Multiband antenna

Abstract

An antenna (100) comprising at least a first resonant cavity (110) and a second resonant cavity (120), each resonant cavity (110, 120) being closed off by a base (112, 122) at one end and comprising a radiating element (111, 121) superimposed on the base of the resonant cavity, the radiating element (111) of the first cavity (110) being able to emit a signal in a first frequency band and the radiating element (121) of the second cavity (120) being able to emit a signal in a second frequency band separate from the first frequency band, characterized in that a first distance between the base (112) and the radiating element (111) of the first cavity (110) is different from a second distance between the base (122) and the radiating element (121) of the second cavity (120).

Description

Technical Field

[0001] The present invention relates to an antenna capable of transmitting in several frequency bands with wide coverage and allowing on its own to carry out several distinct communication functions. Prior art

[0002] Spacecraft are equipped with antennas that ensure communication between these vehicles and ground stations during flight phases. These antennas are used in particular for telemetry, trajectory, or the satellite positioning system ("Global Navigation Satellite System", GNSS).

[0003] Achieving these functions may require the use of a complex system with several antennas, each associated with a particular function.

[0004] In some systems such as base stations, the antennas are multi-band multi-port with a significant need for decoupling between bands. These antennas directly perform a filtering function allowing simultaneous transmission and reception at different frequencies with a low level of interference.

[0005] In systems where platforms are mobile relative to each other, such as trains, launchers, satellites or even aircraft, i.e. systems in which the wireless link can be difficult to maintain, circularly polarized hemispherical coverage antennas may be necessary to maintain the link regardless of the orientation and altitude of the platform. In this context, the needs for hemispherical coverage and circular polarization are added to the multi-band requirement.

[0006] One solution to this need is to use a single-port ultra-wideband or multi-band circularly polarized antenna as in the paper "Single-Feed Ultra-Wideband Circularly Polarized Antenna with Enhanced Front-to-back Ratio" by L. Zhang et al., published in 2016 in IEEE Trans. Antennas Propagation , capable of covering all useful bands and inserting a multiplexing function to separate the communication channels. However, broadband and multi-band antennas have unstable radiation patterns that vary with frequency and / or have lower adaptation levels. Indeed, an increase in gain and side lobes can appear with increasing frequency, which is incompatible with a strict need for hemispherical coverage.

[0007] Base stations have individual radiating elements sized for each frequency band that do not have this problem of radiation pattern instability. Furthermore, the arrangements incorporated, for example in the article "A Dual-broadband, Dual-polarized Base Station Antenna for 2G / 3G / 4G Applications" by H. Huang et al. published in 2017 in IEEE Antennas and Wireless Propagation Letters , interlaced, for example in the article "Suppression of Cross-Band Scattering in Multiband Antenna Arrays" by H.H. Sun et al. published in 2019 in IEEE Trans. Antennas Propagation , and superimposed, for example in the article “Decoupling and Low-Profile Design of Dual-band Dual-polarized Base Station Antennas Using Frequency-selective Surface” by Y. Zhu et al. published in 2019 in IEEE Trans. Antennas Propagation ,The different radiating elements of the base stations allow their proper operation by optimizing the total occupied space. However, these solutions are often limited to two or three frequency bands, because the arrangement for four bands is complex. In addition, the hemispherical coverage rate remains limited and the coupling between the elements can be high. Finally, wave diffraction effects between the different radiating elements are present, which impacts the quality of the circular polarization and the coverage rate.

[0008] US 5,548,299 and EP 0,556,941 disclose antennas comprising several resonant cavities nested together.

[0009] It is therefore desirable to have an antenna capable of transmitting in several distinct frequency bands for the performance of several communication functions while maintaining limited bulk, good hemispherical coverage and circular polarization in all the antenna's frequency bands. Statement of the invention

[0010] The present invention relates to an antenna according to claim 1.

[0011] This invention makes it possible to produce a simple antenna architecture capable of accommodating a multitude of radiating elements operating at different frequencies. Thanks to this architecture, the mutual interaction between these elements is reduced. Each radiating element can therefore function correctly and can therefore produce a quality polarization and hemispherical radiation pattern.

[0012] The invention also provides optimization degrees of freedom that allow the initial dimensions of the largest radiating element and its resonant cavity to be reduced.

[0013] According to the invention, the antenna also comprises a third resonant cavity closed by a bottom at one end and comprising a radiating element superimposed on the bottom of the third resonant cavity, the radiating element of the third cavity being capable of emitting a signal in a third frequency band separate from the first and second frequency bands and a third distance between the bottom and the radiating element of the third cavity being different at least from the first or the second distance.

[0014] According to another particular characteristic of the invention, the antenna also comprises a fourth resonant cavity closed by a bottom at one end and comprising a radiating element superimposed on the bottom of the fourth resonant cavity, the radiating element of the fourth cavity being capable of emitting a signal in a fourth frequency band separate from the first, second and third frequency bands and a fourth distance between the bottom and the radiating element of the fourth cavity being different at least from the first, second or third distance.

[0015] The cavities within the antenna are distinct cavities that define distinct background areas delimited by the walls of these cavities.

[0016] By having three or four cavities, a tri- or quad-band antenna can be made.

[0017] According to another particular characteristic of the invention, a wall of the first cavity and a wall of the second cavity have a common portion, the walls being distinct from the bottoms of the cavities.

[0018] Having a common portion allows the walls of the first and second cavities to be merged on this common portion.

[0019] According to another particular characteristic of the invention, the first cavity and the second cavity are tangent and their walls have a common generator.

[0020] According to another particular characteristic of the invention, at least a part of the second cavity is located inside the first cavity.

[0021] According to one embodiment of the invention, the radiating elements of the resonant cavities are located in the same plane.

[0022] According to another embodiment of the invention, the bottoms of the resonant cavities are located in the same plane.

[0023] According to a particular characteristic of the invention, the resonant cavities are single-mode or predominantly single-mode in the frequency bands of the associated radiating elements.

[0024] By "single-mode", it is meant that only the fundamental mode of the resonant cavity considered can propagate. By "mostly single-mode", it is meant that the resonant cavity considered is single-mode over at least 50%, for example at least 75%, of the frequency band considered. In this case, the resonant cavity may not be single-mode on at least one end of the frequency band, it may be modeless or dual-mode on this end.

[0025] Having single-mode or predominantly single-mode cavities in the frequency bands of the associated radiating elements makes it possible to minimize the dimensions of the antenna while maintaining optimal operation of the radiating elements.

[0026] According to another particular characteristic of the invention, in the case of an antenna comprising at least three resonant cavities as described previously, the distinct resonant cavities of the first cavity are distributed uniformly along a circumferential direction of the first resonant cavity.

[0027] This makes it possible to limit the interactions between the radiating elements of the different resonant cavities.

[0028] According to another particular characteristic of the invention, the resonant cavities have an oval, circular, square or octagonal section.

[0029] According to another particular characteristic of the invention, at least one of the resonant cavities comprises an iris-based filtering structure, absorbers or openings on its wall at an end opposite the bottom of the resonant cavity.

[0030] Another object of the invention is a vehicle equipped with at least one antenna according to the invention.

[0031] According to a particular characteristic of the invention, the vehicle is a space vehicle.

[0032] According to another particular characteristic of the invention, the vehicle is a space launcher, an exploration vehicle or a satellite.

[0033] This makes it possible to obtain a vehicle equipped with a simple antenna architecture that can accommodate a multitude of radiating elements operating at different frequencies with a high-quality polarization and hemispherical radiation pattern, for example with a 90% antenna architecture coverage rate evaluated at -7 dBic, the antenna gain being evaluated taking into account circular polarization. This coverage rate can thus, for example, meet the typical needs of a GPS geolocation system.

[0034] Furthermore, in the base stations of the prior art, diffraction phenomena from one radiating element to another radiating element cause reversals of the direction of rotation of the polarization, that is to say that the circular polarization reverses in a given direction, for example going from a right rotation to a left rotation. Thus, if the gain in right circular polarization is evaluated, it is observed that the gain drops abruptly in certain places, which creates holes in the radiation pattern causing the hemispherical coverage rate to drop drastically. The invention makes it possible to avoid this problem, because no reversal of the direction of rotation of the polarization appears over the entire upper hemisphere. This therefore makes it possible to ensure quality circular polarization over the entire upper hemisphere. Brief description of the drawings

[0035] 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 limiting in nature. [ Fig. 1 ] There figure 1 represents, schematically and partially, an antenna according to one embodiment of the invention. Fig. 2 ] There figure 2 represents, schematically and partially, a section of the figure 1 . [ Fig. 3 ] There figure 3 represents, schematically and partially, an antenna according to another embodiment of the invention. Fig. 4 ] There figure 4 represents, schematically and partially, an antenna according to another embodiment of the invention. Description of the embodiments

[0036] Throughout the description, the wall of a resonant cavity is a wall of the cavity distinct from its bottom which extends around the axis of the height of the antenna. The circumference of a cavity is also called the perimeter of this cavity.

[0037] THE figures 1 et 2 represent, schematically and partially, an antenna 100 according to a first embodiment of the invention, the figure 2 being a sectional view of the antenna 100.

[0038] The antenna 100 comprises four resonant cavities 110, 120, 130 and 140, and extends in height along a Z axis. The four cavities 110, 120, 130 and 140 are distinct cavities which define distinct bottom zones delimited by the walls of the different cavities.

[0039] The first resonant cavity 110 is closed by a bottom 112 at one end and comprises a radiating element 111 superimposed on its bottom 112 along the Z axis of the height of the antenna 100. The radiating element 111 is capable of emitting a signal in a first frequency band.

[0040] The second resonant cavity 120 is closed by a bottom 122 at one end and comprises a radiating element 121 superimposed on its bottom 122 along the Z axis of the height of the antenna 100. The radiating element 121 is capable of emitting a signal in a second frequency band separate from the first frequency band.

[0041] The distance h2 between the bottom 122 and the radiating element 121 of the second cavity 120 is different from the distance h1 between the bottom 112 and the radiating element 111 of the first cavity 110, the distances h1 and h2 being measured along the Z axis of the height of the antenna.

[0042] The second cavity 120 is located at least partially inside the first cavity 110. In addition, the wall 125 of the second cavity 120 shares two common portions 124 with the wall 115 of the first cavity 110.

[0043] The third resonant cavity 130 is closed by a bottom 132 at one end and comprises a radiating element 131 superimposed on its bottom 132 along the Z axis of the height of the antenna 100. The radiating element 131 is capable of emitting a signal in a third frequency band separate from the first and second frequency bands.

[0044] The distance h3 between the bottom 132 and the radiating element 131 of the third cavity 130 is different by at least the distance h1 and / or the distance h2, the distance h3 being measured along the Z axis of the height of the antenna.

[0045] The fourth resonant cavity 140 is closed by a bottom 142 at one end and comprises a radiating element 141 superimposed on its bottom 142 along the Z axis of the height of the antenna 100. The radiating element 141 is capable of emitting a signal in a fourth frequency band separate from the first, second and third frequency bands.

[0046] Since the four cavities are separate cavities, their radiating elements do not overlap. Furthermore, in order to maximize the performance of the radiating elements while minimizing the overall size of the antenna, the radiating elements of one cavity and another cavity with a smaller diameter are separated by a distance Dmin equal to the difference between the radius of the cavity and the radius of the other cavity with a smaller diameter, the distance between the radiating elements of the two cavities being measured along an axis perpendicular to the Z axis of the antenna height. More generally, the greater the distance between two radiating elements of two different cavities, the better the performance, in terms of coupling and diffraction.

[0047] The distance h4 between the bottom 142 and the radiating element 141 of the fourth cavity 140 is different by at least the distance h1, the distance h2 and / or the distance h3, the distance h4 being measured along the Z axis of the height of the antenna. In particular, in this embodiment, the distances h1, h2, h3 and h4 are all different. Generally, the distance h between the bottom and the radiating element of the cavities depends on the transmission frequency of the radiating element, thus the more the distance h increases, the more the transmission frequency decreases. However, the distances h between the bottom and the radiating element of the cavities also depend on the type of radiating element.For example, in the case of resonant cavities filled with vacuum and / or dielectric material and comprising a dipole as a radiating element, the distance h between the bottom of the cavity and the dipole will be close to λ g / 4 with λ g the effective wavelength of the central frequency of the emission frequency band of the dipole.

[0048] The third 130 and fourth 140 resonant cavities are located inside the first cavity 110, for example entirely inside the first cavity 110 as illustrated in the figure 1 The wall 135 of the third cavity 130 and the wall 145 of the fourth cavity 140 share a common portion 134 for the third cavity 130 and 144 for the fourth cavity 140 with the wall 115 of the first cavity 110. On the common portion 134, the walls 115 and 135 are merged and on the common portion 144, the walls 115 and 145 are merged.

[0049] The radiating elements 111, 121, 131 and 141 can be directly powered by a coaxial cable which passes through the corresponding cavity from its bottom to the radiating element, such as for example the cable 123 shown for the element 121 of the second cavity 120.

[0050] In this embodiment, the radiating elements 111, 121, 131 and 141 are located in the same plane, but it is also possible to have the radiating elements in different planes with bottoms 112, 122, 132, 142 also in different planes or with bottoms 112, 122, 132, 142 located in the same plane.

[0051] In this embodiment, the four frequency bands of the different radiating elements 111, 121, 131 and 141 are disjoint. The four frequency bands are for example the UHF band between 432 MHz and 434 MHz, the GNSS band between 1164 MHz and 1591 MHz, the S band between 2200 MHz and 2290 MHz and the C band between 5400 MHz and 5900 MHz. However, it is also possible that only the first two frequency bands, for example those of the radiating elements 111 and 121, are disjoint and that the other two frequency bands, i.e. those of the radiating elements 131 and 141, share common frequencies with the first two frequency bands.

[0052] There figure 3 represents, schematically and partially, an antenna 300 according to another embodiment of the invention.

[0053] The antenna 300 comprises three resonant cavities 310, 320 and 330 and extends in height along the Z axis. Each resonant cavity 310, 320, 330 is closed at one end by a bottom 312, 322, 332 and comprises a radiating element 311, 321, 331. According to the invention, the radiating elements of each cavity are superimposed on the bottom of the cavity along the Z axis of the height of the antenna 300. In addition, the radiating element 311 of the first cavity 310 is capable of emitting a signal in a first frequency band, the radiating element 321 of the second cavity 320 is capable of emitting a signal in a second frequency band separate from the first frequency band, and the radiating element 331 of the third cavity 330 is capable of emitting a signal in a third frequency band which may be separate from the first and second frequency bands or include frequencies in common with one of the first two bands.

[0054] In addition, the distance between the bottom 312 and the radiating element 311 of the first cavity 310 is different by at least the distance between the bottom 322 and the radiating element 321 of the second cavity 320 or the distance between the bottom 332 and the radiating element 331 of the third cavity 330. Similarly, the distance between the bottom 322 and the radiating element 321 of the second cavity 320 is different by at least the distance between the bottom 312 and the radiating element 311 of the first cavity 310 or the distance between the bottom 332 and the radiating element 331 of the third cavity 330.

[0055] The cavity 320 is tangent to the first cavity 310 outside the cavity 310. The walls of the two cavities 310 and 320 have a common portion, and more particularly, in the illustrated embodiment, the cavities 310 and 320 have a common generator 324. The walls of the cavities 310 and 320 are thus merged along this common generator 324. The fact of having the cavity 320 outside the first cavity and sharing a common generator makes it possible to limit the interactions between the radiating elements of these two cavities.

[0056] Cavity 330 is also tangent to first cavity 310 but is located inside cavity 310. Like cavity 320, cavity 330 has a common generator 334 with cavity 310.

[0057] There figure 4 represents, schematically and partially, an antenna 400 according to another embodiment of the invention.

[0058] The antenna 400 comprises three resonant cavities 410, 420 and 430. Each resonant cavity 410, 420, 430 is closed at one end by a bottom 412, 422, 432 and comprises a radiating element 411, 421, 431. According to the invention, the radiating elements of each cavity are superimposed on the bottom of the cavity along the Z axis of the height of the antenna 400. In addition, the radiating element 411 of the first cavity 410 is capable of emitting a signal in a first frequency band, and the radiating element 421 of the second cavity 420 is capable of emitting a signal in a second frequency band separate from the first frequency band. The radiating element 431 of the third cavity 430 is capable of emitting a signal in a third frequency band which may be separate from the first and second frequency bands or which may comprise frequencies common to one of the first two bands.

[0059] In addition, the distance between the bottom 412 and the radiating element 411 of the first cavity 410 is different by at least the distance between the bottom 422 and the radiating element 421 of the second cavity 420 or the distance between the bottom 432 and the radiating element 431 of the third cavity 430. Similarly, the distance between the bottom 422 and the radiating element 421 of the second cavity 420 is different by at least the distance between the bottom 412 and the radiating element 411 of the first cavity 410 or the distance between the bottom 432 and the radiating element 431 of the third cavity 430.

[0060] The second cavity 420 is located partially inside the first cavity 410, while the third cavity 430 is located inside the first cavity 410.

[0061] The wall 425 of the second cavity 420 comprises openings over its entire circumference on the end not closed by the bottom 422. In other words, the edge of the wall 425 has a crenellated shape thus defining a plurality of openings. This makes it possible to obtain improved gain at low elevation angles in the high frequencies of the second frequency band while limiting the drop in gain in the low frequencies of the second frequency band.

[0062] The wall 435 of the third cavity 430 includes openings on a portion of its circumference on the end not closed by the bottom 432. This makes it possible to obtain improved gain at low elevation angles in the high frequencies of the third frequency band.

[0063] In all embodiments of the invention, the resonant cavities are presented with a circular section, however these cavities can also have any section, for example a square, oval, hexagonal section, etc.

[0064] Regardless of the embodiment of the invention, the resonant cavities may be double cavities as described in French patent application FR 20 09240, that is to say that the waveguide forming the double cavity comprises two distinct resonant cavities, one of which is located inside the other and these cavities are single-mode or predominantly single-mode in a separate frequency band. The radiating elements associated with the double cavities are dual-band elements. This makes it possible to obtain improved hemispherical coverage in the high band associated with the double cavity and its radiating element. In addition, if the external cavity also comprises openings on its wall, it is possible to accentuate this effect without impacting the low emission frequency band.

[0065] Regardless of the embodiment of the invention, the resonant cavities may be single-mode or predominantly single-mode in the frequency band of the radiating element associated with the cavity. This makes it possible to minimize the dimensions of the antenna while maintaining optimal operation of the radiating elements.

[0066] Regardless of the embodiment of the invention, the radiating elements of the resonant cavities may be of the patch, slot or dipole type. They may be single-band or multi-band. The radiating elements may also be printed on a substrate on one or more layers and / or be dual, single or circularly polarized. When the radiating elements are printed on a substrate, the substrate may close the end of the cavity opposite that closed by the bottom of the cavity. The radiating elements may also be volumetric, such as for example metal dipoles which may be produced for example by three-dimensional printing in metal and suspended in the resonant cavity.

[0067] Regardless of the embodiment of the invention, the resonant cavities may be filled with a dielectric material, such as dielectric foam. The dielectric material may be of low permittivity or high permittivity. This makes it possible to reduce the dimensions of the resonant cavities by a factor F. F = 1 / ε r with ε r the permittivity of the dielectric material.

[0068] Whatever the embodiment of the invention, the different resonant cavities of the first cavity are distributed over the circumference of the first cavity with a minimum angular deviation θ min = 360 x (1 - 0.25) / n, and a maximum angular deviation θ max = 360 x (1 + 0.25) / n between two consecutive cavities, with n the number of different resonant cavities of the first cavity. Thus, for three resonant cavities distributed over the circumference of the first cavity, the angular deviation Δθ between two consecutive cavities is 120° ± 30°. For two resonant cavities distributed over the circumference of the first cavity, the angular deviation Δθ between two consecutive cavities is 180° ± 45°.

[0069] Regardless of the embodiment of the invention, the different resonant cavities of the first cavity can be distributed uniformly around the circumference of the first cavity.

[0070] Whatever the embodiment of the invention, all the resonant cavities can have a waveguide delimiting them of the same height or of different heights along the Z axis of the height of the antenna.

[0071] Whatever the embodiment of the invention, in the case where there are at least three resonant cavities, two of them may have an equal distance between their bottom and their radiating element.

[0072] Whatever the embodiment of the invention, the cavities can be filled with a dielectric material and their distance between their bottom and their radiating element is between λ g / 8 and λ g / 2 with λ g the wavelength guided in the dielectric material.

[0073] The expression "between ... and ..." must be understood as including the limits.

Claims

1. An antenna (100, 300, 400) comprising at least one first resonant cavity (110, 310, 410) and a second resonant cavity (120, 320, 420), each resonant cavity (110, 120, 310, 320, 420) being closed by a base (112, 122, 312, 322, 422) at one end and comprising a radiating element (111, 121, 311, 321, 421) superimposed on the base of the resonant cavity, the radiating element (111, 311, 411) of the first cavity (110, 310, 410) being able to transmit a signal on a first frequency band and the radiating element (121, 321, 421) of the second cavity (120, 320, 420) being able to transmit a signal on a second frequency band separate from the first frequency band, a first distance (h1) between the base (112) and the radiating element (111) of the first cavity (110) differs from a second distance (h2) between the base (122) and the radiating element (121) of the second cavity (120), the antenna also comprising a third resonant cavity (130, 330, 430) closed by a base (132, 332, 432) at one end and comprising a radiating element (131, 331, 431) superimposed on the base of the third resonant cavity, the radiating element of the third cavity being able to transmit a signal on a third frequency band separate from the first and second frequency bands, and a third distance (h3) between the base (132) and the radiating element (131) of the third cavity (130) differing at least from the first (h1) or second (h2) distance, characterized in that the different resonant cavities of the first cavity being distributed over the circumference of the first cavity with minimum angular spacing θmin = 360 x (1 - 0.25) / n, and maximum angular spacing θmax = 360 x (1 + 0.25) / n between two consecutive cavities, with n the number of different resonant cavities of the first cavity.

2. The antenna (100) according to claim 1 also comprising a fourth resonant cavity (140) closed by a base (142) at one end and comprising a radiating element (141) superimposed on the base of the fourth resonant cavity, the radiating element of the fourth cavity being able to transmit a signal on a fourth frequency band separate from the first, second and third frequency bands, and a fourth distance (h4) between the base (142) and the radiating element (141) of the fourth cavity (140) differing at least from the first (h1), second (h2) or third (h3) distance.

3. The antenna according to any of claims 1 or 2, wherein one wall (115) of the first cavity (110, 310) and one wall (125) of the second cavity (120, 320) have a common portion (124, 324), the walls being different from the bases of the cavities.

4. The antenna according to claim 3, wherein at least one portion of the second cavity (120, 330, 430) is positioned inside the first cavity (110, 310, 410).

5. The antenna according to any of claims 1 to 4, wherein the radiating elements (111, 121, 131, 141) of the resonant cavities (110, 120, 130, 140) are positioned on one same plane.

6. The antenna according to any of claims 1 to 4, wherein the bases of the resonant cavities are positioned on one same plane.

7. The antenna according to any of claims 1 to 6, wherein the resonant cavities are configured to be single-mode or mostly single-mode on the frequency bands of the associated radiating elements.

8. The antenna according to any of claims 2 to 7, wherein the resonant cavities other than the first cavity are uniformly distributed along a circumferential direction of the first resonant cavity.

9. A vehicle equipped with at least one antenna according to any of claims 1 to 8.

10. The vehicle according to claim 9, wherein the vehicle is a space vehicle.

11. The vehicle according to claim 10, wherein the vehicle is a space launcher, an exploration vehicle, or a satellite.

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