Motor vehicle radar system and method for detecting a water layer

Abstract

The invention relates to a motor vehicle radar system (10) with a radome (11) in which at least one transmitting / receiving element for transmitting and / or receiving electromagnetic waves is arranged on a printed circuit board (12) and at least one electrically conductive strip (21-23) is arranged in or on the radome (11) such that it is insulated from the printed circuit board (12) by a dielectric (13). The motor vehicle radar system (10) has a device (30) configured to measure an impedance between the printed circuit board (12) and the electrically conductive strip (21-23). ​​In a method for detecting a water layer (40) on the radome (11), an alternating voltage is applied between the at least one electrically conductive strip (21-23) and a ground plane of the printed circuit board (12). A thickness of the water layer (40) is inferred from a measured electrical impedance or at least a value derivable from the impedance.

Description

[0001] The present invention relates to a motor vehicle radar system with a radome. It further relates to a method for detecting a layer of water on the radome. State of the art

[0002] Vehicle radar systems are an important component of a vehicle's driver assistance system and are used, for example, in automatic speed control to detect vehicles ahead. Radar beams or radar waves are emitted by the radar system and reflected by the vehicles ahead. By analyzing the received signals, a model of the vehicle's surroundings can be created.

[0003] To protect the transmitter / receiver element of a vehicle's radar system, it is housed in a radome. Water on the surface of the radome can absorb or distort the radar beams, thus reducing the radar system's effectiveness.

[0004] DE 196 44 164 C2 describes a motor vehicle radar system whose radome has a dielectric lens in the beam path of the transmitting / receiving element. Several electrically conductive tracks are arranged on this lens, between which an electrical resistance and a capacitance can be measured. The degree of lens contamination can be determined from the measured values. Disclosure of the invention

[0005] The present vehicle radar system features a radome in which at least one transmitting / receiving element for transmitting and / or receiving electromagnetic waves is arranged on a circuit board. A radome is understood to be a closed protective enclosure designed to protect the transmitting / receiving element from external influences such as wind or rain. The radome is made of a material that preferably attenuates the electromagnetic waves emitted by the transmitting / receiving element by no more than 2 dB. The electromagnetic waves are, in particular, radar beams with a wavelength of at least 1 mm.

[0006] At least one electrically conductive strip is arranged in or on the radome in such a way that it is electromagnetically insulated from the circuit board by a dielectric. If the circuit board extends to an inner wall of the radome and the electrically conductive strip is arranged on the corresponding outer wall of the radome, then the dielectric is, in particular, the radome wall. If the electrically conductive strip is arranged inside the radome, then the dielectric is, in particular, the air located between the circuit board and the electrically conductive strip. A strip is considered electrically conductive, in particular, if its electrical conductivity is more than 10 6 S / m is.

[0007] The vehicle radar system incorporates a device designed to measure the impedance between the circuit board and the electrically conductive strip. As will be described in detail below, this impedance measurement allows not only the detection of water on the radome's surface but also the determination of the water layer's thickness. This can be used for radar blindness detection, enabling early identification of whether the vehicle radar system's performance is being impaired by water on the radome's surface.

[0008] In principle, it would be conceivable to arrange the at least one electrically conductive strip in the radar beam path of the transmitting / receiving element. However, to avoid interfering with the operation of the vehicle radar system, the width of the electrically conductive strip should not exceed λ / 10, and multiple conductive strips would each have to be spaced at least λ / 4 apart. Here, λ denotes the free-space wavelength of the electromagnetic waves emitted by the transmitting / receiving element. It is therefore preferred that the at least one electrically conductive strip be arranged outside the beam path of the transmitting / receiving element. This allows for simpler manufacturing of the vehicle radar system and also makes it possible to produce the strip with a greater width, which facilitates impedance measurement.

[0009] It is preferred that the at least one electrically conductive strip is arranged on at least one side wall of the radome. This allows for a defined positioning of the electrically conductive strip. Furthermore, it allows for maximum spacing from the circuit board, which is preferably arranged centrally between the side walls of the radome.

[0010] Some arrangements of one or more electrically conductive strips have proven particularly advantageous for measuring impedance: In one embodiment of the vehicle radar system, it has a first electrically conductive strip that runs parallel to an edge of the circuit board. In particular, this is the only electrically conductive strip of the vehicle radar system.

[0011] In another preferred embodiment of the automotive radar system, it has, in addition to the first electrically conductive strip, a second electrically conductive strip. This second strip runs parallel to the first electrically conductive strip. The circuit board is arranged between the two electrically conductive strips, such that the two electrically conductive strips are located opposite each other at opposite ends of the circuit board.

[0012] In yet another embodiment of the automotive radar system, it features an electrically conductive strip that runs around the circuit board. Specifically, it runs around all the inner walls of the radome that are perpendicular to the circuit board. The electrically conductive strip is perforated, so that it has a first end and a second end.

[0013] In all the aforementioned embodiments, the circuit board usually, but not necessarily, forms a counterpole to the strip(s) in the form of a ground or ground plane.

[0014] This automotive radar system enables a method for detecting a water layer on its radome. In this method, an alternating voltage is applied between at least one electrically conductive strip and a ground plane of the circuit board. The thickness of the water layer is then deduced from a measured electrical impedance or at least a value derivable from the impedance. This method utilizes the effect that an electromagnetic field is generated in the vicinity of the circuit board and the electrically conductive strip when the alternating voltage is applied. The presence of water on the radome alters this electromagnetic field because water has a different permittivity characteristic than air.

[0015] A suitable frequency for the alternating current lies particularly in the range of 0.1 GHz to 4.0 GHz. In this frequency range, the electrical impedance shows a particularly pronounced dependence on the thickness of the water layer on the radome. The procedure can be carried out at a single alternating current frequency within this range. It can also be repeated multiple times at different alternating current frequencies to verify the plausibility of the determined water layer thickness.

[0016] The at least one derivable value is, in particular, a ratio of the amplitudes of the sinusoidal alternating voltage to its corresponding sinusoidal alternating current and / or a shift in the phase angles between the sinusoidal alternating voltage and the sinusoidal alternating current. These derivable values ​​can be empirically determined for different electrical alternating voltages and different water layer thicknesses. The thickness of the water layer can then be inferred by comparing a value derived from the measured electrical impedance with the previously empirically determined values. These can be stored, in particular, in a characteristic curve or in a table.

[0017] The vehicle radar system is specifically designed to carry out the steps of the procedure. For this purpose, it preferably includes a computing device or an electronic control unit. Brief description of the drawings

[0018] Exemplary embodiments of the invention are shown in the drawings and are explained in more detail in the following description. Fig. Figure 1 shows an isometric sectional view of a motor vehicle radar system according to an embodiment of the invention. Fig. Figure 2 shows an isometric sectional view of a motor vehicle radar system according to another embodiment of the invention. Fig. Figure 3 shows an isometric sectional view of a motor vehicle radar system according to yet another embodiment of the invention. Fig. Figure 4 shows in two diagrams the course of an amplitude ratio and a phase angle shift with the alternating voltage frequency for different thicknesses of a water layer in an embodiment of the method according to the invention. Fig. Figure 5 shows an excerpt from the data in two diagrams. Fig. 4 frequency range shown. Exemplary embodiments of the invention

[0019] Fig. Figure 1 shows a motor vehicle radar system 10 according to a first embodiment of the invention. This system has a radome 11 in the form of a rectangular housing. A printed circuit board 12 is arranged on the bottom of this housing, and a transmitter / receiver element (not shown) in the form of a radar transceiver is arranged on its upper surface. In the present embodiment, the radome 11 consists of a plastic material that attenuates radar beams emitted by the radar transceiver orthogonally to the surface of the printed circuit board 12 by a maximum of 1 dB. The interior of the radome 11 is filled with air as a dielectric 13. A first electrically conductive strip 21, which is made of copper, for example, runs along an inner wall of the radome 11. It runs parallel to an edge of the printed circuit board 12 and is spaced apart from it, so that the dielectric 13 is arranged between the printed circuit board 12 and the electrically conductive strip 21.Furthermore, a device 30 is arranged in the radome 11. This device comprises an AC voltage source, a microcontroller, and a measuring device for measuring electrical impedance. The device 30 is electrically connected to a ground plane of the circuit board 12 by means of a first electrical connection 31. The device 30 is electrically connected to the first electrical strip 21 by means of a second electrical connection 32.

[0020] A second embodiment of the motor vehicle radar system 10 according to the invention is described in Fig. Figure 2 shows the embodiment. It differs from the first embodiment in that a second electrically conductive strip 22 is arranged on the inner wall of the radome 11, which is opposite the first electrically conductive strip 21. In addition to its first electrical connection 31 and its second electrical connection 32, the device 30 has a third electrical connection 33, which connects it to the second electrically conductive strip 22.

[0021] Fig. Figure 3 shows a third embodiment of the vehicle radar system 10 according to the invention. Instead of the first two electrically conductive strips 21, 22 according to the first two embodiments, the third embodiment provides a circumferential electrically conductive strip 23. This strip runs around all four inner walls of the radome 11, which are perpendicular to the plane of the circuit board 12. It is perforated such that its first end is located in a corner of the radome and its second end terminates shortly before this corner. As in the first two embodiments, the device 30 is electrically connected to the ground plane of the circuit board 12 via a first electrical connection 31. A further electrical connection 34 connects the device 30 to the first end of the circumferential electrically conductive strip 23.

[0022] The vehicle radar system 10, according to all the embodiments described above, is capable of determining the thickness of a water layer 40 on the radome 11. For this purpose, in one embodiment of the method according to the invention, an alternating electrical voltage is applied by the device 30 via the electrical connections 31 to 34 between the ground plane of the circuit board 12 and the electrically conductive strip 21, 23 in the first or third embodiment of the vehicle radar system 10, or between the ground plane of the circuit board 12 and the electrically conductive strips 21, 22 in the second embodiment of the vehicle radar system 10. The electrical impedance is then determined.The impedance is used to derive the ratio Z of the amplitudes of the sinusoidal alternating voltage to its sinusoidal alternating current and the phase angle φ between the sinusoidal alternating voltage and the sinusoidal alternating current. In the... Fig. 4 and Fig.Figure 5 shows characteristic curves of the values ​​Z and φ plotted against the frequency f of the alternating voltage for different thicknesses of the water layer 40. These characteristic curves were previously determined empirically using the vehicle radar system 10. During operation of the vehicle radar system 10, it is possible to infer the presence of a water layer 40 and, if applicable, its thickness using these characteristic curves. This allows a determination of whether the performance of the vehicle radar system 10 is so severely impaired by the water layer 40 that radar blindness can be assumed. In a simple embodiment of the method, a single impedance measurement at an alternating current frequency f at which characteristic differences for different thicknesses of the water layer 40 are discernible is sufficient for this purpose.In a more robust embodiment of the method, the measurement is repeated at different frequencies f of the alternating current and the results are mutually validated. 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] DE 196 44 164 C2

[0004]

Claims

[1] Motor vehicle radar system (10) with a radome (11) in which at least one transmitting / receiving element for transmitting and / or receiving electromagnetic waves is arranged on a printed circuit board (12) and at least one electrically conductive strip (21-23) is arranged in or on the radome (11) such that it is insulated from the printed circuit board (12) by a dielectric (13), characterized by that the motor vehicle radar system (10) comprises a device (30) which is arranged to measure an impedance between the circuit board (12) and the electrically conductive strip (21-23). [2] Motor vehicle radar system (10) according to claim 1, characterized by that the at least one electrically conductive strip (21-23) is arranged outside a beam path of the transmitting / receiving element. [3] Motor vehicle radar system (10) according to claim 1 or 2, characterized bythat the at least one electrically conductive strip (21-23) is arranged on at least one side wall of the radome (11). [4] Motor vehicle radar system (10) according to one of claims 1 to 3, characterized by that it has a first electrically conductive strip (21) which runs parallel to an edge of the printed circuit board (12). [5] Motor vehicle radar system (10) according to claim 4, characterized by in that it has a second electrically conductive strip (22) which runs parallel to the first electrically conductive strip (21), the printed circuit board (12) being arranged between the two electrically conductive strips (21, 22). [6] Motor vehicle radar system (10) according to one of claims 1 to 3, characterized by that it has a perforated electrically conductive strip (23) which runs around the printed circuit board (12). [7] Method for detecting a water layer (40) on the radome (11) of a motor vehicle radar system (10) according to one of claims 1 to 6, wherein an alternating electrical voltage is applied between the at least one electrically conductive strip (21-23) and a ground plane of the printed circuit board (12) and a thickness of the water layer (40) is inferred from a measured electrical impedance or at least one value derivable from the impedance. [8] Method according to claim 7, characterized by that a frequency (f) of the alternating electrical voltage lies in a range from 0.1 GHz to 4.0 GHz. [9] Method according to claim 7 or 8, characterized by that the at least one derivable value is a ratio (Z) of the amplitudes of the sinusoidal alternating voltage to its sinusoidal alternating current and / or a shift (φ) of the phase angles between the sinusoidal alternating voltage and the sinusoidal alternating current. [10] Motor vehicle radar system (10) according to one of claims 1 to 6, characterized by that its device (30) is arranged to carry out a method according to one of claims 7 to 9.

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