EP3840124B1 - Antenna with leaky wave in afsiw technology - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to the general field of microwave antennas used in radars and telecommunications. It relates more particularly to the field of network antennas or leakage wave antennas.

BACKGROUND OF THE INVENTION - PRIOR ART

Leaky wave antennas in metallic waveguide technology are widely described in the literature. There figure 1 presents a summary illustration of the principle of producing such an antenna 10 by means of slotted waveguides 11.

However, such antennas are difficult to manufacture and expensive due to assembly problems and manufacturing precision.

In order to reduce manufacturing costs and obtain antennas with integrated leakage waves, it is also known to implement waveguide technology integrated into the substrate (in English, SIW, for Substrate Integrated Waveguide). There figure 2 presents an illustration of the structure of such an antenna.

The radiating slot antennas produced using such technology have, compared to other technologies used, the advantage of being compact, light and easy to produce. They can advantageously be mounted on equipment for which the criteria of weight and size are paramount.

However, slot antennas produced using this technology have the known disadvantage of having significant dielectric losses. Consequently, to compensate for these losses we are forced to oversize the amplification functions associated with the antenna, which results in an increase in the overall mass of the system associated with the antenna, so that the gain in mass provided by the use of a planar antenna is reduced by the increase in mass induced by the need to put in place means to compensate for dielectric losses.

Furthermore, oversizing the amplification functions results in an increase in the energy consumption of the system.

Consequently, there is currently a need to find a solution making it possible to produce leaky wave antennas, with a planar structure, having improved (i.e. reduced) dielectric losses compared to antennas in existing planar technologies, in technology SIW in particular.

Recently, Air-Filled Substrate Integrated Waveguide (AFSIW) technology has emerged. It makes it possible to produce guided transmission lines (ie waveguides) with increased performance compared to transmission lines integrated into a SIW type substrate. In this case we can speak of AFSIW waveguides. The prior art document VAN DEN BRANDE QUINTEN ET AL: "Coupled Half-Mode Cavity-Backed Slot Antenna for IR-UWB in Air-Filled SIW Technology", 2018 IEEE APS, July 8, 2018 discloses an antenna formed in AFSIW comprising slots.

PRESENTATION OF THE INVENTION

An aim of the invention is to provide a solution to the problem consisting of finding a solution allowing the design and production of antennas on a substrate capable of reconciling operating performance in terms of radiation pattern and limitation of dielectric losses.

To this end, the subject of the invention is a leakage wave antenna produced using waveguide technology integrated into a hollow substrate (AFSIW, for Air-Filled Substrate Integrated Waveguide) comprising three layers of dielectric substrate, two substrate layers, an upper layer and a lower layer, sandwiching an intermediate layer which itself includes a longitudinal opening of length L defining a waveguide whose upper and lower walls are formed by the conductive planes covering the layers upper and lower and whose width W ₁ is delimited by two conductive side walls.

According to the invention, the internal faces of the conductive side walls are coated with a layer of dielectric material of thickness w(z). The upper layer of the structure has an opening forming a longitudinal radiating slot of width W _f (z) positioned opposite the longitudinal opening formed in the intermediate layer.

The thickness w(z) of the coating of dielectric material placed on the internal face of each of the side walls varies along the longitudinal axis z according to a given law, defined so as to obtain variations along the axis z of the amplitude Alpha(z) and the phase Beta(z) of the leakage wave of the guide, making it possible to produce an antenna having the desired radiation pattern.

According to various arrangements, the antenna according to the invention may have various following complementary technical characteristics, each of which can be considered separately or in combination.

According to a particular characteristic, the law of variation w(z) of the thickness of the dielectric substrate bordering the internal face of each of the side walls of the cavity of the AFSIW guide is a linear law.

According to another characteristic, the thicknesses of dielectric substrate bordering the internal face of each of the side walls of the cavity of the AFSIW guide follow the same law of variation w(z).

According to another characteristic, the thickness of dielectric substrate bordering the internal face of one of the side walls of the cavity of the AFSIW guide follows a linear variation law w(z) , the thickness of dielectric substrate bordering the internal face of the the other side wall of the AFSIW guide being kept constant, or even zero.

According to another characteristic, the median axis of the radiating slot is distant from the median axis of the cavity of the guide by a given distance d which is zero or non-zero.

According to another characteristic, the distance d(z) separating the median axis of the radiating slot from the median axis of the cavity of the guide varies according to a law d(z) along the longitudinal axis z of the antenna .

The distance separating the median axis of the radiating slot from the median axis of the guide cavity is taken along an axis perpendicular to the z axis and perpendicular to a stacking axis of the three layers of dielectric substrate.

According to another characteristic, the radiating slot is a rectangular slot of constant width w _f .

According to another characteristic, the radiating slot is a slot whose width W _f (z) varies along the longitudinal axis z of the guide.

According to another characteristic, the total width W ₁ of the guide along the longitudinal axis z of the antenna is defined as a function W ₁ (z).

According to another characteristic, the longitudinal opening of the intermediate layer forming the cavity of the waveguide, is delimited by the conductive planes covering the lower and upper layers and by two conductive walls each consisting of a row of Vias in electrical contact with said conductive planes and forming the conductive side walls of said waveguide, each of said rows of Vias being arranged so as to form one of the side walls of the guide, the internal face of the wall thus formed being coated with a layer of material dielectric of thickness w(z).

According to another characteristic, the longitudinal opening of the intermediate layer forming the cavity of the waveguide is delimited by the conductive planes covering the lower and upper layers and by two conductive walls forming the side walls of said waveguide; one of the two walls being made up of a row of Vias in electrical contact with said conductive planes, said rows of Vias being arranged so that the internal face of the wall thus formed is coated with a layer of dielectric material of thickness w(z).

The device according to the invention which takes up the emerging technology of AFSIW waveguides advantageously makes it possible to produce leakage wave antennas having dimensions, weight and cost, improved compared to existing antennas, the antennas with leakage waveguides. traditional slot waves in particular, using simple and robust manufacturing techniques, while maintaining good performance.

DESCRIPTION OF FIGURES

• La figure 1 déjà commentée, représente de manière schématique la structure d'une antenne réseau à guides à fentes selon l'art antérieur ;
• La figure 2 déjà commentée, représente de manière schématique une structure planaire de type SIW connue ;
• La figure 3A représente de manière schématique, en vue de profil, la structure standard en trois couches d'un guide d'onde réalisé en technologie AFSIW (i.e. Air-Filled Substrate Integrated Waveguide selon la terminologie anglo-saxonne)
• La figure 3B représente de manière schématique, en vue en coupe transversale, la structure standard en trois couche d'un guide d'onde réalisé en technologie AFSIW (i.e. Air-Filled Substrate Integrated Waveguide selon la terminologie anglo-saxonne) ;
• La figure 4A représente de manière schématique, en vue de profil, la structure type d'une antenne à onde de fuite en technologie AFSIW selon l'invention ;
• La figure 4B représente de manière schématique, en vue en coupe, la structure type d'une antenne à onde de fuite en technologie AFSIW selon l'invention ;
• La figure 5 représente de manière schématique, en vue de dessus, la troisième couche de substrat formant la structure AFSIW de l'antenne selon l'invention, dans un mode de réalisation particulier ;
• La figure 6 représente de manière schématique une vue de dessus de la seconde couche de substrat formant la structure AFSIW de l'antenne selon l'invention, dans le mode de réalisation particulier de la figure 5 ;
• La figure 7 représente des exemples de diagrammes de rayonnement, projetés dans le plan yz ; diagrammes obtenus au moyen d'une antenne selon l'invention.

The characteristics and advantages of the invention will be better appreciated thanks to the description which follows, a description which is based on the appended figures which illustrate the invention:

• There figure 1 already commented on, schematically represents the structure of an array antenna with slotted guides according to the prior art;
• There figure 2 already commented on, schematically represents a known SIW type planar structure;
• There Figure 3A schematically represents, in profile view, the standard three-layer structure of a waveguide produced in AFSIW technology (ie Air-Filled Substrate Integrated Waveguide according to Anglo-Saxon terminology)
• There Figure 3B schematically represents, in cross-sectional view, the standard three-layer structure of a waveguide produced in AFSIW technology (ie Air-Filled Substrate Integrated Waveguide according to Anglo-Saxon terminology);
• There figure 4A schematically represents, in profile view, the typical structure of a leaky wave antenna in AFSIW technology according to the invention;
• There figure 4B schematically represents, in sectional view, the typical structure of a leaky wave antenna in AFSIW technology according to the invention;
• There figure 5 schematically represents, in top view, the third substrate layer forming the AFSIW structure of the antenna according to the invention, in a particular embodiment;
• There Figure 6 schematically represents a top view of the second substrate layer forming the AFSIW structure of the antenna according to the invention, in the particular embodiment of the figure 5 ;
• There Figure 7 represents examples of radiation patterns, projected in the yz plane; diagrams obtained by means of an antenna according to the invention.

DETAILED DESCRIPTION

We have recently used the technology of waveguides integrated into a hollow substrate, or AFSIW technology (for Air-Filled Substrate Integrated Waveguide) according to the Anglo-Saxon terminology, a recently developed technology, to produce guided transmission lines on a substrate. In the remainder of the text, such a structure is referred to as an “AFSIW waveguide”.

This technology advantageously makes it possible to obtain guided transmission lines with increased performance, particularly in terms of dielectric losses compared to the structures in SIW technology used until now, structures illustrated by the figure 2 .

Compared to metallic waveguide type structures, illustrated by the figure 1 , such transmission lines also have advantageous characteristics in terms of mass and size.

From a technological point of view, the leaky wave antenna according to the invention is based on AFSIW waveguide production technology.

As illustrated by Figures 3A and 3B , profile view and, respectively, cross-sectional view respectively, the structure of an AFSIW waveguide comprises three layers of dielectric substrate, an intermediate substrate layer (layer no. 2) having a central longitudinal recess 32, of length L and width W ₂ , sandwiched between a lower substrate layer 31 (layer no. 1) and an upper substrate layer 33 (layer no. 3); the substrate layers n°1 and n°3 closing the upper and lower walls (long sides) of the waveguide.

The three layers of dielectric substrate are stacked along a y axis.

In a classic AFSIW structure, layers n°1 and n°3 have an identical structure consisting of a dielectric substrate whose internal and external surfaces are covered with metallized planes (conductive planes), planes 311 and 313 for layer n °1 and 331 and 333 for layer no. 3 respectively.

The central longitudinal recess 323, constituting the cavity of the guide, is bordered laterally by two rows of conductive crossings or Vias, 322, which pass right through the layer of dielectric substrate and make it possible to ensure electrical continuity between the conductive planes internals of the upper and lower layers. These rows of Vias form the side walls (short sides) of the waveguide.

According to the invention, each of said rows of Vias is arranged so as to form a layer of dielectric material of thickness w(z) bordering the internal face of the side wall of the guide defined by the row of Vias considered; so that the AFSIW waveguide thus formed has side walls (small sides) coated with a layer of dielectric substrate of thickness w(z).

The thickness of the dielectric substrate layer is taken along an x axis perpendicular to the y axis and to the z axis along which the waveguide is elongated.

The AFSIW waveguide thus formed thus has a width W ₁ = W ₂ +2w.

According to the invention, the total width W ₁ is determined so as to allow the propagation of waves at the desired operating frequency.

The Vias 322 are also generally arranged so that the thickness w(z) of substrate bordering the side walls of the guide is as low as possible in order to minimize dielectric losses in the guide.

The AFSIW waveguide structure preferentially considered in the context of the antenna according to the invention is a structure conforming to the Figures 3A and 3B . Such a structure advantageously makes it possible to modify the properties of the wave which propagates inside the guide thus formed.

However, it should be noted that it is possible, using the AFSIW technique, to construct waveguide structures that do not have a dielectric on its side walls, in particular by producing a continuous metallization of these walls.

In this case, a structure equivalent to the structure of Figures 3A and 3B can nevertheless be envisaged, in the context of the invention, by placing in the cavity 323 of the guide on each of the side walls (small sides) of the guide a layer of dielectric material of thickness w(z) allowing as in the previous case to modify the properties of the wave which propagates inside the guide formed.

THE Figures 4A and 4B , being a profile view and a cross-sectional view respectively, schematically present the antenna structure according to the invention, according to an embodiment for which the side walls (small sides) of the AFSIW guide are produced by means of Vias.

Generally speaking, the structure of the antenna according to the invention comprises, unlike an AFSIW waveguide structure, an upper layer of substrate 51 (layer no. 3) having at least one longitudinal slot 52 (oriented along the z axis) placed opposite the cavity 323 of the middle layer 32 of substrate (layer no. 2).

This slot, of width W _f , which passes right through the upper layer of substrate communicates the cavity 323 of the guide with the external environment.

In order to allow the radiation of a leakage wave, the longitudinal slot 52 typically has a length, along the z axis, greater than or equal to twice the operating wavelength of the antenna, i.e. i.e. the wavelength of the radiated wave.

The slot is positioned relative to the cavity so as to be radiant, that is to say so as to radiate the wave which propagates in the guide.

For this purpose, the median axis 53 of the slot 52 is advantageously positioned relative to the median axis 41 of the cavity 323 of the guide so as to radiate the wave which propagates in the guide.

In the non-limiting realization of the Figures 4A and 4B , the longitudinal slot 52 is arranged in such a way that its central axis 53 is offset by a distance d relative to the central axis 41 of the cavity 323 of the guide.

The distance d is the distance separating, in the x direction, the median axis 53 of the slot 52 from the median axis 41 of the cavity 41.

The distance d is non-zero in the realization of the Figures 4A and 4B .

The longitudinal slot 52 thus made makes it possible to produce, from an AFSIW guide, a slot guide capable of radiating the wave which propagates there.

Alternatively, the distance d is zero. This may, for example, be the case in a particular embodiment in which the thicknesses of dielectric material placed on the two side walls of cavity 323 are different.

According to the invention, the various sizing parameters of the cavity 323 of the guide, in particular the widths W ₁ and w(z), as well as those which dimension the radiating slot 52, in particular the width W _f , are defined so to produce an antenna whose radiation pattern has a direction, an aperture and a desired given secondary lobe level. In other words, these dimensional parameters are determined so as to obtain given variation laws of the Beta(z) phase and the Alpha(z) amplitude of the leakage wave of the AFSIW guide along the longitudinal axis z of the antenna according to the invention; the variation of the phase and of the amplitude along the z axis of the leakage wave of the AFSIW guide determining the radiation diagram obtained.

Thus, the invention mainly consists of determining the direction, the aperture, and the level of the secondary lobes of the AFSIW antenna diagram that we wish to achieve, by acting on these parameters Alpha(z) and Beta(z). .

The remainder of the description sets out different embodiments of the invention according to which one or more dimensional parameters are acted upon which define the AFSIW waveguide with a radiating slot constituting the antenna according to the invention, so as to obtain the diagram of desired radiation, by varying along the z axis the phase Beta(z) and the amplitude Alpha(z) of the wave passing through the waveguide.

THE figures 5 And 6 illustrate a particular embodiment taken as a non-limiting example of the scope of the invention. They respectively present a top view of the intermediate substrate layer 32 (layer no. 2) forming the cavity 323 of the guide and a top view of the upper substrate layer 51 (layer no. 3), layers which constitute the structure AFSIW of the antenna according to the invention.

• La longueur de l'antenne L, qui permet d'ajuster le gain de l'antenne et l'ouverture angulaire du son diagramme de rayonnement, un gain plus élevé et une ouverture angulaire plus faible pouvant être obtenus avec une antenne et une fente rayonnante plus longues ;
• La largeur, W1, de la ligne AFSIW qui détermine la largeur totale du guide d'ondes ;
• Le couple W₂ et w détermine la fréquence de coupure du mode fondamentale du guide d'onde. On peut être amené à réduire W₂ , lorsque l'on augmente w afin de garder la même fréquence de coupure du mode fondamentale ;
• La largeur, Wf, de la fente 52 ménagée dans la couche supérieure de substrat 51 (couche n°2) ;
• La distance d, de l'axe longitudinal 53 de la fente 52 par rapport à l'axe longitudinal 41 de la cavité 323.

To obtain an AFSIW antenna according to the invention presenting a radiation pattern having the desired characteristics (gain, directivity and secondary lobe level in particular), it is in particular possible to adjust the following parameters:

• The antenna length L, which allows adjustment of the antenna gain and angular aperture of its radiation pattern, higher gain and lower angular aperture can be obtained with an antenna and a radiating slot longer ;
• The width, W1, of the AFSIW line which determines the total width of the waveguide;
• The pair W ₂ and w determines the cut-off frequency of the fundamental mode of the waveguide. We may have to reduce W ₂ , when we increase w in order to keep the same cut-off frequency of the fundamental mode;
• The width, Wf, of the slot 52 formed in the upper layer of substrate 51 (layer no. 2);
• The distance d, of the longitudinal axis 53 of the slot 52 relative to the longitudinal axis 41 of the cavity 323.

However, in the case of the device according to the invention, the phase and the amplitude of the wave propagating in the cavity 323 of the waveguide per unit length, are controlled mainly by varying the value w of the thickness of dielectric substrate bordering the side walls of cavity 323 of the guide along the longitudinal axis z, the value w of the thickness of dielectric substrate thus being defined as a function w(z).

Advantageously, the thickness w of the dielectric substrate bordering the side walls of the guide cavity is varied, facing the radiating slot, along the z axis.

This control action advantageously makes it possible to control the values of the parameters Alpha( z ) and Beta( z ) which determine the parameters defining the radiation pattern of the antenna.

Indeed, varying the thickness of the substrate bordering the side walls of the cavity 323 advantageously makes it possible to vary the phase per unit length of the wave propagating inside the cavity 323 of the device, the phase variation of the wave propagating along the cavity 323 facing the radiating slit 52 determining the orientation of the radiation diagram.

Depending on the embodiment considered, the variation of the width w can be carried out in different ways, depending on the desired antenna pattern.

Thus according to a first embodiment, the width w of dielectric substrate bordering the side walls of the cavity 323 forming the AFSIW guide varies identically for each of the side walls.

Alternatively, according to another embodiment, the thickness w of dielectric substrate can vary according to different laws w ₁ ( z ) and w ₂ ( z ) along the longitudinal axis of the cavity 323. The thickness w of dielectric substrate can in particular remain constant ( w ₁ ( z )=cte) on one side wall of the cavity 323 and vary according to a given variation law w ₂ ( z ) I on the other side wall of the cavity.

THE figures 5 And 6 , present a first simple example of implementation for which the parameters defining the radiation diagram are exclusively controlled by simply varying the w value of the substrate thickness along the z axis.

The structure of the intermediate layer 32 (layer no. 2) is here perfectly symmetrical with respect to the center of symmetry of the cavity 323 of the AFSIW slot guide according to the invention.

The radiating slot 52 formed in the upper substrate layer 51 is presented as a rectangular slot of length L and width W _f which has a constant value along the longitudinal axis z.

In the embodiment considered, the slot 52 passes through layer No. 3 of substrate right through, its side walls formed in the thickness of the substrate are further metallized using PCB metallization processes.

However, according to an alternative embodiment, the slot is etched on the metallized surfaces forming the external faces of substrate layer No. 3, the side walls of the slot then being made up of metallized Vias passing through the thickness of the substrate.

The distance, d, of the axis of symmetry 53 of the slot 52 relative to the axis of symmetry 41 of the cavity 323 also has a constant value along the longitudinal axis z.

Concerning the intermediate substrate layer 32 (layer no. 2), the total width W ₁ of the cavity 323 of the guide, the width between the two rows of Vias bordering the cavity in the embodiment illustrated by the Figures 4A, 4B , 5 And 6 , is kept constant, at least over the entire length of the cavity 323 of the intermediate substrate layer 32 facing the radiating slot 52.

Furthermore, as shown in Figure 6 , the thickness w of dielectric substrate bordering the side walls of Cavity 323 varies identically, for each of the side walls, according to a law of variation w(z).

This variation law can be a simple linear law as illustrated by the Figure 6 . Such a variation law makes it possible to form a radiation diagram in the desired direction, a radiation diagram such as those, 71 and 72, presented according to a 2D representation (in two dimensions) on the Figure 7 .

In the exemplary embodiment illustrated by the figures 5 And 6 , the antenna produced is symmetrical in the x direction (same value w of thickness of dielectric material bordering the side faces of the cavity 323 of the guide) and the z direction (it has a plane of symmetry 42), with two ports d access making it possible to radiate or receive waves according to two radiation diagrams oriented in two directions forming opposite angles + θ and - θ relative to the vertical plane passing through the axis of symmetry 53 of the radiating slot 52.

However, it is possible to design an antenna with a single port and therefore a single direction of propagation. A non-symmetrical topology with a single power port can indeed be implemented, ending the guide with a load.

It should be noted that, according to the invention, the variation law w(z) considered can be more complex than a simple linear law, in particular in order to reduce the level of the secondary lobes of the radiation diagram produced.

In the exemplary embodiment illustrated by the figures 5 And 6 , the radiating slot 52 has a rectangular shape of length L with a width W _f constant over the entire length L. It is however possible, in the context of the invention, to consider another embodiment of the invention: the radiating slot may not have a rectangular shape.

A non-rectangular shape makes it possible in particular to obtain a radiation pattern having particular given characteristics. Thus, by using for example an “eye” shaped slot, we can limit the radiated energy (ie the gain of the antenna) at the ends of the slot and maximize the energy radiated at the center of the slot. The width of the slot 52 is then defined as a function of the considered position Wf(z) along the slot 52. In this way, good spatial weighting of the illumination law (ie the radiation diagram) can be achieved. and obtaining a radiation pattern having reduced sidelobes.

Furthermore, in the exemplary embodiment illustrated by the figures 5 And 6 , the distance d between the central axis 53 of the slot 52 relative to the central axis 41 of the cavity 323 of the AFSIW line, remains constant over the entire length L of the antenna, the phase and the amplitude of the wave propagating in the cavity 323 of the wave guide by unit of length, being controlled by varying the value w of the thickness of the substrate bordering the side walls of the cavity 323 of the guide along the longitudinal axis z, according to a function w(z).

It is however possible, in the context of the invention, to consider another embodiment in which an adjustment of the radiation pattern of the antenna according to the invention can be obtained by also varying the distance d between the median axis 53 of the slot 52 relative to the median axis 41 of the cavity 323 of the AFSIW line, the distance d being defined in this case as a function d(z) of the position considered along the slot 52.

As explained in the preceding paragraphs, the structure of the device according to the invention advantageously makes it possible to form a leaky wave antenna in AFSIW technology that is easy and inexpensive to produce, the radiation pattern of which can be defined by mainly playing on the thickness of dielectric substrate lining the side walls of the waveguide line formed by the AFSIW structure from which the antenna according to the invention is developed, and in particular by varying this thickness over the length of the line transmission (variation along the longitudinal axis z). The variation of the gain and the phase per unit length of the leakage wave of the radiating AFSIW guide, obtained by varying the thickness of the substrate, advantageously makes it possible to determine the characteristics of the radiation pattern obtained.

There Figure 7 presents the radiation patterns 71 and 72 obtained for two AFSIW antennas according to the invention, formed from AFSIW guides whose side walls of the cavities 323 are coated with layers of substrate whose thicknesses vary along z with different variation profiles. The radiation pattern 72 is obtained from a cavity having on its side walls a substrate thickness w(z) varying along the longitudinal axis z with a greater slope of variation than in the case of the radiation pattern 71.

We note that, in the latter case, the slope of variation of the thickness w(z) being greater, the diagram obtained 72 approaches the vertical plane of the antenna, whereas, conversely, narrowing the interior of the guide waves will make the beam more and more parallel to the longitudinal axis of the antenna.

In the preceding part of the description, the device, the antenna, according to the invention is defined by its basic AFSIW structure and by the dimensional characteristics which make it possible to define the different layers forming the AFSIW structure of the antenna. The technical characteristics described are the dimensional characteristics preferably considered to produce an antenna according to the invention presenting the desired radiation pattern.

It is however possible to integrate other dimensional and/or structural parameters into these various parameters in order in particular to have greater latitude in the choice of the values of the dimensional parameters making it possible to obtain an antenna structure presenting the desired radiation pattern.

It is thus notably possible, in the context of producing the antenna according to the invention, to also play on the total width W ₁ of the guide along the longitudinal axis z of the guide (direction of propagation of the wave ) such that the total width of the guide is defined as a function W ₁ (z)). We thus have an additional means of controlling the variation of the phase Beta(z) and the amplitude Alpha(z) of the leakage wave along the longitudinal axis z of the antenna.

It is also possible to vary the width of the slot and/or the position of its axis of symmetry relative to that of the cavity of the AFSIW guide in order to have an additional means of controlling the variation of the Alpha phase ( z) and the amplitude Beta(z) along the longitudinal axis z of the antenna.

It is also possible to replace the continuous radiating slot 52 with several small slots, constituting a network of slots arranged along the z axis of the antenna facing the cavity 323 of the guide.

From a functional point of view, the AFSIW antenna according to the invention is presented as a device with two access ports, as illustrated by the Figures 4A and 4B , so that, depending on the way in which it is used, can advantageously present two radiation diagrams oriented in two directions having opposite angles with respect to the vertical (use of ports 1 and 2) or, alternatively, a single radiation diagram radiation, one of the ports, unexploited, being terminated by a charge. 1

Claims (12)

1. A leaky wave antenna formed from an Air-Filled Substrate Integrated Waveguide (AFSIW) type waveguide structure (40) having three layers of dielectric substrate, two layers of substrate, an upper layer (51) and a lower layer (31) sandwiching an intermediate layer (32) with a longitudinal opening (323) of length L defining a waveguide, the upper and lower walls of which are formed by the conducting planes covering the upper (51) and lower (31) layers and the width W₁ of which is delimited by two conductive side walls, with the inner faces of the conductive side walls being coated with a layer of dielectric material of thickness w(z), the upper layer (51) of the structure having an opening (52) forming a longitudinal radiating slot of width W_f(z) positioned facing the longitudinal opening (323) provided in the intermediate layer, with the thickness w(z) of the coating made of dielectric material disposed on the inner face of each of the side walls varying along the longitudinal axis z according to a given law, defined so as to acquire variations, along the z-axis, of the amplitude Alpha(z) and of the phase Beta(z) of the leaky wave of the guide, allowing an antenna to be produced with the desired radiation pattern (71, 72).
2. The antenna according to claim 1, wherein the variation law w(z) of the thickness of the dielectric substrate bordering the inner face of each of the side walls of the cavity (323) of the AFSIW guide is a linear law.
3. The antenna according to any one of claim 1 or 2, wherein the thicknesses of the dielectric substrate bordering the inner face of each of the side walls of the cavity (323) of the AFSIW guide follow the same variation law w(z).
4. The antenna according to any one of claim 1 or 2, wherein the thickness of the dielectric substrate bordering the inner face of one of the side walls of the cavity (323) of the AFSIW guide follows a linear variation law w(z), with the thickness of the dielectric substrate bordering the inner face of the other side wall of the AFSIW guide being kept constant, or even null.
5. The antenna according to any one of the preceding claims, wherein the opening (52) forming the longitudinal radiating slot is positioned facing the longitudinal opening (323) provided in the intermediate layer such that the median axis of the radiating slot (52) is separated from the median axis of the cavity (323) by a distance d.
6. The antenna according to the preceding claim, wherein the median axis (53) of the radiating slot is separated from the median axis (41) of the cavity of the guide by a given distance d taken along an axis, perpendicular to the z-axis and to a stacking axis of the three layers of dielectric substrate.
7. The antenna according to claim 5, wherein the distance d(z) separating the median axis of the radiating slot from the median axis of the cavity of the guide varies along the longitudinal axis z of the antenna, with the distance d(z) being taken along an axis perpendicular to the z-axis and to a stacking axis of the three layers of dielectric substrate.
8. The antenna according to any one of the preceding claims, wherein the radiating slot is a rectangular slot with a constant width w_f .
9. The antenna according to any one of claims 1 to 7, wherein the radiating slot (52) is a slot with a width w_f(z) that varies along the longitudinal axis z of the guide.
10. The antenna according to any one of the preceding claims, wherein the total width W₁ of the guide along the longitudinal axis z of the antenna is defined as a function W₁(z).
11. The antenna according to any one of the preceding claims, wherein the intermediate layer (32) has a longitudinal opening (323) of length L and of width W₂ , forming the cavity of the waveguide, delimited by the conducting planes covering the lower (31) and upper (51) layers and by two rows of vias (322) in electrical contact with said conducting planes and forming the side walls of said waveguide, with each of said rows of vias (322) being disposed so as to form one of the side walls of the guide, the inner face of the wall thus formed being coated with a layer of dielectric material of thickness w(z).
12. The antenna according to any one of the preceding claims, wherein the intermediate layer (32) has a longitudinal opening (323) of length L and of width W₂ , forming the cavity of the waveguide, delimited by the conducting planes covering the lower (31) and upper (51) layers, with one of the side walls of said guide being formed by a row of vias (322) in electrical contact with said conducting planes, the other side wall being coated with a layer of conductive material, with said row of vias (322) being disposed so as to form one of the side walls of the guide, the inner face of the wall thus formed being coated with a layer of dielectric material of thickness w(z).

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