Multi-band dipole antenna or antenna element and method for multi-frequency recovery of radio frequency energy implemented by such an antenna or antenna element

Abstract

The invention relates to an omnidirectional multi-band dipole antenna (4) or antenna element comprising at least two metallic strands (14, 15) and a microstrip feed line (13), said at least two metallic strands (14, 15) being configured so as to together form a structure comprising at least two nested radiating loops (B1, B2, B3, B4) nested one inside the other, such that each nested radiating loop (B1, B2, B3, B4) is associated with an electromagnetic coupling between said at least two strands (14, 15) and defines a resonant frequency and a complex access impedance value of the antenna (4) or antenna element. The invention also relates to an electrical or electronic device comprising at least such an antenna (4) or such an antenna element, as well as a multi-frequency radio frequency energy recovery method implemented by an electrical or electronic device.

Description

[0001] The invention relates to the field of radiofrequency antennas of the multi-band dipole antenna type, having omnidirectional radiation. The invention finds particular application in the field of multifrequency recovery of radiofrequency energy.

[0002] The applications of sensors or connected objects (IoT in English terminology, for "Internet of Things") are continuously growing. These sensors or wireless connected objects allow the collection of various data such as temperature, pressure, or humidity, and are used in various fields such as smart surveillance systems, home automation, medical, and military applications.

[0003] Today, these sensors are mainly powered by batteries, which means they have a limited lifespan and are sometimes complicated to replace. A promising method involves harvesting the energy available in the ambient environment of these microsystems, thereby reducing or even eliminating the use of these batteries. This will enable long-term energy autonomy for objects and sensors.

[0004] There is thus a need to be able to recover ambient radiofrequency energy on several distinct frequency bands using a single antenna ideally presenting an access impedance equal, for each of the desired frequencies, to the conjugate value of the complex input impedance of the rectifier circuit, positioned just downstream of this antenna.

[0005] Rectifier antennas are the cornerstone of radiofrequency energy harvesting systems and critically affect the level of DC power delivered to the load at the rectifier output. The antenna collects microwave power and the rectifier circuit converts it into DC power. This DC electrical power typically passes through an energy storage system before being delivered to the load.

[0006] Harvesting and rectifying ambient electromagnetic waves into DC power is an important and necessary feature for any battery-dependent device. The primary objective of any energy harvesting system is therefore to increase its conversion efficiency. Antenna efficiency is at the heart of this design constraint and must be taken with extreme care and consideration.

[0007] A suitable antenna structure must therefore have sufficient gain to capture as many ambient radio frequency signals as possible over a wide field of view and a wide frequency range. Another constraint that must be met is the careful design of the appropriate rectifier circuit. The circuit must satisfy the power matching constraint between all its components. A typical rectifier circuit consists of a receiving antenna followed by a bandpass filter, a rectifier, a lowpass filter, and a load.

[0008] In a design approach for such a radiofrequency module comprising an antenna that needs to be connected to a transmitting or receiving device (in this case a receiving device in the case of energy harvesting), it is therefore imperative to ensure the power matching condition between this radiating element (the antenna) and the device, in order to avoid signal transfer losses. To do this, the value of the access impedance of the antenna must be equal to the conjugate value of the complex access impedance of the device, on each of the operating frequency bands of the radiofrequency module. The major advantage of this approach is that it does not require the use of an intermediate matching circuit between the antenna and the transmitting or receiving device. This therefore limits the number of components required for the proper functioning of the transmitting or receiving chain.The electrical performance of this chain is then significantly improved.

[0009] In radio frequency, moreover, multi-band antennas that need to operate on a set of predetermined frequency values ​​are traditionally optimized to work on a reference impedance of 50 ohms, identical at all these frequencies. In the case where the access impedance of the antenna must have the required complex value on each of the desired frequencies, it is necessary to facilitate the synthesis of these impedance values.

[0010] To this end, a known solution consists of controlling the relative position (angular separation) between two strands of a multi-band dipole antenna, which makes it possible to vary the value of the complex access impedance, at the fundamental radiation frequency of the antenna. This particular geometric configuration of the multi-band dipole antenna makes it possible to have simple control over the determination of the complex access impedance values ​​of the antenna. The key parameter for controlling this impedance is in fact the angular separation between the two strands of the dipole. The variation of the complex access impedance of the antenna then makes it possible to properly adjust this complex access impedance to that of the transmitting or receiving equipment, for frequency bands respectively transmitted or received by the antenna.Varying the angle between the two strands of the antenna allows a large area to be scanned on the Smith chart and therefore a wide range of complex impedances to be synthesized at the antenna access.

[0011] Patent document KR 20160091847 A describes, for example, such an antenna structure that allows the value of the access impedance of the antenna to be varied by dynamically modifying the angle between the two strands of the antenna, depending on the frequency band currently used by the antenna, and at the fundamental radiation frequency of the latter. However, a disadvantage of such an approach is that it requires dynamic control over the relative position of the two strands of the antenna (and therefore an associated electronic control circuit), and that, in addition, it involves the use of a multi-band dipole antenna that is relatively bulky.

[0012] The invention therefore aims to provide an omnidirectional multi-band dipole antenna or antenna element, which makes it possible to ensure the power matching condition between the antenna and a transmitting or receiving device, without requiring dynamic control by an external electronic circuit and allowing miniaturization of the antenna.

[0013] Another object of the invention is to provide an omnidirectional multi-band dipole antenna or antenna element enabling the synthesis of resonant frequencies and complex access impedance values ​​of the antenna or antenna element to be controlled in a simple and reliable manner.

[0014] Another object of the invention is to provide an electrical or electronic device comprising, in addition to the antenna or the antenna element, an electrical element constituting an electrical source or load for the antenna or the antenna element, and requiring no intermediate adaptation circuit between the antenna and the electrical element.

[0015] Another aim of the invention is to provide such an electrical or electronic device operating with a single rectifier core downstream of the antenna or antenna element (the electrical element then being a very wide band rectifier).

[0016] To achieve these objectives, the invention proposes, according to a first aspect, an omnidirectional multi-band dipole antenna or antenna element comprising at least two metal strands and a microstrip feed line, the microstrip feed line comprising a feed strip and a metal pattern defining a ground plane, one end of at least one first metal strand being connected to the feed strip, one end of a second metal strand being connected to the metal pattern, each of the metal strands comprising a main strand portion and at least one secondary strand portion or at least one set of secondary strand portions in a tree structure attached to the main strand portion and forming a branch with the main strand portion, said at least two metal strands being configured so as to form together a structure comprising at least two radiating nested loops nested one inside the other,the main strand portions of the first and second metal strands being electromagnetically coupled to each other at their free ends, and the free end of the or each secondary strand portion of the first metal strand being electromagnetically coupled with the free end of a corresponding secondary strand portion of the second metal strand, such that each radiating nested loop is associated with an electromagnetic coupling between said at least two strands and defines a resonance frequency and a complex access impedance value of the antenna or antenna element.,

[0017] The antenna or antenna element according to the invention is omnidirectional, with multiple frequency bands, and has a complex impedance at the input of the antenna for each of its radiation frequencies. Thanks to the fact that the radiating patterns of the antenna or antenna element are shaped in the form of loops, an electromagnetic coupling zone is produced between the ends of the two metal strands constituting the radiating pattern, at a given frequency. Due to their positions at the ends of the metal strands, these points are of opposite polarities in voltage, which contributes to reducing the resonance frequency of the radiating pattern (frequency associated with the loop in question), and therefore to miniaturizing the antenna.Furthermore, for a given radiation mode, the value of the electromagnetic coupling achieved within the loop associated with this mode makes it possible to adjust the value of the actual input impedance at resonance: the greater the coupling, the more this actual impedance value decreases, and the more the resonance frequency of this mode also decreases. The electromagnetic coupling at the ends of the strands of the radiating pattern therefore makes it possible to open the resonance loop on the Smith chart and therefore to sweep a very wide complex impedance range on this chart, by varying the frequency on either side of the resonance frequency. It is thus possible to synthesize a wide range of complex antenna input impedances, with a low resistive part value and a high inductive part value, and this for several predefined frequencies.

[0018] Each electromagnetic coupling zone also makes it possible to very simply adjust each resonant frequency of the antenna, independently of the other frequencies. The existence of these electromagnetic coupling zones at the ends of the strands constituting the structure thus makes it possible to achieve an ultra-compact structure of the antenna, typically associated with a rather omnidirectional radiation characteristic.

[0019] According to a particular technical characteristic of the invention, the antenna or antenna element further comprises a substrate on which said at least two metal strands are arranged.

[0020] Advantageously, the substrate has two faces and said at least two metal strands are flat ribbons arranged on the two faces of the substrate, said at least two metal strands extending in two distinct planes corresponding to the two faces of the substrate. This makes it possible to facilitate the electromagnetic coupling between the first and second metal strands, by sizing the electromagnetic coupling zone according to the faces of the substrate.

[0021] Advantageously, the substrate has a thickness of the order of a few hundred microns and is made of a material having a relative dielectric permittivity of the order of a few units. This makes it possible to further improve the electromagnetic coupling between the at least two metal strands of the antenna or antenna element.

[0022] According to a particular technical characteristic of the invention, the free ends of the main strand portions of the first and second metal strands extend opposite each other in said two separate planes, and the free end of the or each secondary strand portion of the first metal strand extends opposite the free end of a corresponding secondary strand portion of the second metal strand, said two free ends extending in said two separate planes.

[0023] According to a particular technical characteristic of the invention, at least one of the secondary strand portions of each metal strand is attached to the main strand portion of said metal strand at a point located between the ends of the main strand portion, and / or at least one of the secondary strand portions of each metal strand is attached to the main strand portion of said metal strand at one end of the main strand portion.

[0024] According to a particular technical characteristic of the invention, the main strand portion and all of the secondary strand portions of each metal strand define a comb, rake, tree shape, or a combination of one or more of these shapes.

[0025] Advantageously, the electromagnetic coupling between a free end of one of the metal strands and a free end of another metal strand is carried out over a non-zero coupling length of the strands, the value of the resonant frequency of the radiating nested loop associated with said electromagnetic coupling being a function of the corresponding coupling length and / or of at least one other parameter chosen from the group consisting of: the width of the flat strips, the dielectric permittivity of the substrate and the thickness of the substrate. Typically, all other things being equal regarding the other parameters, the greater the coupling length of the strands, the more the resonant frequency decreases. This electrical coupling at the ends of the two strands therefore makes it possible to adjust the desired frequency value and also contributes very significantly to miniaturization of the antenna.The longer the coupling length, the more open the resonance loop on the Smith chart. This allows us to synthesize antenna input impedances with a very low resistive part value. This coupling also allows us to adjust the desired complex impedance value. In addition, this or these parameters affect the antenna's form factor, which in turn influences the antenna's input impedance value for a given radiation mode. For example, an asymmetry between the lengths of the two strands constituting a radiating pattern increases the actual input impedance value obtained at resonance.

[0026] According to a first embodiment of the invention, the antenna or antenna element comprises two metal strands.

[0027] According to a second embodiment of the invention, the antenna or antenna element comprises three metal strands divided into two first metal strands and a second metal strand, the three metal strands being configured so as to form together a structure comprising two sets of radiating nested loops, each set of radiating nested loops being formed by a part of the second metal strand and by one of the first metal strands and comprising at least two radiating nested loops nested one inside the other, the free end of the main strand portion of each first metal strand being electromagnetically coupled with a free end of the main strand portion of the second metal strand.

[0028] Advantageously, the second metal strand is arranged between the first two metal strands and has a shape such that the second metal strand defines a central axis of symmetry for the antenna or antenna element, the first two metal strands extending on either side of said central axis of symmetry. This second embodiment of the antenna or antenna element has greater symmetry in the substrate plane of the antenna than the first embodiment, making it possible to better balance the detection level on both sides of the substrate plane of the antenna. This makes it possible to significantly improve the omnidirectional nature of the antenna or antenna element, a characteristic which is particularly important in a radiofrequency energy harvesting application for example.

[0029] According to a first variant of this second embodiment, the first two metal strands have identical geometry and dimensions.

[0030] According to a second variant of this second embodiment, the first two metal strands have distinct geometry and / or dimensions. This second variant allows a multiplication of the frequencies of interest of the antenna. It is thus possible to have two sets of asymmetrical mirrored nested loops, so as to make them operate on different sets of frequencies. In this case, the number of frequencies of interest of the antenna is therefore potentially multiplied by two.

[0031] According to a second aspect, the invention also relates to an electrical or electronic device comprising at least one omnidirectional multi-band dipole antenna or antenna element as described above, and an electrical element connected to the microstrip feed line of the antenna or antenna element and constituting an electrical source or load.

[0032] Thanks to the fact that it is possible to simultaneously synthesize and control several values ​​of complex access impedances of the antenna on several predetermined radiation frequencies of the latter, the value of each access impedance of the antenna is advantageously chosen to be equal to the conjugate value of the complex access impedance of the electrical element, on each of the operating frequency bands of the device. This makes it possible to ensure the power matching condition between the antenna and the electrical element, without the need for dynamic control by an intermediate electronic circuit.

[0033] According to a particular technical characteristic of the invention, said electrical element is a very wide band rectifier constituting an electrical load.

[0034] Advantageously, the very wideband rectifier has a single rectifier core. This allows the very wideband rectifier to be miniaturized.

[0035] According to a particular embodiment of the invention, the electrical or electronic device is a multi-frequency radiofrequency energy recovery device which further comprises a DC voltage to DC voltage converter connected to the output of the very wide band rectifier, and an electrical energy storage module connected to the output of the DC voltage to DC voltage converter.

[0036] According to a third aspect, the invention also relates to a method for multi-frequency recovery of radiofrequency energy, implemented by an electrical or electronic device as described above, the method comprising the following steps: reception of a radiofrequency signal by the antenna or the antenna element, the radiofrequency signal corresponding to one or more frequency bands associated with at least one of said at least two resonant frequencies of the antenna or the antenna element; rectification, by the very wide band rectifier, of the electrical signal supplied at the output of the antenna or the antenna element; conversion, by the DC voltage converter into DC voltage, of the output voltage supplied at the output of the very wide band rectifier; and storage, in the electrical energy storage module, of the electrical energy supplied at the output of the DC voltage converter into DC voltage.

[0037] According to a fourth aspect, the invention also relates to a use of an omnidirectional multi-band dipole antenna or antenna element as described above for controlling the synthesis of resonant frequencies and complex access impedance values ​​of the antenna or antenna element, by adjusting, for each radiating nested loop of the antenna or antenna element, the length of the corresponding electromagnetic coupling, between a free end of one of the metal strands and a free end of another metal strand, so as to adjust the resonant frequency of said loop to a predetermined frequency value, and to adjust, for this predetermined frequency value, the complex access impedance of the antenna or antenna element to a predetermined impedance value.

[0038] This provides a simple and reliable way to control the synthesis of resonant frequencies and complex access impedance values ​​of the antenna or antenna element, while keeping the antenna as miniaturized as possible.

[0039] The invention will be further detailed by the description of non-limiting embodiments, and on the basis of the appended figures, among which: [ Fig.1 ] is a schematic view of an electrical or electronic device for harvesting radiofrequency energy comprising an omnidirectional multi-band dipole antenna according to the invention; [ Fig.2 ] is a front view of the omnidirectional multi-band dipole antenna of the figure 1 , according to a first embodiment of the invention; [ Fig.3 ] is a front view of the omnidirectional multi-band dipole antenna of the figure 1 , according to a second embodiment of the invention; [ Fig.4 ] is a flowchart representing a method of multi-frequency recovery of radiofrequency energy, implemented by the electrical or electronic device of the figure 1 ; And [Fig.5] à [Fig.9] are schematic views of different forms of omnidirectional multi-band dipole antenna, according to different exemplary embodiments of the invention.

[0040] In the remainder of the description, the term “electromagnetic coupling” means any coupling of an electrical, magnetic or mixed nature due to the combination of these two types of coupling.

[0041] Furthermore, the term "radiating nested loops" refers to any structure of electromagnetic radiation loops nested within each other on a geometric plane (by analogy with nesting doll structures). Thus, on a geometric plane, a first loop surrounds all the other loops, then a second loop surrounds all the other loops except the first loop, and so on.

[0042] The term "cold wire" also means any metal wire connected to the metal pattern defining the ground plane of the antenna, and the term "hot wire" means any metal wire connected to the antenna's feed strip.

[0043] There figure 1 represents an electrical or electronic device 2 for harvesting radiofrequency energy. The device 2 is typically a multi-frequency radiofrequency energy harvesting device (as is the case in the exemplary embodiment of the figure 1 ), although this is not limiting within the scope of the present invention.

[0044] The device 2 comprises an omnidirectional multi-band dipole antenna 4, and an electrical element 6 constituting an electrical load for the antenna 4. In a variant not shown in the figures, the electrical element can constitute an electrical source for the antenna 4. The electrical element 6 is connected to the antenna 4. In the case where the device 2 is a multi-frequency radiofrequency energy recovery device, the electrical element 6 is typically a rectifier connected to the output of the antenna 4, preferably a very wide band rectifier. In this case, and as illustrated in the figure 1 , the device 2 also comprises a DC voltage to DC voltage converter 8 connected to the output of the rectifier 6, and an electrical energy storage module 10 connected to the output of the DC voltage to DC voltage converter 8. In a variant not shown (in the case where the electrical energy supplied at the output of the rectifier 6 is not consumed immediately), the electrical energy storage module 10 can be connected directly to the output of the rectifier 6. The device 2 for multi-frequency radiofrequency energy recovery is for example connected to a sensor or to an IoT connected object 12 (for "Internet of Things" in English), in order to enable its electrical supply. Preferably, the rectifier 6 comprises only a single rectification core.

[0045] There figure 2 represents the omnidirectional multi-band dipole antenna 4 according to a first embodiment of the invention. According to this first embodiment, the antenna 4 comprises a microstrip feed line 13 and two metal strands 14, 15. Preferably, the antenna 4 also comprises a substrate (not shown in the figure 2 for reasons of clarity) on which the two metal strands 14, 15 are arranged. The substrate has, for example, two faces. Each metal strand 14, 15 is preferably a flat ribbon arranged on a respective face of the substrate. The two metal strands 14, 15 thus extend in two distinct planes corresponding to the two faces of the substrate.

[0046] The microstrip feed line 13 includes a feed strip 16 and a metal pattern 18 defining a ground plane. Although not shown in the figure 2 , the electrical element 6 is connected to the microstrip feed line 13 of the antenna 4. More precisely, the electrical element 6 is connected to both the feed strip 16 and the ground plane 18. The ground plane 18 is planar and can take a circular or rectangular shape, for example, and have several patterns of different shapes and dimensions. It can also be cut from a metal sheet.

[0047] As illustrated in the figure 2 , a first end 14A of a first metal strand 14 is connected to the feed strip 16, and a first end 15A of the other metal strand 15 is connected to the metal pattern 18 defining the ground plane. The first metal strand 14 thus constitutes a “hot” strand of the antenna 4, and the second metal strand 15 constitutes a “cold” strand.

[0048] The first metal strand 14, respectively the second metal strand 15 comprises a main strand portion 141, respectively 151, and three secondary strand portions 142-a, 142-b, 142-c, respectively 152-a, 152-b, 152-c attached to the main strand portion 141, 151 and forming branches with the latter. In the particular embodiment shown in the figure 2 , for each metal strand 14, 15, the main strand portion 141, 151 and all of the secondary strand portions 142-a, 142-b, 142-c, 152-a, 152-b, 152-c define a comb shape. Thus, for each metal strand 14, 15, the main strand portion 141, 151 defines a substantially “7” shape, while each secondary strand portion 142-a, 142-b, 142-c, 152-a, 152-b, 152-c is attached to the main strand portion 141, 151 at a point located between the ends 14A, 14B, respectively 15A, 15B of the main strand portion 141, 151. In a variant not shown, the main strand portion 141, 151 and all of the secondary strand portions 142-a, 142-b, 142-c, 152-a, 152-b, 152-c may define other shapes, such as for example a rake shape, a tree shape, or well a combination of one or more of these forms.

[0049] In the embodiment of the figure 2 , the two metal strands 14, 15 are configured so as to together form a structure comprising four radiating nested loops B1, B2, B3, B4 nested within each other. More precisely, the main strand portions 141, 151 of the first and second metal strands 14, 15 are electromagnetically coupled to each other at their free ends 14B, 15B. Furthermore, the free end of each secondary strand portion 142-a, 142-b, 142-c of the first metal strand 14 is electromagnetically coupled with the free end of a corresponding secondary strand portion 152-a, 152-b, 152-c of the second metal strand 15. Thus, each radiating nested loop B1, B2, B3, B4 is associated with an electromagnetic coupling between the two strands 14, 15 and defines a resonance frequency and a complex access impedance value of the antenna 4.The electromagnetic coupling is preferably of an electrical nature, more precisely of a capacitive nature, because it is located at the ends of the strands which are electrically associated with voltage maxima (or voltage antinodes) or, equivalently, with current minima (or current nodes). Given this electrical state of maximum voltage, the coupling is therefore of a capacitive nature between the ends of these strands. The form factor presented by each radiation loop B1, B2, B3, B4 and the coupling level for each of these loops influence the input impedance value of the antenna 4 for the radiation mode corresponding to this loop.

[0050] In the particular embodiment of the figure 2 according to which the antenna 4 comprises a substrate which has two faces, each metal strand 14, 15 being arranged on a respective face of the substrate, the free ends 14B, 15B of the main strand portions 141, 151 of the first and second metal strands 14, 15 extend opposite each other in two distinct planes, the two planes in question being parallel to the plane of the figure 2 (therefore superimposed on each other in the perspective of this figure). Similarly, the free end of each portion of secondary strand 142-a, 142-b, 142-c of the first metal strand 14 extends opposite the free end of a corresponding portion of secondary strand 152-a, 152-b, 152-c of the second metal strand 15, and the two free ends opposite each other extend in the two aforementioned distinct planes.

[0051] Thus, the electromagnetic coupling between the free end of each main strand portion 141 or secondary strand portion 142-a, 142-b, 142-c of the first metal strand 14 and a corresponding free end 151, 152-a, 152-b, 152-c of the second metal strand 15 is carried out over a non-zero strand coupling length, a space separating the two strands 14, 15 in the direction orthogonal to the two aforementioned planes. The value of the resonant frequency of the nested loop B1, B2, B3, B4 associated with the electromagnetic coupling in question is a function of the corresponding coupling length and / or at least one other parameter chosen from the group consisting of: the width of the flat strips 14, 15, the dielectric permittivity of the substrate and the thickness of the substrate. More precisely, and all things being equal regarding the other parameters, the longer the coupling length of strands 14, 15, the more the associated resonance frequency decreases.Thus, by varying the length of the electromagnetic coupling associated with each radiating loop B1, B2, B3, B4 and by keeping the other aforementioned parameters constant, it is possible to adjust the resonant frequency of the loop B1, B2, B3, B4 to a predetermined frequency value and to adjust, for this predetermined frequency value, the complex access impedance of the antenna 4 to a predetermined impedance value. Indeed, due to the electrical independence between the radiating nested loops B1, B2, B3, B4 which are decorrelated from each other, it is possible to independently adjust the resonant frequencies and the complex access impedances of the antenna 4.Each electromagnetic coupling zone thus makes it possible to play on the parameters of one of the radiating nested loops B1, B2, B3, B4 without impacting the other loops, which makes it possible to optimize the parameters of antenna 4 independently and to provide flexibility and independence in the control of the parameters.

[0052] An example of the embodiment of the antenna 4 according to this particular embodiment of the figure 2 thus makes it possible to obtain an antenna capable of working simultaneously on four frequency bands which are for example (for a coupling length of the strands 14, 15 for each radiating loop B1, B2, B3 and B4 substantially equal to 4.2 mm (for the main strand portions 141, 151 of the first and second metal strands 14, 15), 1.9 mm (for the first secondary strand portions 142-a, 152-a of the first and second metal strands 14, 15), 3.1 mm (for the second secondary strand portions 142-b, 152-b of the first and second metal strands 14, 15) and 2.6 mm (for the third secondary strand portions 142-c, 152-c of the first and second metal strands 14, 15): 945 MHz, 1800 MHz, 2.45 GHz and 3.75 GHz. Furthermore, in this example, the width of the metal strands 14, 15 is 1.5mm, and the substrate used has a thickness of 125µm, a relative dielectric permittivity of 2.9 and a loss tangent of 5.10 -3< .The complex access impedance values ​​of the antenna 4, associated with these four frequency bands, are then: 326 Ω +j322 Ω, 15 Ω +j87 Ω, 7 Ω +j62 Ω and 7 Ω +j19 Ω. Of course, other values ​​of frequency bands and complex access impedances of the antenna are possible depending on the desired uses for the antenna 4, by varying the coupling length of the strands 14, 15 for each radiating loop B1, B2, B3, B4 and / or the width of the flat strips 14, 15, the dielectric permittivity of the substrate and the thickness of the substrate.

[0053] There figure 3 represents the omnidirectional multi-band dipole antenna 4 according to a second embodiment of the invention. Subsequently, the elements identified with the same numerical references as those used for elements of the first embodiment are identical or analogous to these elements and will therefore not be described in more detail. According to this second embodiment, the antenna 4 comprises the microstrip feed line 13 as well as three metal strands 20, 22, 24. The three metal strands 20, 22, 24 are distributed into two lateral “hot” strands 20, 24 extending on either side of a central “cold” strand 22. Another embodiment of the invention, not shown in the figures, consists of an antenna comprising two lateral “cold” strands extending on either side of a central “hot” strand.

[0054] Each metal strand 20, 22, 24 is preferably a flat ribbon. The two lateral “hot” strands 20, 24 extend for example on the same face of the substrate, while the central “cold” strand 22 extends on the other face of the substrate. The two lateral “hot” strands 20, 24 thus extend in the same common plane corresponding to a first face of the substrate, and the central “cold” strand 22 extends in a plane distinct from the first plane, and corresponding to the second face of the substrate.

[0055] As illustrated in the figure 3 , a first end 20A of a first “hot” strand 20 is connected to the power strip 16, a first end 24A of a second “hot” strand 24 is also connected to the power strip 16 and a first end 22A of the “cold” strand 22 is connected to the metal pattern 18 defining the ground plane.

[0056] The first “hot” strand 20, respectively the second “hot” strand 24 comprises a main strand portion 201, respectively 241, and a secondary strand portion 202, respectively 242 attached to the main strand portion 201, 241 and forming a branch with the latter. In the particular embodiment shown in the figure 3 , for each “hot” strand 20, 24, the main strand portion 201, 241 and the associated secondary strand portion 202, 242 define a comb shape. Thus, for each “hot” strand 20, 24, the main strand portion 201, 241 defines a substantially “7” shape, while the secondary strand portion 202, 242 is attached to the main strand portion 201, 241 at a point located between the ends 20A, 20B, respectively 24A, 24B of the main strand portion 201, 241.

[0057] The “cold” strand 22 comprises a main strand portion 221, and two secondary strand portions 222-a, 222-b attached to the main strand portion 221 and forming branches with the latter. The two secondary strand portions 222-a, 222-b extend on either side of the main strand portion 221. In the particular embodiment shown in the figure 3 , the main strand portion 221 and the two secondary strand portions 222-a, 222-b of the “cold” strand 22 define a rake shape. Thus, the main strand portion 221 defines a substantially “T” shape, while each secondary strand portion 222-a, 222-b is attached to the main strand portion 221 at a point located between the ends 22A, 22B, respectively 22A, 22C of the main strand portion 221. In this way, the “cold” strand 22 has a shape such that it defines a central axis of symmetry for the antenna 4, the two “hot” strands 20, 24 extending on either side of the central axis of symmetry. In the particular embodiment of the figure 3 , the two “hot” strands 20, 24 have identical geometry and dimensions. This symmetry of the antenna 4 results in an overall symmetry of its radiation pattern. In a variant not shown, the two “hot” strands 20, 24 may have distinct geometry and / or dimensions.

[0058] The three metal strands 20, 22, 24 are configured so as to together form a structure comprising two sets E1, E2 of radiating nested loops. In the particular embodiment of the figure 3 , each set E1, E2 of radiating nested loops comprises two radiating nested loops E11, E12, respectively E21, E22 which are nested one inside the other. Each set E1, E2 of radiating nested loops is formed by a part of the “cold” strand 22 and by one of the “hot” strands 20, 24.

[0059] More specifically, the main strand portions 201, 221 of the first “hot” strand 20 and of the “cold” strand 22 are electromagnetically coupled to each other at their free ends 20B, 22B. Similarly, the main strand portions 241, 221 of the second “hot” strand 24 and of the “cold” strand 22 are electromagnetically coupled to each other at their free ends 24B, 22C. Furthermore, the free end of the secondary strand portion 202, 242 of each “hot” strand 20, 24 is electromagnetically coupled with the free end of a corresponding secondary strand portion 222-a, 222-b of the “cold” strand 22. Thus, each radiating nested loop E11, E12, E21, E22 is associated with an electromagnetic coupling between one of the “hot” strands 20, 24 and the “cold” strand 22 and defines a resonance frequency and a complex access impedance value of the antenna 4.The electromagnetic coupling is preferably of an electrical nature, more precisely of a capacitive nature. In the particular embodiment of the . figure 3 according to which the antenna 4 has a general symmetry of shape, the sets of resonant frequencies associated with the two sets E1, E2 of radiating loops are identical. Alternatively, when the two sets E1, E2 of nested loops are asymmetrical (the two “hot” strands 20, 24 being for example of distinct geometry and / or dimensions), the resonant frequencies associated with the two sets E1, E2 of radiating loops are distinct, which makes it possible to multiply the number of frequencies of interest of the antenna 4.

[0060] In the particular embodiment of the figure 3 according to which the antenna 4 comprises a substrate which has two faces, the free ends 20B, 24B of the main strand portions 201, 241 of the first and second “hot” strands 20, 24 extend in a first plane, and each free end 22B, 22C of the main strand portion 221 of the “cold” strand 22 extends opposite one of these free ends 20B, 24B in a second plane distinct from the first plane, the two planes in question being parallel to the plane of the figure 3 (therefore superimposed on each other in the perspective of this figure). Similarly, the free end of the portion of secondary strand 202, 242 of each “hot” strand 20, 24 extends in the first plane, and the free end of each portion of secondary strand 222-a, 222-b of the “cold” strand 22 extends opposite one of these free ends of “hot” strand in the second plane.

[0061] An example of the embodiment of the antenna 4 according to this particular embodiment of the figure 3 thus makes it possible to obtain an antenna capable of working simultaneously on two frequency bands which are for example (for a coupling length of the strands substantially equal to 6mm (for the couplings between the strands 201-221 and 241-221) and 4mm (for the couplings between the strands 202-222a and 242-222b): 684 MHz for the radiating loops E11 and E21, and 1.633 GHz for the radiating loops E12 and E22. In addition, in this example, the width of the metal strands 20, 22, 24 is 1.5mm, and the substrate used has a thickness of 125µm, a relative dielectric permittivity of 2.9 and a loss tangent of 5.10 -3< . Of course, other frequency band values ​​are possible depending on the desired uses for the antenna 4, by varying the coupling length of the strands 20, 22, 24 for each radiating loop and / or the width of the flat ribbons 20, 22, 24, the dielectric permittivity of the substrate and the thickness of the substrate.

[0062] The method for multi-frequency recovery of radiofrequency energy according to the invention, implemented by the electrical or electronic device 2, will now be described in more detail, with particular reference to the figure 4 .

[0063] The method comprises an initial step S1 during which the antenna 4 receives a radiofrequency signal RF, the radiofrequency signal RF corresponding to one or more frequency bands associated with one of the resonance frequencies of the antenna 4.

[0064] The method comprises a following step S2 during which the very wide band rectifier 6 rectifies the electrical signal 30 supplied at the output of the antenna 4.

[0065] The method comprises a following step S3 during which the DC voltage converter 8 converts the output voltage 32 supplied at the output of the very wide band rectifier 6.

[0066] The method comprises a final step S4 during which the electrical energy storage module 10 stores the electrical energy 34 supplied at the output of the DC voltage converter into DC voltage 8. This electrical energy is used to electrically power the sensor or the IoT connected object 12. In the case where the electrical energy supplied at the output of the rectifier 6 is not intended to be consumed immediately, the electrical energy storage module 10 stores the electrical energy supplied at the output of the very wideband rectifier 6 (the electrical energy storage module 10 being connected directly at the output of the rectifier 6 - such a topological configuration not being shown in the figures), for subsequent use of the electrical energy by the sensor or the IoT connected object 12.In a variant not shown, the sensor or the IoT connected object 12 can be connected directly to the output of the DC voltage to DC voltage converter 8, for immediate use of the electrical energy supplied by the very wide band rectifier 6.

[0067] THE figures 5 à 9 are schematic representations of different forms of omnidirectional multi-band dipole antenna 4, according to different exemplary embodiments of the invention. In these non-limiting exemplary embodiments of the antenna 4, certain secondary strand portions 40 of the antenna 4 are attached to the main strand portion of the corresponding metal strand at one end of the main strand portion, more precisely at the end connected to the feed strip or to the metal pattern. According to other exemplary embodiments, not shown in the figures, each metal strand may comprise at least one set of secondary strand portions in a tree structure attached to the main strand portion and forming a branch with the main strand portion.In this case, and in a manner analogous to a tree structure, some of the secondary branches of the metal strand are grafted onto other secondary branches of the strand. Each radiating nested loop is then associated with an end electromagnetic coupling either between the main strand portions or between dual secondary branches. Of course, many other shapes and structures than those shown in the . figures 2 , 3 , And 5 à 9 are possible for the antenna or antenna element according to the invention.

Claims

1. Omnidirectional multi-band dipole antenna (4) or antenna element comprising at least two metal strands (14, 15; 20, 22, 24) and a microstrip feed line (13), the microstrip feed line (13) comprising a feed strip (16) and a metal pattern (18) defining a ground plane, one end (14A; 20A, 24A) of at least one first metal strand (14; 20, 24) being connected to the feed strip (16), one end (15A; 22A) of a second metal strand (15; 22) being connected to the metal pattern (18), each of the metal strands (14, 15; 20, 22, 24) comprising a main strand portion (141, 151; 201, 221, 241) and at least one of secondary strand (142-a, 142-b, 142-c, 152-a, 152-b, 152-c; 202, 222-a, 222-b, 242) or at least one set of secondary strand portions in a tree structure attached to the main strand portion (141, 151; 201, 221, 241) and forming a branch with the main strand portion (141, 151;201, 221, 241), said at least two metal strands (14, 15; 20, 22, 24) being configured so as to form together a structure comprising at least two radiating nested loops (B1, B2, B3, B4; E11, E12, E21, E22) nested one inside the other, the main strand portions (141, 151; 201, 221, 241) of the first and second metal strands (14, 15; 20, 22, 24) being electromagnetically coupled to each other at their free ends (14B, 15B; 20B, 22B, 22C, 24B), and the free end of the or each secondary strand portion (142-a, 142-b, 142-c; 202, 242) of the first metal strand (14; 20, 24) being electromagnetically coupled with the free end of a corresponding secondary strand portion (152-a, 152-b, 152-c; 222-a, 222-b) of the second metal strand (15; 22), such that each radiating nested loop (B1, B2, B3, B4; E11, E12, E21, E22) is associated with an electromagnetic coupling between said at least two strands (14, 15;20, 22, 24) and defines a resonant frequency and a complex access impedance value of the antenna (4) or antenna element; the antenna (4) or antenna element further comprising a substrate on which said at least two metal strands (14, 15; 20, 22, 24) are arranged, the substrate having two faces; characterized in that said at least two metal strands (14, 15; 20, 22, 24) are flat ribbons arranged on both faces of the substrate, said at least two metal strands (14, 15; 20, 22, 24) extending in two separate planes corresponding to the two faces of the substrate.; 2. Omnidirectional multi-band dipole antenna (4) or antenna element according to claim 1, characterized in that the free ends (14B, 15B; 20B, 22B, 22C, 24B) of the main strand portions (141, 151; 201, 221, 241) of the first and second metal strands (14, 15; 20, 22, 24) extend opposite each other in said two separate planes, and in that the free end of the or each secondary strand portion (142-a, 142-b, 142-c; 202, 242) of the first metal strand (14; 20, 24) extends opposite the free end of a corresponding secondary strand portion (152-a, 152-b, 142-c; 202, 242) of the first metal strand (14; 20, 24). 152-b, 152-c; 222-a, 222-b) of the second metal strand (15; 22), said two free ends extending in said two separate planes.

3. Antenna (4) or omnidirectional multi-band dipole antenna element according to any one of the preceding claims, characterized in that at least one of the secondary strand portions (142-a, 142-b, 142-c, 152-a, 152-b, 152-c; 202, 222-a, 222-b, 242) of each metal strand (14, 15; 20, 22, 24) is attached to the main strand portion (141, 151; 201, 221, 241) of said metal strand (14, 15; 20, 22, 24) at a point located between the ends (14A, 14B, 15A, 15B; 20A, 20B, 22A, 22B, 22C, 24A, 24B) of the main strand portion (141, 151; 201, 221, 241), and / or in that at least one of the secondary strand portions of each metal strand (14, 15; 20, 22, 24) is attached to the main strand portion of said metal strand (14, 15; 20, 22, 24) at one end of the main strand portion.

4. Antenna (4) or omnidirectional multi-band dipole antenna element according to any one of the preceding claims, characterized in that the main strand portion (141, 151; 201, 221, 241) and all of the secondary strand portions (142-a, 142-b, 142-c, 152-a, 152-b, 152-c; 202, 222-a, 222-b, 242) of each metal strand (14, 15; 20, 22, 24) define a comb, rake, tree shape, or a combination of one or more of these shapes.

5. Antenna (4) or omnidirectional multi-band dipole antenna element according to any one of the preceding claims, characterized in that the electromagnetic coupling between a free end of one of the metal strands (14; 20, 24) and a free end of another metal strand (15; 22) is carried out over a non-zero coupling length of the strands, the value of the resonant frequency of the radiating nested loop (B1, B2, B3, B4; E11, E12, E21, E22) associated with said electromagnetic coupling being a function of the corresponding coupling length and / or of at least one other parameter chosen from the group consisting of: the width of the flat strips (14, 15; 20, 22, 24), the dielectric permittivity of the substrate and the thickness of the substrate.

6. Omnidirectional multi-band dipole antenna (4) or antenna element according to any one of claims 1 to 5, characterized in that the antenna (4) or the antenna element comprises two metal strands (14, 15).

7. Omnidirectional multi-band dipole antenna (4) or antenna element according to any one of claims 1 to 5, characterized in that the antenna (4) or antenna element comprises three metal strands (20, 22, 24) distributed into two first metal strands (20, 24) and a second metal strand (22), the three metal strands (20, 22, 24) being configured so as to form together a structure comprising two sets (E1, E2) of radiating nested loops (E11, E12, E21, E22), each set (E1, E2) of radiating nested loops (E11, E12, E21, E22) being formed by a part of the second metal strand (22) and by one of the first metal strands (20, 24) and comprising at least two radiating nested loops (E11, E12, E21, E22) nested within each other, the free end (20B, 24B) of the main strand portion (201, 241) of each first metal strand (20, 24) being electromagnetically coupled with a free end (22B,22C) of the main strand portion (221) of the second metal strand (22).

8. Omnidirectional multi-band dipole antenna (4) or antenna element according to claim 7, characterized in that the second metal strand (22) is arranged between the two first metal strands (20, 24) and has a shape such that the second metal strand (22) defines a central axis of symmetry for the antenna (4) or the antenna element, the two first metal strands (20, 24) extending on either side of said central axis of symmetry.

9. Antenna (4) or omnidirectional multi-band dipole antenna element according to claim 7 or 8, characterized in that the first two metal strands (20, 24) have identical geometry and dimensions.

10. Antenna (4) or omnidirectional multi-band dipole antenna element according to claim 7 or 8, characterized in that the two first metal strands (20, 24) have distinct geometry and / or dimensions.

11. Electrical or electronic device (2), characterized in that it comprises at least one antenna (4) or an omnidirectional multi-band dipole antenna element according to any one of the preceding claims, and an electrical element (6) connected to the microstrip feed line (13) of the antenna (4) or of the antenna element and constituting an electrical source or load.

12. Electrical or electronic device (2) according to claim 11, characterized in that said electrical element (6) is a very wide band rectifier constituting an electrical load.

13. Electrical or electronic device (2) according to claim 12, characterized in that the very wide band rectifier (6) has a single rectifier core.

14. Electrical or electronic device (2) according to claim 12 or 13, characterized in that it further comprises a direct voltage to direct voltage converter (8) connected to the output of the very wide band rectifier (6), and an electrical energy storage module (10) connected to the output of the direct voltage to direct voltage converter (8), the device (2) being a multi-frequency radiofrequency energy recovery device.

15. Method for multi-frequency recovery of radiofrequency energy, implemented by an electrical or electronic device (2) according to claim 14, characterized in thatthe method comprises the following steps: - a reception (S1) of a radiofrequency (RF) signal by the antenna (4) or the antenna element, the radiofrequency (RF) signal corresponding to one or more frequency bands associated with at least one of said at least two resonant frequencies of the antenna (4) or the antenna element; - a rectification (S2), by the very wide band rectifier (6), of the electrical signal (30) provided at the output of the antenna (4) or the antenna element; - a conversion (S3), by the DC voltage converter into DC voltage (8), of the output voltage (32) provided at the output of the very wide band rectifier (6); and - a storage (S4), in the electrical energy storage module (10), of the electrical energy (34) provided at the output of the DC voltage converter into DC voltage (8).

16. Use of an antenna (4) or an omnidirectional multi-band dipole antenna element according to any one of claims 1 to 10 for controlling the synthesis of resonant frequencies and complex access impedance values ​​of the antenna (4) or the antenna element, by adjusting, for each radiating nested loop (B1, B2, B3, B4; E11, E12, E21, E22) of the antenna (4) or the antenna element, the length of the corresponding electromagnetic coupling, between a free end of one of the metal strands (14; 20, 24) and a free end of another metal strand (15; 22), so as to adjust the resonant frequency of said loop (B1, B2, B3, B4; E11, E12, E21, E22) to a predetermined frequency value, and to adjust, for this value of predetermined frequency, the complex access impedance of the antenna (4) or antenna element to a predetermined impedance value.

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