EP2673842B1 - Waveguide antenna having annular slots - Google Patents

Description

Field of the invention

The present invention relates to the field of telecommunications. Within this field, the invention relates more particularly to antennas intended to receive or transmit a telecommunication signal.

The antenna can be used in a variety of systems. Its design based on the technique of slot guides allows use in embedded systems, that is to say on a typically mobile support such as a train or an aircraft, for which the constraints of size, weight, consumption can be extremely severe. The antenna is more particularly suitable for so-called "high-speed" or even "very high-speed" links, for example for satellite transmissions in the Ka band which extends in transmission from 27.5 to 31 GHz and in reception of 18.3 at 18.8 GHz and 19.7 at 20.2 GHz.

The antenna consists of base antenna elements associated in one dimension to form a slotted guide. The antenna may be composed of several slot guides associated to form a network.

Prior art

The theory of slits in the so-called slot guides, was initially described by A.F.Stevenson in the article [1] in a purely linear polarization context. The waveguide which is normally used for the transport of energy, is transformed into a radiating system by cutting on one of the faces of the generally rectangular guide, thin slots with respect to the wavelength, judiciously placed.

Figure la shows schematically a waveguide basic antenna element with a rectangular slot cut on one of the faces, generally the so-called upper face which is oriented in the direction of the element in communication with the antenna. The slot is excited by the propagation of the field in the waveguide. To improve performance, the basic antenna elements are associated in series along an axis to form a slotted guide as shown figure 1b , then the slot guides are associated in parallel to obtain an antenna as shown in FIG. figure 1c . Such an association to form a network is described in article [2]. The arrangement of the slots as represented on the Figures 1a-1c gives rise to a radiation having a linear polarization.

Some uses, such as satellite communications, require antenna misalignment for the beam to point in the direction of the satellite. A misalignment can be obtained mechanically by means of a mechanical movement of the antenna, controlled manually or by a motor. Congestion constraints, for example for systems embedded (installation of an antenna on a train, an airplane ...) prohibit any mechanism of mechanical misalignment. Such misalignment must therefore be obtained electronically.

Article [5] describes how to control the radiation of an SIW antenna and how to detach the beam in the plane of networking by feeding in parallel each slot guide and controlling the phase of each feed point slotted guides.

Given that the polarization difference between the received signal (polarization related to the transmitting antenna) and the polarization of the receiving antenna can lead to an attenuation of the received signal, total if the two polarizations are crossed, it is then necessary to use a circular polarization that avoids this phenomenon of total attenuation for certain uses. In particular, such a choice is thus made in cases where the orientation of the fixed or mobile "reception" antenna (antenna which can also serve as a transmitting antenna) must evolve over time and follow the antenna Mobile "transmitters" (antennas that can also be used as receiving antennas), cases that are encountered with moving satellites (non-geostationary) or with embedded systems intended to communicate with a satellite.

• une croix centrée par rapport à l'axe du guide avec deux bras faiblement dissymétriques,
• une croix décalée par rapport à l'axe de guide comme décrit dans [3] et illustré par la figure 2a ou
• deux fentes décalées suivant la longueur et la largeur du guide et inclinées d'environ 45° comme décrit dans [4] et illustré par la figure 2b.

Obtaining a circular polarization requires the use of rectangular double slot guides formed by:

• a cross centered with respect to the axis of the guide with two weakly asymmetrical arms,
• a cross offset from the guide axis as described in [3] and illustrated by the figure 2a or
• two slots offset along the length and width of the guide and inclined by about 45 ° as described in [4] and illustrated by the figure 2b .

The curves of the Figure 2c represent the radiation in site of this type of double slot guides corresponding to the Figure 2a or 2b for different planes offset by an angle Phi (0 °, 45 °, 90 °, 135 °) relative to the axis of the guide, this angle Phi is said bearing angle. The main circular polarization (right) radiation pattern corresponding to the DirRHCP lines is characterized by a maximum in the direction perpendicular to the slit surface. DirLHCP lines represent cross-polarized (left) radiation. An adjustment of the dimensions, positions and inclinations of the slots provides a low level of cross polarization in the direction of the maximum radiation. However, outside this axis, the level of cross polarization rises rapidly and returns to the level of the main polarization, at around 40 °, according to the illustration of the Figure 2c . This rise is mainly due to the geometry of the slits which individually generate dissymmetrical E and H planes which, after recombination in amplitude and in phase, create a large level of circular polarization crossed out of the axis.

This high level of cross polarization limits the performance of rectangular slot guide antennas when used with beam misalignment. Indeed, when misalignment of the beam at a given angle, the cross polarization level of the beam is that of the base element. So, in the case of the example illustrated by the Figure 2c ), if the angle of misalignment beam is set at 40 ° then the cross polarization level is equivalent to that of the main polarization. Such an antenna behavior is unacceptable for use which requires a large difference between main and crossed polarization.

Presentation of the invention

The invention proposes an antenna element with a slotted waveguide which is an alternative to known antennal elements, of equivalent or even more efficient performance for certain configurations.

Thus, the subject of the invention is an antenna element with a slotted waveguide comprising at least one conducting surface provided with at least one annular slot which delimits at its central part a conducting zone and which electrically isolates this zone from the rest of the the face.

Such antennal element is typically obtained by means of SIW (Substrate Integrated Waveguide) technology. This technology makes it possible to print the slots by printing. The annular shape of the slot makes it possible to obtain equivalent performances, even more interesting in certain configurations than the rectangular shape, while simplifying the manufacturing process, in particular in cases where a circular polarization must be obtained. Indeed, in these cases, the printing mask has only one annular slot while according to the prior art at least two rectangular slots are required with positioning constraints of one with respect to the other.

According to one embodiment of the invention, the antenna element is such that the annular slot is offset with respect to the axis of the slot guide.

A slotted guide has a shape that is generally close to that of a parallelepiped, therefore characterized by at least one length. The length is the dimension in the axis of the parallelepiped. The offset of the annular slot with respect to the axis advantageously makes it possible to obtain a circular polarization. Thus, compared to the prior art, only the offset of the print mask with respect to the axis is necessary to obtain a circular polarization. According to the prior art, the manufacture of a slit-fence antennal element which is of rectilinear polarization or circular polarization requires a different polarization-specific mask. Indeed, to obtain a circular polarization according to the prior art a double rectangular slot is necessary with a particular arrangement of the double slot. That is to say, the double slot consists of a cross centered relative to the axis of the guide with two weakly asymmetrical arms, or the double slot consists of a cross offset relative to the guide axis, or the double slot consists of two slots offset along the length and width of the guide and inclined by approximately 45 °. Unlike the prior art, which therefore requires changing the mask according to the desired polarization, the same mask makes it possible to obtain an antenna element according to the invention with either a linear polarization or a circular polarization, and this only by shifting the mask on the face of the substrate on which the slot must be printed. The antennal element according to the invention generates radiation in circular polarization with an isolation between the main and crossed polarizations for angles greater than 40 °. larger than that obtained with rectangular slots. In particular, in the plane perpendicular to the axis of the slot guide, this insulation can reach levels greater than 15 dB whereas with an antenna element of the prior art this insulation is almost imperceptible. This significant difference reflects the fact that an antenna element according to the invention is particularly well suited for uses where a misalignment is necessary as in the case of a transmission between a mobile support such as a train or an airplane and a satellite that the antennal elements known.

According to one embodiment of the invention, the antennal element is such that the distance between the inner and outer edges of the annular slot comprises along the perimeter of the slot significant variations which delimit out-breaks.

The offsets typically have the form of notches in the case of an annular slot of circular shape or the shape of triangles in the case of a square-shaped annular slot. These offsets are made on the central zone along the inner edge of the slot or on the outer portion along the outer edge of the slot, which part belongs to the rest of the face. These releases act as disrupters that alter the symmetry of the slot. Thus, even if the slot is wedged on the axis of the slotted guide, the offsets make it possible to obtain a circular polarization. If the slot is offset with respect to the axis of the slot guide, the offsets allow to modify the radiation and limit the frequency band with respect to the same slot without disconnection.

The various previous embodiments can be combined or not between them to define another embodiment.

According to one embodiment of the invention, the antenna element is such that the distance between the inner and outer edges of the annular slot is variable along the periphery of the slot.

The variation in the width of the annular slot may result for example because the inner and outer edges of the slot are not concentric. This asymmetry advantageously makes it possible to modify the radiation of the slot relative to the same element with an invariable distance between the two edges of the slot.

This latter embodiment may or may not be combined with a previous mode to define another embodiment.

According to one embodiment of the invention, the antenna element comprises another annular slot surrounding the annular slot.

The presence of a second annular slot whose central portion includes the first annular slot provides a two-band antennal element. The antennal element is said to have double annular slits. In the case where the annular slots are circular, the two annular slots are typically centered on the same central point.

This latter embodiment may or may not be combined with a previous mode to define another embodiment.

The invention further relates to a slotted guide comprising a plurality of antenna elements conforming to the preceding object, arranged between them in a linear array.

The parallelepipedal shape of the antenna elements makes it possible to easily produce a linear network by placing them in series. Serialization makes it possible to obtain a network with performances superior to that of a single antenna element.

The invention further relates to a plane antenna comprising a plurality of slotted guides in accordance with the preceding object, arranged between them in a two-dimensional network.

An antenna according to the invention combines a small footprint and compatible radiation performance of use with misalignment which requires a large difference between the main polarization and cross polarization beyond the main axis.

According to one embodiment of the invention, the planar antenna comprises a means for feeding the slotted guides in parallel arranged to control the phases between the supply signals of the slot guides.

Controlling the phases between each feeding point of the slotted guides makes it possible to control their relative phase shift and thus to maximize the overall radiation with controlled misalignment.

List of Figures

• La figure 1a représente schématiquement un élément antennaire selon l'art antérieur.
• La figure 1b représente schématiquement un guide à fente selon l'art antérieur réalisé avec un assemblage d'éléments antennaires de la figure 1a.
• La figure 1c représente schématiquement une antenne selon l'art antérieur consistant en un réseau de guides à fente de la figure 1b.
• La figure 2a) est un élément antennaire de l'art antérieur à fentes rectangulaires disposées en croix décalées de l'axe du guide à fente permettant d'obtenir une polarisation circulaire.
• La figure 2b) est un élément antennaire de l'art antérieur à fentes rectangulaires décalées suivant la longueur et la largeur du guide à fente et inclinées d'environ 45° permettant d'obtenir une polarisation circulaire.
• La figure 2c) représente des courbes de directivité en site en polarisations circulaires droite (DirRHCP) et gauche (DirLHCP) à la fréquence de 9GHz de l'élément antennaire de la figure 2b) pour différents angles Phi de gisement.
• La figure 3a est une représentation schématique d'un mode de réalisation d'un élément antennaire selon l'invention.
• La figure 3b rassemble des courbes de directivité en site en polarisations linéaires suivant x (DirL) et suivant y (DirR) à la fréquence de 8,55 GHz de l'élément antennaire correspondant à la figure 3a pour différents plans décalés d'un angle Phi de gisement.
• La figure 4a est une représentation schématique d'un mode de réalisation d'un élément antennaire selon l'invention dans lequel la fente de forme annulaire est décalée par rapport à l'axe du guide à fente.
• La figure 4b rassemble des courbes de directivité en site en polarisations circulaires droite (DirRHCP) et gauche (DirLHCP) à la fréquence de 9,9 GHz de l'élément antennaire correspondant à la figure 5a pour différents plans décalés d'un angle Phi de gisement.
• La figure 4c donne la courbe du taux d'ellipticité de l'élément antennaire de la figure 5a.
• La figure 5a est une représentation schématique d'un mode de réalisation d'un élément antennaire selon l'invention dans lequel la distance entre les bords intérieur et extérieur de la fente comporte le long du pourtour de la fente des variations notables qui délimitent des décochements à la partie centrale métallisée.
• La figure 5b rassemble des courbes de directivité en site en polarisations circulaires droite (DirRHCP) et gauche (DirLHCP) à la fréquence de 9,8 GHz de l'élément antennaire correspondant à la figure 5a pour différents plans décalés d'un angle Phi de gisement.
• La figure 5c donne la courbe du taux d'ellipticité de l'élément antennaire de la figure 5a.
• La figure 5d est une représentation schématique d'un mode de réalisation d'un élément antennaire selon l'invention dans lequel la distance entre les bords intérieur et extérieur de la fente comporte le long du pourtour de la fente des variations notables qui délimitent des décochements au reste de la face (partie extérieure à la fente).
• La figure 6a est une représentation schématique d'un mode de réalisation d'un élément antennaire selon l'invention dans lequel l'élément comporte une double fente annulaire.
• La figure 6b rassemble des courbes de directivité en site en polarisations circulaires droite (DirRHCP) et gauche (DirLHCP) à la fréquence de 8,7 GHz de l'élément antennaire correspondant à la figure 6a pour différents plans décalés d'un angle Phi de gisement.
• La figure 6c donne la courbe du taux d'ellipticité de l'élément antennaire de la figure 6a.
• La figure 7 illustre un mode de réalisation d'un élément antennaire selon l'invention avec une fente annulaire de forme elliptique.
• La figure 8a illustre un mode de réalisation d'un élément antennaire selon l'invention avec une fente annulaire de forme carrée.
• La figure 8b rassemble des courbes de directivité en site en polarisations linéaires suivant x (DirR) et suivant y (DirL) à la fréquence de 10 GHz de l'élément antennaire correspondant à la figure 8a pour différents plans décalés d'un angle Phi de gisement.
• La figure 9a est une représentation schématique d'un mode de réalisation d'un élément antennaire selon l'invention dans lequel la fente annulaire de forme carrée est décalée par rapport à l'axe du guide à fente.
• La figure 9b rassemble des courbes de directivité en site en polarisations circulaires droite (DirRHCP) et gauche (DirLHCP) à la fréquence de 10 GHz de l'élément antennaire correspondant à la figure 9a pour différents plans décalés d'un angle Phi de gisement.
• La figure 9c donne la courbe du taux d'ellipticité de l'élément antennaire de la figure 9a.
• La figure 10a est une représentation schématique d'un mode de réalisation d'un élément antennaire selon l'invention dans lequel la fente annulaire de forme carrée est décalée par rapport à l'axe du guide à fente et subie une rotation pour au finale obtenir une fente annulaire ayant la forme d'un losange.
• La figure 10b rassemble des courbes de directivité en site en polarisations circulaires droite (DirRHCP) et gauche (DirLHCP) à la fréquence de 10 GHz de l'élément antennaire correspondant à la figure 10a pour différents plans décalés d'un angle Phi de gisement.
• La figure 10c donne la courbe du taux d'ellipticité de l'élément antennaire de la figure 10a.
• La figure 11a correspond au cas d'une fente annulaire de forme carrée qui comprend deux perturbateurs sous forme de coins intérieurs coupés disposés symétriquement.
• La figure 11b rassemble des courbes de directivité en site en polarisations circulaires droite (DirLHCP) et gauche (DirRHCP) à la fréquence de 10 GHz de l'élément antennaire correspondant à la figure 11a pour différents plans décalés d'un angle Phi de gisement.
• La figure 11c donne la courbe du taux d'ellipticité de l'élément antennaire de la figure 11a.
• La figure 12 illustre un mode de réalisation d'un élément antennaire selon l'invention dans lequel la distance d entre les bords intérieur et extérieur de la fente annulaire est variable le long du pourtour de la fente.
• La figure 13 illustre un substrat diélectrique plan comprenant une série de trous métallisés reliant les deux faces métalliques du substrat avant découpe sur la face supérieure d'une fente annulaire selon l'invention.
• La figure 14 est une représentation schématique d'un mode de réalisation d'un élément antennaire selon l'invention obtenu en mettant en oeuvre une technologie classique avec un guide d'onde métallique chargé ou pas de diélectrique.

Other features and advantages of the invention will become apparent from the following description given with reference to the accompanying figures given by way of non-limiting examples.

• The figure 1a schematically represents an antennal element according to the prior art.
• The figure 1b schematically represents a slot guide according to the prior art made with an assembly of antenna elements of the figure 1a .
• The figure 1c schematically represents an antenna according to the prior art consisting of an array of slotted guides of the figure 1b .
• The figure 2a ) is an antennal element of the prior art with rectangular slots arranged in cross staggered from the axis of the slotted guide to obtain a circular polarization.
• The figure 2b ) is a antennal element of the prior art with rectangular slots offset along the length and width of the slot guide and inclined by about 45 ° to obtain a circular polarization.
• The Figure 2c ) represents directivity curves in the right (DirRHCP) and left (DirLHCP) circular polarizations at the 9GHz frequency of the antennal element of the figure 2b ) for different angles Phi of deposit.
• The figure 3a is a schematic representation of an embodiment of an antenna element according to the invention.
• The figure 3b gathers site orientation curves in linear polarizations along x (DirL) and following y (DirR) at the frequency of 8.55 GHz of the antennal element corresponding to the figure 3a for different planes offset by a Phi angle of deposit.
• The figure 4a is a schematic representation of an embodiment of an antenna element according to the invention in which the annular-shaped slot is offset with respect to the axis of the slot guide.
• The figure 4b gathers directivity curves in the right (DirRHCP) and left (DirLHCP) circular polarizations at the 9.9 GHz frequency of the antenna element corresponding to the figure 5a for different planes offset by a Phi angle of deposit.
• The figure 4c gives the curve of the ellipticity rate of the antennal element of the figure 5a .
• The figure 5a is a schematic representation of an embodiment of an antenna element according to the invention in which the distance between the inner and outer edges of the slot comprises along the perimeter of the slot significant variations which delimit out of the parts metallized central.
• The figure 5b gathers directivity curves in the right circular (DirRHCP) and left (DirLHCP) circular polarizations at the frequency of 9.8 GHz of the antennal element corresponding to the figure 5a for different planes offset by a Phi angle of deposit.
• The figure 5c gives the curve of the ellipticity rate of the antennal element of the figure 5a .
• The figure 5d is a diagrammatic representation of an embodiment of an antenna element according to the invention in which the distance between the inner and outer edges of the slot comprises along the periphery of the slot significant variations which delimit out of the rest of the slot. the face (outer part to the slot).
• The figure 6a is a schematic representation of an embodiment of an antenna element according to the invention wherein the element comprises a double annular slot.
• The figure 6b gathers directivity curves in the right circular (DirRHCP) and left (DirLHCP) circular polarizations at the 8.7 GHz frequency of the antennal element corresponding to the figure 6a for different planes offset by a Phi angle of deposit.
• The Figure 6c gives the curve of the ellipticity rate of the antennal element of the figure 6a .
• The figure 7 illustrates an embodiment of an antenna element according to the invention with an annular slot of elliptical shape.
• The figure 8a illustrates an embodiment of an antenna element according to the invention with an annular slot of square shape.
• The figure 8b gathers site orientation curves in linear polarizations along x (DirR) and following y (DirL) at the frequency of 10 GHz of the antennal element corresponding to the figure 8a for different planes offset by a Phi angle of deposit.
• The figure 9a is a schematic representation of an embodiment of an antenna element according to the invention in which the square-shaped annular slot is offset with respect to the axis of the slot guide.
• The figure 9b gathers directivity curves in the right (DirRHCP) and left (DirLHCP) circular polarizations at the 10 GHz frequency of the antennal element corresponding to the figure 9a for different planes offset by a Phi angle of deposit.
• The Figure 9c gives the curve of the ellipticity rate of the antennal element of the figure 9a .
• The figure 10a is a schematic representation of an embodiment of an antenna element according to the invention in which the square-shaped annular slot is offset with respect to the axis of the slot guide and is rotated to finally obtain an annular slot having the shape of a diamond.
• The figure 10b gathers directivity curves in the right (DirRHCP) and left (DirLHCP) circular polarizations at the 10 GHz frequency of the antennal element corresponding to the figure 10a for different planes offset by a Phi angle of deposit.
• The figure 10c gives the curve of the ellipticity rate of the antennal element of the figure 10a .
• The figure 11a corresponds to the case of a square shaped annular slot which comprises two disruptors in the form of intersected inner corners arranged symmetrically.
• The figure 11b gathers directivity curves in the right circular (DirLHCP) and left (DirRHCP) circular polarizations at the frequency of 10 GHz of the antennal element corresponding to the figure 11a for different planes offset by a Phi angle of deposit.
• The figure 11c gives the curve of the ellipticity rate of the antennal element of the figure 11a .
• The figure 12 illustrates an embodiment of an antenna element according to the invention wherein the distance d between the inner and outer edges of the annular slot is variable along the periphery of the slot.
• The figure 13 illustrates a planar dielectric substrate comprising a series of metallized holes connecting the two metal faces of the substrate before cutting on the upper face of an annular slot according to the invention.
• The figure 14 is a schematic representation of an embodiment of an antenna element according to the invention obtained by implementing a conventional technology with a charged metal waveguide or no dielectric.

Description of an embodiment of the invention

The figure 3a is a schematic representation of an embodiment of an antenna element ElA according to the invention. The antenna element ElA slotted guide according to the invention comprises at least one conductive face Fs provided with at least one annular slot Fan. An annular slot within the meaning of the invention is a slot which has the particularity of delimiting a conducting central zone Zc and of isolating it electrically from the remainder of the upper face Fs conducting.

The annular slot is delimited by an inner edge and an outer edge separated by a distance d. The depth of the slot is at least that of the thickness of the metallized layer of the upper face Fs to electrically isolate the central zone Zc from the remainder of the face Fs.

The curves of the figure 3b represent the radiation in site of this antennal element corresponding to the figure 3a for different planes offset by a bearing angle Phi (0 °, 45 °, 90 °, 135 °) with respect to the axis of the guide. The main linear polarization radiation pattern (following x) corresponding to the DirL lines is characterized by a maximum in the direction perpendicular to the slit surface. The lines DirR represent the radiation in crossed linear polarization (following y).

The figure 4a is a schematic representation of an embodiment of an antenna element ElA according to the invention in which the annular-shaped slot is offset with respect to the axis of the slot guide. The offset with respect to the axis of the slotted guide makes it possible to obtain a circular polarization.

The curves of the figure 4b represent the radiation in site of this antennal element corresponding to the figure 4a for different planes offset by a bearing angle Phi (0 °, 45 °, 90 °, 135 °) with respect to the axis of the guide. The main circular polarization (right) radiation pattern corresponding to the DirRHCP lines is characterized by a maximum in the direction perpendicular to the slit surface. The DirLHCP lines represent the radiation in circular cross polarization (left).

The curves of the figure 4b allow to illustrate the significant gain in isolation between the main and cross polarizations for angles greater than 40 ° obtained with an annular slot antenna element according to the invention compared to an antenna element of the prior art with rectangular slots whose radiation is illustrated by the Figure 2c . In particular, in the plane perpendicular to the axis of the guide (Phi = 90 °) this insulation can reach levels higher than 15 dB while on the Figure 2c this insulation is at best 3dB.

This notable improvement allows the use of the antennal element according to the invention for uses which requires a certain misalignment.

The offset of the annular slot with respect to the axis of the guide makes it possible to generate a right circular polarization if the slot is on the left following the propagation of the field and vice versa.

The figure 5a is a diagrammatic representation of an embodiment of an antenna element ElA according to the invention in which the distance between the inner and outer edges of the slot comprises along the periphery of the slot significant variations which delimit unobstructions at the central part metallized. According to another embodiment illustrated by the figure 5d , the offsets are made on the outer contour of the slot. These offsets play the role of disrupters which allow to modify the symmetry of the annular slot and to obtain a circular polarization even if the slot is wedged on the axis of the slot guide. The figure 5a corresponds to the case of a circular annular slot which comprises two disruptors in the form of notches arranged symmetrically.

The curves of the figure 5b represent the radiation in site of this antennal element corresponding to the figure 5a for different planes offset by a bearing angle Phi (0 °, 45 °, 90 °, 135 °) with respect to the axis of the guide. The main circular polarization radiation pattern (right) corresponding to DirRHCP lines is characterized by a maximum in the direction perpendicular to the surface where the slot is located. The DirLHCP lines represent the radiation in circular cross polarization (left). Given that the offsets allow to modify the radiation and limit the frequency band with respect to the same slot without disconnection, limitation that appears by comparing the ellipticity rate curves of the Figures 4c and 5c , the choice between the embodiment with offsets and the non-off mode can be guided according to the desired operating frequency band.

The figure 6a is a schematic representation of an embodiment of an antenna element ElA according to the invention wherein the element comprises a double annular slot which advantageously allows to obtain a dual band operation. According to the illustration, the double annular slot has a circular shape. In this case, the two slots are typically centered on the same central point.

The curves of the figure 6b represent the radiation in site of this antennal element corresponding to the figure 6a for different planes offset by a bearing angle Phi (0 °, 45 °, 90 °, 135 °) with respect to the axis of the guide. The main circular polarization (right) radiation pattern corresponding to the DirRHCP lines is characterized by a maximum in the direction perpendicular to the surface where the double slot is located. The DirLHCP lines represent the radiation in circular cross polarization (left).

Dual-band operation is revealed by the Figure 6c ellipticity rate that has two troughs.

The annular slot can have very variable shapes which is similar to that of a ring. The shape can be regular and belong to the list including circular, oval, elliptical, square, rectangular shapes.

The figure 7 illustrates an embodiment of an antenna element according to the invention with an annular slot of elliptical shape.

The figure 8a illustrates an embodiment of an antenna element according to the invention with an annular slot of square shape.

The curves of the figure 8b represent the radiation in site of this antennal element corresponding to the figure 8a for different planes offset by a bearing angle Phi (0 °, 45 °, 90 °, 135 °) with respect to the axis of the guide. The main linear polarization radiation pattern (along x) corresponding to the DirR lines is characterized by a maximum in the direction perpendicular to the slit surface. The DirL lines represent the radiation in crossed linear polarization (following y).

The figure 9a is a schematic representation of an embodiment of an antenna element ElA according to the invention in which the square-shaped annular slot is offset with respect to the axis of the slot guide. The offset with respect to the axis of the slotted guide makes it possible to obtain a circular polarization.

The curves of the figure 9b represent the radiation in site of this antennal element corresponding to the figure 9a for different planes offset by a bearing angle Phi (0 °, 45 °, 90 °, 135 °) with respect to the axis of the guide. The main circular polarization (right) radiation pattern corresponding to the DirRHCP lines is characterized by a maximum in the direction perpendicular to the slit surface. The DirLHCP lines represent the radiation in circular cross polarization (left).

The figure 10a is a schematic representation of an embodiment of an antenna element ElA according to the invention in which the square-shaped annular slot is offset with respect to the axis of the slot guide and is rotated to finally obtain a slot annular having the shape of a rhombus. The offset with respect to the axis of the slotted guide makes it possible to obtain a circular polarization.

The curves of the figure 10b represent the radiation in site of this antennal element corresponding to the figure 10a for different planes offset by a bearing angle Phi (0 °, 45 °, 90 °, 135 °) with respect to the axis of the guide. The main circular polarization (right) radiation pattern corresponding to the DirRHCP lines is characterized by a maximum in the direction perpendicular to the slit surface. The DirLHCP lines represent the radiation in circular cross polarization (left).

The figure 11a is a diagrammatic representation of an embodiment of an antenna element ElA according to the invention in which the distance between the inner and outer edges of the slot comprises along the periphery of the slot significant variations which delimit unobstructions at the central part metallized or in another mode on the outer contour of the slot. These offsets play the role of disrupters which allow to modify the symmetry of the annular slot and to obtain a circular polarization even if the slot is wedged on the axis of the slot guide. The figure 11a corresponds to the case of a square shaped annular slot which comprises two disruptors in the form of intersected inner corners arranged symmetrically.

The curves of the figure 11b represent the radiation in site of this antennal element corresponding to the figure 11a for different planes offset by a bearing angle Phi (0 °, 45 °, 90 °, 135 °) with respect to the axis of the guide. The main circular polarization (right) radiation pattern corresponding to the DirRHCP lines is characterized by a maximum in the direction perpendicular to the slit surface. The DirLHCP lines represent the radiation in circular cross polarization (left).

The shape of the annular slot may just as well not be regular and have a variable distance d between these edges, the shape may for example be of the potatooid type.

The figure 12 illustrates an embodiment of an antenna element according to the invention wherein the distance d between the inner and outer edges of the annular slot is variable along the periphery of the slot. A particular embodiment consists in producing an annular slot with two circular and non-concentric inner and outer edges as illustrated by FIG. figure 12 .

Whatever the shape of the annular slot, its thickness or depth is such that the metallized layer of the surface Fs on which the slot is printed is removed on the space occupied by the slot Fan. In other words, the slot breaks the electrical continuity that existed on the face Fs hosting the slot. Thus, the annular slot defines two zones on the surface Fs: the zone lying inside the slot or central zone Zc at the slot, delimited by the inner edge of the slot, and the zone outside the slot or remainder of the face, delimited by the outer edge of the slot. These two areas that are part of the face are electrically insulated from each other by the annular slot.

The antennal element can be obtained by implementing SIW technology. The SIW technology as described in [6] makes it possible to produce waveguides from planar dielectric substrates. This technology typically employs a conventional technique for producing a printed circuit (in the English terminology Printed Circuit Board, PCB). As illustrated by figure 13 , the two metallized faces Fs, Fi of the Sub substrate form the upper and lower sides of the guide. The upper side Fs is typically the side that is oriented in the direction of the transmitted or received signal. The vertical metal walls of the short sides of the guide are made by a series of metallized holes Tr connecting the two faces Fs, Fi metal of the substrate. This printed technology is advantageous because it makes it possible to produce low thickness and low cost antennas as described in [5].

Such a technology is particularly well suited for obtaining an antenna element with annular slot according to the invention because it allows for annular slots by printing their pattern on one side of the antennal element. Such a printing technique is well known to those skilled in the art, known for example under the name Anglo-Saxon PCB, and is therefore not described. At the end of the PCB process, the annular slot delimits a central zone and electrically isolates it from the remainder of the upper face.

The figure 14 is a schematic representation of an embodiment of an antenna element ElA according to the invention obtained by implementing a conventional technology with a charged metal waveguide or no dielectric. In the case where the waveguide is not loaded the central portion is maintained at the lower face by means of a pin or pad Pi which can be made of dielectric and optionally metallized.

The antennal elements according to the invention can be associated in one dimension, in the same way as the antenna elements of the prior art, to form a slotted guide. These latter slot guides can themselves be networked in the same way as the slotted guides of the prior art to form a planar antenna.

1. [1] A.F.Stevenson, « Theory of slots in rectangular waveguides », Journal of applied Physics, vol.19, pp 24-28, Jan.1948 .
2. [2] R.S. Elliot, L.A. Kurtz, "The design of small Slot Arrays", IEEE trans. AP, vol. 26, n° 2, pp214-219, March 1978 .
3. [3] A.J. Simmons, "Circularly Polarized Slot Radiaors" IRE trans AP, Vol. 5, n° 1, PP31-36, Jan. 1957 .
4. [4] G. Montisci" M. Musa, G. Mazzarella, "Waveguide Slot Antennas for Circularly Polarized Radiated Field", IEEE trans. AP, vol. 52, n° 2, pp 619-623, Feb. 2004 .
5. [5] Y.J. Cheng, W. Hong, K? Wu, Z. Q. Kuai, C. Yu, J.X. Chen, J. Y. Zhou, H. J. Tang, Substrate Integrated Waveguide (SIW) Rotman Lens and Its Ka-Band Multibeam Array Antenna Applications", IEEE trans. AP, vol. 56, n° 8, pp 2504-2513, Aug. 2008 .
6. [6] K. Wu, D. Deslandes, Y. Cassivi, "The Substrate Integrated Circuit - A New Concept for High-Frequency Electronics and Optoelectronics" Proc. 6th Int. Conf. Telecomm. Modern Satellite, Cable and Boadcasting Service, Vol. 1, pp3-5, Oct. 2003 .

The antenna may be associated with a means for supplying the slot guides in parallel. The control of the relative phases between the feed points of the slotted guides makes it possible to maximize the overall radiation and thus to control the misalignment of the antenna.

1. [1] AFStevenson, "Theory of slots in rectangular waveguides," Journal of Applied Physics, vol.19, pp 24-28, Jan.1948 .
2. [2] RS Elliot, LA Kurtz, "The Design of Small Slot Arrays", IEEE trans. AP, vol. 26, No. 2, pp214-219, March 1978 .
3. [3] AJ Simmons, "Circularly Polarized Slot Radiaors" IRE trans AP, Vol. 5, No. 1, PP31-36, Jan. 1957 .
4. [4] G. Montisci "M. Musa, G. Mazzarella," Waveguide Slot Antennas for Circularly Polarized Radiated Field, "IEEE Trans., AP, 52, 2, pp 619-623, Feb. 2004 .
5. [5] YJ Cheng, W. Hong, K? Wu, ZQ Kuai, C. Yu, Chen JX, JY Zhou, HJ Tang, Integrated Waveguide Substrate (SIW) Rotman Lens and Its Ka-Band Multibeam Array Antenna Applications, "IEEE Trans., AP, Vol 56, No. 8, pp 2504-2513, Aug. 2008 .
6. [6] K. Wu, D. Deslandes, Y. Cassivi, "The Substrate Integrated Circuit - A New Concept for High-Frequency Electronics and Optoelectronics" Proc. 6th Int. Conf. Telecomm. Modern Satellite, Cable and Boadcasting Service, Vol. 1, pp3-5, Oct. 2003 .

Claims (8)

1. Slotted waveguide antennal element (ElA) of generally parallelepipedal shape comprising several conductive surfaces , of which one of the conductive surfaces (Fs) is provided with at least one slot excited by the propagation of the electromagnetic field of the wave in the waveguide along the axis of the latter, the slot delimiting in its central part a conductive region (Zc) and electrically insulating this region (Zc) from the rest of the surface (Fs), characterized in that the slot (Fan) is annular.
2. Antennal element (ElA) according to Claim 1, in which the annular slot is offset with respect to the axis of the waveguide.
3. Antennal element (ElA) according to either of Claims 1 and 2, in which the distance between the inner and outer edges of the annular slot is variable along the perimeter of the slot.
4. Antennal element (ElA) according to Claim 3, in which the perimeter of the slot comprises variations which delimit stubs.
5. Antennal element (ElA) according to one of Claims 1 to 4, containing at least one other annular slot surrounding the annular slot.
6. Slotted guide comprising several antennal elements in accordance with one of the preceding claims, arranged together in a linear array.
7. Planar antenna comprising several slotted guides in accordance with the preceding claim, arranged together in a two-dimensional array.
8. Planar antenna according to the preceding claim, comprising a means for feeding the slotted guides in parallel, which means is arranged for steering the phases between the feed signals of the slotted guides.

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