Waveguide member for antenna device, antenna device, and method for manufacturing waveguide member for antenna device

Abstract

The invention relates to a waveguide component for an antenna arrangement, comprising a one-piece, two-piece or multi-piece waveguide (10) which at least partially encloses an inner volume (12) and which has an aluminum mass fraction of at least 50% by weight, and / or a metal coating (22) having an aluminum mass fraction of at least 50% by weight is formed on and / or above at least one surface (16) of the waveguide, said surface facing the inner volume (12). In particular, the waveguide (10) can be formed at least partially from plastic and has a metal coating (22) which is arranged on and / or over at least one surface (16) of the waveguide (10) oriented toward the inner volume (12) and which has an aluminum mass fraction of at least 50% by weight. Alternatively, all at least three waveguide components of the two waveguide components (10a, 10b) of the one-piece waveguide, the two-piece waveguide (10) or the multi-piece waveguide can be structured from at least one material block, each having a mass fraction of aluminum of at least 90% by weight.

Description

Technical Field

[0001] This invention relates to a waveguide component for an antenna device. The invention also relates to an antenna device. Furthermore, the invention relates to a method for manufacturing a waveguide component for an antenna device. Background Technology

[0002] WO 2024 / 153357 A1 describes a waveguide antenna and a method for manufacturing it, or a power distribution device constructed using the waveguide antenna. Summary of the Invention

[0003] This invention provides a waveguide component for an antenna device, an antenna device, and a method for manufacturing the waveguide component for the antenna device. The waveguide component comprises: a one-piece, two-piece, or multi-piece waveguide, the waveguide at least partially surrounding an internal volume; the waveguide having at least 50% by weight of aluminum mass fraction, and / or having a metal coating with at least 50% by weight of aluminum mass fraction formed on and / or above at least one surface of the waveguide oriented toward the internal volume. The antenna device has the waveguide component. The manufacturing method includes the steps of: forming a one-piece, two-piece, or multi-piece waveguide such that the waveguide at least partially surrounds an internal volume (S1); forming the waveguide with at least 50% by weight of aluminum mass fraction (S1a), and / or forming a metal coating with at least 50% by weight of aluminum mass fraction formed on and / or above at least one surface of the waveguide oriented toward the internal volume (S2).

[0004] Advantages of the invention

[0005] This invention provides waveguide components, or antenna devices equipped with waveguide components, which are significantly superior in their standard functions compared to conventional aluminum-free waveguides. This is because the respective waveguide construction of each waveguide component has at least 50% by weight (weight percentage) of aluminum mass, and / or its metal coating has at least 50% by weight (weight percentage) of aluminum mass. In particular, the waveguide components obtained by this invention have high conductivity, especially for electromagnetic waves in the radio frequency range, particularly those between 76 GHz and 81 GHz, thus enabling such electromagnetic waves to propagate with relatively low loss. Since aluminum is a relatively cost-effective material, this invention also enables the manufacture of waveguide components and antenna devices equipped with them at relatively low manufacturing costs. Another advantage of the waveguide component obtained by means of this invention is that, thanks to the use of aluminum, the waveguide component itself can achieve high robustness even in environments with extreme temperatures (e.g., temperature ranges between -40°C and 130°C), extreme (impact) temperature fluctuations, and the presence of chemically active materials. Therefore, the waveguide component obtained by means of this invention is also very suitable for the automotive field, but its applications are not limited thereto.

[0006] In an advantageous embodiment of the waveguide component, the waveguide is at least partially formed of plastic and has a metallic coating disposed on and / or above at least one surface of the waveguide oriented inwards, the metallic coating having an aluminum mass share of at least 50%. By manufacturing the waveguide from plastic and subsequently constructing the metallic coating described herein, a robust material combination with high conductivity is achieved in the waveguide component, and thus it is well-suited for low-loss operation in the high-frequency range. Additionally, the low-cost materials described herein (plastic and metallic coating materials) are processed using readily implementable processes. Therefore, embodiments of the waveguide component described herein can be manufactured at relatively low production costs.

[0007] Preferably, the plastic comprises polyphenylene sulfide (PPS), polyamide (PA), polybutylene terephthalate (PBT), and / or polycarbonate (PC). These types of plastics, even at extreme temperatures (e.g., in the range of -40°C to 130°C), extreme temperature fluctuations, relative humidity, and relative to chemically reactive gases, enable the co-acting metallic coating to maintain good robustness.

[0008] For example, a metallic coating disposed on and / or over at least one surface of the waveguide oriented toward the inward volume can have an aluminum mass share of at least 90%. The metallic coating can also be understood, in particular, as an aluminum coating. Such a high aluminum mass share of at least 90% not only saves on material costs but also generally helps improve the adhesion of the metallic coating to the corresponding waveguide.

[0009] Preferably, the metal coating is adjacent to the protective layer on its respective side oriented inwards towards the interior volume, the protective layer comprising natural alumina. In this case, the protective layer prevents additional oxidation of the metal coating and / or prevents chemical reactions between the metal coating and chemically active materials in the space environment in which the illustrated embodiment of the waveguide component is located.

[0010] As an advantageous extension, a buffer layer with at least 50% by weight of nickel and / or chromium can be disposed between the metal coating and the adjacent surface of the waveguide. This buffer layer helps improve the adhesion of the metal coating to the corresponding waveguide.

[0011] Preferably, the buffer layer has a nickel mass share between 70% and 90% by weight and a chromium mass share between 10% and 30% by weight. This nickel-chromium ratio of the buffer layer, especially due to the relatively high aluminum mass share of the metal coating, significantly improves the adhesion of the metal coating.

[0012] As another advantageous extension, the metal coating and / or protective layer may cover at least one passivation layer on the respective side oriented toward the inward volume, the passivation layer comprising aluminum oxide, aluminum nitride, silver, gold, chromium, and / or nickel. In this case, at least one passivation layer achieves improved robustness of the waveguide component relative to chemically active liquids and gases.

[0013] In another advantageous embodiment of the waveguide component, a one-piece waveguide, two waveguide components of a two-piece waveguide, or all at least three waveguide components of a multi-piece waveguide are structured from at least one material block, each of which has at least 90% aluminum mass fraction. The waveguide component embodiments described herein exhibit high robustness even at extreme temperatures (especially in the temperature range of -40°C to 130°C), extreme temperature fluctuations, and relative to chemically active materials.

[0014] In particular, the waveguide may include a first waveguide component and a second waveguide component, wherein the first and second waveguide components are arranged relative to each other without being connected by conductive brazing or adhesive, such that a longitudinal axis extending from a first open end of the internal volume through the internal volume to a second open end of the internal volume can be defined, with the first waveguide component located on a first side of the longitudinal axis and the second waveguide component located on a second side of the longitudinal axis opposite to the first side. Because the waveguide described herein, although implemented by the first and second waveguide components, does not require conductive brazing or adhesive connection, the waveguide itself or its metal coating can have a relatively high aluminum mass share of at least 50% by weight. Therefore, constructing the waveguide by the first and second waveguide components does not preclude the advantageous use of aluminum.

[0015] The same advantages can be ensured for antenna devices equipped with such waveguide components.

[0016] Furthermore, the aforementioned advantages can also be achieved by implementing a corresponding manufacturing method for waveguide components of an antenna device. It should be clearly noted that the manufacturing method can be extended based on the aforementioned implementation of the waveguide component. Attached Figure Description

[0017] Other features and advantages of the invention will now be described with reference to the accompanying drawings. These drawings show:

[0018] Figure 1 A schematic diagram of a first embodiment of the waveguide component;

[0019] Figures 2 to 9 These are schematic diagrams illustrating another embodiment of the waveguide component;

[0020] Figure 10 A flowchart illustrating an implementation method for manufacturing waveguide components of an antenna device. Detailed Implementation

[0021] Figure 1 A schematic diagram of a first embodiment of the waveguide component is shown.

[0022] Figure 1 The waveguide component schematically shown has a waveguide 10 that at least partially surrounds an internal volume 12. The internal volume 12 can be understood as a volume that can be filled / has been filled with at least one gaseous material, and more particularly as a volume that can be filled / has been filled with air. This is merely an example. Figure 1 The waveguide 10 in the embodiment is a two-piece waveguide 10, which includes a first waveguide component 10a and a second waveguide component 10b. However, the waveguide 10 may also be a one-piece waveguide or a multi-piece waveguide having at least three waveguide components.

[0023] The waveguide component can be used to propagate electromagnetic waves through the internal volume 12, particularly along the longitudinal axis 14 of the internal volume 12, which extends from a first open end through the internal volume 12 to a second open end. The propagating electromagnetic waves will generate a surface current at at least one surface 16 of the waveguide 10 oriented toward the internal volume 12. Figure 1 The so-called transverse electric wave TE10 is also shown by arrow 18. It can also be seen here that the transverse electric wave TE10 does not trigger surface currents at at least one surface 16 of the waveguide 10 oriented toward the inner volume 12 within the plane of symmetry 20, about which the first waveguide member 10a and the second waveguide member 10b are arranged mirror-symmetrically. Therefore, the first waveguide member 10a and the second waveguide member 10b can also be separated from each other without being connected by conductive brazing or adhesive. Instead, it is sufficient to arrange the first waveguide member 10a and the second waveguide member 10b to each other in a manner that does not require conductive brazing or adhesive, such that the first waveguide member 10a is located on a first side of the longitudinal axis 14, and the second waveguide member 10b is located on a second side of the longitudinal axis 14 opposite to the first side.

[0024] Because it eliminates the need for conductive brazing or adhesive connections between the first waveguide component 10a and the second waveguide component 10b, the waveguide 10 can be constructed with an aluminum mass share of at least 50%. In particular, the waveguide 10 can have an aluminum mass share of at least 90%, such as at least 95%, and especially at least 99.95%. Aluminum allows for the use of a relatively cost-effective and relatively easy-to-process / form material for the waveguide 10. The presence of at least 50% aluminum mass share in the waveguide 10 facilitates high electrical conductivity of the waveguide component, particularly for electromagnetic waves in the radio frequency range, especially those between 76 GHz and 81 GHz. Therefore, the waveguide component described herein is advantageously suited for the propagation of such electromagnetic waves. Furthermore, aluminum exhibits high temperature resistance and good robustness relative to chemically active materials.

[0025] A two-piece waveguide 10, or a corresponding one-piece waveguide, or a multi-piece waveguide having at least three waveguide components, can be structured from at least one block of material having a corresponding aluminum mass share of at least 90% by weight, preferably at least 95% by weight, and particularly at least 99.95% by weight. The structuring of the corresponding waveguide 10 or its waveguide components 10a, 10b can be achieved, for example, by means of milling, stamping, and / or punching processes. Alternatively, the waveguide 10 having an aluminum mass share of at least 50% by weight can also be manufactured by means of pressure die casting. However, it should be clearly noted that the examples of structuring or manufacturing processes listed herein are merely illustrative.

[0026] Figure 2 A schematic diagram of a second embodiment of the waveguide component is shown.

[0027] Unlike the implementation methods described above, Figure 2 The waveguide component has a waveguide 10, which is at least partially formed of plastic. Furthermore, a metal coating 22 is provided on and / or above at least one surface 16 of the waveguide 10 oriented toward the inner volume 12, the metal coating having an aluminum mass share of at least 50% by weight. Such a high aluminum mass share can be achieved in the metal coating 22 because electromagnetic waves can propagate uninterrupted along the longitudinal axis 14 of the inner volume 12 even without conductive brazing or adhesive connections between the first waveguide component 10a and the second waveguide component 10b. Therefore, when constructing the metal coating 22, there is no need to consider the robustness of at least one of its materials relative to conductive brazing or adhesive connections that are no longer needed.

[0028] The metal coating 22, with an aluminum mass share of at least 50%, makes the waveguide component highly suitable for electromagnetic wave propagation, particularly for electromagnetic waves in the radio frequency range, especially those between 76 GHz and 81 GHz. It should also be noted that the use of this high-aluminum-content metal coating 22 enables electromagnetic waves to propagate through the waveguide component with relatively low loss. Preferably, at least one surface 16 of the waveguide 10 oriented toward the internal volume 12 is (substantially) completely covered by the metal coating 22.

[0029] The metal coating 22 disposed on and / or above at least one surface 16 of the waveguide 10 oriented toward the inner volume 12 preferably has an aluminum mass share of at least 90% by weight, more preferably at least 95% by weight, and particularly at least 99.95% by weight. Therefore, the metal coating 22 can also be referred to as an aluminum metal coating. Thus, the metal coating 22 achieves both cost optimization and high electrical conductivity. Additionally, the waveguide 10 made of plastic can also be cost-effectively manufactured, for example, by performing an injection molding process. In particular, the waveguide 10 or its waveguide components 10a and 10b can be respectively so-called injection-molded plastic parts.

[0030] The plastics used to manufacture the waveguide 10 or its waveguide components 10a, 10b preferably include / are polyphenylene sulfide (PPS), polyamide (PA), polybutylene terephthalate (PBT), and / or polycarbonate (PC). Therefore, relatively cost-effective plastic materials can be used, which also additionally ensure good adhesion of the high-aluminum-content metal coating 22 to the waveguide 10. It should also be noted that the examples of plastics listed herein have good robustness relative to extreme temperatures and chemically active materials (liquids and gases). In particular, polyphenylene sulfide (PPS) has a coefficient of thermal expansion similar to that of aluminum. This also helps to improve the adhesion of the metal coating 22 to the waveguide 10. If desired, the plastic can also be filled with minerals, glass fibers, and / or glass microspheres.

[0031] To construct a metal coating 22 on and / or over at least one surface 16 of the waveguide 10 oriented toward the inner volume 12, PVD (Physical Vapor Deposition), sputtering / cathode sputtering (e.g., especially DC sputtering and / or RF sputtering), evaporation, and / or electroplating processes can be implemented. However, the processes listed herein for constructing the metal coating 22 are not exhaustive. The thickness of the metal coating 22 is preferably between 300 nm and 3000 nm.

[0032] Preferably, the metal coating 22 is adjacent to the protective layer 24 on its corresponding side oriented toward the internal volume 12, the protective layer comprising natural alumina. The protective layer 24 is particularly (essentially) a natural aluminium oxide layer. With the aid of the protective layer 24, the metal coating 22 is reliably protected from (further) oxidation. The protective layer 24 also ensures relatively low dielectric loss during electromagnetic wave propagation at frequencies in the radio frequency range (particularly electromagnetic waves with frequencies between 76 GHz and 81 GHz). The protective layer 24 can also be constructed using so-called natural oxidation, which involves briefly exposing the metal coating 22 to oxygen-containing air. Therefore, there is no need to form the protective layer 24 through artificial deposition. Furthermore, during the exposure of the metal coating 22 to oxygen-containing air, there is no need to control the layer thickness of the protective layer 24, as the protective layer 24 typically forms a favorable layer thickness automatically.

[0033] about Figure 2 For other features, properties, and advantages of waveguide components, please refer to the descriptions above. Figure 1 The implementation method shown.

[0034] Figure 3 A schematic diagram of a third embodiment of the waveguide component is shown.

[0035] Figure 3 The waveguide component is schematically shown in the diagram, as an example of the previously described... Figure 2 A supplementary embodiment includes a buffer layer 26 disposed between the metal coating 22 and the adjacent surface 16 of the waveguide 10. The buffer layer 26 is constructed with at least 50% by weight (weight percentage) of nickel and / or chromium. The buffer layer 26 improves the adhesion of the high-aluminum-content metal coating 22 to the waveguide 10. Materials, especially nickel and chromium, are particularly suitable for improving the adhesion of the high-aluminum-content metal coating 22 to the waveguide 10. Therefore, the buffer layer 26 can also be referred to as an adhesion-enhancing layer or an adhesion-improving layer.

[0036] Preferably, at least one surface 16 of the waveguide 10 oriented toward the inner volume 12 is substantially completely covered by the buffer layer 26, wherein at least one interface of the buffer layer 26 oriented toward the inner volume 12 is covered by a metallic coating 22. Preferably, the buffer layer 26 has a nickel and / or chromium mass share of at least 65% by weight, more preferably at least 80% by weight, and particularly at least 95% by weight. For example, the buffer layer 26 may be a chromium layer.

[0037] Alternatively, the buffer layer 26 may also be a nickel-chromium alloy layer. More preferably, the buffer layer 26 here has a nickel mass share between 70% and 90% by weight and a chromium mass share between 10% and 30% by weight. In particular, the buffer layer 26 has a nickel mass share between 75% and 85% by weight and a chromium mass share between 15% and 25% by weight. In a particularly advantageous embodiment, the buffer layer 26 is a nickel-chromium alloy layer with a nickel mass share between 79% and 81% by weight and a chromium mass share between 19% and 21% by weight.

[0038] When constructing the buffer layer 26, PVD (Physical Vapor Deposition), sputtering / spraying (e.g., especially DC sputtering and / or RF sputtering), evaporation, and / or electroplating processes can also be implemented. The preferred thickness of the buffer layer 26 is between 10 nm and 300 nm, particularly between 20 nm and 200 nm.

[0039] about Figure 3 For other features, properties, and advantages of waveguide components, please refer to the descriptions above. Figure 1 and Figure 2 The implementation method shown.

[0040] Figure 4 and Figure 5 Schematic diagrams of another embodiment of the waveguide component are shown.

[0041] Figure 4 and Figure 5 The waveguide component schematically shown in the diagram is... Figure 3 The main difference in the implementation methods lies in their metal coating 22 (see Figure 4 ) or their protective layer 24 (see Figure 5 At least one passivation layer 28 is provided on the corresponding side of the metal coating 22 oriented toward the internal volume 12. The at least one passivation layer 28 is capable of additionally preventing undesirable (further) oxidation of the metal coating 22, which has a weight percentage of at least 50% aluminum. Figure 4It is evident that the protective layer 24 can be omitted if necessary. In particular, at least one interface of the metal coating 22 or the protective layer 24 oriented toward the internal volume 12 can be (substantially) completely covered by at least one passivation layer 28. The at least one passivation layer 28 preferably comprises aluminum oxide (Al2O3), aluminum nitride (AlN), silver, gold, chromium, and / or nickel. Preferably, the at least one passivation layer 28 is an aluminum oxide layer, an aluminum nitride layer, a silver layer, a gold layer, a chromium layer, and / or a nickel-chromium alloy layer, especially a nickel-chromium alloy layer with a nickel mass share between 70% and 90% by weight and a chromium mass share between 10% and 30% by weight.

[0042] For a single passivation layer 28 and / or a stack of layers consisting of at least two passivation layers 28, a layer thickness of less than 200 nm is advantageous. More preferably, the layer thickness of a single passivation layer 28 or a stack of layers is between 50 nm and 100 nm. It should also be noted that although at least one passivation layer 28 can also be a silver or gold layer, since an electrical contact is no longer required between waveguide components 10a and 10b, it is entirely possible to forgo using relatively expensive materials such as silver and gold to fabricate at least one passivation layer 28.

[0043] Advantageously, the same deposition techniques used to construct the metal coating 22 are typically used when forming at least one passivation layer 28. For example, at least one passivation layer 28 can be formed by means of a PVD (Physical Vapor Deposition) process, by means of a sputtering / spraying process (e.g., especially by means of DC sputtering and / or RF sputtering), by means of an evaporation process, and / or by means of an electroplating process. In particular, when at least one passivation layer 28 is / comprises an aluminum oxide layer and / or an aluminum nitride layer, a “seamless” transition from the deposition of the metal coating 22 to the deposition of at least one passivation layer 28 can be achieved by adding oxygen or nitrogen in the respective deposition process.

[0044] about Figure 4 and Figure 5 For other features, properties, and advantages of waveguide components, please refer to the descriptions above. Figures 1 to 3 The implementation method.

[0045] Figures 6 to 9 Schematic diagrams of another embodiment of the waveguide component are shown.

[0046] Figures 6 to 9 The waveguide component is the same as described above. Figures 2 to 5The difference in the implementation lies only in that the first waveguide component 10a and the second waveguide component 10b of the waveguide 10 are arranged far apart from each other, such that even after the layers (22 to 28) deposited and / or formed therein remain a gap 30 between the coated waveguide components 10a and 10b. This gap extends from the external environment of the waveguide 10 into the internal volume 12, and at least one gaseous material (e.g., especially air) may be present within the gap. This gap 30 has no (substantial) effect on the electromagnetic wave to be transmitted. The maximum width of the gap 30 is preferably less than 2 mm, especially less than 1 mm, and particularly less than 0.5 mm.

[0047] about Figures 6 to 9 For other features, properties, and advantages of waveguide components, please refer to the descriptions above. Figures 1 to 5 The implementation method.

[0048] All the waveguide components described above are well-suited for use in corresponding waveguide components within antenna devices. In particular, these waveguide components can also be used in radar sensors.

[0049] Figure 10 A flowchart illustrating an embodiment of a method for manufacturing a waveguide component of an antenna device is shown.

[0050] All the waveguide components described above can be manufactured using the manufacturing methods described below. However, the feasibility of these manufacturing methods is not limited to manufacturing these waveguide components.

[0051] In step S1 of the manufacturing method, a one-piece, two-piece, or multi-piece waveguide is formed such that the waveguide at least partially surrounds an internal volume. In an advantageous embodiment of the manufacturing method, as a sub-step S1a of step S1, a waveguide with an aluminum mass share of at least 50% by weight is formed. Alternatively, step S2 may be performed (optionally): a metal coating with an aluminum mass share of at least 50% by weight is constructed on at least one surface of the waveguide oriented toward the internal volume.

[0052] Therefore, waveguide components manufactured using the manufacturing method described herein can also achieve the aforementioned advantages.

Claims

1. A waveguide component for an antenna device, having: a one-piece, two-piece or multi-piece waveguide tube (10) which at least partially encloses an inner volume (12); characterized in that: the waveguide tube (10) has a mass fraction of aluminum of at least 50% by weight, and / or a metal coating (22) with a mass fraction of aluminum of at least 50% by weight is configured on and / or above at least one surface (16) of the waveguide tube (10) which is oriented toward the inner volume (12). the waveguide tube (10) is at least partially made of plastic and has a metal coating (22) arranged on and / or above the at least one surface (16) of the waveguide tube (10) which is oriented toward the inner volume (12), the metal coating having a mass fraction of aluminum of at least 50% by weight. the plastic comprises polyphenylene sulfide (PPS), polyamide (PA), polybutylene terephthalate (PBT) and / or polycarbonate (PC). the metal coating (22) arranged on and / or above the at least one surface (16) of the waveguide tube (10) which is oriented toward the inner volume (12) has a mass fraction of aluminum of at least 90% by weight.

2. The waveguide component of claim 1, wherein, the metal coating (22) adjoins on its respective side oriented toward the inner volume (12) a protective layer (24) which comprises natural aluminum oxide.

3. The waveguide component of claim 2, wherein, between the metal coating (22) and the adjacent surface (16) of the waveguide tube (10), a buffer layer (26) is arranged which has a mass fraction of nickel and / or chromium of at least 50% by weight.

4. A waveguide component according to claim 2 or 3, wherein, the buffer layer (26) has a mass fraction of nickel of between 70% by weight and 90% by weight and a mass fraction of chromium of between 10% by weight and 30% by weight.

5. The waveguide component of any of claims 2-4, wherein, the metal coating (22) and / or the protective layer (24) are covered on their respective side oriented toward the inner volume (12) with at least one passivation layer (28) which comprises aluminum oxide, aluminum nitride, silver, gold, chromium and / or nickel.

6. The waveguide component of any of claims 2-5, wherein, the one-piece waveguide tube, the two waveguide tube components (10a, 10b) of the two-piece waveguide tube (10) or all at least three waveguide tube components of the multi-piece waveguide tube are structured from at least one material block which has a mass fraction of aluminum of at least 90% by weight, respectively.

7. The waveguide component of claim 6, wherein, the waveguide tube (10) comprises a first waveguide tube component (10a) and a second waveguide tube component (10b), wherein the first waveguide tube component (10a) and the second waveguide tube component (10b) are arranged in relation to one another without an electrically conductive solder or adhesive connection in such a way that a longitudinal axis (14) can be defined which extends through the inner volume (12) from a first open end of the inner volume (12) to a second open end of the inner volume (12), with respect to which longitudinal axis the first waveguide tube component (10a) is located on a first side of the longitudinal axis (14) and the second waveguide tube component (10b) is located on a second side of the longitudinal axis (14) which faces away from the first side.

8. The waveguide component of any one of claims 2-7, wherein, 11. An antenna device having a waveguide component according to any one of the preceding claims.

9. The waveguide component of claim 1, wherein, ​ 10. The waveguide component of any of the preceding claims, wherein, ​ ​ 12. A manufacturing method for a waveguide component of an antenna device, the method comprising the following steps: forming a one-piece, two-piece or multi-piece waveguide tube (10) such that the waveguide tube (10) at least partially encloses an inner volume (10) (SI); characterized in that: forming the waveguide tube (10) with a mass share of aluminum of at least 50% by weight (Sla), and / or constructing a metal coating (22) with a mass share of aluminum of at least 50% by weight on and / or above at least one surface (16) of the waveguide tube (10) which is oriented towards the inner volume (12) (S2).

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