of a radio frequency wave by the antenna in order to ensure the agreement at the determined frequency.

The invention also relates to a method for controlling the antenna in which the first conductive material is subjected to an electric field such that the inductance value of the inductance 50 is tuned with the capacitance of the bundle F at a predetermined frequency, when the antenna transmits or receives an electromagnetic wave at the predetermined frequency.

To check that the inductance value is tuned with the capacitance of the bundle F at a predetermined frequency, it is possible to measure a reflection coefficient of a wave emitted or received by the antenna from which it is possible to deduce and, for example, display , the real part and the imaginary part of the antenna input impedance. By following these impedances during the voltage variation, for a given frequency, it is possible to deduce the impedance value for which there is resonance.

Advantageously, the antenna comprises means for measuring a reflection coefficient of a wave emitted or received by the antenna and processing means making it possible to adjust the inductance value of an inductor in order to tune the value of inductance to the capacitance of the bundle at a predetermined frequency, from measurements of the reflection coefficient measured by the measuring means for different values of a DC voltage applied by the variable DC voltage generator between two terminals of the inductor 50.

The inductance setting can be done collectively for an array antenna.

Advantageously, the antenna comprises means for measuring a reflection coefficient of a wave emitted or received by the antenna and processing means making it possible to adjust the inductance values of the inductances 50 of the antenna to substantially tune the inductance values at the capacitance of the bundle at a predetermined frequency, from measurements of the reflection coefficient measured by the measuring means for different values of a direct voltage or direct voltages applied by one or more generators of variable DC voltage between two terminals of the inductors 50.

Advantageously, the inductance has an inductance value capable of varying within an interval comprised between 1 nanoHenry and 10 nanoHenrys. According to one embodiment, the inductance value is, for example, capable of being equal to 5 nanoHenrys.

The invention relates to an array antenna comprising two radiating elements each comprising a bundle or set of wire nanostructures). The bundles of the two radiating elements have distinct respective capacities. The inductance of each radiating element is tunable with the capacitance of the corresponding bundle, that is to say, with the capacitance of the assembly of at least one wire nanostructure of the same radiating element.

There figure 8 schematically represents the variation in the reactance of a bundle of carbon nanotubes as a function of the frequency of a first electrical signal which is applied to it, for example between 7 and 13 GHz. The reactance varies with frequency which means that the capacitance of this bundle also varies with frequency. Consequently, by varying the voltage U1 to vary the inductance value of the inductor 50, the whole of the resonant cell formed by the inductor 50 and a bundle F can be tuned for several resonance frequencies . This makes it possible to obtain an antenna transmitting or receiving waves with high gain at different frequencies, therefore exhibiting the behavior of a broadband antenna or of a frequency-tunable antenna.

There figure 9 represents an array antenna 100 comprising a one-dimensional array of radiating elements 20b of which only one is referenced figure 9 to clarify more.

The radiating element 20b differs from that of the figure 6 in that the electrode EL is coplanar with the inductor 50. Alternatively, the electrode EL is deposited on the inductor 50 as on the figure 6 .

The electrode can, as a variant, be partly deposited on the inductor 50 and be partly coplanar with the inductor 50.

Alternatively, just as in the example of the figure 10 , the network could be two-dimensional. Antenna 100 includes a transmission line 25, as previously described, for each radiating element 20b. The transmission lines 25, and more particularly the conductive areas 85, are electrically connected to a main transmission line LP making it possible to apply the first electric current to each of the conductive areas 85.

The first electric current is advantageously a radiofrequency signal.

The ground planes 90 are connected to a ground plane PC located on the rear face, that is to say contiguous to the face of the substrate 15 opposite the support face 30.

The ground planes are, for example, connected to the ground plane PC by metallized holes VI.

The EL electrodes of each of the radiating elements 20b are partly deposited on the support face 30. The electrodes can be controlled collectively by the same variable DC voltage generator or independently by different generators.

During collective control, the same electric field is applied within each inductance.

When individually controlled, it is possible to apply different, independently adjustable electric fields and obtain frequency and/or impedance matching.

In another embodiment, the antenna may have radiating elements having beams F having different capacities and/or all identical capacities. The capacity of each beam is defined by its aspect ratio.

The antenna 1000 of the embodiment of the figure 10 , differs from that of the figure 9 in that the electrodes EL are connected to the ground planes 90 of the radiating elements 20c. The radiating elements 20c differ from the radiating elements 20b of the figure 9 in that they are devoid of metallized holes.

The line LP makes it possible to apply a signal comprising simultaneously a radiofrequency signal and the DC voltage generating the electric field within the inductors 50 thus making it possible to adjust the inductance value of the inductor 50.

This solution makes it possible to adjust the inductors 50 collectively.

The capacity of a wire nanostructure depends on its aspect ratio. Consequently, the fact of providing radiating elements having wire nanostructures having different aspect ratios makes it possible to obtain radiating elements resonating at different frequencies and thus to transmit and/or receive at several frequencies. It is thus possible to produce an antenna formed of elements radiators that radiate at different frequencies. The antenna therefore exhibits broadband antenna behavior.

The antenna has, for example, a first radiating element having a wire nanostructure having a first aspect ratio and a second radiating element having a nanostructure having a second aspect ratio.

Advantageously, the antenna has first means making it possible to vary the inductance value of the inductance of the first radiating element and second means making it possible to vary the value of the inductance of the second radiating element.

Advantageously, the antenna has first means making it possible to vary the inductance value of the inductance of the first radiating element independently of the inductance value of the second radiating element and second means making it possible to vary the value of the inductance of the second radiating element independently of the inductance of the first radiating element.

The first and second means advantageously each comprise a variable DC voltage generator.

Such an antenna is also easy to manufacture, as illustrated with reference to the figure 11 which is a flowchart of a method of manufacturing a radiating element 20.

The manufacturing process includes a supply step 100, a deposit step 110, an etch step 120, a placement step 130 and a growth step 140.

During the supply step 100, the substrate 15 is supplied.

During the deposition step 110, a layer of the first conductive material is deposited on the substrate 15.

When the material is graphene, the deposition is for example carried out in the vapor phase by transfer. A transfer deposition includes a step of exfoliating a layer of graphene from a block of graphite, during which a monolayer of carbon is extracted using an adhesive tape and a step of thermal transfer of the atomic monolayer of carbon on the substrate 15.

It should be noted that other deposition techniques can be envisaged.

During the etching step 120, the layer of the first conductive material is etched to form the inductor 50.

The etching step 120 includes, for example, a photolithography step and/or an ion beam etching step. Etching by ion beam consists in projecting onto the layer to be etched a beam of ions, in particular Argon ions, at high energy to machine the layer to be etched.

It should be noted that other techniques for etching the layer of first conductive material can be envisaged.

During the placement step 130, a catalyst C for the growth of nanostructures 45 is deposited on the inductor 50.

Catalyst C is a metallic material. The C catalysts most used to grow nanotubes or nanowires are nickel, cobalt, iron and gold. For example, catalyst C is iron. As a variant, the catalyst C consists of an alloy of at least two metals.

Catalyst C is, for example, in the form of a set of nanoparticles.

The particles of catalyst C are nanoparticles. Preferably, each particle has three nanometric dimensions. For example, each dimension of each particle is strictly between 1 nanometer and 100 nanometers.

The particles of catalyst C are, for example, obtained by lithography. Lithography makes it possible to obtain a perfectly periodic network of catalyst C particles.

As a variant, the particles are obtained by fragmentation and controlled dewetting of a layer of catalyst C deposited on the inductor 50.

According to another variant, the particles of the catalyst C are obtained by spraying, on the inductor 50, a solution comprising these particles. As a variant, the particles are deposited by electrostatic grafting on the inductor 50.

The preceding methods different from lithography make it possible to obtain a random network for which the average distance between particles is controlled.

The particles are, for example, liquid when the catalyst C is at the setpoint temperature Te. This is for example the case of silicon nanowires whose growth is catalyzed using gold particles. Alternatively, the particles are solid when the catalyst C is at the setpoint temperature Te. This is for example the case of the growth of carbon nanotubes.

Alternatively, catalyst C forms a homogeneous layer.

During the placement step 130, the catalyst C is deposited so as to form a layer having, in a plane perpendicular to the normal direction Z, a shape identical to the shape of the section of the beam F.

It should be noted that, in certain cases, it is possible to envisage not using any catalyst.

This is for example the case for certain types of nanostructures. It is then conceivable to replace the step 130 of placement of a catalyst C by a step of depositing a layer preventing the growth of nanostructures elsewhere than on the inductor 50.

For example, this step of depositing a growth-preventing layer comprises an etching step during which an opening is formed at the level of the inductor 50 in the growth-preventing layer in order to allow the growth of a beam F of nanostructures 45.

During the growth step 140, at least one nanostructure 45 is obtained. In particular, the nanostructures 45 grow on the inductor 50 to form a beam F.

According to one embodiment, a nanostructure 45 is obtained for each catalyst particle C.

The nanostructures 45 are, for example, obtained by chemical vapor deposition. Chemical vapor deposition (commonly referred to by the acronym CVD, for “Chemical Vapor Deposition”) is a technique frequently used to deposit a material on a substrate. Chemical vapor deposition is practiced in a closed enclosure, delimiting a chamber isolated from the outside atmosphere and containing at least one substrate, generally maintained at a high temperature. A so-called "precursor" gas is injected into the enclosure and decomposes on contact with the heated substrate, releasing atoms of one or more predetermined elements onto the substrate.

The released atoms form chemical bonds between them leading to the formation, on the substrate, of the desired material.

The thermal process of chemical vapor deposition, also known by the English name "Thermal Chemical Vapor Deposition", is a technique in which the substrate 15 is heated to a high temperature of the order of 600 degrees Celsius or more is a type of CVD particularly adapted to the growth of carbon nanotubes.

According to one embodiment, during growth by chemical vapor deposition, a plasma is generated in the growth chamber.

Several radiating elements 20 are manufactured simultaneously. For example, during the etching step 120, the inductors 50 of several radiating elements are formed. During the placement step 130, a catalyst C is deposited on each inductor 50. During the growth step 140, at least one nanostructure 45 is formed on each inductor 50.

It should be noted that the manufacturing method is also likely to comprise the manufacturing of each transmission line 25. For example, each transmission line 25 is formed, in the layer of first conductive material, during the etching step. 120.

According to a variant, when the second conductive material is not identical to the first conductive material, the manufacturing method comprises a step of depositing a layer of second conductive material and a step of etching the layer of second conductive material to form transmission lines 25.

The method of manufacturing the radiating elements 10 is simple.

Molybdenum is a material which resists well the conditions prevailing in a nanostructure growth frame 45, in particular a CVD frame. The inductance 50 and the transmission lines 25 are therefore not degraded during the growth of the nanostructures 45, in particular when the nanostructures 45 are carbon nanotubes.

Cathodic sputtering is a deposition method for obtaining good quality molybdenum layers.

The method may include a step of depositing one or more electrodes.

The electrodes are made of a conductive material, for example molybdenum.

The step of depositing an electrode includes depositing the molybdenum layer by sputtering.

Cathodic sputtering (also referred to as "sputtering") is a technique for depositing thin layers in which a target material to be deposited is provided, generally in the form of solid material, in a deposition chamber and a plasma is formed in a low pressure gas occupying the deposition chamber. The application of a potential difference between the target and the walls of the deposition chamber causes a bombardment of the target by electrically positively charged species of the plasma. The bombardment causes the sputtering of the target and thus the release into the atom deposition chamber of the material to be deposited. The condensation of the atoms thus released on a substrate then forms a layer of the material to be deposited.

Claims (13)

1. A radiating element (20) for an antenna (10) containing:

   - an assembly of at least one wire-like nanostructure (45), each wire-like nanostructure (45) extending in the same direction (D), referred to as common direction, between a first end (55) and a second end (60), said radiating element (20) being characterised in that it further contains:

   - an inductor (50) connected to each first end (55) of said at least one wire-like nanostructure (45), the inductor (50) being made from a first conductive material, the inductor (50) extending in a plane normal to the common direction (D), the first conductive material having an electrical conductivity varying under the effect of a variation of an electric field applied within the first conductive material.
2. The radiating element according to the preceding claim, wherein the inductor (50) is configured so as to have an inductance value that may be matched with a capacitance of the assembly of at least one wire-like nanostructure.
3. The radiating element according to any one of the preceding claims, wherein the first conductive material comprises a semi-metal.
4. The radiating element according to any one of claims 1 and 2, wherein the first material is graphene.
5. The radiating element according to any one of the preceding claims, wherein the first conductive material is a transition metal dichalcogenide.
6. The radiating element according to any one of the preceding claims, wherein at least one wire-like nanostructure (45) is a carbon nanotube.
7. The radiating element according to any one of the preceding claims, wherein the inductor (50) has a spiral-like shape.
8. The radiating element according to any one of the preceding claims, wherein the assembly of at least one wire-like nanostructure comprises multiple wire-like nanostructures.
9. The radiating element according to the preceding claim, wherein the inductor (50) is configured so as to have an inductance value that may be matched with a capacitance of the assembly of wire-like nanostructures.
10. An elementary antenna (10) comprising:

    - a radiating element (20) according to any one of claims 1 to 9, and

    - a transmission line (25) having a region (85) made of a second conductive material and two ground planes (90), the transmission line (25) extending in the same plane as the inductor (50) and the region (85) being connected to the inductor (50), each ground plane (90) being made of a third conductive material, the region (85) being arranged between the two ground planes (90) and,

    - a variable DC voltage generator capable of applying the electric field within the first conductive material.
11. The elementary antenna according to the preceding claim, comprising an electrode in physical contact with the inductance, the voltage generator applying the electric field within the first conductive material by means of the electrode.
12. An antenna array comprising a plurality of elementary antennas according to any one of claims 10 to 11.
13. The antenna array according to the preceding claim, comprising a first elementary antenna and a second elementary antenna having radiating elements having assemblies of at least one wire-like nanostructure with different capacitances.

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