Level gauge

Abstract

The invention relates to a radar-based level measuring device (1) which operates in several, clearly different frequency bands (f 1,2,3 ) can measure and for this purpose comprises a corresponding number of high-frequency units (10, 11, 12). One of the high-frequency units (10) is designed to measure the radar signal (S) in the respective frequency band (f1). HF1 ) along a defined transmit / receive axis (a) towards the filling material (2) and, after its reflection at the surface of the filling material, a corresponding first received signal (R) HF1 ) to be received via this transmit / receive axis (a). The radar signals (S,R) HF2,3 ) all other frequency bands (f 2,3 ) or all other high-frequency units (11, 12) are deflected into the transmit / receive axis (a) via a reflector arrangement (111, 112; 121, 122) according to the Cassegrain principle, with an evaluation unit selecting the appropriate frequency band (f 1,2,3) determines the fill level (L). An advantage of this is the compact design of the level measuring device (1), without interference in any of the frequency bands (f 1,2,3 Compromises regarding bundling and transmission efficiency must be made.

Description

[0001] The invention relates to a radar-based level measuring device that can be designed compactly and adapted to various fields of application.

[0002] In process automation technology, field devices are used to acquire relevant process parameters. Suitable measurement principles are implemented in these field devices to acquire process parameters such as fill level, flow rate, pressure, temperature, pH value, redox potential, or conductivity. A wide variety of field device types are manufactured and distributed by the Endress+Hauser Group.

[0003] Non-contact measuring methods have become established for measuring the fill level of contents in containers due to their robustness and low maintenance requirements. A further advantage of non-contact measuring methods is their ability to measure the fill level almost continuously. Therefore, radar-based measuring methods are predominantly used in the field of continuous level measurement. In the context of this invention, the term "radar" refers to signals or electromagnetic waves with frequencies between 0.03 GHz and 300 GHz. By principle, the higher the absolute bandwidth or frequency, the higher the measurement resolution achievable. Pulse time-of-flight measurement and FMCW (Frequency Modulated Continuous Wave) have become established as measurement methods. Radar-based level measurement is described in more detail, for example, in "Radar Level Detection," Peter Devine, 2000.

[0004] Typical frequency bands approved for radar-based level measurement are 26 GHz, 80 GHz, and 120 GHz, and increasingly 180 GHz. Higher frequency bands are advantageous for many applications because, given antenna dimensions, they allow for greater beam focusing and generally provide more bandwidth, which can be used for higher distance resolution. One such application is, for example, high-precision level measurement in refinery tanks.

[0005] However, several disadvantages of radar signals with higher frequencies or in higher frequency bands are also known, which can lead to impairments or even failure of level measurement in certain applications. These disadvantages are largely due to interactions between the radar measurement and the contents being measured, the atmosphere above the contents, and partly also to container shapes, environmental and installation conditions, as well as regulatory requirements. Level measurement in grain silos, among other applications, represents an area where a wide beam cone or a low frequency band is advantageous: Due to the granular nature of the contents, this can lead to diffuse reflection of the radar signal. With a narrow beam cone or a high frequency band, the reflected received signal can be deflected so strongly from the vertical that it is lost by the antenna.The transmit / receive structure of the level gauge is not being received.

[0006] To leverage the advantages of different frequencies or frequency bands, publication WO 2023099269 A1 describes a level gauge that can determine the fill level in several clearly defined frequency bands, depending on the situation or application. However, this requires efficient transmission and reception of radar signals in all frequency bands. Conventional radar antennas, such as horn antennas, can only be designed for a very limited frequency band. Maintaining multiple antennas, in turn, increases space requirements. Particularly in cases where the container on which the level gauge is to be installed only has small-diameter flange connections, level gauges with multiple antennas may be impractical due to space constraints.not be attached.

[0007] The invention is therefore based on the objective of overcoming this problem.

[0008] The invention solves this problem by means of a level measuring device for determining the fill level of a product, which comprises the following components: - A first high-frequency unit designed to to emit a first radar signal in a first frequency band in the direction of a transmit / receive axis towards the contents and o to receive a corresponding first reception signal after its reflection at the surface of the contents, - a second high-frequency unit designed to to transmit a second radar signal in a second frequency band, and o to receive a corresponding second receiving signal after its reflection at the surface of the contents, - a first reflector arrangement designed to to redirect the second generated radar signal into the transmit / receive axis and to redirect the second received signal arriving from the transmit / receive axis to the second high-frequency unit, and - an evaluation unit designed to determine the fill level based on at least one of the received signals.

[0009] The advantage of this approach is that the radar signals from all frequency bands are transmitted to and received from the contents along a common transmit / receive axis, thus reducing the number of components and the space required. If the radar signals need to be focused towards the contents, this is also easily achievable: For this purpose, the level gauge can incorporate a common, focusing radar lens for all frequency bands, positioned along the transmit / receive axis. Since higher frequency bands generally offer better focusing, it is also advantageous in this context if the radar signal in the highest frequency band is transmitted or received directly along the transmit / receive axis without deflection. This means that the high-frequency units should be designed so that the first frequency band is higher than the second.Thus, the radar signal emitted by the second high-frequency unit, which lies in the lower frequency band, can be pre-focused by the reflector arrangement.

[0010] The first reflector arrangement can be designed according to the Cassegrain principle. That is, the first reflector arrangement comprises: - A first reflector arranged in this manner, by means of which the second radar signal to be transmitted is deflected from the second high-frequency unit towards the transmit / receive axis, or vice versa with respect to the second received signal, and - a second reflector arranged in this manner, by means of which the deflected second radar signal is directed into the transmit / receive axis, or vice versa with respect to the second received signal.

[0011] The second radio frequency unit must be positioned so that its radiation axis for the second radar signal is parallel to the transmit / receive axis. The second reflector is to be positioned behind the first reflector relative to the second radio frequency unit. To pre-focus the second radar signal, the first reflector can be designed to be concave, so that the second reflector is located at the focal point of the first reflector.

[0012] The level measuring device according to the invention is not, in principle, limited to just two frequency bands. Depending on the application, the level measuring device can additionally include a third high-frequency unit, which is designed to to transmit a third radar signal in the second frequency band or in a third frequency band, and o to receive a corresponding third receiving signal after its reflection at the surface of the contents.

[0013] Analogous to the first reflector arrangement, a second reflector arrangement is provided in this case in order to, to redirect the third generated radar signal into the transmit / receive axis and to redirect the third received signal arriving from the transmit / receive axis to the third high-frequency unit.

[0014] Thus, with appropriate design, the evaluation unit can alternatively or additionally determine the fill level using the third received signal. The third radar signal does not necessarily have to differ from the other radar signals in its frequency band. It is also conceivable that the third radar signal is generated or transmitted with a polarization that differs from the second and first radio-frequency signals. If the third radar signal is also transmitted in the second frequency band and serves only to amplify the signal of the second radio-frequency unit, the third radio-frequency unit must be synchronized with the second radio-frequency unit or the second radar signal with respect to the phase and frequency response of the third radar signal.

[0015] In principle, it is practical for all high-frequency units of the level measuring device according to the invention to be arranged on the same printed circuit board substrate. However, considering the footprint of the high-frequency units and the required lateral wiring, appropriate minimum distances must be provided in the design. In this respect, the level measuring device according to the invention can be made more compact if the first high-frequency unit is arranged on a first surface of the printed circuit board substrate facing away from the first reflector arrangement, while the second high-frequency unit is arranged on the second surface facing the reflector arrangement. By means of a waveguide feedthrough aligned with the transmit / receive axis, the first radar signal can be passed through the printed circuit board substrate in this embodiment and accordingly emitted from the second surface.Correspondingly, the first received signal is coupled into the first high-frequency unit via the waveguide feedthrough. This waveguide feedthrough can be manufactured using established printed circuit board (PCB) manufacturing processes, for example, by metallizing a bore. This results in a waveguide with a circular cross-section. However, a rectangular cross-section or a design as a dielectric waveguide is also conceivable. In this quasi-nested embodiment, the first high-frequency unit can, for example, be arranged on the first surface of the PCB substrate using a flip-chip method.

[0016] With regard to the level measuring device according to the invention, the term "unit" is generally understood to mean any circuit group intended for a specific purpose, e.g., as an interface or for high-frequency signal processing. Depending on the intended use, the respective unit may therefore comprise corresponding analog circuits for generating or processing corresponding analog signals. However, the respective unit may also comprise digital circuits, such as FPGAs, microcontrollers, or storage media, in conjunction with corresponding programs. The program is designed to perform the necessary process steps or to apply the required arithmetic operations. In this context, various electronic circuits of the unit according to the invention can potentially also access a common physical memory or be operated by means of the same physical digital circuit.It is irrelevant whether different electronic circuits within the unit are arranged on a common circuit board or on several interconnected circuit boards.

[0017] According to the invention, frequency bands are clearly delineated from one another if their center frequencies differ by at least a factor of two and their bandwidth is each less than one-fifth of their center frequency. A clear delineation is also present, according to the invention, if the center frequencies of the frequency bands differ by at least a factor of four and their bandwidth is each less than half of their center frequency. The center frequency of a frequency band is defined as the frequency that lies exactly in the middle of the frequency band. According to this definition, for example, a frequency band with a center frequency of 26 GHz and a bandwidth of 2 GHz extends from 25 GHz to 27 GHz.

[0018] The invention is explained in more detail using the following figures. It shows: Fig. 1: A radar-based level gauge on a container, and Fig. 2: A detailed view of the level measuring device according to the invention.

[0019] For a basic understanding of the invention, in Fig. Figure 1 shows a container 3 with a substance 2, the fill level L of which is to be determined by a radar-based level gauge 1. The container 3 can be up to 100 m high, depending on the type of substance 2 and the application. The optimal frequency band f also depends on the type of substance 2 and the application. 1,2,3 from, in which the level measuring device 1 determines the fill level L: In the case of a coarse-grained fill material 2 and correspondingly diffuse reflection, a comparatively low frequency band f is generally suitable. 1,2,3at, for example, 26 GHz. Lower frequency bands are also more suitable for foaming materials 2, as the foam does not reflect light in this case. In the case of a refinery tank as container 3, a higher frequency band is preferable due to the flat surface of the material being transported. 1,2,3 This is advantageous because, by its very nature, it allows for a potentially higher distance resolution.

[0020] The level sensor 1 is typically connected to a higher-level unit 4, such as a local process control system or a decentralized server system, via a separate interface unit implementing, for example, "4-20 mA", "PROFIBUS", "HART", or "Ethernet". This allows the measured level value L or the distance value d to be transmitted, for example, to control the inflow or outflow of the tank 3. Other information about the general operating status of the level sensor 1 can also be communicated. To determine the level L, the level sensor 1 is mounted above the contents 2 at a known installation height h above the bottom of the tank 3.The level gauge 1 is attached and aligned to a corresponding opening of the container 3 in such a pressure- and media-tight manner that only an electrically passive radar lens 13 of the level gauge 1 is directed vertically downwards into the container 3 towards the contents 2. The active units 10, 11, 12 of the level gauge 1 are located outside the container 3 in a separate housing, which is attached to the opening of the container 3, for example, via a flange.

[0021] Radar signals are detected via the radar lens 13 within predefined frequency bands. HF1,2,3 emitted in the direction of the surface of the fill material 2. After reflection of the radar signals S HF1,2,3 The level measuring device 1 receives the reflected reception signals R at the surface of the contents. HF1,2,3 again via the radar lens 13. The signal travel time t between transmission and reception of the respective radar signal S, R is... HF1,2,3according to t=2∗dc proportional to the distance d between the level measuring device 1 and the material 2, where c is the medium-dependent and usually at least roughly known propagation speed of the respective radar signal S, R HF1,2,3 The signal propagation time t can be determined by the level sensor 1, for example, using the FMCW or pulse propagation time method. In the case of FMCW, the frequency f represents the signal propagation time. ZF1,2,3 of that intermediate frequency signal IF 1,2,3 , each after receiving and mixing the radar signal S, R HF1,2,3 will be obtained according to t=fZF1,2,3f'1,2,3 The signal propagation time t between transmission and reception. At f' 1,2,3 This refers to the preset and therefore known frequency change rate of the emitted radar signal S. HF1,2,3 The frequency f can be ZF1,2,3 of the intermediate frequency signal IF 1,2,3for example, by its Fourier transform. This allows the level gauge 1, for instance, to assign the measured transit time t to the respective distance d based on a corresponding calibration. Using this, the level gauge 1 can, according to d=h−L in turn determine the fill level L, provided that the installation height h is stored in the level measuring device 1 or in the higher-level unit 4.

[0022] To determine the signal propagation time t or the corresponding fill level value L using the low-frequency intermediate frequency signal IF. 1,2,3 The level measuring device 1 includes a correspondingly designed evaluation unit in which the FMCW or pulse transit-time measurement principle is implemented. To generate the radar signal S to be transmitted in each case... HF1,2,3 and to generate the corresponding intermediate frequency (IF) signal 1,2,3 based on the received signal R HFIn the level gauge 1, a high-frequency unit 10, 11, 12 serves this purpose. If the FMCW method is implemented, the corresponding high-frequency unit 10, 11, 12 can, for example, comprise a suitably designed phase-locked control loop (PLL) on the transmitting side. On the receiving side, the evaluation unit in this case uses a mixer and subsequent Fourier transform logic to determine the frequency f corresponding to the distance d. ZF1,2,3 of the intermediate frequency signal IF 1,2,3 to record.

[0023] As in Fig. As shown in Figure 1, the radar lens 13 is located inside the container 3, while the radio frequency units 10, 11, 12 are located in a separate housing outside the container 3. To protect the radio frequency units 10, 11, 12 from any thermal stresses from inside the container, and to separate the container interior from the radio frequency units 10, 11, 12 in an explosion-proof manner, the housing is accordingly spaced from the radar lens 13 by a housing neck 14. For this purpose, the housing neck 14 is designed to be sufficiently long.

[0024] The center frequency or frequency band f 1,2,3 of the radar signal S HF1,2,3 The choice depends primarily on the area of ​​application and, in particular, on the type of material being filled: For highly accurate level measurement, such as in oil storage tanks, a frequency band that is as high as possible is required by principle. 1,2,3This is advantageous, whereas with an uneven or wavy surface of the fill material, the widest possible beam angle of the radar lens 13 and thus a comparatively low frequency band f is required. 1,2,3 This is advantageous. In the context of the present invention, the term "radiation angle" generally refers to the solid angle within which, relative to the beam axis a, a defined, uniform transmit intensity or receive sensitivity of, for example, -3 dB prevails. The beam axis a, in turn, is the vector along which the transmit intensity or receive sensitivity is at its maximum.

[0025] In order to be used under these different application conditions, the in Fig. 1 level gauge shown 1 capable of receiving radar signals S HF1 , S HF2 , S HF3 in three different frequency bands f 1,2,3 to transmit, whereby the frequency bands f 1,2,3They do not overlap, but are clearly distinct from one another. The choice of the frequency band f can be used for this purpose. 1,2,3 , on the basis of which the level gauge 1 determines the level value L, either can be manually specified, or the level gauge 1 selects the most suitable frequency band f 1,2,3 itself. In the second case, the level measuring device 1 can be designed such that, depending on certain parameters, such as a possible rate of change of the level value L, it uses the underlying frequency band f. 1,2,3 selects independently. This is also described in publication DE 10 2021 131 690 A1.

[0026] As shown in the detailed view of Fig. As shown in Figure 2, the level measuring device 1 comprises three separate high-frequency units 10, 11, 12 which are designed to operate within the respective frequency band f 1,2,3 corresponding radar signals S HF1,2,3to generate and, after reflection, the corresponding received signals R HF1,2,3 to receive or process the signal. In the illustrated version, the first high-frequency unit 10 operates, for example, at a center frequency of 180 GHz or in a corresponding first frequency band f1. The second frequency band f2, in which the second radar signal S is received, is located in the following frequency band: HF,2 The frequency generated by the second high-frequency unit 11 is, for example, at a center frequency of 80 GHz. The third high-frequency unit 12 generates a frequency in the lowest of the three frequency bands. 1,2,3 the corresponding third radar signal S HF3 with a center frequency of 26 GHz.

[0027] All three frequency bands f 1,2,3 or the underlying radar signals S, R HF1,2,3 are transmitted and received via the same radar lens 13. For this purpose, the following are required in the Fig. In the variant of the level measuring device 1 shown in Figure 2, the three high-frequency units 10, 11, 12 are arranged on a common printed circuit board substrate 15. For the transmission of the radar signals S, R HF1,2,3 Between the circuit board substrate 15 and the radar lens 13, the length of the housing neck 14 must be overcome. Furthermore, this allows for efficient radiation of the individual frequency bands f. 1,2,3 required that each of the frequency bands f 1,2,3 in relation to the radar lens 13, it is emitted and received centrally. That is, all three frequency bands f 1,2,3 are to be transmitted and received along the same transmit / receive axis a, in which the beam axis of the radar lens 13 runs. The transmission and reception of the radar signals S and R take place in this manner. HF1,2,3directly via the IC package (better known in English as “AiP = Antenna in Package”) or even directly on the semiconductor chip (“AoC = Antenna on Chip”) of the respective high-frequency unit 10, 11, 12.

[0028] The combined axial radiation is achieved by the in Fig. 2 shown, inventive setup of the level measuring device 1: Accordingly, the first high-frequency unit 10 is arranged on the printed circuit board substrate 15 such that the radar signal S HF1 of the first frequency band f1 directly along the transmit / receive axis a and the first received signal R HF1 The signal is received along the transmit / receive axis a. For this purpose, the first high-frequency unit 10 is arranged directly in the transmit / receive axis a.

[0029] The second high-frequency unit 11 and the third high-frequency unit 12 are also arranged on the printed circuit board substrate 15, but unlike the first high-frequency unit 10, they are positioned away from the transmit / receive axis a. Instead, the second high-frequency unit 11 and the third high-frequency unit 12 emit the respective radar signal S. HF2,3 along a respective radiation axis parallel to the transmit / receive axis a. In the radiation axis of the second radio frequency unit 11 and the third radio frequency unit 12, a concave first reflector 111 and a concave third reflector 121, respectively, are arranged. Both of these reflectors 111, 121 are oriented such that they receive the respective radar signal S HF2,3 from the radiation axis of the second or third high-frequency unit 11, 12 in the direction of the transmit-receive axis a. The reverse case also applies to the incoming, received signals R. HF2,3 .

[0030] To obtain the second radar signal S HF2 and the third radar signal S HF3 In the signal path, after deflection by the first reflector 111 or the third reflector 121, the signal is redirected according to the invention into the transmit / receive axis a, comprising the following: Fig. 2. The illustrated embodiment includes a second or fourth reflector 112, 122 arranged accordingly on the transmit / receive axis a: In the Fig. The second of the two shown versions is the second.

[0031] The second reflector 112 and the fourth reflector 112 are designed planar, i.e. neither focusing nor scattering.

[0032] The second reflector 112 and the fourth reflector 122 are arranged in relation to the transmit / receive axis a in front of the first reflector 111 and the third reflector respectively, such that - the second reflector 112 is located at the focal point of the concave, first reflector 111, and - the fourth reflector 122 is located at the focal point of the concave, third reflector 121.

[0033] This design results in a reflector arrangement 111; 112, 121; 122 for each of the second high-frequency unit 11 and the third high-frequency unit 12, according to the principle of Cassegrain telescopes. Accordingly, in contrast to the schematic representation in Fig. 2. It is not necessarily the case that the first reflector 111 and the third reflector 121 are arranged at the same height with respect to the transmit / receive axis a and have the same beamforming. Rather, the respective beamforming, positioning, and size of the first reflector 111 and the third reflector 121 depend primarily on the location of the corresponding frequency band f. 2,3 and the beam angle α 11,12 dependent on the respective high-frequency unit 11, 12. Overall, this design according to the invention enables a high degree of focusing of the radar signals S,R. HF1,2,3in all frequency bands f 1,2,3 with a compact neck width of 14.

[0034] As in Fig. As shown in Figure 2, it is advantageous in this context if the first reflector 111 is designed in such a way that its outer contour is in accordance with a11≈N∗λHF2 approximately congruent with the beam angle α 11 the second high-frequency unit 11. Thus, the total cross-sectional area of ​​the first reflector 111 in this case corresponds to an integer multiple N of the number of wavelengths λ. HF2 of the second radar signal S HF . where the beam angle α 11 The second high-frequency unit 11, due to the generally reciprocal radar characteristics, functions independently of whether transmitting or receiving. The same design rule also applies to the third reflector 121 with respect to the beam angle α. 12The third high-frequency unit 12 is advantageous. Overall, this results in optimized transmit / receive efficiency.

[0035] In addition to this advantageous interpretation, in Fig. 2 represents a further optimization possibility insofar as the first high-frequency unit 10, unlike the other high-frequency units 11, 12, is not arranged on the first surface of the printed circuit board substrate 15 that faces the radar lens 13. Rather, the first high-frequency unit 10 is arranged on a second surface facing away from it. This allows the printed circuit board substrate 15 to be designed more compactly overall than if all three high-frequency units 10, 11, 12 were arranged on the same surface of the printed circuit board substrate 15. So that the radar signal S HF1 of the first frequency band f1 along the transmit / receive axis a can be emitted towards radar lens 13, or the received signal R HF1To enable coupling into the first high-frequency unit 10, a feedthrough 151 in the printed circuit board substrate 15 is formed along the transmit / receive axis a between the surfaces of the printed circuit board substrate 15 in the form of an inserted dielectric waveguide. The cross-section of the waveguide is adapted to the first and thus highest of the three frequency bands f. 1,2,3 designed. In order for the first high-frequency unit 10 to couple RF-technically into the feedthrough 151, it is designed according to the illustration in Fig. 2 contacted via flip-chip method on the first surface of the printed circuit board substrate 15. Reference symbol list 1 level gauge 2 Filling material 3 containers 4. Higher-level unit 10 First high-frequency unit 11 Second high-frequency unit 12 Third high-frequency unit 13 radar lens 14 Case neck 15 printed circuit board substrate 111 First reflector 112 Second reflector 121 Third reflector 122 Fourth reflector 151 Waveguide feedthrough a transmit / receive axis d distance f 1,2,3 Frequency bands h Installation height L level R HF1,2,3 Received signals S HF1,2,3 Radar signals α 11,12 Beam angle QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] WO 2023099269 A1

[0006] DE 10 2021 131 690 A1

[0025]

Claims

[1] Level measuring device for determining the level (L) of a product (2), comprising the following components: - A first high-frequency unit (10) designed to ◯ in a first frequency band (f1) a first radar signal (S HF1 ) in the direction of a transmit / receive axis (a) towards the filling material (2) and ◯ after its reflection at the surface of the contents, a corresponding first receiving signal (R) HF1 to receive, - a second high-frequency unit (11) designed to ◯ in a second frequency band (f2) a second radar signal (S HF2 ) to radiate, and ◯ after its reflection at the surface of the contents, a corresponding second received signal (R) HF2 to receive, - a first reflector arrangement (111, 112) designed, ◯ the second generated radar signal (S HF2 ) to redirect into the transmit / receive axis (a) and ◯ the second received signal arriving from the transmit / receive axis (a) (R) HF2 ) to redirect to the second high-frequency unit (11), and - an evaluation unit designed to use at least one of the received signals (R HF1,2 ) to determine the fill level (L). [2] Level measuring device according to claim 1, comprising: - A focusing radar lens (13) arranged in the transmit / receive axis (a). [3] Level measuring device according to claim 1 or 2, wherein the high-frequency units (10, 11) are designed such that the first frequency band (f1) is higher than the second frequency band (f2). [4] Level measuring device according to any of the preceding claims, wherein the first reflector arrangement comprises: - A first reflector (111) arranged in this manner, by means of which the second radar signal to be emitted (S) HF2) from the second high-frequency unit (11) towards the transmit / receive axis (a), or with respect to the second received signal (R HF2 ) conversely, and - a second reflector (112) arranged in this manner, by means of which the deflected second radar signal (S HF2 ) is directed into the transmit / receive axis (a), or with respect to the second received signal (R HF2 ) vice versa. [5] Level measuring device according to claim 4, - wherein the second radio frequency unit (11) is arranged such that it transmits / receives a transmit / receive axis of the second radar signal (S) parallel to the transmit / receive axis (a). HF2 ) exhibits, and - wherein the second reflector (112) is arranged behind the first reflector (111) in relation to the second radio frequency unit (11). [6] Level measuring device according to claim 5, wherein the first reflector (111) is designed to be concave such that the second reflector (112) is arranged in the focus of the first reflector (111). [7] Level measuring device according to any of the preceding claims, comprising: - A third high-frequency unit (12) designed to o in the second frequency band (f2) or in a third frequency band (f3) a third radar signal (S HF3 ) to radiate, and o after its reflection at the surface of the contents, a corresponding third receiving signal (R) HF3 to receive, and - a second reflector arrangement (121, 122) designed to o the third generated radar signal (S HF3 ) to redirect into the transmit / receive axis (a) and o the third received signal (R) arriving from the transmit / receive axis (a) HF3) to redirect to the third high-frequency unit (12), wherein the evaluation unit is designed to use the third received signal (R) HF3 ) to determine the fill level (L). [8] Level measuring device according to claim 7, wherein the third radio frequency unit (12) is used in the event that the third radar signal (S HF3 ) is radiated in the second frequency band (f2), - is synchronized with the second high-frequency unit (11) with respect to phase and frequency response, and / or - the third radar signal (S HF3 ) with a polarization determined by the second high-frequency signal (S HF2 ) deviates, is emitted. [9] Level measuring device according to any one of the preceding claims; comprising: - A printed circuit board substrate (15), with o a first surface which is facing away from the first reflector arrangement (111, 112) on which the first radio frequency unit (10) is arranged, ◯ a second surface facing the reflector arrangement (111, 112) on which the second radio frequency unit is arranged, and ◯ a waveguide bushing (151) aligned in the transmit / receive axis (a), by means of which the first radar signal (S HF1 ) is radiable from the second surface, and by means of which the first received signal (R) HF1 ) can be coupled into the first high-frequency unit (10). [10] Level measuring device according to claim 9, wherein the waveguide feedthrough (151) is designed as a dielectric waveguide or hollow conductor, in particular with a rectangular or round cross-section.

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