Mode converter and antenna system

Abstract

Mode converter (10) for a level radar, wherein the mode converter (10) comprises a housing (20), an input line (24) for supplying a high-frequency signal to the mode converter (10), a waveguide (27), a converter body (30), and a mode converter structure (35) made of a plurality of electrical conductors for converting the high-frequency signal supplied by the input line (24) into a defined mode of the waveguide (27), wherein the mode converter structure (35) is arranged inside the waveguide (27) such that a resonance chamber (26) is formed between the mode converter structure (35) and the inner wall of the waveguide (27) facing the mode converter structure (35), characterized in that at least a part of the surfaces of the resonance chamber (26) is covered with an absorber material (28).wherein absorber material (28) is arranged on all wall sections bounding the resonance chamber and the absorber material (28) is designed as ferromagnetic absorber mats.

Description

[0001] The invention relates to a mode converter for a level radar and an antenna system for a level radar with such a mode converter.

[0002] One of the well-known methods for determining the fill level in a container is the use of a level radar. This involves determining the travel time of a high-frequency signal (the radar signal) to the surface of a medium, and then deriving the distance between the emitting device, e.g., the antenna system of the level radar, and the medium.

[0003] It is known that a targeted selection of the propagating radar signal mode can improve the measurement accuracy of level radar. For example, EP 2 796 840 A1 discloses that, particularly for level measurements in standpipes or bypass lines, a significant improvement in measurement accuracy can be achieved by converting the radar signal to an H01 mode using a mode converter. However, even such mode conversion does not result in a completely interference-free signal.

[0004] US 2015 / 0022287 A1 discloses a mode converter for converting a rectangular TE10 waveguide mode into a circular TE01 waveguide mode. Reference is also made to US 2009 / 0212996 A1.

[0005] The object of the invention is therefore to provide a mode converter for a level radar and an antenna system for a level radar, with which the signal quality of the measurement signal is further improved. This object is achieved by a mode converter for a level radar with the features of claim 1 and an antenna system for a level radar with the features of claim 7. Advantageous developments of the invention are the subject of the respective dependent claims. The mode converter for a level radar according to the invention has an input line for feeding a high-frequency signal into the mode converter. This input line can be designed, for example, as a coaxial cable or as a waveguide.

[0006] The mode converter according to the invention further comprises a waveguide and a mode converter structure comprising a plurality of electrical conductors for converting the high-frequency signal supplied through the input line into a defined mode of the waveguide, wherein the mode converter structure is arranged within the waveguide so that a resonance chamber is formed between the mode converter structure and the inner wall of the waveguide facing the mode converter structure.

[0007] The specific design of the mode converter structure depends on the desired mode to be used. For example, conversion to the H01 mode occurs when the mode converter structure is formed from coiled electrical conductors. In particular, these conductors can be arranged symmetrically to a central axis of a helical structure and spiral around this central axis. In particular, an axis of symmetry of the resonant cavity and an axis of symmetry of the mode converter structure can be coaxial.

[0008] Essential to the invention is that at least part of the surfaces of the resonance chamber is covered with an absorber material, with absorber material being arranged on all wall sections bordering the resonance chamber. According to the invention, the absorber material is designed as ferromagnetic absorber mats. Surprisingly, it has been shown that this can improve signal quality, although conventional practice has always aimed for the most complete reflection of energy in the resonance chamber or at its boundaries.

[0009] A noticeable effect is achieved not only when the inner wall of the waveguide facing the mode converter structure is at least partially covered with absorber material, but also when an annular surface that defines the resonance chamber in or against the radiation direction is at least partially covered with such an absorber material. Of course, it is also possible to arrange absorber material on all wall sections defining the resonance chamber or to completely cover these wall sections with a layer of absorber material.

[0010] In a particularly preferred embodiment of the mode converter, the latter comprises a converter body which is designed as a dielectric body with a cylindrical section which is surrounded by the mode converter structure and which has a recess in the cylindrical section for receiving the input line for supplying the high-frequency signal to the mode converter.

[0011] The cylindrical section, which can particularly preferably run coaxially with the waveguide through which the mode converter structure is located, can support the mode converter structure. For example, if the input line is designed as a coaxial cable, its inner conductor can be accommodated in the recess. It has proven advantageous if the recess is deep enough that the accommodated input line has an overlap of more than 10%, preferably more than 40%, and particularly preferably more than half the length of the mode converter structure with the mode converter structure.

[0012] The converter body can additionally have a second cylindrical section that adjoins the first cylindrical section coaxially and can serve to mount it on a housing of the mode converter. Furthermore, the converter body can also have a radiation cone.

[0013] According to an embodiment of the invention which is particularly preferred due to its simplicity and cost-effective production, it is provided that the waveguide is formed by a housing, so that the inner walls of the housing defining the waveguide form boundary surfaces of the resonance chamber.

[0014] The radiation of the mode converter is further improved if an antenna body with an antenna horn is arranged directly or indirectly on the mode converter. Particularly when the mode converter is part of an antenna system that must absorb pressure due to its installation, as is often the case with measurements on standpipes, stability can be significantly improved if the antenna horn has a single- or multi-part filling made of a dielectric material. This filling should preferably be arranged at a distance from the inner side of the antenna horn, as otherwise negative effects of temperature fluctuations due to thermal expansion of the filling can occur.

[0015] It is particularly preferred if an absorber mat is arranged between the filling and the inside of the antenna horn.

[0016] According to the present application, the antenna horn is understood to be the conically widening part of the horn antenna. Sections in which the horn antenna continues cylindrically are therefore explicitly not considered part of the antenna horn.

[0017] In order to achieve optimal positioning of the absorber mat, it can additionally or alternatively be glued to the inside of the antenna horn.

[0018] Another fastening option, which can also be used additionally or alternatively, is an absorber mat that is at least partially ferromagnetic. Here, the absorber mat can be pulled to the inner wall of the antenna horn by means of at least one magnet, preferably arranged on the outside of the antenna horn.

[0019] Alternatively, the absorber mat itself can be magnetic or have magnetic sections so that the absorber mat fits snugly against the inside of the antenna horn.

[0020] It is also advantageous if the absorber mat has recesses optimized for high-frequency performance. Such recesses can be designed, for example, as slots running in the main radiation direction. Alternatively, the recesses can be designed as slots running transversely to the main radiation direction and preferably offset in the main radiation direction.

[0021] The antenna system according to the invention for a level radar is characterized in that it has a mode converter according to the invention and thus has the advantages resulting from the use of such a mode converter, as described in detail above.

[0022] The invention is explained in more detail below with reference to a figure showing an exemplary embodiment. It shows: Fig. 1: a cross-section through an antenna system for a level radar.

[0023] The figure shows a cross-section through an antenna system 100 with a mode converter 10, which is connected via a mount 40 to an antenna body 50 with an antenna horn 60. The antenna system 100 is designed to be essentially rotationally symmetrical about an axis A.

[0024] The mode converter 10 has a substantially cylindrical housing 20 with a radiation-side opening, which is not visible in the figure because a converter body 30 is inserted through it into the interior of the housing 20, and with a cover 21, which in this example is fastened to the housing 20 with screws 22. The cover 21 has a feedthrough 23 for an input line 24 designed as a coaxial cable for supplying a high-frequency signal, more precisely for the inner conductor 25 of the coaxial cable.

[0025] The converter body 30 has a radiation cone 31 that protrudes from the housing 20 in the radiation direction. Adjacent to the radiation cone 31 is a cylindrical section 32, in which two sealing rings 33, each inserted into a groove, create a seal between the housing 20 and the converter body 30. The cross-section of the section 32 increases abruptly at the wide end of the radiation cone 31, forming a step 37 that supports the converter body 30 on the holder 40.

[0026] In the end region of the converter body 30 opposite the radiation cone 31, there is another cylindrical section 34, which has a slightly smaller cross-section than section 32 and serves as a support for the mode converter structure 35, so that it is surrounded by it. Also provided in this end region is a recess 36 for receiving the inner conductor 25, which extends approximately halfway into the converter body 30, allowing a high-frequency signal to be fed in or supplied.

[0027] In the area of ​​the mode converter structure 35, the cross-section of the interior of the housing 20 is larger than the cross-section of the converter body 30, including the mode converter structure 35 arranged thereon, creating a resonance chamber 26 whose inner walls form a waveguide 27 within which the mode converter structure 35 is arranged. The resonance chamber 26 further has a circular top section formed by a section of the cover 21 and a likewise circular bottom section formed by a section of the bottom of the housing. The surfaces of the resonance chamber—i.e., the inner walls, top section, and bottom section—are each covered with absorber material 28.

[0028] The mode converter 30 is screwed into the holder 40, which in turn is connected by a screw connection to the antenna body 50 with the antenna horn 60. A dielectric filling 62 is arranged inside the antenna horn 60, spaced from its inner surface 61. An absorber mat 63 is located between the inner surface 61 of the antenna horn 60 and the dielectric filling 62. An elastic pressing means 64, designed as an elastic O-ring, prestresses the dielectric filling into the antenna horn 60, so that the absorber mat 63 is held in a form-fitting manner against the inner surface of the antenna horn 60 or pressed against it.

[0029] The antenna body 60 is screwed into a flange 70, which allows the antenna system to be arranged, for example, with a container whose fill level is to be monitored. The flange 70 also serves as a support for a dielectric lens 71 for achieving a desired radiation pattern for the signal emitted by the antenna system 10. List of reference symbols 10 mode converters 20 housings 21 lids 22 Screw 23 Implementation 24 input line 25 inner conductors 26 Resonance chamber 27 waveguides 28 Absorber material 30 converter bodies 31 beam cones 32 cylindrical section 33 Sealing ring 34 cylindrical section 35 Mode converter structure 36 recess 37th level 40 bracket 50 antenna bodies 60 antenna horn 61 Inside 62 filling 63 Absorber mat 64 contact pressure devices 70 flange 71 dielectric lens 100 antenna system A axis

Claims

[1] Mode converter (10) for a level radar, wherein the mode converter (10) comprises a housing (20), an input line (24) for supplying a high-frequency signal to the mode converter (10), a waveguide (27), a converter body (30), and a mode converter structure (35) comprising a plurality of electrical conductors for converting the high-frequency signal supplied through the input line (24) into a defined mode of the waveguide (27), wherein the mode converter structure (35) is arranged within the waveguide (27) such that a resonance chamber (26) is formed between the mode converter structure (35) and the inner wall of the waveguide (27) facing the mode converter structure (35). characterized bythat at least part of the surfaces of the resonance chamber (26) is covered with an absorber material (28), wherein absorber material (28) is arranged on all wall sections delimiting the resonance chamber and the absorber material (28) is designed as ferromagnetic absorber mats. [2] Mode converter (10) according to claim 1, characterized by that the mode converter (10) has a converter body (30) designed as a dielectric body with a cylindrical section (34) which is surrounded by the mode converter structure (35) and which has a recess (36) in the cylindrical section (34) for receiving the input line (24) for feeding the high-frequency signal into the mode converter (10). [3] Mode converter (10) according to claim 1 or 2, characterized by that the waveguide (27) is formed by a housing (20). [4] Mode converter (10) according to one of claims 1 to 3, characterized bythat an antenna body (50) with an antenna horn (60) is arranged on the mode converter (10). [5] Mode converter (10) according to claim 4, characterized by that the antenna horn (60) has a single-part or multi-part filling (62) made of a dielectric material, which is arranged at a distance from an inner side (61) of the antenna horn. [6] Mode converter (10) according to claim 5, characterized by that an absorber mat (63) is arranged between the filling (62) and the inside (61) of the antenna horn (60), which absorber mat is held in a form-fitting manner on the inside (61) of the antenna horn (60) by at least one pressing means (64). [7] Antenna system (100) for a level radar, characterized by that the antenna system (100) comprises a mode converter (10) according to one of claims 1 to 6.

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