EP0014605B1 - Reverse cassegrain antenna for multipurpose radar - Google Patents

Reverse cassegrain antenna for multipurpose radar Download PDF

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Publication number
EP0014605B1
EP0014605B1 EP80400037A EP80400037A EP0014605B1 EP 0014605 B1 EP0014605 B1 EP 0014605B1 EP 80400037 A EP80400037 A EP 80400037A EP 80400037 A EP80400037 A EP 80400037A EP 0014605 B1 EP0014605 B1 EP 0014605B1
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EP
European Patent Office
Prior art keywords
reflecting
plane
polarization
mirror
elements
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Expired
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EP80400037A
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German (de)
French (fr)
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EP0014605A1 (en
Inventor
Yves Commault
François Gautier
Robert Pierrot
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Thales SA
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Thomson CSF SA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q3/00—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system
    • H01Q3/01—Arrangements for changing or varying the orientation or the shape of the directional pattern of the waves radiated from an antenna or antenna system varying the shape of the antenna or antenna system
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q19/00—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic
    • H01Q19/10—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces
    • H01Q19/18—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces having two or more spaced reflecting surfaces
    • H01Q19/19—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces having two or more spaced reflecting surfaces comprising one main concave reflecting surface associated with an auxiliary reflecting surface
    • H01Q19/195—Combinations of primary active antenna elements and units with secondary devices, e.g. with quasi-optical devices, for giving the antenna a desired directional characteristic using reflecting surfaces having two or more spaced reflecting surfaces comprising one main concave reflecting surface associated with an auxiliary reflecting surface wherein a reflecting surface acts also as a polarisation filter or a polarising device
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q25/00—Antennas or antenna systems providing at least two radiating patterns
    • H01Q25/002—Antennas or antenna systems providing at least two radiating patterns providing at least two patterns of different beamwidth; Variable beamwidth antennas

Definitions

  • the subject of the present invention is an inverted “Cassegrain” antenna intended to be used in standby or in pursuit and capable of providing an enlarged beam either in the ground view site plan or in the field plan (anti-collision) while retaining the qualities of 'a fine primary beam.
  • the inverted Cassegrain antenna is known and has for example been described in American patent US Pat. No. 3,771,160 which relates to an inverted Cassegrain antenna with polarization rotation.
  • the antenna described in this patent comprises a planar auxiliary reflector constituted by a plurality of arrays of parallel conductive wires and by a metal plate, the plate and the arrays of wires being parallel and separated by a dielectric. It operates at at least two frequencies but cannot be used in combination with a multi-function radar, standby or tracking.
  • the beam emitted by the antenna has a shape adapted, at a given moment, to the function for which it is used. This has already been done on simple antennas, by switching from primary sources or by modifying the shape of the antenna. However, this means of adapting an antenna to the different functions of a radar does not give good results in the case of an inverted “Cassegrain” antenna. In fact, the performance of the Cassegrain antenna is reduced if the primary sources of this antenna are multiplied or if the parabolic reflector is deformed, which makes it necessary to modify the beam focusing device.
  • An advantageous means for producing an inverted Cassegrain antenna, with multiple functions, is to modify the shape of the polarization rotation mirror with which it is provided.
  • an inverted Cassegrain antenna making it possible to widen the beam in a plane during operation, associated with a multi-function radar and comprising a primary source of HF electromagnetic waves with rectilinear polarization, a curved primary reflector having an axis of revolution and intended to reflect the waves coming directly from the primary source and to selectively transmit the electromagnetic waves having a rectilinear crossed polarization, the primary source being disposed substantially at the focus of this primary reflector and a mirror with polarization rotation ensuring the return to the primary reflector of the reflected radiation having undergone a rotation of its plane of polarization, is characterized in that this mirror with polarization rotation is formed of several reflector-polarizing elements planes, articulated with respect to each other by parallel hinges , orthogonal to the desired beam widening plane of the antenna and in that these elements are associated with means for controlling their relative positioning.
  • a reverse Cassegrain antenna comprises, as shown in FIG. 1, a primary source S intended for emitting high frequency electromagnetic waves, a primary parabolic reflector R i , of axis xx of revolution, reflecting the radiation of the primary source S and selectively transmitting radiation having a rectilinear crossed polarization, and an auxiliary reflector R 2 (or mirror) with polarization rotation, of planar shape, the assembly constituting a focusing system.
  • the primary source S has the role, on emission, of illuminating the focusing system with an electromagnetic wave with rectilinear polarization (horizontal polarization for example), radiating a well-defined amplitude, phase and polarization revolution diagram and stable in the frequency band used, and, on reception, to collect in the best conditions, the energy provided by the echo and concentrated by the focusing system in the vicinity of its focus F, in the form of a diffraction diagram .
  • the primary source S (FIG. 1) disposed at the focal point F of the parabolic reflector R i emits radiation with linear (horizontal) polarization which is totally reflected by the parabolic reflector R i , the angle formed by the incident ray with the reflected ray being equal to the angle of the incident ray with the axis xx of the reflector R i .
  • the reflected rays, parallel to the axis xx, are received by the auxiliary reflector R 2 (or mirror), and reflected, after a rotation of ⁇ / 2 of their plane of polarization (the horizontal polarization of the incident wave is transformed in vertical polarization), towards the parabolic reflector R i allowing the radiation having a plane of vertical polarization, the beam from the antenna then being a substantially parallel beam.
  • an inverted Cassegrain antenna comprises, as shown in FIG. 2, a primary source S, a primary parabolic reflector R, reflecting the primary radiation coming from the source S and being able to selectively transmit the radiation having a rectilinear crossed polarization, this source S being substantially disposed at the focal point F of the primary reflector R, a mirror M l with polarization rotation formed of two elements e 1 , e 2 reflector-polarizers of planar shape, joined by a hinge c 1 allowing their articulation.
  • the hinge C 1 is arranged in a direction perpendicular to the beam widening plane, namely in the case of Figure 2 the plane of symmetry of the antenna, coincident with the plane of the figure.
  • These reflector-polarizing elements e 1 , e 2 can be in known manner (FIG. 7), consisting of a metal plate P and a sheet N of parallel wires inclined at 45 ° relative to the direction of the incident rectilinear polarization , this sheet N being placed at k ⁇ / 4 of the plate P, k being an odd integer and ⁇ the operating wavelength of the antenna.
  • an incident wave O 1 with horizontal rectilinear polarization can be considered as the superposition of two component wave equiphase O ' 1 and O'' 1 whose polarization planes are inclined at 45 ° relative to the polarization plane of the 'incident wave O 1 , the first component O' 1 being parallel to the wires of the sheet N and the second component O '' 1 being perpendicular to these wires.
  • the first component O ' 1 is therefore reflected by the wires while the second component 0 ", crosses the sheet N after having traveled a path equal to 2 K ⁇ / 4, that is to say a path equal to k ⁇ / 2.
  • the second reflected 0 " 2 component is therefore depressed by ⁇ with respect to the first reflected 0 ' 2 component and the combination of the two components then creates an O2 wave with vertical polarization which can pass through the parabolic reflector letting the vertically polarized radiation pass and reflecting horizontally polarized radiation. It is also possible to use systems with parallel metal blades also inclined at 45 ° relative to the direction of incident polarization of the radiation to produce these reflector-polarizer elements without departing from the scope of the present invention.
  • This reflector R can consist, for example, of a layer of horizontal wires when the rectilinear polarization of the incident one from the primary source S is horizontal.
  • the mirror M 1 comprises, as shown in FIGS. 2 and 3, a hinge C 1 situated at one third of the diameter of the mirror and perpendicular to the vertical plane of symmetry of the antenna represented by the plane of FIG. 2.
  • a hinge C 1 situated at one third of the diameter of the mirror and perpendicular to the vertical plane of symmetry of the antenna represented by the plane of FIG. 2.
  • D the diameter perpendicular to the hinges
  • D 'the diameter parallel to the hinges we will designate by D the diameter perpendicular to the hinges and by D 'the diameter parallel to the hinges.
  • the element e 2 which is the smallest element, is inclined at an angle a of approximately 7 ° relative to the element e 1 .
  • Such a mirror M 1 allows coverage on site with a decrease in gain substantially obeying a square cosecant law, such that the level at -17 dB is reached at 20 ° from the axis instead of the 5 ° obtained with a beam.
  • conventional end Figure 8
  • the characteristics of the beam are also preserved for any orientation of the mirror M 1 and are not very selective in frequency.
  • the elements e 1 , e 2 of the mirror M 1 can have relative inclinations in one direction or the other.
  • the movement of these elements e 1 , e 2 around the hinge Ci and their immobilization in a determined position are obtained in the antenna according to the invention, by means of a control device 20 intended to be actuated during operation from the radar.
  • the remote control device 20 is shown only, by way of nonlimiting example, in FIG. 2 so as not to overload the drawings and in order to allow a better understanding of the latter.
  • the control device 20 is, for example, constituted by a motor integral with the mirror M 1 , the axis 201 of which is constituted by an endless screw provided with a slider 202 driven by the endless screw 201 in translation ⁇ in the direction of the mirror M 1 in the plane of FIG. 2.
  • the movable cursor 202 is provided with an index 203 movable in a direction y perpendicular to the direction of translation ⁇ of the cursor and driven in this direction by a gear system.
  • the movable index 203 has one of its ends engaged in a slide disposed on the back of the reflecting surface of the polarizing reflective element e 2 .
  • the slide for reasons of simplification, is not shown in FIG. 2.
  • the motor 20 is controlled by control signals at the level of a control input 200.
  • each angular position of the motor shaft corresponds to a value ⁇ , ⁇ representative of an angle a.
  • Any other equivalent control means for the reflective element e 2 does not depart from the scope of the present invention.
  • This mirror M 1 therefore makes it possible to return to the reflector R (FIG. 2) parabolic rays having different angles of reflection depending on the element e 1 or e 2 towards which they fall.
  • R parabolic rays having different angles of reflection depending on the element e 1 or e 2 towards which they fall.
  • the polarizing mirror is a mirror M 2 FIGS. 5, 6 formed of three plane reflector-polarizing elements e 10 , e 20 , e 30 articulated around two hinges c 1 , c 2 .
  • the hinges c 2 , c 2 are according to FIGS. 5 and 6 respectively arranged according to a diameter D 'perpendicular to the diameter D and to two thirds of the diameter D.
  • the two hinges c 1 , c 2 are perpendicular to the diameter D.
  • Such a mirror M 2 makes it possible to operate the antenna according to the invention with a fine beam and single pulse channels (in this case the elements e lo , e 20 , e 30 are coplanar), or with an asymmetrical beam for viewing the ground ( in this case only the elements e lo , e 20 are coplanar, which corresponds to an articulation situated at the third of the mirror M 2 ) or even with a symmetrical widened beam, the inclination of the reflector-polarizing elements e 10 , e 30 causing a widening of the radiation pattern in the vertical plane of symmetry of the antenna, and possibility of using the monopuls channels (M 2 mirror articulated only in the center, e 20 and e 30 then being coplanar), this widened beam being able to be used for a ve It is close to rapid exploration.
  • a fine beam and single pulse channels in this case the elements e lo , e 20 , e 30 are coplanar
  • the polarizing mirror M 2 is made up of three reflector-polarizing elements e 10 , e 20 , e 30 hinged together by two hinges c 1 , c 2 symmetrical with respect to a diameter D ′ of the mirror, perpendicular to the diameter D.
  • Such a mirror in the same manner as above, makes it possible to obtain operation of the antenna with a fine beam and “monopulse” channels, c ’ ie channels making it possible to obtain a signal of deviation from a target echo with respect to the axis xx of the antenna, or a wide beam and “monopulse” channels when the reflector-polarizer elements e 10 , e 20 , e 30 are respectively coplanar or symmetrically inclined by the same dihedral angle a relative to the plane of the element e 20 , and operation with an asymmetric widened beam, as shown in FIG. 8, when the elements reflector-polarizers are tilted asymmetrically.
  • FIG. 8 represents, along the vertical plane of symmetry of the antenna, a radiation diagram as a function of a direction 0 relative to the axis xx. A relative maximum of radiation is obtained in direction 2a.
  • the characteristics of the beam emitted by the antenna according to the invention are preserved whatever the orientation of the whole of the mirror (M 1 or M 2 ) and are not very selective in frequency.

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  • Aerials With Secondary Devices (AREA)
  • Variable-Direction Aerials And Aerial Arrays (AREA)

Description

La présente invention a pour objet une antenne «Cassegrain» inversée destinée à être utilisée en veille ou en poursuite et pouvant fournir un faisceau élargi soit dans le plan de site visualisation au sol soit dans le plan gisement (anticollision) tout en conservant les qualités d'un faisceau primaire fin.The subject of the present invention is an inverted “Cassegrain” antenna intended to be used in standby or in pursuit and capable of providing an enlarged beam either in the ground view site plan or in the field plan (anti-collision) while retaining the qualities of 'a fine primary beam.

L'antenne Cassegrain inversée est connue et a par exemple été décrite dans le brevet américain US 3 771 160 qui concerne une antenne Cassegrain inversée à rotation de polarisation. L'antenne décrite dans ce brevet comprend un réflecteur auxiliaire plan constitué par une pluralité de réseaux de fils conducteurs parallèles et par une plaque métallique, la plaque et les réseaux de fils étant parallèles et séparés par un diélectrique. Elle fonctionne à au moins deux fréquences mais ne peut pas être utilisée en association avec un radar à fonctions multiples, veille ou poursuite.The inverted Cassegrain antenna is known and has for example been described in American patent US Pat. No. 3,771,160 which relates to an inverted Cassegrain antenna with polarization rotation. The antenna described in this patent comprises a planar auxiliary reflector constituted by a plurality of arrays of parallel conductive wires and by a metal plate, the plate and the arrays of wires being parallel and separated by a dielectric. It operates at at least two frequencies but cannot be used in combination with a multi-function radar, standby or tracking.

Dans un radar à fonctions multiples il est en effet souhaitable que le faisceau émis par l'antenne ait une forme adaptée, à un moment donné, à la fonction pour laquelle il est utilisé. Ceci a déjà été réalisé sur des antennes simples, par commutation de sources primaires ou par modification de la forme de l'antenne. Mais ce moyen d'adaptation d'une antenne aux différentes fonctions d'un radar ne donne pas de bons résultats dans le cas d'une antenne «Cassegrain» inversée. En effet, les performances de l'antenne Cassegrain sont réduites si l'on multiplie les sources primaires de cette antenne ou si l'on déforme le réflecteur parabolique, ce qui oblige à modifier le dispositif de focalisation du faisceau.In a multifunction radar it is indeed desirable that the beam emitted by the antenna has a shape adapted, at a given moment, to the function for which it is used. This has already been done on simple antennas, by switching from primary sources or by modifying the shape of the antenna. However, this means of adapting an antenna to the different functions of a radar does not give good results in the case of an inverted “Cassegrain” antenna. In fact, the performance of the Cassegrain antenna is reduced if the primary sources of this antenna are multiplied or if the parabolic reflector is deformed, which makes it necessary to modify the beam focusing device.

Un moyen avantageux pour réaliser une antenne Cassegrain inversée, à fonctions multiples, est de modifier la forme du miroir à rotation de polarisation dont elle est munie.An advantageous means for producing an inverted Cassegrain antenna, with multiple functions, is to modify the shape of the polarization rotation mirror with which it is provided.

Suivant l'invention, une antenne Cassegrain inversée permettant d'élargir, pendant le fonctionnement, le faisceau dans un plan, associée à un radar à fonctions multiples et comprenant une source primaire d'ondes électromagnétiques H.F. à polarisation rectiligne, un réflecteur primaire galbé ayant un axe de révolution et destiné à réfléchir les ondes issues directement de la source primaire et à transmettre sélectivement les ondes électromagnétiques ayant une polarisation rectiligne croisée, la source primaire étant disposée sensiblement au foyer de ce réflecteur primaire et un miroir à rotation de polarisation assurant le renvoi vers le réflecteur primaire du rayonnement réfléchi ayant subi une rotation de son plan de polarisation, est caractérisée en ce que ce miroir à rotation de polarisation est formé de plusieurs éléments réflecteurs-polariseurs plans, articulés les uns par rapport aux autres par des charnières parallèles, orthogonales au plan désiré d'élargissement du faisceau de l'antenne et en ce que ces éléments sont associés à des moyens de commande de leur positionnement relatif.According to the invention, an inverted Cassegrain antenna making it possible to widen the beam in a plane during operation, associated with a multi-function radar and comprising a primary source of HF electromagnetic waves with rectilinear polarization, a curved primary reflector having an axis of revolution and intended to reflect the waves coming directly from the primary source and to selectively transmit the electromagnetic waves having a rectilinear crossed polarization, the primary source being disposed substantially at the focus of this primary reflector and a mirror with polarization rotation ensuring the return to the primary reflector of the reflected radiation having undergone a rotation of its plane of polarization, is characterized in that this mirror with polarization rotation is formed of several reflector-polarizing elements planes, articulated with respect to each other by parallel hinges , orthogonal to the desired beam widening plane of the antenna and in that these elements are associated with means for controlling their relative positioning.

L'invention sera mieux comprise et d'autres caractéristiques apparaîtront à l'aide de la description ci-après et des dessins qui l'accompagnent et sur lesquels:

  • - la figure 1 représente une antenne Cassegrain inversée à miroir plan polariseur de type classique;
  • - la figure 2 représente un exemple de réalisation d'une antenne Cassegrain inversée, suivant l'invention;
  • - les figures 3 et 4 montrent respectivement une vue de profil et de face du miroir utilisé dans la figure 2;
  • - les figures 5 et 6 montrent respectivement les vues de profil et de face d'un autre exemple de réalisation d'un miroir utilisé dans une antenne suivant l'invention;
  • - la figure 7 montre un détail de réalisation d'un miroir à rotation de polarisation suivant l'invention;
  • - la figure 8 montre les caractéristiques d'un faisceau large obtenu avec une antenne suivant l'invention;
  • - la figure 9 montre respectivement en a et b un mode de réalisation particulier d'un miroir à rotation de polarisation selon l'invention.
The invention will be better understood and other characteristics will appear from the following description and the accompanying drawings, in which:
  • - Figure 1 shows an inverted Cassegrain antenna with plane polarizing mirror of conventional type;
  • - Figure 2 shows an embodiment of an inverted Cassegrain antenna, according to the invention;
  • - Figures 3 and 4 respectively show a side and front view of the mirror used in Figure 2;
  • - Figures 5 and 6 respectively show the side and front views of another embodiment of a mirror used in an antenna according to the invention;
  • - Figure 7 shows a detail of embodiment of a polarization rotation mirror according to the invention;
  • - Figure 8 shows the characteristics of a wide beam obtained with an antenna according to the invention;
  • - Figure 9 shows respectively in a and b a particular embodiment of a polarization rotation mirror according to the invention.

Une antenne Cassegrain inversée, de type connu, comporte, comme le montre la figure 1, une source S primaire destinée à émettre des ondes électromagnétiques haute fréquence, un réflecteur Ri primaire parabolique, d'axe xx de révolution, réfléchissant le rayonnement de la source S primaire et transmettant sélectivement le rayonnement ayant une polarisation rectiligne croisée, et un réflecteur auxiliaire R2 (ou miroir) à rotation de polarisation, de forme plane, l'ensemble constituant un système focalisant. La source S primaire a pour rôle, à l'émission, d'illuminer le système focalisant avec une onde électromagnétique à polarisation rectiligne (polarisation horizontale par exemple), rayonnant un diagramme de révolution d'amplitude, de phase et de polarisation bien définies et stables dans la bande de fréquence utilisée, et, à la réception, de recueillir dans les meilleures conditions, l'énergie fournie par l'écho et concentrée par le système focalisant au voisinage de son foyer F, sous forme d'un diagramme de diffraction.A reverse Cassegrain antenna, of known type, comprises, as shown in FIG. 1, a primary source S intended for emitting high frequency electromagnetic waves, a primary parabolic reflector R i , of axis xx of revolution, reflecting the radiation of the primary source S and selectively transmitting radiation having a rectilinear crossed polarization, and an auxiliary reflector R 2 (or mirror) with polarization rotation, of planar shape, the assembly constituting a focusing system. The primary source S has the role, on emission, of illuminating the focusing system with an electromagnetic wave with rectilinear polarization (horizontal polarization for example), radiating a well-defined amplitude, phase and polarization revolution diagram and stable in the frequency band used, and, on reception, to collect in the best conditions, the energy provided by the echo and concentrated by the focusing system in the vicinity of its focus F, in the form of a diffraction diagram .

En fonctionnement, la source S primaire (figure 1) disposée au foyer F du réflecteur Ri parabolique émet un rayonnement à polarisation linéaire (horizontale) qui est totalement réfléchi par le réflecteur Ri parabolique, l'angle formé par le rayon incident avec le rayon réfléchi étant égal à l'angle du rayon incident avec l'axe xx du réflecteur Ri. Les rayons réfléchis, parallèles à l'axe xx, sont reçus par le réflecteur R2 auxiliaire (ou miroir), et réfléchis, après une rotation de π/2 de leur plan de polarisation (la polarisation horizontale de l'onde incidente est transformée en polarisation verticale), vers le réflecteur Ri parabolique laissant passer le rayonnement ayant un plan de polarisation vertical, le faisceau issu de l'antenne étant alors un faisceau sensiblement parallèle.In operation, the primary source S (FIG. 1) disposed at the focal point F of the parabolic reflector R i emits radiation with linear (horizontal) polarization which is totally reflected by the parabolic reflector R i , the angle formed by the incident ray with the reflected ray being equal to the angle of the incident ray with the axis xx of the reflector R i . The reflected rays, parallel to the axis xx, are received by the auxiliary reflector R 2 (or mirror), and reflected, after a rotation of π / 2 of their plane of polarization (the horizontal polarization of the incident wave is transformed in vertical polarization), towards the parabolic reflector R i allowing the radiation having a plane of vertical polarization, the beam from the antenna then being a substantially parallel beam.

Dans un exemple de réalisation, une antenne Cassegrain inversée suivant l'invention comprend, comme le montre la figure 2, une source S primaire, un réflecteur R primaire parabolique, réfléchissant le rayonnement primaire issu de la source S et pouvant transmettre sélectivement le rayonnement ayant une polarisation rectiligne croisée, cette source S étant sensiblement disposée au foyer F du réflecteur R primaire, un miroir Ml à rotation de polarisation formé de deux éléments e1, e2 réflecteurs-polariseurs de forme plane, réunis par une charnière c1 permettant leur articulation. La charnière C1 est disposée selon une direction perpendiculaire au plan d'élargissement du faisceau, à savoir dans le cas de la figure 2 le plan de symétrie de l'antenne, confondu avec le plan de la figure.In an exemplary embodiment, an inverted Cassegrain antenna according to the invention comprises, as shown in FIG. 2, a primary source S, a primary parabolic reflector R, reflecting the primary radiation coming from the source S and being able to selectively transmit the radiation having a rectilinear crossed polarization, this source S being substantially disposed at the focal point F of the primary reflector R, a mirror M l with polarization rotation formed of two elements e 1 , e 2 reflector-polarizers of planar shape, joined by a hinge c 1 allowing their articulation. The hinge C 1 is arranged in a direction perpendicular to the beam widening plane, namely in the case of Figure 2 the plane of symmetry of the antenna, coincident with the plane of the figure.

Ces éléments réflecteurs-polariseurs e1, e2 peuvent être de façon connue (figure 7), constitués d'une plaque P métallique et d'une nappe N de fils parallèles inclinés à 45° par rapport à la direction de la polarisation rectiligne incidente, cette nappe N étant disposée à k λ/4 de la plaque P, k étant un nombre entier impair et λ la longueur d'onde de fonctionnement de l'antenne. En fonctionnement, une onde incidente O1 à polarisation rectiligne horizontale, peut être considérée comme la superposition de deux ondes composantes équiphase O'1 et O''1 dont les plans de polarisation sont inclinés à 45° par rapport au plan de polarisation de l'onde incidente O1, la première composante O'1 étant parallèle aux fils de la nappe N et la seconde composante O''1 étant perpendiculaire à ces fils. La première composante O'1 est donc réfléchie par les fils alors que la seconde composante 0", traverse la nappe N après avoir parcouru un chemin égal à 2 K λ/4, soit un chemin égal à k λ/2. A ce moment, la seconde composante 0"2 réfléchie est donc déphassée de π par rapport à la première composante 0'2 réfléchie et la combinaison des deux composantes crée alors une onde O2 à polarisation verticale qui pourra traverser le réflecteur parabolique laissant passer les rayonnements à polarisation verticale et réfléchissant les rayonnements à polarisation horizontale. On peut également utiliser des systèmes à lames métalliques parallèles également inclinées à 45° par rapport à la direction de polarisation incidente du rayonnement pour réaliser ces éléments réflecteurs-polariseurs sans sortir du cadre de la présente invention.These reflector-polarizing elements e 1 , e 2 can be in known manner (FIG. 7), consisting of a metal plate P and a sheet N of parallel wires inclined at 45 ° relative to the direction of the incident rectilinear polarization , this sheet N being placed at k λ / 4 of the plate P, k being an odd integer and λ the operating wavelength of the antenna. In operation, an incident wave O 1 with horizontal rectilinear polarization, can be considered as the superposition of two component wave equiphase O ' 1 and O'' 1 whose polarization planes are inclined at 45 ° relative to the polarization plane of the 'incident wave O 1 , the first component O' 1 being parallel to the wires of the sheet N and the second component O '' 1 being perpendicular to these wires. The first component O ' 1 is therefore reflected by the wires while the second component 0 ", crosses the sheet N after having traveled a path equal to 2 K λ / 4, that is to say a path equal to k λ / 2. , the second reflected 0 " 2 component is therefore depressed by π with respect to the first reflected 0 ' 2 component and the combination of the two components then creates an O2 wave with vertical polarization which can pass through the parabolic reflector letting the vertically polarized radiation pass and reflecting horizontally polarized radiation. It is also possible to use systems with parallel metal blades also inclined at 45 ° relative to the direction of incident polarization of the radiation to produce these reflector-polarizer elements without departing from the scope of the present invention.

La réalisation du réflecteur R parabolique est connue en soi. Ce réflecteur R peut être constitué par exemple d'une nappe de fils horizontaux lorsque la polarisation rectiligne de l'one incidente issue de la source S primaire est horizontale.The production of the parabolic reflector R is known per se. This reflector R can consist, for example, of a layer of horizontal wires when the rectilinear polarization of the incident one from the primary source S is horizontal.

Dans un exemple de réalisation de l'antenne Cassegrain inversée, suivant l'invention, le miroir M1 comporte, comme le montrent les figures 2 et 3, une charnière C1 située au tiers du diamètre du miroir et perpendiculaire au plan vertical de symétrie de l'antenne représenté par le plan de la figure 2. Dans la suite de la description, nous désignerons par D le diamètre perpendiculaire aux charnières et par D' le diamètre parallèle aux charnières. L'élément e2, qui est l'élément le plus petit, est incliné d'un angle a de 7° environ par rapport à l'élément e1. Un tel miroir M1 permet une couverture en site présentant une décroissance du gain obéissant sensiblement à une loi en cosécante carrée, telle que le niveau à -17 dB soit atteint à 20° de l'axe au lieu des 5° obtenues avec un faisceau fin conventionnel (figure 8). Les caractéristiques du faisceau sont en outre conservées pour toute orientation du miroir M1 et sont peu sélectives en fréquence.In an exemplary embodiment of the inverted Cassegrain antenna, according to the invention, the mirror M 1 comprises, as shown in FIGS. 2 and 3, a hinge C 1 situated at one third of the diameter of the mirror and perpendicular to the vertical plane of symmetry of the antenna represented by the plane of FIG. 2. In the following description, we will designate by D the diameter perpendicular to the hinges and by D 'the diameter parallel to the hinges. The element e 2 , which is the smallest element, is inclined at an angle a of approximately 7 ° relative to the element e 1 . Such a mirror M 1 allows coverage on site with a decrease in gain substantially obeying a square cosecant law, such that the level at -17 dB is reached at 20 ° from the axis instead of the 5 ° obtained with a beam. conventional end (Figure 8). The characteristics of the beam are also preserved for any orientation of the mirror M 1 and are not very selective in frequency.

Les éléments e1, e2 du miroir M1 peuvent présenter des inclinaisons relatives dans un sens ou dans l'autre. Le mouvement de ces éléments e1, e2 autour de la charnière Ci et leur immobilisation dans une position déterminée sont obtenus dans l'antenne suivant l'invention, au moyen d'un dispositif de commande 20 destiné à être actionné au cours du fonctionnement du radar.The elements e 1 , e 2 of the mirror M 1 can have relative inclinations in one direction or the other. The movement of these elements e 1 , e 2 around the hinge Ci and their immobilization in a determined position are obtained in the antenna according to the invention, by means of a control device 20 intended to be actuated during operation from the radar.

Le dispositif de télécommande 20 est représenté uniquement, à titre d'exemple non limitatif, sur la figure 2 afin de ne pas surcharger les dessins et afin de permettre une meilleure compréhension de ces derniers. Le dispositif de commande 20 est, par exemple, constitué par un moteur solidaire du miroir M1 dont l'axe 201 est constitué par une vis sans fin munie d'un curseur 202 eintraîné par la vis sans fin 201 en translation δ suivant la direction du miroir M1 dans le plan de la figure 2. Le curseur mobile 202 est muni d'un index 203 mobile selon une direction y perpendiculaire à la direction de translation δ du curseur et entraîné dans cette direction par un système d'engrenage. L'index mobile 203 a une de ses extrémités engagées dans une glissière disposée au dos de la surface réfléchissante de l'élément réflecteur polariseur e2. La glissière, pour raisons de simplification, n'est pas représentée figure 2. Le moteur 20 est commandé par des signaux de commande au niveau d'une entrée de commande 200. Ainsi à chaque position angulaire de l'arbre moteur correspond une valeur Δδ, Δγ représentative d'un angle a. Tout autre moyen de commande équivalent de l'élément réflecteur e2 ne sort pas du cadre de la présente invention.The remote control device 20 is shown only, by way of nonlimiting example, in FIG. 2 so as not to overload the drawings and in order to allow a better understanding of the latter. The control device 20 is, for example, constituted by a motor integral with the mirror M 1 , the axis 201 of which is constituted by an endless screw provided with a slider 202 driven by the endless screw 201 in translation δ in the direction of the mirror M 1 in the plane of FIG. 2. The movable cursor 202 is provided with an index 203 movable in a direction y perpendicular to the direction of translation δ of the cursor and driven in this direction by a gear system. The movable index 203 has one of its ends engaged in a slide disposed on the back of the reflecting surface of the polarizing reflective element e 2 . The slide, for reasons of simplification, is not shown in FIG. 2. The motor 20 is controlled by control signals at the level of a control input 200. Thus, each angular position of the motor shaft corresponds to a value Δδ , Δγ representative of an angle a. Any other equivalent control means for the reflective element e 2 does not depart from the scope of the present invention.

Ce miroir M1 permet donc de renvoyer sur le réflecteur R (figure 2) parabolique des rayons ayant des angles de réflexion différents suivant l'élément e1 ou e2 vers lequel ils tombent. On peut donc considérer qu'il existe deux pupilles rayonnantes ayant des distributions d'amplitudes complexes légèrement différentes qui coopèrent pour former dans l'espace le faisceau désiré.This mirror M 1 therefore makes it possible to return to the reflector R (FIG. 2) parabolic rays having different angles of reflection depending on the element e 1 or e 2 towards which they fall. We can therefore consider that there are two radiating pupils with slightly different complex amplitudes distributions which cooperate to form in space the desired beam.

Un calcul simple permet de déterminer la loi de phase dans le cas du miroir Ml à deux éléments e1, e2 (figure 3).A simple calculation makes it possible to determine the phase law in the case of the mirror M l with two elements e 1 , e 2 (FIG. 3).

En fait, l'articulation c1 introduit une loi de phase linéaire proportionnelle à l'angle a que font entre eux les éléments e1 et e2. Si Y est la distance de la charnière c1 à l'axe xx de l'antenne et D le diamètre du miroir Mi, la loi de phase peut s'écrire:

  • pour
    Figure imgb0001
     par convention
  • et pour:
    Figure imgb0002
    ;
  • Figure imgb0003
     étant le diamètre du miroir M2.
In fact, the articulation c 1 introduces a linear phase law proportional to the angle a that the elements e 1 and e 2 make between them. If Y is the distance from the hinge c 1 to the axis xx of the antenna and D the diameter of the mirror Mi, the phase law can be written:
  • for
    Figure imgb0001
     by convention
  • and for:
    Figure imgb0002
     ;
  • Figure imgb0003
     being the diameter of the mirror M 2 .

Dans un autre exemple de réalisation de l'antenne suivant l'invention, le miroir polariseur est un miroir M2 figures 5, 6 formé de trois éléments réflecteurs-polariseurs plans e10, e20, e30 articulés autour de deux charnières c1, c2. Les charnières c2, c2 sont selon les figures 5 et 6 respectivement disposées selon un diamètre D' perpendiculaire au diamètre D et aux deux tiers du diamètre D. Les deux charnières c1, c2 sont perpendiculaires au diamètre D. Un tel miroir M2 permet de faire fonctionner l'antenne suivant l'invention avec un faisceau fin et des voies monopulses (dans ce cas les éléments elo, e20, e30 sont coplanaires), ou avec un faisceau asymétrique pour la visualisation du sol (dans ce cas seuls les éléments elo, e20 sont coplanaires, ce qui correspond à une articulation située au tiers du miroir M2) ou encore avec un faisceau élargi symétrique, l'inclinaison des éléments réflecteurs-polariseurs e10, e30 entraînant un élargisement du diagramme de rayonnement dans le plan vertical de symétrie de l'antenne, et possibilité d'utiliser les voies monopulses (miroir M2 articulé uniquement au centre, e20 et e30 étant alors coplanaires), ce faisceau élargi pouvant être utilisé pour une veille rapprochée à exploration rapide.In another embodiment of the antenna according to the invention, the polarizing mirror is a mirror M 2 FIGS. 5, 6 formed of three plane reflector-polarizing elements e 10 , e 20 , e 30 articulated around two hinges c 1 , c 2 . The hinges c 2 , c 2 are according to FIGS. 5 and 6 respectively arranged according to a diameter D 'perpendicular to the diameter D and to two thirds of the diameter D. The two hinges c 1 , c 2 are perpendicular to the diameter D. Such a mirror M 2 makes it possible to operate the antenna according to the invention with a fine beam and single pulse channels (in this case the elements e lo , e 20 , e 30 are coplanar), or with an asymmetrical beam for viewing the ground ( in this case only the elements e lo , e 20 are coplanar, which corresponds to an articulation situated at the third of the mirror M 2 ) or even with a symmetrical widened beam, the inclination of the reflector-polarizing elements e 10 , e 30 causing a widening of the radiation pattern in the vertical plane of symmetry of the antenna, and possibility of using the monopuls channels (M 2 mirror articulated only in the center, e 20 and e 30 then being coplanar), this widened beam being able to be used for a ve It is close to rapid exploration.

Selon un autre mode de réalisation non limitatif de l'invention, représenté figure 9a et 9b, le miroir polariseur M2 est constitué de trois éléments réflecteurs-polariseurs e10, e20, e30 articulés entre eux par deux charnières c1, c2 symétriques par rapport à un diamètre D' du miroir, perpendiculaire au diamètre D. Un tel miroir de la même manière que précédemment, permet d'obtenir un fonctionnement de l'antenne avec un faisceau fin et des voies «monopulse», c'est-à-dire des voies permettant d'obtenir un signal d'écartométrie d'un écho de cible par rapport à l'axe xx de l'antenne, ou un faisceau large et des voies «monopulse» lorsque les éléments réflécteurs-polariseurs e10, e20, e30 sont respectivement coplanaires ou inclinés symétriquement d'un même angle dièdre a par rapport au plan de l'élément e20, et un fonctionnement avec un faisceau élargi asymétrique, tel que représenté figure 8, lorsque les éléments réflecteurs-polariseurs sont inclinés asy- métriquement.According to another nonlimiting embodiment of the invention, shown in FIGS. 9a and 9b, the polarizing mirror M 2 is made up of three reflector-polarizing elements e 10 , e 20 , e 30 hinged together by two hinges c 1 , c 2 symmetrical with respect to a diameter D ′ of the mirror, perpendicular to the diameter D. Such a mirror in the same manner as above, makes it possible to obtain operation of the antenna with a fine beam and “monopulse” channels, c ’ ie channels making it possible to obtain a signal of deviation from a target echo with respect to the axis xx of the antenna, or a wide beam and “monopulse” channels when the reflector-polarizer elements e 10 , e 20 , e 30 are respectively coplanar or symmetrically inclined by the same dihedral angle a relative to the plane of the element e 20 , and operation with an asymmetric widened beam, as shown in FIG. 8, when the elements reflector-polarizers are tilted asymmetrically.

La figure 8 représente suivant le plan vertical de symétrie de l'antenne un diagramme de rayonnement en fonction d'une direction 0 par rapport à l'axe xx. Un maximum relatif de rayonnement est obtenu dans la direction 2a.FIG. 8 represents, along the vertical plane of symmetry of the antenna, a radiation diagram as a function of a direction 0 relative to the axis xx. A relative maximum of radiation is obtained in direction 2a.

Il convient de noter que dans le cas de voies «monopulse» dans une antenne suivant l'invention, le faisceau élargi asymétrique étant obtenu sur la voie somme, la voie différence formée selon le plan vertical de symétrie de l'antenne perpendiculaire aux charnières devient également asymétrique et, de ce fait est inutilisable. Par contre une voie différence formée selon le plan parallèle aux charnières, la symétrie selon ce plan étant conservée, conserve ses propriétés selon ce plan tout en bénéficiant dans l'autre plan d'un élargissement analogue à celui de la voie somme.It should be noted that in the case of “monopulse” channels in an antenna according to the invention, the asymmetric widened beam being obtained on the sum channel, the difference channel formed along the vertical plane of symmetry of the antenna perpendicular to the hinges becomes also asymmetrical and therefore unusable. On the other hand, a difference path formed along the plane parallel to the hinges, the symmetry along this plane being preserved, retains its properties according to this plane while benefiting in the other plane of a widening similar to that of the sum path.

Notons encore que les caractéristiques du faisceau émis par l'antenne suivant l'invention sont conservées quelle que soit l'orientation de l'ensemble du miroir (M1 ou M2) et sont peu sélectives en fréquence.Note also that the characteristics of the beam emitted by the antenna according to the invention are preserved whatever the orientation of the whole of the mirror (M 1 or M 2 ) and are not very selective in frequency.

Claims (4)

1. Reversed Cassegrain aerial for, in operation, widening the beam in a plane, associated with a multiple function radar and comprising a rectilinear polarization electromagnetic waves primary source (S), a curved primary reflector (R1) having an axis of revolution and designed for reflecting waves directly emitted by the primary source and for selectively transmitting electromagnetic waves having a rectilinear cross polarization, the primary source (S) being located substantially at the focus point of that primary reflector, and a mirror (R2) operating a polarization rotation for reflecting to the primary reflector (R1) the reflected radiation which has undergone a rotation of its polarization plane, characterized in that said mirror (R2) is comprised of several planes reflecting polarizing elements (e1, e2) hing- edly connected to each other by parallel hinges (C1) perpendicular to the plane chosen as the widening plane of the aerial beam and in that these elements (el, e2) are associated with means (20, 202) for controlling their relative positions.
2. Aerial according to claim 1, characterized in that the reflecting-polarizing elements are made of a plane metal plate (P) in front of which is arranged at a kX/4 distance a plane array (N) of metal wire at a 45° angle from the polarization direction of the incident radiation, λ being the operating wavelength of said aerial and k being an uneven integer.
3. Aerial according to claim 1, characterized in that the reflecting-polarizing, elements are made of metal blades slanting at an angle of 45° with respect to the incident radiation polarization direction.
4. Aerial according to claim 1, characterized in that the means (20) for controlling the relative position of the reflecting-polarizing elements (e1, e2) comprise a motor integral with mirror (M1) and the shaft (201) of which is comprised of an endless screw having a movable slider (202) translation dirven by this screw, the moving slider (202) having a pointer (203) movable along a direction perpendicular to the translation direction of the slider (202), the movable pointer (203) having an end located within a slide positioned on the back of the reflecting surface of reflecting-polarizing element (C2).
EP80400037A 1979-02-02 1980-01-11 Reverse cassegrain antenna for multipurpose radar Expired EP0014605B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR7902768A FR2448233A1 (en) 1979-02-02 1979-02-02 REVERSE CASSEGRAIN ANTENNA FOR MULTI-FUNCTION RADAR
FR7902768 1979-02-02

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FR2524720A2 (en) * 1982-04-02 1983-10-07 Thomson Csf REVERSE CASSEGRAIN ANTENNA FOR MULTI-FUNCTION RADAR
US4504835A (en) * 1982-06-15 1985-03-12 The United States Of America As Represented By The Secretary Of The Navy Low sidelobe, high efficiency mirror antenna with twist reflector
US4574287A (en) * 1983-03-04 1986-03-04 The United States Of America As Represented By The Secretary Of The Navy Fixed aperture, rotating feed, beam scanning antenna system
GB2277408B (en) * 1989-05-16 1995-03-08 Plessey Co Plc Radar
US5455589A (en) * 1994-01-07 1995-10-03 Millitech Corporation Compact microwave and millimeter wave radar
US5469181A (en) * 1994-03-18 1995-11-21 Celwave Variable horizontal beamwidth antenna having hingeable side reflectors
SE514305C2 (en) * 1999-04-22 2001-02-05 Celsiustech Electronics Ab Method and apparatus for determining a scanning position for a scanning reflector of an antenna device
US7564419B1 (en) 2006-04-14 2009-07-21 Lockheed Martin Corporation Wideband composite polarizer and antenna system
CN107271796B (en) * 2017-05-18 2020-04-07 陕西长岭电子科技有限责任公司 Airspace stability function test system and test method for inverted card antenna

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FR2448233A1 (en) 1980-08-29
EP0014605A1 (en) 1980-08-20

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