Radar-based filling level measuring device for detecting the filling level of low-dielectric-constant medium present in a container.

Abstract

A radar filling level measuring device (1) for detecting the filling level of a low dielectric constant medium (3) present in a container (2) is shown and described, comprising a supply / receiving element (3) located on the outside of the container (2) for generating and receiving electromagnetic radiation (5), a measurement window (6) on the inner wall of the container (2) that allows electromagnetic radiation (5) to pass through, and a waveguide (7) located inside the container (2) and extending over a filling level measurement area, which is immersable in the medium (3), wherein the supply / receiving element (4), the measurement window (6), and the waveguide (7) form a measurement path through which electromagnetic radiation (5) generated by the supply / receiving element (4) during a measurement operation propagates through the measurement window (6) and the waveguide (7), and electromagnetic radiation (9) reflected from the surface (8) of the medium inside the waveguide (7) returns to the supply / receiving element (4) through the waveguide (7) and the measurement window (6).

Description

Technical Field

[0001] The present invention relates to a radar filling level measuring device for detecting the filling level of a low dielectric constant medium present in a container.

[0002] Detection of the filling level of the medium in the container by a radar filling level measuring device is a standard measurement task in process measurement technology, and the specific implementation of the radar filling level measuring device can vary greatly. In radar-based filling level measurement, substantially two different configurations and associated technologies are used.

[0003] In both methods, the supply and reception elements for generating and receiving electromagnetic radiation are usually located outside the container whose filling level is to be monitored, and accordingly, the associated control and evaluation system is also arranged outside the container. The electromagnetic radiation generated and emitted by the supply and reception elements reaches the internal space of the container through an opening in the container, is partially reflected at the surface of the medium present in the container, and the reflected electromagnetic radiation is received by the transmission and reception elements. Then, the evaluation system directly or indirectly obtains the time-of-flight information, which gives information about the distance to the medium surface and thus the filling level of the medium in the container.

[0004] The electromagnetic radiation guided into the internal space of the container through the opening in the container is radiated as a free space wave inside the container, or the electromagnetic radiation is guided into the internal space of the container in a cable-connected state, provided that the cable path also defines the measurement path at the same time. A radar filling level measuring device that functions using a free space wave usually functions as a frequency-modulated continuous wave radar (FMCW) in most cases, while a cable-connected radar filling level measuring device usually functions by direct time-of-flight evaluation of a pulse-shaped radar signal in most cases.

[0005] In the prior art, waveguides are also known to function when measuring the filling level. In this case, electromagnetic radiation generated by the supply and receive elements is coupled directly to the waveguide outside the container. The waveguide extends from the outer space of the container through an opening in the inner wall of the container into the inner space of the container, and extends through the inner space over the target measurement distance. The supply and receive elements and the waveguide, including the accessories necessary for mounting the radar filling level measuring device, form a mechanical unit as described herein.

[0006] For radar range measurement, it is essential that the surface of the target medium within the container reflects some of the electromagnetic radiation; more precisely, that the interface between the target medium and the unfilled container produces appropriate reflection. The reflectivity of the boundary layer depends on the refractive index of the mediums involved, that is, on the refractive index of the medium within the container and the refractive index of the unfilled space, which may be filled with, for example, air, a protective gas, or another medium. Air has a dielectric constant close to 1.

[0007] The refractive index of a medium can be determined from the root of the product of its relative permeability and relative permittivity. Since the relative permeability of a non-ferromagnetic material is approximately equal to 1, the refractive index is critically dependent on the relative permittivity. When a medium has a refractive index (and therefore relative permittivity) close to 1, the contribution of electromagnetic radiation reflected at the air interface is very small, and the reflected electromagnetic signal also has only a small intensity. In some cases, evaluating the reflected signal originating from the medium can be very difficult. The problem described arises, for example, when the medium in a container is liquid hydrogen with a relative permittivity close to 1.

[0008] The object of the present invention is to provide a radar filling level measuring device that can reliably calculate the filling level of the low dielectric constant medium inside a container using radar measurement.

[0009] The aforementioned problems are solved in the radar fill level measuring device, which includes a supply / receiving element located outside the container for generating and receiving electromagnetic radiation, a measurement window on the inner wall of the container that allows electromagnetic radiation to pass through, and a waveguide located inside the container and extending across the fill level measurement area (Fullstandmessbereich), which is immersable by a medium (flutbar). The supply element, measurement window, and waveguide form a measurement path, through which the electromagnetic radiation generated by the supply element during the measurement operation propagates through the measurement window and then through the waveguide. Since the waveguide is immersable by a medium, the medium inside the container easily penetrates into the waveguide, and as a result, the electromagnetic radiation reflected by the surface of the medium inside the waveguide passes through the waveguide and then through the measurement window and back to the supply / receiving element.

[0010] The radar fill level measuring device described operates in conjunction with a waveguide within a container. The waveguide has the advantage that the energy of the electromagnetic radiation coupled into the waveguide is maintained virtually completely over the measurement distance, meaning the measurement configuration operates with minimal attenuation. Furthermore, the use of a waveguide has the advantage that it can operate with relatively high energies of electromagnetic radiation, resulting in a reflected signal that can be evaluated relatively well even with small reflection contributions.

[0011] The radar fill level measuring device is preferably realized from multiple parts, so that the supply / receiving elements, the measuring window, and the waveguide are mechanically separated from each other. This has the advantage that the sealing of the container achieved by the measuring window is not subjected to loads from possible movements and / or mechanical loads of the supply / receiving elements and / or the waveguide, and therefore the sealing effect is not adversely affected, which is especially important in the case of volatile media, hydrogen in extreme cases.

[0012] A first variant of the radar filling level measuring device is characterized in that the waveguide is implemented in a single mode with respect to the frequency of electromagnetic radiation generated by the supply and receive elements. This means that only electromagnetic waves whose half wavelength corresponds to the maximum dimension of the waveguide propagate within the waveguide.

[0013] In an alternative configuration of a radar filling level measuring device, the waveguide is assumed to be implemented in an overmode (ubermodet) with respect to the frequency of electromagnetic radiation generated by the supply and receive elements, particularly as a circular waveguide or a rectangular waveguide. Preferably, the waveguide dimensions are up to 3.5 times larger than in the corresponding single-mode implementation, and especially preferably, up to 2.5 times larger than in the waveguide's corresponding single-mode implementation. The waveguide is called overmode because its dimensions are actually chosen to be larger than what would be necessary for guiding only the excited modes. For example, even if only the fundamental mode is actually excited, the waveguide has dimensions that allow for the transmission of higher-order modes as well. This type of configuration has various advantages related to the fact that the group velocity of the excited modes increases with the waveguide dimensions (cross-section, diameter, and axis of the cross-section) with respect to the same frequency. At the same time, the frequency dependence of the group velocity decreases with increasing waveguide cross-section. This means that the proposed design has the effect of expanding the measurement range due to the reduction in dispersion effect associated with higher group velocities, and therefore the reduction in temporal "signal smearing." This relationship can be explained more appropriately with reference to the corresponding diagram, which will be done in the explanation of the diagram.

[0014] In one advanced form of a radar fill level measuring device, it is noted that the supply and receive elements intentionally excite only the fundamental mode, particularly at frequencies above the cutoff frequency of the fundamental mode, i.e., in the region of reduced dispersion and higher group velocity. Particularly preferred is to operate at frequencies as far above the cutoff frequency of the fundamental mode as possible without intentionally exciting higher-order modes, the advantages being the same as described above.

[0015] Another advantage is that, at a given frequency of electromagnetic radiation, overmode waveguides have a larger cross-section, in which case the capillary effect of the medium within the waveguide plays a less significant role. In this case, the reflective surface is flatter, and consequently, there is a larger available reflective surface than in the case of a single-mode waveguide design.

[0016] A further development of the radar filling level measuring device is envisioned in which the end of the waveguide facing the measurement window has an antenna for the purpose of coupling electromagnetic radiation into and out of the waveguide. In particular, this antenna is a horn antenna.

[0017] A preferred further embodiment of a radar fill level measuring device is characterized in that the supply / receive element has an antenna for radiating the generated electromagnetic waves and receiving the reflected electromagnetic waves, in which case the antenna is preferably finished as a horn antenna. The use of an antenna in the waveguide or supply / receive element improves the overall directivity of the components, thus improving the overall signal-to-noise ratio of the measurement path.

[0018] In a further preferred embodiment, beam shaping elements are positioned in the measurement window region to align and / or bundle (Bundelung) electromagnetic radiation between the supply / receive elements and the waveguide, also to improve the directivity of the components and the signal-to-noise ratio. In a particular embodiment, the beam shaping elements are mounted on the outside and / or inside of the measurement window, for example, in the form of lens elements. In a further embodiment, the measurement window itself is finished as a beam shaping element, thereby partially or completely realizing the function of a beam shaping element.

[0019] In the radar fill level measuring apparatus described herein, electromagnetic transmission signals radiated from the supply and receive elements travel through the entire measurement path and leave the waveguide at an opening located at the end of the waveguide that does not face the measurement window. In this case, the opening of the waveguide typically faces the inner wall of the container. The electromagnetic radiation leaving the waveguide there is then reflected by the inner wall of the container, or, where appropriate, by other mounting components within the container, and at least partially reaches the waveguide again, where it is guided back towards the transmitting and receiving elements. This interference signal may, in some cases, be significantly larger than the electromagnetic radiation reflected from the surface of the medium, which is the useful signal of the original target, and this is especially true for low dielectric constant media, as considered herein. Therefore, in a preferred embodiment of the radar fill level measuring apparatus, a reflector is placed in the region of the waveguide's opening that does not face the measurement window, so that the electromagnetic radiation emanating from the waveguide is not reflected back towards the opening of the waveguide that does not face the measurement window. The reflector can be placed, for example, on the inner wall of the container, but it can also be fixed to the waveguide itself.

[0020] Another measure to mitigate the problem of interference signals caused by reflection is, in a further development of the radar filling level measuring device, to place a polarizer in the region of the waveguide's opening that does not face the measurement window, which polarizes the electromagnetic radiation emanating from the waveguide into reflected electromagnetic radiation that does not trigger a reaction in the transmitting and receiving elements. The polarizer can, for example, ensure a 90° phase rotation of the electromagnetic radiation. The polarizer can also be placed on the inner wall of the container or on the waveguide itself.

[0021] In a further development of the radar fill level measuring device, an encoded reflector is placed in the region of the waveguide's opening that does not face the measurement window, generating reflected electromagnetic radiation with a corresponding encoded signature (codierte Signatur). In this variant, the reflected interference signal is not suppressed (as in the case of a polarizer), but the interference signal can be subtracted from the received signal during signal processing based on its known signature, i.e., based on a known temporal signal transition. In other words, this solution assumes that the evaluation unit performs the corresponding signal processing, for example, based on a digital signal processor.

[0022] In a further embodiment of the radar fill level measuring device, the supply / receiving elements and the measuring window, or the supply / receiving elements and a beam shaping element (placed on the measuring window) facing the supply / receiving elements, are aligned with each other such that electromagnetic radiation emitted from the transmitting / receiving elements is not reflected back to the transmitting / receiving elements, or only partially reflected back. This measure can also suppress interference signals and improve the signal-to-noise ratio.

[0023] An alternative or additional measure for reducing reflection is to finish the measurement window and / or beamforming element with an optically tuned layer for reducing reflection. Preferably, the optically tuned layer is a dielectrically tuned layer, wherein the dielectric constant of the material used for the tuned layer is tuned to the dielectric constant of the measurement window and / or beamforming element to which the tuned layer is applied.

[0024] In a further preferred embodiment of the radar fill level measuring device, a mode converter is arranged in the region of the opening of the waveguide facing the measurement window, which converts the electromagnetic radiation from the measurement window towards the opening of the waveguide facing the measurement window into a desired mode. For example, the mode converter can convert a TE11 wave into a TE01 wave and vice versa. The advantage of the mode conversion exemplified is that the TE01 mode requires a larger waveguide, which acts advantageously on the capillary effect (reduction of the capillary effect). In this mode, there is less electromagnetic field in the outer region, so the deposits in the waveguide are less obstructive. Similarly, additional openings in the inner wall of the waveguide are also possible.

[0025] In an alternative embodiment of the radar fill level measuring device, a mode converter is arranged behind the supply and reception element, which converts the generated electromagnetic radiation into a desired mode outside the container.

[0026] In particular, there will be a number of means for finishing and developing the radar fill level measuring device according to the invention.

[0027] In this regard, on the one hand, reference is made to the claims that depend on the independent claims, and on the other hand, to the following description of the embodiments in connection with the drawings.

Brief Description of the Drawings

[0028] [Figure 1] A schematic diagram of a radar fill level measuring device for detecting the fill level of a low dielectric constant medium present in a container is shown. [Figure 2a] Schematic diagrams of three variants of a radar fill level measuring device with various measures for suppressing the effect of the interference reflection signal (Stor - Reflexionssignal) are shown. [Figure 2b] Schematic diagrams of three variants of a radar fill level measuring device with various measures for suppressing the effect of the interference reflection signal (Stor - Reflexionssignal) are shown. [Figure 2c]Schematic views of three variants of a radar fill level measuring device with various measures for suppressing the effect of the interference reflection signal (Stor - Reflexionssignal) are shown. [Figure 3] A schematic view of a radar fill level measuring device using an adjustment layer for reducing reflections is shown. [Figure 4] A schematic view of a radar fill level measuring device using a mode converter is shown. [Figure 5a] A graph explaining the frequency dependence of the group velocity of the waveguide wave (Hohlleiterwelle) is shown. [Figure 5b] A graph explaining the frequency dependence of the effect of an increase in waveguide dimensions on the group velocity of the waveguide wave based on the over - mode design of the waveguide is shown.

[0029] In FIGS. 1 to 4, a radar fill level measuring device 1 and various embodiments of its implementation are shown respectively. What is common to the shown radar fill level measuring device 1 is that it is used to detect the fill level of the low - dielectric - constant medium 3 present in the container 2. In this case, the medium 3 is liquid hydrogen. The radar fill level measuring device 1 has a supply and receiving element 4 for generating and receiving electromagnetic radiation 5 outside the container 2. Further, it has a measurement window 6 arranged on the inner wall of the container 2 for transmitting the electromagnetic radiation 5, and a waveguide 7 extending over the fill level measurement region inside the container 2. However, the waveguide 7 can be flooded by the medium 3, that is, the fill level of the medium 3 inside the container 2 is the same inside and outside the waveguide 7.

[0030] The supply / receiving element 4, the measurement window 6, and the waveguide 7 form a measurement path, through which the electromagnetic radiation 5 generated by the supply / receiving element 4 during the measurement operation propagates through the measurement window 6 and then through the waveguide 7. The electromagnetic radiation 9 reflected from the medium surface 8 of the medium 3 inside the waveguide 7 passes through the waveguide 7 and the measurement window 6 and returns to the supply / receiving element 4. In cases like this, where the medium 3 has a dielectric constant close to 1, the electrical properties important for electromagnetic wave propagation do not change or only change very slightly at the medium surface 8. Therefore, only a small portion of the electromagnetic radiation 5 emitted from the supply / receiving element 4 is reflected from the medium surface 8 as reflected electromagnetic radiation 9. As a result, the original target measurement signal in the form of reflected electromagnetic radiation 9 is considerably weak, making evaluation difficult.

[0031] The use of waveguide 7 has the advantage of very slight attenuation of electromagnetic radiation 5 or reflected electromagnetic radiation 9. Furthermore, since the entire energy of electromagnetic radiation 5 is concentrated and guided by a certain surface region 8 of the medium 3, a certain useful signal is also produced in the form of reflected electromagnetic radiation 9.

[0032] The radar filling level measuring device 1 in Figure 1 is implemented in a single mode for the frequency of electromagnetic radiation 5 generated by the supply / receive element 4, in this case, that is, it functions with a waveguide 7 as a circular waveguide. In a single-mode implementation, a characteristic dimension (i.e., the diameter in the case of a circular waveguide) is selected in the cross-section of the circular waveguide so that only one wave mode, in this case the fundamental mode, can propagate.

[0033] To better understand the behavior of waveguide waves within a waveguide, refer to Figure 5a. The group velocities of various waveguide wave modes (TE11, TM01, TE01 / TM11, TM21) are plotted against the waveguide wave frequency, where TE11 is the fundamental mode, and subsequent wave shapes represent progressively higher-order wave modes. The curves show the behavior of a waveguide with constant related cross-sectional dimensions (a circular waveguide with a diameter of 2.6 mm). As the frequency of electromagnetic radiation increases, and therefore the wavelength decreases, increasingly higher-order wave modes become propagable within the waveguide, and these, when excited, can also propagate together. A characteristic feature of waveguide waves is their clear dispersion behavior, i.e., their frequency-dependent group velocity. The frequency dependence of the group velocity is clearly more pronounced at lower frequencies of the wave modes than at higher frequencies. Even in single-mode operation of the radar filling level measuring device 1, dispersion effects usually occur. This is because the excitation of wave modes is performed by a signal with a certain bandwidth, and therefore by a frequency within a corresponding frequency range.

[0034] In contrast, the radar filling level measuring device 1 shown in Figures 2 to 4 works with a waveguide 7 that is implemented overmode with respect to the frequency of electromagnetic radiation 5 generated by the supply / receive element 4. This means that the dimensions of the waveguide are selected to be larger than actually required for guiding only excited modes. In those embodiments, the dimensions of the waveguide 7, which are important for wave modes, are 2.5 times larger than in the case of the waveguide 7's corresponding single-mode implementation. This design of the waveguide 7 has proven to be very advantageous because it is a good compromise between achieving high group velocities with low frequency dependence of group velocity (i.e., with low dispersion) and the resulting structural limitation to the slight propagation possibility of higher-order wave modes.

[0035] As explained earlier with reference to Figure 5a, further wave modes can also be transmitted within the overmode-designed waveguide 7, similar to how wave modes achieve higher group velocities with lower dispersion as frequency increases.

[0036] Based on Figure 5b, we can see how the group velocity changes in the frequency range of the excited wave modes when the dimensions of the waveguide 7 are changed, that is, when the waveguide is made increasingly overmode (from 2.6 mm to 5.0 mm, 10 mm, and finally 20 mm). In this case, the group velocity increases with increasing overmode, that is, it approaches the speed of light, and at the same time the dispersion decreases, meaning that the curve extends more flatly.

[0037] If it can be ensured that only the fundamental mode is excited and propagates during the operation of the radar filling level measuring device 1, then there should be no limit to overmodulation. However, practice shows that higher-order modes are also formed despite the intentional excitation of the fundamental mode by the supply / receive element 4. This is particularly true in interference in the measurement path, for example, on a moving or inclined reflective surface by the medium 3 in the waveguide 7. In that case, since higher-order modes are also excited, energy from the intentionally excited fundamental mode is transmitted to the unexpectedly occurring higher-order modes. This results in attenuation of the reflected signal in the fundamental mode, making it difficult for the supply / receive element 4 to detect and evaluate the reflected signal in the fundamental mode. A moderate overmodulation of the waveguide 7 with a geometric factor of 2.5 compared to the single-mode case has been found to be a favorable limitation of propagable higher-order modes, accompanied by a good increase in the group velocity of the waveguide wave in the fundamental mode and a favorable decrease in the dispersion of the waveguide wave in the fundamental mode (allowable energy loss to higher-order modes). An increase in the measurement range is achieved while maintaining good detectability of reflected signals.

[0038] In the radar fill level measuring device 1 shown in Figures 2 to 4, the supply / receive element 4 intentionally excites only the fundamental mode at a frequency above the fundamental mode's cutoff frequency, that is, in a region of reduced dispersion and higher group velocity. In particular, it is important to note that the device is operated at a frequency as far above the fundamental mode's cutoff frequency as possible, without intentionally exciting higher-order modes.

[0039] In all radar filling level measuring devices 1, the end 10 of the waveguide 7 facing the measurement window 6 has an antenna 11 for the purpose of coupling electromagnetic radiation 5 into and separating it from the waveguide 7. As a result, better directivity of the configuration is achieved, which in turn leads to an improvement in the signal-to-noise ratio.

[0040] The same applies to the antenna 12, which is assumed to be part of the supply / receive element 4 and serves to emit the generated electromagnetic radiation 5 and receive the reflected electromagnetic radiation 9. In the illustrated embodiment, both antennas 11 and 12 are finished as horn antennas.

[0041] The radar fill level measuring device 1 shown in Figures 2a, 2b, and 2c has a beam shaping element 13 positioned in the area of ​​the measuring window 6, which helps to align and / or converge electromagnetic radiation 5 between the supply / receive element 4 and the waveguide 7. The beam shaping element 13 consists of two lens-shaped elements, one of which is mounted outside the measuring window 6, and the other beam shaping element 13, as a lens-shaped element, is mounted inside the measuring window 6. This measure also results in an improvement in the signal-to-noise ratio of the measurement path.

[0042] The radar filling level measuring device 1 shown in Figures 2a, 2b, and 2c demonstrates various measures to suppress undesirable effects caused by reflected electromagnetic radiation, which is not originating from the medium surface 8, i.e., interference signals. This concerns the effects of electromagnetic radiation 16 emitted from the waveguide 7, which, assuming that it is reflected, for example, by the inner wall of the container 2 and then reflected back into the waveguide 7, returns to the supply / receiving element 4. Therefore, this electromagnetic radiation needs to be distinguished from useful signals.

[0043] The radar filling level measuring device 1 shown in Figure 2a shows a reflector 15 positioned in the region of the opening 14 of the waveguide 7 that does not face the measurement window 6. This reflector 15 is positioned so that electromagnetic radiation 16 emitted from the waveguide 7 is not reflected back towards the opening 14 of the waveguide 7 that does not face the measurement window 6. In this case, the reflector 15 is positioned on the inner wall of the container 2. In other embodiments not shown here, the reflector 15 is fixed to the waveguide 7.

[0044] In the radar filling level measuring device 1 shown in Figure 2b, it is assumed that a polarizer 17 is placed in the region of the opening 14 of the waveguide 7 that does not face the measurement window 6, to polarize the electromagnetic radiation 16 emitted from the waveguide 7 so that the supply / receiving element 4 does not react to the reflected electromagnetic radiation. In this case as well, the polarizer 17 is placed on the inner wall of the container 2. However, it is also possible for the polarizer 17 to be fixed to the waveguide 7. The polarizer 17 shown in Figure 2b rotates the phase of the electromagnetic radiation 16 by 90°, so the polarized electromagnetic radiation returning to the supply / receiving element 4 is effectively unable to exert an effect as an interference signal. This is because the supply / receiving element 4 does not react to electromagnetic radiation that is polarized in this way.

[0045] The radar filling level measuring device 1 shown in Figure 2c has an encoded reflector 18 in the region of the opening 14 of the waveguide 7 that does not face the measurement window 6, which generates reflected electromagnetic radiation having a corresponding encoded signature. This known encoded signature can then be subtracted from the received signal as a whole by signal processing by an evaluation unit.

[0046] Figure 3 shows that the measurement window 6 is equipped with an adjustment layer 19 to reduce reflection. In this case, the adjustment layer is a dielectric adjustment layer 19. The dielectric constant of the adjustment layer 19 should be selected depending on the dielectric constant of the measurement window 6 and the dielectric constant of the medium between the adjustment layer 19 and the supply / receive element 4 or waveguide 7—in this case, air (usually the square root of the product of both dielectric constants).

[0047] Finally, Figure 4 shows a radar filling level measuring device 1 having a mode converter 20 positioned in the region of the opening 10 of the waveguide 7 facing the measurement window 6. The mode converter 20 converts the electromagnetic radiation 5 traveling from the measurement window 6 to the opening 10 of the waveguide 7 facing the measurement window 6 into a desired mode. In this case, the mode converter 20 converts the TE11 wave to the TE01 wave. The advantage is that the waveguide needs to be larger than a single-mode waveguide when transmitting the TE11 mode, thus minimizing possible capillary effects. Furthermore, the TE01 mode has lower losses compared to the TE11 mode. In addition, its electromagnetic field distribution reduces the effect of sediment at the ends and allows for the insertion of further openings. [Explanation of Symbols]

[0048] 1. Radar filling level measuring device 2 containers 3 Medium 4. Supply and Receiving Elements 5. Electromagnetic radiation 6. Measurement window 7 Waveguide 8 Media surface 9 Reflected electromagnetic radiation 10 The end of the waveguide facing the measurement window 11 Waveguide Antennas 12. Antennas of supply and receive elements 13 Beam forming 14. Ends / openings of the waveguide that do not face the measurement window. 15 Reflectors 16. Electromagnetic radiation emitted from waveguides 17 Polarizer 18 Encoded Reflector 19 Adjustment layer 20 Mode Converters

Claims

1. A radar filling level measuring device (1) for detecting the filling level of a low dielectric constant medium (3) present in a container (2), comprising a supply / receiving element (3) located outside the container (2) for generating and receiving electromagnetic radiation (5), a measurement window (6) in the inner wall of the container (2) that allows electromagnetic radiation (5) to pass through, and a waveguide (7) located inside the container (2) and extending across a filling level measuring area, which is immersable by the medium (3), wherein the supply A radar filling level measuring device (1) wherein a receiving element (4), a measurement window (6), and a waveguide (7) form a measurement path, and electromagnetic radiation (5) generated by the supply / receiving element (4) during a measurement operation propagates through the measurement window (6) and the waveguide (7) via the measurement path, and electromagnetic radiation (9) reflected from the medium surface (8) inside the waveguide (7) returns to the supply / receiving element (4) again via the waveguide (7) and the measurement window (6).

2. The radar filling level measuring device (1) according to claim 1, characterized in that the waveguide (7) is implemented in a single mode with respect to the frequency of the electromagnetic radiation (5) generated by the supply / receiving element (4), particularly as a circular waveguide or as a rectangular waveguide.

3. The radar filling level measuring device (1) according to claim 1, characterized in that the waveguide (7) is implemented in an overmode with respect to the frequency of the electromagnetic radiation (5) generated by the supply / receiving element (4), particularly as a circular waveguide or a rectangular waveguide, preferably the dimensions of the waveguide (7) are up to 3.5 times larger than in the corresponding single-mode implementation, and particularly preferably the dimensions of the waveguide (7) are up to 2.5 times larger than in the corresponding single-mode implementation of the waveguide (7).

4. The radar filling level measuring device (1) according to claim 3, characterized in that the supply / receiving element (4) intentionally excites only the fundamental mode at a frequency that is as far above the cutoff frequency of the fundamental mode as possible, particularly in the region of reduced dispersion and higher group velocity, without intentionally exciting higher-order modes.

5. The radar filling level measuring device (1) according to any one of claims 1 to 4, characterized in that the end (10) of the waveguide (7) facing the measurement window (6) has an antenna (11) for the purpose of coupling electromagnetic radiation into the waveguide (7) and separating it from the waveguide (7).

6. The radar filling level measuring device (1) according to any one of claims 1 to 5, wherein the supply / receiving element (4) has an antenna (12) for emitting generated electromagnetic radiation (5) and for receiving reflected electromagnetic radiation (5), and in particular the antenna (12) is a horn antenna.

7. A radar filling level measuring device (1) according to any one of claims 1 to 6, characterized in that a beam shaping element (13) for aligning and / or converging the electromagnetic radiation (5) between the supply / receiving element (4) and the waveguide (7) is arranged in the region of the measurement window (6).

8. The radar filling level measuring device (1) according to claim 7, characterized in that the beam shaping element (13) is mounted on the outside of the measuring window (6) and / or the beam shaping element (13) is mounted on the inside of the measuring window (6), and / or the measuring window (6) itself is finished as at least a part of the beam shaping element (13).

9. A radar filling level measuring device (1) according to any one of claims 1 to 8, characterized in that a reflector (15) is arranged in the region of the opening (14) of the waveguide (7) that does not face the measurement window (6), so that electromagnetic radiation (16) emitted from the waveguide (7) is not reflected back toward the opening (14) of the waveguide (7) that does not face the measurement window (6), and in particular the reflector (15) is arranged on the inner wall of the container (2).

10. A radar filling level measuring device (1) according to any one of claims 1 to 9, wherein a polarizer (17) is arranged in the region of the opening (14) of the waveguide (7) that does not face the measurement window (6), and polarizes the electromagnetic radiation (16) emitted from the waveguide (7) into reflected electromagnetic radiation such that the supply / receiving element (4) does not react when reflected, and in particular, the polarizer (17) is arranged on the inner wall of the container (2).

11. A radar filling level measuring device (1) according to any one of claims 1 to 10, characterized in that an encoded reflector (18) that generates reflected electromagnetic radiation having a corresponding encoded signature is arranged in the region of the opening (14) of the waveguide (7) that does not face the measurement window (6).

12. A radar filling level measuring device (1) according to any one of claims 1 to 11, characterized in that the supply / receiving element (4) and the measuring window (6), or the supply / receiving element (4) and the beam shaping element (13) facing the supply / receiving element (4), are aligned with each other such that the electromagnetic radiation (5) emitted from the supply / receiving element (4) is not reflected back to the supply / receiving element (4), or only a small portion of it is reflected back.

13. The radar filling level measuring device (1) according to any one of claims 1 to 12, characterized in that the measuring window (6) and / or the beam shaping element (13) are finished with an adjustment layer (19) for reducing reflection.

14. A radar filling level measuring device (1) according to any one of claims 1 to 13, characterized in that a mode converter (20) is arranged in the region of the opening (10) of the waveguide (7) facing the measurement window (6) to convert the electromagnetic radiation (5) directed from the measurement window (6) to the opening (10) of the waveguide (7) facing the measurement window (6) into a desired mode.

15. A radar filling level measuring device (1) according to any one of claims 1 to 13, characterized in that a mode converter (20) is arranged after the supply / receiving element (4) to convert the generated electromagnetic radiation (5) into a desired mode outside the container (2).

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