Patent Application
20230349746
The invention relates to an antenna for radar-based fill level measurement and to a production method for producing such an antenna.
In process automation technology, field devices for capturing or modifying process variables are generally used. For this purpose, the functioning of the field devices is in each case based on suitable measuring principles in order to capture the corresponding process variables, such as fill level, flow rate, pressure, temperature, pH value, redox potential or conductivity. A wide variety of such field devices is manufactured and distributed by the Endress+Hauser company.
For measuring the fill-level of filling materials in containers, radar-based measuring methods have become established, since they are sound and low-maintenance. Thereby, the pulse transit time principle and the FMCW (“frequency modulated continuous wave”) principle are predominantly implemented. These measurement principles are described in greater detail, for example, in “Radar Level Detection, Peter Devine, 2000.” A key advantage of radar-based measuring methods lies in the ability to measure the fill-level more or less continuously. In the context of this patent application, the term “radar” refers to radar signals having frequencies between 0.03 GHz and 300 GHz. Typical frequency bands with which fill level measurement is performed are 2 GHz, 6 GHz, 26 GHz or 79 GHz. The higher the frequency band that is selected, the narrower the beam cone of the radiated radar signal is with otherwise identical antenna dimensions.
Irrespective of the implemented measurement principle, the transmitting and receiving units of the fill level measuring device can be implemented for radar frequencies starting at approximately 20 GHz and higher than a common integrated circuit. In principle, fill level measuring devices with higher radar frequencies can therefore be produced more compactly and with better installation characteristics. It is true that the dimensioning of the antenna to be used can also be reduced with increasing frequency without undesirably increasing the beam cone. Nevertheless, compared to the further components of the fill level measuring device, the antenna still has comparatively large dimensions. Furthermore, the beam cone is increased or side lobes are formed when the antenna is reduced in size. Moreover, the media-tight manufacturability of the antenna is more difficult when dimensions are reduced, because undercuts and cavities of small dimensions can hardly be produced.
The invention is therefore based on the object of providing an efficient and easily producible antenna for radar-based fill level measuring technology with which the corresponding fill level measuring device can be designed to be extremely compact.
The invention achieves this objective by an antenna for radar-based fill level measuring devices, which comprises the following components:
The term “media-tight” within the scope of the invention relates to particle and liquid impermeability, and not necessarily also to gas or overpressure tightness.
By means of the lens, the antenna can be made according to the invention extremely compactly and with a narrow beam cone. Accordingly, the lens is preferably convex or semi-convex with respect to the radar signal.
The efficiency of the antenna can be further optimized if the lens has a diameter matched to the input coupling structure in such a way that the lens completely covers the main emission lobe, in which lobe the input coupling structure transmits the radar signal along the main beam axis. In the context of the present patent application, the term “main emission lobe” means the region, which is enclosed by those spatial angles at which, starting from the main emission axis (i.e., the vector of the maximum power of the emitted radar signal), the power has decreased to 50% or by −3 dB. Furthermore, the antenna according to the invention can be optimized with respect to its efficiency if the lens, the cavity and/or a surface of the lens facing the cavity have an anti-reflection layer for the radar signal, such as, in particular, an in some cases chemically based surface texture. The cavity can also have a metallic coating at least in a partial region. Depending on this, the dimensions of the antenna may in some cases be further reduced.
Due to the compact design of the antenna according to the invention, it is particularly expedient to use the antenna in radar-based fill level measuring devices, the transmitting/receiving unit of which is designed to generate the underlying electrical high-frequency signal with a high frequency of at least 60 GHz, in particular more than 100 GHz, because at such high frequencies the fill level measuring device can, in general, already be designed very compactly. A corresponding fill level measuring device for measuring a fill level of a filling material located in a container comprises at least the following components:
It is not relevant within the scope of the invention whether the transmitting/receiving unit is designed to generate the high-frequency signal according to the FMCW method or to determine the fill level according to the FMCW method, or whether the pulse transit time principle is implemented.
With reference to the fill level measuring device, the term “unit” within the scope of the invention is understood in principle to mean all electronic circuits that are suitably designed for the proposed purpose. It can therefore be an analog circuit for generating or processing corresponding analog signals. However, it can also be a digital circuit, such as an FPGA, or a storage medium in interaction with a program. Thereby, the program is designed to perform the corresponding method steps or to apply the necessary calculation operations of the respective unit. In this context, various electronic units of the measuring device in the sense of the invention can potentially also access a common physical memory or be operated by means of the same physical digital circuit.
An advantage of the antenna according to the invention is also the potentially low-cost manufacturability. In particular, the medium-tight cavity can be realized without elaborate manufacturing steps when the mount is produced on the basis of at least two sub-components. For this purpose, the sub-components are to be designed such that, in each case, one of the sub-components comprises the lens and/or the input coupling structure in addition to the pure mount shape, and that the sub-components in each case comprise a corresponding joint seam along the cavity. The corresponding method for manufacturing the antenna provides in this case the following method steps:
This method makes it possible for all components of the antenna, i.e., the mount, the input coupling structure and the lens to be made of an identical material, in particular a plastics material. For this purpose, the first sub-component and the second sub-component are accordingly made of the same material, for example by means of injection molding or hot stamping. In particular, PEEK, PFA or PTFE can be used as the plastics material for manufacturing the two sub-components, because these materials have a suitable dielectric value of greater than 2, in particular greater than 4, with regard to the radar refraction properties.
The invention is explained in more detail with reference to the following figures. The following are shown:
For a basic understanding of the invention,
As a rule, the fill level measuring device 1 can be connected via an interface, which is based on a corresponding bus system such as “Ethernet,” “PROFIBUS,” “HART” or “Wireless HART,” to a superordinate unit 4, for example a process control system, a decentralized database or a handheld device such as a mobile radio device. On the one hand, information about the operating status of the fill level measuring device 1 can thus be communicated. However, further information relating to the fill level L can also be transmitted via the interface.
Since the fill level measuring device 1 shown in
The transmitted radar signal SHF is reflected by the surface of the filling material 3 and received as a reception signal RHF by the antenna 11 or the downstream transmitting/receiving unit of the fill level measuring device 1 after a corresponding signal transit time. Since the signal transit time of the radar signals SHF, EHF has a linear dependence on the distance d=h−L of the fill level measuring device 1 from the filling material surface, the transmitting/receiving unit can determine the fill level L on the basis of the reception signal RHF according to the respectively implemented measuring principle.
The fill level measuring device 1 explained in reference to
In terms of manufacturing technology, however, a correspondingly compact antenna 11 can be produced only with difficulty, because it has to be manufactured with chip-removing and thus cost-intensive methods, such as turning, for example, because, for example, the injection molding process can lead to cavities and depressions in or on the antenna 11. Furthermore, a filled dielectric antenna 11, in which the focal length space is filled with a plastics material, generally has a significantly poorer efficiency than classical lens antennas, in which air or vacuum prevails in the focal length space.
An antenna 11 according to the invention, which from this perspective, can be compactly designed and easily manufactured, is shown in more detail as a cross-sectional view in
For corresponding contacting with the transmitting/receiving unit, the input coupling structure 112 outside the mount 110 can be further guided, for example, as a dielectric waveguide that can optionally be adapted in its length (not explicitly shown in
For decoupling the radar signal SHF from the cavity 111 toward the filling material 3, the mount 110 is designed in such a way that the rod-shaped end of the input coupling structure 112 is located within the focus of the lens 113, wherein the lens 113 is aligned in the main beam axis a of the input coupling structure 112. As a result, the radar signal SHF is bundled correspondingly when it exits from the antenna 11 toward the filling material 3. By virtue of the resulting narrow transmission cone of the antenna 11, said antenna can therefore be produced according to the invention with very compact dimensions. The reciprocal properties for antennas likewise apply to the reception signal RHF to be coupled in.
As is indicated in
The method shown in
The joining technique of sub-components A, B to be used is to be selected, inter alia, depending on the material from which the sub-components A, B are manufactured. Depending on the material, welding or gluing, for example, can be used for the joining. Thereby, it is essential that the resulting cavity 111 is sealed media-tight, i.e., particle- and moisture-impermeable during the joining. As a result, the cavity 111 is protected against unwanted dirt accumulation, so that the beam properties of the antenna 11 are not impaired by the measurement operation. Depending on the atmosphere under which the sub-components A, B are joined, the cavity 111 can also be subjected to a vacuum or an inert gas in order to further improve the beam characteristic of the antenna 11.
It is also advantageous in connection with the joining of the sub-components A, B if both sub-components A, B are made of an identical material, such as PEEK or PTFE, so that the resulting mount 110, the lens 113 and the input coupling structure 112 each consist of the same material. With regard to the material selection, it must be taken into account here that the material for beam refraction in the lens 113 and for beam guidance in the input coupling structure 112 has a suitable dielectric value of, for example, at least 2, optimally greater than 4. An advantage of manufacturing the antenna 11 on the basis of two sub-components A, B is that the cavity 111 and any later undercuts may be realized without excessive material outlay, without elaborate process steps and thus cost-effectively.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 119 435.8 | Jul 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/066755 | 6/21/2021 | WO |
