Multi-band dipole antenna or antenna element, and multi-frequency radio frequency energy harvesting method 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 method for multi-frequency radio frequency energy harvesting implemented by an electrical or electronic device. Figure from the abstract: Fig. 2

Description

Title of the invention: Multi-band dipole antenna or antenna element, and method for multi-frequency radio frequency energy harvesting implemented by such an antenna or antenna element

[0001] The invention relates to the field of radio frequency antennas of the multi-band dipole type, exhibiting omnidirectional radiation. The invention finds particular application in the field of multi-frequency radio frequency energy harvesting.

[0002] Applications of sensors or connected objects (IoT, for "Internet of Things") are constantly growing. These wireless sensors or connected objects make it possible to collect various data such as temperature, pressure, or humidity, and are used in various fields such as intelligent monitoring systems, home automation, medical or military applications.

[0003] Today, these sensors are primarily powered by batteries, which implies a limited lifespan and sometimes complicated replacement. A promising process involves harvesting energy available in the ambient environment of these microsystems, thereby reducing or even eliminating the use of these batteries. This will enable, in the long term, energy autonomy for objects and sensors.

[0004] There is therefore a need to be able to recover ambient radio frequency energy on several distinct frequency bands using a single antenna ideally having 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 indeed the cornerstone of radio frequency energy harvesting systems and critically affect the level of continuous power supplied to the load at the rectifier output. The antenna collects microwave power, and the rectifier circuit converts it into direct current (DC) power. This DC electrical power generally passes through an energy storage system before being delivered to the load.

[0006] The collection and rectification of ambient electromagnetic waves into direct current power is an important and necessary feature for any battery-dependent device. The main objective of any energy harvesting system is therefore to increase its conversion efficiency. Antenna efficiency is central to this. 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 rectification circuit. The circuit must satisfy the power matching constraint between all its components. A typical rectification circuit consists of a receiving antenna followed by a bandpass filter, a rectifier, a low-pass filter, and a load.

[0008] In the design of such a radio frequency module with an antenna that needs to be connected to a transmitting or receiving device (in this case, a receiving device for energy harvesting), it is therefore essential to ensure power matching between the radiating element (the antenna) and the device to avoid signal transfer losses. To achieve this, the antenna's access impedance must be equal to the conjugate value of the device's complex access impedance on each of the operating frequency bands of the radio frequency 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 reduces the number of components needed for the proper functioning of the transmitting or receiving chain.The electrical performance of this chain is therefore greatly improved.

[0009] In radio frequency, multi-band antennas that need to operate on a set of predetermined frequency values ​​are traditionally optimized to work with a reference impedance of 50 ohms, identical at all these frequencies. In cases where the antenna's access impedance must have the required complex value at 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 elements of a multiband 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 multiband dipole antenna allows for simple control over the determination of the complex access impedance values ​​of the antenna. The key parameter for controlling this impedance is indeed the angular separation between the two elements of the dipole. Varying the complex access impedance of the antenna then makes it possible to precisely match this complex access impedance to that of the transmitting or receiving equipment, for frequency bands respectively emitted or received by the antenna. The fact of Varying the angle between the two elements of the antenna allows a large area to be swept on the Smith chart and thus a wide range of complex impedances to be synthesized at the antenna access point.

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

[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 simple and reliable control of the synthesis of resonance frequencies and complex access impedance values ​​of the antenna or antenna element.

[0014] Another object of the invention is to provide an electrical or electronic device comprising, in addition to the antenna or antenna element, an electrical element constituting a source or an electrical charge for the antenna or antenna element, and not requiring any intermediate matching circuit between the antenna and the electrical element.

[0015] Another object 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 wideband rectifier).

[0016] To achieve these objectives, the invention proposes, according to a first aspect, an omnidirectional multiband dipole antenna or antenna element comprising at least two metallic elements and a microstrip feed line, the microstrip feed line comprising a feed ribbon and a metallic pattern defining a ground plane, one end of at least a first metallic element being connected to the feed ribbon, one end of a second metallic element being connected to the metallic pattern, each of the metallic elements comprising a portion of a main element and at least one portion of a secondary element or at least a set of secondary element portions in a tree structure attached to the portion of the main element and forming a branch with the main strand portion, said at least two metallic strands being configured so as to together form a structure comprising at least two nested radiating loops, the main strand portions of the first and second metallic 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 metallic strand being electromagnetically coupled with the free end of a corresponding secondary strand portion of the second metallic strand, such that each radiating nested loop is associated with an electromagnetic coupling between said at least two strands and defines a resonant 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, multi-frequency band, and exhibits a complex input impedance for each of its radiating frequencies. Because the radiating patterns of the antenna or antenna element are shaped into loops, an electromagnetic coupling zone is created between the ends of the two metallic strands constituting the radiating pattern at a given frequency. Due to their positions at the ends of the metallic strands, these points have opposite voltage polarities, which helps to lower the resonant frequency of the radiating pattern (the frequency associated with the loop in question), and thus to miniaturize the antenna.Furthermore, for a given radiation mode, the electromagnetic coupling within the loop associated with that mode allows for adjusting the actual input impedance at resonance: the greater the coupling, the lower this actual impedance value, and consequently, the lower the resonant frequency of that mode. The electromagnetic coupling at the ends of the radiating pattern's elements thus allows the resonant loop to be opened on the Smith chart, thereby sweeping a very wide range of complex impedances across this chart by varying the frequency on either side of the resonant frequency. It is therefore possible to synthesize a wide range of complex antenna input impedances, with low resistive and high inductive components, for several predefined frequencies.

[0018] Each electromagnetic coupling zone also allows for very simple adjustment of each antenna's resonant frequency, independently of the other frequencies. The existence of these electromagnetic coupling zones at the ends of the elements constituting the structure thus makes it possible to achieve an ultra-compact antenna structure, typically associated with a rather omnidirectional radiation pattern.

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

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

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

[0022] According to a particular technical feature 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 distinct planes, and the free end of the or of 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 distinct planes.

[0023] According to a particular technical feature 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 an end of the main strand portion.

[0024] According to a particular technical feature of the invention, the main strand portion and the set of 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 metallic strands and a free end of another metallic strand is carried out over a non-zero coupling length of the strands, the value of the resonance 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 with respect to the other parameters, the longer the coupling length of the strands The greater the coupling length, the lower the resonant frequency. This electrical coupling at the ends of the two elements allows for tuning the desired frequency and also contributes significantly to antenna miniaturization. The longer the coupling length, the more open the resonant loop on the Smith chart. This allows for the synthesis of antenna input impedances with very low resistive values. This coupling also allows for tuning the desired complex impedance value. Furthermore, this parameter (or these parameters) affects the antenna's shape factor, which in turn influences the antenna's input impedance for a given radiation pattern. For example, an asymmetry between the lengths of the two elements forming a radiating pattern increases the actual input impedance obtained at resonance.

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

[0027] According to a second embodiment of the invention, the antenna or antenna element comprises three metal strands distributed 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, with the first two metal strands extending on either side of said central axis of symmetry. This second embodiment of the antenna or antenna element exhibits greater symmetry in the antenna substrate plane than the first embodiment, allowing for a better balance of the detection level on both sides of the antenna substrate plane. This significantly improves the omnidirectional nature of the antenna or antenna element, a characteristic that is particularly important in a radio frequency 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 elements have distinct geometries and / or dimensions. This second variant allows for a multiplication of the antenna's frequencies of interest. Thus, two sets of mirrored, asymmetrical nested loops can be used to operate on different frequency ranges. In this case, the number of antenna frequencies of interest is potentially doubled.

[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 charge.

[0032] Thanks to the fact that it is possible to simultaneously synthesize and control several complex access impedance values ​​of the antenna over several predetermined radiation frequencies, the value of each antenna access impedance is advantageously chosen to be equal to the conjugate value of the complex access impedance of the electrical element, over each of the operating frequency bands of the device. This ensures 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 feature of the invention, said electrical element is a very wideband rectifier constituting an electrical load.

[0034] Advantageously, the very wideband rectifier comprises 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 radio frequency energy recovery device which further comprises a DC voltage to DC voltage converter connected at the output of the very wideband rectifier, and an electrical energy storage module connected at the output of the DC voltage to DC voltage converter.

[0036] According to a third aspect, the invention also relates to a multi-frequency radio frequency energy recovery method, implemented by an electrical or electronic device as described above, the method comprising the following steps:

[0037] - reception of a radio frequency signal by the antenna or antenna element, the radio frequency signal corresponding to one or more frequency band(s) associated with at least one of said at least two resonant frequencies of the antenna or antenna element;

[0038] - a rectification, by the very wideband rectifier, of the electrical signal supplied in antenna or antenna element output;

[0039] - a conversion, by the DC-to-DC voltage converter, of the output voltage supplied at the output of the very wideband rectifier; and

[0040] - a storage, in the electrical energy storage module, of energy electrical supply at the output of the DC-to-DC converter.

[0041] According to a fourth aspect, the invention also relates to the use of an omnidirectional multi-band dipole antenna or antenna element as described above for controlling the synthesis of resonance 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 set the resonance frequency of said loop to a predetermined frequency value, and to set, for this predetermined frequency value, the complex access impedance of the antenna or antenna element to a predetermined impedance value.

[0042] This provides a simple and reliable means of controlling the synthesis of resonance frequencies and complex access impedance values ​​of the antenna or antenna element, while keeping the antenna as miniaturized as possible.

[0043] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures, among which: - [Fig.1] is a schematic view of an electrical or electronic radio frequency energy harvesting device comprising an omnidirectional multi-band dipole antenna according to the invention;

[0044] - [Fig.2] is a front view of the omnidirectional multi-band dipole antenna of the [Fig.1], according to a first embodiment of the invention;

[0045] - [Fig.3] is a front view of the omnidirectional multi-band dipole antenna of the [Fig.1], according to a second embodiment of the invention;

[0046] - [Fig.4] is a flowchart representing a recovery process multifrequency radio frequency energy, implemented by the electrical or electronic device of [Fig. 1]; and

[0047] - [Fig.5] to [Fig.9] are schematic views of different antenna shapes omnidirectional multi-band dipole, according to different embodiments of the invention.

[0048] In the following description, "electromagnetic coupling" means any coupling of an electrical, magnetic or mixed nature due to the combination of these two types of coupling.

[0049] Furthermore, the term "radiating nested loops" refers to any structure of electromagnetic radiation loops nested one inside the other on a geometric plane (by analogy with the structures of nesting dolls). 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.

[0050] The term "cold strand" also means any metallic strand connected to the metallic pattern defining the ground plane of the antenna, and the term "hot strand" means any metallic strand connected to the feed ribbon of the antenna.

[0051] Figure 1 represents an electrical or electronic recovery device 2 radio frequency energy. Device 2 is typically a multifrequency radio frequency energy harvesting device (as is the case in the exemplary embodiment of [Fig.1]), although this is not limiting within the scope of the present invention.

[0052] The device 2 comprises an omnidirectional multiband dipole antenna 4, and an electrical element 6 constituting an electrical load for the antenna 4. In an alternative not shown in the figures, the electrical element may 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 multifrequency radio frequency energy harvesting device, the electrical element 6 is typically a rectifier connected to the output of the antenna 4, preferably a very wideband rectifier. In this case, and as illustrated in [Fig. 1], the device 2 also comprises a DC-to-DC converter 8 connected to the output of the rectifier 6, and an electrical energy storage module 10 connected to the output of the DC-to-DC converter 8.In an alternative not shown (where the electrical energy supplied at the output of rectifier 6 is not consumed immediately), the electrical energy storage module 10 can be connected directly to the output of rectifier 6. The multi-frequency radio frequency energy harvesting device 2 is, for example, connected to a sensor or an IoT (Internet of Things) device 12 to provide it with power. Preferably, rectifier 6 has only one rectification core.

[0053] 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 [Fig. 2] for clarity) on which the two metal strands 14, 15 are arranged. The substrate, for example, has two faces. Each metal strand 14, 15 is preferably a flat ribbon arranged on one face respective to the substrate. The two metal strands 14, 15 thus extend in two distinct planes corresponding to the two faces of the substrate.

[0054] The microstrip feed line 13 comprises a feed ribbon 16 and a metallic pattern 18 defining a ground plane. Although not shown in [Fig. 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 ribbon 16 and the ground plane 18. The ground plane 18 is planar and can be circular or rectangular, for example, and have several patterns of different shapes and sizes. It can also be cut from a metal sheet.

[0055] As illustrated in [Fig. 2], a first end 14A of a first metal strand 14 is connected to the feed ribbon 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.

[0056] 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 it. In the particular embodiment shown in [Fig. 2], for each metal strand 14, 15, the main strand portion 141, 151 and the set of 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 shape substantially of "7", 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 an alternative not shown, the main strand portion 141, 151 and the set of secondary strand portions 142-a, 142-b, 142-c, 152-a, 152-b, 152-c can define other shapes, such as for example a rake shape, a tree shape, or a combination of one or more of these shapes.

[0057] In the embodiment of [Fig. 2], the two metal strands 14, 15 are configured to form together a structure comprising four nested radiating loops B1, B2, B3, B4. More specifically, 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 portion of the secondary strand 152-a, 152-b, 152-c of the second metallic strand 15. Thus, each radiating nested loop B1, B2, B3, B4 is associated with electromagnetic coupling between the two strands 14, 15 and defines a resonant frequency and a complex access impedance value of the antenna 4. The electromagnetic coupling is preferably electrical in nature, more precisely capacitive, 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 capacitive 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 antenna 4 for the radiation mode corresponding to that loop.

[0058] In the particular embodiment of [Fig.2] in which the antenna 4 comprises a substrate which has two faces, each metal strand 14, 15 being disposed 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 [Fig.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 distinct planes mentioned above.

[0059] Thus, the electromagnetic coupling between the free end of each portion of the main strand 141 or secondary strand 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 effected over a non-zero coupling length of the strands, a space separating the two strands 14, 15 in the direction orthogonal to the two aforementioned planes. The value of the resonance 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 of 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 specifically, and all other things being equal with regard to the other parameters, the longer the coupling length of the strands 14, 15, the lower the associated resonance frequency.Thus, by playing on the length of the electromagnetic coupling associated with each radiating loop Bl, B2, B3, B4 and keeping the other parameters constant. As mentioned above, it is possible to adjust the resonant frequency of loops B1, B2, B3, and B4 to a predetermined frequency value and, for this predetermined frequency value, to adjust the complex access impedance of antenna 4 to a predetermined impedance value. Indeed, due to the electrical independence between the nested radiating loops B1, B2, B3, and B4, which are uncorrelated with each other, it is possible to independently adjust the resonant frequencies and complex access impedances of antenna 4. Each electromagnetic coupling zone thus allows adjustment of the parameters of one of the nested radiating loops B1, B2, B3, and B4 without affecting the other loops. This allows for independent optimization of the parameters of antenna 4 and provides flexibility and independence in parameter control.

[0060] An example of an embodiment of the antenna 4 according to this particular embodiment of [Fig. 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 elements 14, 15 for each radiating loop B1, B2, B3 and B4 approximately equal to 4.2 mm (for the main element portions 141, 151 of the first and second metallic elements 14, 15), 1.9 mm (for the first secondary element portions 142-a, 152-a of the first and second metallic elements 14, 15), 3.1 mm (for the second secondary element portions 142-b, 152-b of the first and second metallic elements 14, 15) and 2.6 mm (for the third secondary element portions 142-c, 152-c of the first and second metallic elements 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 1.5 mm, and the substrate used has a thickness of 125 μm, a relative dielectric permittivity of 2.9 and a loss tangent of 5.103. The complex access impedance values ​​of antenna 4, associated with these four frequency bands, are then: 326 Q + j322 Q, 15 Q + j87 Q, 7 Q + j62 Q and 7 Q + j19 Q. Of course, other values ​​of frequency bands and complex access impedances of the antenna are possible depending on the desired uses for antenna 4, by changing the coupling length of the elements 14, 15 for each radiating loop B1, B2, B3, B4 and / or on the width of the flat strips 14, 15, the dielectric permittivity of the substrate and the thickness of the substrate.

[0061] Figure 3 represents the omnidirectional multi-band dipole antenna 4 according to a second embodiment of the invention. Hereafter, elements identified with the same reference numerals as those used for elements of the first embodiment are identical or analogous to these elements and will therefore not be described in further detail. According to this second embodiment, the antenna 4 comprises the microstrip feed line 13 and three metallic elements 20, 22, 24. The three metallic elements 20, 22, 24 are divided into two lateral "hot" elements 20, 24 extending on either side of a central "cold" element 22. Another embodiment The 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.

[0062] 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.

[0063] As illustrated in [Fig.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 metallic pattern 18 defining the ground plane.

[0064] 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 [Fig. 3], for each "hot" strand 20, 24, the main strand portion 201, 241 and the associated secondary strand portion 202, 242 define a comb-like shape. Thus, for each "hot" strand 20, 24, the main strand portion 201, 241 defines a shape substantially of "7", 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.

[0065] 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 it. 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 [Fig. 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 shape substantially of "T", 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" element 22 has a shape such that it defines a central axis of symmetry for the antenna 4, with the two "hot" elements 20, 24 extending on either side of the central axis of symmetry. In the particular embodiment example of the... [Fig. 3], the two "hot" elements 20 and 24 have identical geometry and dimensions. This symmetry of the antenna 4 results in an overall symmetry of its radiation pattern. In an alternative not shown, the two "hot" elements 20 and 24 may have different geometries and / or dimensions.

[0066] The three metal strands 20, 22, 24 are configured to form a structure comprising two sets El, E2 of radiating nested loops. In the particular embodiment of [Fig. 3], each set El, E2 of radiating nested loops comprises two radiating nested loops Eli, E12, respectively E21, E22, which are nested one inside the other. Each set El, E2 of radiating nested loops is formed by a portion of the "cold" strand 22 and by one of the "hot" strands 20, 24.

[0067] More specifically, the main strand portions 201, 221 of the first "hot" strand 20 and 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 the "cold" strand 22 are electromagnetically coupled to each other at their free ends 24B, 22C. In addition, 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 Eli, 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 resonant frequency and a complex access impedance value of the antenna 4.The electromagnetic coupling is preferably electrical in nature, more precisely capacitive. In the particular embodiment shown in [Fig. 3], where antenna 4 has a general symmetry of form, the sets of resonant frequencies associated with the two sets El, E2 of radiating loops are identical. Alternatively, when the two sets El, E2 of nested loops are asymmetrical (the two "hot" elements 20, 24 being, for example, of different geometry and / or dimensions), the resonant frequencies associated with the two sets El, E2 of radiating loops are distinct, which makes it possible to multiply the number of frequencies of interest for antenna 4.

[0068] In the particular embodiment shown in [Fig. 3] in which the antenna 4 comprises a substrate having 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 [Fig. 3] (therefore superimposed on each other in perspective of this figure). Similarly, the free end of the secondary strand portion 202, 242 of each "hot" strand 20, 24 extends in the first plane, and the free end of each secondary strand portion 222-a, 222-b of the "cold" strand 22 extends opposite one of these free "hot" strand ends in the second plane.

[0069] An example of an embodiment of the antenna 4 according to this particular embodiment of [Fig. 3] thus makes it possible to obtain an antenna capable of operating simultaneously on two frequency bands which are, for example (for a coupling length of the elements approximately equal to 6 mm (for the couplings between elements 201-221 and 241-221) and 4 mm (for the couplings between elements 202-222a and 242-222b): 684 MHz for the radiating loops E1 and E21, and 1.633 GHz for the radiating loops E12 and E22. Furthermore, in this example, the width of the metallic elements 20, 22, 24 is 1.5 mm, and the substrate used has a thickness of 125 µm, a relative dielectric permittivity of 2.9, and a loss tangent of 5 x 10³.Of course, other frequency band values ​​are possible depending on the desired uses for antenna 4, by playing with the coupling length of the strands 20, 22, 24 for each radiating loop and / or with the width of the flat strips 20, 22, 24, the dielectric permittivity of the substrate and the thickness of the substrate.

[0070] The multi-frequency radio frequency energy recovery process according to the invention, implemented by the electrical or electronic device 2, will now be described in more detail, with reference in particular to [Fig.4].

[0071] The method includes an initial step SI during which the antenna 4 receives a radio frequency RF signal, the radio frequency RF signal corresponding to one or more frequency band(s) associated with one of the resonant frequencies of the antenna 4.

[0072] The process includes a subsequent step S2 in which the very wideband rectifier 6 rectifies the electrical signal 30 supplied at the output of the antenna 4.

[0073] The process includes a subsequent step S3 in which the DC-to-DC voltage converter 8 converts the output voltage 32 supplied at the output of the very wideband rectifier 6.

[0074] The method includes a final step S4 in which the electrical energy storage module 10 stores the electrical energy 34 supplied at the output of the DC-to-DC converter 8. This electrical energy is used to power the sensor or connected object 12. In the case where the electrical energy supplied at the output of the rectifier 6 is not intended for immediate consumption, 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 to the output of the rectifier 6 - such a topological configuration not being shown in the figures), for a subsequent use of electrical energy by the sensor or connected object loT 12. In an alternative not shown, the sensor or connected object loT 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 wideband rectifier 6.

[0075] Figures 5 to 9 are schematic representations of different forms of omnidirectional multiband dipole antenna 4, according to various embodiments of the invention. In these non-limiting embodiments of the antenna 4, certain secondary element portions 40 of the antenna 4 are attached to the corresponding main element portion of the metal element at one end of the main element portion, more precisely at the end connected to the feed ribbon or the metal pattern. According to other embodiments, not shown in the figures, each metal element may comprise at least one set of secondary element portions arranged in a tree structure attached to the main element portion and forming a branch with the main element portion.In this case, and analogously 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 electromagnetic end coupling either between the main strand portions or between dual secondary branches. Of course, many other shapes and structures than those shown in Figures 2, 3, and 5 to 9 are possible for the antenna or antenna element according to the invention.

Claims

1. Demands An omnidirectional multiband dipole antenna (4) or antenna element comprising at least two metallic elements (14, 15; 20, 22, 24) and a microstrip feed line (13), the microstrip feed line (13) comprising a feed ribbon (16) and a metallic pattern (18) defining a ground plane, one end (14A; 20A, 24A) of at least one first metallic element (14; 20, 24) being connected to the feed ribbon (16), one end (15A; 22A) of a second metallic element (15; 22) being connected to the metallic pattern (18), each of the metallic elements (14, 15; 20, 22, 24) comprising a main element portion (141, 151; 201, 221, 241) and at least one secondary element portion (142-a, 142-b, 142-c, 152-a, 152-b, 152-c ; 202, 222-a, 222-b, 242) or at least a set of secondary strand portions in a tree-like arrangement 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 metallic strands (14, 15; 20, 22, 24) being configured so as to form together a structure comprising at least two nested radiating loops (B1, B2, B3, B4; E1, E12, E21, E22) embedded one inside the other, the main strand portions (141, 151; 201, 221, 241) of the first and second metallic 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 metallic 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 metallic strand (15; 22), such that each radiating nested loop (B1, B2, B3, B4; E1, E12, E21, E22) is associated with an electromagnetic coupling between said at least two strands (14, 15;20, 22, 24) and defines a resonance 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 metallic strands (14, 15; 20, 22, 24) are arranged, the substrate having two faces; characterized in that said at least two metallic strands (14, 15; 20, 22, 24) are flat ribbons arranged on both faces of the substrate, said at least two metallic strands (14, 15; 20, 22, 24) extending in two distinct planes corresponding to the two faces of the substrate.

2. Antenna (4) or omnidirectional multi-band dipole antenna element according to claim 1, characterized in that the free ends (14B, 15B; 20B, 22B, 22C, 24B) of the main element portions (141, 151; 201, 221, 241) of the first and second metal elements (14, 15; 20, 22, 24) extend opposite each other in said two distinct planes, and in that the free end of the or each secondary element portion (142-a, 142-b, 142-c; 202, 242) of the first metal element (14; 20, 24) extends opposite the free end of a corresponding secondary element portion (152-a, 152-b, 152-c; 222-a, 222-b) of the second metallic strand (15; 22), said two free ends extending in said two distinct 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 element portions (142-a, 142-b, 142-c, 152-a, 152-b, 152-c; 202, 222-a, 222-b, 242) of each metal element (14, 15; 20, 22, 24) is attached to the main element portion (141, 151; 201, 221, 241) of said metal element (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 the set of 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 resonance frequency of the radiating nested loop (B1, B2, B3, B4; E1, 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 antenna element comprises two metallic strands (14, 15).

7. An omnidirectional multiband 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) divided into two first metal strands (20, 24) and a second metal strand (22), the three metal strands (20, 22, 24) being configured to form together a structure comprising two sets (E1, E2) of radiating nested loops (E1, E12, E21, E22), each set (E1, E2) of radiating nested loops (E1, E12, E21, E22) being formed by a portion of the second metal strand (22) and by one of the first metal strands (20, 24) and comprising at least two radiating nested loops (E1, E12, E21, E22) nested one inside the other, the free end (20B, 24B) of the main strand portion (201, 241) of each first metallic 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. Antenna (4) or omnidirectional multi-band dipole antenna element according to claim 7, characterized in that the second metal element (22) is arranged between the first two metal elements (20, 24) and has a shape such that the second metal element (22) defines a central axis of symmetry for the antenna (4) or the antenna element, the first two metallic 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 metallic elements (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 first two metallic elements (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 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 antenna element and constituting an electrical source or charge.

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

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

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

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

16. Use of an omnidirectional multiband dipole antenna (4) or 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 antenna element, by adjusting, for each radiating nested loop (B1, B2, B3, B4; E1, E12, E21, E22) of the antenna (4) or 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 set the resonant frequency of said loop (B1, B2, B3, B4; E1, E12, E21, E22) to a predetermined frequency value, and to adjust, for this frequency value predetermined, the complex access impedance of the antenna (4) or antenna element on a predetermined impedance value.

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