DUAL-POLARIZED ANTENNA ARRAY

Abstract

An antenna array includes at least two antennas with dual polarization, each antenna including: at least one first port intended for a first signal with a first polarization; at least one second port intended for a second signal with a second polarization; a polarizer including a septum for combining the signal on the first port with the signal on the second port; a polarization-preserving evanescent filter, one end of which is directly coupled to the polarizer and the other end is directly coupled to the ether. The evanescent filter includes an internal channel with at least one internal face provided with protuberances to match the impedance of the antenna to that of the ether.

Claims

1. Antenna array produced in a monolithic way, comprising at least two antennas with dual polarization, each antenna comprising: at least one first port intended for a first signal with a first polarization; at least one second port intended for a second signal with a second polarization; a polarizer, comprising a septum for combining the signal on the at least one first port with the signal on the at least one second port; and a polarization-preserving evanescent filter, one end of which is directly coupled to the polarizer and the other end is directly coupled to the ether, that is the free space outside the antenna, to serve as radiating element of the antenna, said evanescent filter comprising an internal channel with at least one internal face provided with protuberances to match the impedance of the antenna to that of the ether.

2. Antenna array according to claim 1, wherein the diameter of the internal channel of each antenna is smaller than the nominal wavelength of the signal for which the antenna is designed.

3. Antenna array according to claim 1, wherein the septum does not extend until the end of the antenna on the ether side.

4. Antenna array according to claim 1, wherein said polarizer is provided with longitudinal ridges in addition to said septum.

5. Antenna array according to claim 4, wherein the longitudinal ridges do not extend until the end of each respective antenna on the ether side.

6. Antenna array according to claim 1, wherein said evanescent filter is provided with a plurality of successive protuberances along longitudinal lines.

7. Antenna array according to claim 6, wherein the protuberances do not extend until the end of each respective antenna on the ether side.

8. Antenna array according to claim 7, wherein said protuberances are arranged along 3 or 4 longitudinal lines.

9. Antenna array according to claim 4, wherein said longitudinal lines are in the extension of said longitudinal ridges.

10. Antenna array according to claim 1, wherein the diameter of the second end of the evanescent filter of each respective antenna is smaller than the nominal half-wavelength of said signals.

11. (canceled)

12. Antenna array according to claim 1, produced by 3D printing of at least two metal or polymer cores, then depositing a conductive layer at least on the internal faces of each antenna.

13. Antenna array according to claim 12, wherein said protuberances each comprises, in the direction of signal transmission, a first and a second surface, the first surface, referred to as the inclined surface, being inclined with respect to the second surface.

14. Antenna array according to claim 13, wherein said inclined surface of each protuberance is oblique with respect to a plane perpendicular to the longitudinal axis of the antenna.

15. Antenna array according to claim 13, wherein the inclined surface of each protuberance forms an angle of between 20 and 80, preferably between 20 and 40, with respect to said internal face.

16. Antenna array according to claim 1, wherein the internal channel of each antenna has a circular, square, rectangular, hexagonal or octagonal cross-section at its longitudinal axis, the protuberances being arranged along three faces of the internal channel.

17. Antenna array according to claim 1, wherein the internal channel of each antenna has a circular cross-section orthogonal to its longitudinal axis, the protuberances being arranged along three lines spaced 120 apart.

18. Antenna array according to claim 1, wherein the internal channel of each antenna has a cross-section orthogonal to its longitudinal axis invariant to rotation by 120 about said longitudinal axis, the protuberances being spaced apart by 120.

19. Antenna array according to claim 1, the periodicity of at least two antennas being smaller than or equal to 80% of the nominal wavelength of said signals.

20. Antenna array according to claim 4, the longitudinal ridges being spaced 120 apart.

Description

BRIEF DESCRIPTION OF FIGURES

[0061] Examples of implementation of the invention are shown in the description illustrated by the appended figures in which:

[0062] FIG. 1 shows a cross-section of a dual-polarized antenna without an evanescent filter;

[0063] FIG. 2 shows a perspective view of an antenna with dual polarization and including an evanescent filter;

[0064] FIG. 3 shows a cross-sectional view of the antenna shown in FIG. 2;

[0065] FIG. 4 shows a perspective view of another variant of an antenna with dual polarization;

EXAMPLE(S) OF EMBODIMENT OF THE INVENTION

[0066] FIG. 1 schematically illustrates a dual-polarized antenna 1 of an antenna array seen in longitudinal cross-section. The antenna comprises a 3D-printed core 15, at least the internal faces of which are coated with metallization 16. The core can be made of metal or insulating material, such as polymer or ceramic. Metallization 16 can also be provided on the antenna's external faces.

[0067] As the antennas of the array of the present invention are essentially identical, the term the antenna is to be understood in the sense of each antenna of the antenna array throughout the present description.

[0068] The antenna is provided with a longitudinal channel 11 opening onto an aperture 10 at one end of the antenna. The cross-section of channel 11 (disregarding any ridges, protuberances and the septum) may be for example square, rectangular, round, oval, ellipsoidal, hexagonal, octagonal, pentagonal, etc.

[0069] Channel 11 is divided by a septum 2 into two volumes 12 and 13. The first volume 12 opens onto a first port 17 intended to receive a first signal P1 with a first polarization. The second volume 13 opens onto a second port 18 intended to receive a second signal P2 with a second polarization. The polarizations can be circular polarizations. The second polarization may be orthogonal to the first polarization. The first signal may be an LHCP signal. The second signal can be an RHCP signal. The two signals P1 and P2 combine at the antenna output to form a single dual-polarized signal transmitted into the ether.

[0070] The term ether is used in the context of this application to designate the free space outside the antenna, and in which the signals emitted by the antenna propagate. In particular, this means that no device is intended to be coupled to the end of the antenna on the ether side. Hence, the ether may correspond, for example, to space itself when the antenna is mounted on an orbiting satellite, but more generally, the ether refers to any free space outside the antenna. The ether has its own impedance, which depends on the characteristics of the space surrounding the antenna.

[0071] One problem related to this arrangement concerns the reflection of part of the transmitted signal. As shown with arrows in FIG. 1, only part P.sub.11 of the first signal P1 is diffused towards the ether; another part P.sub.12 is reflected at the antenna output and returns to aperture 12, or even aperture 13. The result is a reduction in the power of the signal P11 actually transmitted, and a disturbance of the signals in channel 11.

[0072] The problem is amplified if the antenna is subwavelength, i.e. if the diameter of aperture 10 at the output of antenna 1 is less than half the wavelength of the nominal signal to be transmitted. The problem is also amplified if the antenna impedance does not match the impedance of the transmission channel through the ether.

[0073] The antennas shown schematically in FIGS. 2 to 4 allow to solve, or at least attenuate, this reflection of the transmitted signal at the antenna output. The characteristics of these antennas are identical to those of the antenna discussed above in connection with FIG. 1, and the above description also applies to the antennas of FIGS. 2 to 4; in particular, identical reference numbers designate identical elements.

[0074] The main difference between the embodiments shown in FIGS. 2 to 4 and the antenna shown in FIG. 1 is the presence of an evanescent filter 4 mounted directly at the output of polarizer 5, whose output aperture 10 is directly coupled to the ether. The evanescent filter thus acts directly as a radiating element to emit a dual-polarized signal P1+2 combining the polarized signals P1 and P2. The antenna thus consists of a polarizer 5 directly coupled to an evanescent filter 4.

[0075] The evanescent filter 4 preferably does not modify the polarizations of the signals through the antenna.

[0076] Polarizations can be circular polarizations.

[0077] The polarizer 5 may conform to the polarizer described in relation to FIG. 1; however, its output is coupled to the input of evanescent filter 4, instead of being coupled to the ether.

[0078] The polarizer of the antenna 1 shown in FIGS. 2 to 4 has two input ports 17 and 18, with only port 17 visible in the cross-section of FIG. 3. Each port can receive a signal P1 or P2 with a first or second polarization. Each port can be connected to a waveguide by means of a flange 170, respectively 180 as shown in FIG. 4, or directly connected to an active electronic circuit, for example by means of a coaxial cable.

[0079] The two ports 17, 18 are coupled to volumes 12 respectively 13 of the internal channel 11 of the antenna. These two volumes are separated from each other by a septum 2. As can be seen in FIG. 3, the height of this septum can decrease progressively or in steps from the ports 17, 18 towards the output opening 10.

[0080] The polarizer 5 can also be fitted with one or more longitudinal ridges 19. The use of ridges makes it possible to favor the transmission of a preferred transmission mode in a compact device.

[0081] In one embodiment, the polarizer 5 is provided with two longitudinal ridges 19, in addition to the septum 2. The two ridges can be at 120 to each other and to the septum. The two ridges can be 180 apart and 90 on either side of the septum.

[0082] The use of two ridges 19 in addition to the septum 2 significantly increases the antenna's single-mode bandwidth.

[0083] In an embodiment with two ridges in addition to the septum 2, 120 spacing of the two ridges on either side of the septum results in a channel geometry that is invariant to 120 rotation around the longitudinal axis of the channel. This configuration of ridges significantly increases the discrimination of higher-order modes with respect to the fundamental mode.

[0084] In one embodiment, the polarizer is provided with three longitudinal ridges 19, in addition to the septum 2. The three ridges can be at 90 to each other and to the septum.

[0085] A number of ridges greater than three can be used.

[0086] The ridges can be straight or twisted.

[0087] The average height of the ridges 19 in the radial direction is less than that of the septum 2. The height of the ridges may decrease from the ports 17, 18 towards the output opening 10.

[0088] In the example shown in FIGS. 2 to 3, the polarizer 5 has an external face shaped like a right prism, for example. Other external shapes, and other channel cross-sections 11, can also be considered. The shape of the polarizer's cross-section, as well as its surface, can gradually evolve from the polarizer input in direction of the evanescent filter 4, as shown in FIGS. 2 to 4.

[0089] In the context of the present invention, the evanescent filter can be seen as an impedance adapter between the polarizer and the ether.

[0090] When the array is miniaturized, the diameter of the internal channel of each evanescent filter no longer allows signal propagation as such, i.e. the filter waveguide is below the cut-off frequency. The protuberances on the filter's internal channel are therefore necessary for signal propagation in the antenna.

[0091] The evanescent filter 4 coupled to the output of polarizer 5 is provided with protuberances 3 (or teeth). To this end, the channel 11 of antenna 1 comprises several protuberances 3 separated from each other by portions of the channel 11.

[0092] The adjacent protuberances 3 are longitudinally spaced in pairs by a regular or variable pitch p.

[0093] The protuberances 3 can be arranged symmetrically around the longitudinal axis of the evanescent filter.

[0094] The protuberances 3 can be arranged in several rows, for example in line with the polarizer's ridges 19.

[0095] The protuberances 3 do not extend until the end of the antenna on the ether side. The ridges 19 do not extend until the end of the antenna on the ether side. The internal channel of the antenna therefore terminates on the ether side in a section devoid of ridges, protuberances and septum. This internal channel of the antenna ends on the ether side with an empty section, forming an iris between the polarizer and the ether for impedance matching.

[0096] In the example shown in FIGS. 2 to 4, the evanescent filter 4 has an outer face shaped like a cylinder, for example, while the channel 11 within the filter comprises a number of protuberances forming filtering sections. Other external shapes, and other sections of channel 11, may also be considered.

[0097] Antennas 1 with a square, rectangular, hexagonal or octagonal external cross-section can also be used. Likewise, the number of lines of protuberances can be different from three, although three lines is a preferred mode of execution in view of the advantages described above.

[0098] The cross-sectional shape of the evanescent filter can be different from the cross-sectional shape of the associated polarizer 5; for example, in FIGS. 2 and 3, polarizer 5 has a rectangular or square input cross-section, this gradually evolving to a circular shape to couple directly to an evanescent filter 4 of circular cross-section.

[0099] The geometric shape of the protuberances 3, and their arrangement, can for example be determined by computing software as a function of the desired bandwidth. The calculated geometric shape can be stored in a computer data medium.

[0100] It's important to note that the evanescent filter has identical phase performance for both modes. This means that the evanescent filter does not act as a polarizer, i.e. the phases of the two polarizations are unchanged in the filter.

[0101] The core 15 of the antenna 1 is preferably manufactured using an additive manufacturing process. The polarizer 5 and the evanescent filter 4 are preferably realized in a monolithic way, their core 15 being manufactured in a single additive printing step. In the present application, the expression additive manufacturing refers to any process for manufacturing the core by adding material, according to the computer data stored on the computer medium and defining the core's geometric shape.

[0102] Core 15 can, for example, be manufactured by an additive manufacturing process of the SLM (Selective Laser Melting) type. Core 15 can also be manufactured by other additive manufacturing methods, such as liquid or powder curing or coagulation, including but not limited to methods based on stereolithography, binder jetting, DED (Direct Energy Deposition), EBFF (Electron Beam Freedom Fabrication), FDM (Fused Deposition Modeling) PFF (Plastic Free Forming), aerosol, BPM (Ballistic Particle Manufacturing), SLS (Selective Laser Sintering), ALM (Additive Layer Manufacturing), polyjet, EBM (Electron Beam Melting), photopolymerization, etc.

[0103] The core may, for example, be a photopolymer made by several surface layers of liquid polymer cured by ultraviolet radiation in an additive manufacturing process.

[0104] The core can also be formed from a conductive material, such as a metallic material, by an additive manufacturing process of the SLM type, in which a laser or electron beam melts or sinter several thin layers of a powdery material.

[0105] In one embodiment, the metal layer 16 is deposited as a film by electroplating or galvanoplasty on the internal faces of the core 15. The metallization covers the internal faces of the core with a conductive layer.

[0106] The application of the metal layer can be preceded by a surface treatment step on the internal faces of the core to favor adhesion of the metal layer. The surface treatment may involve increasing the surface roughness and/or depositing an intermediate bonding layer.

[0107] Conventional additive manufacturing processes are not, however, particularly well-suited to conventional evanescent filters, especially filters that feature a number of protuberances 3 or cavities, since the arrangement of these protuberances creates cantilevered portions in the channel, which are difficult to maintain when printing the various strata. Reinforcements for these cantilevered portions must therefore be placed during the additive manufacturing process to prevent these parts from collapsing under the effect of gravity.

[0108] According to one aspect, and in order to remedy this drawback, the antenna 1 can be printed with the longitudinal axis z of the channel 11 in a vertical, or at least substantially vertical, position.

[0109] In another aspect, the protuberances 3 of channel 11 can be designed to facilitate this additive printing in a vertical position. Each protuberance 3 can thus have a face that is cantilevered when the filter is manufactured in a vertical position. In the example shown in FIGS. 2 and 3, the face 30 of protuberances 3 is cantilevered during additive manufacturing. The upper face 31 of protuberances 3 can extend in a plane substantially perpendicular to the longitudinal axis of channel 11, i.e. a horizontal plane during manufacturing. Alternatively, the top surface 31 may be inclined to this plane.

[0110] To enable additive printing, the cantilevered lower face 30 during printing can be inclined to the horizontal in the vertical manufacturing position. In a preferred embodiment, the lower face 30 forms an angle with the horizontal which is between 20 and 80 and preferably between 20 and 40.

[0111] The geometrical configuration of the antenna 1 according to this example has the advantage of enabling the core to be produced by an additive manufacturing process in a vertical direction opposite to gravity, without having to resort, during the core manufacturing process, to any reinforcement intended to avoid sagging of part of the core under the effect of gravity. Indeed, preferably, the angle of the cantilevered faces 30 to the horizontal is sufficient to allow the superimposed layers to adhere before they harden during printing.

[0112] The protuberances 3 shown in the examples have polygonal longitudinal cross-sections, for example in the shape of a triangle or trapezium. However, other protuberance or tooth shapes can also be imagined, including, for example, protuberances with rounded portions (undulations) in cross-section.

[0113] The protuberances 3 shown in the examples have constant dimensions and, in particular, constant depths and heights. However, crenellations and/or teeth of variable depth and/or height can also be produced. In addition, the pitch p between successive crenellations or teeth can be variable.

[0114] In one embodiment, the channel 11 of each antenna 1 of the antenna array has a cross-section orthogonal to the longitudinal axis of the channel which is invariant to rotation through 120 about the longitudinal axis. This is particularly the case when the protuberances are spaced apart by 120 and/or when the polarizer has three longitudinal ridges spaced apart by 120.

[0115] The 120 rotation invariance of the channel cross-section also imposes restrictions on the channel geometry. The external profile of the channel cross-section is thus, for example, circular, triangular, hexagonal, etc.

[0116] The antenna array of the present invention comprises at least two antennas 1, but is generally intended to include several tens of antennas 1 arranged in a parallel and contiguous manner. In such antenna arrangements, the periodicity of the array refers to the distance separating the centers of two successive antennas in the array, this distance typically being measured in a plane comprising the apertures of the antennas on the ether side.

[0117] In a particular embodiment, the periodicity of the antenna array is less than or equal to 80% of the nominal wavelength of the signals intended to be emitted/transmitted by each antenna. This value generally constitutes the threshold value below which reflection of signals towards adjacent antennas becomes problematic.

REFERENCE NUMBERS USED ON FIGS

[0118] 1 Antenna with dual polarization [0119] 2 Septum [0120] 3 Protuberances [0121] 4 Evanescent filter [0122] 5 Septum polarizer [0123] 10 Opening [0124] 11 Internal channel [0125] 12 Volume [0126] 13 Volume [0127] 15 Core [0128] 16 Metallization [0129] 17 First port [0130] 18 Second port [0131] 30 Bottom face of the protuberances [0132] 31 Top face of the protuberances [0133] 170 First flange [0134] 180 Second flange [0135] P1 First signal [0136] P2 Second signal [0137] P1+2 Dual-polarized signal