Patent Application
20210184361
The present application claims priority to French Application No. 1914577 filed with the Intellectual Property Office of France on Dec. 17, 2019 which is incorporated herein by reference in its entirety for all purposes.
The invention relates to the general field of microwave antennas used in radars and telecommunications. It relates more particularly to the field of array antennas or leaky wave antennas.
The leaky wave antennas in metallic waveguide technology are broadly described in the literature.
Such antennas are however difficult to manufacture and costly because of the issue of assembly and production accuracy.
In order to reduce the manufacturing costs and obtain integrated leaky wave antennas, it is also known practice to implement the substrate integrated waveguide technology (SIW).
Radiating slotted antennas produced by implementing such a technology offer, by comparison to the other technologies employed, the advantage of being compact, lightweight and easy to produce. They can advantageously be mounted on equipment for which the criteria of weight and of bulk are predominant.
However, the slotted antennas, produced by implementing this technology have the known drawback of exhibiting significant dielectric losses. Consequently, to compensate for these losses the amplification functions associated with the antenna have to be overdimensioned, which is reflected in an increase in overall weight of the system associated with the antenna, such that the weight saving provided by the use of a planar antenna is reduced by the increase in weight induced by the need to include means to compensate for the dielectric losses.
Moreover, overdimensioning the amplification functions is reflected by an increase in the energy consumption of the system.
Consequently, there is currently a need to find a solution allowing for the production of leaky wave antennas, with planar structure, that exhibit enhanced (i.e. reduced) dielectric losses compared to the antennas in existing planar technologies, in SIW technology in particular.
Recently, hollow substrate, or air-filled substrate integrated waveguide technology (AFSIW) has emerged. It allows guided transmission lines (i.e. waveguides) to be produced that exhibit enhanced performance levels compared to the transmission lines integrated in a substrate of SIW type. Such waveguides can be referred to as AFSIW waveguides.
One aim of the invention is to provide a solution to the problem of finding a solution allowing for the design and production of antennas on substrates that can reconcile operating performance levels in terms of radiating pattern with limited dielectric losses.
To this end, the subject of the invention is a leaky wave antenna produced in air-filled substrate integrated waveguide (AFSIW) technology comprising three dielectric substrate layers, two substrate layers, a top layer and a bottom layer, sandwiching an intermediate layer which itself comprises a longitudinal aperture of length L defining a waveguide whose top and bottom walls are formed by the conductive planes covering the top and bottom layers and whose width W1 is delimited by two conductive lateral walls.
According to the invention, the inner faces of the conductive lateral walls are coated with a layer of dielectric material of thickness w(z). The top layer of the structure has an aperture forming a longitudinal radial slot of width Wf (z) positioned facing the longitudinal aperture formed in the intermediate layer.
The thickness w(z) of the coating of dielectric material disposed on the inner face of each of the lateral 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 of the phase Beta(z) of the leaky wave of the guide, allowing the production of an antenna having the desired radiating pattern.
According to various provisions, the antenna according to the invention can have various of the following complementary technical features, which in each case can be considered separately or in combination.
According to a particular feature, the law of variation w(z) of the thickness of dielectric substrate bordering the inner face of each of the lateral walls of the cavity of the AFSIW guide is a linear law.
According to another feature, the thicknesses of dielectric substrate bordering the inner face of each of the lateral walls of the cavity of the AFSIW guide follow one and the same law of variation w(z).
According to another feature, the thickness of dielectric substrate bordering the inner face of one of the lateral walls of the cavity of the AFSIW guide follows a linear law of variation w(z), the thickness of dielectric substrate bordering the inner face of the other lateral wall of the AFSIW guide being kept constant, even zero.
According to another feature, the median axis of the radiating slot is distant from the median axis of the cavity of the guide by a zero or non-zero given distance d.
According to another feature, 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 cavity of the guide is taken on an axis at right angles to the axis z and at right angles to an axis of stacking of the three layers of dielectric substrate.
According to another feature, the radiating slot is a rectangular slot of constant width wf.
According to another feature, the radiating slot is a slot whose width Wf(z) varies along the longitudinal axis z of the guide.
According to another feature, the total width W1 of the guide along the longitudinal axis z of the antenna is defined as a function W1(z).
According to another feature, the longitudinal aperture of the intermediate layer forming the cavity of the waveguide is delimited by the conductive planes covering the bottom and top layers and by two conductive walls each composed of a row of vias in electrical contact with said conductive planes and forming the conductive lateral walls of said waveguide, each of said rows of vias being disposed so as to form one of the lateral walls of the guide, the inner face of the wall thus formed being coated with a layer of dielectric material of thickness w(z).
According to another feature, the longitudinal aperture of the intermediate layer forming the cavity of the waveguide is delimited by the conductive planes covering the bottom and top layers and by two conductive walls forming the lateral walls of said waveguide; one of the two walls being composed of a row of vias in electrical contact with said conductive planes, said row of vias being disposed so that the inner 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 applies the emergent technology of AFSIW waveguides advantageously allows the production of leaky waveguides that have dimensions, a weight and a cost that are enhanced compared to the existing antennas, the traditional slotted waveguide antennas in particular, by using simple and robust manufacturing techniques, while keeping good performance levels.
The features and advantages of the invention will be better appreciated from the following description, a description which is based on the attached figures which illustrate the invention:
The recently developed air-filled substrate integrated waveguide (AFSIW) technology has only recently been used to produce guided transmission lines on a substrate. Hereinafter in the text, such a structure is qualified as “AFSIW waveguide”.
This technology advantageously allows guided transmission lines to be obtained that exhibit enhanced performance levels, notably in terms of dielectric losses, compared to the structures in SIW technology used hitherto, structures illustrated by
Compared to the structures of metal waveguide type, illustrated by
From the technological point of view, the leaky wave antenna according to the invention relies on the AFSIW waveguide production technology.
As
The three dielectric substrate layers are stacked on an axis y.
In a conventional AFSIW structure, the layers n° 1 and n° 3 have an identical structure composed of a dielectric substrate whose inner and outer surfaces are covered by metallized planes (conductive planes), the planes 311 and 313 for the layer n° 1 and 331 and 333 for the layer n° 3 respectively.
The central longitudinal void 323, constituting the cavity of the guide, is bordered laterally by two rows of conductive vias, or simply vias, 322, which pass right through the dielectric substrate layer and allow an electrical continuity to be ensured between the inner conductive planes of the top and bottom layers. These rows of vias form the lateral walls (small sides) of the waveguide.
According to the invention, each of said rows of vias is disposed so as to form a layer of dielectric material of thickness w(z) bordering the inner face of the lateral wall of the guide defined by the row of vias considered; such that the AFSIW waveguide thus constituted has lateral walls (small sides) coated with a layer of dielectric substrate of thickness w(z).
The thickness of the dielectric substrate layer is taken on an axis x at right angles to the axis y and to the axis z along which the waveguide extends.
The AFSIW waveguide thus formed thus has a width W1=W2+2 w.
According to the invention, the total width W1 is determined so as to allow the propagation of waves at the desired operating frequency.
The vias 322 are, moreover, generally arranged so that the thickness w(z) of substrate bordering the lateral walls of the guide is as small as possible in order to minimize the dielectric losses in the guide.
The structure of the AFSIW waveguide considered preferentially in the context of the antenna according to the invention is a structure conforming to
However, it should be noted that it is possible, through the AFSIW technique, to construct waveguide structures that do not have dielectric on their lateral walls, notably by producing a continuous metallization of these walls.
In this case, a structure equivalent to the structure of
Generally, the structure of the antenna according to the invention comprises, unlike an AFSIW waveguide structure, a top substrate layer 51 (layer n° 3) having at least one longitudinal slot 52 (oriented along the axis z) placed facing the cavity 323 of the median substrate layer 32 (layer n° 2).
This slot, of width Wf, which passes right through the top substrate layer connects the cavity 323 of the guide with the outside environment.
In order to allow the radiation of a leaky wave, the longitudinal slot 52 typically has a length, along the axis z, greater than or equal to twice the operating wavelength of the antenna, that is to say of the wavelength of the radiated wave.
The slot is positioned with respect to the cavity so as to be radiating, that is to say so as to radiate the wave which is propagated in the guide.
To this end, the median axis 53 of the slot 52 is, advantageously, positioned with respect to the median axis 41 of the cavity 323 of the guide so as to radiate the wave which is propagated in the guide.
In the nonlimiting embodiment of
The distance d is the distance separating, in the direction x, 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 embodiment of
The longitudinal slot 52 thus formed makes it possible to produce, from an AFSIW guide, a slotted guide capable of radiating the wave which is propagated therein.
As a variant, the distance d is zero. That can, for example, be the case in a particular embodiment in which the thicknesses of dielectric material disposed on the two lateral walls of the cavity 323 are different.
According to the invention, the various dimensioning parameters of the cavity 323 of the guide, in particular the widths W1 and w(z), and those which dimension the radiating slot 52, in particular the width Wf, are defined so as to produce an antenna whose radiating pattern exhibits a desired direction, aperture and level of given side lobes. In other words, these dimensional parameters are determined so as to obtain given laws of variation of the phase Beta(z) and of the amplitude Alpha(z) of the leaky wave of the AFSIW guide on the longitudinal axis z of the antenna according to the invention; the variation of the phase and of the amplitude on the axis z of the leaky wave of the AFSIW guide determining the radiation pattern obtained.
Thus, the invention consists primarily in determining the direction, the aperture, and the level of the side lobes of the pattern of the AFSIW antenna that is to be produced by acting on these Alpha(z) and Beta(z) parameters.
The rest of the description explains different embodiments of the invention according to which one or more dimensional parameters which define the AFSIW waveguide with radiating slot that constitutes the antenna according to the invention are adjusted, so as to obtain the desired radiation pattern, by varying, along the axis z, the phase Beta(z) and the amplitude Alpha(z) of the wave passing through the waveguide.
To obtain an AFSIW antenna according to the invention that exhibits a radiation pattern having the desired characteristics (gain, directivity and level of side lobes in particular), it is notably possible to adjust the following parameters:
However, in the case of the device according to the invention, the phase and the amplitude of the wave being propagated in the cavity 323 of the waveguide per unit of length, are controlled primarily by varying the value w of the thickness of dielectric substrate bordering the lateral walls of the cavity 323 of the guide along the longitudinal axis z, the value w of the thickness of dielectric substrate being thus defined as a function w(z).
Advantageously, the thickness w of dielectric substrate bordering the lateral walls of the cavity of the guide are varied, facing the radiating slot, along the axis z.
This control action advantageously allows the values of the parameters Alpha(z) and Beta(z) which determine the parameters defining the radiation pattern of the antenna to be controlled.
Indeed, varying the thickness of substrate bordering the lateral walls of the cavity 323 advantageously allows the phase per unit of length of the wave being propagated inside the cavity 323 of the device to be varied, the variation of phase of the wave being propagated along the cavity 323 facing the radiating slot 52 determining the orientation of the radiation pattern.
According to the embodiment considered, the variation of the width w can be done in different ways, depending on the antenna pattern desired.
Thus, according to a first embodiment, the width w of dielectric substrate bordering the lateral walls of the cavity 323 forming the AFSIW guide varies identically for each of the lateral walls.
Alternatively, according to another embodiment, the thickness w of dielectric substrate can vary according to different laws w1(z) and w2(z) along the longitudinal axis of the cavity 323. The thickness w of dielectric substrate can notably remain constant (w1(z)=cte) on one lateral wall of the cavity 323 and vary according to a given law of variation w2(z) I on the other lateral wall of the cavity.
The structure of the intermediate layer 32 (layer n° 2) is, here, perfectly symmetrical with respect to the centre of symmetry of the cavity 323 of the AFSIW slotted guide according to the invention.
The radiating slot 52 formed in the top substrate layer 51 appears as a slot of rectangular form of length L and of width Wf which has a constant value along the longitudinal axis z.
In the exemplary embodiment considered, the slot 52 passes right through the substrate layer n° 3, its lateral walls formed in the thickness of the substrate are also metallized by using the PCB metallization methods.
However, according to an alternative embodiment, the slot is etched on the metallized surfaces forming the outer faces of the substrate layer n° 3, the lateral walls of the slot then consisting of metallized vias passing through the thickness of the substrate.
The distance, d, from the axis of symmetry 53 of the slot 52 with respect 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 n° 2), the total width W1 of io the cavity 323 of the guide, the width between the two rows of vias bordering the cavity in the embodiment illustrated by
Moreover, as
This law of variation can be a simple linear law as illustrated by
In the exemplary embodiment illustrated by
It is however possible to design an antenna with a single port and therefore a single direction of propagation. A non-symmetrical topology with a single supply port can in fact be implemented, by terminating the guide with a load.
It should be noted that, according to the invention, the law of variation w(z) considered can be more complex than a simple linear law, notably in order to reduce the level of the side lobes of the radiation pattern produced.
In the exemplary embodiment illustrated by
In particular, a non-rectangular form allows a radiation pattern to be obtained that has given particular characteristics. Thus, by using, for example, a slot in the form of an “eye”, it is possible to limit the radiated energy (i.e. the gain of the antenna) at the ends of the slot and maximize the radiated energy at the centre of the slot. The width of the slot 52 is then defined as a function of the position considered Wf(z) along the slot 52. It is in this way possible to produce a good spatial weighting of the law of illumination (i.e. of the radiation pattern) and obtain a radiation pattern that has reduced side lobes.
Moreover, in the exemplary embodiment illustrated by
It is however possible, in the context of the invention, to envisage 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 with respect 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 the paragraphs above explain, the structure of the device according to the invention advantageously allows a leaky wave antenna to be formed in AFSIW technology that is easy and inexpensive to produce, in which the radiation pattern can be defined by acting primarily on the thickness of dielectric substrate carpeting the lateral walls of the waveguide line formed by the AFSIW structure from which the antenna according to the invention is developed, and by varying in particular this thickness over the length of the transmission line (variation along the longitudinal axis z). The variation of the gain and of the phase per unit of length of the leaky wave of the radiating AFSIW guide, obtained by varying the thickness of substrate, advantageously allows the characteristics of the radiation pattern obtained to be determined.
It can be seen that, in the latter case, the slope of variation of the thickness w(z) being greater, the pattern obtained 72 approaches the vertical plane of the antenna whereas, reciprocally, narrowing the interior of the waveguide brings the beam increasingly parallel to the longitudinal axis of the antenna.
In the part of the description above, the device, the antenna, according to the invention, is defined by its basic AFSIW structure and by the dimensional characteristics which allow the different layers forming the AFSIW structure of the antenna to be defined. The technical characteristics described are the dimensional characteristics preferentially considered to produce an antenna according to the invention that exhibits the desired radiation pattern.
It is however possible to incorporate, with these various parameters, other dimensional and/or structural parameters in order, in particular, to have a greater latitude in the choice of the values of the dimensional parameters that allow an antenna structure exhibiting the radiation pattern sought to be obtained.
It is thus notably possible, in the context of the production of the antenna according to the invention, to act also on the total width W1 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 W1(z)). There is thus an additional means for controlling the variation of the phase Beta(z) and of the amplitude Alpha(z) of the leaky 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 with respect to that of the cavity of the AFSIW guide in order to have an additional means of controlling the variation of the phase Alpha(z) and of the amplitude Beta(z) along the longitudinal axis z of the antenna.
It is even also possible to replace the continuous radiating slot 52 with several small slots, forming a network of slots disposed along the axis z of the antenna facing the cavity 323 of the guide.
From a functional point of view, the AFSIW antenna according to the invention appears as a device with two access ports, as
| Number | Date | Country | Kind |
|---|---|---|---|
| 1914577 | Dec 2019 | FR | national |
