Radar level gauge system with temperature resistant microwave absorber device

Abstract

A radar level gauge system with temperature resistant microwave absorber arrangement is provided. A radar level gauge system (1) for determining a fill level (L) of a product (9) in a tank (3) under high temperature conditions comprises a transceiver (11) for generating, transmitting and receiving microwave signals, a lens antenna (23) arranged along a signal path (35) of an electromagnetic transmission signal (S T ) from the transceiver, configured to direct the transmission signal (S T ) towards a surface (21) of the product in the tank and to direct electromagnetic reflection signals (S R ) resulting from reflections of the transmission signal at said surface (21) back towards the transceiver, a microwave absorber arrangement (31) at least partially surrounding said signal path and comprising a carrier (41) and a temperature resistant microwave absorber material (43) supported by the carrier, and processing circuitry (15) coupled to the transceiver and configured to determine the fill level based on a timing relationship between the transmission signal and the reflection signals.

Description

Technical Field

[0001] This invention relates to a radar level gauge system and its manufacturing method. Background Technology

[0002] Radar level gauge (RLG) systems are widely used to determine the fill level in tanks. Radar level measurement is typically performed using either non-contact or contact methods. In non-contact measurement, an electromagnetic signal is radiated towards the product in the tank. Contact measurement, often referred to as guided wave radar (GWR), involves a probe directing the electromagnetic signal towards and into the product. The probe is typically arranged to extend vertically from the top of the tank towards the bottom.

[0003] The transceiver generates an electromagnetic transmission signal and propagates the electromagnetic transmission signal toward the surface of the product in the can. The electromagnetic reflection signal generated by the reflection of the transmission signal at the surface is propagated back to the transceiver.

[0004] The distance to the product surface can be determined based on the timing relationship between the transmitted and reflected signals.

[0005] For some applications, such as non-contact radar level gauge systems that use microwave signals in relatively high frequency bands, antenna assemblies including lens antennas can be advantageously used.

[0006] High-frequency non-contact radar level gauges offer several advantages, such as a narrower measurement beam and a more compact size. The latter, in particular, allows for the installation of radar level gauge systems in a variety of tanks where pre-existing openings might be too small for conventional non-contact radar level gauge systems operating at lower frequencies, such as approximately 26 GHz or lower.

[0007] For high-temperature (HT) or high-temperature-high-pressure (HTHP) applications, GWR-type radar level gauge systems are currently preferred. While GWR-type radar level gauge systems are generally well-suited for applications, they also have limitations. For example, special considerations are needed for applications where violent fluid movement is anticipated.

[0008] The goal is to provide high-frequency non-contact radar level gauge systems for high-temperature applications as well. Summary of the Invention

[0009] In view of the above, the overall objective of the present invention is to provide a high-frequency non-contact radar level gauge system for high-temperature applications.

[0010] Therefore, according to a first aspect of the invention, a radar level gauge system is provided for determining the filling level of a product in a can under high-temperature conditions. The radar level gauge system includes: a transceiver for generating, transmitting, and receiving microwave signals; a lens antenna arranged along a signal path of an electromagnetic transmission signal from the transceiver, the lens antenna being configured to direct the transmission signal toward the surface of the product in the can and to direct an electromagnetic reflection signal generated by reflection of the transmission signal at the surface of the product in the can back toward the transceiver; a microwave absorber device at least partially surrounding the signal path of the transmission signal, the microwave absorber device including a carrier and a heat-resistant microwave absorber material supported by the carrier; and a processing circuit system coupled to the transceiver and configured to determine the filling level based on a timing relationship between the transmission signal and the reflection signal.

[0011] In existing radar level gauge systems that include lens antennas, microwave absorber devices can be provided to suppress sidelobes, thereby improving, for example, the directivity of the lens antenna and / or the near-field performance of the radar level gauge system. This invention is based on the understanding that one of the main obstacles to overcoming in adapting high-frequency non-contact radar level gauge systems to high-temperature applications is that existing microwave absorber devices cannot withstand the high temperatures (e.g., above 400°C) that may result from use in high-temperature applications.

[0012] The inventors have further recognized that microwave absorber devices capable of withstanding elevated temperatures can be formed by using a heat-resistant carrier supporting the heat-resistant microwave absorber material. The carrier can advantageously be a ceramic material, known for its high thermal stability and low thermal expansion. Alternatively, metals with low coefficients of thermal expansion, such as Invar or Covar alloys, can be used. Both Invar (iron-nickel) and Covar (iron-nickel-cobalt) alloys are recognized for their dimensional stability under temperature fluctuations, making them suitable for high-temperature applications.

[0013] This configuration of the microwave absorber device opens up the use of heat-resistant microwave absorber materials, which, when not supported by a carrier, would at most result in a very fragile microwave absorber device, making the radar level gauge system difficult to assemble and less resistant to handling.

[0014] Furthermore, the use of a carrier not only integrates heat-resistant microwave absorber materials but also provides mechanical stability and durability in harsh industrial environments. By structurally reinforcing the microwave absorber material, the carrier reduces the risk of cracking, detachment, or degradation over time, thereby improving the long-term reliability of the radar level gauge system. In addition, this configuration allows for precise positioning of the absorber material, ensuring consistent sidelobe suppression and optimizing antenna performance across a wide operating temperature range.

[0015] In an example of a radar level gauge system according to the invention, the microwave absorber device may surround the signal path of the transmitted signal along an arc angle of at least 300°. The microwave absorber device may completely surround the signal path, but in some configurations, it may alternatively extend around a substantial portion of the signal path while leaving open portions to accommodate structural or assembly constraints.

[0016] In either case, the microwave absorber material can be present along at least a specified arc angle to provide effective suppression of sidelobes and reduction of unwanted reflections. This configuration allows for flexibility in implementation while maintaining reliable performance in high-temperature environments.

[0017] In an example of a radar level gauge system according to the invention, the carrier may include a non-uniform surface structure for structurally reinforcing the heat-resistant microwave absorber material. By providing a non-uniform surface, the mechanical interlock between the carrier and the microwave absorber material can be improved, thereby reducing the risk of detachment or degradation over time.

[0018] The difference in thermal expansion between the carrier and the microwave absorber material can lead to mechanical stress, especially in high-temperature environments. Non-uniform surface structures can help manage such stress by improving adhesion and providing additional mechanical anchoring, thereby enhancing the durability of the microwave absorber device.

[0019] In an example of a radar level gauge system according to the invention, the carrier may have a cage-like structure with an opening between the interior of the carrier facing the signal path and the exterior of the carrier facing away from the signal path. A heat-resistant microwave absorber material may at least partially fill the opening in the carrier. This configuration provides structural reinforcement to the microwave absorber material while allowing for a reduced material volume within the carrier. Reducing the material volume decreases the weight of the carrier, improves material efficiency in manufacturing, and helps reduce internal stress caused by thermal expansion mismatch between the carrier and the microwave absorber material.

[0020] In an example of the radar level gauge system according to the invention, the heat-resistant microwave absorber material can completely fill the opening in the carrier. This configuration maximizes microwave absorption while ensuring uniform mechanical support for the absorber material, thereby reducing the risk of detachment or deterioration over time.

[0021] In an example of the radar level gauge system according to the invention, the opening of the carrier can be circular. This configuration can reduce stress concentration in the carrier, thereby providing improved mechanical strength and resistance to thermal cycling. It can also facilitate manufacturing, particularly in additive manufacturing processes, and provide a more uniform distribution of heat-resistant microwave absorber material within the opening.

[0022] In an example of the radar level gauge system according to the invention, the carrier can be made of a ceramic material. This configuration provides high-temperature resistance and mechanical stability, thereby allowing the carrier to maintain its structural integrity during thermal cycling and prolonged exposure to elevated temperatures. Suitable ceramic materials may include alumina, which provides thermal stability and mechanical strength; silicon carbide, which provides high thermal conductivity and low thermal expansion; and yttrium-stabilized zirconia, which exhibits high fracture toughness and heat resistance.

[0023] Ceramic carriers can be manufactured using additive manufacturing techniques such as robotic extrusion. In this process, a ceramic slurry with a high concentration of ceramic particles relative to a liquid binder is extruded through a nozzle to build the desired structure layer by layer. The high particle content in the slurry provides minimal shrinkage and deformation during drying and sintering, resulting in dense and mechanically robust ceramic components. After printing, the structure can undergo a drying stage, followed by sintering at elevated temperatures to achieve the final material properties. This method allows for the creation of complex geometries, including cage-like structures with precise control over the internal architecture. By leveraging 3D printing technology, carrier designs can be optimized for both performance and material efficiency, providing tailored solutions for specific high-temperature radar level metering applications.

[0024] In an example of a radar level gauge system according to the invention, the heat-resistant microwave absorber material may comprise carbon or iron. This configuration can provide effective attenuation of unwanted microwave signals because both carbon-based and iron-based materials can exhibit strong microwave absorption properties.

[0025] An example of a microwave absorber material containing both carbon and iron is carbonyl iron, which consists of spherical particles of high purity. However, those skilled in the art will recognize alternative materials that can be used depending on the specific absorption characteristics required for a given application.

[0026] In an example of a radar level gauge system according to the invention, the heat-resistant microwave absorber material can be a thermosetting composite material. This configuration can provide beneficial mechanical stability and adhesion to the carrier after curing, thereby allowing the microwave absorber material to maintain its shape and position under high-temperature conditions. By using a thermosetting composite material, the absorber material can be applied in a moldable or flowable state and subsequently hardened by thermosetting.

[0027] Suitable thermosetting composite materials may include materials such as black refractory cement, which contains quartz and sodium silicate and can withstand temperatures of at least 1100°C. Other possible materials may include silicate-based refractory cement or ceramic slurries, which provide a durable, high-temperature resistant structure upon curing. These materials may be applied in slurry form, and where the carrier includes openings, these materials may be used to fill these openings prior to curing to form a mechanically stable absorber device.

[0028] In an example of a radar level gauge system according to the invention, the ceramic carrier can be selected to have a coefficient of thermal expansion (CTE) within about 20% of that of the heat-resistant microwave absorber material. For example, black refractory cement comprising quartz and sodium silicate may be present. to The CTE is within the range of [specific range]. In this context, a suitable support material could be alumina, whose CTE is approximately [specific range]. This combination can provide reduced thermal stress at the interface between the carrier and the microwave absorber material, thereby allowing for improved durability and mechanical stability of the microwave absorber device in high-temperature environments. Those skilled in the art will recognize alternative material combinations that can provide similar benefits.

[0029] In an example of a radar level gauge system according to the invention, the radar level gauge system may include a hollow waveguide connecting a transceiver and a lens antenna, wherein a microwave absorber device is arranged inside the hollow waveguide. This configuration can provide attenuation of unwanted microwave reflections within the waveguide, thereby reducing interference and improving signal integrity.

[0030] As an alternative or supplement, a microwave absorber device can at least partially surround the lens antenna. This configuration can provide further attenuation of unwanted microwave radiation around the antenna, thereby reducing sidelobes and minimizing interference from reflections within the system. By selecting a suitable placement for the microwave absorber device, the system can provide improved directivity and more accurate level measurements.

[0031] In an example of the radar level gauge system according to the invention, the lens antenna can be made of a non-plastic dielectric. This configuration provides high-temperature resistance, thereby allowing the antenna to maintain its shape and function when subjected to elevated process temperatures.

[0032] Suitable materials can include ceramics, such as alumina or machinable ceramics like Macor®, and high-temperature glass materials such as fused silica. These materials can exhibit both mechanical stability and dielectric properties suitable for microwave transmission, making them ideal for radar level gauge systems operating in harsh environments.

[0033] According to a second aspect of the present invention, a method for manufacturing a microwave absorber device for a radar level gauge system is provided, the method comprising: providing a carrier; distributing a slurry comprising a microwave absorbing component and a refractory binder on the carrier; and curing the slurry.

[0034] The inventors have recognized that by applying microwave absorber material in slurry form prior to curing, the absorber material can conform to the structure of the carrier, thereby allowing for strong mechanical bonding and uniform distribution. This method can be particularly advantageous when the carrier comprises a non-uniform surface structure, as the slurry can flow into surface variations or openings before hardening, thus providing a mechanically stable absorber device. Attached Figure Description

[0035] These and other aspects of the invention will now be described in more detail with reference to the accompanying drawings, which illustrate exemplary embodiments of the invention, in which:

[0036] Figure 1 A radar level gauge system according to an exemplary embodiment of the present invention is schematically illustrated in an exemplary HTHP application;

[0037] Figure 2 It is shown schematically. Figure 1 Block diagram of the radar level gauge system in the image;

[0038] Figure 3A It can be included in Figure 2 A schematic cross-sectional view of a first example of the antenna assembly configuration in a radar level gauge system;

[0039] Figure 3B The illustration shows that it can be included in Figure 3A An example of a microwave absorber device in an antenna assembly configuration;

[0040] Figure 4A It can be included in Figure 2 A schematic cross-sectional view of a second example of the antenna assembly configuration in a radar level gauge system;

[0041] Figure 4B The illustration shows that it can be included in Figure 4A Examples of microwave absorber devices in antenna assembly configurations; and

[0042] Figure 5 This is an example of a manufacturing method according to the present invention. Detailed Implementation

[0043] Figure 1 A radar level gauge system 1 according to an exemplary embodiment of the present invention is schematically illustrated in an exemplary high-temperature and high-pressure (HTHP) application. Figure 1In the example shown, the HTHP application is a simplified boiler 3 having a boiler drum 5 and a chamber 7 (also commonly referred to as a constraint). The boiler drum 5 is in fluid communication with the chamber 7 such that the level L of the product 9 in the chamber 7 corresponds to the level in the boiler drum 5. Thus, the boiler drum 5 and the chamber 7 together form a tank, and the opening at the top of the chamber 7 is an opening in the tank wall. The radar level gauge system 1 according to this example will also be suitable for other applications, such as measuring the level of solids at a grid cooler in a cement plant. The latter application does not involve high pressure but is an example of a purely high-temperature (HT) application.

[0044] Reference Figure 2 , Figure 1 The radar level gauge system 1 includes a transceiver 11, an antenna assembly 13, a processing circuit system 15, and a communication interface 17, all located within a housing 19. The transceiver 11 is configured to generate, transmit, and receive microwave signals. The antenna assembly 13 transmits electromagnetic signals S from the transceiver 11. T The signal path 35 is arranged and configured to transmit the signal S. T The product 9 is guided toward the surface 21 of the product 9 in the can 3 and will be emitted by the signal S. T The electromagnetic reflection signal S generated by the reflection at surface 21 of product 9 R The signal is directed back towards transceiver 11. Processing circuitry 15 is coupled to transceiver 11 and configured to use techniques known per se based on the transmitted signal S. T and reflected signal S R The timing relationship between the parameters determines the filling level L. The determined filling level L can be transmitted to a remote host using communication interface 17, which can be any suitable wired or wireless communication interface known in the art. It should be noted that the opening in the tank wall can alternatively be located in the wall of the boiler drum 5, and the antenna device 13 can be arranged at such an opening to directly measure the level L in the boiler drum 5. In this configuration, a ball valve can exist between the interior of the boiler drum 5 and the antenna device 13.

[0045] Included Figure 2 The antenna assembly 13 in the radar level gauge system 1 is suitable for both transmitting and receiving signals at high frequencies, and for addressing the specific challenges associated with HTHP applications, particularly high-temperature applications. HTHP applications can be categorized as those where the antenna assembly 13 may be subjected to pressures up to 400 bar and temperatures up to 450°C. These harsh process conditions impose requirements on the mechanical integrity of the components included in the antenna assembly 13, especially at very high temperatures.

[0046] Therefore, first refer to Figure 3AIn the first example configuration, the radar level gauge system 1 includes a heat-resistant microwave absorber device 31 configured to suppress unwanted microwave radiation. The microwave absorber device 31 may be disposed within a hollow waveguide 33 connecting the transceiver 11 and the antenna assembly 13. The microwave absorber device 31 may surround at least a portion of the space defined by the hollow waveguide 33 and may comprise a heat-resistant microwave absorber material.

[0047] Figure 3A The antenna device 13 may further include a lens antenna 23, which transmits the electromagnetic signal S from the transceiver 11 along the path of the signal. T The signal path 35 is arranged. The lens antenna 23 can be configured to transmit the signal S. T The product 9 is guided toward the surface 21 of the product 9 in the can 3 and will be emitted by the signal S. T The reflected signal S generated by the reflection at surface 21 of product 9 R Guided back toward transceiver 11. When lens antenna 23 is arranged as... Figure 1 When the lens antenna 23 is located at the opening in the can wall shown, it can be made of a non-plastic dielectric material and can be configured to receive and transmit signal S. T The inner surface 25 and configured to transmit the signal S T And receive the reflected signal S R The outer surface 27. The antenna device 13 may also include a feed section 29, which is arranged to transmit the signal S. T Guided toward the inner surface 25 of the lens antenna 23.

[0048] exist Figure 3A In the example configuration, the microwave absorber device 31 can be arranged inside the hollow waveguide connecting the transceiver 11 and the lens antenna 23. This configuration can provide attenuation of unwanted microwave reflections within the waveguide, thereby reducing interference and improving signal integrity. The microwave absorber device 31 can be formed using a heat-resistant microwave absorber material supported by a carrier, which can be a ceramic structure. This will be referred to below. Figure 3B To describe in more detail.

[0049] The lens antenna 23 can advantageously be made of suitable ceramic or glass. Examples of suitable ceramics may include alumina or machinable ceramics such as Macor®. Alternatively, suitable high-temperature glass materials, such as fused silica, may be used.

[0050] exist Figure 3A In an exemplary configuration of the lens antenna 23, the inner surface 25 of the lens antenna 23 can be shaped to transmit the signal S from the feed section 29. TThe focus is on a plane wave propagating towards the outer surface 27 within the lens antenna 23. In this configuration, the wavefront of the plane wave can be parallel to the outer surface 27, allowing the transmitted signal S to be focused. T It will not be refracted at the interface between the lens antenna 23 and the atmosphere inside the tank 3.

[0051] Figure 3B The illustration shows that it can be included in Figure 3A An example of a microwave absorber device 31 in antenna assembly 13. In this example configuration, the microwave absorber device 31 is conical and its dimensions are set to be suitable for mounting on... Figure 3A Inside a conical or horn-shaped hollow waveguide. Figure 3B In this configuration, the carrier 41 is visible inside the microwave absorber device 31, while the exterior is completely covered by the heat-resistant microwave absorber material 43. Figure 3B In the specific example shown, the carrier 41 has a non-uniform surface structure, particularly exhibiting a cage-like structure, when the carrier 41 faces the transmitted signal S. T The signal path 35 is internal and the signal S is emitted from the carrier 41 in the opposite direction. T The signal path 35 has an opening 45 between its outer edges. For example... Figure 3B As shown, opening 45 can be circular.

[0052] Figure 3B The configuration of the microwave absorber device 31 provides structural reinforcement for the heat-resistant microwave absorber material 43. The cage-like structure of the carrier 41 enhances mechanical stability and durability by providing mechanical anchoring for the heat-resistant microwave absorber material 43, thereby reducing the risk of detachment or degradation over time. Furthermore, the openings 45 in the carrier 41 allow a sufficient portion of the total surface area of ​​the microwave absorber device 31 to efficiently absorb microwaves, while simultaneously providing structural reinforcement. The interior of the microwave absorber device 31 can be completely coated with the heat-resistant microwave absorber material 43, which can benefit microwave absorption performance.

[0053] Figure 4A Another example configuration of the antenna assembly 13, which may be included in the radar level gauge system 1, is schematically shown. In this example, the lens antenna 23 has a flat inner surface 25 and a raised outer surface 27. The inner surface 25 is located at the bottom of a cup-shaped notch formed in the lens antenna 23. A hollow waveguide 33 terminates at the inner surface 25 at the bottom of the cup-shaped notch, thereby providing a transmitted signal S. T Transmission to the lens antenna 23. The microwave absorber device 31 is configured as a generally cylindrical shell and arranged around the lens antenna 23.

[0054] Figure 4B The illustration shows that it can be included in Figure 4AAn example of a microwave absorber device 31 in antenna assembly 13. In this example configuration, the microwave absorber device 31 is cylindrical and its dimensions are set to surround the lens antenna 23. Figure 4B In this configuration, the carrier 41 is visible inside the microwave absorber device 31, while the exterior is completely covered by the heat-resistant microwave absorber material 43. Figure 4B In the specific example shown, the carrier 41 has a non-uniform surface structure, particularly exhibiting a cage-like structure, when the carrier 41 faces the transmitted signal S. T The signal path 35 is internal and the signal S is emitted from the carrier 41 in the opposite direction. T The signal path 35 has an opening 45 between its outer edges. The opening 45 can be circular, such as... Figure 4B As shown.

[0055] Figure 5 An example of a method for manufacturing a microwave absorber device 31 according to the present invention is illustrated schematically. The method includes: providing a carrier 41, S51.

[0056] The carrier 41 may be pre-formed or provided. S51 The carrier 41 may include: forming the carrier 41. In an example, the carrier 41 may be a ceramic structure formed using 3D printing technology. One example of this technology is robotic extrusion molding, where a ceramic slurry with a high concentration of ceramic particles relative to a liquid binder can be extruded through a nozzle to build the desired structure layer by layer. The high particle filling amount in the slurry can provide minimal shrinkage and deformation during drying and sintering, resulting in a dense and mechanically robust ceramic part. After printing, the structure may undergo a drying stage, followed by sintering at elevated temperatures to achieve the final material properties. In some examples, the carrier 41 may include a non-uniform surface structure, such as a cage-like device with openings 45.

[0057] Figure 5 The method proceeds to the application of slurry 43 (S52) on carrier 41, slurry 43 comprising a microwave-absorbing component and a refractory binder. Depending on the consistency of slurry 43 and the structure of carrier 41, slurry 43 can be applied in a moldable or flowable state using methods such as brushing, spraying, dipping, or casting. In an example where carrier 41 includes openings 45, slurry 43 can at least partially fill these openings. Slurry 43 can be prepared by combining the microwave-absorbing component with a refractory binder and a liquid medium (e.g., water) to achieve a workable consistency. The refractory binder can be used to gel the materials together in the applied state, thereby ensuring cohesion before further processing.

[0058] Figure 5The method described herein proceeds to the curing of S53 slurry 43. Curing S53 slurry 43 may include subjecting the applied slurry 43 to a thermal curing process to achieve a mechanically stable and heat-resistant structure. Depending on the composition of slurry 43, the curing process may involve drying, dehydration, evaporation of the binder, and / or sintering at elevated temperatures. Curing conditions may be selected to allow the refractory binder to solidify while maintaining the microwave-absorbing properties of the microwave-absorbing components.

[0059] Those skilled in the art will recognize that the present invention is by no means limited to the embodiments described above. Rather, many modifications and variations are possible within the scope of the appended claims. For example, depending on specific application requirements, the microwave absorber device may have alternative geometries or configurations, and different materials may be used for the carrier and the heat-resistant microwave absorber material.

Claims

1. A radar level gauge system (1) for determining the filling level (L) of product (9) in a tank (5) under high temperature conditions, the radar level gauge system (1) comprising: Transceiver (11) for generating, transmitting and receiving microwave signals; Lens antenna (23), the lens antenna (23) along the electromagnetic transmission signal (S) from the transceiver (11) T The signal path (35) is arranged such that the lens antenna (23) is configured to transmit the signal (S) T The signal is directed toward the surface (21) of the product (9) in the can (5) and will be transmitted by the signal (S). T The electromagnetic reflection signal (S) generated by the reflection at the surface (21) of the product (9) in the can (5) R ) is guided back toward the transceiver (11); Microwave absorber device (31), said microwave absorber device (31) at least partially surrounds the transmitted signal (S T The signal path (35) of the microwave absorber device (31) includes a carrier (41) and a heat-resistant microwave absorber material (43) supported by the carrier (41); and Processing circuitry (15), coupled to the transceiver (11), and configured to operate based on the transmitted signal (S) T ) and the reflected signal (S) R The timing relationship between the filling material (L) and the filling material (L) is used to determine the filling material position.

2. The radar level gauge system (1) according to claim 1, wherein the microwave absorber device (31) surrounds the transmitted signal (S) along an arc angle of at least 300°. T The signal path (35) of the signal path.

3. The radar level gauge system (1) according to claim 1 or 2, wherein the carrier (41) includes a non-uniform surface structure for structurally reinforcing the heat-resistant microwave absorber material (43).

4. The radar level gauge system (1) according to claim 3. The carrier (41) has a cage-like structure, and the carrier (41) faces the transmitted signal (S). T An opening (45) is provided between the interior of the signal path (35) of the carrier (41) and the exterior of the signal path (35) facing away from the transmitted signal (ST); and The heat-resistant microwave absorber material (43) at least partially fills the opening (45) of the carrier (41).

5. In the radar level gauge system (1) according to claim 4, the heat-resistant microwave absorber material (43) completely fills the opening (45) of the carrier (41).

6. In the radar level gauge system (1) according to claim 4, the opening (45) of the carrier (41) is circular.

7. The radar level gauge system (1) according to claim 1 or 2, wherein the carrier (41) is made of ceramic material.

8. The radar level gauge system (1) according to claim 1 or 2, wherein the heat-resistant microwave absorber material (43) comprises carbon or iron.

9. The radar level gauge system (1) according to claim 1 or 2, wherein the heat-resistant microwave absorber material (43) is a thermosetting composite material.

10. The radar level gauge system (1) according to claim 9, wherein the heat-resistant microwave absorber material (43) comprises a refractory binder.

11. The radar level gauge system (1) according to claim 1 or 2. The radar level gauge system (1) includes a hollow waveguide (33) connecting the transceiver (11) and the lens antenna (23); and The microwave absorber device (31) is arranged inside the hollow waveguide (33).

12. The radar level gauge system (1) according to claim 1 or 2, wherein the microwave absorber device (31) is at least partially surrounding the lens antenna (23).

13. The radar level gauge system (1) according to claim 1 or 2, wherein the lens antenna (23) is made of a non-plastic dielectric.

14. The radar level gauge system (1) according to claim 1 or 2, wherein the lens antenna (23) is configured to converge the transmitted signal (S T ).

15. A method for manufacturing a microwave absorber device (31) for use in a radar level gauge system (1) according to claim 1 or 2, the method comprising: Provide (S51) carrier (41); A slurry (43) comprising a microwave-absorbing component and a refractory binder is disposed (S52) on the carrier (41); and The slurry (43) is cured (S53).

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