EP3446362B1 - System for deflecting and pointing a microwave beam - Google Patents

Description

The field of the invention is that of deflection and pointing systems of a microwave beam.

• des télécommunications par satellite à partir de plateformes mobiles,
• des liaisons de données reconfigurables pour communications à haut-débit, ou
• des radars bas coût à ondes millimétriques ou centimétriques.

The invention applies to the processing of a microwave beam, corresponding to frequencies between 300 MHz and 300 GHz, with typical wavelengths of 1 mm to 1 m. Such frequencies are used in particular in the field:

• satellite telecommunications from mobile platforms,
• reconfigurable data links for high-speed communications, or
• low cost millimeter or centimeter wave radars.

Several systems require the ability to control the direction in which the beam is transmitted or received. This property is called the score. Among these systems, mention may be made, for example, of on-board radars, missile homing systems, “sense and avoid” systems, communication systems, jammers and periscope radar systems.

For pointing the antenna must be configured to emit and receive a wave in a given direction in space. For example today, in the field of telecommunications, one is more and more brought to have to redirect an antenna, following the updating of the coverage of the territory. It is important to have smart and remote-controlled antennas, intelligent for their ability to orient themselves to cover different areas in space and remote-controlled for their ability to be remotely controlled from a central.

For "tracking" or pursuit, the antenna must be configured to follow a target such as a satellite or an airplane.

In addition, it is increasingly sought to obtain steerable beam antennas, compact, of reduced mass and size, easy to use and to integrate into a platform, and at reduced cost.

Various known techniques make it possible to produce an antenna with a steerable beam, but have certain drawbacks.

The Cassegrain-type parabolic antenna is handicapped by shading effects due to the position of the source (more specifically by the secondary reflector) in front of the reflector. Also to maintain good efficiency, a large diameter to wavelength ratio is required. At low frequency, this antenna cannot then be integrated into a small volume.

In addition, traditional mechanical solutions for orienting the antenna use a fragile 2-axis gimbal mechanism. This pointing system requires a significant mechanical clearance since the volume occupied by the antenna varies according to its orientation. Furthermore, to avoid moving parts with active RF radiation, the transmit and receive signals must pass through microwave rotary joints which degrade performance and can be expensive and bulky when high power levels (several tens of Watts) are required.

This type of antenna also suffers from its range of travel generally limited to 60 °.

To get rid of the moving parts, a known solution consists in using an active electronic scanning antenna which makes it possible to avoid having to resort to a pointing mechanism: its profile remains flat whatever the orientation direction, which provides an advantage. major when integrating into a fairing. Orientation is electrically controlled. But this antenna has drawbacks in terms of price, power consumption, complexity, management of heating temperature, power maintenance and also accessible angular range which remains limited to less than 60 °.

One solution for making an RF deflection system is to use two diffractive components capable of rotating around the same axis, combined with a lens and an RF source. Such a system is described in the patent FR 3 002 697 . These diffractive components and the lens each have a plurality of periodic subwavelength MS microstructures formed in a dielectric material in a Risley scan pattern; these microstructures are arranged so as to form an artificial material exhibiting a periodic variation of effective refractive index, this arrangement making it possible to perform the diffractive function. As shown in figure 15 of the patent FR 3 002 697 , the structure of the diffractive component C1 can be produced on one side of the component, the structure of the lens L being produced on its other side. The aiming of the beam emitted by the source S is ensured by independent rotations (symbolized by the arrows) of the double lens-diffractive grating component L + C1 and of the diffractive component C2 around an axis Ω as illustrated figure 1 ; the components L + C1 and C2 are arranged in a plane normal to the axis of rotation Ω and the axis of symmetry of the beam emitted by the source S and which passes through its center coincides with this axis Ω. The advantage of such a deflection system is that it is compact, with a fixed power source S and mechanical orientation capabilities while ensuring high efficiency. For example for an application at 30 GHz (Ka band), using a dielectric material with a refractive index of 1.5 (dielectric constant 2.25), the thickness of the diffractive component is approximately 30 mm. The total thickness of the deflection system is therefore approximately 100 mm. For a source located in the object focal plane of the lens L, ie approximately 200 mm from the latter, the total thickness of the agile antenna is approximately 300 mm. But this thickness may nevertheless still be too great for certain applications embedded on mobile platforms.

In addition, certain zones located in particular around and in the direction of the axis of rotation Ω of the components are difficult to point dynamically, in particular quickly. In fact, in the same way as for the cardan pointing systems controlled in azimuth and in elevation, in this direction, the pointing system of the antenna has a singular zone (“keyhole” in English) which requires the use. very high (or even infinite) rotation speeds of the prisms when a pointed object passes near the axis of rotation Ω.

The following documents can also be cited. The patent FR 2 570 886 presents a microwave antenna scanning by rotating prisms. The patent US 3,242,496 describes a scanning antenna. The patent EP 2,584,650 describes a steerable beam antenna with hemispherical coverage.

Consequently, there remains to this day a need for a deflection system with an orientable beam simultaneously satisfying all of the aforementioned requirements, in particular in terms of reduced mass and bulk, of travel, ease of use and integration into a platform, and at reduced cost.

The deflection system according to the invention uses two deflection devices, at least one of which comprises a diffractive dielectric component structured on a scale smaller than the wavelength. Combined with a simple mechanics based on rotations, this approach makes it possible to obtain at a lower cost angular deflections of up to 120 ° with one (s) microwave source (s), i.e. a solid angle coverage of 3π sr , that is to say three times that which is accessible with an electronic scanning antenna, without a singular control point and without a mobile active microwave part.

• un dispositif de formation configuré pour collimater ledit faisceau en mode émission ou focaliser ledit faisceau en mode réception,
• un premier dispositif de déflexion d'un faisceau hyperfréquence incident comprenant un premier composant diélectrique diffractif à microstructures sub-longueur d'onde agencées de manière à former un matériau artificiel présentant une variation périodique d'indice de réfraction effectif, désigné premier composant diffractif, ce premier composant diélectrique diffractif étant associé à un premier mécanisme de rotation autour d'un premier axe pilotable.

More precisely, the subject of the invention is a controllable deflection system of a microwave beam having a wavelength of between 1 mm and 1 m, which comprises:

• a forming device configured to collimate said beam in transmission mode or to focus said beam in reception mode,
• a first device for deflecting an incident microwave beam comprising a first diffractive dielectric component with subwavelength microstructures arranged so as to form an artificial material exhibiting a periodic variation of the effective refractive index, referred to as the first diffractive component, this first diffractive dielectric component being associated with a first mechanism of rotation about a first controllable axis.

• un deuxième dispositif de déflexion configuré pour défléchir un faisceau hyperfréquence incident issu du dispositif de formation vers le premier dispositif de déflexion en mode émission, ou pour défléchir un faisceau hyperfréquence incident issu du premier dispositif de déflexion vers le dispositif de formation en mode réception, ce deuxième dispositif de déflexion étant associé à un deuxième mécanisme de rotation autour d'un deuxième axe pilotable qui coïncide avec l'axe optique du dispositif de formation,

en ce que l'angle formé par le premier et le deuxième axes de rotation est supérieur à 0° et inférieur ou égal à 90°, et en ce que le premier mécanisme de rotation est solidaire du deuxième mécanisme de rotation de manière à ce qu'une rotation du deuxième mécanisme de rotation autour de son axe pilotable entraîne une rotation du premier mécanisme de rotation autour de ce même axe.It is mainly characterized in that it comprises upstream of the first deflection device in transmission mode or downstream of the first deflection device in reception mode:

• a second deflection device configured to deflect an incident microwave beam coming from the training device towards the first deflection device in transmission mode, or to deflect an incident microwave beam coming from the first deflection device towards the training device in reception mode, this second deflection device being associated a second rotation mechanism around a second controllable axis which coincides with the optical axis of the training device,

in that the angle formed by the first and second axes of rotation is greater than 0 ° and less than or equal to 90 °, and in that the first rotation mechanism is integral with the second rotation mechanism so that 'a rotation of the second rotation mechanism around its controllable axis causes a rotation of the first rotation mechanism around this same axis.

According to one characteristic of the invention, the first deflection device comprises another diffractive dielectric component with subwavelength microstructures, arranged parallel to the first diffractive dielectric component (designated third diffractive dielectric component), this third diffractive dielectric component being associated a third rotation mechanism around the first controllable axis, independent of the first rotation mechanism but integral with the second rotation mechanism.

The second deflection device may comprise a second diffractive dielectric component with sub-wavelength microstructures (designated second diffractive dielectric component) and the device for forming the beam emitted by the transmitting means or received by the receiving means may comprise a lens. It optionally comprises a fourth diffractive dielectric component with sub-wavelength microstructures (designated fourth diffractive dielectric component) arranged parallel to the first diffractive dielectric component.

Each diffractive dielectric component can typically be a prism or a grating.

The lens of the beam-forming device and the second diffractive dielectric component are advantageously combined to form a non-resonant two-sided holographic component, with sub-wavelength microstructures formed on one side only in a non-periodic arrangement determined by a calculation. interference on said face between an incident beam and a predetermined output beam; the holographic component is associated with the second rotation mechanism.

The microstructures of the holographic component can be formed on a predetermined 3D surface. According to one alternative, they are formed in a predetermined volume which rests on said face of the holographic component, and implanted according to a non-periodic three-dimensional arrangement.

According to another characteristic of the invention, the beam forming device and the second deflection device are combined to form a system of Cassegrain type mirrors.

Preferably, the second deflection device is configured to deflect the beam onto the first deflection device with normal incidence.

The first deflection device deflects the beam with a first deflection angle relative to the first axis, the second deflection device deflects the beam with a second deflection angle relative to the second axis. The first angle of deflection is advantageously greater than or equal to the second angle of deflection.

The subject of the invention is also an antenna with a steerable beam which comprises means for transmitting / receiving a microwave beam having a wavelength of between 1 mm and 1 m and a system for deflecting the beam as described.

The transmission / reception means, the shaping device and the second deflection device can be combined to form an assembly capable of forming an incident beam on the first deflection device in emission mode or of receiving a beam coming from the first deflection device in reception mode; this assembly is associated with the second rotation mechanism. This assembly is in this case a network antenna.

• la figure 1 représente schématiquement une antenne orientable selon l'état de la technique,
• les figures 2 représentent schématiquement vu en coupe une antenne orientable équipée d'un premier exemple de réalisation d'un système de déflexion selon l'invention, à deux prismes et avec une lentille de mise en forme du faisceau émis par la source (fig 2a), à un prisme et avec un composant holographique combinant le deuxième prisme et la lentille de mise en forme (fig 2b),
• la figure 3 représente schématiquement vu en coupe une antenne orientable équipée d'un deuxième exemple de réalisation d'un système de déflexion selon l'invention, à trois prismes,
• la figure 4 représente schématiquement vu en coupe une antenne orientable équipée d'un troisième exemple de réalisation d'un système de déflexion selon l'invention, à quatre prismes,
• la figure 5a représente schématiquement vu de dessus un premier exemple d'implémentation de microstructures sub-longueur d'onde d'un composant holographique, à sections constantes sur leur hauteur selon un maillage cartésien carré détaillé à une échelle plus grande figure 5b, et vu en perspective (fig 5c),
• la figure 6a représente schématiquement vu de dessus un autre exemple d'implémentation de microstructures sub-longueur d'onde d'un composant holographique, selon un maillage à lignes iso-phase et lignes à gradient de phase, détaillé à une échelle plus grande figure 6b,
• les figures 7 représentent schématiquement vu en coupe une antenne orientable équipée d'un quatrième exemple de réalisation d'un système de déflexion selon l'invention, dont le second dispositif de déflexion comporte une configuration de type Cassegrain à deux miroirs, avec un miroir primaire concave (fig 7a) et un miroir primaire à réflecteurs (fig 7b),
• les figures 8 représentent schématiquement vu en coupe une antenne orientable comportant une antenne réseau à patchs (fig 8a) et un antenne réseau blazée (fig 8b).

Other characteristics and advantages of the invention will become apparent on reading the detailed description which follows, given by way of non-limiting example and with reference to the appended drawings in which:

• the figure 1 schematically represents a steerable antenna according to the state of the art,
• the figures 2 schematically show a sectional view of a steerable antenna equipped with a first embodiment of a deflection system according to the invention, with two prisms and with a lens for shaping the beam emitted by the source ( fig 2a ), to a prism and with a holographic component combining the second prism and the shaping lens ( fig 2b ),
• the figure 3 schematically shows a sectional view of a steerable antenna equipped with a second embodiment of a deflection system according to the invention, with three prisms,
• the figure 4 schematically shows a sectional view of a steerable antenna equipped with a third exemplary embodiment of a deflection system according to the invention, with four prisms,
• the figure 5a schematically represents, seen from above, a first example of implementation of sub-wavelength microstructures of a holographic component, with constant sections over their height according to a square Cartesian mesh detailed on a larger scale figure 5b , and seen in perspective ( fig 5c ),
• the figure 6a shows schematically seen from above another example of implementation of sub-wavelength microstructures of a holographic component, according to a mesh with iso-phase lines and phase gradient lines, detailed on a larger scale figure 6b ,
• the figures 7 schematically show a sectional view of a steerable antenna equipped with a fourth embodiment of a deflection system according to the invention, the second deflection device of which comprises a Cassegrain type configuration with two mirrors, with a concave primary mirror ( fig 7a ) and a primary mirror with reflectors ( fig 7b ),
• the figures 8 schematically show a sectional view of a steerable antenna comprising a patch array antenna ( fig 8a ) and a blazed network antenna ( fig 8b ).

From one figure to another, the same elements are identified by the same references.

In the remainder of the description, the expressions “front”, “rear” are used with reference to the orientation of the figures described. Of even the “upstream-downstream” direction is that of the beam; in the figures, the direction of the beam indicated by arrows is that of the transmission mode. Since the device may be positioned in other orientations, directional terminology is given by way of illustration and is not limiting.

Insofar as the deflection system according to the invention is intended to be used in collaboration with a source capable of transmitting (and / or with a receiver capable of receiving) a microwave beam, a source is shown in the figures to illustrate the beam deflections. The description is given considering that the antenna is in transmission mode; but of course the invention applies to the reception mode. We will take dielectric prisms as an example of diffractive dielectric components; but we could just as easily consider dielectric networks. The expression “diffractive component” is of course used with the same meaning as that indicated in the preamble with reference to the patent. FR 3 002 697 , that is to say a component with subwavelength microstructures arranged so as to form an artificial material exhibiting a periodic variation of the effective refractive index to thereby perform the diffractive function.

We describe in relation to the figure 2a , an example of a deflection system according to the invention.

• Un dispositif de mise en forme (ou dispositif de formation) du faisceau incident configuré pour collimater en mode émission (le front d'onde émis par la source qui est quasi sphérique dans le cas d'une source S ponctuelle, est mis sous forme d'une onde plane), ou pour focaliser en mode réception.
• Un premier dispositif de déflexion du faisceau hyperfréquence qui comprend un premier prisme C1 diélectrique à microstructures sub-longueur d'onde. Ce prisme C1 est associé à un premier mécanisme R1 de rotation (indiquée par la flèche) autour d'un premier axe Ω1 normal au plan du prisme C1. Ce premier dispositif de déflexion est ainsi configuré pour défléchir le faisceau incident d'un premier angle θ1 fixe non nul par rapport à l'axe de rotation Ω1. La rotation de C1 autour de l'axe Ω1 assurée par le premier mécanisme de rotation R1 pilotable, permet au faisceau de décrire un cercle autour de Ω1. Par construction cet angle θ1 peut être fixé entre 0 et 60°.
• Entre les moyens d'émission-réception et le premier dispositif de déflexion, un deuxième dispositif de déflexion associé à un deuxième mécanisme R2 de rotation autour d'un deuxième axe Ω2 (indiquée par la flèche) pilotable. Il est configuré pour, en mode émission, défléchir vers le premier dispositif de déflexion d'un angle θ2 fixe non nul par rapport à l'axe de rotation Ω2, le faisceau hyperfréquence incident issu de la source, et pour en mode réception, défléchir vers le dispositif de formation d'un angle θ2 fixe non nul par rapport à l'axe de rotation Ω2, le faisceau hyperfréquence incident issu du premier dispositif de déflexion. L'angle (Ω1, Ω2) formé par les premier et deuxième axes de rotation est supérieur à 0° et inférieur ou égal à 90° : 0°< (Ω1,Ω2) ≤ 90° ; dit autrement le prisme C1 du premier dispositif de déflexion est incliné par rapport à Ω2.
• Le premier mécanisme de rotation R1 est monté sur le deuxième mécanisme de rotation R2. Ainsi le premier mécanisme de rotation R1 est solidaire du deuxième mécanisme de rotation R2 : la rotation du deuxième dispositif de déflexion autour de l'axe Ω2 entraîne le premier dispositif de déflexion dans une rotation autour de Ω2. Mais la rotation du premier dispositif de déflexion autour de l'axe Ω1 est indépendante de la rotation autour de l'axe Ω2 : elle n'entraîne pas la rotation du deuxième dispositif de déflexion.

The deflection system of a microwave beam having a wavelength between 1 mm and 1 m intended to be associated with transmission means S - reception comprises:

• A shaping device (or forming device) of the incident beam configured to collimate in emission mode (the wavefront emitted by the source which is quasi-spherical in the case of a point source S, is put in the form of 'plane wave), or to focus in receive mode.
• A first microwave beam deflection device which comprises a first dielectric C1 prism with subwavelength microstructures. This prism C1 is associated with a first mechanism R1 of rotation (indicated by the arrow) about a first axis Ω1 normal to the plane of the prism C1. This first deflection device is thus configured to deflect the incident beam by a first fixed non-zero angle θ1 with respect to the axis of rotation Ω1. The rotation of C1 around the axis Ω1 ensured by the first controllable rotation mechanism R1 allows the beam to describe a circle around Ω1. By construction, this angle θ1 can be fixed between 0 and 60 °.
• Between the transmission-reception means and the first deflection device, a second deflection device associated with a second mechanism R2 for rotation about a second axis Ω2 (indicated by the arrow) which can be controlled. It is configured to, in transmission mode, deflect towards the first deflection device by a fixed non-zero angle θ2 with respect to the axis of rotation Ω2, the incident microwave beam coming from the source, and in reception mode, to deflect towards the device for forming a fixed non-zero angle θ2 with respect to the axis of rotation Ω2, the incident microwave beam coming from the first deflection device. The angle (Ω1, Ω2) formed by the first and second axes of rotation is greater than 0 ° and less than or equal to 90 °: 0 ° <(Ω1, Ω2) ≤ 90 °; in other words, the prism C1 of the first deflection device is inclined with respect to Ω2.
• The first rotation mechanism R1 is mounted on the second rotation mechanism R2. Thus the first rotation mechanism R1 is integral with the second rotation mechanism R2: the rotation of the second deflection device around the axis Ω2 drives the first deflection device in a rotation around Ω2. But the rotation of the first deflection device around the axis Ω1 is independent of the rotation around the axis Ω2: it does not cause the rotation of the second deflection device.

In order to ensure complete angular coverage, it is then necessary for the prism C1 and the second deflection device to deflect the beam with θ1≥θ2. The rotation of C1 around the axis Ω1 ensured by the first rotation mechanism R1, allows the beam to describe a circle around Ω1, which combined with a rotation of the second deflection device around the roll axis Ω2 ensured by the second rotation mechanism R2, makes it possible to place the beam in a solid angle cone with a value of 2π (1-cos (2 θ1)).

The second deflection device may itself include one or more dielectric prisms with subwavelength microstructures, as shown in the figures. figures 2a, 2b , 3 and 4 .

According to a first embodiment described in relation to the figure 2a , the second deflection device comprises a single dielectric prism C2 with subwavelength microstructures, designated second prism, just as the first deflection device comprises only a single prism C1. This improves the compactness of the antenna.

This second prism makes it possible to pre-deflect the beam upstream of the first deflection device in emission mode, by a fixed non-zero angle θ2 with respect to the axis Ω2 normal to the plane of the prism C2. The angle between the axes Ω1 and Ω2 can also be equal to θ2 as shown in the figures; in this case, the beam deflected by this second prism C2 advantageously has a normal incidence on the prism C1 in emission mode. By construction, this angle θ2 can be set between 0 and 60 °. Combined with the first prism C1, this makes it possible to achieve a maximum deflection θ1 + θ2 of 120 °. For the angular coverage to be complete (i.e. including the direction of Ω2), the angle θ1 must be greater than or equal to the angle θ2. The addition of a roll rotation mechanics around the Ω2 axis leads to a solid angle pointing domain 3π sr.

According to a second embodiment described in relation to the figure 3 , the second deflection device comprises a single prism designated second prism C2, and the first deflection device comprises, in addition to the first prism C1, another prism designated third prism C3.

This dielectric C3 prism with subwavelength microstructures, is arranged parallel to the first prism C1 (it is therefore normal to the axis Ω1) and on the latter; it is able to deflect the incident beam by a fixed non-zero angle θ3 with respect to the axis Ω1. By construction, this angle θ3 can be fixed between 0 and 60 °. It is associated with a third mechanism R3 of rotation around the axis Ω1 (indicated by the arrow) controllable, independent of the first rotation mechanism R1 associated with C1. As the first mechanism of rotation R1, this third rotation mechanism R3 is mounted on the second rotation mechanism R2. Thus the first and third rotation mechanisms R1 and R3 are integral with the second rotation mechanism R2. This first deflection device with two dielectric prisms C1 and C3 structured in independent rotations around the axis Ω1, allows the beam to be dynamically offset in a solid cone of angle with a deflection angle (with respect to Ω1) variable θ13 = θ3 + θ1, which can reach an angle 013max. Depending on the configuration of C1 and C3, by construction, θ13max can reach 60 ° to 70 ° depending on the level of performance sought. The directions of rotation of the first and of the third rotation mechanisms R1, R3 can optionally be opposed; we then speak of counter-rotating C1 and C3 prisms.

The combination of these two deflection devices makes it possible to achieve a maximum deflection θ13max + θ2 of 120 °. For the angular coverage to be complete, the angle θ13max must be greater than or equal to the angle θ2. Combined with the roll rotation mechanism around the Ω2 axis, we obtain a solid angle pointing domain 3π sr.

The rotation mechanisms R1, R2 and R3 can be controlled, for example manually or preferably by a motor controlled by a servomechanism.

According to a third embodiment described in relation to the figure 4 , the second deflection device comprises, in addition to the prism C2, a second prism with sub-wavelength microstructures, designated fourth prism C4. This fourth prism C4 is arranged parallel to the prism C1 of the first deflection device and just before (= upstream) in transmission mode as shown in the figure, and is therefore normal to the axis Ω1; consequently, it is inclined relative to the prism C2 by an angle formed by the axes Ω1 and Ω2. It is configured to deflect the incident beam (coming from the prism C2 and therefore already deflected by an angle θ2) by a fixed non-zero angle θ4. This prism is associated with the rotation mechanism R2 of the second deflection device, around the axis Ω2. By construction this angle θ4 can be fixed between 0 and 60 °. The deflection angle of the second deflection device is then equal to θ2 + θ4 with respect to the axis Ω2. In the figure the angle formed by the axes Ω1 and Ω2 is also equal to θ2 + θ4: thus the beam coming from C4 has a normal incidence on C1.

For all these embodiments, the device for forming the beam coming from the source comprises a lens at the focus of which are placed the emission means S. This lens makes it possible to shape the quasi-spherical wavefront emitted by a point source S. The shaping lens L can be fixed and independent of the second prism C2 and its rotation mechanism as shown in the figures 2a , 3, 4 . In this case, the source S and shaping lens L assembly is fixed with respect to the rotations around Ω1 and Ω2 and allows easy interconnection with the microwave emission and / or reception circuits.

• diffractive massive à profil hyperbolique, ou
• à microstructures comme décrit dans les brevets FR 2 980 648 ou FR 3 002 697 , et peut être diffractive ou réfractive.

This shaping lens L can be a dielectric lens:

• massive diffractive with hyperbolic profile, or
• with microstructures as described in the patents FR 2 980 648 or FR 3 002 697 , and can be diffractive or refractive.

avec λ la longueur d'onde cible choisie dans la plage de longueurs d'onde correspondant aux ondes hyperfréquences, soit une longueur d'onde typiquement comprise entre 1mm et 1m, et n l'indice de réfraction du matériau diélectrique dans lequel les microstructures sont formées.According to a variant which applies to the previously described embodiments, the lens L for shaping the beam emitted by the emission means S (or to the reception means) is combined with the second prism C2 in a holographic component CH , to obtain a single component which performs a dual function of shaping and deflection of the beam emitted by the source S, as illustrated figure 2b . In this case, the sub-wavelength microstructures are implanted on a single face of the component CH according to a non-periodic arrangement determined by an interference calculation on said face, between the beam emitted by the source incident on this face and the desired output beam (of this component CH), in this case a plane wave deflected with an angle θ2. It is recalled that the microstructures are qualified as sub-wavelength when the following condition for the cells (or meshes) where they are implanted, is fulfilled: $$\left(\mathrm{Distance}\mathrm{Between}\mathrm{the}\mathrm{centers}\mathrm{of}\mathrm{cells}\mathrm{adjacent}\right)<\mathrm{\lambda }/\mathrm{not}$$

with λ the target wavelength chosen in the range of wavelengths corresponding to microwave waves, i.e. a wavelength typically between 1mm and 1m, and n the refractive index of the dielectric material in which the microstructures are trained.

In the event that this holographic component has a flat face (2D surface) as shown on the figure 2b , it is a calculation of interference on this plane face between the incident beam emitted by the source and the output beam which, in the case of an antenna with a steerable beam, is a plane wave with an angle of output (in emission mode) corresponding to the orientation angle of the beam. The height and size of each MS of CH microstructure (which can also be seen figure 5c ) are determined experimentally or calculated so as to make the modulo 2π phase delay locally introduced by each microstructure correspond to the conjugate of the phase of the hologram at this same point.

The sub-wavelength implementation of MS microstructures is carried out from a geometric mesh M generally based on Cartesian, that is to say with a rectangular or even square base, as shown figures 5a, 5b and 5c . A hexagonal, or even circular, mesh can also be considered. Within this mesh, the base of a microstructure cannot of course exceed a mesh (or cell) of the mesh, but can only partially occupy it. Some meshes may be empty, others entirely occupied by the base of the microstructure and for others, finally, the base of the microstructure only partially occupies the corresponding mesh, according to the determined implementation.

This simple to implement implementation, however, causes a phase error due to the resolution of the sampling and therefore to a reduction in the opening efficiency of the antenna. To solve this problem one chooses a base of mesh in a system of coordinates adapted to adjust the phase as well as possible. A sub-wavelength geometric structure is produced from an M mesh which coincides with isophase lines in one direction and with phase gradient lines in directions respectively perpendicular to the isophase lines as illustrated figure 6a and 6b .

In order to improve the orientation efficiency for low elevation angles (high θ angle), the microstructures of the holographic component can be formed on a non-planar surface i.e. on a predetermined 3D surface, such as 'a surface with symmetry of revolution such as a cone, a sphere or any arbitrary 3D surface.

The microstructures are all formed in a dielectric material according to shapes determined a priori, either protruding in the form of pillars, or hollow in the form of holes. A combination of holes and pillars is also possible. The microstructures are of any shape, preferably with axes of symmetry. They have a square, hexagonal or circular section, or a combination of different geometries, or a section conforming to isophase lines and phase gradient lines. They can be of constant section over their height or variable as in the case of a pyramidal structure, conical, etc. The height of MS microstructures is generally the same (as shown figure 5c ), but not necessarily. They can be perpendicular to the surface of the component or inclined, for example at 30 °. It is also possible to have a variable inclination on the same component. The inclination is determined experimentally, typically as a function of the direction of inflection or incidence of the beam.

According to a generalization of the previous embodiment, and still to achieve the function of collimation or focusing (depending on the transmission or reception mode) and deflection of the beam, the holographic component CH comprises superimpositions of layers of sub-length MS microstructures waveforms, formed in the volume thereof, and implanted according to a non-periodic three-dimensional arrangement determined by a calculation of interference on said volume, between the beam emitted by the source incident in this volume and the desired output beam. This volume is of course based on the face of the component CH on which the microstructures are formed; this volume is delimited in particular by this face. The calculation of the volume interference can be carried out experimentally by successive adjustments or by calculation for example by transforming the volume of CH into a stack of K 2D or 3D surfaces parallel to each other (with K an integer typically between 2 and 100) on each of which a surface interference figure is calculated. The stacking of layers of microstructures is obtained for example by making correspond for each point of calculation of the volume, a microstructure of height reduced by a factor K and whose section makes it possible to generate a local phase delay corresponding to the conjugate of the phase of the hologram at this same point reduced by a factor of K.

Another mode to obtain the distribution of 3D microstructures consists of the calculation of interference obtained on the face of the component CH between the incident beam emitted by the source and the output beam, in projecting the section of each of the microstructures in the volume component by following the curves resulting from the intersection between the isophase planes of the volume hologram and the planes containing the phase gradients.

• de manière discrète pour différentes valeurs de z (dimension de l'empilement) ; il s'agit en quelque sorte d'une réitération pour plusieurs surfaces d'implémentation considérées à différentes valeurs de z, du calcul d'interférences 2D précédemment décrit pour une seule surface d'implémentation. La hauteur et la section des microstructures est alors à déterminer sur chacune de ces surfaces comme indiqué précédemment, ou
• de manière continue sur z, la hauteur et la section des microstructures étant alors déterminée par le calcul lui-même.

In other words, this interference calculation on said volume can be carried out:

• discretely for different values of z (dimension of the stack); it is in a way a reiteration for several implementation surfaces considered at different values of z, of the 2D interference calculation previously described for a single implementation surface. The height and the section of the microstructures must then be determined on each of these surfaces as indicated previously, or
• continuously on z, the height and the section of the microstructures then being determined by the calculation itself.

This component CH is hosted by the second deflection device and is therefore subjected to rotation about the axis Ω2 by the second rotation mechanism. This CH holographic component saves weight and efficiency.

An example configuration with a CH holographic component is shown figure 2b : a single prism C1 deflecting the beam at an angle θ1 fixed with respect to its axis of rotation Ω1, is used in the opening of the antenna. As already indicated, in order to ensure complete angular coverage, it is then necessary for the prism C1 and the holographic component CH to deflect the beam with θ1≥θ2. The rotation of C1 around the axis Ω1 provided by the first rotation mechanism, allows the beam to describe a circle around Ω1, which combined with a rotation of the set C1 and CH around the roll axis Ω2 provided by the second rotation mechanism, allows to place the beam in a cone of solid angle of a value of 2π (1-cos (2 θ1)).

It is also possible to add to the previous configurations, a translation mechanism of the transmission S / reception means along the vertical axis (parallel to the Ω2 axis) in order to control the opening of the transmitted and received beam.

To assist the two deflection devices, and / or to compensate for the variation in deflection of C2 when the frequency of the wave emitted by the source S is modified, it is also possible to add to the previous configurations a translation mechanism of the means transmission S / reception in the plane normal to the Ω2 axis. This is particularly useful for generating small angles of deflection and this avoids performing a full roll turn (= a full turn of the second rotation mechanism), especially around singular points such as those in the direction of Ω2 for example. This allows easy and complete control of the beam (position and opening).

• une configuration de type Cassegrain hors d'axe avec un miroir primaire parabolique M1 et un miroir secondaire concave M2, comme on peut le voir figure 7a,
• une configuration de type Cassegrain dans laquelle le miroir M1 est un miroir à réseau de réflecteurs (« reflectarray miror » en anglais), comme on peut le voir figure 7b.

In the previous examples, the second deflection device included one or more prisms, but it may not include a prism. This alternative to the embodiments described above, which makes it possible to save space, is based on a combination of the device for shaping the beam emitted by the source and of the second deflection device, using configurations of the reflector antenna type; this combination remains associated with the second mechanism of rotation R2 around the axis Ω2. The beam emitted by the source is for example deflected and distributed on the first deflection device by:

• an off-axis Cassegrain type configuration with an M1 parabolic primary mirror and an M2 concave secondary mirror, as can be seen figure 7a ,
• a Cassegrain type configuration in which the mirror M1 is a mirror with an array of reflectors (“reflectarray miror”), as can be seen figure 7b .

For these two reflector variants, the concave secondary mirror M2 can be replaced by any other type of reflector in order to realize configurations of the Gregorian type, ADE (acronym of the Anglo-Saxon expression “Axially Displaced Ellipse”) or Dielguide (configuration also known under the Anglo-Saxon name of Splashplate).

The subject of the invention is also a steerable antenna comprising a deflection system as described, and point microwave S / reception means arranged at the focus of the shaping device as shown in the figures already described.

In all the configurations described, the source S can be monopulse, connected or not to a 'magic T' allowing the direct extraction of monopulse signals (sum and differences according to the two axes of the horn). These signals make it possible to know the difference in angle between the target and the aiming angle of the sum beam, which is known by adding encoders on the three axes of rotation of the device. This therefore makes it possible to measure the deviation of a target in the main radiation lobe of the source radiation pattern.

It is also possible to produce variants of all these steerable antenna embodiments by combining a non-point source (or more generally non-point transmission-reception means), its shaping device, and the second deflection device. to form an assembly configured to emit a plane wave on the first deflection device in transmission mode or to receive a plane wave coming from the first deflection device in reception mode. This assembly is for example itself an A network antenna ("patch antenna" in English) as shown. figure 8a , slot, Vivaldi, ...), without phase shifters or with fixed phase shifters. Indeed, this array antenna does not have to be provided with phase shifters since the angle shift θ2 + θ13 is performed by the deflection system. On the other hand, it can include several channels in order to carry out advanced radar processing. The array antenna can be placed perpendicular to the Ω2 axis as shown on the figures 8a and 8b , but it is not necessary. It can also be placed directly against the C1 prism. Whatever its configuration, this network antenna A is associated with the second rotation mechanism R2 around the axis Ω2.

It is possible to blazer the network antenna A as shown figure 8b . The blaze angle θ2 makes it possible not to lose the efficiency of the plates (“patches” in English) in the direction of fixed pointing of the antenna.

This assembly configured to emit a plane wave deflected towards the first deflection device in transmission mode (or to receive a plane wave deflected by the first deflection device in reception mode), can also be a reflector antenna, a large gain horn, Or other.

These alternatives described in relation to the figures 7a, 7b , 8a, 8b , also apply with a first deflection device comprising only one prism C1.

For these embodiments, each prism (C1 and possibly C3) of the first deflection device is associated with a rotation mechanism around Ω1 (R1 and possibly R3), while a single rotation mechanism around Ω2 (R2) is associated with the second deflection device which comprises one or more prisms (C2 or CH and possibly C4), or a Cassegrain type configuration, or an array antenna. And we have: 0 ° <(Ω1, Ω2) ≤ 90 °.

A fairing is advantageously used to encompass the source and optionally the shaping device or also the first deflection device. This fairing is either covered on the outside or lined on the inside with absorbent making it possible to absorb the waves emitted by the source S but not intercepted by the lens L, as well as the parasitic reflections in the device. This helps to improve the radiation pattern of the antenna and to reduce its radar equivalent area. This absorbent can be made of dielectric and / or magnetic material (or composite), structured on a sub-wavelength scale in order to reduce the level of reflections at the air / absorbent interfaces.

• Soit à l'aide d'une couche comportant des microstructures sub-longueur d'onde pour que la structure soit localement adaptée en hauteur et en épaisseur pour présenter l'indice effectif équivalent (tel que présenté dans le brevet FR 2 980 648 ) qui permet de réaliser une couche antireflet adaptée localement à l'incidence et à la fréquence de l'onde incidente.
• Soit en utilisant une structuration tridimensionnelle de type pyramidal par exemple, (cf. article de W. H. Southwell "Pyramid-array surface-relief structures producing antireflection index matching on optical surfaces", J. Opt. Soc. A., Vol 8, No 3, March 1991 ) à l'interface en orientant, par exemple, les microstructures sub-longueur d'onde en fonction de l'incidence du faisceau. Cette orientation n'est pas indispensable, on peut conserver une orientation normale à la surface du carénage.

En fonction de la longueur d'onde de fonctionnement du dispositif, la taille des microstructures est donc différente. La réalisation de ces surfaces structurées peut se faire par usinage, par fabrication additive, ou par gravure chimique.This structuring can be done in two ways:

• Either using a layer comprising sub-wavelength microstructures so that the structure is locally adapted in height and thickness to present the equivalent effective index (as presented in the patent FR 2 980 648 ) which allows making an antireflection layer adapted locally to the incidence and frequency of the incident wave.
• Either by using a three-dimensional structuring of pyramidal type for example, (cf. article by WH Southwell "Pyramid-array surface-relief structures producing antireflection index matching on optical surfaces", J. Opt. Soc. A., Vol 8, No 3, March 1991 ) at the interface by orienting, for example, the sub-wavelength microstructures according to the incidence of the beam. This orientation is not essential, one can keep an orientation normal to the surface of the fairing.

Depending on the operating wavelength of the device, the size of the microstructures is therefore different. The production of these structured surfaces can be done by machining, by additive manufacturing, or by chemical etching.

• ❖ La mécanique à mettre en place pour ce genre de système de déflexion est plus fiable que les biellettes (moteurs annulaires). La masse tournante est faible car l'utilisation de matériaux diélectriques plastiques permet l'utilisation de techniques de fabrication additive, et assure un poids raisonnable pour une mécanique rapide et légère. Le dimensionnement des actionneurs et la commande d'asservissement des mécanismes de rotation ne dépendent pas de la répartition de masse dans la partie émetteur, ce qui facilite la modularité.
• ❖ Le domaine angulaire accessible par le système en émission/réception est de 3π sr (déflexion max 120°) contre moins de π sr (déflexion max 60°) pour les autres systèmes.
• ❖ L'utilisation de prismes diélectriques assure la largeur de bande et rend ce système accessible aux plus hautes fréquences.
• ❖ L'utilisation d'un émetteur central permet de réduire les coûts par l'utilisation d'un émetteur à puissance centralisée (ex : tube à onde progressive - TOP) pour les hautes fréquences ; il n'y a pas besoin d'avoir recours à des joints tournants pour passer le signal hyperfréquence.
• ❖ La maitrise du positionnement de la source par rapport à la lentille suivant l'axe perpendiculaire permet de contrôler l'ouverture du faisceau.

The advantages of the invention are as follows:

• ❖ The mechanics to put in place for this type of deflection system are more reliable than rods (annular motors). The rotating mass is low because the use of plastic dielectric materials allows the use of additive manufacturing techniques, and ensures a reasonable weight for rapid and light mechanics. The sizing of the actuators and the servo control of the rotation mechanisms do not depend on the mass distribution in the transmitter part, which facilitates modularity.
• ❖ The angular range accessible by the system in transmission / reception is 3π sr (max deflection 120 °) against less than π sr (max deflection 60 °) for the other systems.
• ❖ The use of dielectric prisms ensures the bandwidth and makes this system accessible to the highest frequencies.
• ❖ The use of a central transmitter makes it possible to reduce costs by using a transmitter with centralized power (eg: traveling wave tube - TOP) for high frequencies; there is no need to use rotary joints to pass the microwave signal.
• ❖ The control of the positioning of the source relative to the lens along the perpendicular axis makes it possible to control the beam opening.

Claims (20)

1. A system for steerably deflecting an incident microwave beam having a wavelength comprised between 1 mm and 1 m, which comprises:

   - a forming device arranged according to an optical axis and configured to collimate said beam in emission mode or to focus said beam in reception mode,

   - a first device for deflecting an incident microwave beam comprising a first diffractive dielectric component (C1) comprising subwavelength microstructures arranged so as to form an artificial material presenting a periodic variation in effective refractive index, called the first diffractive dielectric component, this first diffractive dielectric component being associated with a first mechanism (R1) for rotating about a first steerable axis (Ω1),

   characterized in that it comprises, upstream of the first deflecting device in emission mode or downstream of the first deflecting device in reception mode:

   - a second deflecting device configured to deflect an incident microwave beam issued from the forming device towards the first deflecting device in emission mode, or to deflect an incident microwave beam issued from the first deflecting device towards the forming device in reception mode, this second deflecting device being associated with a second mechanism (R2) for rotating about a second steerable axis (Ω2) which coincides with the optical angle of the forming device,

   in that the angle (Ω1, Ω2) made by the first and second axes of rotation is larger than 0° and smaller than or equal to 90°, and in that the first rotating mechanism (R1) is securely fastened to the second rotating mechanism (R2) so that a rotation of the second rotating mechanism about its steerable axis (Ω2) leads to a rotation of the first rotating mechanism about the same axis.
2. The steerable deflecting system according to the preceding claim, characterized in that the first deflecting device comprises another diffractive dielectric component (C3) comprising subwavelength microstructures being placed parallel to the first diffractive dielectric component (C1), and being called the third diffractive dielectric component, this third diffractive dielectric component being associated with a third mechanism (R3) for rotating about the first steerable axis (Ω1), which is independent of the first rotating mechanism (R1) and securely fastened to the second rotating mechanism (R2).
3. The steerable deflecting system according to one of the preceding claims, characterized in that the second deflecting device includes a diffractive dielectric component (C2) comprising subwavelength microstructures, said component being called the second diffractive dielectric component, and in that the device for forming the beam emitted by the emitting means or received by the receiving means includes a lens (L).
4. The steerable deflecting system according to the preceding claim, characterized in that the second deflecting device includes another diffractive dielectric component (C4) comprising subwavelength microstructures, said component being placed parallel to the first diffractive dielectric component (C1) and being called the fourth diffractive dielectric component.
5. The steerable deflecting system according to any one of claims 3 to 4, characterized in that the lens (L) of the device for forming the beam is a microstructured dielectric diffractive lens.
6. The steerable deflecting system according to any one of claims 3 to 4, characterized in that the lens (L) of the device for forming the beam is a microstructured dielectric refractive lens.
7. The steerable deflecting system according to any one of claims 3 to 4, characterized in that the lens (L) of the device for forming the beam is a bulk dielectric refractive lens.
8. The steerable deflecting system according to any one of claims 3 to 4, characterized in that the lens (L) of the device for forming the beam and the second diffractive dielectric component (C2) are combined to form a non-resonant two-faced holographic component (CH) comprising subwavelength microstructures formed on a single face in a non-periodic arrangement determined by a calculation of the interference on said face between an incident beam and a predetermined exit beam, and in that the holographic component (CH) is associated with the second rotating mechanism (R2).
9. The steerable deflecting system according to the preceding claim, characterized in that the microstructures (MS) of the holographic component (CH) are formed on a predetermined 3D surface.
10. The steerable deflecting system according to claim 9, characterized in that the microstructures of the holographic component (CH) are formed in a predetermined volume that abuts against said face of the holographic component, and arranged in a nonperiodic three-dimensional arrangement.
11. The steerable deflecting system according to any one of claims 1 to 2, characterized in that the device for forming the beam and the second deflecting device are combined to form a Cassegrain-type system of mirrors.
12. The steerable deflecting system according to any one of the preceding claims, characterized in that each diffractive dielectric component is a prism or a grating.
13. The steerable deflecting system according to any one of the preceding claims, characterized in that the second deflecting device is configured to deflect the beam onto the first deflecting device with a normal incidence.
14. The steerable deflecting system according to any one of the preceding claims, characterized in that the first deflecting device deflects the beam with a first deflection angle (θ1, θ13) with respect to the first axis (Ω1) and the second deflecting device deflects the beam with a second deflection angle (θ2, θ2+θ4) with respect to the second axis (Ω2), and in that the first deflecting angle is larger than or equal to the second deflecting angle.
15. An orientable-beam antenna that includes means for emitting/receiving a microwave beam having a wavelength comprised between 1 mm and 1 m and a system for deflecting the beam according to any one of the preceding claims.
16. The orientable-beam antenna according to the preceding claim, characterized in that the emitting means (S) are configured to be monopulse.
17. The orientable-beam antenna according to any one of claims 15 or 16, characterized in that it includes a mechanism for translating the emitting/receiving means along the second axis (Ω2) and/or in a plane normal to the second axis (Ω2).
18. An orientable-beam antenna that includes

    - means for emitting/receiving a microwave beam having a wavelength comprised between 1 mm and 1 m comprising an antenna array (A) arranged perpendicular or not to an optical axis, and

    - a system for deflecting the beam, which comprises a first device for deflecting an incident microwave beam comprising a first diffractive dielectric component (C1) comprising subwavelength microstructures arranged so as to form an artificial material presenting a periodic variation in effective refractive index, called the first diffractive dielectric component, this first diffractive dielectric component being associated with a first mechanism (R1) for rotating about a first steerable axis (Ω1),

    wherein the emitting/receiving means are associated with a second rotating mechanism (R2) about a second steerable axis (Ω2) coinciding with the optical axis of the antenna array (A),
    the angle (Ω1, Ω2) made by the first and second axes of rotation is larger than 0° and smaller than or equal to 90°,
    the first rotating mechanism (R1) is securely fastened to the second rotating mechanism (R2) so that a rotation of the second rotating mechanism about its steerable axis (Ω2) leads to a rotation of the first rotating mechanism about the same axis;
    the emitting/receiving means are configured to collimate said beam in emission mode or to focus said beam in reception mode and to form an incident beam on the first deflecting device in emission mode or to receive a beam issued from the first deflecting device in reception mode.
19. The orientable-beam antenna according to the preceding claim, characterized in that the antenna array (A) is arranged perpendicular to the optical axis.
20. The orientable-beam antenna according to any one of claim 18 or 19, characterized in that the antenna array is blazed.

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