Compact antenna having a directable beam

Abstract

The invention relates to an antenna having a directable hyperfrequency beam which comprises: a first dielectric component having subwavelength microstructures formed on a surface of a dielectric substrate; a second diffractive dielectric component (C2) having subwavelength microstructures formed on a surface of a dielectric substrate, designed to deflect an incident hyperfrequency beam. The microstructures of the first component are implanted in a non-periodic arrangement so as to form a non-resonant, dual-function holographic component (CH) for collimating and / or focussing and deflecting an incident beam; said component is associated with a first mechanism for rotation about a first axis, the second component (C2) is associated with a second mechanism for rotation about a second axis.

Description

COMPACT ANTENNA WITH ADJUSTABLE BEAM The field of the invention is that of steerable beam antennas. The invention relates 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 particularly in the following fields: - satellite telecommunications from mobile platforms, - reconfigurable data links for high-speed communications, or - inexpensive millimeter wave radars. Many applications require the ability to control the direction in which the beam is emitted and / or received. This property is called beam pointing. For pointing, the antenna must be configured to transmit. To receive a wave in a given direction in space. For example, today in the telecommunications sector, it is increasingly necessary to redirect antennas following updates to coverage areas. For instance, each antenna removal is followed by a repositioning of neighboring antennas. Furthermore, coverage is constantly changing as efforts are continuously made to improve coverage while optimizing costs, thus minimizing the number of antennas. It also happens that some antennas are removed or relocated, which necessitates the reorientation of nearby antennas. It is therefore important to have intelligent, remotely controlled antennas: intelligent because they can orient themselves to cover different areas in space, and remotely controlled because they can be operated from a central control unit. For "tracking" or following, the antenna must be configured to follow a target such as a satellite. For scanning, the beam must illuminate a defined part of the space or scene in order to analyze it. Furthermore, there is a growing demand for steerable beam antennas that are compact, lightweight, easy to use and integrate into a platform, and cost-effective. Several known techniques allow for the creation of a steerable beam antenna, but they have some drawbacks. The Cassegrain parabolic antenna is hampered by shading effects caused by the position of the source (specifically the secondary reflector) in front of the reflector. Therefore, to maintain good efficiency, a large diameter-to-wavelength ratio is required. At low frequencies, this type of antenna cannot be integrated into a small enclosure. Furthermore, traditional mechanical solutions for antenna orientation use a two-axis gimbal mechanism. This pointing system requires significant mechanical travel since the volume occupied by the antenna varies depending on its orientation. Moreover, to avoid moving parts that emit active RF radiation, the transmit and receive signals must pass through microwave-resistant rotary joints, which degrade performance and can be expensive and bulky when high power levels (several tens of watts) are required. To eliminate moving parts, a well-known solution is to use an active antenna: its profile remains flat regardless of the orientation, providing a major advantage when integrating it into a fairing. The orientation is electrically controlled. However, this antenna has drawbacks in terms of price, power consumption (even in the "off" position), complexity, temperature management, and power maintenance. One solution for implementing 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 patent application WO 2014 / 128015. These diffractive components and the lens each exhibit a plurality of periodic sub-wavelength MS microstructures formed in a dielectric material according to a Risley sweep configuration. As shown in Figure 1, the structure of the diffractive component C1 can be fabricated on one face of the component, while the structure of the lens L is fabricated on its other face. The beam emitted by the source is pointed by independent rotations around the same axis of the diffractive lens-grating double component L+C1 and the diffractive component C2.The advantage of such a deflection system is its compact design, with a fixed feed source S and mechanical orientation capabilities, while still ensuring high efficiency. For example, for a 30 GHz (Ka-band) application, 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, i.e., approximately 200 mm from it, the total thickness of the agile antenna is approximately 300 mm. However, this thickness may still be too great for some embedded applications on mobile platforms. Furthermore, certain areas, particularly around and in the direction of the z-axis of rotation of the components, are difficult to point dynamically, especially at high speeds. Indeed, just as with gimbal pointing systems controlled in azimuth and elevation, in this direction, the antenna pointing system presents a singular area (a "keyhole") which requires the use of very high (or even infinite) rotation speeds of the prisms when a pointed object passes close to the axis of rotation. Another solution, based on a concept similar to that of a pair of dielectric prisms placed in front of a primary antenna, uses phase-shifting surface (PSS) technology, described in the publication "Using Rotatable Planar Phase Shifting Surfaces to Steer a High Gain Beam" by N. Gagnon and A. Petosa, 2013. The authors use a phase-corrected Fresnel zone plate with a PSS-type phase shift to generate an off-axis beam, and a plate with a single linear phase progression. A phase-shifting surface, as described in the publication "Thin Microwave Quasi-Transparent Phase-Shifting Surface" by N. Gagnon and A. Petosa, 2010, is a thin, self-supporting structure that introduces a phase shift into an electromagnetic wave propagating through that surface.Figure 2 shows the configuration of a portion of PSS with three layers of metallization, made of elementary square conductive pieces, with: Fig. 2a is a cross-sectional view (in a yz plane) showing the three conducting layers 1, 3, 5 of total thickness h, separated by two dielectric layers 2, 4, of permittivity εΓ, the sides of the conducting parts being a1 for the outer layers 1 and 5 and a2 for the inner layer 3, and fig 2b a top view (in an xy plane) showing square cells (of side s) of the first conductive layer 1 with for each, a square conductive piece of side a1 placed on a dielectric layer 2. The phase shift between the incident and transmitted waves, and the transmission itself, are controlled by adjusting the geometric parameters a1 and a2. This allows for resonance within the structure and therefore maximum transmission for a desired phase shift. The best parameters allow for phase shifts between 0 and 360°. However, this solution has some drawbacks: Total transmission cannot be achieved for all phase shifts, and some configurations only allow a maximum of -2.2 dB (60%) transmission. These calculated values ​​are also optimistic, as they do not take into account metallic and dielectric losses. These metallic and dielectric losses are accentuated in such a resonant cell configuration. To counteract this effect, low-loss PCBs (Printed Circuit Boards) are required, but they are expensive, especially with a multilayer implementation. Furthermore, this configuration restricts the use of the concept to frequencies below approximately 30GHz because metallic and dielectric losses increase sharply beyond these frequencies. Furthermore, at high incidence angles (greater than 30°), this type of cell can exhibit very different transmission coefficients (in phase and amplitude) for the components of light polarized in the sagittal plane (s or TE polarization) or in the plane perpendicular to it (p or TM polarization) relative to the phase-shifting surface. This results in significant beam depolarization when the beam is pointed at planes that do not exhibit any particular symmetry with the arrangement of the antenna components. Finally, due to the resonant cell configuration, the operating bandwidth is reduced because of off-resonance operation and because the beam shaping is controlled in terms of phase rather than true delay compensation. A bandwidth of 7.4% (defined at 1 dB of maximum gain) has been achieved for lens antennas based on this concept, which may prove insufficient for certain applications (particularly communications). Consequently, there remains a need for a steerable beam antenna that simultaneously meets all the aforementioned requirements, particularly in terms of reduced mass and size, ease of use and integration into a platform, and low cost. The approach according to the invention is based on the use of one or two dielectric components with microstructures arranged in a configuration determined by holographic calculation. More specifically, the invention relates to a steerable microwave beam antenna having a wavelength between 1 mm and 1 m which comprises: a first dielectric component with sub-wavelength microstructures formed on one face of a dielectric substrate, a second diffractive dielectric component with sub-wavelength microstructures formed on one face of a dielectric substrate, configured to deflect an incident microwave beam. It is mainly characterized in that the microstructures of the first dielectric component are implanted in a non-periodic arrangement to form a dual-function non-resonant holographic component that is configured to collimate in emission mode and / or focus in reception mode and to deflect an incident microwave beam, in that this non-resonant holographic component is associated with a first rotation mechanism around a first axis of rotation, and in that the second diffractive dielectric component is associated with a second rotation mechanism around a second axis of rotation. This antenna configuration allows for good compactness, low weight and good efficiency. Unlike a Cassegrain type parabolic antenna which is penalized by shading effects due to the position of the source in front of the reflector, the antenna according to the invention operates in transmission, which makes it possible to obtain good efficiency and a low level of sidelobes despite a small antenna diameter. Furthermore, the antenna according to the invention has no moving parts with active RF radiation: all the electronics can therefore be integrated as close as possible to the source for simpler, more efficient and cheaper integration. Like an active network antenna, the profile of the antenna according to the invention remains flat regardless of the direction of orientation, which provides a decisive advantage when integrating into the fairing. Unlike the PSS antenna, the antenna according to the invention, which is based on dielectric components, does not require the implantation of metal; therefore, it does not generate metal losses. Furthermore, this non-resonant configuration allows for wider bandwidth operation. For example, a bandwidth (defined at 1 dB of maximum gain) of as high as 18% has been measured with such an antenna, which is 240% wider than with a PSS lens structure. All these advantages lead to simpler integration into a system and platform, at a reduced cost, particularly for small, compact antennas operating on mobile platforms (trucks, trains, aircraft, etc.) at high frequencies between 300 MHz and 300 GHz. According to one feature of the invention, the microstructures of the first and / or second component are formed on a 3D surface; when the microstructures of the second diffractive component are formed on a 3D surface, they are implemented in a non-periodic arrangement. According to another feature of the invention, the microstructures of the holographic component are formed in a volume that rests on said face of the holographic component, and implanted in a non-periodic three-dimensional arrangement. The same applies to the microstructures of the second component. The beam at the output of the holographic component in transmission mode or at the input of the holographic component in reception mode, can be a plane wave with an angle of incidence corresponding to the angle of orientation. The first rotation mechanism is possibly associated with a first translation mechanism of the holographic component in a plane perpendicular to the first axis of rotation. The antenna includes means of transmission and / or reception which can be associated with a translation mechanism (designated second translation mechanism) in a plane perpendicular to the axis of rotation of the first rotation mechanism. The microstructures of the holographic component and / or the second diffractive component are advantageously implanted from a mesh delimited by iso-phase lines and phase gradient lines. The mesh used for the microstructures of the holographic component may be different from the mesh used for the microstructures of the second diffractive component. The microstructures may consist of primary and secondary microstructures that provide an impedance matching layer (anti-reflective layer) for both low and high pointing angles, thus preventing depolarization of the wave passing through the component. The steerable beam antenna preferably comprises a shroud made of a microwave-absorbing material, possibly with sub-wavelength microstructures arranged within the shroud. The invention also relates to a method for manufacturing a steerable beam antenna, as described, which comprises the following steps: - manufacturing of means of transmission and / or reception, - fabrication of the holographic component and the second diffractive component in a dielectric material, - manufacturing of the mechanisms for moving the holographic component and the second diffractive component, characterized in that it includes a manufacturing step of a fairing in an absorbent material. Other features and advantages of the invention will become apparent from the following detailed description, given by way of non-limiting example and with reference to the accompanying drawings in which: Figure 1, already described, schematically represents, in cross-section, an example of a state-of-the-art RF deflection system based on a dual component with periodic microstructures, with a lens on one face and a first diffractive grating on the other face, and a second periodic diffractive grating. Figures 2, already described, schematically represent a cross-sectional view (fig 2a) and a top view (fig 2b) of a portion of a metal plate with 3 layers of metallization, from an example of a PSS type antenna. Figures 3 schematically represent cross-sectional views of non-periodic dielectric components of an example of an antenna according to the invention, with a single layer of microstructures (Fig. 3a) and a detail of microstructures with primary and secondary microstructures (Fig. 3b), Figure 4 represents the phase of an example of a holographic off-axis diffractive lens according to the invention, Figures 5a and 5b respectively represent the amplitude and phase of a beam exiting an example of an off-axis holographic diffractive lens according to the invention, as a function of X and Y in mm, with the corresponding gain as a function of the angles Θ and φ in degrees (Fig. 5c), and the corresponding far-field gain diagram, as a function of Θ (and for φ = 0°) in degrees (Fig. 5d). Figure 6a schematically represents, viewed from above, a first example of the implementation of sub-wavelength microstructures with a constant cross-section over their height, according to a detailed square Cartesian mesh (Figure 6b), and viewed in perspective (Fig. 6c). Figure 7a schematically represents, viewed from above, another example of the implementation of sub-wavelength microstructures using a mesh with iso-phase lines and phase-gradient lines, detailed at a larger scale in Figure 7b. Figure 8 illustrates, in perspective, an example of the rotation mechanism of the second holographic component and the rotation and translation mechanism of the first holographic component, with a fixed receiver and source. Figure 9 shows several curves of the gain diagram (in dBi) in the zOx plane as a function of Θ (and for φ = 0°) in degrees, for different translational shifts (along the x-axis) of the first holographic component, with a fixed source horn, Figures 10 illustrate the increase in the visible area of ​​an antenna for grazing incidences, between an antenna with planar holographic components (with a 2D surface) (fig 10a), and an antenna with holographic components with a 3D surface (fig 10b), seen in cross-section, and curves of apparent areas Sa expressed in dBm2 as a function of the viewing angle for different spherical surfaces of diameter D and height H and of apparent area of ​​1 m2 at zero viewing angle (fig 10c), Figure 11a schematically illustrates the generation of parasitic rays, Figure 11b schematically represents in cross-section an example of the internal structure of the fairing with microstructures in the form of straight pillars, Figure 11c another example of the internal structure of the fairing with microstructures in the form of straight and inclined pyramids. From one figure to the other, the same elements are identified by the same references. The antenna according to the invention comprises two dielectric components: a diffractive grating and a component with a dual function of lens and diffractive grating, these two dielectric components being capable of each performing a rotation around an axis of rotation. As shown in Figures 3a and 3b, the antenna comprises, on a single non-resonant dielectric component and on the same face, the lens and the first diffractive grating, thus combining on this same face the collimation functions of the lens and the deflection functions of the diffractive grating (in transmit mode), and the deflection functions of the diffractive grating and the focusing functions of the lens (in receive mode). This reduces the number of components from three dielectric components (the lens, the first and second diffractive gratings) to two dielectric components (an off-axis diffractive lens and the second diffractive grating), thereby reducing the complexity and weight of the antenna, particularly by decreasing the number of rotation mechanisms associated with these components. It also reduces the total thickness of the three components by approximately 33%.This results in reduced dielectric absorption and consequently increased efficiency: at 42 GHz for a material with a permittivity of 2.6 and with a dissipation factor of 5.10"3, the improvement in efficiency is 0.4 dB (i.e. 10%), for example. According to a first embodiment, this dual-function component, designated an off-axis diffractive lens or first holographic component (HC), comprises sub-wavelength MS microstructures, as shown in Figure 3a, formed on a single face of the component and arranged in a non-periodic configuration determined by an interference calculation on said face, between the beam incident on that face and the desired output beam. The description considers the antenna's transmit mode, with the incident beam being the beam emitted by the source; however, a receive mode also exists, with the output beam then directed towards the receiving equipment. The phase of an example of such a first holographic component is shown in Figure 4. It is worth recalling that microstructures are classified as subwavelength when the following condition is met for the cells (or meshes) in which they are implanted: (Distance between centers of adjacent cells) < λ0 / η with λ0 the target wavelength chosen in the range of wavelengths corresponding to microwave waves, i.e. a wavelength typically between 1 mm and 1 m, and n the refractive index of the dielectric material in which the microstructures are formed. In the case where this first holographic component has a flat face (2D surface) as shown in Figures 3, 8, and 10a, the calculation involves interference on this flat face between the incident beam emitted by the source and the output beam, which, in the case of a steerable beam antenna, is a plane wave with an angle of incidence (output angle in transmit mode / angle of incidence in receive mode) corresponding to the beam's orientation angle. The height and size of each CH microstructure are determined experimentally or calculated so as to match the phase delay modulo 2π introduced locally by each microstructure to the conjugate of the hologram's phase at that same point.Figures 5 show an example of the amplitude (fig 5a) and phase (fig 5b) of the beam at the output of a first circular holographic component of 150 mm diameter operating at 42 GHz and placed 75 mm from the source; a deflection of 29° is obtained as shown in figures 5c and 5d with the angle Θ. The implementation of sub-wavelength microstructures on one face of the second diffractive grating C2 (or second diffractive component) can also be determined by an interference calculation on that face between the beam transmitted by the off-axis diffractive lens (first holographic component CH) and the desired output beam, but not necessarily. Indeed, the microstructures of C2 can be determined as described in French patent FR 3 002 697. When the microstructure implementation is determined by the interference calculation, this second component is designated the second holographic component; this calculation is applicable independently of the interference calculation applied to the first holographic component. The sub-wavelength implementation of the microstructures of one or both dielectric components is based on a geometric mesh M, generally Cartesian in basis, i.e., rectangular or even square, as shown in the examples in Figures 6a, 6b, and 6c. A hexagonal or even circular mesh can also be considered. The meshes of the first (CH) and second (C2) components can be identical, but not necessarily so. Within this mesh, the base of a microstructure cannot, of course, extend beyond a unit cell, but may occupy only part of it. As can be seen in the example in Figure 6a, some units are empty, others are entirely occupied by the base of the microstructure, and for still others, the base of the microstructure only partially occupies the corresponding unit cell, depending on the implementation.The filling rate is defined as the ratio between the surface area of ​​the microstructure at its base and the surface area of ​​the cell. This simple implementation, however, introduces a phase error due to the sampling resolution, thus reducing the antenna's aperture efficiency. To resolve this issue, a mesh basis is chosen in a suitable coordinate system to optimize phase adjustment. According to the invention, a sub-wavelength geometric structure is created from a mesh M that coincides with iso-phase lines in one direction and with phase-gradient lines in directions perpendicular to the iso-phase lines, as illustrated in Figures 7a and 7b. Beam tracking and orientation are achieved by rotating the off-axis diffractive lens CH and the diffractive component C2 relative to each other. If CH and C2 are designed to deflect beams at the same angle, a common rotation of both components allows for azimuth orientation, while a counter-rotation of one relative to the other allows for elevation orientation. The zenith then becomes a singular point that can only be targeted if the deflection angles of the two components are equal. In the case of azimuthal tracking, this requires very high accelerations on both components, which is extremely difficult to achieve. In other words, azimuthal tracking can only be performed at near-zero speed. To overcome this difficulty, the CH rotation mechanism is combined with a two-axis translation mechanism, as shown in Figure 8. In this figure, the rotation mechanism (symbolized by a dashed circular arrow) of the first holographic component, CH, is complemented by a two-axis translation mechanism in a plane perpendicular to the first axis of rotation; the second component, C2, is equipped only with a rotation mechanism (symbolized by a solid circular arrow). This allows the receiver R and the source S of the antenna to remain fixed, while also enabling beam orientation along two additional axes without a singular point, and improved tracking agility near the zenith. The first and second axes of rotation are no longer superimposed. The orientation mechanisms of the CH and C2 components can be independent. The source or more generally the means of transmission and / or reception can themselves be associated with a translation mechanism (designated second translation mechanism) in a plane perpendicular to the axis of rotation of the first rotation mechanism. In addition, these extra orientation capabilities can be used to generate an error signal used to control the tracking. This orientation capability was calculated for a first circular holographic component with a diameter of 150 mm, placed 75 mm above a 42 GHz source horn, designed to orient the beam at an angle of 28.5°. As can be seen in Figure 9, a translation of this component between -10 and 10 mm induces an additional deflection between -7.75° and +8.5°, with a gain reduction of -1 dB in the worst case. To improve orientation efficiency at low elevation angles (high viewing angle Θ), the microstructures of the first and / or second component can be formed on a non-planar surface, i.e., on a predetermined 3D surface for each of the two components, such as a surface with rotational symmetry like a cone, a sphere, or any arbitrary 3D surface. The choice of the 3D surface is made, for example, according to the desired trade-off between zenith performance and grazing angles, or according to a desired size. A 3D surface allows for an increase in the apparent area Sa of the antenna and therefore the gain at grazing angles, as illustrated in Figure 10, which shows an increase in the visible area (expressed in dBm²) Sa as a function of the viewing angle Θ for different spherical 3D surfaces with diameter D and height H and an apparent area of ​​1 m² at zero viewing angle.The configuration H=0xD corresponds to a flat circular surface (Figure 10a), the surface H=0.5xD corresponds to a hemispherical surface, and the surface H=0.25xD (Figure 10b) to an intermediate configuration. As can be seen from the curves in Figure 10c, at 70° incidence, a hemispherical surface (H=0.5 D) compared to a flat circular surface (H=0.0 D) allows the apparent surface area to decrease from -4.7 dBm² to -1.8 dBm², representing an increase of 2.9 dB (nearly a 95% increase). In this case (= when the face of the second component is a 3D surface), the implementation of the sub-wavelength microstructures of the second component C2 is necessarily determined by the interference calculation indicated previously; in other words, the second component is necessarily a holographic component. The microstructures are all formed in a dielectric material according to predetermined shapes, either protruding as pillars or recessed as holes. A combination of holes and pillars is also possible. The microstructures can be of arbitrary shape, preferably with axes of symmetry to make them independent of the polarization of the incident beam at normal incidence, thus enabling the deflection system according to the invention to exhibit behavior that is relatively insensitive to polarization. Microstructures have a square, hexagonal, or circular cross-section, or a combination of different geometries, or a cross-section conforming to isophase lines and phase gradient lines. Their cross-section may be constant along their height or variable, as in the case of a pyramidal, conical, etc., structure. The height of MS microstructures is generally identical within a single component (as illustrated in Figure 3a), but not necessarily; it may also be identical from one component to another, but not necessarily. They may be perpendicular to the component surface or inclined, for example, at 30°. A variable inclination is also possible within the same component. The inclination is determined experimentally, typically as a function of the beam's inflection or incidence direction. According to a generalization of the previous embodiment, and still to perform the beam collimation and deflection function, the first holographic component CH comprises superimposed layers of sub-wavelength MS microstructures, formed within its volume and arranged in a non-periodic three-dimensional configuration determined by an interference calculation on said volume, between the beam emitted by the source incident in this volume and the desired output beam. This volume naturally rests on the face of the CH component on which the microstructures are formed; this volume is delimited, in particular, by this face.The calculation of volumetric interference can be performed experimentally through successive adjustments or computationally, for example, by transforming the volume of CH into a stack of K parallel 2D or 3D surfaces (with K typically an integer between 2 and 100), on each of which a surface interference pattern is calculated. The stacking of microstructure layers is obtained, for example, by assigning to each calculation point of the volume a microstructure whose height is reduced by a factor K and whose cross-section generates a local phase delay corresponding to the conjugate of the hologram's phase at that same point, reduced by a factor K. Another method for obtaining the 3D microstructure distribution involves starting with the interference calculations performed on the face of the CH component between the incident beam emitted by the source and the output beam. The cross-section of each microstructure is then projected onto the volume of the component, following the curves resulting from the intersection between the isophase planes of the volumetric hologram and the planes containing the phase gradients. The height and cross-section of each CH microstructure are calculated to match the phase delay (modulo 2π) introduced by each microstructure to the phase conjugate of the hologram calculated on the CH surface. In other words, this interference calculation on the volume can be performed: - discretely for different values ​​of z (stack size); this is essentially a reiteration, for several implementation surfaces considered at different z values, of the 2D interference calculation previously described for a single implementation surface. The height and cross-section of the microstructures must then be determined on each of these surfaces as indicated previously, or - continuously along z, the height and section of the microstructures then being determined by the calculation itself. In the case where C2 is a holographic component, this embodiment can also be applied to implement the deflection function of C2. According to a second embodiment, the microstructures of the CH component and / or C2 consist of primary microstructures MSp and secondary microstructures MSs arranged in a second layer on top of the first layer of primary microstructures, as shown in Figure 3b. Their arrangement on the primary microstructures and their shape are determined by known means (parametric optimization algorithms) to maximize and equalize the transmissions of the structure for both TE and TM polarizations and for different beam incidence angles, i.e., to implement the impedance matching function. Secondary microstructures are preferentially pillars or holes, or a combination of both, and preferentially have cross-sections such as squares, hexagons, or circles. They can also be located between the pillars of the primary microstructures, as shown in Figure 3b. They can have a constant cross-section or vary in height, as in the case of a pyramidal, conical, etc., structure. They can be perpendicular to the component surface or inclined, for example, at 30°. This addition of a layer of secondary microstructures (one on CH and / or C2) allows the impedance to be matched in order to obtain similar transmission levels regardless of the incident polarization, under high and low incidence, so as not to depolarize the incident wave. The use of secondary microstructures allows: - to fine-tune the desired effective index value in order to reduce the energy diffracted by the system in parasitic orders other than that of the main beam, - to implement an impedance matching layer (antireflective layer), and - not to depolarize the wave emitted by the source, which is not the case with PSS. The portion emitted by the source and not collected ("spillover") by CH and C2 devices can disrupt the antenna's radiation pattern. Indeed, the holographic component is held mechanically in front of the source, using a metallic or dielectric fairing. In both cases, these solutions lead to the creation of parasitic radiation, either by reflection off these mechanical elements, or by transmission through this structure, or both, as illustrated in Figure 11a. One obvious, but suboptimal, solution is to line the inside of the fairing with absorbent materials. However, given the variety of angles of incidence to be covered, controlling reflections on the surface of the absorbent material is difficult across all the surfaces to be covered. The antenna preferably incorporates a shroud in the form of a microwave-absorbing tube, which holds the CH and C2 dielectric components in front of the source horn S. This shroud is made of microwave-absorbing materials (e.g., organic materials loaded with absorbent materials such as metals, magnetic materials, carbon, or lightly doped semiconductor materials), either as a lining to the structural material of the shroud or directly. The external structure of the shroud is typically smooth, while the internal structure of the tube is designed to dampen microwave reflections that occur inside the tube during signal transmission and reception.This structuring can be done in two ways: - Either using a layer containing subwavelength microstructures so that the structure is locally adapted in height and thickness to present the equivalent effective index (as presented in patent FR 2 980 648) which makes it possible to create an anti-reflective layer adapted locally to the incidence and frequency of the incident wave as shown in figure 1 1 b. - Either by using a three-dimensional pyramidal structure, for example (see 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 beam incidence as shown in Figure 11c. This orientation is not essential; a normal orientation to the fairing surface can be maintained. The size of the microstructures therefore varies depending on the operating wavelength of the device. These structured surfaces can be produced by machining, additive manufacturing, or chemical etching. The fabrication of an antenna according to the invention comprises the following steps: manufacturing of the means of transmission (the source) and / or reception, manufacturing of the first holographic component and the second component (possibly holographic) in a dielectric substrate, possibly during the same step, possible manufacturing of the fairing, manufacturing of the movement mechanisms (rotation and possibly translation) of the first holographic component and the second component (possibly holographic), - assembly of all these elements. The manufacture of these components and / or the sub-wavelength microstructured fairing can be carried out using conventional molding or machining processes, employing prohibitively expensive machines that are particularly difficult to amortize for a small number of components to be manufactured. Examples of dielectric materials that can be used include: polyamide (PA), acrylonitrile butadiene styrene (ABS), polypropylene (PP), high-density polyethylene (HDPE), polytetrafluoroethylene (PTFE), polyetherimide (PEI or ULTEM), polyetheretherketone (PEEK), polycarbonate (PC), cycloolefin copolymers (COC and COP), polystyrene (PE or Rexolite), and polyphenylene sulfide (PPS and PPSF).Other examples include ceramic materials such as alumina (Al₂O₃), aluminum nitride (Al₂O₅), zirconia (ZrO₂), barium titanate (BaTiO₃), titanium dioxide (TiO₂), and silica, as well as all organic-based composite materials filled with organic or inorganic dielectric materials (of the ceramic type). These materials can also be manufactured by chemical etching or laser etching. In cases where microstructures are formed within the substrate, pillars and / or holes are created directly in the substrate, for example, using conventional manufacturing methods. However, to obtain microstructures with cross-sections ranging from 500 μm to 2 mm and a cross-section width-to-height ratio of up to 20, a mold would cost between €50,000 and €100,000. The dielectric components and / or the fairing are advantageously manufactured using additive manufacturing processes characterized by high flexibility, large-scale production, and low-cost manufacturing. Among these additive manufacturing processes are 3D printing by fused deposition modeling (FDM), stereolithography (SLA), and selective laser sintering (SLS): the dielectrics used are compatible with minimal signal absorption (estimated at -1 dB per component) and the required mechanical precision. They can also be manufactured by a combination of these manufacturing processes. Although the invention has been described in connection with particular embodiments, it is clearly evident that it is by no means limited to them and that it includes all technical equivalents of the means described as well as their combinations if these fall within the scope of the invention.

Claims

DEMANDS A steerable microwave beam antenna with a wavelength between 1 mm and 1 m, which includes: a first dielectric component with sub-wavelength microstructures formed on one face of a dielectric substrate, a second diffractive dielectric component (C2) with sub-wavelength microstructures formed on one face of a dielectric substrate, configured to deflect an incident microwave beam, characterized in that the microstructures of the first dielectric component are implanted in a non-periodic arrangement to form a dual-function non-resonant holographic component (CH) that is configured to collimate and / or focus and to deflect an incident microwave beam, in that this non-resonant holographic component is associated with a first rotation mechanism about a first axis of rotation, and in that the second diffractive dielectric component (C2) is associated with a second rotation mechanism about a second axis of rotation. Steerable microwave beam antenna according to the preceding claim, characterized in that the microstructures of the holographic component (HC) are formed on a 3D surface. Steerable microwave beam antenna according to one of the preceding claims, characterized in that the microstructures of the holographic component (HC) are formed in a volume which rests on said face of the holographic component, and implanted according to a non-periodic three-dimensional arrangement. Steerable microwave beam antenna according to one of the preceding claims, characterized in that the microstructures of the second diffractive component (C2) are formed on a 3D surface, and implanted according to a non-periodic arrangement. Steerable microwave beam antenna according to one of the preceding claims, characterized in that the microstructures of the second diffractive component (C2) are formed in a volume which rests on said face of the diffractive component, and implanted according to a non-periodic three-dimensional arrangement. Steerable microwave beam antenna according to one of the preceding claims, characterized in that the beam at the output of the holographic component (HC) in transmission mode or at the input of the holographic component (HC) in reception mode is a plane wave with an angle of incidence corresponding to the angle of orientation.

7. Steerable microwave beam antenna according to one of the preceding claims, characterized in that the first rotation mechanism is associated with a first translation mechanism of the holographic component (CH) in a plane perpendicular to the first axis of rotation.

8. Steerable microwave beam antenna according to one of the preceding claims, characterized in that it comprises transmission (S) and / or reception means associated with a translation mechanism in a plane perpendicular to the axis of rotation of the first rotation mechanism.

9. Steerable microwave beam antenna according to any one of the preceding claims, characterized in that the microstructures of the holographic component and / or the second diffractive component are implanted from a mesh (M) delimited by iso-phase lines and phase gradient lines.

10. Steerable microwave beam antenna according to the preceding claim, characterized in that the mesh for forming the microstructures of the holographic component (CH) is different from the mesh for forming the microstructures of the second diffractive component (C2). 1 1. Steerable microwave beam antenna according to one of the preceding claims, characterized in that the microstructures of the holographic component and / or the second diffractive component are made up of primary microstructures (MSp) and secondary microstructures (MSs).

12. Steerable microwave beam antenna according to any one of the preceding claims, characterized in that it comprises a fairing in an absorbing microwave material.

13. Steerable microwave beam antenna according to the preceding claim, characterized in that the fairing comprises sub-wavelength microstructures.

14. Steerable microwave beam antenna according to the preceding claim, characterized in that the microstructures of the fairing are inside the fairing.

15. A method for manufacturing a steerable microwave beam antenna according to any one of the preceding claims, comprising the following steps: - manufacturing of means of transmission (S) and / or reception, - fabrication of the holographic component (CH) in a dielectric substrate, - fabrication of the second diffractive component (C2) in a dielectric substrate, - manufacturing of the mechanisms for moving the holographic component and the second diffractive component, characterized in that it includes a manufacturing step of a fairing in an absorbent material.

16. Method of manufacturing a steerable microwave beam antenna according to the preceding claim, characterized in that the holographic component (CH) and the second diffractive component (C2) are manufactured together.

17. Method of manufacturing a steerable microwave beam antenna according to one of claims 15 or 16, characterized in that the holographic component (CH) and the second diffractive component (C2) are made by additive manufacturing and / or molding and / or machining and / or chemical etching and / or laser etching.