Corrugated passive radiofrequency device adapted for an additive manufacturing process

Abstract

The invention relates to a corrugated passive radio frequency device (1), in particular a waveguide or horn antenna. The device (1) comprises a core (2) with at least one inner face (4, 5, 6, 7; 12) that defines a channel (3) for filtering and guiding waves. This inner face (4, 5, 6, 7; 12) of the channel has several cavities (9) or slots (10). Each cavity (9) or slot (10) is formed by adjacent walls (11a, 11b) that are practically parallel for filtering the waves traveling through the channel. The adjacent walls (11a, 11b) are inclined with respect to the central axis of the channel (3).

Description

technical field

[0001] The present invention relates to a passive radio frequency device and in particular a corrugated waveguide filter or a corrugated horn-type antenna adapted for an additive manufacturing process. State of the art

[0002] Passive radio frequency devices are used to propagate or manipulate radio frequency signals without the use of active electronic components. Examples of passive radio frequency devices include passive waveguides based on wave guidance within hollow metallic channels, filters, antennas, mode converters, and so on. Such devices can be used for signal routing, frequency filtering, signal separation or recombination, transmission or reception into or from free space, and more.

[0003] There is a wide range of different types of waveguide filters. For example, corrugated waveguide filters, also called ribbed or corrugated waveguide filters, have a channel with a number of ridges, or teeth, that periodically reduce the internal height of the waveguide. They are used in applications that simultaneously require a wide bandwidth, good bandwidth matching, and a wide stopband. These are essentially low-pass designs, unlike most other shapes, which are generally band-pass. The distance between the teeth is much smaller than the typical λ / 4 spacing between elements in other filter types.

[0004] As an example, US2010 / 308938 describes a corrugated waveguide consisting of a rectangular metallic waveguide. The waveguide has, on two opposing walls, a first and second series of corrugations extending along the waveguide in a sinusoidal profile facing each other. The first and second series of corrugations act as rejection elements.

[0005] The above-mentioned conductive waveguides can be manufactured by extrusion, bending, cutting, and electroforming, for example. However, producing waveguides with complex cross-sections, particularly corrugated waveguide filters, using these conventional manufacturing methods is difficult and expensive.

[0006] Recent work has demonstrated the possibility of manufacturing waveguides, including filters, using additive manufacturing methods. In particular, the additive manufacturing of waveguides formed from conductive materials is well-established.

[0007] Waveguides with walls made of non-conductive materials, such as polymers or ceramics, manufactured using an additive manufacturing process and then coated with a metallic layer, have also been proposed. For example, US2012 / 00849 proposes manufacturing waveguides using 3D printing. In this process, a non-conductive plastic core is printed using an additive manufacturing method and then coated with a metallic layer by electrodeposition. The internal surfaces of the waveguides must be electrically conductive to function.

[0008] The use of a non-conductive core makes it possible, on the one hand, to reduce the weight and cost of the device and, on the other hand, to implement 3D printing methods adapted to polymers or ceramics and allowing the production of high-precision parts with low wall roughness.

[0009] We also know of waveguides with a metallic core produced by 3D printing in the prior art. In this case, additive manufacturing allows, in particular, a great deal of freedom in the shapes that can be created.

[0010] Additive manufacturing is typically performed by successive layers parallel to the filter's cross-section, ensuring the longitudinal axis of the aperture through the waveguide remains vertical during printing. This arrangement guarantees the aperture's shape and prevents deformation that would occur due to the upper wall of the aperture sagging before curing, which would happen if printed in a different direction.

[0011] Some waveguide filters, particularly corrugated waveguide filters, are difficult to manufacture using additive manufacturing methods due to their shape. Indeed, attempts at additive manufacturing have revealed that certain parts of the waveguide filter can be cantilevered, especially the cavity walls or the teeth of corrugated waveguide filters. These cantilevered parts can therefore sag under the effect of gravity during the manufacturing process.

[0012] It is therefore necessary to interrupt the additive manufacturing process during the manufacturing process in order to add reinforcements to ensure the stability of the structure to be printed, which can prove complicated and tedious and can have a significant impact on the speed and control of the manufacture of this type of filter by additive methods.

[0013] The document "Selective Laser Melting Manufacturing of Microwave Waveguide Devices", Peverini O. et al., Proceedings of the IEEE, Vol. 105, No. 4, April 1, 2017, discloses a waveguide filter with lateral cavities adapted for additive manufacturing.

[0014] Document US3274603A discloses a microwave horn antenna with concentric corrugations. The orientation of the corrugations of this antenna relative to the internal surface of the horn makes its additive manufacturing difficult, if not impossible.

[0015] Document US4012743A discloses a parabolic antenna whose horn can include concentric corrugations. Again, the orientation of the corrugations on this antenna relative to the horn's internal surface makes additive manufacturing difficult, if not impossible.

[0016] Document US4472721A discloses an antenna with a horn featuring concentric corrugations. Again, the orientation of the corrugations on this antenna relative to the horn's internal surface makes additive manufacturing difficult, if not impossible.

[0017] One aim of the present invention is therefore to propose a corrugated passive radio frequency device that is better suited to an additive manufacturing process. Brief summary of the invention

[0018] This objective is achieved by means of a corrugated passive radio frequency device comprising a core with at least one inner face defining a channel for filtering and guiding the waves. This at least one inner face of the channel comprises a plurality of cavities or grooves. Each cavity or groove is formed by substantially parallel adjacent walls to filter the waves passing through the channel. The adjacent walls of each cavity or groove are inclined with respect to the central axis of the channel.

[0019] According to one embodiment, the soul has several internal faces. Two opposing internal faces each have said plurality of cavities.

[0020] According to one embodiment, the said adjacent walls forming the cavities or the grooves are inclined at an angle between 20° and 55° with respect to the central axis of the channel.

[0021] According to one embodiment, the angle is between 40° and 50° with respect to the central axis of the channel, preferably at an angle of 45°.

[0022] According to one embodiment, the inclination of the adjacent walls forming a cavity or a groove is substantially identical between them.

[0023] According to one embodiment, the inclination of the adjacent walls forming a cavity or a groove is identical to the inclination of the adjacent walls forming any other cavity or any other groove.

[0024] According to one embodiment, the periodicity of the distribution of cavities with respect to the central axis of the radio frequency device is constant.

[0025] According to one embodiment, the periodicity of the distribution of cavities with respect to the central axis of the radio frequency device is variable.

[0026] Depending on one embodiment, the depth of the cavities relative to each other is constant or variable.

[0027] According to one embodiment, the radio frequency device is a waveguide.

[0028] According to one embodiment, the radio frequency device is a horn-type antenna.

[0029] According to the invention, the adjacent walls forming the annular grooves are inclined at a second angle between 30° and 80° with respect to an internal surface of the antenna.

[0030] In one embodiment, the adjacent walls forming the annular grooves are circular walls arranged on a conical internal surface. The diameter of the annular grooves changes monotonically or non-monotonally along the central axis.

[0031] According to one embodiment, the periodicity of the annular grooves adjacent to the central axis of the antenna is constant.

[0032] According to one embodiment, the periodicity of the adjacent annular grooves with respect to the central axis of the antenna is variable.

[0033] According to one embodiment, the circular walls are of constant thickness relative to each other.

[0034] According to one embodiment, the circular walls are of varying thickness relative to each other.

[0035] According to one embodiment, the depth of the annular grooves relative to each other is constant or variable.

[0036] According to one embodiment, the adjacent walls forming the annular grooves are rounded in the direction of the central axis of the antenna. Brief description of the figures

[0037] Examples of implementation of the invention are given in the description illustrated by the accompanying figures, in which: [ FIG. 1 ] there figure 1illustrates a schematic view of a longitudinal section of a corrugated waveguide filter according to the prior art, [ FIG. 2 ] there figure 2 illustrates a schematic view of a longitudinal section of a corrugated waveguide filter according to one embodiment of the invention; [ FIG. 3 ] there figure 3 illustrates a perspective view of a corrugated waveguide filter according to another embodiment of the invention, [ FIG. 4 ] there figure 4 illustrates a perspective view of a corrugated horn antenna according to another embodiment of the invention, [ FIG. 5 ] there figure 5 illustrates an axial section of the figure 4 , [ FIG. 6 ] there figure 6 illustrates a partial view of the internal surface of the horn antenna of the figure 4 , And [ FIG. 7 ] THE figures 7a, 7b, 7c schematically represent an axial section of a horn antenna according to different core profiles. Example(s) of an embodiment of the invention

[0038] According to one embodiment, the corrugated passive radio frequency device is a waveguide filter 1 which can take different forms depending, for example, on the figures 2 and 3 The filter has a core 2 comprising several internal faces 4, 5, 6, 7 which define a channel 3 configured to filter an electromagnetic signal according to a predefined bandwidth and operating band. For example, the filter is designed to allow a narrow bandwidth within a frequency range of approximately 1 GHz - 80 GHz.

[0039] The core 2 has an external face comprising several extensions 8 whose shape resembles, for example, right prisms, each having substantially parallel adjacent walls 11a, 11b, and which extend in a plane inclined with respect to the central axis of the channel 3. According to the figure 2, these right prisms are hollow so as to form a plurality of 9 resonance cavities extending along channel 3 in order to filter high frequency signals in a determined frequency range.

[0040] The adjacent walls 11a, 11b of each extension 8 are inclined with respect to the longitudinal axis of the channel 3. The core 2 of the waveguide filter, for example, of the figure 3 has several internal faces 4, 5, 6, 7 (see figure 2 also). Two opposite internal faces 4, 5 each have a first, respectively a second plurality of cavities 9.

[0041] The adjacent walls 11a, 11b forming the cavities 9 are inclined at an angle α between 20° and 55° with respect to the central axis of the channel 3. The angle α is preferably between 40° and 50° with respect to the axis of the channel 3, for example 45°.

[0042] The inclination of the adjacent walls 11a, 11b of the waveguide filter forming a cavity 9 is substantially identical to each other and to the adjacent walls 11a, 11b of any other cavity. However, the inclination between walls forming a cavity may vary relative to the inclination of the walls of other cavities according to one embodiment.

[0043] Furthermore, the periodicity p of the distribution of the cavities 9 with respect to the central axis of the channel 3 of the waveguide 1 is constant or can be variable depending on the implementation variant. The depth of the cavities 9 of the waveguide 1 relative to each other can be constant or variable.

[0044] According to another form of realization illustrated by the figures 4 to 6The corrugated passive radio frequency device is a horn-type antenna 1. The antenna has a core 2 having a conical internal surface 12. A plurality of circular walls 11a, 11b extend from the conical surface towards the central axis of the antenna 1 and are adjacent so as to form a plurality of annular grooves 10. These annular grooves are concentric to the central axis of the antenna 1, the diameter of each annular groove 10 being different with respect to the diameter of an adjacent annular groove.

[0045] According to the figure 6 The circular walls 11a, 11b forming the annular grooves 10 are inclined at an angle α between 20° and 55° with respect to the central axis of the antenna. The angle α is preferably between 40° and 50° with respect to the longitudinal axis of channel 3, for example 45°.

[0046] Furthermore, the inclination of the adjacent circular walls 11a, 11b forming an annular groove 10 is substantially identical to each other and to the adjacent walls 11a, 11b of any other annular groove. However, the inclination between circular walls forming an annular groove may vary relative to the inclination of the walls of other annular grooves according to an alternative embodiment.

[0047] As illustrated on the figure 5 The circular walls 11a and 11b forming the annular grooves can also be inclined at an angle of less than 90° with respect to the internal surface of the horn antenna. According to the invention, this angle is between 30° and 80°.

[0048] This inclination allows, on the one hand, for influencing the antenna's bandwidth spectrum. On the other hand, it facilitates the additive manufacturing of the antenna. Indeed, overhanging surfaces, such as the adjacent walls forming the annular grooves, are difficult to produce without using supports during manufacturing, which must then be removed. Inclining the adjacent walls forming the annular grooves relative to the internal surface of the antenna horn thus reduces stress on the overhanging faces and eliminates the need for supports during manufacturing.

[0049] Depending on the antenna horn's opening angle, the adjacent walls forming the annular grooves can be inclined both relative to the antenna's central axis at an angle between 20° and 55°, and relative to the antenna horn's surface at an angle between 30° and 80°. This inclination relative to both the antenna's central axis and the horn's internal surface minimizes stresses caused by cantilevered parts during additive manufacturing.

[0050] The periodicity p of the adjacent annular grooves with respect to the central axis of the antenna 1 is constant or variable.

[0051] The circular walls may have the same thickness t relative to each other or different thicknesses. The depth of the annular grooves relative to each other is constant or variable.

[0052] According to other forms of embodiment illustrated by the figures 7a, 7b, 7c The horn antenna 1 can have a core 2 whose profile varies arbitrarily along the central axis. For example, the profile of the antenna core according to the figures 7a and 7b varies along the central axis according to a monotonic function, while the profile of the antenna core according to the figure 7c varies along the central axis according to a non-monotonic function.

[0053] In the embodiment illustrated on the figure 7a , the angle between the adjacent walls forming the annular grooves and the central axis of the antenna is constant along the antenna, and the angle between the adjacent walls and the surface of the antenna horn is also constant.

[0054] In the embodiments illustrated on the figures 7b and 7c, the angle between the adjacent walls and the central axis of the antenna is constant along the antenna, while the angle between the adjacent walls and the surface of the horn varies according to the change in the antenna profile along the central axis.

[0055] The geometric shape of core 2 can, for example, be determined by calculation software based on the desired bandwidth. The calculated geometric shape can then be stored on a computer data storage medium.

[0056] Core 2 is manufactured using an additive manufacturing process. In this application, the term "additive manufacturing" refers to any manufacturing process of core 2 by adding material, according to computer data stored on the computer medium and defining the geometric shape of core 2.

[0057] Core 2 can, for example, be manufactured by an additive manufacturing process such as SLM (Selective Laser Melting). Core 2 can also be manufactured by other additive manufacturing methods, for example by curing or coagulation of liquid or powder, including but not limited to methods based on stereolithography, inkjet printing (binder jetting), DED (Direct Energy Deposition), EBFF (Electron Beam Freedom Fabrication), FDM (Fused Deposition Modeling), PFF (Plastic Free Forming), aerosols, BPM (Ballistic Particle Manufacturing), SLS (Selective Laser Sintering), ALM (Additive Layer Manufacturing), polyjet, EBM (Electron Beam Melting), photopolymerization, etc.

[0058] Core 2 can, for example, be made of photopolymer manufactured by several surface layers of liquid polymer hardened by ultraviolet radiation during an additive manufacturing process.

[0059] The core 2 can also be formed from a conductive material, for example a metallic material, by an additive manufacturing process of the SLM type in which a laser or an electron beam melts or sinters several thin layers of a powdery material.

[0060] According to one embodiment, a layer of metal (not illustrated) is deposited as a film by electrodeposition or electroplating on the inner faces 4, 5, 6, 7 of the core 2. The metallization makes it possible to cover the inner faces of the core 2 with a conductive layer.

[0061] The application of the metal layer may be preceded by a surface treatment step on the internal faces 4, 5, 6, 7 of the core 2 to promote adhesion of the metal layer. The surface treatment may involve increasing the surface roughness and / or deposition of an intermediate adhesion layer.

[0062] Conventional additive manufacturing processes are not particularly well suited for conventional waveguide filters, especially corrugated waveguide filters which have a number of cavities depending on the figure 1 Because the arrangement of these cavities creates cantilevered sections outside the channel, which are difficult to maintain during the printing of the different layers, reinforcements for these cantilevered sections must be placed during the additive manufacturing process to prevent them from sagging under the effect of gravity.

[0063] According to one aspect, and in order to remedy this drawback, the waveguide 1 is printed with the longitudinal axis z of the channel 3 in a vertical position, or at least substantially vertical.

[0064] The geometric configuration of the waveguide filter 1 in this embodiment has the advantage of allowing the core 2 to be manufactured using an additive manufacturing process in a vertical direction opposite to gravity, without requiring any reinforcement during the core 2 manufacturing process to prevent sagging of a portion of the core under the effect of gravity. In fact, the angle α of the cantilevered extensions relative to the horizontal is preferably sufficient to allow adhesion of the superimposed layers before they harden during printing.

[0065] It is also possible to create a waveguide with an elliptical or oval cross-section.

[0066] In an embodiment illustrated on the figure 6, the adjacent walls 11a and 11b forming the annular grooves are rounded in the direction of the axis of antenna 3. This rounding makes it easier in particular to facilitate the additive manufacturing of these cantilevered elements.

Claims

1. A corrugated passive horn antenna (1) comprising a core (2) having at least one inner face (4, 5, 6, 7; 12) delimiting a channel (3) for filtering and guiding waves, said at least one inner face (4, 5, 6, 7; 12) of the channel comprising a plurality of annular grooves (10), each annular groove (10) being formed by substantially parallel adjacent walls (11a, 11b) in order to filter the waves passing through the channel, said adjacent walls (11a, 11b) being inclined relative to a central axis of the channel (3), characterised in that said adjacent walls (11a, 11b) forming the annular grooves (10) are inclined at a second angle between 30° and 80° relative to an internal surface of the antenna.

2. Passive horn antenna (1) according to claim 1, characterised in that said adjacent walls (11a, 11b) forming the annular grooves (10) are inclined at an angle (α) between 20° and 55° relative to the central axis of the channel (3).

3. Passive horn antenna (1) according to claim 2 , characterised in that said angle (α) is between 40° and 50° relative to the central axis of the channel (3), preferably at an angle of 45°.

4. Passive horn antenna (1) according to one of the preceding claims, characterised in that the inclination of said adjacent walls (11a, 11b) forming the plurality of annular grooves (10) are substantially identical from one annular groove to any other annular groove.

5. Passive horn antenna (1) according to one of the preceding claims, characterised in that said adjacent walls (11a, 11b) forming the annular grooves (10) are circular walls which are arranged on a conical inner surface (12), the diameter of the annular grooves changing along the central axis of the channel in a monotonic or non-monotonic manner.

6. Passive horn antenna (1) according to one of the preceding claims, characterised in that the periodicity (p) of the adjacent annular grooves relative to the central axis of the channel is constant.

7. Passive horn antenna (1) according to one of claims 1 to 5, characterised in that the periodicity (p) of the adjacent annular grooves relative to the central axis of the channel is variable.

8. Passive horn antenna (1) according to one of claims 5 to 7, characterised in that the circular walls (11a, 11b) have the same thickness (t) relative to each other.

9. Passive horn antenna (1) according to one of claims 5 to 7, characterised in that the circular walls (11a, 11b) have different thicknesses (t) relative to each other.

10. Passive horn antenna (1) according to one of the preceding claims, characterised in that the depth of the annular grooves (10) relative to each other is constant or variable.

11. Passive horn antenna (1) according to one of the preceding claims, characterised in that the said adjacent walls (11a, 11b) forming the annular grooves are rounded in the direction of the central axis of the channel.

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