EP2573872A1 - Lens antenna comprising a diffractive dielectric component able to shape a hyperfrequency wave front. - Google Patents
Lens antenna comprising a diffractive dielectric component able to shape a hyperfrequency wave front. Download PDFInfo
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- EP2573872A1 EP2573872A1 EP12186157A EP12186157A EP2573872A1 EP 2573872 A1 EP2573872 A1 EP 2573872A1 EP 12186157 A EP12186157 A EP 12186157A EP 12186157 A EP12186157 A EP 12186157A EP 2573872 A1 EP2573872 A1 EP 2573872A1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/02—Refracting or diffracting devices, e.g. lens, prism
- H01Q15/08—Refracting or diffracting devices, e.g. lens, prism formed of solid dielectric material
Definitions
- the present invention relates to a lens antenna comprising a diffractive dielectric component capable of forming a microwave wavefront.
- the invention finds a particular application in the field of Hertzian telecommunications, extending in a known manner from about 400 MHz to 300 GHz and corresponding to centimetric and millimeter wavelength wavelengths.
- An antenna family capable of meeting the need to reduce congestion is the family of lens antennas, in which a radiofrequency source is placed at the focus of a dielectric lens.
- the focal length / diameter (F / D) ratio of the lens is less than 0.5 for the 30GHz to 50GHz frequency band known as the Q band, corresponding respectively to a wavelength range of 6mm (corresponding to 50GHz) to 10mm ( corresponding to 30GHz).
- a Fresnel lens 12 comprises a plurality of concentric annular zones 14, 16, also called Fresnel zones, arranged in the same plane.
- the known disadvantages of Fresnel lenses are a lower diffraction efficiency and losses due to a shading effect of the zoning. The shading effect has been shown to be particularly important for large numerical apertures corresponding to low F / D values.
- the manufactured lenses have a rounded shape at the discontinuities. This rounded shape significantly reduces the diffraction efficiency, especially when the size of a Fresnel zone is not large in front of the wavelength. In general, the more optics are open (small F / D) the smaller the size of the Fresnel areas.
- the lens is formed of four concentric zones each pierced with holes of constant diameter, spaced apart by zones of dielectric material without holes, thus forming four separate Fresnel zones.
- the holes are small in diameter relative to a target wavelength, corresponding to a frequency of 30GHz.
- the solution proposed by Petosa et al. therefore shows unsatisfactory performance.
- the invention proposes a lens antenna comprising at least one diffractive dielectric component capable of shaping a microwave wavefront having a wavelength in a range of 1 millimeter to 50 centimeters.
- said diffractive dielectric component comprises a plurality of main microstructures formed in a substrate refractive index substrate material so as to form an artificial material of effective refractive index, each main microstructure having a size smaller than a length target waveform taken in said wavelength range, said main microstructures being arranged in zones, so as to vary a surface filling ratio, the effective refractive index being a function of said surface filling ratio, the arrangement being such that the effective refractive index varies within a said zone said dielectric diffractive component in a quasi-monotonic manner between a minimum value and a maximum value less than or equal to the substrate refractive index.
- a lens antenna according to the invention has a good performance and has a small footprint.
- a diffractive dielectric component with an arrangement of main microstructures smaller than the target wavelength, called subwavelength microstructures allows the synthesis, for a zone of the component, of a quasi-monotone variation. almost continuous the effective refractive index with a large number of sub-wavelength microstructure patterns. This makes it possible to improve the diffraction efficiency and to avoid shading losses.
- the solution proposed by the invention makes it possible to maximize the guiding effects and thus maximize the efficiency of the dielectric component, which makes it possible to obtain effective lens antennas in the microwave range.
- the invention will be described more particularly in the application of diffractive dielectric lenses or diffractive dielectric components for a lens antenna in the microwave range in the range of 30 GHz to 50 GHz (known as the Q band), which is a particular range of the microwave domain.
- a lens antenna is composed of a source of microwave electromagnetic waves and a lens, which is a diffractive dielectric component and which collects and reshapes the wave generated by the source, resulting in a front of modified wave.
- the source is located at the focus of this component, or more generally near the focus of this component.
- Component 20 of the figure 2 is a so-called ladder grating diffractive component made of a substrate material 21 and composed of two rungs 22 of period A, each step corresponding to a zone of the component. It is a conventional diffractive dielectric component, made of a substrate material of given substrate refractive index, in which the monotonic variation of refractive index is obtained by the variation of height between the height h1 and the height h2 of each step 22.
- the refractive index will be called simply index.
- the maximum height h (h 2 -h 1 ) is calculated, as a function of the index variation nn 0 , to obtain a phase shift of 2 ⁇ .
- Component 23 of the figure 2 is made of a substrate material 24 and comprises two zones or steps 25 of constant height, corresponding to the steps 22 of the component 20, increasing monotonically increasing index per zone, or index gradient, between the minimum value 1, which is the index of vacuum, and n, n being greater than 1, the variation being schematically represented by an arrow.
- the component 26 of the figure 2 is formed by a substrate 27 comprising subwavelength microstructures 28, which are in this example pillars.
- the sub-wavelength microstructures may be holes or pillars, these microstructures having the effect of locally varying the amount of dielectric material.
- the microstructures of the component 26 are arranged in zones, which are zones of period A in the case of a network, or Fresnel zones in the case of a lens, or any zones in the case of a component. non-periodic.
- the effective refractive index varies in a quasi-monotonic manner, between a minimum value and a maximum value less than or equal to the refractive index of the substrate 27.
- the diffraction efficiency is improved because the use of the sub-wavelength microstructures avoids the shading effect obtained with the embodiment in echelette 20, and therefore makes it possible to increase the efficiency of the dielectric component 26 by relative to the efficiency of the echelette component 20.
- the pillars 28 which are square section, circular or hexagonal for example, have variable widths, the maximum width being equal to d which is less than ⁇ 0 , the target wavelength in the microwave domain considered.
- the pillars are arranged in a periodic structure of period ⁇ s which is the distance between the centers of two consecutive pillars in the example of the figure 2 .
- the arrangement structure is pseudo-periodic, with ⁇ s near distances, typically ranging between about 0.75 ⁇ s 1,25 ⁇ s and to induce a little disorder which would allow in some cases to smooth or reduce the unwanted diffraction orders.
- the microstructures are arranged in zones according to a mesh which is square, rectangular or hexagonal, for example.
- the dielectric component behaves as an artificial material whose effective index varies locally per area monotonously, forming a material with a gradient of effective index.
- ⁇ s ⁇ 0 max not s ⁇ not Inc. + not Inc. ⁇ sin ⁇
- n s the refractive index of the substrate dielectric material
- ⁇ the incidence angle of the wave beam on the dielectric component. If the period ⁇ s is chosen greater than the value given by the formula of Eq2, the dielectric component no longer has the property of artificial material with a desired index gradient.
- the effective index depends on the geometry of the sub-wavelength microstructure.
- a surface filling ratio is defined which is equal to the area occupied by the pillars contained in a surface unit divided by the same surface unit.
- a surface unit is defined as the area of the side square ⁇ s .
- the effective index is almost proportional to the surface fill rate.
- the surface coverage ratio is equal to the area of remaining substrate dielectric material per unit area divided by the same surface unit.
- the surface filling ratio represents the surface of the substrate material constituting the artificial material per unit area.
- Component 29 of the figure 2 represents an alternative embodiment of variation of index in a substrate dielectric material 30 according to the invention, making it possible to obtain an effective index variation similar to that obtained with the component 26: a set of pillars 31 of given width d 1 , which is an order of magnitude lower than that of the target wavelength ⁇ 0 , d 1 ⁇ ⁇ 0 , which are arranged in a variable density per unit area.
- the variation of the density also makes it possible to vary the surface filling ratio, and thus the effective index of the component 29.
- a graded index dielectric component is constructed based on holes-like microstructures on the same principle, by drilling holes of fixed diameter or size into the dielectric material, and varying the number of holes per unit of area.
- the figure 3 illustrates a view from above of various embodiments of diffractive dielectric components with echelette gratings according to the invention.
- a first view of the top 32 illustrates a first embodiment of a diffractive dielectric component 26, with two zones or steps, comprising microstructures 33 with a square section of variable size, and arranged in a square mesh.
- a second view of the top 34 illustrates a second embodiment of a diffractive dielectric component 26, with two zones or rungs, comprising microstructures 35 of circular cross section and of variable diameter, arranged in a hexagonal mesh.
- the view 36 illustrates an embodiment of a diffractive dielectric component 29, with two zones or steps, comprising microstructures 37 of square section of constant size, arranged with a variable surface density.
- microstructures - holes or pillars, of round section, square or in another geometric form - are suitable for the realization of diffractive dielectric components for microwave waves, of microwave wavelength, because the dimensions of the microstructures , calculated from the target wavelength, are greater than 1 mm, and therefore do not require expensive manufacturing technology.
- the diffractive dielectric component is made with pillar type microstructures, which have the advantage of optimizing the waveguiding and thus increasing the diffraction efficiency.
- holes and pillars are associated in the same component.
- microstructures are, according to one embodiment, microstructures of square section, round, oval, hexagonal, of width equal to the depth, that is to say to the right flank or quasi-right in the thickness of the component.
- the microstructures are cone-shaped, that is to say having flanks that are not straight in the thickness of the substrate, for example with a smaller diameter on the air side and wider side. substrate.
- the Figures 4 to 6 provide several examples of microstructure sizing to obtain various effective indices.
- the figure 4 is a graph representing the effective index of the dielectric component composed of periodic pillar microstructures as a function of the surface filling ratio.
- the target wavelength ⁇ 0 is 7.14 mm, corresponding to a frequency of approximately 42 GHz.
- the period ⁇ s is in this example equal to 0.336 x ⁇ 0 .
- This choice corresponds to an opening of f / 1.4.
- the effective index is almost proportional to the surface fill rate.
- five points of the graph noted P 1 to P 5 have been distinguished.
- the surface filling ratio of the pillars is represented schematically by a top view of each square-section pillar 38 centered per unit area 40.
- the zone 38 represents the dielectric material composing the pillar, zone 42 corresponds to the air (zone left empty around the pillars).
- the graph of the figure 5 is similar to that of the figure 4 for a dielectric component composed of periodic holes.
- the surface filling ratio is given here by the area occupied by the dielectric material, namely the surface 44 minus the hole area 46 of square section of side d. Naturally, the d side is inversely proportional in this case to the surface filling rate.
- the effective index obtained is almost proportional to the surface filling rate.
- the figure 6 is a graph representing the effective index of the dielectric component composed of pillars and periodic holes of constant size and density per unit of variable area, as a function of the surface fill rate.
- each microstructure (hole or pillar)
- the size d on the side of the square section of each microstructure is constant and equal to 0.2mm, and it is the density of material per unit area that varies.
- Curve 50 corresponds to pillar-shaped microstructures
- curve 52 corresponds to hole-shaped microstructures
- the hatched areas correspond to the dielectric material and the non-filled areas correspond to air.
- the two geometries namely pillars and holes
- the two geometries are combined in order to be able to use the entire index excursion and to reduce the height of the structures.
- the index excursion becomes equal to 1.54, resulting in a height about 4.6mm.
- the combination of pillars and holes makes it possible to further reduce the bulk of the diffractive dielectric component.
- the dielectric component in order to facilitate the manufacturing process, is composed of pillars of constant size, and arranged so as to vary their density to obtain a quasi index gradient, with a variable number of pillars per unit of surface.
- Such microstructures can be manufactured easily by molding, and thus produced in large numbers.
- the pillar microstructures arranged in zones are positioned on the two opposite faces of the dielectric component, so as to associate two phase functions, one on each side of the component.
- the height of the microstructures is then distributed on the two opposite faces, involving microstructures that are easier to manufacture.
- the second face has an effective index which varies between one and the index of the substrate, and therefore a lower effective index on average, which makes it possible to reduce the losses on the second interface.
- the diffractive dielectric component comprises, on a first so-called diffractive face, microstructures, for example of the pillar type, arranged in zones, and on the opposite face, which is the first face encountered by the wavefront. resulting from the source and which is a non-diffractive face in this case, a structuring with sub-wavelength microstructures realizing a sub-wavelength phase function, allowing a shaping of the wavefront resulting from source.
- the treatment applied to the face first encountered by the wavefront corrects the wavefront, in particular to make it perfectly spherical, before reaching the diffractive face.
- the sub-wavelength microstructures are, for example, pillars of variable sizes or of fixed size and of variable density, realizing a slow variation of effective index.
- the microstructures of the first face are not arranged in several zones with effective index variation as for the diffractive face.
- the dielectric component formed of pillar microstructures also comprises an impedance matching, so as to reduce the losses due to incident wave reflections at the interfaces between the air and the artificial dielectric material.
- the Figures 7 to 10 illustrate various profiles of the dielectric component with impedance matching.
- the dielectric component 60 comprises on one face, which is the diffractive face, main microstructures arranged in zones, in the form of pillars 62, of variable sizes to obtain a index gradient as explained above.
- projection micropiliers 64 which are secondary subwavelength microstructures, period ⁇ 1 an order of magnitude less than the period ⁇ s pillars 62, typically ⁇ s / 10 ⁇ ⁇ 1 ⁇ s / 2 and of size d 2 less than the width of the pillar 62 of smaller section.
- the secondary microstructures are periodic and are not arranged in several zones, such as the main microstructures.
- the period ⁇ 1 and the size d 2 are chosen by simulation so as to locally reduce the index of the dielectric component at the interface with the air.
- the dielectric component 70 also comprises on a first face, the diffractive face, main microstructures, arranged in zones, in the form of pillars 72, of varying sizes to obtain a gradient index as explained above.
- micropiliers 74 On these pillars 72 are embedded projecting secondary subwavelength microstructures, which are micropiliers 74, with a period of an order of magnitude less than the period ⁇ s of the pillars 72.
- micropiliers 76 are also integrated on the second face of the dielectric component 70, which is opposite the first face, thus making it possible to achieve an impedance matching on the two interfaces of the lens and thus to further reduce the reflection losses.
- the micropiliers 76 When the second face does not have sub-main wavelength microstructures, the micropiliers 76 have a period ⁇ 1 in the wider range, such that ⁇ s / 10 ⁇ ⁇ 1 ⁇ ⁇ s .
- the dielectric component 78 is constructed by adding, with respect to the embodiment of the figure 8 a neutral dielectric plate 80 of thickness e equal to ⁇ 0 / 2n 'where ⁇ 0 is the target wavelength and n' is the refractive index of the blade.
- the dielectric plate has a transmission coefficient of 1 at the wavelength ⁇ 0 , in normal incidence.
- the sub-wavelength microstructures of the dielectric component 78 are better protected with respect to the external environment, this blade placed at the output of the dielectric component being usable as a protective blade against dust and rain, for example.
- the dielectric plate 80 is positionable in the part where the beam is weakly divergent, and therefore for a very open system (small F / D, F / D ⁇ 1 for example) behind the dielectric component 78, that is to say on the side of the dielectric component 78 which is not facing the source.
- a very open system small F / D, F / D ⁇ 1 for example
- An example would be a Rexolite blade of 2.25mm thick to ensure blade transmission greater than 99.5% between 40.5GHz and 43.5GHz.
- the dielectric component 82 is formed of a stack of geometries of sub-wavelength pillars in several layers.
- main microstructures 84 which are pillars in this embodiment, are added two layers of secondary subwavelength microstructures, which are formed of micropiliers 86 and 88 of respectively smaller and smaller sizes.
- the width of the micropiliers 86 is smaller than the width of the pillars 84
- the width of the micropiliers 88 is smaller than the width of the micropiliers 86.
- Such a component is easier to manufacture than a component having a single antireflection layer formed of a plurality of very fine micropiliers.
- the example of figure 10 has two layers of secondary microstructures, but a higher number of layers is realized in an alternative mode.
- a lens antenna according to the invention comprises a dielectric system consisting of a matrix, square or more generally rectangular, of diffractive dielectric components comprising subwavelength microstructures as described above.
- the figure 11 illustrates such a dielectric system 90 formed of a 2x2 square matrix of four components 92, 94, 96 and 98.
- Each of the components is formed of concentric zones or rings z1, z2, z3 and z4, each zone being composed of subwavelength microstructures, for example pillars, as described above.
- the proposed matrix has the advantage of not having any overlap of one component over the other which composes it, while ensuring the use of the whole of the useful area (no dead zone in the matrix): the the whole of the wave beam arriving on the matrix is transformed by the matrix, there is no zone between the components of the matrix which does not contribute to the collimation of the beam.
- the arrangement in the form of matrix pxq makes it possible to further miniaturize the dielectric system, because to obtain a given numerical aperture, the focal length and therefore the diameter of each lens of the matrix is divided by the dimension p of the matrix in one direction and the dimension q of the matrix in the other direction.
- the Figures 12 to 14 illustrate other useful features for antennas in the microwave domain achievable with diffractive dielectric systems as described above. These features allow for example to direct the beam in a desired direction, or to cover multiple directions, and / or could be combined with a matrix of sources to reduce the thickness of the antenna, to obtain point-to-multipoint links.
- the point-to-multipoint functionality is implemented in a node of a capillary network for example.
- the figure 12 illustrates the deflection of microwave electromagnetic waves by the use of a dielectric component which is an off-axis lens L formed of sub-wavelength microstructures.
- the microwave waves come from the source S.
- the lens L deflects the rays of the source to obtain a single beam F1.
- the figure 13 illustrates a lens L 'formed of subwavelength microstructures for generating two beams F1, F2 from a single source S, with identical or different energy distributions.
- the figure 14 illustrates an embodiment with a plurality of sources in the same plane, S1, S2, which generate wave beams to a dielectric system composed of a matrix of dielectric components L1, L2, making it possible to obtain two F1 wave beams , F2.
- wavefront shaping includes the various wavefront shaping types described above with reference to the Figures 12 to 14 such as the deflection of a wave beam and the separation of a wave beam into two or more wave beams.
- diffractive dielectric components as described are associated, for example one behind the other with air layers separating them, in a lens antenna according to the invention.
- the dielectric components with subwavelength microstructures are also able to obtain a better broadband focusing efficiency (nominal wavelength ⁇ 20%) than the conventional ladder profile components.
- one of the advantages of the dielectric components according to the invention is their manufacture, which can be easily performed for series of components and at low cost, because of their dimensioning. It is possible to manufacture a usable mold for mass production, and thus each diffractive dielectric component is manufactured by molding / demolding, in a single manufacturing step.
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Abstract
Description
La présente invention concerne une antenne lentille comprenant un composant diélectrique diffractif apte à mettre en forme un front d'onde hyperfréquence.The present invention relates to a lens antenna comprising a diffractive dielectric component capable of forming a microwave wavefront.
L'invention trouve une application particulière dans le domaine des télécommunications Hertziennes, s'étendant de manière connue d'environ 400MHz à 300GHZ et correspondant à des ondes de longueurs d'ondes respectives centimétriques et millimétriques.The invention finds a particular application in the field of Hertzian telecommunications, extending in a known manner from about 400 MHz to 300 GHz and corresponding to centimetric and millimeter wavelength wavelengths.
Dans ce domaine il est courant d'avoir des antennes grandes devant la longueur d'onde afin de réaliser des émissions de grande puissance et grande directivité, et d'obtenir un grand gain d'antenne.In this area, it is common to have antennas large in front of the wavelength in order to achieve high power and high directivity emissions, and to obtain a large antenna gain.
Un des problèmes posés par ce type d'antenne est son encombrement et son poids. En effet, dans de nombreuses applications, à la fois pour des raisons esthétiques et pour des raisons de coût, il est préférable d'avoir des antennes à faible encombrement.One of the problems with this type of antenna is its size and weight. Indeed, in many applications, both for aesthetic reasons and for reasons of cost, it is preferable to have compact antennas.
Une famille d'antennes permettant de répondre au besoin de réduire l'encombrement est la famille des antennes lentilles, dans lesquelles une source radiofréquence est placée au foyer d'une lentille diélectrique.An antenna family capable of meeting the need to reduce congestion is the family of lens antennas, in which a radiofrequency source is placed at the focus of a dielectric lens.
Afin de rendre une telle antenne plus compacte, une solution connue est de réduire le ratio distance focale/diamètre (F/D) de la lentille, en ayant ainsi une optique à forte ouverture numérique. Typiquement, le ratio F/D est inférieur à 0,5 pour la bande de fréquence de 30GHz à 50GHz connue sous le nom de bande Q, correspondant respectivement à une plage de longueur d'onde de 6mm (correspondant à 50GHz) à 10mm (correspondant à 30GHz).In order to make such an antenna more compact, a known solution is to reduce the focal length / diameter (F / D) ratio of the lens, thus having a high numerical aperture optics. Typically, the F / D ratio is less than 0.5 for the 30GHz to 50GHz frequency band known as the Q band, corresponding respectively to a wavelength range of 6mm (corresponding to 50GHz) to 10mm ( corresponding to 30GHz).
On peut utiliser des lentilles épaisses réfractives, mais dans ce cas le faible ratio F/D induit une très grande courbure sur les bords, ce qui rend leur fabrication complexe pour maintenir un bon rendement. De plus, ces lentilles sont épaisses, donc leur encombrement et leur poids ne sont pas satisfaisants.It is possible to use refractive thick lenses, but in this case the low F / D ratio induces a very large curvature on the edges, which makes their manufacture complex to maintain a good yield. In addition, these lenses are thick, so their size and weight are not satisfactory.
Alternativement, il est connu d'utiliser des lentilles diffractives, également appelées lentilles de Fresnel, dont l'épaisseur est faible et reste constante même lorsque le ratio F/D décroît. Comme illustré sur la
D'autre part, même pour une lentille idéale sans arrondi au niveau des discontinuités, on observe pour chaque discontinuité une zone d'ombrage dans laquelle les rayons incidents sont déviés par le bord de la zone de Fresnel adjacente et ne participent pas à la diffraction.On the other hand, even for an ideal lens without rounding at the discontinuities, there is observed for each discontinuity a shading zone in which the incident rays are deflected by the edge of the adjacent Fresnel zone and do not participate in the diffraction .
Une application des lentilles de Fresnel pour l'utilisation dans le domaine hyperfréquence a été proposée par
Dans cette solution, la lentille est formée de quatre zones concentriques chacune percée de trous de diamètre constant, espacées par des zones de matériau diélectrique dépourvues de trous, formant ainsi quatre zones de Fresnel séparées. Les trous sont de diamètre petit par rapport à une longueur d'onde cible, correspondant à une fréquence de 30GHz. Un matériau diélectrique de fort indice de réfraction n=2,4 a été utilisé pour faciliter la fabrication des trous. Les résultats expérimentaux ont montré que l'amélioration escomptée n'a pas été atteinte par cette lentille diélectrique perforée, à cause notamment des pertes par réflexions passant de 4% par interface à une valeur située entre 0% et 17% (avec le matériau d'indice n=2,4), puisque l'indice effectif synthétisé prend quatre valeurs entre 1 et 2,4. De fait, cette solution a apporté un gain plus faible qu'une lentille de Fresnel classique à quatre niveaux d'indice de réfraction fabriquée dans un matériau de plus bas indice, comme le plexiglas d'indice n=1,61, comme mentionné dans
Il est donc souhaitable de remédier aux inconvénients de l'état de la technique, et de proposer une solution permettant d'obtenir un bon rendement en ayant de faibles pertes par réflexion et un faible encombrement dans le domaine hyperfréquences.It is therefore desirable to overcome the drawbacks of the state of the art, and to propose a solution to obtain a good performance by having low reflection losses and a small footprint in the microwave range.
A cet effet, selon un premier aspect, l'invention propose une antenne lentille comportant au moins un composant diélectrique diffractif apte à mettre en forme un front d'onde hyperfréquence ayant une longueur d'onde comprise dans une plage de 1 millimètre à 50 centimètres, caractérisée en ce que ledit composant diélectrique diffractif comporte une pluralité de microstructures principales formées dans un matériau substrat d'indice de réfraction substrat de manière à former un matériau artificiel d'indice de réfraction effectif, chaque microstructure principale ayant une taille inférieure à une longueur d'onde cible prise dans ladite plage de longueurs d'onde, lesdites microstructures principales étant agencées par zones, de manière à faire varier un taux de remplissage surfacique, l'indice de réfraction effectif étant fonction dudit taux de remplissage surfacique, l'agencement étant tel que l'indice de réfraction effectif varie à l'intérieur d'une dite zone dudit composant diélectrique diffractif de manière quasi-monotone entre une valeur minimale et une valeur maximale inférieure ou égale à l'indice de réfraction substrat.For this purpose, according to a first aspect, the invention proposes a lens antenna comprising at least one diffractive dielectric component capable of shaping a microwave wavefront having a wavelength in a range of 1 millimeter to 50 centimeters. characterized in that said diffractive dielectric component comprises a plurality of main microstructures formed in a substrate refractive index substrate material so as to form an artificial material of effective refractive index, each main microstructure having a size smaller than a length target waveform taken in said wavelength range, said main microstructures being arranged in zones, so as to vary a surface filling ratio, the effective refractive index being a function of said surface filling ratio, the arrangement being such that the effective refractive index varies within a said zone said dielectric diffractive component in a quasi-monotonic manner between a minimum value and a maximum value less than or equal to the substrate refractive index.
Avantageusement, une antenne lentille selon l'invention a un bon rendement et présente un faible encombrement. En effet, un composant diélectrique diffractif avec un agencement de microstructures principales de taille inférieure à la longueur d'onde cible, appelées microstructures sub-longueur d'onde, permet la synthèse, pour une zone du composant, d'une variation quasi-monotone quasiment continue de l'indice de réfraction effectif avec un grand nombre de motifs de microstructures sub-longueur d'onde. Cela permet d'améliorer l'efficacité de diffraction et d'éviter les pertes par effet d'ombrage. De plus, la solution proposée par l'invention permet de maximiser les effets de guidage et donc de maximiser l'efficacité du composant diélectrique, ce qui permet l'obtention d'antennes lentilles efficaces dans le domaine des hyperfréquences.Advantageously, a lens antenna according to the invention has a good performance and has a small footprint. Indeed, a diffractive dielectric component with an arrangement of main microstructures smaller than the target wavelength, called subwavelength microstructures, allows the synthesis, for a zone of the component, of a quasi-monotone variation. almost continuous the effective refractive index with a large number of sub-wavelength microstructure patterns. This makes it possible to improve the diffraction efficiency and to avoid shading losses. In addition, the solution proposed by the invention makes it possible to maximize the guiding effects and thus maximize the efficiency of the dielectric component, which makes it possible to obtain effective lens antennas in the microwave range.
L'antenne lentille selon l'invention peut également présenter une ou plusieurs des caractéristiques ci-dessous :
- la densité de microstructures principales par unité de surface varie dans une zone dudit composant diélectrique, la taille de chaque microstructure principale étant fixée ;
- la taille desdites microstructures principales est variable pour une zone dudit composant diélectrique ;
- lesdites microstructures principales sont à section carrée ou circulaire, de largeur égale à K fois la longueur d'onde cible prise dans ladite plage de longueurs d'onde, K étant compris entre 1/50 et 1/1,5 ;
- lesdites microstructures principales sont des piliers formés en saillie sur ledit matériau substrat et/ou des trous formés dans ledit matériau substrat ;
- lesdites microstructures principales étant des piliers formés en saillie sur ledit matériau substrat, le composant diélectrique diffractif comporte en outre, en plus desdites microstructures principales, au moins une couche comportant des microstructures secondaires de taille inférieure à la taille desdites microstructures principales, lesdites microstructures secondaires étant adaptées à diminuer les réflexions d'onde hyperfréquence incidente ;
- ledit composant diélectrique diffractif comporte plusieurs couches de microstructures secondaires empilées, chaque couche de microstructures secondaires comprenant des piliers formés en saillie sur lesdites microstructures principales ou secondaires de la couche précédant ladite couche de microstructures secondaires ;
- lesdites microstructures principales sont positionnées sur une première face dudit composant diélectrique diffractif, caractérisée en ce que ledit composant diélectrique diffractif comporte une couche de microstructures secondaires positionnée sur une deuxième face dudit composant diélectrique diffractif, opposée à ladite première face ;
- lesdites microstructures principales et/ou lesdites microstructures secondaires ont une forme conique ;
- lesdites microstructures principales étant positionnées sur une première face dudit composant diélectrique diffractif, ledit composant diélectrique diffractif comporte une couche non diffractive de microstructures sub-longueur d'onde, réalisant une fonction de phase associée, sur une deuxième face dudit composant diélectrique diffractif, opposée à ladite première face ;
- ledit composant diélectrique diffractif comporte en outre une lame diélectrique neutre de protection d'épaisseur fonction de ladite longueur d'onde cible, et
- ledit composant diélectrique diffractif est une matrice rectangulaire de dits composants diélectriques diffractifs de section carrée ou rectangulaire.
- the density of principal microstructures per unit area varies in an area of said dielectric component, the size of each main microstructure being set;
- the size of said main microstructures is variable for an area of said dielectric component;
- said main microstructures are square or circular in cross section, of width equal to K times the target wavelength taken in said wavelength range, K being between 1/50 and 1 / 1.5;
- said main microstructures are pillars formed protruding from said substrate material and / or holes formed in said substrate material;
- said main microstructures being pillars formed protruding from said substrate material, the diffractive dielectric component further comprises, in addition to said main microstructures, at least one layer having secondary microstructures smaller than the size of said main microstructures, said secondary microstructures being adapted to reduce incident microwave radiation reflections;
- said diffractive dielectric component comprises several layers of stacked secondary microstructures, each layer of secondary microstructures comprising pillars formed protruding from said main or secondary microstructures of the layer preceding said layer of secondary microstructures;
- said main microstructures are positioned on a first face of said diffractive dielectric component, characterized in that said diffractive dielectric component comprises a layer of secondary microstructures positioned on a second face of said diffractive dielectric component, opposite said first face;
- said main microstructures and / or said secondary microstructures have a conical shape;
- said main microstructures being positioned on a first face of said diffractive dielectric component, said diffractive dielectric component comprises a non-diffractive layer of subwavelength microstructures, realizing an associated phase function, on a second face of said diffractive dielectric component, opposite to said first face;
- said dielectric diffractive component further comprises a neutral thickness protective dielectric plate of said target wavelength, and
- said diffractive dielectric component is a rectangular matrix of said diffractive dielectric components of square or rectangular section.
D'autres caractéristiques et avantages de l'invention ressortiront de la description qui en est donnée ci-dessous, à titre indicatif et nullement limitatif, en référence aux figures annexées, parmi lesquelles :
- la
figure 1 , déjà décrite, est une vue en coupe mettant en correspondance des lentilles classiques, à savoir une lentille réfractive et une lentille diffractive de Fresnel à profil en échelette ; - la
figure 2 est une vue en coupe de différentes réalisations d'un composant diélectrique diffractif de type réseau à échelette ; - la
figure 3 est une vue de dessus de différentes réalisations d'un composant diffractif de type réseau à échelette selon l'invention ; - la
figure 4 est un graphe représentant l'indice effectif du composant diélectrique diffractif composé de piliers périodiques en fonction du taux de remplissage surfacique, sur un substrat d'indice 2,54 ; - la
figure 5 est un graphe représentant l'indice effectif du composant diélectrique diffractif composé de trous périodiques en fonction du taux de remplissage surfacique, sur un substrat d'indice 2,54 ; - la
figure 6 est un graphe représentant les indices effectifs respectifs du composant diélectrique diffractif composé de piliers ou de trous périodiques de taille fixée en fonction du taux de remplissage surfacique, sur un substrat d'indice 2,54 ; - la
figure 7 est une vue de coupe d'un composant diélectrique diffractif selon un premier mode de réalisation avec adaptation d'impédance ; - la
figure 8 est une vue de coupe d'un composant diélectrique diffractif selon un deuxième mode de réalisation avec adaptation d'impédance ; - la
figure 9 est une vue de coupe d'un composant diélectrique diffractif selon un troisième mode de réalisation avec adaptation d'impédance ; - la
figure 10 est une vue de coupe d'un composant diélectrique diffractif selon un quatrième mode de réalisation avec adaptation d'impédance ; - la
figure 11 est une vue du dessus d'une matrice de composants diélectriques diffractifs à microstructures sub-longueur d'onde ; - la
figure 12 est un schéma représentant le défléchissement d'ondes par une lentille hors d'axe ; - la
figure 13 est un schéma représentant la génération de deux faisceaux d'ondes, et - la
figure 14 est un schéma représentant la génération de deux faisceaux d'ondes à partir de multiples sources d'ondes.
- the
figure 1 , already described, is a cross-sectional view mapping conventional lenses, namely a refractive lens and a diffractive Fresnel diffractive echelette lens; - the
figure 2 is a sectional view of different embodiments of a diffractive dielectric ladder-type dielectric component; - the
figure 3 is a top view of different embodiments of a ladder array type diffractive component according to the invention; - the
figure 4 is a graph representing the effective index of the diffractive dielectric component composed of periodic pillars as a function of the surface filling ratio, on a substrate of index 2.54; - the
figure 5 is a graph representing the effective index of the diffractive dielectric component composed of periodic holes as a function of the surface charge ratio, on a substrate of index 2.54; - the
figure 6 is a graph representing the respective effective indices of the diffractive dielectric component composed of periodic size-fixed piers or holes as a function of the surface coverage ratio, on a 2.54 index substrate; - the
figure 7 is a sectional view of a diffractive dielectric component according to a first embodiment with impedance matching; - the
figure 8 is a sectional view of a diffractive dielectric component according to a second embodiment with impedance matching; - the
figure 9 is a sectional view of a diffractive dielectric component according to a third embodiment with impedance matching; - the
figure 10 is a sectional view of a diffractive dielectric component according to a fourth embodiment with impedance matching; - the
figure 11 is a top view of a matrix of diffractive dielectric components with subwavelength microstructures; - the
figure 12 is a diagram showing the deflection of waves by an off-axis lens; - the
figure 13 is a diagram representing the generation of two beams of waves, and - the
figure 14 is a diagram representing the generation of two beams of waves from multiple wave sources.
L'invention sera décrite plus particulièrement dans l'application de lentilles diélectriques diffractives ou composants diélectriques diffractifs pour antenne lentille dans le domaine hyperfréquence dans une plage de 30 GHz à 50 GHz (connue sous le nom de bande Q), qui est une plage particulière du domaine hyperfréquence. Une telle antenne lentille est composée d'une source d'ondes électromagnétiques hyperfréquence et d'une lentille, qui est un composant diélectrique diffractif et qui collecte et remet en forme l'onde générée par la source, ce qui résulte en un front d'onde modifié. La source se situe au niveau du foyer de ce composant, ou plus généralement à proximité du foyer de ce composant..The invention will be described more particularly in the application of diffractive dielectric lenses or diffractive dielectric components for a lens antenna in the microwave range in the range of 30 GHz to 50 GHz (known as the Q band), which is a particular range of the microwave domain. Such a lens antenna is composed of a source of microwave electromagnetic waves and a lens, which is a diffractive dielectric component and which collects and reshapes the wave generated by the source, resulting in a front of modified wave. The source is located at the focus of this component, or more generally near the focus of this component.
Afin d'illustrer la réalisation d'un matériau artificiel à variation monotone d'indice effectif ou quasi gradient d'indice, diverses réalisations d'un réseau en échelette fonctionnant en transmission sont décrites en référence à la
Le composant 20 de la
Par la suite, l'indice de réfraction sera appelé simplement indice.Subsequently, the refractive index will be called simply index.
Un réseau en échelette permet de réaliser une fonction de phase ou décalage de phase ΔΦ(λ0,x,y ), ΔΦ étant le retard de phase introduit par le composant diélectrique aux coordonnées (x,y) du composant, qui dépend l'indice n et de la hauteur du composant :
où λ0, la longueur d'onde cible dans le domaine considéré et n0 l'indice le plus faible atteint, et h(x,y) est la fonction donnant la hauteur du composant en un point spatial de coordonnées (x,y) dans un repère spatial. Sur un réseau en échelette dans de l'air, la fonction de phase est obtenue par la variation de la hauteur, en gardant n(x,y)=n, l'indice de réfraction du matériau. La fonction de phase ou décalage de phase devient :
where λ 0 , the target wavelength in the domain considered and n 0 the lowest index reached, and h (x, y) is the function giving the height of the component at a spatial point of coordinates (x, y ) in a spatial reference. On an echelette grating in air, the phase function is obtained by varying the height, keeping n (x, y) = n, the refractive index of the material. The phase function or phase shift becomes:
La hauteur maximale h=(h2-h1) est calculée, en fonction de la variation d'indice n-n0, pour obtenir un déphasage de 2π.
entouré d'air (n0=1). A titre d'indication la hauteur d'un réseau dans du verre est égale à 12,3mm à λ0=7,14mm.The maximum height h = (h 2 -h 1 ) is calculated, as a function of the index variation nn 0 , to obtain a phase shift of 2π.
surrounded by air (n 0 = 1). As an indication the height of a network in glass is equal to 12.3mm at λ 0 = 7.14mm.
Le composant 23 de la
En pratique, un tel gradient d'indice à hauteur constante à cette échelle est très difficile à obtenir dans le domaine des radio/hyperfréquences, Cela nécessite l'utilisation de techniques complexes de combinaison et d'incorporation de matériaux (par exemple tissu de verre et teflon PTFE).In practice, such a constant height index gradient at this scale is very difficult to obtain in the radio / microwave field. This requires the use of complex techniques for combining and incorporating materials (for example glass cloth and PTFE teflon).
Une alternative pour l'obtention d'une variation monotone de l'indice ou gradient d'indice selon l'invention est représentée par le composant 26 de la
Avantageusement, l'efficacité de diffraction est améliorée, car l'utilisation des microstructures sub-longueur d'onde évite l'effet d'ombrage obtenu avec la réalisation en échelette 20, et donc permet d'augmenter le rendement du composant diélectrique 26 par rapport au rendement du composant en échelette 20. Les piliers 28 qui sont à section carrée, circulaire ou hexagonale par exemple, ont des largeurs variables, la largeur maximale étant égale à d qui est inférieure à λ0, la longueur d'onde cible dans le domaine hyperfréquence considéré. Les piliers sont agencés dans une structure périodique de période Λs qui est la distance entre les centres de deux piliers consécutifs dans l'exemple de la
Lorsque la période Λs est inférieure à la longueur d'onde à λ0, le composant diélectrique se comporte comme un matériau artificiel dont l'indice effectif varie localement par zone de manière monotone, formant un matériau à quasi gradient d'indice effectif. Cet agencement des microstructures permet de synthétiser un grand nombre d'indices effectifs différents N, avec N>4, typiquement N=8, les N indices effectifs variant de façon progressive par petits pas.When the period Λ s is less than the wavelength at λ 0 , the dielectric component behaves as an artificial material whose effective index varies locally per area monotonously, forming a material with a gradient of effective index. This arrangement of the microstructures makes it possible to synthesize a large number of different effective indices N, with N> 4, typically N = 8, the N effective indices varying gradually in small steps.
De préférence,
où ns est l'indice de réfraction du matériau diélectrique substrat, ninc est l'indice de réfraction du milieu incident (généralement le milieu incident est l'air, ninc=1), et θ est l'angle d'incidence du faisceau d'ondes sur le composant diélectrique. Si la période Λs est choisie supérieure à la valeur donnée par la formule de Eq2, le composant diélectrique n'a plus la propriété de matériau artificiel à quasi gradient d'indice souhaitée.Preferably,
where n s is the refractive index of the substrate dielectric material, n inc is the refractive index of the incident medium (generally the incident medium is air, n inc = 1), and θ is the incidence angle of the wave beam on the dielectric component. If the period Λ s is chosen greater than the value given by the formula of Eq2, the dielectric component no longer has the property of artificial material with a desired index gradient.
Dans le cas d'une lentille diffractive ou d'un réseau, la hauteur h du composant est calculée pour obtenir un multiple de déphasage de 2π, généralement simplement 2π, ce qui induit :
où nmax et nmin sont les indices effectifs maximum et minimum, l'indice effectif maximum étant inférieur ou égal à l'indice du substrat.In the case of a diffractive lens or a grating, the height h of the component is calculated to obtain a phase shift multiple of 2π, generally just 2π, which induces:
where n max and n min are the maximum and minimum effective indices, the maximum effective index being less than or equal to the index of the substrate.
L'indice effectif dépend de la géométrie de la microstructure sub-longueur d'onde.The effective index depends on the geometry of the sub-wavelength microstructure.
Pour les microstructures en forme de piliers, on définit un taux de remplissage surfacique qui est égal à la surface occupée par les piliers contenus dans une unité de surface divisée par cette même unité de surface. Une unité de surface est définie comme la surface du carré de côté Λs. L'indice effectif est quasiment proportionnel au taux de remplissage surfacique.For pillar-shaped microstructures, a surface filling ratio is defined which is equal to the area occupied by the pillars contained in a surface unit divided by the same surface unit. A surface unit is defined as the area of the side square Λ s . The effective index is almost proportional to the surface fill rate.
Pour les microstructures en forme de trous, le taux de remplissage surfacique est égal à la surface de matériau diélectrique substrat restante par unité de surface divisée par cette même unité de surface.For hole-shaped microstructures, the surface coverage ratio is equal to the area of remaining substrate dielectric material per unit area divided by the same surface unit.
D'une manière générale, le taux de remplissage surfacique représente la surface de matériau substrat composant le matériau artificiel par unité de surface.In general, the surface filling ratio represents the surface of the substrate material constituting the artificial material per unit area.
Le composant 29 de la
Il est également envisageable de combiner les microstructures de taille variable et leur agencement de densité variable dans un même composant diélectrique diffractif.It is also conceivable to combine the microstructures of variable size and their variable density arrangement in the same diffractive dielectric component.
Alternativement, un composant diélectrique à gradient d'indice est construit à base de microstructures de type trous sur le même principe, en perçant dans le matériau diélectrique des trous de diamètre ou de taille fixe, et en faisant varier le nombre de trous par unité de surface.Alternatively, a graded index dielectric component is constructed based on holes-like microstructures on the same principle, by drilling holes of fixed diameter or size into the dielectric material, and varying the number of holes per unit of area.
La
Une première vue du dessus 32 illustre un premier mode de réalisation d'un composant diélectrique diffractif 26, avec deux zones ou échelons, comprenant des microstructures 33 à section carrée de taille variable, et agencées selon un maillage carré.A first view of the top 32 illustrates a first embodiment of a
Une deuxième vue du dessus 34 illustre un deuxième mode de réalisation d'un composant diélectrique diffractif 26, avec deux zones ou échelons, comprenant des microstructures 35 à section circulaire et de diamètre variable, agencées selon un maillage hexagonal.A second view of the top 34 illustrates a second embodiment of a
Enfin la vue 36 illustre un mode de réalisation d'un composant diélectrique diffractif 29, avec deux zones ou échelons, comprenant des microstructures 37 de section carrée de taille constante, agencées avec une densité surfacique variable.Finally, the
Tous les types de microstructures - trous ou piliers, de section ronde, carrée ou selon une autre forme géométrique - sont adaptés à la réalisation des composants diélectriques diffractifs pour des ondes hyperfréquence, de longueur d'onde micro-onde, car les dimensions des microstructures, calculées à partir de la longueur d'onde cible, sont supérieures à 1 mm, et donc ne nécessitent pas de technologie de fabrication très coûteuse.All types of microstructures - holes or pillars, of round section, square or in another geometric form - are suitable for the realization of diffractive dielectric components for microwave waves, of microwave wavelength, because the dimensions of the microstructures , calculated from the target wavelength, are greater than 1 mm, and therefore do not require expensive manufacturing technology.
Dans le mode de réalisation préféré de l'invention, le composant diélectrique diffractif est réalisé avec des microstructures de type piliers, qui ont l'avantage d'optimiser le guidage d'onde et donc d'augmenter l'efficacité de diffraction.In the preferred embodiment of the invention, the diffractive dielectric component is made with pillar type microstructures, which have the advantage of optimizing the waveguiding and thus increasing the diffraction efficiency.
Dans une variante, trous et piliers sont associés dans un même composant.In a variant, holes and pillars are associated in the same component.
De façon non restrictive, ces microstructures sont, selon un mode de réalisation, des microstructures de section carrée, ronde, ovale, hexagonale, de largeur égale sur la profondeur, c'est-à-dire à flanc droit ou quasi-droit dans l'épaisseur du composant.Without limitation, these microstructures are, according to one embodiment, microstructures of square section, round, oval, hexagonal, of width equal to the depth, that is to say to the right flank or quasi-right in the thickness of the component.
Selon un mode de réalisation alternatif, les microstructures sont en forme de cônes, c'est-à-dire ayant des flancs qui ne sont pas droits dans l'épaisseur du substrat, par exemple avec un diamètre plus faible côté air et plus large côté substrat.According to an alternative embodiment, the microstructures are cone-shaped, that is to say having flanks that are not straight in the thickness of the substrate, for example with a smaller diameter on the air side and wider side. substrate.
Les
La
En abscisse est représenté le taux de remplissage surfacique, qui varie entre 0 et 1, et en ordonnée l'indice effectif du matériau artificiel obtenu, qui varie entre 1 et 2,6.On the abscissa is represented the surface filling ratio, which varies between 0 and 1, and on the ordinate the effective index of the artificial material obtained, which varies between 1 and 2.6.
Le graphe correspond à des piliers de période Λs=2,4mm, fabriqués dans un matériau diélectrique substrat d'indice substrat ns=2,54. La longueur d'onde cible λ0 est de 7,14mm, correspondant à une fréquence d'environ 42 GHz. La période Λs est dans cet exemple égale à 0,336 x λ0. Ce choix correspond à une ouverture de f/1.4. Pour une ouverture de f/0.25, on calcule la valeur de Λs en utilisant la formule Eq2 avec θ = 63° , qui est l'angle d'incidence correspondant à l'ouverture f/0.25.The graph corresponds to pillars of period Λ s = 2.4mm, made of substrate substrate dielectric material n s = 2.54. The target wavelength λ 0 is 7.14 mm, corresponding to a frequency of approximately 42 GHz. The period Λ s is in this example equal to 0.336 x λ 0 . This choice corresponds to an opening of f / 1.4. For an opening of f / 0.25, the value of Λ s is calculated using the formula Eq2 with θ = 63 °, which is the angle of incidence corresponding to the opening f / 0.25.
Comme illustré sur la
En regard de chacun des points P1 à P5, le taux de remplissage surfacique des piliers est représenté schématiquement par une vue du dessus de chaque pilier à section carrée 38 centré par unité de surface 40. La zone 38 représente le matériau diélectrique composant le pilier, la zone 42 correspond à l'air (zone laissée vide autour des piliers).With respect to each of the points P 1 to P 5 , the surface filling ratio of the pillars is represented schematically by a top view of each square-
Le côté d de la section carrée de chaque pilier varie entre une valeur de d=1,28mm, qui correspond à 0,179 x λ0 pour le point P1 à d=2,3mm, qui correspond à 0,322 x λ0 pour le point P5. Si on suppose l'utilisation de piliers de largeur variant entre 0 et la taille de P4, l'excursion d'indice obtenue est égale à ∼ 1, entraînant une hauteur du composant de h=7,1 mm environ.The d-side of the square section of each pillar varies between a value of d = 1.28mm, which corresponds to 0.179 x λ 0 for the point P 1 to d = 2.3mm, which corresponds to 0.322 x λ 0 for the point P 5 . If we assume the use of pillars of width varying between 0 and the size of P4, the index excursion obtained is equal to ~ 1, resulting in a component height of h = 7.1 mm.
Le graphe de la
Similairement au graphe de la
Le graphe de la
Le taux de remplissage surfacique est donné ici par la surface occupée par le matériau diélectrique, soit la surface 44 moins la zone de trou 46 de section carrée de côté d. Naturellement, le côté d est inversement proportionnel dans ce cas au taux de remplissage surfacique.The surface filling ratio is given here by the area occupied by the dielectric material, namely the
Comme illustré sur la
La
Comme dans les figures précédentes, en abscisse est représenté le taux de remplissage surfacique, qui varie entre 0 et 1, et en ordonnée l'indice effectif du matériau obtenu, qui varie entre 1 et 2,6.As in the previous figures, on the abscissa is represented the surface filling ratio, which varies between 0 and 1, and on the ordinate the effective index of the material obtained, which varies between 1 and 2.6.
Dans ce mode de réalisation, les conditions ont été conservées : indice de réfraction du matériau diélectrique substrat ns=2,54 et longueur d'onde cible λ0=7,14mm.In this embodiment, the conditions have been preserved: refractive index of the dielectric material substrate n s = 2.54 and target wavelength λ 0 = 7.14 mm.
La taille d du côté de la section carrée de chacune des microstructures (trou ou pilier) est constante et égale à 0,2mm, et c'est la densité de matériau par unité de surface qui varie. Pour ce mode de réalisation, l'avantage de la facilité de fabrication subsiste également, la fabrication des microstructures étant aisée du fait de leur taille constante. La période macroscopique d'une cellule élémentaire est deΛs= 2,4mm, donc chaque unité de surface carrée 48 correspond à 2,4mm2.The size d on the side of the square section of each microstructure (hole or pillar) is constant and equal to 0.2mm, and it is the density of material per unit area that varies. For this embodiment, the advantage of ease of manufacture also remains, the manufacture of microstructures being easy because of their constant size. The macroscopic period of an elementary cell is deΛ s = 2.4mm, so each unit of
La courbe 50 correspond à des microstructures en forme de piliers, et la courbe 52 correspond à de microstructures en forme de trous.
Dans les carrés 48, les zones hachurées correspondent au matériau diélectrique et les zones sans remplissage correspondent à l'air.In
Dans une variante, on combine les deux géométries, à savoir piliers et trous, afin de pouvoir utiliser l'intégralité de l'excursion d'indice et de diminuer la hauteur des structures. Par exemple en utilisant une combinaison de trous et de piliers dont les tailles varient entre 0 et celle de P4 pour les piliers et 0 et celle de Q2 pour les trous, l'excursion d'indice devient égale à 1,54, entrainant une hauteur de 4,6mm environ. Ainsi, la combinaison piliers et trous permet de diminuer encore l'encombrement du composant diélectrique diffractif.In a variant, the two geometries, namely pillars and holes, are combined in order to be able to use the entire index excursion and to reduce the height of the structures. For example using a combination of holes and pillars whose sizes vary between 0 and that of P4 for the pillars and 0 and that of Q2 for the holes, the index excursion becomes equal to 1.54, resulting in a height about 4.6mm. Thus, the combination of pillars and holes makes it possible to further reduce the bulk of the diffractive dielectric component.
Dans une autre variante, afin de faciliter le procédé de fabrication, le composant diélectrique est composé de piliers de taille constante, et agencés de manière à faire varier leur densité pour obtenir un quasi gradient d'indice, avec un nombre de piliers variable par unité de surface. Dans le domaine hyperfréquence d'application, les longueurs d'ondes cibles se situent typiquement dans une plage de 1 mm à 75cm, et la taille de côté typique des microstructures piliers est d= K x λ0, avec K compris entre 1/50 et 1/1,5. De telles microstructures peuvent être fabriquées aisément par moulage, et donc produites en grand nombre.In another variant, in order to facilitate the manufacturing process, the dielectric component is composed of pillars of constant size, and arranged so as to vary their density to obtain a quasi index gradient, with a variable number of pillars per unit of surface. In the microwave application domain, the target wavelengths are typically in a range of 1 mm to 75 cm, and the typical size of the pillar microstructures is d = K x λ 0 , with K between 1/50 and 1 / 1.5. Such microstructures can be manufactured easily by molding, and thus produced in large numbers.
En variante, les microstructures piliers agencées en zones sont positionnées sur les deux faces opposées du composant diélectrique, de manière à associer deux fonctions de phase, une de chaque côté du composant. Avantageusement, la hauteur des microstructures est alors répartie sur les deux faces opposées, impliquant des microstructures plus faciles à fabriquer. De plus, la deuxième face a un indice effectif qui varie entre un et l'indice du substrat, donc un indice effectif plus faible en moyenne, ce qui permet de réduire les pertes sur la deuxième interface.In a variant, the pillar microstructures arranged in zones are positioned on the two opposite faces of the dielectric component, so as to associate two phase functions, one on each side of the component. Advantageously, the height of the microstructures is then distributed on the two opposite faces, involving microstructures that are easier to manufacture. In addition, the second face has an effective index which varies between one and the index of the substrate, and therefore a lower effective index on average, which makes it possible to reduce the losses on the second interface.
Selon une autre variante, le composant diélectrique diffractif comporte, sur une première face dite face diffractive, des microstructures, par exemple de type piliers, agencées en zones, et sur la face opposée, qui est la première face rencontrée par le front d'onde résultant de la source et qui est une face non diffractive dans ce cas, une structuration avec des microstructures sub-longueur d'onde réalisant une fonction de phase sub-longueur d'onde, permettant une mise en forme du front d'ondes issu de la source. Ainsi, le traitement appliqué sur la face rencontrée en premier par le front d'onde permet de corriger le front d'onde, notamment pour le rendre parfaitement sphérique, avant d'atteindre la face diffractive. Sur la face non diffractive, les microstructures sub-longueur d'onde sont par exemple des piliers de tailles variables ou de taille fixe et de densité variable, réalisant une variation lente d'indice effectif. Les microstructures de la première face ne sont pas agencées en plusieurs zones à variation d'indice effectif comme pour la face diffractive.According to another variant, the diffractive dielectric component comprises, on a first so-called diffractive face, microstructures, for example of the pillar type, arranged in zones, and on the opposite face, which is the first face encountered by the wavefront. resulting from the source and which is a non-diffractive face in this case, a structuring with sub-wavelength microstructures realizing a sub-wavelength phase function, allowing a shaping of the wavefront resulting from source. Thus, the treatment applied to the face first encountered by the wavefront corrects the wavefront, in particular to make it perfectly spherical, before reaching the diffractive face. On the non-diffractive face, the sub-wavelength microstructures are, for example, pillars of variable sizes or of fixed size and of variable density, realizing a slow variation of effective index. The microstructures of the first face are not arranged in several zones with effective index variation as for the diffractive face.
Dans un mode de réalisation particulièrement avantageux, le composant diélectrique formé de microstructures piliers comprend également une adaptation d'impédance, de manière à réduire les pertes dues aux réflexions d'onde incidente aux interfaces entre l'air et le matériau diélectrique artificiel. En effet, de manière connue, pour un matériau diélectrique d'indice n=2,4, la perte par réflexion (ou par désadaptation) à chaque interface avec l'air d'indice n=1 est égale à 17%.In a particularly advantageous embodiment, the dielectric component formed of pillar microstructures also comprises an impedance matching, so as to reduce the losses due to incident wave reflections at the interfaces between the air and the artificial dielectric material. Indeed, in a known manner, for a dielectric material of index n = 2.4, the loss by reflection (or mismatch) at each interface with air index n = 1 is equal to 17%.
La diminution de ces pertes est connue sous le nom de traitement anti-reflets en optique et d'adaptation d'impédance dans le domaine des hyperfréquences.The reduction of these losses is known under the name anti-reflection treatment in optics and impedance matching in the microwave domain.
Les
Dans un premier mode de réalisation illustré sur la
La période Λ1 et la taille d2 sont choisies par simulation de manière à diminuer localement l'indice du composant diélectrique au niveau de l'interface avec l'air.The period Λ 1 and the size d 2 are chosen by simulation so as to locally reduce the index of the dielectric component at the interface with the air.
Dans un deuxième mode de réalisation, illustré sur la
Sur ces piliers 72 sont intégrés en saillie des microstructures sub-longueur d'onde secondaires, qui sont des micropiliers 74, de période d'un ordre de grandeur inférieur à la période λs des piliers 72. De plus, des micropiliers 76 sont également intégrés sur la deuxième face du composant diélectrique 70, qui est à l'opposé de la première face, permettant ainsi de réaliser une adaptation d'impédance sur les deux interfaces de la lentille et donc de réduire encore plus les pertes par réflexion. Lorsque la deuxième face ne comporte pas de microstructures sub-longueur d'onde principales, les micropiliers 76 ont une période Λ1 comprise dans la plage plus large, telle que Λ s /10 ≤ Λ1 ≤ Λ s .On these
Selon un troisième mode de réalisation, illustré à la
La lame diélectrique 80 est positionnable dans la partie où le faisceau est faiblement divergent, et donc pour un système très ouvert (F/D petit, F/D≤1 par exemple) derrière le composant diélectrique 78, c'est-à-dire sur le côté du composant diélectrique 78 qui n'est pas en regard de la source. Un exemple serait une lame de Rexolite de 2,25mm d'épaisseur pour garantir une transmission de la lame supérieure à 99,5% entre 40,5GHz et 43,5GHz.The
Selon un quatrième mode de réalisation, illustré à la
Dans un autre mode de réalisation, une antenne lentille selon l'invention comprend un système diélectrique constitué d'une matrice, carrée ou plus généralement rectangulaire, de composants diélectriques diffractifs comprenant des microstructures sub-longueur d'onde tels que décrits ci-dessus. La
Chacun des composants est formé de zones ou anneaux concentriques z1, z2, z3 et z4, chaque zone étant composée de microstructures sub-longueur d'onde, par exemple des piliers, comme décrit ci-dessus. La matrice proposée a pour avantage de ne pas présenter de recouvrement d'un composant sur l'autre qui la compose, tout en assurant l'utilisation de l'ensemble de la zone utile (pas de zone morte dans la matrice) : l'ensemble du faisceau d'onde arrivant sur la matrice est transformé par la matrice, il n'y a pas de zone entre les composants de la matrice qui ne contribue pas à la collimation du faisceau.Each of the components is formed of concentric zones or rings z1, z2, z3 and z4, each zone being composed of subwavelength microstructures, for example pillars, as described above. The proposed matrix has the advantage of not having any overlap of one component over the other which composes it, while ensuring the use of the whole of the useful area (no dead zone in the matrix): the the whole of the wave beam arriving on the matrix is transformed by the matrix, there is no zone between the components of the matrix which does not contribute to the collimation of the beam.
L'agencement sous forme de matrice pxq permet de miniaturiser plus le système diélectrique, car pour obtenir une ouverture numérique donnée, la distance focale et donc le diamètre de chaque lentille de la matrice est divisé par la dimension p de la matrice dans une direction et la dimension q de la matrice dans l'autre direction.The arrangement in the form of matrix pxq makes it possible to further miniaturize the dielectric system, because to obtain a given numerical aperture, the focal length and therefore the diameter of each lens of the matrix is divided by the dimension p of the matrix in one direction and the dimension q of the matrix in the other direction.
Les
La
La
La
Ainsi, on comprendra que le terme mettre en forme un front d'onde inclut les divers types de mise en forme d'un front d'onde décrits ci-dessus en référence aux
Selon une variante non représentée dans les figures, plusieurs composants diélectriques diffractifs tels que décrits sont associés, par exemple les uns derrière les autres avec des couches d'air les séparant, dans une antenne lentille selon l'invention.According to a variant not shown in the figures, several diffractive dielectric components as described are associated, for example one behind the other with air layers separating them, in a lens antenna according to the invention.
On note également que les composants diélectriques à microstructures sub-longueur d'onde sont également aptes à obtenir un meilleur rendement de focalisation en large bande (longueur d'onde nominale ± 20%) que les composants classiques à profil en échelette.It is also noted that the dielectric components with subwavelength microstructures are also able to obtain a better broadband focusing efficiency (nominal wavelength ± 20%) than the conventional ladder profile components.
D'une manière générale, un des avantages des composants diélectriques selon l'invention est leur fabrication, qui peut être effectuée aisément pour des séries de composants et à bas coût, du fait de leur dimensionnement. Il est possible de fabriquer un moule utilisable pour une fabrication en série, et donc chaque composant diélectrique diffractif est fabriqué par moulage/démoulage, en une seule étape de fabrication.In general, one of the advantages of the dielectric components according to the invention is their manufacture, which can be easily performed for series of components and at low cost, because of their dimensioning. It is possible to manufacture a usable mold for mass production, and thus each diffractive dielectric component is manufactured by molding / demolding, in a single manufacturing step.
Suivant le domaine de fréquence et la taille des antennes, il existe différents types de technologie de réalisation de lentille en fonction des matériaux.Depending on the frequency domain and the size of the antennas, there are different types of lens realization technology depending on the materials.
Par exemple, les matériaux sont sélectionnés parmi les matériaux suivants, pour lesquels on indique la permittivité ε et l'indice de réfraction n : Rexolite 1422 (ε=2.53, n=1,59), Plexiglas ε= n=1,6 , teflon (PTFE - ε=2,07 n=1,43), Pyrex 7740 (ε =4,6 n=2,14), Rogers RO3006 (ε =6,15 n=2,48), Rogers R0301 0 (ε =10,2 n=3,19), Alumine Al2O3 (ε=9,9 n=3,14), Titanate de Barium SH110 (ε=110 n=10,5).For example, the materials are selected from the following materials, for which the permittivity ε and the refractive index n: Rexolite 1422 (ε = 2.53, n = 1.59), Plexiglas ε = n = 1.6, are indicated. teflon (PTFE - ε = 2.07 n = 1.43), Pyrex 7740 (ε = 4.6 n = 2.14), Rogers RO3006 (ε = 6.15 n = 2.48), Rogers R0301 0 (ε = 10.2 n = 3.19), Alumina Al 2 O 3 (ε = 9.9 n = 3.14), Titanate of Barium SH110 (ε = 110 n = 10.5).
Diverses techniques de fabrication sont envisageables, comme par exemple :
- l'usinage mécanique ;
- le moulage ;
- le frittage (ou le cofrittage à basse température, LTCC) : dans un matériau composite à base de céramique, on fabrique la forme de base, puis on presse et on cuit à haute température (e.g. 900°C), ce qui permet d'enlever le polymère de la forme de base ;
- les techniques d'empilement de céramique ou de circuits imprimés ;
- l'usinage laser.
- mechanical machining;
- molding ;
- sintering (or LTCC): in a ceramic-based composite material, the basic form is made, then pressed and baked at high temperature (eg 900 ° C), which allows remove the polymer from the base form;
- stacking techniques of ceramics or printed circuits;
- laser machining.
Le point commun de ces modes de fabrication est la facilité de réalisation de composants diélectriques diffractifs à microstructures sub-longueur d'onde pour une antenne lentille en grand nombre et à faible coût de fabrication.The common point of these methods of manufacture is the ease of realization of diffractive dielectric components subwavelength microstructures for a lens antenna in large numbers and low manufacturing cost.
Claims (12)
Priority Applications (1)
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PL12186157.9T PL2573872T4 (en) | 2011-09-26 | 2012-09-26 | Lens antenna comprising a diffractive dielectric component able to shape a hyperfrequency wave front. |
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FR1102910A FR2980648B1 (en) | 2011-09-26 | 2011-09-26 | LENS ANTENNA COMPRISING A DIFERACTIVE DIELECTRIC COMPONENT CAPABLE OF SHAPING A MICROWAVE SURFACE FRONT |
Publications (2)
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EP2573872A1 true EP2573872A1 (en) | 2013-03-27 |
EP2573872B1 EP2573872B1 (en) | 2016-01-20 |
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US (1) | US8963787B2 (en) |
EP (1) | EP2573872B1 (en) |
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PL (1) | PL2573872T4 (en) |
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CN103268985A (en) * | 2013-04-24 | 2013-08-28 | 同济大学 | Electromagnetic wave beam regulating and controlling device |
WO2018091587A1 (en) | 2016-11-17 | 2018-05-24 | Thales | Device for squinting a beam by displacement of effective dielectric rolls |
US10746903B2 (en) | 2017-09-20 | 2020-08-18 | The Boeing Company | Gradient index (GRIN) spoke lens and method of operation |
US10777905B2 (en) | 2018-09-07 | 2020-09-15 | The Boeing Company | Lens with concentric hemispherical refractive structures |
US10916853B2 (en) | 2018-08-24 | 2021-02-09 | The Boeing Company | Conformal antenna with enhanced circular polarization |
US10923831B2 (en) | 2018-08-24 | 2021-02-16 | The Boeing Company | Waveguide-fed planar antenna array with enhanced circular polarization |
US10938082B2 (en) | 2018-08-24 | 2021-03-02 | The Boeing Company | Aperture-coupled microstrip-to-waveguide transitions |
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FR3116910A1 (en) * | 2020-12-01 | 2022-06-03 | Valeo Vision | Vehicle assembly comprising a radar sensor and a gradient index lens |
FR3116909A1 (en) * | 2020-12-01 | 2022-06-03 | Valeo Vision | Vehicle assembly comprising a radar sensor and an arrangement of layers forming a logo |
US11385384B2 (en) | 2020-05-12 | 2022-07-12 | The Boeing Company | Spoke dielectric lens |
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CN103268985A (en) * | 2013-04-24 | 2013-08-28 | 同济大学 | Electromagnetic wave beam regulating and controlling device |
WO2018091587A1 (en) | 2016-11-17 | 2018-05-24 | Thales | Device for squinting a beam by displacement of effective dielectric rolls |
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US10938082B2 (en) | 2018-08-24 | 2021-03-02 | The Boeing Company | Aperture-coupled microstrip-to-waveguide transitions |
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US11177548B1 (en) | 2020-05-04 | 2021-11-16 | The Boeing Company | Electromagnetic wave concentration |
US11385384B2 (en) | 2020-05-12 | 2022-07-12 | The Boeing Company | Spoke dielectric lens |
FR3116910A1 (en) * | 2020-12-01 | 2022-06-03 | Valeo Vision | Vehicle assembly comprising a radar sensor and a gradient index lens |
FR3116909A1 (en) * | 2020-12-01 | 2022-06-03 | Valeo Vision | Vehicle assembly comprising a radar sensor and an arrangement of layers forming a logo |
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WO2022117349A1 (en) * | 2020-12-01 | 2022-06-09 | Valeo Vision | Vehicle assembly comprising a radar sensor and a gradient-index lens |
Also Published As
Publication number | Publication date |
---|---|
FR2980648B1 (en) | 2014-05-09 |
ES2570679T3 (en) | 2016-05-19 |
US20130076581A1 (en) | 2013-03-28 |
US8963787B2 (en) | 2015-02-24 |
EP2573872B1 (en) | 2016-01-20 |
PL2573872T3 (en) | 2016-08-31 |
PL2573872T4 (en) | 2016-09-30 |
FR2980648A1 (en) | 2013-03-29 |
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