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EP-4278412-B1 - RADOME AND ANTENNA SYSTEM WITH ELEVATION COMPENSATION FUNCTION

EP4278412B1EP 4278412 B1EP4278412 B1EP 4278412B1EP-4278412-B1

Inventors

  • LOISEAUX, BRIGITTE
  • HOANG, Thi-Quynh-Van
  • DEMOTES-MAINARD, Bernard

Dates

Publication Date
20260513
Application Date
20220113

Claims (10)

  1. Radome (RDM) comprising a shell (CD) made of dielectric material having an outer face (FE) and an inner face (FI), the inner face defining, together with a supporting surface (PS), a volume (V) that is intended to contain an antenna (A), characterized in that it has, in or close to the at least one peripheral region of its inner face, a transmission diffracting structure (SD, SD', SD") operating within a spectral range in the microwave domain, the diffracting structure comprising alternating layers (CM1, CM2) of at least two dielectric materials of different dielectric permittivities, inclined with respect to said supporting surface, the diffracting structure being configured so that an incident electromagnetic wave (OEI), of at least one wavelength λ 0 of said spectral range in the microwave domain propagating at an elevation angle θ 0 between 5° and 30° with respect to the supporting surface, satisfies the Bragg condition, and so that a wave diffracted (OED) by the structure propagates with an elevation angle (θ') greater than that of said incident electromagnetic wave; and so that the diffraction efficiency is less than 50% for the electromagnetic waves propagating at an elevation angle greater than or equal to 40°.
  2. Radome (RDM) comprising a shell (CD) made of dielectric material having an outer face (FE) and an inner face (FI), the inner face defining, together with a supporting surface (PS), a volume (V) that is intended to contain an antenna (A), characterized in that it has, in or close to the at least one peripheral region of its inner face, a diffracting structure (SD, SD', SD") operating in a spectral range in the microwave domain, the diffracting structure comprising alternating layers (CS1, CS2, CS3, CS2', CS3') at least some of which have a structuring at a scale less than one wavelength of said spectral range modifying their effective dielectric permittivity, the diffracting structure being configured so that an incident electromagnetic wave (OEI), of at least one wavelength λ 0 of said spectral range in the microwave domain propagating at an elevation angle θ 0 between 5° and 30° with respect to the supporting surface, satisfies the Bragg condition, and so that a wave diffracted (OED) by the structure propagates with an elevation angle (θ') greater than that of said incident electromagnetic wave; and so that the diffraction efficiency is less than 50% for the electromagnetic waves propagating at an elevation angle greater than or equal to 40°.
  3. Radome according to one of the preceding claims wherein the diffracting structure is locally akin to a dense transmission network in said spectral range of the microwave domain.
  4. Radome according to one of the preceding claims wherein the diffracting structure is configured so that an incident electromagnetic wave (OEI), of at least one wavelength λ 0 of said spectral range in the microwave domain propagating at an elevation angle θ 0 between 10° and 20°, with respect to the supporting surface, satisfies the Bragg condition, and so that a wave diffracted (OED) by the structure propagates with an elevation angle (θ') greater than that of said incident electromagnetic wave.
  5. Radome according to claim 4 wherein the diffracting structure is configured so that the diffraction efficiency is less than 20%, for the electromagnetic waves propagating at an elevation angle greater or equal to 40°, and preferably greater than or equal to 30°.
  6. Radome according to one of claims 4 or 5 wherein the inclination of the diffracting structure is dimensioned in such a way that an incident electromagnetic wave at the wavelength λ 0 and having an elevation angle θ 0 is deflected at an angle between 20° and 40°.
  7. Radome according to one of the preceding claims wherein the diffracting structure (SD) is physically separated from the shell made of dielectric material.
  8. Radome according to one of claims 1 to 6 wherein the diffracting structure (SD', SD") is made from a single piece with the shell made of dielectric material.
  9. Radome according to claim 8, manufactured by additive manufacturing.
  10. Antenna system comprising a radome (RDM) according to one of the preceding claims and an depointable antenna (A) located inside the volume (V) delimited by the supporting surface (PS) and the inner face (FI) of the shell (CD) of the radome, the antenna being adapted to transmit or receive electromagnetic waves within a spectral range in the microwave domain, the transmission diffracting structure being adapted to deflect one said electromagnetic wave of which the elevation angle with respect to the supporting surface is less than a predetermined threshold (θ) by increasing its elevation angle.

Description

The invention relates to a radome having a function for compensating the elevation of incident electromagnetic waves; it also relates to an antenna system comprising such a radome. It falls within the field of antennas for telecommunications, particularly space-based antennas, and more specifically space-based telecommunications antennas intended to be deployed on mobile platforms, whether terrestrial, such as trains or buses, or airborne (in English, "satcom on the move"). In this type of application, and particularly in the case of airborne platforms, the antennas used are generally planar due to space and aerodynamic considerations. While steerable parabolic antennas are sometimes mounted on the tail of business jets, these solutions are unsuitable for widespread commercial operation due to the increased power consumption caused by the protrusion formed by the antenna and its radome. Furthermore, their installation often requires a specific and costly certification process. On the other hand, planar antennas that can be pointed – mechanically or electronically – have a gain that decreases with elevation (defined as the angle between a direction and the horizon). This leads to a reduction in data rate, or even a loss of connection, to or from a satellite low on the horizon (typically 30° or less). Various solutions have been proposed to increase the operating angular range of these antennas. For example WO 2010144170 discloses the use of metamaterials with a negative refractive index. However, this technology is not yet mature enough for industrial use. The article from E. Gandini et al. “A Low-Profile Low-Cross Polarization Dielectric Dome Antenna for Wide-Scanning Applications” 13th European Conference on Antennas and Propagation (EuCAP 2019) , as well as the document WO 2019/067474 propose the use of a variable-thickness radome, behaving like a Diverging lens. The disadvantage of this approach is that the radome distorts the radiation lobe of the antenna even for large elevation angles. Yet another approach is to combine a metasurface radome with the use of an active antenna where the emission law includes an angular pre-compensation for the formation of the radiation pattern complementary to the function of the radome ( Alice Benini et al, “Phase-Gradient Meta-Dome for Increasing Grating-Lobe-Free Scan Range in Phased Arrays,” IEEE Transactions On Antennas And Propagation, Vol. 66, No. 8, August 2018, 3973 ; WO 2019/165684 This solution is very complex and expensive. There is therefore a need for a simple and economical solution to increase the operating angular range of a planar antenna, and more specifically to increase its gain at low elevation angles. The invention aims to provide such a solution. According to the invention, this objective is achieved by means of a radome equipped, in its inner peripheral region, with a diffractive structure that can be locally approximated as a diffraction grating designed to operate in the Bragg regime during transmission. This diffractive structure introduces a deflection of grazing electromagnetic waves, which increases their elevation angle without significantly affecting the propagation of waves whose propagation direction is closer to the normal to the antenna. The diffractive structure is supported by a structure that can be either integrated into the peripheral region of the radome's shell or located nearby but physically separated from it. In both cases, it can advantageously be made of polymer or composite materials using three-dimensional (3D) printing, particularly by fused filament fabrication. The use of diffraction gratings to introduce a deflection of electromagnetic waves emitted by or directed towards an antenna is known, for example, from AU 2018 311 770 , US 2007/002305 And US 2,638,588 However, it is not known to use diffraction grating-type structures arranged at the periphery of a radome to deflect electromagnetic waves with a low elevation angle without disturbing, or marginally disturbing, the propagation of electromagnetic waves with a higher elevation angle. An object of the invention is therefore a radome comprising a shell made of dielectric material having an external face and an internal face, the internal face defining, with a support surface, a volume intended to contain an antenna, characterized in that it has, on or near at least a peripheral region of its internal face, a diffracting structure locally assimilable to a transmission diffraction grating operating in a spectral range in the microwave domain, the diffracting structure being configured so that an incident electromagnetic wave (OEI), at at least one wavelength λ 0 of said spectral range in the microwave domain propagating at an elevation angle θ 0 between 5° and 30° with respect to the support surface, satisfies the Bragg condition, and that a diffracted wave (OED) by the structure propagates with an elevation angle (θ') greater than that of said incident electromagn