WO2014147097A1

WO2014147097A1 - Radio antenna and radio device

Info

Publication number: WO2014147097A1
Application number: PCT/EP2014/055456
Authority: WO
Inventors: Yasmina Layouni; Dhaou BOUCHOUICHA
Original assignee: Université Lyon 1 Claude Bernard; Institut National Des Sciences Appliquées De Lyon; Ecole Centrale De Lyon; Centre National De La Recherche Scientifique
Priority date: 2013-03-19
Filing date: 2014-03-18
Publication date: 2014-09-25
Also published as: FR3003696A1; FR3003696B1

Abstract

The invention concerns a radio antenna, comprising - a dielectric substrate (8); - an electrically conductive track (10), of width W, extending longitudinally between two terminal ends (20, 22), only within a strip (24) of width L delimited, on one side, by an outer limit (26) and, on the other side, by an inner limit (28), said limits each forming a closed loop; and in which: - the track defines a periodic "U"- or "V"-shaped pattern (30), repeated N times, and comprising strands of track, separated from each other by a spacing distance S and forming side bars of the "U" or "V", -L is less than 5 mm; -N is greater than 3; -W is greater than or equal to 0.15 mm; -S is greater than or equal to 0.01 mm.

Description

RADIO ANTENNA AND RADIO DEVICE

[Ooi] The invention relates to a radio antenna. The invention also relates to a radio device comprising this radio antenna.

[002] Flat radio antennae are known having an electrical conductor extending on a generally flat surface forming meanders. This meandering arrangement makes it possible to increase the length of the antenna (on which the antenna resonance frequency depends in particular) while minimizing the area occupied by the antenna. These antennas are typically used in RFID applications ("Radio-Frequency Identification Device" in English), in particular to electrically power miniaturized passive electronic circuits.

[003] However, these antennas have the disadvantage of having electromagnetic properties that are unsatisfactory for certain energy harvesting applications ("energy harvesting" in English) or contactless communication ("Radio Frequency Identification Device"). English language). For example, this antenna has a negative antenna gain for a frequency of 2.4 GHz. It is therefore necessary to associate this antenna with a signal amplifier received or transmitted. Thus, the decrease in the size of the antenna is partly offset by the need to associate an amplifier all the more bulky that the amplification to achieve is important. In addition, the use of such an amplifier tends to increase the power consumption of the antenna, which is unacceptable.

[004] The inventors know personally patent application US-6147655-A (BRUCE B. ROESNER) which describes an example of such an antenna.

However, this document is not relevant because it does not make it possible to obtain an antenna having a positive antenna gain at the desired frequency. On the contrary, the inventors have carried out numerical simulations of such an antenna, which conclude that it has a negative antenna gain.

[005] There is therefore a need for a radio antenna having a ratio of length to area which is high, without requiring significant amplification of the transmitted or received signal.

[006] The invention therefore relates to a radio antenna according to claim 1.

[007] Surprisingly, it has been discovered that with this choice of values of L, N, S and W above, the antenna has a positive antenna gain for high frequencies, that is to say say greater than or equal to 300MHz or 500MHz.

[008] Embodiments of the invention may have one or more of the features of dependent claims 2 to 10.

[009] These embodiments also have the following characteristics: the fact that the inner limit has at least three symmetries of rotation makes it possible to increase the gain of the antenna;

the choice of values of W and S between 0.2 mm and 0.5 mm makes it possible to improve the characteristics of the antenna and, in particular, to obtain a large bandwidth; - By attaching the antenna to the parabolic reflector, the antenna gain of the radio device thus formed is twice as great as the antenna gain of the antenna alone.

[Ooi o] In another aspect, the invention also relates to a radio device according to claim 11.

The invention will be better understood on reading the description which follows, given solely by way of nonlimiting example and with reference to the drawings in which:

FIG 1 is a schematic illustration of a radio device comprising a radio antenna associated with a parabolic reflector;

FIG. 2 is a schematic illustration, in a view from above, of the radio antenna of FIG. 1;

FIG. 3 is a schematic illustration of the detail of a periodic pattern of the antenna of FIG. 2;

FIG. 4 is a sectional view of a portion of the pattern of FIG. 3;

FIG. 5 is a graphical representation, as a function of frequency, of the respective electromagnetic reflection coefficients Su of an antenna according to the state of the art and of the antenna of FIG. 2;

FIGS. 6 to 10 show schematically other embodiments of the radio antenna of FIG. 2;

FIG. 11 is a graphical representation, as a function of frequency, of the respective reflection coefficients Su of the antennas of FIGS. 2 and 6 to 8;

FIGS. 12 and 13 are schematic illustrations of other embodiments of the periodic pattern of any of the antennas of FIGS. 2 or 6 to 10.

In these figures, the same references are used to designate the same elements.

In the following description, the features and functions well known to those skilled in the art are not described in detail.

FIG. 1 represents a radioelectric device 2. This device 2 comprises:

a planar radio microstrip antenna ("planar microstrip antenna" in English), and

a parabolic reflector 6.

The antenna 4 comprises:

a dielectric substrate 8, and an electrically conductive track 10 deposited on a face 12 of the substrate 8 and forming a geometric center antenna circuit O.

The substrate 8 has a static relative dielectric permittivity greater than or equal to 2 or 3 or 3.5 and, preferably, greater than or equal to 4. This permittivity is here equal to 4.4. This substrate 8 comprises, for example, the composite material based on epoxy resin known under the name "FR4". This substrate 8 here has a flat shape. In what follows, the face 12 is plane and defines a plane, called "plane of the substrate", which extends in a horizontal direction. This substrate has a thickness h, measured in a direction perpendicular to the substrate 8, here equal to 0.8 mm.

The track 10 is here a differential transmission line ("coplanar strip" in English) made of an electrically conductive material, such as copper. This track 10 here has a constant width W, defined as being the smallest track width, and measured parallel to the plane of the substrate. This width W is here greater than or equal to 0.15mm or 0.2mm.

The reflector 6 is configured to reflect incident electromagnetic radiation and to focus this radiation in a focus point, or focus. Here, this reflector 6 is a paraboloid of revolution, of diameter D and depth d. This reflector 6 thus has a circular edge which defines an opening. The diameter D is the diameter of this circular edge. Depth d is measured along the axis of rotation of this paraboloid of revolution, between the origin of this paraboloid and the geometric center of the surface delimited by the circular edge. This diameter D is here greater than or equal to 3cm and less than or equal to 20cm. Preferably, this diameter D is equal to 6cm. The depth d here is less than or equal to 0.8 * D or 0.6 * D and is greater than or equal to 0.1 * D. This depth d is here equal to 0.5 * D, ie 3cm. The reflector 6 is attached to a rear face of the substrate 8 (here opposite to the face 12) and is positioned so that the focusing point of the reflector 6 is included in the plane of the substrate. To do this, here, the substrate 8 completely covers the opening of the reflector 6 and is in contact with the entire edge of the reflector 6. The distance separating the center O from the focusing point is advantageously less than or equal to 17.5 mm or 10mm and preferably less than or equal to 3mm or 2mm. Here, this point of focus coincides with the center O. This reflector 6 is here formed of a rigid polymer coated with a layer of a metallic material.

The combination of the reflector 6 to the antenna 4 improves the electromagnetic properties of the antenna 4. The configuration of the reflector 6 and its arrangement relative to the antenna 4 can increase the total gain of the antenna. device 2.

Figure 2 shows in more detail the antenna 4 and the track 10. The track 10 extends longitudinally on the face 12, between two terminal ends 20 and 22. The track 10 here does not cross with it -even. These ends 20 and 22 are able to be electrically connected to an electrical contact. More specifically, the track 10 extends in a plane parallel to the plane of the substrate, only inside a band 24 of width L. This band 24 is bounded on one side by an outer limit 26 and, the other side, by an inner limit 28. Each of these boundaries 26 and 28 forms a closed loop. The width L is here measured in the plane of the substrate, as being the smallest distance separating the boundaries 26 and 28.

The limit 28 has the shape of an ellipse or a polygon inscribed in a circle and whose geometric center is the center O. It is considered here that a circle can be a degenerate case of an ellipse. However, we do not consider here that a segment or point is a degenerate case of an ellipse. A shape factor for this ellipse or inscribed polygon is defined as the ratio of the length to the width of the smaller area rectangle containing the entire limit 28. This form factor is greater than or equal to 1. This form factor is furthermore less than 1, 43 or 1, 4 and, preferably, less than 1, 2. In this description, the geometric center O is both the geometric center of the limit 28 and the geometric center of the antenna circuit formed by the winding of the track 10.

Advantageously, the limit 28 has at least three symmetries of rotation with respect to a vertical axis passing through the center O.

The limit 26 is deduced from the limit 28, by means of a mathematical operation homothety center O and report k, where k is a number strictly greater than 1. The value of k is chosen so that the band 24 has the width L. This width L is here less than or equal to 5mm.

In this example, the limits 26 and 28 are squares of center O. These limits thus comprise four symmetries of rotation.

Inside the band 24, the track 10 describes a plurality of patterns, meander-shaped. For example, the same pattern 30 is repeated N times, where N is an integer greater than or equal to three. For example, N is greater than or equal to 10 or 15, or 20. Here, this number N is equal to 36. To simplify FIG. 2, however, the antenna 4 illustrated does not include 36 copies of the pattern 30.

In this example, the copies of the pattern are evenly distributed inside the band 24 and are in direct contact with the limits 26 and 28. These patterns fill most of the band 24, the except for zones 29 located at the corners of the strip, where no pattern is in contact with the limit 26. Here, the strip 24 comprises four such areas, located in the right angles of the limit 26. To facilitate the reading of the Figure 2 and the following figures, the copies of the pattern are not always drawn in direct contact with the limits 26 and 28.

FIG. 3 represents in more detail such a pattern 30. This pattern here has a "U" shape and comprises first 40, second 42 and third 44 runway strands 10. The strands 40 and 42 form lateral bars of the "U". For this purpose, these strands 40 and 42 extend, face to face with respect to each other, along respective trajectories having at most one point of inflection, between inner and outer ends. The respective inner ends of the strands 40 and 42 are located on the boundary 28. The respective outer ends of the strands 40 and 42 are located on the boundary 26. The strands 40 and 42 are separated from each other and are spaced apart from each other. A spacing distance S. This distance S is defined as the smallest distance separating the edges of these strands 40 and 42 and being measured parallel to the plane of the substrate. Here, this distance S is measured between points of intersection of the limit 26 with two straight lines 45 and 47. These lines 45 and 47 are tangent, respectively, to the strands 40 and 42 at respective points of these strands located:

on an inner side of this strand, and

at the intersection of this strand with a line 46. This line 46 is equidistant at the boundaries 26 and 28. When the line 46 is not rectilinear, the distance S is measured along the trajectory of the line 46 between edges of these strands.

The inner side of the strands 40 and 42 corresponds to the side of this strand which extends inside the pattern 30.

In this example, the strands 40 and 42 are parallel to each other and extend perpendicularly to the boundaries 26 and 28. The pattern 30 thus delimits here a rectilinear crenel. The distance S is measured in a direction parallel to the line 46. This distance S is greater than or equal to 0.001 mm or 0.002 mm or 0.005 mm or 0.1 mm or 0.2 mm or 0.5 mm.

The strand 44 connects directly to each other the inner ends of the strands 40 and 42 and extends along the boundary 28, thus forming the bottom of the "U".

The pattern 30 is here connected to other copies of the pattern, located immediately upstream or downstream, through fourth strands 48 of the track 10. These strands 48 directly connect the outer end of a strand 42 of an upstream copy of the pattern at the outer end of the strand 40 of the copy of the pattern 30 immediately downstream. The strand 48 extends along the boundary 26. Each of the copies of this pattern 30, except for the copies which are directly connected to the ends 20 and 22, is thus connected to the immediately adjacent copies of the pattern 30.

Figure 4 shows a sectional view of the pattern 30, in a vertical plane containing the line 46. The track 10 has a height h 'greater than or equal to 2μηη. Advantageously, this height h 'is greater than or equal to 4μηη or 8μηη or 10μηη. This height h 'is advantageously less than or equal to 40μηη or 35μηη. Here, this height h 'is between 17μηη and 34μηη. This height h 'is measured in a vertical direction. The height h 'is typically constant over the entire length of the track 10.

In this example, the antenna 4 has the following characteristics:

the outer limit 26 has a side length equal to 22.7 mm; the distance S is equal to 0.3 mm;

the width W is equal to 0.3 mm;

the number N is equal to 48;

the width L is equal to 3 mm.

FIG. 5 shows the evolution, as a function of the frequency of a radio signal, of the respective reflection coefficients Su of this antenna 4 (curve 60) and of the known radio antenna described in the US patent application. -6147655-A (BRUCE B. ROESNER) previously mentioned (curve 62), obtained by means of numerical simulations, carried out using the Ansoft software, distributed by the company "Ansys". More precisely, these simulations were carried out with the "HFSS" version 14 and "Optimetrics" modules of this software.

In this description, the reflection coefficient Su is defined for a radio antenna as follows: | Sn | ² = PJP _r ,

where P. is the incident power of an electromagnetic signal received by the antenna and P _r power reflected by the antenna in response to this received electromagnetic signal. The antenna 4 has a resonance frequency equal to 2.44GHz, with a bandwidth at -10dB equal to 1 10MHz and an antenna gain equal to 1, 57dBi. In contrast, the known antenna does not have resonance in this frequency band and, in particular, not in the band from 2.3GHz to 2.8GHz. In fact, this known antenna has no adaptation, and therefore can not have a positive antenna gain. This known antenna has been simulated with the following characteristics, as described in the aforementioned patent application: L = 4mm, S = W = 0.05mm, N = 92 and a total track length of 382mm.

The inventors have also carried out additional tests illustrating the influence of the parameters L, W, S and N on the properties of the antenna 4. Unless otherwise stated, in the following description, the electromagnetic properties of each of the antennas were obtained by digital simulation with the same software.

The following table summarizes the influence of the number N of patterns on the performance of the antenna 4, with the characteristics L = 3mm and S = W = 0.3mm:

It is noted that the antenna gain has a positive value for values of N greater than or equal to 20. Other simulations, not illustrated here, show that we obtain a positive antenna gain for values N greater than three. For example, for N = 7 and with the values of L, S and W previously selected, simulations show that we obtain an antenna gain equal to 1. 59dBi for a resonance frequency of 7.75GHz. On the other hand, it is observed that the resonant frequency as well as the bandwidth at -10 dB decrease as the value of N increases. Also, when it is desired to obtain a resonance frequency around 2.45GHz, the value of N is preferably chosen to be greater than or equal to 35 and less than or equal to 70, for the values of S, W and L given.

The following table summarizes the influence of the width L on the performance of the antenna 4, with the characteristics N = 30 and S = W = 0.3mm:

There is thus a significant degradation of the performance of the antenna for L values strictly greater than 5mm. In particular, the antenna gain becomes negative for L values greater than or equal to 7 mm

The following table summarizes the influence of the width W on the performance of the antenna 4, with the characteristics L = 3mm, N = 24 and S = W:

There is thus a degradation of the performance of the antenna when W is strictly less than 0.2mm, in particular the antenna gain, which then has a negative value. On the other hand, it is observed that the bandwidth at -10 dB decreases when the value of W increases beyond a certain value, here 0.6 mm. Also, the value of W will preferably be greater than or equal to 0.2 mm and less than or equal to 0.5 mm if it is desired to obtain, in addition to a positive antenna gain, a wide bandwidth at -10 dB. .

The following table summarizes the influence of the distance S on the performance of the antenna 4, with the characteristics L = 3mm, N = 24 and W = 0.4mm:

S (mm) 0.1 0.2 0.3 0.4 0.5 0.6

Resonance frequency (GHz) 3.24 2.74 2.38 2.16 1, 98 1, 84

Su (dB) at the frequency of -22.4 -26.3 -32.6 -28.23 -28.41 -22.3 resonance

Bandwidth at -10dB (MHz) 200 150 120 105 98 90 Antenna gain (dBi) 1, 85 1, 89 1, 88 1, 91 1, 92 1, 94

There are thus satisfactory properties when S is greater than or equal to 0.1 mm, such as the antenna gain, which then has a positive value. On the other hand, we observe that the bandwidth at -10 dB decreases as the value of S increases. Also, the value of S will preferably be greater than or equal to 0.2 mm and less than or equal to 0.5 mm if it is desired to obtain, in addition to a positive antenna gain, a wide bandwidth at -10 dB. . Other simulations, whose results are summarized in the table below, show that the antenna still has satisfactory properties when S is greater than or equal to 0.01 mm. These simulations were performed with the following characteristics: L = 3mm, W = 0.3mm, N = 64:

Thus, with the dimensions and values of L, W, N and S chosen, the antenna 4 has improved electromagnetic properties and, in particular, a positive antenna gain. The antenna 4 is thus able to operate, for example, in an electromagnetic energy recovery device. In this example, the antenna 4 is advantageously able to be used for applications in the frequency band ISM ("Industrial, Scientific, Medical" in English) as defined by the standard NF EN 5501 1.

Figure 6 shows an antenna 70 adapted to be used instead of the antenna 4. To simplify Figure 6 and following, the substrate 8 is not illustrated. This antenna 70 is identical to the antenna 4, except that the square band 24 is replaced by a band 72 of triangular shape. For this purpose, the boundaries 26 and 28 are replaced, respectively, by limits 74 and 76 which have an equilateral triangle shape of center O. These limits thus have three symmetries of rotation. The dimensions of the substrate of this antenna are adapted to take account of the change in shape of the strip, so that this substrate forms a square of 27mm side in which the strip 72 is inscribed. The values of L, W, S and N are unchanged compared to those of the antenna 4. This antenna thus has a resonance frequency equal to 2.39GHz, a bandwidth at -10dB equal to 100MHz and a gain of antenna equal to 1, 318dBi. Again, to simplify Figure 6 and following, the number of copies of the illustrated pattern is different from N.

Figure 7 shows an antenna 90 adapted to be used instead of the antenna 4. This antenna 90 is identical to the antenna 4, except that the square band 24 is replaced by a band 92 of circular shape . For this purpose, the limits 26 and 28 are replaced, respectively, by limits 94 and 96 which each describe a circle of center O. These limits here have an infinity of rotation symmetries. In this case, the strands 40 and 42 of each of the patterns of the track 10 are no longer parallel to each other, but are aligned along the radii of the boundaries 26 or 28. The dimensions of the substrate of this antenna are adapted to take account of of the shape change of the band, so that the face 12 forms a square of 22mm side in which the band 92 is inscribed. The values of L, W, S and N are unchanged from those of the antenna 4. This antenna thus has a resonance frequency equal to 2.97GHz, a bandwidth at -10dB equal to 120MHz and a gain of antenna equal to 1, 577dBi.

FIG. 8 represents an antenna 110 suitable for use in place of the antenna 4. This antenna 1 10 is identical to the antenna 4, except that the square band 24 is replaced by a band 1 12 of hexagonal shape. For this purpose, the limits 26 and 28 are replaced, respectively, by limits 114 and 1 16 which each form a regular hexagon of center O. These limits here have six symmetries of rotation. The dimensions of the substrate of this antenna are adapted to take account of the change in shape of the strip, so that the latter forms a square of 27mm side in which the band 1 12 is inscribed. The values of L, W, S and N are unchanged with respect to those of the antenna 4. This antenna thus has a resonance frequency equal to 2.39GHz, a bandwidth at -10dB equal to 1 10MHz and a gain of antenna equal to 1. 599dBi.

FIG. 9 represents an antenna 120 suitable for use in place of the antenna 4. This antenna 120 is identical to the antenna 4, except that the square band 24 is replaced by a band 122 of rectangular shape. . For this purpose, the boundaries 26 and 28 are replaced, respectively, by limits 124 and 126 which have a rectangular shape, of center O, and whose form factor is less than 1, 4. These limits present here two symmetries of rotation. The values of L, W, S are unchanged from those of the antenna 4. The value of N is chosen equal to 48. This antenna thus has a resonance frequency equal to 2.4 GHz and an equal antenna gain at 1, 25dBi.

Figure 10 shows an antenna 130 adapted to be used instead of the antenna 4. To simplify Figure 10, the substrate 8 is not illustrated. This antenna 130 is identical to the antenna 120, except that at each corner, in the zones 29, the strand 48 forms additional patterns. These additional patterns here have the same shape as the pattern 30 except that their lower ends are not on the boundary 126. These additional units are for example formed by strands 48. These additional units are here N 'in number all over the world. Antenna 130. To simplify this figure, the position of the ends 20 and 22 is modified. This antenna 130 has properties close to the antenna 4, with the following parameters: L = 3mm, S = W = 0.3mm, N + N '= 48. This antenna 130 has in particular a resonance frequency equal to 2, 45 GHz and a positive antenna gain at this frequency. FIG. 11 represents the evolution, as a function of the frequency of a radio signal, of the respective Su coefficients of the antennas 4 (curve 150), 70 (curve 152), 90 (curve 154) and 110 (curve 156 ).

Figure 12 shows a pattern 170 adapted to replace the pattern 30. This pattern here has a shape "V". For this purpose, the strands 40 and 42 are replaced, respectively, by strands 172 and 174 of track 10, forming lateral bars of the "V". These strands 172 and 174 are identical, respectively, to the strands 40 and 42, except that they are not parallel to each other and do not extend perpendicular to the boundaries 26 and 28. In addition, these strands 172 and 174 are straight segments and are connected directly to each other. More specifically, the inner ends of the strands 170 and 172 merge with each other and are located on the boundary 28. The outer ends of the strands 170 and 172 are located on the boundary 26. For these strands 172 and 174, respectively, tangent lines 176 and 178, in the same way as for the strands 40 and 42. The outer ends of each copy of the pattern are here confused with the outer ends of the immediately adjacent copies of this pattern located upstream or downstream. downstream, with the exception of the patterns that are directly connected to the ends 20 and 22. Thus, the pattern 170 does not include the strands 46 and 50. The pattern 170 thus has a triangular shape. For example, an antenna identical to the antenna 4 except that the pattern 170 is used in place of the pattern 30 has a resonance frequency of 2.45GHz and an antenna gain of 2.33dBi.

13 shows a pattern 190 capable of replacing the pattern 30. This pattern 190 is identical to the pattern 170, except that the strands 172 and 174 are replaced, respectively, by strands 192 and 194 of track 10. These strands 192 and 194 are, respectively, identical to the strands 172 and 174, except that they do not extend straight, but have a single inflection point, so that the pattern 190 has a substantially sinusoidal shape. For example, an antenna identical to the antenna 4 except that the pattern 190 is used in place of the pattern 30 has a resonance frequency of 1.8GHz.

Many other embodiments are possible.

The reflector 6 may be omitted. The reflector 6 can be made differently. For example, the reflector is made of metallic material. The values of D and / or d may be chosen differently, depending in particular on the dimensions of the antenna 2.

The substrate 8 may have a thickness h and / or static relative permittivity different from those described. The substrate 8 may be formed of a flexible material; in this case, the face 12 is not flat. The plane of the substrate then has a non-zero curvature, so as to match the curvature of the face 12. The substrate 8 may comprise a different material, such as the material marketed under the name "Kapton" by the company DuPont, or a polymer to liquid crystals, or paper. In this case, the height h 'of the track 10 is different. For example, when the substrate 8 is made by means of a Kapton film, the height h is equal to 125μηη, and h 'is then advantageously between 4μηη and 10μηη.

The strand 44 may be located on the outer limit 26 instead of on the inner limit 28 and connect the outer ends of the strands 40 and 42. In this case, the strand 50 is placed on the inner limit 28 and connects the inner ends of the strands 40 and 42. In this case, the distance S is defined with reference to the limit 28 rather than the limit 26.

The pattern 170 may be used in place of the pattern 30 in any of the antennas 4, 70, 90, 1 10, 120 and 130. The same applies to the pattern 190.

The periodic pattern may be different from the patterns 30, 170 and 190 and may have many shape adaptations, provided that it still has the following properties:

the pattern comprises the first and second track strands, separated from one another by a spacing distance S and extending along respective trajectories having at most one point of inflection;

the first and second strands extend between the outer and inner ends respectively placed on the outer and inner limits of the strip;

each copy of the pattern is connected to the outer ends of other copies of this pattern located immediately upstream and downstream in the same band, with the exception of the copies which are directly connected to the terminal ends of the track.

The antennas may have a resonance frequency included outside the ISM frequency band. For example, this resonance frequency is included in the GSM-900 or GSM-1800 frequency bands. The total length of the track 10 must therefore be adapted to correspond to the desired resonance frequency. In this case, the values of N may be different from those described.

The antenna 4 may have a band shape different from the band 24 or any of the strips 72, 92, 1 12, 122. For example, the band has an ellipse shape, the foci of which are located equidistant and on both sides of the center O.

Alternatively, at least two copies of the device 2 are networked to form an antenna array adapted to receive the same radio signal.

Claims

1. Radio antenna (4), comprising:

a dielectric substrate (8) having a static relative permittivity greater than or equal to 2, this substrate having a face (12);

an electrically conductive track (10), of width W, made on the face of the substrate, extending longitudinally between two end ends (20, 22), only inside a band (24) of width L bounded on one side by an outer boundary (26) and on the other side by an inner boundary (28), these boundaries each forming a closed loop and the outer boundary being further from a center O the inner boundary, where the center O is the geometric center of the surface delimited by the inner boundary, the inner boundary forming an ellipse or a polygon inscribed in a circle and having a form factor of between 1 and 1, 43, that factor of form being defined as being the ratio of the length to the width of the smaller-area rectangle wholly containing the inner limit and in which:

the track draws a periodic pattern (30) repeated N times and having a "U" or "V" shape, this pattern being composed of:

First (40) and second (42) track strands, separated from each other by a spacing distance S, said first and second track strands forming lateral bars of the "U" or "V" Said first and second strands extending along respective trajectories having at most one point of inflection, the so-called inner ends of the first and second strands being located on the inner boundary and the so-called outer ends thereof. first and second strands being on the outer boundary, the spacing distance S being measured between intersections of the outer boundary (26) with first (45) and second (47) straight lines, these first and second straight lines being respectively tangent to the first and second strands at points of intersection of said strands with a line (46) equidistant to the inner and outer boundaries, the inner ends being merged only in the case of the "V-shape" », And

• only in the case of the "U-shape", a third strand (44) extending along the inner boundary, directly connecting the inner ends of the first and second strands, to form the bottom of the "U" ;

the outer ends of each copy of the periodic pattern are connected to the outer ends of other examples of this periodic pattern located, respectively, immediately upstream and downstream in the same band, except for those which are directly connected to the terminal ends of the runway; this antenna being characterized in that:

the width L of the strip is less than 5 mm;

the number N of units is greater than 3;

the width W is greater than or equal to 0.15 mm;

the spacing distance S is greater than or equal to 0.01 mm.

2. Antenna according to any one of the preceding claims, wherein the inner boundary (28) has at least three symmetries of rotation with respect to an axis passing through the center O and being perpendicular to the plane of the face of the substrate.

An antenna according to any one of the preceding claims, wherein the outer ends of each copy of the periodic pattern are connected to the outer ends of other copies of that pattern by means of a fourth strand (48) extending along the outer limit (26).

4. Antenna according to any one of the preceding claims, wherein the first and second strands are rectilinear and each extend perpendicular to the inner and outer limits.

5. Antenna according to any one of the preceding claims, wherein the width W is greater than or equal to 0.2 mm and less than or equal to 0.5 mm.

6. Antenna according to any one of the preceding claims, wherein the spacing distance S is greater than or equal to 0.2 mm and less than or equal to 0.5 mm.

Antenna according to any one of the preceding claims, wherein the spacing distance S is equal to the width W.

8. Antenna according to any one of the preceding claims, wherein the periodic pattern is evenly distributed throughout the band.

9. Antenna according to any one of the preceding claims, wherein the first and second strands extend parallel to each other.

10. Antenna according to any one of the preceding claims, wherein the track (10) has a height (h ') greater than or equal to 2μηη.

11. radio device (2) characterized in that it comprises:

a radio antenna (4) according to any one of the preceding claims;

a reflector (6) for radio waves, having a parabolic shape, this radio wave reflector being attached to a rear face of the antenna substrate opposite to the face on which the track extends, and being formed of in such a way that the radio waves reflected by this radio-wave reflector converge at a focusing point, located at a distance from the center O less than or equal to half the depth (d) of this radio-wave reflector.