Monopolar wire-plate antenna

Abstract

This antenna comprises: - a ground plane (1); - a capacitive roof (2), extending parallel to the ground plane (1); - a feed probe (3, 30), electrically isolated from the ground plane (1), and extending between the ground plane (1) and the capacitive roof (2) so as to electrically supply the capacitive roof (2), the feed probe (3, 30) being intended to be connected to a transmission line; - a set of short-circuit wires (4), arranged parallel around the feed probe (3, 30) so that each short-circuit wire (4) electrically connects the capacitive roof (2) to the ground plane (1), each short-circuit wire (4) being coated with a magneto-dielectric material (5).

Description

technical field

[0001] The invention relates to the technical field of monopolar wire-plate antennas.

[0002] The invention finds particular application in the Internet of Things (IoT) (acronym for "Internet of Things" (in English), radio-frequency identification (RFID, acronym for “Radio Frequency IDentification” (in English), communication for sensor networks, M2M machine-to-machine communication (" Machine-to-Machine (in English), communication in the fields of aeronautics and space. Prior art

[0003] A monopolar wire-plate antenna known from the prior art, notably from the document L. Batel et al., "Design of a monopolar wire-plate antenna loaded with magneto-dielectric material", EuCAP Conference (European Conference on Antennas and Propagation), April 2018, comprises: a ground plane; a capacitive roof, extending parallel to the ground plane; a feed probe, electrically isolated from the ground plane, and extending between the ground plane and the capacitive roof so as to electrically supply the capacitive roof, the feed probe being intended to be connected to a transmission line; a single shorting wire, arranged at a distance from the feed probe so that the shorting wire electrically connects the capacitive roof to the ground plane, the shorting wire being coated with a magneto-dielectric material.

[0004] The paper by Liu et al., "Design and analysis of a low-profile and broadband microstrip monopolar patch antenna," describes a wire-patch antenna in which the feed probe is arranged at the center of the ground plane and in which there are two short-circuit wires; the antenna includes a substrate extending between the capacitive roof and the ground plane, where the substrate encloses the feed probe and each short-circuit wire. The paper by Delaveaud et al., "New kind of microstrip antenna: the monopolar wire-patch antenna," describes a wire-patch antenna in which the feed probe is arranged at the center of the ground plane and is surrounded by a plurality of short-circuit wires; the antenna includes a substrate extending between the capacitive roof and the ground plane, where the substrate encloses the feed probe and each short-circuit wire.A state-of-the-art antenna of this kind, thanks to the magneto-dielectric material coating the short-circuit wire, can have dimensions reduced by about 15% compared to an architecture without magneto-dielectric material, while maintaining similar performance.

[0005] A monopolar wire-plate antenna architecture is sought that allows for improved antenna miniaturization, with an equal amount of magneto-dielectric material. Description of the invention

[0006] To this end, the invention relates to a monopolar wire-plate antenna, comprising: a ground plane; a capacitive roof; a feed probe, electrically isolated from the ground plane, and extending between the ground plane and the capacitive roof so as to electrically supply the capacitive roof, the feed probe being intended to be connected to a transmission line; a set of shorting wires, arranged parallel around the feed probe so that each shorting wire electrically connects the capacitive roof to the ground plane, each shorting wire being coated with a magneto-dielectric material, made in the form of a hollow cylinder inside which the shorting wire extends.

[0007] Thus, such an antenna according to the invention makes it possible to improve the miniaturization of the antenna, with an equal quantity of magneto-dielectric material, thanks to the parallel connection of a plurality of short-circuit wires each coated with a magneto-dielectric material.

[0008] It is known that putting a plurality of wires in parallel is equivalent to the presence of a single wire with an equivalent radius greater than the individual radius of the wires put in parallel, as mentioned in the document EA Wolff “Antenna analysis”, Wiley, 1966, or in the document C. Harrison et al., “Folded dipoles and loops”, IEEE Transactions on Antennas and Propagation, vol.9, issue 2, pp.171-187, 1961.

[0009] However, the inventors found that, with equal quantities of magnetodielectric material, connecting a series of short-circuit wires in parallel, each coated with a magnetodielectric material, reduces the antenna's resonant frequency towards lower frequencies by more than 30% compared to a single equivalent short-circuit wire coated with a magnetodielectric material. In other words, connecting a series of short-circuit wires in parallel, each coated with a magnetodielectric material, allows for better interaction between the antenna and the magnetodielectric material, and consequently, greater miniaturization efficiency for the antenna loaded by the magnetodielectric material.For a single short-circuit wire architecture, it is estimated that a volume of magneto-dielectric material 20 times greater would be required to reduce the antenna's resonant frequency towards lower frequencies by more than 30%, which would lead to substantial bulk, additional losses (related to the amount of additional material), and a greater antenna weight. Definitions

[0010] A "capacitive roof" is defined as a generally flat, electrically conductive surface, which may be rectangular or circular, for example, and which creates a capacitive effect with the ground plane. The term "flat" refers to the usual tolerances related to the experimental conditions under which the capacitive roof is formed, and not to perfect flatness in the geometric sense. A "feed probe" is defined as an antenna excitation probe, typically connected to the center conductor of a coaxial waveguide, and electrically connected to the capacitive roof. A "transmission line" is defined as an element enabling the guided propagation of electromagnetic waves (e.g., in the radio frequency range); the transmission line may be a coaxial feed cable or another waveguide. "Coated" means that the magnetodielectric material covers (in contact with) the entire free surface of the corresponding short-circuit wire.By "magneto-dielectric material" we mean a material having, at the operating wavelength of the antenna, a relative permittivity (εr) strictly greater than 1 and a relative permeability (µr) strictly greater than 1.

[0011] The antenna according to the invention may include one or more of the following characteristics.

[0012] According to one feature of the invention, the power supply probe is arranged at the center of the ground plane, and the short-circuit wire assembly comprises at least one pair of short-circuit wires arranged around the power supply probe with central symmetry.

[0013] Thus, one advantage obtained is to achieve symmetry for the antenna radiation and to reduce cross-polarization (" cross polarization (in English).

[0014] According to one feature of the invention, the short-circuit wire assembly comprises a number of short-circuit wires chosen such that, for a given amount of magnetodielectric material, the capacitive roof and the feed probe each have a maximum characteristic dimension such that the antenna is contained within a sphere with an electric radius less than or equal to λ / 2π, where λ is the operating wavelength of the antenna.

[0015] Thus, one advantage is obtaining a miniature antenna. By "miniature," we mean that the antenna is contained within a sphere (called a Wheeler sphere) with an electric radius less than or equal to λ / 2π. For example, in the case of a circular capacitive roof, the radius of the Wheeler sphere is the hypotenuse of the right triangle whose right angle is formed by the radius of the capacitive roof and the height of the antenna, and which must be less than or equal to λ / 2π.

[0016] According to one feature of the invention, the power supply probe is coated with the magneto-dielectric material.

[0017] Thus, one advantage provided is to increase the amount of magneto-dielectric material in the antenna, and thereby the efficiency of the antenna loading by the magneto-dielectric material to reduce its dimensions.

[0018] According to an example not part of the invention, the antenna includes a magnetodielectric layer extending between the ground plane and the capacitive roof so as to encapsulate each short-circuit wire and the feed probe.

[0019] Thus, one advantage provided is the simplicity of manufacturing the antenna.

[0020] According to one feature of the invention, the capacitive roof and the ground plane delimit a cylindrical volume, and the magneto-dielectric layer extends into all or part of the cylindrical volume.

[0021] The term "cylindrical" refers to the shape of a cylinder whose surface is generated by a family of straight lines in the same direction (generators). For example, the cross-section of the cylinder (i.e., the intersection of the surface with a plane perpendicular to the direction of the generators) can be circular or quadrangular (e.g., rectangular).

[0022] According to one feature of the invention, the magneto-dielectric material is chosen such that the relation µr > εr > 1 is verified at the operating wavelength of the antenna, where: µr is the relative permeability of the magneto-dielectric material, εr is the relative permittivity of the magneto-dielectric material.

[0023] Thus, one advantage provided by a magneto-dielectric material is to contribute to the miniaturization of the antenna by reducing the guided wavelength (λg) in the material according to the following formula: λ g = λ ε r μ , where λ is the operating wavelength of the antenna.

[0024] We are therefore looking for the highest possible product ε r µ r to promote the miniaturization of the antenna.

[0025] More specifically, the fact that µr > εr > 1 allows for a preference for a high µr over a high εr, because an excessively high εr generally leads to a strong concentration of the electromagnetic field within the antenna, with potential impedance matching problems, and thus resulting in a loss of electromagnetic power transfer (e.g., radio frequency) in free space. Furthermore, the monopolar wire-plate antenna interacts effectively with the magnetic properties of the material via the short-circuiting wires, giving it a specific magnetic behavior in the near field.

[0026] According to one feature of the invention, the magneto-dielectric material is chosen from Ni 0.5 Zn 0.3 Co 0.2 In 0.075 Fe 1.925 O 4 , Ni 0.76 Mn 0.24 -xCo x Fe 2 O 4 with x between 0 and 0.04, and Ni 0.61 Zn 0.35 Co 0.04 Fe 1.98 O 4 .

[0027] Thus, one advantage provided by such materials is to verify µr > εr > 1.

[0028] According to one feature of the invention, the short-circuit wires are separated from the feed probe by a distance chosen to adapt the input impedance of the antenna to 50 ohms.

[0029] Thus, one advantage provided is to maximize the transfer of electromagnetic power.

[0030] An example not forming part of the invention is a method for manufacturing a monopolar wire-plate antenna, comprising the following steps: a) provide a substrate, made of a magneto-dielectric material, and having first and second planar surfaces opposite each other; b) form a first interconnection hole through the substrate so as to obtain a power probe; c) form a set of interconnection holes through the substrate, arranged parallel around the first interconnection hole, so as to obtain a set of short-circuit wires; d) form a capacitive roof on the first surface of the substrate; e) form a ground plane on the second surface of the substrate; step e) being carried out so that the power probe is electrically isolated from the ground plane.

[0031] Thus, such a process makes it easy to manufacture a monopolar wire-plate antenna, from a substrate made of a magneto-dielectric material which encases both the feed probe and the set of short-circuit wires.

[0032] By "interconnection hole" (" via "In English), we mean a metallized hole allowing an electrical connection to be established between two levels of interconnection. Brief description of the drawings

[0033] Other features and advantages will become apparent in the detailed description of different embodiments of the invention, the description being accompanied by examples and references to the accompanying drawings. Figure 1 is a schematic perspective view of a monopolar wire-plate antenna, illustrating a set of shorting wires arranged parallel around the feed probe so that each shorting wire electrically connects the capacitive roof to the ground plane, the shorting wires not being coated with a magneto-dielectric material. Figure 2 is a schematic view analogous to the figure 1 , on an enlarged scale, where the short-circuit wires are coated with a magneto-dielectric material. Figure 3is a schematic perspective view of an antenna according to the invention, illustrating a first embodiment of the coating (individual coating of the short-circuit wires) by the magneto-dielectric material. Figure 4 is a schematic perspective view of an antenna according to the invention, illustrating a second embodiment of the coating (individual coating of the short-circuit wires and the feed probe) by the magneto-dielectric material. Figure 5 is a schematic perspective view of an antenna according to an example not part of the invention, illustrating a third embodiment of the encapsulation (overall encapsulation of the short-circuit wires and the feed probe) by the magneto-dielectric material. Figure 6 is a schematic top view (in transparency) of a magneto-dielectric substrate in which interconnection holes are formed so as to obtain a monopolar wire-plate antenna according to the invention. Figure 7 is a schematic cross-sectional view along axis AA of the magneto-dielectric substrate illustrated in the figure 6 .

[0034] It should be noted that the drawings described above are schematic and not to scale for the sake of readability. Detailed description of the implementation methods

[0035] Identical elements or elements performing the same function will bear the same references for the different embodiments, for the sake of simplification.

[0036] As illustrated in figures 1 to 4 One object of the invention is a monopolar wire-plate antenna, comprising: a ground plane 1; a capacitive roof 2; a power probe 3, electrically isolated from the ground plane 1, and extending between the ground plane 1 and the capacitive roof 2 so as to electrically power the capacitive roof 2, the power probe 3 being intended to be connected to a transmission line (not shown); a set of shorting wires 4, arranged parallel around the power probe 3 such that each shorting wire 4 electrically connects the capacitive roof 2 to the ground plane 1, each shorting wire 4 being coated with a magneto-dielectric material 5. Site plan

[0037] The ground plane 1 can be made of a metallic material, such as copper. The ground plane 1 can be circular in shape, as illustrated in figures 1 and 2 However, other shapes are possible for the site plan 1, such as a rectangular shape (illustrated in figures 3 to 5 ) or square.

[0038] The ground plane 1 can be formed on a dielectric substrate (not shown). An opening is made in the ground plane 1 (and where applicable in the dielectric substrate) to allow the passage of the power supply probe 3.

[0039] It is possible to equip ground plane 1 with components, for example a direct current (DC) circuit, a radio frequency (RF) circuit or a power supply battery, without altering the operation of the antenna. Capacitive roof

[0040] The capacitive roof 2 comprises a flat, electrically conductive surface, preferably metallic. Advantageously, the capacitive roof 2 extends parallel to the ground plane 1. The term "parallel" is understood within the usual tolerances related to the experimental conditions for forming the antenna elements, and not as perfect parallelism in the mathematical (geometric) sense. However, the capacitive roof 2 may be inclined relative to the ground plane 1 when a capacitive effect is created with the ground plane 1. The angle of inclination formed between the capacitive roof 2 and the ground plane 1 is preferably less than or equal to 30°.

[0041] The capacitive roof 2 thus creates a capacitive effect with the ground plane 1 allowing the antenna resonance frequency to be lowered, or the length of the monopole (i.e. the feed probe 3) to be reduced for a given resonance frequency.

[0042] The capacitive roof 2 is preferably circular in shape, for example with a radius on the order of λ / 11, where λ is the operating wavelength of the antenna. As a non-limiting example, in the very high frequency band (VHF for " Very High Frequency "in English), at 135 MHz, the radius of the capacitive roof 2 is on the order of 200 mm.

[0043] However, other shapes are conceivable for the capacitive roof 2, such as a square, rectangular, elliptical, or even star shape. Power supply probe

[0044] The power supply probe 3 is not in contact with the ground plane 1 so as to be electrically isolated from the ground plane 1. As a non-limiting example, the power supply probe 3 can be made to the ground plane 1 by means of a spacer (not shown) which is not electrically conductive.

[0045] The feed probe 3 advantageously extends perpendicularly to the ground plane 1, and therefore perpendicularly to the capacitive roof 2, in order to eliminate the perturbation of the antenna's radiation pattern by the ground plane 1. The feed probe 3 can be connected to a metallic center core 30 of a coaxial waveguide. The feed probe 3 extends between the ground plane 1 and the capacitive roof 2, for example, over a height on the order of λ / 11, where λ is the operating wavelength of the antenna. By way of non-limiting example, in the very high frequency band (VHF for " Very High Frequency " in English), at 135 MHz, the height of the feed probe 3 (between the ground plane 1 and the capacitive roof 2) is on the order of 200 mm.

[0046] The power supply probe 3 is preferably arranged in the center of the ground plane 1, as illustrated in figures 1 to 5The feed probe 3 is advantageously coated with the magneto-dielectric material 5, as illustrated in Figures 4 and 5 .

[0047] The feed probe 3 is intended to be connected to a transmission line enabling the guided propagation of electromagnetic waves (e.g. in the radio frequency domain), the transmission line being a coaxial feed cable or another waveguide. Short circuit wire assembly

[0048] As illustrated in figures 1 to 5 , the set of short-circuit wires 4, preferably metallic, advantageously extends perpendicularly to the ground plane 1, and therefore perpendicularly to the capacitive roof 2. The short-circuit wires 4 of the set are parallel to each other.

[0049] When the feed probe 3 is arranged at the center of the ground plane 1, the short-circuit wire assembly 4 advantageously includes at least one pair of short-circuit wires 4 arranged around the feed probe 3 with central symmetry. The short-circuit wire assembly 4 includes a number (denoted N) of short-circuit wires 4 chosen such that, for a given amount of magnetodielectric material 5, the capacitive roof 2 and the feed probe 3 each have a maximum characteristic dimension such that the antenna is contained within a sphere with an electric radius less than or equal to λ / 2π, where λ is the operating wavelength of the antenna.

[0050] If we consider that each short-circuit wire 4 has a radius, denoted a, and that each short-circuit wire 4 is separated by a distance, denoted b, from the power supply probe 3, the inventors have shown that the set of short-circuit wires 4 is equivalent to a single wire having a radius (called equivalent radius R eq ) satisfying: R eq = ab N − 1 1 / N , N ∈ 1 6

[0051] The inventors postulate that this formula works regardless of the number of short-circuit wires 4 separated by a distance, denoted b, from the power supply probe 3, that is to say that the set of short-circuit wires 4 is equivalent to a single wire having an equivalent radius R eq satisfying: R eq = ab N − 1 1 / N , N ∈ ℕ *

[0052] The inventors found that, with equal quantities of magneto-dielectric material 5, connecting in parallel a set of N short-circuit wires 4, each coated with a magneto-dielectric material 5, reduces the antenna's resonant frequency towards lower frequencies by more than 30% compared to a single short-circuit wire 4, coated with the magneto-dielectric material 5, and having an equivalent radius Req calculated using the preceding formulas. In other words, connecting in parallel a set of N short-circuit wires 4, each coated with a magneto-dielectric material 5, allows for more efficient loading of the antenna by the magneto-dielectric material 5.For a single short-circuit wire architecture 4, it is estimated that a volume of magneto-dielectric material 20 times greater would be required to reduce the antenna's resonant frequency towards lower frequencies by more than 30%, which would lead to substantial bulk, additional losses (related to the amount of additional material), and a greater antenna weight.

[0053] By way of non-limiting examples, as illustrated in figures 1 and 2 The short-circuit wire assembly 4 may comprise three pairs of short-circuit wires 4 arranged around the power supply probe 3 with central symmetry. Each short-circuit wire 4 may have a radius (a) of approximately 2.4 mm. Each pair of short-circuit wires 4 may be separated by a distance (b) of approximately 80 mm on either side of the power supply probe 3 with central symmetry.

[0054] The short-circuit wires 4 are advantageously separated from the feed probe 3 by a distance chosen to adapt the input impedance of the antenna to 50 ohms.

[0055] As illustrated in figures 3 to 5 It should be noted that the set of short-circuit wires 4 may contain an odd number of short-circuit wires 4. However, this can lead to an asymmetry in the antenna radiation and the appearance of cross-polarization (“ cross (in English). Magnetodielectric material

[0056] The magneto-dielectric material 5 is advantageously chosen so that the relation µr > εr > 1 is verified at the operating wavelength of the antenna, where: µr is the relative permeability of the magneto-dielectric material 5, εr is the relative permittivity of the magneto-dielectric material 5.

[0057] The magneto-dielectric material 5 is advantageously chosen from Ni 0.5 Zn 0.3 Co 0.2 In 0.075 Fe 1.925 O 4 , Ni 0.76 Mn 0.24-x Co x Fe 2 O 4 with x between 0 and 0.04, and Ni 0.61 Zn 0.35 Co 0.04 Fe 1.98 O 4 .

[0058] As illustrated in the example not forming part of the invention in the figure 5 The antenna advantageously includes a magnetodielectric layer 5 (made of the magnetodielectric material) extending between the ground plane 1 and the capacitive roof 2 so as to encase each short-circuit wire 4 and the feed probe 3. The capacitive roof 2 and the ground plane 1 delimit a cylindrical volume, and the magnetodielectric layer 5 extends into all or part of the cylindrical volume.

[0059] As illustrated in figures 3 and 4 , the magneto-dielectric material 5 can also be made in the form of a hollow cylinder inside which extends a short-circuit wire 4 or the supply probe 3. Manufacturing process

[0060] As illustrated in figures 6 and 7 An example not forming part of the invention is a method for manufacturing a monopolar wire-plate antenna, comprising the following steps: a) provide a substrate 6, made of a magneto-dielectric material 5, and having first and second plane surfaces 60, 61 opposite; b) form a first interconnecting hole 7a through the substrate 6 so as to obtain a power probe 3; c) form a set of interconnecting holes 7b through the substrate 6, arranged parallel around the first interconnecting hole 7a, so as to obtain a set of short-circuit wires 4; d) form a capacitive roof 2 on the first surface 60 of the substrate 6; e) form a ground plane 1 on the second surface 61 of the substrate 6; step e) being carried out so that the power probe 3 is electrically isolated from the ground plane 1.

[0061] The interconnection holes 7a, 7b can be metallized by sputtering (“ sputtering (in English).

[0062] At the end of step e), the short-circuit wire assembly 4 and the power supply probe 3 are coated with the magneto-dielectric material 5 of the substrate 6.

[0063] The scope of protection of the invention is determined solely by the claims.

Claims

1. Monopole wire-plate antenna, comprising: - a ground plane (1); - a capacitive roof (2); - a probe feed (3, 30), which is electrically insulated from the ground plane (1), and which extends between the ground plane (1) and the capacitive roof (2) so as to electrically feed the capacitive roof (2), the probe feed (3, 30) being intended to be connected to a transmission line; - a set of shorting wires (4), which are arranged in parallel around the probe feed (3, 30) so that each shorting wire (4) electrically connects the capacitive roof (2) to the ground plane (1), each shorting wire (4) being coated in a magneto-dielectric material (5) taking the form of a hollow cylinder through the interior of which the shorting wire (4) extends.

2. Antenna according to Claim 1, wherein the probe feed (3, 30) is arranged at the centre of the ground plane (1), and the set of shorting wires (4) comprises at least one pair of shorting wires (4) that is arranged around the probe feed (3, 30) in such a way as to exhibit central symmetry.

3. Antenna according to Claim 1 or 2, wherein the set of shorting wires (4) contains a number of shorting wires (4) chosen such that, for a given amount of magneto-dielectric material (5), the capacitive roof (2) and the probe feed (3, 30) each have a maximum characteristic dimension such that the antenna is contained in a sphere with an electric radius smaller than or equal to λ / 2π, where λ is the wavelength of operation of the antenna.

4. Antenna according to any of Claims 1 to 3, wherein the probe feed (3, 30) is coated in the magneto-dielectric material (5).

5. Antenna according to any of Claims 1 to 4, wherein the magneto-dielectric material (5) is chosen such that the relationship µr > εr > 1 is respected at the wavelength of operation of the antenna, where: - µr is the relative permeability of the magneto-dielectric material (5); - εr is the relative permittivity of the magneto-dielectric material (5).

6. Antenna according to any of Claims 1 to 5, wherein the magneto-dielectric material (5) is chosen from Ni0.5Zn0.3CO0.2In0.075Fe1.925O4, Ni0.76Mn0.24-xCoxFe2O4 with x between 0 and 0.04, and Ni0.61Zn0.35Co0.04Fe1.98O4.

7. Antenna according to any of Claims 1 to 6, wherein the shorting wires (4) are separated from the probe feed (3, 30) by a distance chosen to match the input impedance of the antenna to 50 ohms.

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