EP1416586B1 - Antenna with an assembly of filtering material - Google Patents

Abstract

The high directivity antenna has a transmitter patch (10) with a rear reflector (30a), and a set of elements (22) of differential permittivity and permeability. The elements pass one or several frequencies within a frequency band gap.

Description

The present invention relates to a transmitting or receiving antenna achieving significant directivity levels at microwave frequencies.

Antennas are known comprising at least one probe capable of transforming electrical energy into electromagnetic energy and vice versa.

Today, conventionally used antennas include parabolic reflector antennas, lens antennas and horn type antennas.

Parabolic reflector antennas have a parabolic reflective plane at the focus of which is a probe. This results in a congestion related to the focal length of the parabolic reflector.

The lens antennas comprise a lens at the focus of which is a probe. In addition to the congestion related to the focal length, such an antenna also has a high weight, due to the weight of the lens, which weight may be disadvantageous for certain applications.

Cornet type antennas are cumbersome and heavy to achieve high directivity levels.

Cylindrical antennas comprising a stack of dielectric layers are known from GB-A-1555756 and WO 95/33287 A. GB-A-1555756 discloses an antenna according to the preamble of claim 1.

A resonant device comprising a defective BIP material is known from US-A-5,471,180.

The invention aims to overcome the disadvantages of conventional antennas by creating a less bulky and less heavy antenna capable of transmitting or receiving an electromagnetic wave with significant directivity levels.

The subject of the invention is therefore an antenna according to claim 1

Said antenna thus makes it possible to obtain reduced bulk and weight by the use of a simplified feed system and a assembly, of small thickness, of elements made of materials differing in their permittivity and / or their permeability and / or their conductivity.

The antenna according to the invention may further comprise one or more of the features which appear in the dependent claims.

• la figure 1 représente une antenne selon l'invention dans le cas général ;
• la figure 2 représente une antenne comprenant un plan réflecteur d'ondes électromagnétiques ;
• la figure 3 représente schématiquement en perspective un exemple de structure de couches planes de matériaux se différenciant par leur permittivité et/ou par leur perméabilité et/ou leur conductivité agencées selon un motif périodique à une dimension ;
• la figure 4 représente schématiquement en perspective un exemple de structure présentant une double périodicité selon deux directions spatiales distinctes des matériaux la constituant ;
• la figure 5 représente schématiquement en perspective un exemple de structure présentant une triple périodicité selon trois directions spatiales distinctes des matériaux la constituant ;
• la figure 6 représente schématiquement en perspective une autre antenne ;
• la figure 7 représente une courbe donnant le coefficient de transmission en fonction de la fréquence de l'onde électromagnétique émise ou reçue par une antenne selon l'invention ;
• la figure 8 représente un diagramme de directivité de l'antenne selon le mode de réalisation présenté dans la figure 6 ; et -
• la figure 9 représente schématiquement en perspective une antenne selon un autre mode de réalisation.

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

• FIG. 1 represents an antenna according to the invention in the general case;
• FIG. 2 represents an antenna comprising a reflective plane of electromagnetic waves;
• FIG. 3 is a diagrammatic perspective view of an exemplary structure of flat layers of materials differing in their permittivity and / or in their permeability and / or their conductivity arranged in a one-dimensional periodic pattern;
• FIG. 4 diagrammatically represents in perspective an example of structure having a double periodicity according to two spatial directions distinct from the materials constituting it;
• FIG. 5 schematically represents in perspective an example of a structure having a triple periodicity according to three spatial directions distinct from the materials constituting it;
• Figure 6 shows schematically in perspective another antenna;
• FIG. 7 represents a curve giving the transmission coefficient as a function of the frequency of the electromagnetic wave emitted or received by an antenna according to the invention;
• FIG. 8 represents a directivity diagram of the antenna according to the embodiment presented in FIG. 6; and -
• Figure 9 shows schematically in perspective an antenna according to another embodiment.

• une sonde 10 capable de transformer une onde électrique en onde électromagnétique et réciproquement. Des antennes, telles que des antennes plaque, les dipôles, les antennes à polarisation circulaire, les fentes, les antennes fil-plaque coplanaires peuvent par exemple convenir comme sonde 10 dans une antenne selon la présente invention.

An antenna shown in Figure 1 comprises:

• a probe 10 capable of transforming an electric wave into an electromagnetic wave and vice versa. Antennas, such as plate antennas, dipoles, circular polarization antennas, slots, coplanar wire-plate antennas may for example be suitable as a probe 10 in an antenna according to the present invention.

An assembly 20 of elements in at least two materials differing in their permittivity and / or permeability and / or conductivity within which the probe 10 is disposed. Low loss materials, such as for example plastic, ceramic, ferrite, metal, etc., will preferably be selected.

An advantage of the present invention is that the probe 10 can be very simple to design from the moment it fills the type of polarization (linear or circular), the ellipticity rate and the electrical characteristics desired by the manufacturer, this probe 10 to be nevertheless small in front of the overall dimensions of the antenna.

An interest of the assembly 20 is to make it possible to design an antenna allowing one or more frequency propagation modes inside a non-conducting band, according to one or more allowed spatial directions d, spatial filtering being itself dependent the frequency and nature of the materials in the assembly 20.

Another advantage of this assembly 20, comprising a structure 22 designed on the principle of photonic bandgap materials in which is located one or more cavity (s) 21 is to have one or more mode (s) frequency (s) ) of very isolated propagation of its (their) nearest neighbors.

A structure designed on the principle of photonic bandgap materials is a structure of elements differing in their permittivity and / or permeability and / or conductivity, which structure has a periodicity of at least one dimension.

A cavity 21 placed within the assembly 20 gives it, by association with the photonic bandgap material 22, the behavior of a material known to those skilled in the art photonic bandgap material failing.

• une modification locale des caractéristiques diélectriques et/ou magnétiques et/ou de conductivité des matériaux utilisés,
• une modification locale des dimensions d'un ou plusieurs matériaux.

She may be :

• a local modification of the dielectric and / or magnetic characteristics and / or conductivity of the materials used,
• a local modification of the dimensions of one or more materials.

An antenna shown in FIG. 2 may further comprise an electromagnetic reflective plane 30 placed in the middle of the assembly 20 and containing the probe 10, making it possible to halve the dimensions of the antenna, particularly when the radiation is not useful only in a half space.

An interest of an antenna comprising an electromagnetic reflective plane 30 is to increase the gain of the main lobe of the directivity diagram of said antenna.

An antenna shown in FIG. 3 comprises a structure 22 designed on the principle of photonic bandgap materials having a one-dimensional periodicity, that is to say that said structure 22 comprises an alternation of plane layers of two materials 23 and 24, for example respectively alumina and air, distinguished by their permittivity and / or their permeability and / or their conductivity.

An antenna shown in Figure 4 comprises a structure 22 designed on the principle of photonic bandgap materials having a two-dimensional periodicity, that is to say that said structure 22 has bars, of cylindrical shape arranged regularly , a first material 25, for example alumina, separated from each other by a second material 26, for example air, the second material being distinguished from the first by its permittivity and / or its permeability and / or its conductivity.

For example, the structure is composed of cylindrical bars arranged in a succession of superposed layers.

In each layer, the bars extend parallel to each other and are placed with a regular pitch.

In addition, the bars of successive layers are aligned with a regular pitch. Preferably, the bars are metallic.

An antenna shown in FIG. 5 comprises a structure 22 designed on the principle of photonic bandgap materials, having a three-dimensional periodicity, such that said structure 22 comprises an alternation of bars, for example of parallelepipedal shape arranged in a regular manner, a first material 27, for example alumina or metal, separated from each other by a second material 28, for example air, said second material being distinguished from the first material by its permittivity and / or its permeability and / or its conductivity.

For example, the structure 22 is composed of substantially parallelepiped shaped bars arranged in a stack of superposed layers. In each layer, the bars extend parallel to each other and are placed in a regular pitch, and the bars of two adjacent layers form a constant angle, for example an angle of 90 °.

In addition, the bars of layers separated by an intermediate layer are parallel to each other and aligned with a regular pitch.

• Une sonde plaque 10a utilisant un seul fil d'alimentation 11 ;

With reference to FIG. 6, a preferred embodiment of an antenna comprises:

• A plate probe 10a using a single feed wire 11;

• Une plaque métallique formant un réflecteur plan électromagnétique 30a ;
• Une couche plane formant une cavité 21a en contact avec le réflecteur plan 30a, ladite cavité 21a étant constituée d'un matériau, de préférence à faible permittivité ou perméabilité afin de limiter le guidage des ondes de surface, lequel matériau peut être de l'air comme représenté à la figure 6 à titre d'exemple ;
• Une structure 22 dont les matériaux 23a, 24a, 23b se différenciant par leur permittivité et/ou leur perméabilité et/ou leur conductivité sont agencés en couches planes successives, selon un motif périodique à une dimension.

An interest of this probe is to be very simple in design and to limit the metallic and dielectric losses of the antenna.

• A metal plate forming an electromagnetic plane reflector 30a;
• A planar layer forming a cavity 21a in contact with the planar reflector 30a, said cavity 21a being made of a material, preferably of low permittivity or permeability in order to limit the guidance of the surface waves, which material may be air as shown in Figure 6 by way of example;
• A structure 22 whose materials 23a, 24a, 23b differing in their permittivity and / or their permeability and / or their conductivity are arranged in successive planar layers, in a periodic one-dimensional pattern.

The number of useful periods in the direction orthogonal to the plane of the antenna depends on the contrasts of permittivity and / or permeability and / or conductivity of the materials used. To reduce the number of periods, it is necessary to increase the index contrasts between the different materials.

By way of example, in the embodiment shown in FIG. 6, the materials used are the high permittivity index alumina and the low permittivity index air, which allows the structure 22 to comprise only three layers of materials.

The structure 22 thus consists of a first planar layer 23a of alumina in contact with a second plane layer 24a of air itself in contact with a third planar layer 23b of alumina.

• a) L'épaisseur e_21a de la couche plane 21a constituée d'un matériau de permittivité relative ε_r et de perméabilité relative µ_r est donnée par la formule ${\mathrm{e}}_{21\mathrm{a}}~0,5\frac{\lambda }{\sqrt{\epsilon r\mu r}}$
  
  où λ est la longueur d'onde correspondant à la fréquence de fonctionnement de l'antenne, et où le symbole "~" signifie " égal ou à peu près égal ".
  A titre d'exemple, l'épaisseur de la couche plane d'air 21a représentée figure 6 vaut e_21a = 0,5 λ.
• b) L'épaisseur e d'une couche plane d'un matériau diélectrique ou magnétique de permittivité relative ε_r et de perméabilité relative µ_r à l'intérieur de la structure 22 est donnée par la formule $\mathrm{e}~0,25\frac{\lambda }{\sqrt{\epsilon r\mu r}}.$
  
  
  A titre d'exemple, l'épaisseur de la couche plane d'alumine 23a représentée figure 6 vaut environ e_23a = 0,08 λ ; l'épaisseur de la couche plane d'air 24a représentée figure 6 vaut e_24a = 0,25 λ ; l'épaisseur de la couche plane d'alumine 23b représentée figure 6 vaut environ e_23b = 0,08λ.
• c) Les dimensions latérales de la structure 22, de la plaque 30a et de la cavité 21a sont choisies en fonction du gain désiré de l'antenne. La forme utile pour l'antenne s'inscrit dans un cercle dont le diamètre Φ est relié au gain recherché, selon la formule empirique connue suivante : ${\mathrm{G}}_{\mathrm{dB}}\ge 20\log \frac{\pi \mathrm{\Phi }}{\lambda }-2,5.$
  
  
  A titre d'exemple, pour obtenir un gain de 20 dB tel que représenté figure 8, un système d'antenne peut avoir des dimensions latérales de 4,3 λ. La forme latérale de l'antenne est ensuite choisie pour obtenir une certaine forme du rayonnement de l'antenne, selon un procédé connu.
• d) Compte tenu des dimensions latérales et des épaisseurs des différentes couches de matériaux entrant dans la composition de l'antenne telle que décrite dans la figure 6, lesdites épaisseurs et dimensions latérales étant mentionnées ci-dessus, les dimensions générales de l'antenne sont donc: une épaisseur H d'environ λ et une dimension latérale L de 4,3 λ. Ainsi, pour une fréquence de fonctionnement de 10 Ghz correspondant à une longueur d'onde de 3 cm, un exemple particulier d'antenne tel que représenté figure 6 aura un volume de l'ordre de 3 x 13 x 13 cm³ , alors qu'un système d'antenne parabolique classique, fonctionnant à la même fréquence de 10 Ghz, qui a une distance focale d'environ 70 cm, occupe un volume nettement supérieur.

In the embodiment as shown in FIG. 6, where the assembly 20 of successive planar layers of dielectric or magnetic materials where the first layer 21a constitutes the cavity and where the following 23a, 24a and 23b constitute the structure 22:

• a) The thickness e _21a of the plane layer 21a made of a material of relative permittivity ε _r and relative permeability μ _r is given by the formula ${\mathrm{e}}_{}$${\mathrm{}}_{21\mathrm{at}}~0,5\frac{\lambda }{\sqrt{\epsilon r\mu r}}$
  
  where λ is the wavelength corresponding to the operating frequency of the antenna, and where the symbol "~" means "equal or nearly equal".
  By way of example, the thickness of the plane air layer 21a shown in FIG. 6 is e _21a = 0.5λ.
• b) The thickness e of a plane layer of a dielectric or magnetic material of relative permittivity ε _r and relative permeability μ _r inside the structure 22 is given by the formula $\mathrm{e}~0,25\frac{\lambda }{\sqrt{\epsilon r\mu r}}.$
  
  
  By way of example, the thickness of the planar alumina layer 23a shown in FIG. 6 is approximately e _23a = 0.08λ; the thickness of the plane air layer 24a shown in FIG. 6 is e _24a = 0.25λ; the thickness of the planar alumina layer 23b shown in FIG. 6 is approximately e _23b = 0.08λ.
• c) The lateral dimensions of the structure 22, the plate 30a and the cavity 21a are chosen according to the desired gain of the antenna. The useful form for the antenna fits into a circle whose diameter Φ is related to the desired gain, according to the following empirical formula: ${\mathrm{BOY\; WUT}}_{\mathrm{dB}}\ge 20\log \frac{\pi \mathrm{\Phi }}{\lambda }-\mathrm{two},5.$
  
  
  By way of example, to obtain a gain of 20 dB as represented in FIG. 8, an antenna system can have lateral dimensions of 4.3λ. The lateral shape of the antenna is then selected to obtain a certain shape of the antenna radiation, according to a known method.
• d) Given the lateral dimensions and the thicknesses of the various layers of materials used in the composition of the antenna as described in FIG. 6, said thicknesses and lateral dimensions being mentioned above, the general dimensions of the antenna are therefore: a thickness H of approximately λ and a lateral dimension L of 4.3 λ. Thus, for an operating frequency of 10 Ghz corresponding to a wavelength of 3 cm, a particular example of an antenna as represented in FIG. 6 will have a volume of the order of 3 × 13 × 13 cm ³ , while a conventional parabolic antenna system, operating at the same frequency of 10 Ghz, which has a focal length of about 70 cm, occupies a much larger volume.

It therefore clearly appears that the present invention very clearly improves the congestion problem related to the antennas, in particular thanks to the low thickness of an antenna according to the invention.

Moreover, since the thickness of the successive plane layers of an antenna, as described in FIG. 6, is proportional to λ and therefore inversely proportional to the operating frequency of the antenna, such an embodiment makes it possible to design an antenna operating at very high frequency thanks to multilayer technologies.

An antenna as shown in FIG. 6 provides the radiation and a spatial and frequency filtering of the electromagnetic waves produced or received by said antenna, as represented in FIG. 7. Said filtering notably allows one or more operating frequencies f of said antenna within a non-conducting frequency band B.

An antenna as shown in Figure 6 is designed to achieve a gain of 20db and has a radiation pattern shown in Figure 8.

It appears that the antenna according to the invention achieves significant gains in a given direction such as conventional aperture antennas.

It is also visible that this radiation pattern has low levels of sidelobes.

The operation of the antenna described with reference to Figure 6, will now be examined. The antenna has two modes of operation: a transmitter mode and a receiver mode.

In the transmitter operating mode, an electric current led by the power supply wire 11 reaches the level of the probe 10a which transforms it into an electromagnetic wave. This electromagnetic wave then passes through the assembly 20 of elements made of materials differing in their permittivity and / or their permeability and / or their conductivity, the arrangement of which makes it possible to operate by construction a spatial and frequency filtering on the wave electromagnetic and thus conform the radiation pattern of the antenna system according to properties desired by the user.

In the receiver operating mode, an electromagnetic wave arriving at the antenna is filtered spatially and frequently during its crossing of the assembly 20 of elements made of materials differing in their permittivity and / or permeability and / or their conductivity, before reaching the probe 10a. Then, the electromagnetic wave filtered according to properties desired by construction of the antenna, is transformed into electric current by the probe 10a and transmitted to the supply wire 11.

According to a particular embodiment, the probe of the antenna is of a nature capable of generating a linear or circular polarization in the antenna, causing an operation thereof, either in linear polarization or in circular polarization.

According to another particular embodiment, the shape of the planar layers is arranged to obtain a radiation pattern and desired gain according to the theory of radiating openings.

According to another embodiment, the constituent elements of the structure are coaxial cylinders surrounding the probe, the arrangement thus having a radial periodicity, and the inner cylindrical element forms a cavity receiving said probe.

According to yet another embodiment, the constituent elements of the structure 22 are coaxial cylinders consisting of photonic bandgap materials having a periodicity in two or three dimensions.

According to yet another embodiment of the invention, at least one of the materials has variable dielectric and / or magnetic characteristics as a function of an external source such as an electric or magnetic field, so as to make it possible to achieve tunable antennas.

According to another characteristic of the invention, the assembly exhibits multiple periodicity defects generated by a cavity or the juxtaposition of several cavities and making it possible to widen the bandwidth of the antenna and / or to create multiband antennas.

Finally, according to another embodiment of the invention, the assembly of elements 20 has a periodicity of at least one dimension and at least one defect in one of the dimensions of this periodicity which generates at least one cavity in its entirety. breast, the elements remaining arranged in a regular step in the other dimensions.

• une sonde plaque 10a utilisant un seul fil d'alimentation 11;
• une plaque métallique formant un réflecteur plan électromagnétique 30a ;
• une couche plane formant une cavité 21 a en contact avec le réflecteur plan 30a, identique à celle représentée à la figure 6 ; et
• une structure 22 en contact avec la couche plane formant cavité 21 a.

Thus, the antenna represented in FIG. 9 comprises:

• a plate probe 10a using a single feed wire 11;
• a metal plate forming an electromagnetic plane reflector 30a;
• a planar layer 21 forming a cavity in contact with the plane reflector 30a, identical to that shown in Figure 6; and
• a structure 22 in contact with the planar cavity layer 21a.

This structure has a two-dimensional periodicity: it comprises bars 25, of cylindrical shape arranged in two layers 32 and 34 identical and superimposed. In each layer 32 and 34, the bars 25 extend parallel to each other and are placed with a regular pitch.

Thus, the assembly 20 constituted by the cavity 21a and the structure 22 has a defect in its periodicity, in the dimension corresponding to the direction orthogonal to the planar reflector 30a and the layers 32 and 34. On the other hand, the periodic arrangement of the bars 25 in each layer 32 and 34 is not affected by the presence of the cavity 21a.

The dimensions of this antenna are also dependent on the operating frequency for which it was designed. For example, to operate at a frequency of 4.75 GHz, the lateral dimensions of the antenna are 258 mm, the thickness of the cavity 21 is 33.54 mm, the two layers 32 and 34 are distant from each other. 22.36 mm and in each layer, the bars 25 have a diameter of 10.6 mm and their respective axes are spaced 22.36 mm.

The bars may be made of dielectric, magnetic or metallic materials.

Under these conditions, the antenna shown in FIG. 9 has, like that shown in FIG. 6, a radiation pattern such as that represented in FIG. 8.

In a variant, the antenna comprises a multiplicity of probes of different natures.

• antenne haute fréquence à haut débit d'informations, en raison de sa capacité à fonctionner à des fréquences élevées grâce aux techniques de dépôts multicouches ;
• antenne pour des applications embarquées de type aérospatial ou militaire, par exemple, en raison de son faible encombrement et en raison de ces caractéristiques de furtivité dues à l'étroitesse de sa bande passante ;
• antenne à ouverture classique en remplacement des antennes à ouverture connues du type antenne parabolique ou antenne à lentille.

An antenna according to the invention can be used as:

• a high-frequency information broadband antenna due to its ability to operate at high frequencies using multilayer deposition techniques;
• antenna for aerospace or military type embedded applications, for example, because of its small footprint and because of these stealth characteristics due to the narrow bandwidth;
• conventional aperture antenna to replace known aperture antennas such as dish antenna or lens antenna.

Claims (13)

1. Antenna comprising at least one probe (10) capable of converting electrical energy into electromagnetic energy and vice versa, and also comprising an assembly (20) of elements made of at least two materials that differ by their permittivity and/or their permeability and/or their conductivity, within which assembly (20) said probe is arranged, characterised in that the assembly comprises a structure (22) designed according to the principle of forbidden photonic band (BIP) materials, within which structure (22) there are located one or more cavities (21) which confer on the assembly the behaviour of a BIP defect material in which the arrangement of the elements in said assembly provides for the radiation and a spatial and temporal filtering of the electromagnetic waves produced or received by said probe, which filtering permits in particular the transmission through the assembly of one or more operating frequencies (f) of the antenna within a non-passing frequency band, and in that said assembly of elements (20) has a radial periodicity and at least one defect (21) in that radial periodicity.
2. Antenna according to claim 1, characterised in that said assembly of elements (20) comprises a first material of given permittivity, permeability and conductivity forming at least one cavity (21; 21a) and a structure (22) composed of two other materials (23, 24; 25, 26; 27, 28; 23a, 23b, 24a) which differ by their permittivity and/or their permeability and/or their conductivity, said structure having a radial periodicity.
3. Antenna according to claim 2, characterised in that the elements constituting the structure (22) are coaxial cylinders surrounding the probe, the arrangement thus having a radial periodicity, and in that the inner cylindrical element forms said at least one cavity receiving said probe.
4. Antenna according to claim 3, characterised in that said assembly of elements comprises a first cylindrical layer of material (21a) produced with said first material forming at least one cavity within which the probe is arranged, said first layer being in contact with at least one succession of cylindrical layers (23a, 23b, 24a) of materials which differ by their permittivity and/or their permeability and/or their conductivity, which layer(s) is/are arranged according to an at least one-dimensional periodic pattern to form said structure of coaxial cylinders.
5. Antenna according to claim 3, characterised in that the coaxial cylinders are homogeneous.
6. Antenna according to claim 3 or 4, characterised in that the coaxial cylinders are constituted by forbidden photonic band materials having a periodicity in two or three dimensions.
7. Antenna according to any one of the preceding claims, characterised in that it further comprises an electromagnetic wave reflector (30; 30A) which supports said probe and is in contact with said assembly of elements.
8. Antenna according to claim 4, characterised in that it comprises a cylindrical metal plate which forms an electromagnetic wave reflector (30a) and on which there is arranged the probe (10; 10a), said cylindrical metal plate being in contact with the first cylindrical layer, the thickness e₁ of said first layer being given by the relationship ${\mathrm{e}}_1=0.5\frac{\lambda }{\sqrt{\epsilon r\mu r}},$

   

   said first layer itself being in contact with said succession of layers (23a, 23b, 24a), the thickness e of each of the layers of said succession of layers being given by the relationship $\mathrm{e}=0.25\frac{\lambda }{\sqrt{\epsilon r\mu r}},$

   

   where λ is the wavelength corresponding to the operating frequency (f) of the antenna desired by the user, ε_r and µ_r being the relative permittivity and the relative permeability, respectively, of the material of the layer in question.
9. Antenna according to any one of the preceding claims, characterised in that the probe of the antenna is capable of generating a linear or circular polarisation in the antenna, resulting in operation thereof either in linear polarisation or in circular polarisation.
10. Antenna according to any one of the preceding claims, characterised in that the probe is located within the cavity (21).
11. Antenna according to any one of the preceding claims, characterised in that at least one of the materials has dielectric and/or magnetic characteristics which are variable as a function of an external source such as an electric or magnetic field, so as to permit the production of tuneable antennae.
12. Antenna according to any one of the preceding claims, characterised in that the assembly has a cavity or a juxtaposition of a plurality of cavities forming multiple defects in periodicity, allowing the passing band of the antenna to be enlarged and/or multi-band antennae to be created.
13. Antenna according to claim 6, characterised in that the structure (22) comprises metal bars arranged with a two-or three-dimensional periodicity.

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