Compact directional antenna

Abstract

Compact Direct IV Antenna. Antenna (100) comprising at least: - an electrically conductive enclosure (110) formed by a lower surface (111) surrounded by lateral edges (112) and closed by a cover (140) having a partially reflective outer surface; - a substrate (120) placed at the bottom of the enclosure on the lower surface of the enclosure; and - a radome (150) placed in the enclosure opposite the substrate and capable of protecting the antenna from temperatures exceeding 1000 °C; characterized in that the antenna also comprises a radiating element (130) placed on the substrate in the enclosure and capable of emitting a signal at at least a first frequency, and a grid (160) placed on a surface of the radome opposite the radiating element so as to form an air gap (170) between the grid and the substrate. Figure for the abstract: Fig. 1

Description

Title of the invention: Compact directional antenna technical field

[0001] The present invention relates to a compact directional antenna adapted to atmospheric reentry conditions. Previous technique

[0002] Some applications require a directional antenna to concentrate the radiated energy in a particular direction in space, such as long-distance communications, radars or radio altimeters.

[0003] Furthermore, in the case of an atmospheric reentry spacecraft, it is preferable to have a compact antenna on this vehicle. Thus, it is necessary to minimize the mass of the antenna, minimize its thickness to facilitate its integration into the vehicle, and minimize its external dimensions (present on the outer shell of the vehicle) so that it disturbs the aerodynamics of the vehicle as little as possible and is able to withstand the same environmental conditions (such as temperature) as the vehicle.

[0004] Currently, the directional antennas used for atmospheric reentry space vehicles are large in size and thickness, not very resistant to environmental conditions, and / or are difficult to integrate into the vehicle due to their mass or size, and / or have performance (adaptation, gain) sensitive to significant evolution (heating, recession) of the radome material.

[0005] It is therefore desirable to have a new directional antenna, compact and able to withstand the environmental conditions of atmospheric reentry and reduced mass. Description of the invention

[0006] The present invention relates to an antenna comprising at least: - an electrically conductive enclosure formed by a lower surface surrounded by lateral edges and closed by a lid whose outer surface is partially reflective; - a substrate placed at the bottom of the enclosure on the lower surface of the enclosure; and - a radome placed in the enclosure opposite the substrate and capable of protecting the antenna from temperatures exceeding 1000 °C;

[0007] characterized in that the antenna also comprises a radiating element placed on the substrate within the enclosure and capable of emitting a signal at at least a first frequency, and a grid placed on a surface of the radome opposite the radiating element so as to form an air gap between the grid and the substrate.

[0008] Thanks to the grid, and in particular the patterns present on the grid, the reflectivity of the antenna can be varied. The directivity of the antenna can then be adjusted by also varying its dimensions, such as the height of the air gap or the thickness of the substrate.

[0009] This antenna is capable of withstanding extreme atmospheric reentry temperatures thanks to the presence of the radome.

[0010] Furthermore, thanks to the air gap and the grid, a resonant cavity is created which makes it possible to reduce the size and mass of the antenna. The antenna according to the invention is thus particularly compact and of reduced mass.

[0011] According to a particular feature of the invention, the grid is metallic.

[0012] According to another particular feature of the invention, the grid is movable on the surface of the radome.

[0013] This allows the reflectivity of the grid to be varied in order to vary the directivity of the antenna.

[0014] According to another particular feature of the invention, the radome is made of silica-silica.

[0015] According to another particular feature of the invention, the air blade has a height between the grid and the substrate equal to half the wavelength corresponding to the first frequency.

[0016] According to another particular feature of the invention, the radiating element is a radiating patch.

[0017] It is also possible to replace the radiating patch with a horn if a more directional antenna is desired. Since the patch is smaller than a horn, if the antenna's compactness is preferred over its directivity, the patch should be chosen as the radiating element.

[0018] According to another particular feature of the invention, the thickness of the radome is variable.

[0019] By varying the thickness of the radome, its geometry above the grid can be adapted to offset the antenna beam so that its main lobe is oriented laterally. This allows Synthetic-Aperture Radar (SAR) or radio altimeter or electromagnetic homing applications to target the antenna beam trajectory ahead of it before it reaches the target area.

[0020] Another object of the invention is a vehicle equipped with at least one antenna according to the invention.

[0021] According to a particular feature of the invention, the vehicle is a space vehicle.

[0022] According to another particular feature of the invention, the vehicle is a space launcher, an exploration vehicle or a satellite. Brief description of the drawings

[0023] Other features and advantages of the present invention will become apparent from the description given below, with reference to the attached drawings which illustrate examples of embodiment without any limiting character.

[0024] [Fig-1] [Fig.1] represents, schematically and partially, an antenna according to an embodiment of the invention.

[0025] [Fig.2A] Fig.2A represents, schematically and partially, a first example of the realization of the grid.

[0026] [Fig.2B] Fig.2B represents, schematically and partially, a second example of the realization of the grid.

[0027] [Fig.2C] Fig.2C represents, schematically and partially, a third example of the realization of the grid.

[0028] [Fig.3] Fig.3 schematically represents the directivity of the antenna the [Fig.l] as a function of the reflectivity of the grid.

[0029] [Fig.4] Fig.4 represents cross-sections of an antenna according to the invention.

[0030] [Fig.5A] The [Fig.5A] represents, schematically and partially, an antenna according to another embodiment of the invention.

[0031] [Fig.5B] Fig.5B represents, schematically and partially, an antenna according to another embodiment of the invention.

[0032] [Fig.5C] The [Fig.5C] represents, schematically and partially, an antenna according to another embodiment of the invention. Description of the implementation methods

[0033] Fig. 1 represents an antenna 100 according to a first embodiment of the invention.

[0034] The antenna 100 comprises a housing 110 including a lower surface 111 and lateral edges 112. The housing 110 is closed by a cover 140.

[0035] The enclosure 110 is metallic and / or made of a perfectly electrically conductive material.

[0036] The cover 140 forms a partially reflective outer surface. More specifically, the lower the reflectivity coefficient, the lower its gain. The cover 140 is, for example, made of conductive material in metallic form or as a printed patch.

[0037] The antenna 100 also includes a substrate 120 placed at the bottom of the enclosure 110 on its lower surface 111 on which is placed a radiating element 130, and a radome 150 placed in the enclosure 110 opposite the substrate 120 and the radiating element 130. A grid 160 is placed on a surface of the radome 150 opposite the substrate 120 and the radiating element 130.

[0038] The radiating element 130 is configured to emit a signal at at least a first frequency f.

[0039] The substrate 120 has a thickness t, for example between 0.1 mm and 10 mm. The substrate is for example made of glass-teflon.

[0040] An air gap 170 of height H is formed between the grid 160 and the radiating element 130 and forms a resonant cavity thanks to the grid 160. The height H of the air gap 170 is for example equal to X / 2 with X the wavelength corresponding to the frequency f of emission of the radiating element 130.

[0041] The radome 150 is for example made of silica-silica and makes it possible to protect the antenna 100 from temperatures above 1000 °C, and more advantageously from temperatures above 2500 °C.

[0042] The antenna 100, and more specifically the enclosure 110, is, for example, circular in shape. The circular shape simplifies the seal between the antenna 100 and the envelope of the spacecraft carrying the antenna 100 under reentry flux. However, other shapes are possible. The antenna 100, and in particular its enclosure 110, can, for example, be square or rectangular, which allows the gain of the antenna 100 to be adjusted independently in several directions, for example, by having a very open antenna 100 in one plane and a highly directional antenna 100 in another plane.

[0043] The grid 160 can have different types of patterns. The patterns can be regular or irregular, and their dimensions can also vary. These patterns are chosen to control the reflectivity of the grid 160. These patterns also allow control of the shape of the antenna 100's lobe and its polarization. Furthermore, the dimensions of these patterns are related to the wavelength chosen for the antenna 100 and can therefore vary between two antennas of different frequencies exhibiting similar lobe and / or polarization characteristics.

[0044] Figures 2A, 2B and 2C give examples of the realization of patterns for grid 160. On these three figures, the radome 250 is represented in dotted lines in front of grid 260A ([Fig.2A]), or 260B ([Fig.2B]) or 260C ([Fig.2C]).

[0045] In [Fig.2A], the grid 260A is formed of a succession of metallic bands 270, 271, 272 present on a semiconductor 280. For example, the bands 270, 271, 272 have a thickness e of 3.4 mm and are spaced a width 1 of 4.3 mm apart.

[0046] On [Fig.2B], the grid 260B is formed of a succession of bands 201, 202, 203 having a thickness eb of 1 mm and a height hb of 2 mm and are spaced at a width 1b of 5.5 mm.

[0047] In [Fig. 2C], the pattern of the grid 260C is, for example, a succession of holes 210, 211, 212 all having the same diameter DC and whose centers are all spaced at the same distance of. For example, the holes 210, 211, 212 have a diameter DC of 6.5 mm and their centers are spaced at a distance of = 1 mm.

[0048] The grid 160 (or the grids 260A, 260B, 260C of figures 2A, 2B and 2C) can be formed by a semiconductor whose metallization produces the patterns of the grid 160, or it can be conductive, for example metallic, and machined according to the patterns of the grid 160.

[0049] Figure 3 schematically represents the directivity of antenna 100 as a function of the reflectivity p of grid 160. The more reflective grid 160 is, the greater the directivity of antenna 100. However, increasing the directivity of antenna 100 decreases its bandwidth. The pattern of grid 160 is therefore chosen to find a compromise between directivity and bandwidth depending on the application.

[0050] Figure 4 shows cross-sections of an antenna 400 according to the invention. The antenna 400 is, for example, the antenna 100 of Figure 1 with a grid 160 whose pattern can be chosen from those of Figures 2A, 2B or 2C or can be another pattern.

[0051] Compared with a prior art antenna comprising, like the 400 antenna, a radiating element capable of emitting an electromagnetic signal at a frequency of 13.5 GHz, the prior art antenna has a mass of a few kilograms, whereas the 400 antenna has a mass of about 0.7 kg.

[0052] The prior art antenna has a height of approximately one hundred millimeters and a total diameter of several hundred millimeters; whereas the antenna 400 has a height h400 of 63 mm and a total diameter DT400 of 130 mm, its enclosure 410 having a diameter D400 of 80 mm. The total diameter DT400 includes the dimensions of the mounting elements 435 of the antenna 400 on a vehicle.

[0053] In addition to being more compact and lighter, the 400 antenna has a gain almost 4 dB higher than the prior art antenna. This increases the range of a transmission system requiring this type of antenna by a factor of 2.5 to 3.

[0054] Figures 5A, 5B and 5C represent, schematically and partially, an antenna 500 according to a second ([Fig.5A]), a third ([Fig.5B]) and a fourth ([Fig.5C]) embodiment of the invention.

[0055] As previously described in [Fig. 1], the antenna 500 comprises an enclosure 510 formed by a lower surface 511 and lateral edges and closed by a lid whose outer surface is partially reflective; a substrate 520 placed at the bottom of the enclosure 510 on the lower surface 511; a radiating element 530 placed on the substrate 520 and a radome 550 placed in the enclosure 510 opposite the substrate 520. The radome 550 protects the antenna from temperatures exceeding 1000 °C, or even exceeding 2500 °C.

[0056] The antenna 500 also includes a grid 560 placed on a surface of the radome opposite the radiating element 530 so as to form an air blade 570 between the grid 560 and the substrate 520.

[0057] As previously stated, the 560 grid has a pattern whose geometry and dimensions can be adapted to play on its reflectivity and obtain a more or less directional antenna.

[0058] In these embodiments, the thickness of the radome is variable and ranges between thicknesses E1 and E2. This allows the beam of antenna 500 to be deflected relative to the beam of antenna 100 in [Fig. 1] so that the main lobe is oriented laterally. In other words, the electromagnetic beam emitted by antenna 500 can be angularly deflected thanks to this variable thickness. This makes it possible to target the beam trajectory upstream before it reaches the signal reception area emitted by the antenna.

[0059] For example, if the difference between El and E2 is 10 mm, the beam can be pointed 5° while having a loss of 1 dB in the signal emitted by the antenna 500.

[0060] In Figures 5A, 5B, and 5C, the grid 560 and the substrate 520 are parallel to each other. In [Fig. 5A], they are also parallel to the upper surface 512 of the enclosure 510, while the radome 550 has a surface inclined relative to this same surface 512. In Figures 5B and 5C, the grid 560 and the substrate 520 are inclined relative to the upper surface 512 of the enclosure 510, and the radome 550 has an upper surface parallel to the surface 512 of the enclosure 510. The enclosure 510 may have a flat bottom (Figures 5A and 5C) or an inclined bottom ([Fig. 5B]).

[0061] It is also possible to have a movable grid to obtain a dual-mode antenna. Thus, according to a first operating mode, the grid can be placed over the entire surface of the radome opposite the radiating element. In this first mode, the grid is then highly reflective and therefore the directivity of the antenna is improved.

[0062] According to a second operating mode, the grid can be moved to reduce its reflectivity, thereby decreasing the antenna's directivity and resulting in an omnidirectional antenna. The advantage of these two grid operating modes is that it allows, for example, the search for a target in the second mode and then the signal to be transmitted to the target in the first mode. The antenna is thus adaptable to the vehicle's flight phases.

Claims

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9. Demands Antenna (100, 400, 500) comprising at least: - an electrically conductive enclosure (110, 410, 510) formed by a lower surface (111, 511) surrounded by lateral edges (112) and closed by a lid (140) of which an outer surface is partially reflective; - a substrate (120, 520) placed at the bottom of the enclosure on the lower surface of the enclosure; and - a radome (150, 250, 550) placed in the enclosure opposite the substrate and capable of protecting the antenna from temperatures exceeding 1000 °C; characterized in that the antenna also comprises a radiating element (130, 530) placed on the substrate in the enclosure and capable of emitting a signal at at least one first frequency (f), and a grid (160, 260A, 260B, 260C, 560) placed on a surface of the radome opposite the radiating element so as to form an air gap (170, 570) between the grid and the substrate. Antenna according to claim 1, wherein the grid is metallic. Antenna according to any one of claims 1 or 2, wherein the radome is made of silica-silica. Antenna according to any one of claims 1 to 3, wherein the air blade has a height (H) between the grid and the substrate equal to half the wavelength corresponding to the first frequency (f). Antenna according to any one of claims 1 to 4, wherein the radiating element is a radiating patch. Antenna (500) according to any one of claims 1 to 5, wherein the thickness (El, E2) of the radome (550) is variable. Vehicle equipped with at least one antenna according to any one of claims 1 to 6. Vehicle according to claim 7, wherein the vehicle is a space vehicle. Vehicle according to claim 8, wherein the vehicle is a space launcher, an exploration vehicle or a satellite.

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