Compact directive antenna

Abstract

The invention relates to an antenna (100) comprising at least: - an electrically conductive enclosure (110) formed by a lower surface (111) surrounded by side edges (112) and closed by a cover (140), an outer surface of which is partially reflective; - a substrate (120) placed at the bottom of the enclosure on the lower surface of the enclosure; and - a radome (150) placed inside the enclosure opposite the substrate and capable of protecting the antenna from temperatures above 1000°C; characterised in that the antenna also comprises a radiating element (130) placed on the substrate inside 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.

Description

[0001] Description

[0002] Title of the invention: COMPACT DIRECTIVE ANTENNA

[0003] Technical Field

[0004] The present invention relates to a compact directional antenna adapted to atmospheric re-entry conditions.

[0005] Prior art

[0006] Some applications require a directional antenna to focus radiated energy in a particular direction in space, such as long-distance communications, radar, or radio altimeters.

[0007] Furthermore, in the case of an atmospheric re-entry space vehicle, 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 external envelope 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.

[0008] Currently, the directional antennas used for atmospheric re-entry space vehicles are large and thick, not very resistant to environmental conditions, and / or are difficult to integrate into the vehicle due to their mass or size, and / or have performances (adaptation, gain) sensitive to significant changes (heating, recession) in the radome materials.

[0009] It is therefore desirable to have a new, compact, directional antenna that can withstand the environmental conditions of atmospheric re-entry and has a reduced mass.

[0010] Presentation of the invention The present invention relates to an antenna comprising at least:

[0011] - an electrically conductive enclosure formed by a lower surface surrounded by lateral edges and closed by a cover, an outer surface of which is partially reflective;

[0012] - a substrate placed at the bottom of the enclosure on the lower surface of the enclosure; and

[0013] - a radome placed in the enclosure facing the substrate and capable of protecting the antenna from temperatures above 1000°C; characterized in that the antenna also comprises a radiating element placed on the substrate in the enclosure and capable of emitting a signal at at least a first frequency, and a grid placed on a surface of the radome facing the radiating element so as to form an air gap between the grid and the substrate.

[0014] Thanks to the grid, 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.

[0015] This antenna is capable of withstanding the extreme temperatures of atmospheric re-entry thanks to the presence of the radome.

[0016] In addition, 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.

[0017] According to a particular characteristic of the invention, the grid is metallic.

[0018] According to another particular characteristic of the invention, the grid is movable on the surface of the radome.

[0019] This allows the reflectivity of the grid to be varied in order to vary the directivity of the antenna.

[0020] According to another particular characteristic of the invention, the radome is made of silica-silica. According to another particular characteristic of the invention, the air gap has a height between the grid and the substrate equal to half the wavelength corresponding to the first frequency.

[0021] According to another particular characteristic of the invention, the radiating element is a radiating patch.

[0022] It is also possible to replace the radiating patch with a horn if you want the antenna to be more directional. Since the patch is smaller than a horn, if you want to prioritize the antenna's compactness over its directivity, you will prefer to choose the patch as the radiating element.

[0023] According to another particular characteristic of the invention, the thickness of the radome is variable.

[0024] By varying the thickness of the radome, its geometry can be adapted above the grid to depoint the antenna beam so that its main lobe is oriented laterally. This allows for Synthetic Aperture Radar (SAR) or radio altimeter or electromagnetic seeker applications to aim upstream of the antenna beam trajectory before arriving at the target area.

[0025] Another object of the invention is a vehicle equipped with at least one antenna according to the invention.

[0026] According to a particular characteristic of the invention, the vehicle is a space vehicle.

[0027] According to another particular characteristic of the invention, the vehicle is a space launcher, an exploration vehicle or a satellite.

[0028] Brief description of the drawings

[0029] Other characteristics and advantages of the present invention will emerge from the description given below, with reference to the appended drawings which illustrate exemplary embodiments thereof which are not in any limiting nature. [Fig. 1] Figure 1 represents, schematically and partially, an antenna according to one embodiment of the invention.

[0030] [Fig. 2A] Figure 2A represents, schematically and partially, a first example of the production of the grid.

[0031] [Fig. 2B] Figure 2B represents, schematically and partially, a second example of the grid's construction.

[0032] [Fig. 2C] Figure 2C represents, schematically and partially, a third example of the grid's construction.

[0033] [Fig. 3] Figure 3 schematically represents the directivity of the antenna of Figure 1 as a function of the reflectivity of the grid.

[0034] [Fig. 4] Figure 4 shows sections of an antenna according to the invention.

[0035] [Fig. 5A] Figure 5A shows, schematically and partially, an antenna according to another embodiment of the invention.

[0036] [Fig. 5B] Figure 5B represents, schematically and partially, an antenna according to another embodiment of the invention.

[0037] [Fig. 5C] Figure 5C shows, schematically and partially, an antenna according to another embodiment of the invention.

[0038] Description of the embodiments

[0039] Figure 1 represents an antenna 100 according to a first embodiment of the invention.

[0040] The antenna 100 comprises an enclosure 110 comprising a lower surface 111 and side edges 112. The enclosure 110 is closed by a cover 140.

[0041] The enclosure 110 is metallic and / or made of a perfect electrically conductive material.

[0042] The cover 140 forms a partially reflective outer surface. More particularly, the lower the reflectivity coefficient, the lower its gain.

[0043] The cover 140 is for example made of conductive material in metallic form or in the form of a printed patch. The antenna 100 also comprises a substrate 120 placed at the bottom of the enclosure 110 on its lower surface 111 on which a radiating element 130 is placed, and a radome 150 placed in the enclosure 110 facing the substrate 120 and the radiating element 130. A grid 160 is placed on a surface of the radome 150 facing the substrate 120 and the radiating element 130.

[0044] The radiating element 130 is configured to emit a signal at at least a first frequency f.

[0045] 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.

[0046] An air blade 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 blade 170 is for example equal to λ / 2 with λ the wavelength corresponding to the emission frequency f of the radiating element 130.

[0047] 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.

[0048] The antenna 100, and more particularly the enclosure 110, is for example of circular shape. The circular shape simplifies the holding of the joint between the antenna 100 and the envelope of the space vehicle carrying the antenna 100 under re-entry flux. However, other shapes are possible. The antenna 100, and in particular its enclosure 110, may for example be of square or rectangular shape, which makes it possible to adjust the gain of the antenna 100 in several directions independently, for example by having an antenna 100 that is very open in one plane and very directional in another plane.

[0049] The grid 160 may have different types of patterns. The patterns may be regular or irregular, and their dimensions may also vary. These patterns are chosen so as to control the reflectivity of the grid 160. These patterns also make it possible to control the shape of the lobe of the antenna 100 as well as its polarization. In addition, the dimensions of these patterns are linked to the wavelength chosen for the antenna 100 and may therefore vary between two antennas of different frequencies having similar characteristics at the lobe and / or polarization level.

[0050] Figures 2A, 2B and 2C give examples of the production of patterns for the grid 160. In these three figures, the radome 250 is shown in dotted lines in front of the grid 260A (figure 2A), or 260B (figure 2B) or 260C (figure 2C).

[0051] In Figure 2A, the gate 260A is formed from a succession of metallic strips 270, 271, 272 present on a semiconductor 280. For example, the strips 270, 271, 272 have a thickness e of 3.4 mm and are spaced apart by a width I of 4.3 mm.

[0052] In Figure 2B, the grid 260B is formed from a succession of strips 201, 202, 203 having a thickness eb of 1 mm and a height hb of 2 mm and are spaced apart by a width Ib of 5.5 mm.

[0053] In Figure 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 apart by the same distance of. For example, the holes 210, 211, 212 have a diameter DC of 6.5 mm and their centers are spaced apart by de = 1 mm.

[0054] The gate 160 (or the gates 260A, 260B, 260C of FIGS. 2A, 2B and 2C) may be formed by a semiconductor whose metallization produces the patterns of the gate 160, or it may be conductive, for example metallic, and machined according to the patterns of the gate 160.

[0055] Figure 3 schematically represents the directivity of the antenna 100 as a function of the reflectivity p of the grid 160. The more reflective the grid 160 is, the more the directivity of the antenna 100 increases. However, by increasing the directivity of the antenna 100, its bandwidth decreases. The pattern of the grid 160 is therefore chosen so as to find a compromise between directivity and bandwidth according to the application.

[0056] Figure 4 shows 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. In comparison with an antenna of the prior art comprising, like the antenna 400, a radiating element capable of emitting an electromagnetic signal at a frequency of 13.5 GHz, the antenna of the prior art has a mass of a few kilograms, whereas the antenna 400 has a mass of approximately 0.7 kg.

[0057] The antenna of the prior art has a height of about a hundred millimeters for a total diameter of a few hundred millimeters; whereas the antenna 400 has a height h400 of 63 mm for 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 fixing elements 435 of the antenna 400 on a vehicle.

[0058] In addition to being more compact and lighter, the 400 antenna has a gain of almost 4 dB higher than the prior art antenna. This makes it possible to increase the range of a transmission system requiring this type of antenna by a factor of 2.5 to 3.

[0059] Figures 5A, 5B and 5C represent, schematically and partially, an antenna 500 according to a second (figure 5A), a third (figure 5B) and a fourth (figure 5C) embodiment of the invention.

[0060] 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 cover 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 makes it possible to protect the antenna from temperatures above 1000°C, or even above 2500°C.

[0061] The antenna 500 also comprises a grid 560 placed on a surface of the radome opposite the radiating element 530 so as to form an air gap 570 between the grid 560 and the substrate 520.

[0062] As indicated previously, the grid 560 has a pattern whose geometry and dimensions can be adapted to play on its reflectivity and obtain a more or less directional antenna. In these embodiments, the thickness of the radome is variable and between the thicknesses E1 and E2. This makes it possible to depoint the beam of the antenna 500 relative to the beam of the antenna 100 of FIG. 1 so that the main lobe is oriented laterally. In other words, the electromagnetic beam emitted by the antenna 500 can be angularly deflected thanks to this variable thickness. This makes it possible to aim the trajectory of the beam upstream before arriving at the reception zone of the signal emitted by the antenna.

[0063] For example, if the difference between E1 and E2 is 10 mm, the beam can be shifted by 5° while still having a loss of 1 dB in the signal emitted by antenna 500.

[0064] In Figures 5A, 5B and 5C, the grid 560 and the substrate 520 are parallel to each other. In Figure 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 a inclined bottom (Figure 5B).

[0065] It is also possible to have a movable grid in order to obtain a dual-mode antenna. Thus, according to a first mode of operation, the grid can be placed over the entire surface of the radome opposite the radiating element. In this first mode, the grid is then very reflective and therefore the directivity of the antenna is improved.

[0066] According to a second mode of operation, the grid can be moved in order to reduce the reflectivity of the grid to reduce the directivity of the antenna and have an omnidirectional antenna. The interest of these two modes of operation of the grid is to be able, for example, to search for a target in the second mode then carry out the emission of the signal towards the target in the first mode. The antenna is then adaptable according to the flight phases of the vehicle.

Claims

Claims

1. 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 cover (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 facing the substrate and capable of protecting the antenna from temperatures above 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 a first frequency (f), and a grid (160, 260A, 260B, 260C, 560) placed on a surface of the radome facing the radiating element so as to form an air gap (170, 570) between the grid and the substrate.

2. An antenna according to claim 1, wherein the grid is metallic.

3. An antenna according to any one of claims 1 or 2, wherein the radome is made of silica-silica.

4. Antenna according to any one of claims 1 to 3, in which the air blade has a height (H) between the grid and the substrate equal to half the wavelength corresponding to the first frequency (f).

5. An antenna according to any one of claims 1 to 4, wherein the radiating element is a radiating patch.

6. Antenna (500) according to any one of claims 1 to 5, wherein the thickness (E1, E2) of the radome (550) is variable.

7. Vehicle equipped with at least one antenna according to any one of claims 1 to 6.

8. A vehicle according to claim 7, wherein the vehicle is a space vehicle.

9. A vehicle according to claim 8, wherein the vehicle is a space launcher, an exploration vehicle or a satellite.

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