Angle-resolved level measurement device

Abstract

The invention relates to a radar-based filling level measuring device (1) for determining a three-dimensional filling level distribution (L(α, #)) by means of the MIMO principle. According to the invention, the filling level measuring device (1) comprises for this purpose an antenna assembly (11) which comprises, in addition to a main antenna array, a sub antenna array. By means of the main antenna array, it is possible to create a height-angle-separable solid angle spectrum A i,j (d x , α, #) but, due to the large separation distance (a, a' > λ / 2), no unambiguous assignment of a solid angle (α, #) over the entire solid angle range (α, #) is possible. In order to solve this problem, the solid angle spectra A i,j (d x , α, #) are merged with the solid angle spectrum of the sub antenna array according to the invention. The sub antenna array is therefore designed such that its solid angle spectrum A k,l (d x , α, #) allows an unambiguous assignment of any solid angle (α, #) over the entire solid angle range (α, #). For this purpose, the corresponding antennas (k, l) are arranged on an intermediate grid ([s; s']). The advantage of this is that, using a total of very few antennas or using associated fast evaluation over a wide solid angle range (α, #), a height-angle-separable filling level distribution (L(α, #)) can be recorded.

Description

TECHNICAL FIELD

[0001] The present invention relates to an antenna assembly for a fill level measuring device for determining a fill level distribution within a defined solid angle range, and to a method for operating the measuring device. BACKGROUND

[0002] In process automation, corresponding field devices are used to capture relevant process parameters. In order to capture the respective process parameters, suitable measurement principles are therefore implemented in the corresponding field devices in order to capture, for example, fill level, flow rate, pressure, temperature, pH value, redox potential or conductivity as process parameters. The Endress+Hauser company produces and sells various such field devices.

[0003] In order to measure the fill level of a filling material in a container, contactless measuring methods have been established, as they are stable and require minimal maintenance. Within the scope of the present invention, the term "container" is also to be understood as meaning an unenclosed container, such as a basin, a lake or a flowing body of water. A further advantage of contactless measuring methods is the ability to measure the fill level quasi-continuously. Radar-based measuring methods are therefore predominantly used in the field of continuous fill level measurement (in the context of the present patent application, "radar" means signals or electromagnetic waves with a frequency of between 0.03 GHz and 300 GHz).

[0004] An established measuring method is FMCW ("Frequency Modulated Continuous Wave"). The basic measurement principle is based on the emission of a continuous radar signal with a modulated frequency. FMCW is characterized in that the emission frequency is periodically changed within a defined frequency band. In view of regulatory requirements, higher frequency bands within the standardized center frequency range are widely used as development progresses. In addition to the 6 GHz frequency band, the 26 GHz frequency band or the 79 GHz frequency band, frequencies above 100 GHz have now also been implemented. The advantage of high frequencies is that, at higher frequencies, a larger absolute bandwidth can be used (for example, 4 GHz in the 100 GHz frequency band). As a result, a higher resolution or a higher accuracy of the fill level measurement is again achieved.

[0005] By default, the change in frequency within the frequency band over time is linear and has a sawtooth or triangular shape. In principle, a sinusoidal change can also be implemented. In the FMCW method, the distance or the fill level is determined on the basis of the instantaneous frequency difference between the currently received radar signal after reflection at the measurement object and the radar signal currently emitted by the measuring device. A fill level measurement method based on FMCW is described, for example, in the published patent application DE 10 2013 108 490 A1.

[0006] By means of the FMCW method, it is possible at least to measure distances or fill levels selectively. In this case, the point at which the fill level is measured is guided by the orientation of the transmitting / receiving antenna or the direction of its beam lobe (due to the general reciprocity property of antennas, the characteristic or beam angle of the beam lobe of a respective antenna is independent of whether the antenna is transmitting or receiving; in the context of the present patent application, the term "angle" or "beam angle" means the angle at which the beam lobe has the greatest transmission strength or reception sensitivity).

[0007] In the case of a liquid filling material with a uniform fill level, a selective fill level measurement suffices. In these cases, the fill level measurement device is oriented in such a way that the beam lobe of the antenna is directed approximately vertically downwards and the distance to the filling material is determined. In the case of a solid-like filling material, for example gravel or granulate, the fill level can be inhomogeneous, for example due to a bulk material pile, so that the fill level value determined by the fill level measurement device is only meaningful to a limited extent. In particular in such cases, it is therefore desirable to be able to determine the distance or fill level in the form of a two- or three-dimensional distribution.

[0008] In order to achieve this, the fill level measurement device must be designed in such a way that it is able to distribute the incident radar signals to the relevant solid angle. This can be achieved, for example, by means of the MIMO principle ("Multiple Input Multiple Output"). This principle is based on an antenna assembly consisting of a plurality of transmitting and receiving antennas. In this case, each transmitting antenna emits a radar signal that is orthogonal to the radar signals of the other transmitting antennas, which are received by each receiving antenna and optionally digitized in order to be subsequently subjected to common radar signal processing. Thus, from an antenna assembly of N transmitting antennas and K receiving antennas, a virtual antenna arrangement of K*N antennas with a largely expanded virtual aperture is created mathematically. The corresponding evaluation unit must be able to digitize the radar signals received in each case by the K receiving antennas or to process them by means of signal technology and to create the corresponding K*N measurement curves by means of the orthogonality of the transmitted signals. As a result, a MIMO-based radar system improves the spatial resolution capability compared to a system without an actually enlarged aperture and achieves a significantly improved interference immunity.

[0009] If all transmitting and receiving antennas are arranged at approximately the same location or on a common substrate, such that they cover the same solid angle range, this is referred to as "collocated MIMO". In one possible embodiment, within the antenna assembly, the transmitting antennas are arranged in a column, while the receiving antennas are arranged in a row. Thus, the transmitting and receiving antennas are each arranged along a straight line at a separation distance, wherein the straight lines extend approximately at right angles to one another and thus span a grid having K*N points, which represents the locations of the virtual antennas. In order to be able to assign the resulting measurement curves to the individual points or individual antennas, various techniques are known for controlling the transmitting antennas or for evaluating the receiving antennas. In this regard, "TDMA (Time Division Multiple Access)" is preferably implemented, according to which technique the transmitting antennas are activated one after the other along the arrangement of the transmitting antennas in a time-division multiplexing method.

[0010] According to the prior art, the entire hardware required for implementing the MIMO principle can already be integrated so compactly that the transmitting and receiving antennas are accommodated as patch antennas on a common printed circuit board, or even as an IC ("integrated circuit") packaged together with the semiconductor components, which include the signal generation unit and the evaluation unit. A more detailed description of MIMO-based radar systems is given, for example, in "MIMO radar signal processing" (Jian Li), 2009.

[0011] A prerequisite for an unambiguous, solid angle-dependent fill level measurement is that the individual transmitting and receiving antennas are arranged in a row within the antenna assembly or along a straight line at a separation distance which is equal to or less than half the wavelength of the radar signal. Otherwise, in addition to the main lobe, so-called "grating lobes" also occur. These are side lobes whose beam strength is equal to that of the main lobe, in contrast to the side lobes. If the transmitting or receiving antennas are spaced apart from one another by a distance which is greater than half the wavelength of the radar signal, the angle at which a possible object causes a radar echo signal will no longer be unambiguously assignable due to the grating lobes within the solid angle range.

[0012] In turn, in the case of a limited number of transmitting and receiving antennas, for example, due to a limited number of evaluation channels of the evaluation unit, a sufficient angular separation can not be achieved in the case of a close arrangement of the antennas, in other words when the antenna separation distance is less than half the wavelength, depending on the width of the required solid angle range. SUMMARY

[0013] It is therefore an object of the present application to provide a fill level measuring device with which a fill level profile with a high angular separation can be captured over a larger solid angle range, even in the case of a small number of available evaluation channels.

[0014] The invention achieves this object by a corresponding antenna assembly for a radar-based filling level measuring device for determining a filling level profile of a filling material within a defined solid angle range. To this end, the antenna assembly according to the invention comprises a main antenna array having at least two transmitting antennas arranged along a first straight line, by means of which a radar signal having a defined wavelength can be transmitted in the direction of the filling material in accordance with the MIMO principle. Thereby, the transmitting antennas of the main antenna array are arranged at a defined first separation distance from one another, which is greater than half the wavelength of the radar signal. In addition to the transmitting antennas, the main antenna array also has at least two receiving antennas arranged along a second straight line, by means of which the radar signal reflected by the filling material surface can be received. The receiving antennas are therefore arranged at a second defined separation distance from one another, which is also greater than half the wavelength of the radar signal. In addition, the second straight line is arranged at a defined angle of a certain 90° to the first straight line, so that the transmitting antennas and the receiving antennas form a corresponding grid.

[0015] Since in each case the separation distance between the transmitting antennas and the receiving antennas in the main antenna array is greater than half the wavelength of the radar signal, respectively, the main antenna array can have a small number of transmitting antennas and transmitting antennas which actually achieve a higher angular separation over a large solid angle range of a maximum of 180° or 2*π, but not necessarily every solid angle within the defined solid angle range can be unambiguously assigned by the main antenna array. Therefore, according to the invention, in addition to the main antenna array, the antenna assembly also comprises a sub-antenna array having at least two independent transmitting or receiving antennas, which in turn is designed to transmit radar signals or to receive radar signals after reflection at the filling material surface.

[0016] The at least two independent receiving or transmitting antennas of the sub-antenna array are arranged on an intermediate grid relative to the grid of the main antenna array in such a way that at least one transmitting antenna (or receiving antenna, if the sub-antenna array has two or more transmitting antennas as independent antennas) is assigned in such a way that by means of the sub-antenna array within the defined solid angle range every solid angle can be unambiguously assigned.

[0017] The at least one assigned antenna of the sub-antenna array can be one of the transmitting or receiving antennas of the main antenna array. Alternatively or additionally, the sub-antenna array can comprise as assigned antennas at least one separate transmitting or receiving antenna arranged on the intermediate grid.

[0018] Due to the design of the antenna assembly with two antenna arrays according to the application, in each case a corresponding measurement curve can be recorded by means of the main antenna array and the sub antenna array according to the MIMO principle, and a separate solid angle spectrum of each of the two antenna arrays can be created therefrom. According to the application, this makes it possible to combine the corresponding solid angle spectra of the main antenna array and the sub antenna array to form a conjugated solid angle spectrum in order to create a level distribution related to the solid angle on the basis of the conjugated solid angle spectrum. The advantage of this is that the conjugated solid angle spectrum has a high angular separation over the entire solid angle range of up to 180° due to the main antenna array, and that each solid angle within the conjugated solid angle spectrum can be assigned unambiguously at the same time due to the sub antenna array. In comparison with an antenna assembly according to the prior art, which consists of only one antenna array and the antennas of which are arranged at a distance of less than or equal to λ / 2, with the aid of the antenna assembly according to the application, the same solid angle range and the same angular separation can be achieved with a significantly reduced number of antennas or evaluation channels.

[0019] The design of the transmitting and receiving antennas of the main antenna array and the sub antenna array is not fixedly predefined within the scope of the application. They can not only be designed to be planar, for example as patch antennas on a corresponding substrate, but also as waveguide antennas.

[0020] In particular, within the scope of the application, the grid of the main antenna array, i.e. the respective separation distances between the transmitting antennas and the respective separation distances between the receiving antennas, can for example be dimensioned such that the first separation distance and the second separation distance in each case correspond to the wavelength of the radar signal. In this case, the offset of the individual transmitting or receiving antennas of the sub antenna array must be half the wavelength of the radar signal, so that the individual transmitting or receiving antennas of the sub antenna array are arranged on a corresponding intermediate grid relative to the grid of the main antenna array.

[0021] In order to be able to map a symmetrical solid angle range, the main antenna array is preferably designed such that it has the same number of transmitting antennas and receiving antennas. As regards the number of individual transmitting or receiving antennas of the sub antenna, according to the number of antennas in the main antenna array, it will be sufficient if the sub antenna array has at most half, in particular only one third, of the transmitting or receiving antennas compared to the main antenna array, so that the total number of antennas in the two antenna arrays can also be kept within limits. The antenna assembly according to the application can therefore also be evaluated by an evaluation unit which can only provide a limited number of channels simultaneously to evaluate the antennas.

[0022] On the basis of the antenna assembly according to the application, a radar-based level measurement device can be implemented by means of which a level profile of a filling material surface can be determined in a wide solid angle range with high angular intervals. In addition to the antenna assembly according to one of the preceding embodiments variants, the level measurement device accordingly comprises the following components:

[0023] - a signal generation unit designed to generate radar signals with defined wavelengths and to couple them into the transmitting antennas of the main antenna array and the sub antenna array according to the MIMO principle (i.e. individual coding or TDMA based on one after the other for each subsequent transmitting antenna), and

[0024] - an evaluation unit designed to

[0025] o capture corresponding measurement curves on the basis of the radar signals received at the main antenna array according to the MIMO principle,

[0026] o capture corresponding measurement curves on the basis of the radar signals received at the sub antenna array according to the MIMO principle,

[0027] o in order to create a corresponding solid angle spectrum on the basis of the measurement curves captured at the level of the defined measurement points of the measurement region by means of the main antenna array,

[0028] o in order to create a corresponding solid angle spectrum on the basis of the measurement curves captured at the level of the defined measurement points of the measurement region by means of the sub antenna array,

[0029] o in order to combine the solid angle spectra of the main antenna array and the sub antenna array, which correspond to the measurement points, into a conjugated solid angle spectrum, and

[0030] o in order to create a level profile related to the solid angle on the basis of the conjugated solid angle spectrum.

[0031] Within the scope of the present application, the term "unit" refers in principle to any electronic circuit designed to be suitable for the intended purpose. It can thus be an analog circuit for generating or processing corresponding analog signals, as required. However, it can also be a digital circuit, for example an FPGA, or a storage medium interacting with a program. In this case, the program is designed to perform the corresponding method steps or the necessary calculation operations applying the respective unit. In this context, the various electronic units of the measurement device according to the application can also potentially access a common physical memory or operate by means of the same physical digital circuit.

[0032] Within the scope of the present application, it is not explicitly prescribed which basic radar method has to be implemented in order to create the individual measurement curves. In principle, for example, an FMCW or a pulsed time-of-flight method can be used. In the case of the FMCW method, the signal generation unit of the level measurement device would be designed in such a way that it is able to generate radar signals with a corresponding frequency ramp in accordance with the FMCW method. Using FMCW, the evaluation unit should accordingly be designed in such a way that the measurement curves of the main antenna array and the sub antenna array are created by means of a Fourier transformation of the received radar signals in accordance with the FMCW method. In the case of FMCW, the evaluation unit can preferably also weight the Fourier-transformed measurement curves of the main antenna array and the sub antenna array by means of a window function, in particular by means of a Hanning window or a Chebyshev window, in order to suppress interfering echoes from the edges of the measurement range.

[0033] Corresponding to the level measurement device according to the present application, the object on which the present application is based is also achieved by a corresponding measurement method for operating a level measurement device. The method therefore comprises at least the following method steps:

[0034] - capturing, in accordance with the MIMO principle, a corresponding measurement curve within a defined level measurement range by means of the main antenna array,

[0035] - creating, on the basis of the measurement curve captured by means of the main antenna array, an omnidirectional spectrum at a plurality of defined measurement points of the measurement range,

[0036] - capturing, in accordance with the MIMO principle, a corresponding measurement curve within a defined level measurement range by means of the sub antenna array,

[0037] - creating, on the basis of the measurement curve captured by means of the sub antenna array, an omnidirectional spectrum at a plurality of defined measurement points of the measurement range,

[0038] - combining the omnidirectional spectra corresponding to the measurement points of the main antenna array and the sub antenna array into a conjugated omnidirectional spectrum, and

[0039] - creating a level profile in relation to the solid angle on the basis of the conjugated omnidirectional spectrum.

[0040] If each omnidirectional spectrum is scaled logarithmically, the omnidirectional spectra corresponding to the measurement points of the main antenna array and the sub antenna array are combined by addition. If each omnidirectional spectrum is scaled linearly, the omnidirectional spectra corresponding to the measurement points of the main antenna array and the sub antenna array will need to be combined by multiplication. The omnidirectional spectra can be created on the basis of any digital beamforming method (“digital beamforming”). BRIEF DESCRIPTION OF DRAWINGS

[0041] The application is explained in more detail below with reference to the drawings. The following is shown:

[0042] Figure 1 : Radar-based fill level measuring device on a container,

[0043] Figure 2 : Schematic representation of a detected fill level as a function of a solid angle within a container,

[0044] Figure 3 : Schematic structure of an antenna assembly of a fill level measuring device according to the invention, and

[0045] Figure 4 : Method for determining a fill level in relation to a solid angle by means of an antenna assembly according to the invention. DETAILED DESCRIPTION

[0046] In order to understand the invention, Figure 1 A container 3 with a filling material 2 is shown, the fill level L of which is to be captured in the form of a three-dimensional fill level profile L(a, b). For this purpose, a fill level measuring device 1 is mounted on the container 3 at a known mounting height h above the filling material 2. In this case, the container 3 can be up to 100 m or more, depending on the type and field of application. The fill level measuring device 1 is aligned with the container 3 and is fixed to the container 3 in such a way that it emits radar signals S HF with a corresponding wavelength l continuously, periodically or also aperiodically in the surface direction of the filling material 2 through the antenna assembly 11. The radar signals S HF are reflected at the filling material surface and are received by the fill level measuring device 1 through the antenna assembly 11 as reflected radar signals R HF The reflected radar signals are a function of the separation distance d between the fill level measuring device 1 and the filling material surface according to the following equation:

[0047] d = h - L

[0048] In general, the fill level measuring device 1 is connected to a superior unit 4, for example a process control system, by means of an interface, for example “PROFIBUS”, “HART” or “Wireless HART”. In this way, the fill level value L can be emitted in order to control any inflow or outflow of the container 3, for example, if necessary. However, other information about the general operating state of the fill level measuring device 1 can also be transmitted.

[0049] According to the prior art, it has already been possible to selectively do so with an accuracy in the range below a micrometer by means of a corresponding radar method, for example FMCW or pulse transit time method, under ideal conditions (highly reflective filling material 2, flat filling material surface, no obstacles such as stirrers or other fittings in the signal path of the radar signals S HF . Even in the case of a rough or undulating filling material surface or a dusty atmosphere, the fill level L of a certain point on the filling material surface can be reliably measured by means of the FMCW method.

[0050] However, when the surface of filling material 2 (such as...) Figure 1 When the surface (as shown) is not planar, the selective measurement of the material level L reaches its limit. This is especially likely to occur in the case of bulk filler material 2, for example, when a bulk pile is formed during the filling of container 3. Additionally, a conical indentation may appear on the surface of the filler material 2 as it is pumped out. If the material level measuring device 1 selectively determines the material level L at only one point on the surface of the filler material 2, this could lead to misinterpretation of the material level L. For example, when the radar module 1 detects an empty container 3, the emptying process may stop even if filler material 2 is still present at the edge of the container's interior. Conversely, when the container 3 is full, the filling process may not stop even if the maximum material level at one location on the surface of the filler material has been exceeded because the material level measuring device 1 has not detected this.

[0051] For this reason, such as Figure 1 As shown, the material level measuring device 1 according to the present invention can determine the material level L in a three-dimensional material level distribution L(α,β) within a defined solid angle range [α; β]. In this case, the angles α and β within the solid angle range [α; β] extending perpendicularly to each other are related to the vertical line in each case. Therefore, the material level distribution L(α,β) is created relative to the polar coordinate system. In order to create the corresponding angles α and β of the three-dimensional material level distribution L(α,β) in the Cartesian coordinate system (since this is known, that is, the distances d(α,β) are measured respectively), a transformation can be performed by means of a sine function to form corresponding lateral values ​​x and y related to the cross-section of the container. Therefore, a corresponding transformation from the polar coordinate system to the Cartesian coordinate system occurs.

[0052] Figure 2 The material level distribution L(α,β) determined from the angle of the material level measuring device 1 is schematically shown. In this case, the material level distribution L(α,β) relative to the wall of the container 3 is visualized as a contour line. Therefore, according to the design, the material level measuring device 1 can, for example, present the material level distribution L(α,β) on a display, for example, in each of the present cases, as a contour plot with corresponding contour lines. Regardless of any visualization of the material level distribution L(α,β), in the context of the invention, this includes a data matrix in which the material level value L is stored according to two solid angles α, β. The size of the data matrix is ​​correspondingly derived from the angular separation and width of the solid angle range.

[0053] refer to Figure 3 and 4 A more detailed explanation of the design according to the invention and the operating mode of the material level measuring device 1 according to the invention, which can be used to create a material level distribution L(α,β) with height angle accuracy:

[0054] Figure 3 The antenna assembly 11 of the fill level measuring device 1 according to the application is shown in a simplified form. The antenna assembly 11 is based on a main antenna array and an additional sub antenna array, wherein both antenna arrays are arranged on a common substrate 110. Thus, the main antenna array and the sub antenna array cover approximately the same solid angle range [a; b]. Thus, the solid angle range [a; b] covers the filling material 2, in the installed state of the fill level measuring device 1, the entire antenna assembly 11 is aligned such that the normal vector of the substrate 110 and thus the main lobe of emission of the antennas i, j, k, 1 points approximately horizontally towards the filling material 2.

[0055] In Figure 3 for the sake of simplicity of the illustration, the main antenna array comprises only three transmitting antennas i, each of which is arranged along a first straight line 111 at a first separation distance a > λ / 2. In this case, the transmitting antennas i of the main antenna array serve to emit radar signals S HF in the direction of the filling material 2. The transmitting antennas i of the main antenna array are controlled by the signal generation unit 10 of the fill level measuring device 1. If FMCW is implemented as a radar method, the transmitting antennas i will be controlled such that they emit radar signals S HF according to the following equation with the sawtooth modulation frequency f characteristic of the FMCW:

[0056] f = c * λ -1

[0057] For this purpose, the signal generation unit 10 can be based, for example, on a phase-controlled control loop (also called PLL, "Phase-Locked Loop"). In order to implement the MIMO principle, in addition, the signal generation unit 10 must also feed the correspondingly coded radar signals S HF to the transmitting antennas i of the main antenna array, or after a time delay according to the TDMA principle with the arrangement sequence i = 1, 2,...

[0058] In order to receive the reflected radar signals R HF after reflection at the filling material surface, Figure 3 the main antenna array in the simplified illustration in the reflected radar signals R HF comprises four receiving antennas j, which are arranged in turn on a second straight line 112. In this case, the first straight line 111 and the second straight line 112 are arranged at a 90° angle to each other and have the same origin 114. The receiving antennas j of the main antenna array are also arranged uniformly from each other on the second straight line 112 at a second defined separation distance a', wherein the second separation distance a' is again greater than half the wavelength λ of the radar signals S HF , R HF at the frequency f of the radar signals S

[0059] c = λ * f

[0060] The separation distances a and a' between adjacent transmitting antenna i or adjacent receiving antenna j correspond to approximately 1.5 mm (where c is the speed of light in a vacuum).

[0061] As a result of the rectangular arrangement of the two straight lines 111 and 112, the main antenna array consists of three transmitting antennas i and four receiving antennas j. Figure 3 The exemplary example has a grid [a; a'] with 3*4 = 12 grid points, which reflect the virtual aperture of the main antenna array according to the MIMO principle. In practice, for example, the main antenna array can include 24 transmit antennas i and 24 receive antennas j in each case, resulting in 24*24 channels for evaluation. In this context, it should be mentioned that the corresponding grids are formed not only at 90° angles between the two straight lines 111, 112, but theoretically at any angle less than 180°. Therefore, within the scope of this invention, the angle between the two straight lines 111, 112 need not be specified as 90°, but can actually be between 30° and 150°. However, in this case, the resulting solid angle range [α; β] of the main antenna array is not automatically symmetrical.

[0062] According to the present invention, the separation distances a and a' of the transmitting antenna i or the receiving antenna j in the main antenna array are greater than the radar signal S. HF The wavelength λ is half of the wavelength λ, therefore, even with only a few transmitting and receiving antennas i and j across the entire angular range, the elevation angle separation of the measured distance or level value can be achieved by means of the main antenna array. However, not every solid angle α and β can be definitively assigned within the solid angle range [α; β]. According to the invention, this is overcome by means of a sub-antenna array, because by means of a sub-antenna array, every solid angle α and β can be definitively assigned across the entire solid angle range [α; β]. For this purpose, Figure 3 A simplified embodiment variation includes two independent receiving antennas k. The receiving antennas k of the sub-antenna array are arranged on an intermediate grid [s; s'] relative to the grid [a; a'] of the main antenna array. In the context of this invention, each location on the substrate is defined as the intermediate grid [s; s'].

[0063] -It has been shifted by offset s in the direction of the first straight line 111.

[0064]

[0065] Or, it may be shifted by an integer multiple of one of the transmitting antennas i or one of the receiving antennas j of the main antenna array, and / or

[0066] - At any position, the position is shifted by offset s' in the direction of the second straight line 112.

[0067]

[0068] or shifted by an integer multiple thereof from one of the receiving antennas j or one of the transmitting antennas i of the main antenna array.

[0069] As described in equation 4.21 in "Array and Phased Array Antenna Basics" (Hubregt J. Visser, 2005), the shifts s, s' between the intermediate grid areas [s; s'] must also be dimensioned according to the following formula

[0070]

[0071] in order to prevent the sub antenna array from forming any grating lobes and to enable each solid angle a, b to be uniquely assigned within the defined solid angle range [a; b] by means of the sub antenna array. For example, if the separation distances a and a' between the transmitting antennas i and between the receiving antennas j in the main antenna array correspond to the wavelength l of the radar signal S HF , and if the shifts s, s' of the transmitting or receiving antennas k, I of the sub antenna array correspond to half the wavelength l of the radar signal S HF , then both this formula and the positioning of the receiving antennas k of the sub antenna array required according to the invention are fulfilled.

[0072] In the embodiment variant of the antenna assembly 11 according to the invention shown in Fig. Figure 3 , the sub antenna array comprises, in addition to the two receiving antennas k, also independent transmitting antennas I, which are arranged on the intermediate grid [s; s'] in succession, analogously to the receiving antennas k. Alternatively or in addition to one or more independent transmitting antennas I, it is also conceivable within the meaning of the invention to assign one or more selected transmitting antennas i and / or receiving antennas j of the main antenna array to the sub antenna array. In this case, the antennas i, j assigned from the main antenna array are also selected or positioned, again taking into account the intermediate grid positions [s; s'] of the pure receiving and transmitting antennas k, I of the sub antenna array, in such a way that each solid angle a, b can be uniquely assigned within the defined solid angle range [a; b] by means of the sub antenna array. In this respect, for example, the corresponding simulation of the group factor of the sub antenna array produced by means of the antennas i, j, k, I in the sub antenna array can be used to find or optimize the corresponding number and position of the antennas i, j, k, I of the sub antenna array, for example on the basis of MatLab.

[0073] Since the required angular separation of the sub-antenna array does not need to be as high as that of the main antenna array, it is sufficient within the scope of this invention if the sub-antenna array has only one-third the number of antennas in the main antenna array. Figure 3 The illustrated embodiments are not subject to variation. In this manner, the material level distribution L(α,β) can be determined according to the present invention with a total of a small number of antennas i, j, k, l and a correspondingly low computational workload.

[0074] Figure 4 The evaluation unit 12, corresponding to the design of the material level measuring device 1 using the antenna assembly 11 according to the present invention, is shown in more detail as to how it can determine the material level distribution L(α,β). Based on the MIMO principle, this is determined by the received radar signal R... HF The corresponding measurement curves A are generated for the main antenna array and the sub-antenna array, respectively. i,j (d) A k,l (d). In the context of this invention, the term "measurement curve" generally refers to the radar signal R reflected from the distance d to the horizontal measuring device 1. HF The signal amplitude A (possibly in dB). Under the FMCW principle, the corresponding measurement curve A. i,j (d) A k,l (d) Specifically, it refers to the radar signal S output through the corresponding transmitting antenna i. HF The radar signal R input at the corresponding receiving antennas j and k HF The frequency difference is represented by the signal amplitude A. Therefore, the frequency difference is, in principle, linear with respect to the distance d, and thus represents the same content in the case of FMCW.

[0075] Since the activation of the two antenna arrays is performed using the MIMO principle, the evaluation unit 12 generates measurement curves A for each receiving antenna j and each transmitting antenna i of the main antenna array, as well as for each receiving antenna k and each transmitting antenna i of the main antenna array, in each case. i,j (d) A k,l (d). For the purpose of allocating transmit antennas i and l, the signal generation unit 10 controls the transmit antennas i and l sequentially in a time-off manner according to the TDMA method of (linear) sequence i, k = 1, 2… For Figure 3 The simplified sub-antenna array of antenna assembly 11 shown is irrelevant to this control, as the sub-antenna array comprises only a single transmitting antenna 1 for clarity. For Figure 3 The antenna assembly 11 shown also means that 3*4=12 measurement curves A are captured by means of the main antenna array. i,j (d); The evaluation unit captures 1*2+1*1=3 measurement curves A by means of the sub-antenna array.k,l (d)

[0076] Based on the measurement curve A captured by the main antenna array i,j (d) Then, the evaluation unit 12 generates the defined measurement points d within the measurement range d. x Corresponding solid angle spectrum A i,j (d x Similarly, based on those measurement curves A captured by means of a sub-antenna array... k,l (d) Create the corresponding identical measurement point d within the measurement range d. x Additional solid angle spectrum A at the horizontal position k,l (d x Therefore, within the scope of this invention, a "solid angle spectrum" is used to reproduce a defined distance d in two dimensions based on two solid angles α and β. x Radar signal R reflected at a horizontal position HF The signal amplitude A or signal strength. Use "Digital Beamforming" to create a solid angle spectrum A. i,j (d x ,α,β),A k,l (d x (α, β). For this purpose, for example, a suitable "digital beamforming processor" architecture can be implemented within the evaluation unit 12. For more measurement points d x Create solid angle spectrum A i,j (d x ,α,β),A k,l (d x (α,β), or measurement point d x The closer they are to each other, the higher the potential distance accuracy of the resulting material level distribution L(α,β).

[0077] To obtain the material level distribution L(α,β), according to the present invention, the material level distribution at measurement point d is first... x The corresponding solid angle spectrum A of the main antenna array and the sub-antenna array i,j (d x ,α,β),A k,l (d x In each case, α,β) combine to form a conjugate solid angle spectrum (d x In this case, the evaluation unit 12 combines the solid angle spectrum A by adding and multiplying the amplitude values ​​at the corresponding solid angles α and β, according to the proportion (linear or logarithmic) of the signal amplitude A. i,j (d x ,α,β),A k,l (d x ,α,β).

[0078] The advantages of the present invention are reflected in the conjugate solid angle spectrum A(d)x In the context of α, β), i.e., using the main antenna array and sub-antenna array: the reflected radar signal R HF The signal amplitude A can be separated by elevation angle in the conjugate solid angle spectrum A(d) over a wide solid angle range [α, β]. x The evaluation unit 12 can also create a level distribution L(α,β) within the corresponding solid angle range [α,β] by separating the level distribution at elevation angles.

[0079] For example, it can be based on the obtained conjugate solid angle spectrum A(d) x (α, β), by evaluating which measurement point d in the measurement range d for each solid angle α, β. x At which location or in which corresponding conjugate solid angle spectrum A(d) x The signal amplitude A at point (α, β) is at its maximum value to create the material level distribution L(α, β). Distance d x It can be converted into the corresponding material level value L(α,β) according to the following formula.

[0080] d x，max (α, β) = hL(α, β)

[0081] If the installation height h of the level measuring device 1 is stored in the evaluation unit 12, then the level distribution L(α,β) can finally be transmitted to the upper unit 4 and / or visualized on the display of the level measuring device 1, for example, in the form of a contour line.

[0082] List of reference numerals

[0083] 1. Material level measuring device

[0084] 2. Filling material

[0085] 3 containers

[0086] 4. Upper-level unit

[0087] 11 Antenna Assembly

[0088] 110 substrate

[0089] 111 First straight line

[0090] 112 Second straight line

[0091] 113. Origin of the line

[0092] A signal amplitude

[0093] a, a′ Distances between antennas of the main antenna array

[0094] A i,j(d) measurement curve

[0095] A i,j (dx, α, β) solid angle spectrum

[0096] b container cross section

[0097] D antenna distance

[0098] d distance, separation distance

[0099] f frequency of the emitted signal

[0100] h installation height

[0101] i transmitting antenna of the main antenna array

[0102] j receiving antenna of the main antenna array

[0103] k receiving antenna of the sub antenna array

[0104] l transmitting antenna of the sub antenna array

[0105] L(α, β) stock level distribution

[0106] R HF reflected radar signal

[0107] S HF radar signal

[0108] s, s' offset

[0109] α, β solid angle

[0110] λ wavelength of the radar signal

Claims

1. A radar-based level measuring device (1) for determining the level distribution (L(α,β)) of filler material (2) within a defined solid angle range (α; β), comprising the following components: - Main antenna array, the main antenna array comprising: At least two transmitting antennas arranged along the first straight line (111) are capable of transmitting radar signals S with a defined wavelength (λ) in the direction of the filling material (2). HF The transmitting antennas are positioned relative to each other at a distance greater than the radar signal S. HF The first separation distance is defined by half the wavelength (λ). At least two receiving antennas arranged along the second straight line (112) are capable of receiving radar signals R reflected from the surface of the filling material. HF The receiving antennas are positioned relative to each other at a distance greater than the radar signal S. HF The second separation distance is defined by half the wavelength (λ), and the second straight line (112) is arranged at a defined angle to the first straight line (111) such that the transmitting antenna and the receiving antenna form a grid. - A sub-antenna array having at least two receiving antennas, the sub-antenna array being designed to receive the radar signal R after reflection at the surface of the filling material. HF , In this configuration, two receiving antennas of the sub-antenna array are arranged on the middle grid relative to the grid of the main antenna array, and at least one transmitting antenna is assigned to the sub-antenna array, such that each solid angle (α, β) can be uniquely assigned within the defined solid angle range (α; β) by means of the sub-antenna array. Each position on the substrate (110) is defined as the intermediate grid. Wherein, at least one assigned transmitting antenna of the sub-antenna array is one of the transmitting antennas of the main antenna array, and / or wherein, as an associated transmitting antenna, the sub-antenna array includes at least one transmitting antenna arranged on the intermediate grid. - Signal generation unit (10), the signal generation unit (10) is designed to generate a radar signal S with a defined wavelength (λ). HF The radar signal is then coupled to the transmitting antennas of the main antenna array and the sub-antenna array. - Evaluation unit, the evaluation unit is designed ○ Based on the MIMO principle, based on the radar signal R received at the main antenna array HF Capture the corresponding measurement curve. ○ Based on the MIMO principle, based on the radar signal R received at the sub-antenna array HF Capture the corresponding measurement curve. ○ To facilitate measurement based on a defined measurement point (d) in the measurement area using the main antenna array. x The measurement curve captured at the horizontal position creates the corresponding solid angle spectrum. ○ To facilitate measurement based on a defined measurement point (d) in the measurement area using the sub-antenna array x The measurement curve captured at the horizontal position creates the corresponding solid angle spectrum. ○ In order to facilitate the measurement of the main antenna array and the sub-antenna array corresponding to the measurement point (d) x The solid angle spectra of ) are combined to form a conjugate solid angle spectra, and ○ This facilitates the creation of a solid angle-related material level distribution (L(α,β)) based on the conjugate solid angle spectrum.

2. A radar-based level measuring device (1) for determining the level distribution (L(α,β)) of filler material (2) within a defined solid angle range (α; β), comprising the following components: - Main antenna array, the main antenna array comprising: At least two transmitting antennas arranged along the first straight line (111) are capable of transmitting radar signals S with a defined wavelength (λ) in the direction of the filling material (2). HF The transmitting antennas are positioned relative to each other at a distance greater than the radar signal S. HF The first separation distance is defined by half the wavelength (λ). At least two receiving antennas arranged along the second straight line (112) are capable of receiving radar signals R reflected from the surface of the filling material. HF The receiving antennas are positioned relative to each other at a distance greater than the radar signal S. HF The second separation distance is arranged at half the wavelength (λ), and wherein the second straight line (112) is arranged at a defined angle to the first straight line (111). - A sub-antenna array having at least two transmitting antennas, the sub-antenna array being designed to transmit the radar signal R to the filling material (2). HF , In this sub-antenna array, two transmitting antennas are arranged on the middle grid relative to the grid of the main antenna array, and at least one receiving antenna is assigned to the sub-antenna array, such that each solid angle (α, β) can be uniquely assigned within the defined solid angle range (α; β) by means of the sub-antenna array. Each position on the substrate (110) is defined as the intermediate grid. Wherein, at least one assigned receiving antenna of the sub-antenna array is one of the receiving antennas of the main antenna array, and / or wherein, as an assigned receiving antenna, the sub-antenna array includes at least one receiving antenna arranged on the intermediate grid. - Signal generation unit (10), the signal generation unit (10) is designed to generate a radar signal S with a defined wavelength (λ). HF The radar signal is then coupled to the transmitting antennas of the main antenna array and the sub-antenna array. - Evaluation unit, the evaluation unit is designed ○ Based on the MIMO principle, based on the radar signal R received at the main antenna array HF Capture the corresponding measurement curve. ○ Based on the MIMO principle, based on the radar signal R received at the sub-antenna array HF Capture the corresponding measurement curve. ○ To facilitate measurement based on a defined measurement point (d) in the measurement area using the main antenna array. x The measurement curve captured at the horizontal position creates the corresponding solid angle spectrum. ○ To facilitate measurement based on a defined measurement point (d) in the measurement area using the sub-antenna array x The measurement curve captured at the horizontal position creates the corresponding solid angle spectrum. ○ In order to facilitate the measurement of the main antenna array and the sub-antenna array corresponding to the measurement point (d) x The solid angle spectra of ) are combined to form a conjugate solid angle spectra, and ○ This facilitates the creation of a solid angle-related material level distribution (L(α,β)) based on the conjugate solid angle spectrum.

3. The material level measuring device according to claim 1 or 2, wherein, The first straight line and the second straight line are arranged at a 90° angle to each other.

4. The material level measuring device according to any one of claims 1-3, wherein, The first separation distance between the transmitting antennas in the main antenna array and the second separation distance between the receiving antennas correspond to the radar signal S. HF The wavelength (λ), and / or The offset of the transmitting and receiving antennas in the sub-antenna array corresponds to the radar signal S. HF Half of the wavelength (λ).

5. The material level measuring device according to any one of claims 1-4, wherein, The main antenna array has the same number of transmitting antennas and receiving antennas.

6. The material level measuring device according to any one of claims 1-5, wherein, Compared to the main antenna array, the sub-antenna array has up to half the number of transmitting or receiving antennas.

7. The material level measuring device according to claim 6, wherein, Compared to the main antenna array, the sub-antenna array has one-third of the transmitting or receiving antennas.

8. The material level measuring device according to any one of claims 1-7, wherein, The signal generation unit (10) is configured to generate the radar signal S according to the FMCW method. HF Furthermore, the evaluation unit is designed to calculate the measurement curves of the main antenna array and the sub-antenna array according to the FMCW method.

9. The material level measuring device according to claim 8, wherein, The evaluation unit is configured to calculate the measurement curves of the main antenna array and the sub-antenna array using a window function.

10. The material level measuring device according to claim 9, wherein, The evaluation unit is configured to calculate the measurement curves of the main antenna array and the sub-antenna array using a Hanning window or a Chebyshev window.

11. A radar-based method for determining the level distribution (L(α,β)) within a defined solid angle range (α; β) using a level measuring device (1) according to any one of claims 1-10, the method comprising the following steps: Based on the MIMO principle, the corresponding measurement curve within a defined material level measurement range is captured using the main antenna array. -Based on the measurement curve captured by means of the main antenna array, at multiple defined measurement points (d) within the measurement range. x Create a solid angle spectrum at the horizontal level. Based on the MIMO principle, the corresponding measurement curve within a defined material level measurement range is captured using the sub-antenna array. -Based on the measurement curve captured by means of the sub-antenna array, at the defined measurement point (d) within the measurement range. x Create a solid angle spectrum at the horizontal level. - The measurement points (d) corresponding to the main antenna array and the sub-antenna array x The solid angle spectra of ) are combined to form a conjugate solid angle spectra, and - Create a solid angle-related material level distribution (L(α,β)) based on the conjugate solid angle spectrum.

12. The method according to claim 11, wherein, Given that the solid angle spectrum is logarithmically scaled in each case, the measurement points (d) corresponding to the main antenna array and the sub-antenna array are combined by addition. x solid angle spectrum, or Wherein, provided that the solid angle spectrum is linearly scaled in each case, the measurement points (d) corresponding to the main antenna array and the sub-antenna array are combined by means of multiplication. x ) solid angle spectrum.

13. The method according to claim 11 or 12, wherein, The solid angle spectrum is created based on a digital beamforming method.

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