EP2681583A1

EP2681583A1 - Driver assistance device for a vehicle and method for operating a radar unit

Info

Publication number: EP2681583A1
Application number: EP12704035.0A
Authority: EP
Inventors: Frank Sickinger; Stefan Olejniczak
Original assignee: Valeo Schalter und Sensoren GmbH
Current assignee: Valeo Schalter und Sensoren GmbH
Priority date: 2011-03-03
Filing date: 2012-02-08
Publication date: 2014-01-08
Also published as: CN103502838A; JP2014513272A; WO2012116876A1; US20140168006A1; DE102011012843A1; US9482745B2; KR20140036155A; CN103502838B

Abstract

The invention relates to a driver assistance device (2) for a vehicle (1), having a radar unit (3, 4) for detecting a measured variable (α₁, α₂, R₁, R₂) in relation to an object (10) outside the vehicle, wherein the radar unit (3, 4) comprises: at least one first and one second receiving antenna (14, 15) for receiving signals (S_E1, S_E2); a first down-conversion mixer (17) coupled to the first receiving antenna (14) via a first receiving path (16), and a second down-conversion mixer (23) coupled to the second receiving antenna (15) via a second receiving path (21) for down-converting the received signals (S_E1, S_E2) to respective base band signals (S_B1, S_B2); a control unit (5) for determining the measured variable (α₁, α₂, R₁, R₂) on the basis of the base band signals (S_B1, S_B2); and testing means (32) for generating a local pilot signal (S_P) and for inserting the pilot signal (S_P) into the first receiving path (16) and into the second receiving path (21) such that the control unit (5) receives the pilot signal (S_P) down-converted by the first down-conversion mixer (17) as a first test signal (S_T1), and receives the pilot signal (S_P) down-converted by the second down-conversion mixer (23) as a second test signal (S_T2). From the test signals (S_T1, S_T2), the control unit (5) determines a frequency-dependent correcting quantity (δ(f)) for correcting the measured variable (α₁, α₂, R₁, R₂). The invention further relates to a corresponding method.

Description

Driver assistance device for a vehicle and

Method for operating a radar device

The invention relates to a driver assistance device for a vehicle which has a radar device for determining at least one measured variable related to an object external of the vehicle. The radar apparatus includes at least a first and a second receiving antenna for receiving signals, respectively. It also includes a first and a second downmixer: the first downmixer is coupled to the first receive antenna via a first receive path, and the second downmixer is coupled to the second receive antenna via a second receive path. The down-converters serve to down-mix the received signals into respective baseband signals. The radar device also includes a control device for receiving the baseband signals and for determining the at least one measured variable based on the baseband signals. There are test means for generating a local

Test signal and for coupling the test signal in the first receiving path on the one hand and in the second receiving path on the other hand provided. The control device thus receives the test signal mixed down by the first down-converter as the first test signal on the one hand, and the test signal mixed down by the second down-converter as the second test signal on the other hand. The controller then determines from the test signals a correction quantity for the correction of

Measured variable. The invention also relates to a vehicle with such

Driver assistance device, as well as a method for operating a radar device in a motor vehicle.

In the present case the interest of a calibration, as well as the checking of the

Functioning of a radar device in a motor vehicle, namely in particular of such a radar device, which serves for determining a target angle of an object. The target angle is an angle between a radar device and the

vehicle-external object connecting line and a reference line which passes through the radar device. The interest is directed in particular at the

Phase monopulse measurement. This method is used to determine the target angle and represents a known method in radar technology. To determine the target angle, as well as possibly other measured variables, at least two are required

Receiving antennas, which two individual antennas or two

Receive antenna arrays (arrays). The through the receiving antennas received signals are in two separate receiving channels or

Receive path prepared and processed as digital signals using a control device. The target angle - and possibly other measured variables - is determined as a function of the phase shift between the received signals.

So a radar needs two receiving channels to determine the measured quantities with high accuracy. A receive channel includes a receive antenna and a down converter (receive mixer). The down-converter is typically coupled to a baseband amplifier which serves to amplify the baseband signal. However, the phase of the down-mixed signals is not determined solely by the propagation path and the propagation properties in the air, so not only by the position of the object relative to the radar device, but is also highly dependent on the operating temperature, as well as the deviations of the Production parameters of the components of the radar, namely in particular the down-mixer and the baseband amplifier and their integration into the housing of the radar. The following problematic is thus given: The first reception path including the first downmixer and the

Baseband amplifier may cause a different shift in the phase of the received signal than the second receive path including the second

Down mixer and the second baseband amplifier. When determining the measured quantities, it is assumed, however, that the respective

Phase shifts through the first and second receive paths are the same. If these shifts differ in phase, the most accurate determination of the measured variables-in particular of the target angle-can not be achieved.

A remedy here radar systems in which test means are provided which generate a local high-frequency test signal and this signal in the two

Coupling in receiving channels. This test signal is then passed through the respective

Down mixer mixed down, namely baseband. The down in the first receiving channel mixed test signal is then used as the first test signal through the

Receive control device, while the mixed down in the second receiving channel test signal is present as a second test signal. The controller can then the

Determine phase difference between the phases of the two test signals and use this phase difference as a correction variable for the correction of the target angle. In the subject matter according to document US 2003/0160718 A1, a transmission signal emitted by the radar device is used as a test signal, which is coupled as a known signal into the two reception channels. The transmission signal is from a Transmit path or transmission channel tapped and a switch to the

Receiving channels led.

It is also state of the art, one separate from the transmission signal or

provide independent test signal and couple into the respective receiving channels. This approach has the advantage over the use of the transmission signal as a test signal that the correction value is also determined or the

Calibration of the radar device can be made even if the radar sends no transmission signal.

It is an object of the invention to show a way how the

Driver assistance device of the type mentioned can be further developed such that the at least one measured variable can be determined even more accurately at different relative speeds of the vehicle external object with respect to the vehicle.

This object is achieved by a driver assistance device with the features according to claim 1, as well as by a vehicle according to

Claim 14 and solved by a method having the features of claim 15. Advantageous embodiments of the invention are the subject of the dependent claims and the description.

A radar device of a driver assistance device according to the invention serves for

Determining at least one on a vehicle external object related measure. It comprises at least a first and a second receiving antenna (single antenna or an antenna group or an array) respectively for receiving signals, i. H.

electromagnetic waves. With the first receiving antenna is a first

Coupled down converter, namely via a first reception path; A second down-converter is coupled to the second receiving antenna, namely via a second receiving path. The down-converters serve to down-mix the received signals into respective baseband signals. A controller receives the

Baseband signals and determines the at least one measure using the

Baseband signals. The radar device has test means which are designed to generate a local test signal and to couple the same test signal into the first reception path on the one hand and into the second reception path on the other hand. The controller receives the test signal mixed down by the first down-converter as the first test signal on the one hand and the second down-converter on the other hand down-mixed test signal as a second test signal on the other. The control device can determine a correction variable for the correction of the measured variable from the test signals. According to the invention, it is provided that the control device determines the correction variable as a frequency-dependent variable on the basis of the test signals.

In other words, a core idea of the invention is to use the two test signals to determine a correction quantity which is dependent on the frequency in the baseband and with which the measured variable-for example, the target angle-can be corrected. It can thus almost a frequency-dependent calibration of

Phase difference between the phases of the received signals are made. The invention is based on the recognition that in addition to the two

Downstream mixers also the respective ones, coupled with the downwards mixers

Baseband amplifier cause a frequency-dependent fluctuation of the phase difference over the entire baseband and thus frequency-dependent fluctuations in the phase difference between the phases of the received signals are to be expected. Because of the two baseband amplifiers and the mixers, the difference between the phases of the received signals is thus subject to frequency dependent variations caused by the uneven variations in the phase characteristics of the two baseband amplifiers and the mixers. The invention now goes the way of determining the correction quantity-that is, in particular the phase difference between the phase shift in the first receiving channel and that in the second receiving channel-for a plurality of frequency points of the baseband, so that a frequency-dependent calibration can be performed. Regardless of the frequency of the received signals and thus independent of each

instantaneous relative speed of the object with respect to the motor vehicle (Doppler effect) can thus be determined with the highest accuracy at least one measured variable.

The invention further builds on the knowledge that the by the

Baseband amplifier caused fluctuations in the phase, in principle, due to the fact that the baseband amplifier is usually a

Gain characteristic that increases by about 20 dB per frequency decade. On the one hand, this is advantageous because it compensates for the decreasing level of the received signal with increasing distance of the object from the motor vehicle.

On the other hand, the phase characteristics of the radar receiver thus change over the entire baseband, so that a frequency-independent correction of the

Phase difference proves to be insufficient. A remedy here creates the inventive approach by the correction quantity is determined as dependent on the frequency in the baseband size.

The test signal provided by the test means is preferably a separate or independent signal from a transmission signal emitted by the radar device. Unlike in the subject matter according to document US 2003/0160718 A1, the correction quantity can thus also be determined and the radar device can be calibrated even if no transmission signal for measuring the measured variable is transmitted.

Preferably, the correction quantity is a phase difference between a phase of the first test signal and a phase of the second test signal. Thus, for a plurality of different frequency points in the baseband, the phase difference between the reception paths including the respective downconverters and the respective baseband amplifiers can be determined. It is thus possible to determine such measured quantities with the highest accuracy, which are determined as a function of the respective phase information of the received signals. Namely, for example, a target angle can be determined with high accuracy, such as according to the phase monopulse method.

So the measurand can be a target angle. It is defined as follows: an angle between a reference line passing through the radar and a

Connecting line that passes through the radar device and the object.

In principle, the frequency-dependent correction variable can be determined in such a way that the fundamental frequency of the test signal and thus of the test signals is varied over the baseband and thus the correction variable for a wide variety of frequency values is determined. Then, however, always the filter characteristic in terms of

Signal level are taken into account. It thus proves to be particularly advantageous if, to determine the frequency-dependent correction variable, the test signals-at a constant fundamental frequency-are evaluated at integer multiples of the fundamental frequency of the test signals. In other words, the harmonics or the harmonics of the test signals can be evaluated to determine the frequency-dependent correction variable. In particular, the phase difference between the phases of the test signals for a plurality of frequency points corresponding to the different integer multiples of the fundamental frequency is determined here. This "multitone method" allows correction values to be corrected within the entire baseband or the entire frequency range of the radar application Measured variable can be determined without causing an override of the receiver due to the increase of the gain characteristic of the baseband amplifier. With the evaluation of the harmonic signals phase inequalities between the gain characteristics of the two receive paths to the harmonic

Frequency points are calibrated.

Particularly preferably, the test signal is single-sideband modulated. Numerous measurements have shown that such a single-sideband modulation of the test signal, the detection of the total phase error of the two receive paths including the

Down mixer and the baseband amplifier with a very high accuracy allows. In contrast, this is not possible with the aid of conventional double-sideband modulation or only with increased effort; in fact, no phase error can be detected at all in principle with a simple double-sideband up-conversion mixer. The single-sideband modulation thus ensures a highly accurate determination of the phase difference between the two test signals and thus also the measured variables of the radar device. In this embodiment, for example, a single-sideband up-converter may be provided which generates the local test signal. For this purpose, the up-converter can receive a first pilot signal-with a predefined frequency-as well as a second pilot signal shifted in phase by the first pilot signal by 90 ° from the control device. Then the

Up-converters from the first and second pilot signals generate the single-sideband modulated test signal.

Thus, the control device to the test means - in particular to the

Upconverter - output a first pilot signal and a second pilot signal phase-shifted by 90 ° with respect to the first pilot signal, from which the test signal is generated. This enables the provision of the single sideband modulated test signal.

With regard to the evaluation of the harmonics of the test signals, it proves to be particularly advantageous if the two pilot signals from which the test signal is generated are square-wave signals. Just then, the local test signal has a plurality of harmonics or harmonics, which can then be evaluated after downsampling into baseband. Thus, by using a square wave signal, the correction quantity for a plurality of frequency points can be determined, and the measured quantity can be corrected frequency-dependent virtually over the entire base band. As already stated, the radar apparatus may comprise a first baseband amplifier coupled to the first downmixer and a second baseband amplifier coupled to the second downmixer configured to amplify the baseband signals. In this embodiment, the

Baseband amplifier have a frequency-dependent gain characteristic which increases by a slope factor per frequency decade, which is in a Werdebereich 17 dB to 23 dB. The slope factor may be, for example, 20 dB. With such a gain characteristic, the decreasing level of the received signal can be compensated with increasing distance of the object from the motor vehicle; on the other hand, the determination of the frequency-dependent correction variable is required especially in the case of such a gain characteristic.

The test means may comprise an up-converter - in particular a single-sideband up-mixer - for generating the local test signal, whose output with the first receiving path on the one hand and with the second receiving path

on the other hand is coupled. An output of the up-converter may be coupled to the first receive path on the one hand and to the second receive path on the other hand. The respective coupling can be done for example by means of a directional coupler. The two directional couplers are then preferably constructed the same, so that there is a symmetrical coupling of the test signal in the two receiving paths. By using an up-converter, a pilot signal generated by the control device with a predefined frequency can be mixed up to an operating frequency of the respective reception paths or of the radar, so that it is possible to check the reception paths in the operating frequency of the radar device. The downconverters may then mix the test signal back into the baseband, namely the respective test signals.

It proves to be particularly advantageous in terms of a compact, component-reduced and space-saving radar device if the same radar device has a common for the first and the second down mixer on the one hand and for the up-mixer on the other hand local oscillator, which for providing a

Oscillator signal is used. The up-converter can thus be fed with the oscillator signal of a local oscillator already present in the radar. The radar thus comes without an additional oscillator; it is unnecessary to use an additional component with the associated disadvantages in terms of space, weight and cost. For putting, therefore, are a phase error and a

Frequency error due to different oscillators excluded. The local oscillator is preferably coupled via a directional coupler or a power divider or a similar component to an input of the up-converter. For the up-converter is preferred only a small part of the power of

Tapped oscillator signal. Namely, the directional coupler or the power divider, a part of a value range of -25 dB to -15 dB from the performance of

Pick up oscillator signal for the up-mixer. Absolutely can for the

For example, a power in a value range from -25 dBm to -15 dBm can be picked up. By feeding the up-converter with such a low-power oscillator signal, the use of an additional is unnecessary

Amplifier for that part of the oscillator signal, which is used for the supply of the downmixer. Also for the oscillator signal of the up-converter no additional amplifier is required. Although the up-converter is fed with a relatively low level oscillator signal, the power of the up-converter can be reduced

Pilot signal, from which the up-mixer generates the local test signal to be correspondingly higher, so that the diodes of the up-mixer are turned on.

In one embodiment, the control device checks on the one hand and / or on the basis of the second test signal on the other hand, the first and the second reception path on the basis of the first test signal on its functionality. It can thus the

Readiness to receive the respective functional paths are checked, and the

Control device may optionally detect an operating error or a defective reception path, as well as issue a corresponding error message. Such an error message can / may clearly identify the faulty receive path and / or the entire radar device, so that a technician is clearly informed about which radar device or which receive path is actually defective. The technician then does not have to separately check all the radars available in the vehicle. Thus, checking the respective receive paths may involve generating the test signal and the controller

Presence of the respective test signals checked. The control device thus checks whether the respective test signals are present or not.

As already stated, the control device can use the local test signal to determine the correction variable for the correction of the measured variable and, if appropriate, also to check the reception paths for their respective functionality. Such a calibration and in particular also the said verification of the functioning can be done in the radar in a test mode. This test mode is preferably a separate mode to a normal mode in which the radar transmits transmit signals and processes the received signals. In the test mode, the radar thus preferably transmits no transmission signals. In one implementation of this form of excursion, for example, such a method can be carried out: In the radar device, the local test signal is generated in the test mode and coupled into the two reception paths. During the period during which the test signal is provided, the radar sends no

Transmission signals, so that in principle no signals are received by the receiving antennas. The test signal is down-converted by both the first down-mixer and the second down-mixer, namely, the baseband; the first downmixer outputs a first test signal to the controller, and the second downmixer outputs a second test signal to the controller. The controller calculates a difference between the phases of the first and second test signals. This difference in phase is stored by the control device, namely for a later correction of a measured variable, for example the target angle. Such a test mode may last a very short period of time. For example, the duration of such a test mode can be in a value range of 100 με to 1 ms. Is the difference in phase and / or another correction quantity by the

Control device has been determined, the test mode can be terminated, and the radar goes into an operating mode. In such an operating mode, the radar may transmit a predetermined number of frequency-modulated signal pulses (also known as "chirps.") The first and second

Receiving antennas then each receive a received signal which is the transmitted signal reflected by an object. The downconverters downconvert the receive signals and provide respective baseband signals to the controller. From the baseband signals, the control device determines the measured variable - for example the target angle - initially independent of the phase difference determined in the test mode. The measured variable determined in this way is subsequently corrected on the basis of the phase difference. The radar device may transition to the test mode prior to each operating mode or cycle in which a predetermined number of frequency modulated signal pulses are transmitted by the radar device, respectively. Determining the correction quantity before each measurement cycle ensures that the measurement variable can be determined with highest accuracy after each measurement cycle.

Instead of generating the local test signal only in a test mode of the radar device, the same test signal can also be generated permanently by the control device, namely during operation of the radar device. Then results continuously - the control device known - frequency component in the respective baseband signals. Since this frequency - and more specifically a plurality of frequency components - is known, it can then be suppressed by the controller, such as by means of a notch filter.

The radar device is preferably a continuous wave radar which is designed to emit a frequency-modulated continuous electromagnetic wave (also known as FMCW (Frequency Modulated Continuous Wave) radar). With such a radar device, it is possible to determine the distance of an object from the same radar device, as well as the relative speed of the object with respect to the radar device and the target angle. A receiver of the radar can - except for the two downmixers - for each reception path also one

Low-pass filter, an amplifier and an analog-to-digital converter include. The signals received by the first and the second receiving antenna are then mixed down in the receiver in the baseband, low-pass filtered and analog-digital converted.

The radar device preferably uses a separate transmission antenna, be it a single transmission antenna or a transmission antenna array, which is fed by means of a local oscillator to generate a transmission signal. The transmitting antenna can be phased, so overall a relatively wide

To be able to detect ambient area with a narrow main lobe of the directional characteristic in the horizontal direction.

There are a variety of applications of the driver assistance device in the

Motor vehicle reasonably possible: For example, the driver assistance device for lane change assistance, for monitoring the blind spot, as well as for

Serve accident detection. The driver assistance device can also the

Function of an automatic distance warning, a distance control, a

Lane Departure Warning and / or a parking aid.

A vehicle according to the invention, in particular a motor vehicle, comprises a driver assistance device according to the invention or a preferred embodiment thereof. In a method according to the invention for operating a radar device in a vehicle, at least one measured quantity related to an object external to the vehicle is determined by the same radar device. Signals are received through at least a first and a second receiving antenna. There is a down-mixing of the received signals into respective baseband signals by one with the first

Receiving antenna via a first receiving path coupled first down mixer on the one hand and one with the second receiving antenna via a second

Receive path coupled second down mixer on the other. A

Control device receives the baseband signals and determines the at least one measured variable based on the baseband signals. A local test signal is generated in the radar device and coupled into the first reception path and into the second reception path. The control device receives the test signal mixed down by the first down converter as a first test signal on the one hand and the test signal mixed down by the second down mixer as a second test signal on the other hand. The controller determines from the test signals

Frequency-dependent correction variable for the correction of the measured variable.

The preferred embodiments presented with reference to the driver assistance device according to the invention and their advantages apply correspondingly to the vehicle according to the invention and to the method according to the invention.

Further features of the invention will become apparent from the claims, the figures and the description of the figures. All the features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures are not only in the respectively indicated combination but also in others

Combinations or even usable in isolation.

The invention will now be explained in more detail with reference to individual preferred embodiments, as well as with reference to the accompanying drawings.

Show it:

1 is a schematic representation of a plan view of a motor vehicle with a driver assistance device according to an embodiment of the invention; 2 is a schematic representation of a plan view of the motor vehicle according to FIG. 1, the detection of different partial areas being explained in more detail by a radar device;

3 shows a schematic illustration of a radar device of the driver assistance device;

4 is a schematic representation of a general layout (RF layout) of an up-converter of the radar;

5 is a schematic representation of a general layout plan (HF layout) of the radar device;

6 shows a frequency-dependent gain characteristic as well as a phase characteristic of a baseband amplifier of the radar device; and

Fig. 7 shows the frequency spectrum of a test signal, as determined by test means of

Radar generated and coupled into receiving paths of the radar device.

In the figures, the same and functionally identical elements are the same

Provided with reference numerals.

A motor vehicle 1, as shown in Fig. 1, comprises a

Driver assistance device 2, which supports the driver when driving the motor vehicle 1. The motor vehicle 1 is a passenger car in the embodiment. The driver assistance device 2 can be, for example, a blind spot monitoring system and / or an accident early warning system and / or an ACC (Adaptive Cruise Control) system.

The driver assistance device 2 comprises a first radar device 3 and a second radar device 4. The first radar device 3 is arranged in a left corner of a rear bumper and the second radar device 4 in a right corner of the same bumper. The first and second radars 3, 4 are Frequency Modulated Continuous Wave (FMCW) radars. The radar devices 3, 4 also include a control device 5, which may comprise, for example, a common for the first and the second radar 3, 4 microcontroller 6, as well as a digital signal processor, not shown in the figures. alternative It is also possible to provide two separate microcontrollers 6 and / or two digital signal processors, for example via an existing one in the motor vehicle 1

Communication bus communicate with each other.

The first radar device 3 has a detection area 7, which in FIG. 1 is delimited by two lines 7a, 7b. The opening angle of the detection area 7 - ie the angle between the lines 7a, 7b - is in the example about 170 °. Accordingly, the second radar device 4 has a detection area 8, which is delimited by two lines 8a, 8b. The opening angle of the detection area 8 - ie the angle between the lines 8a, 8b - is also about 170 ° in the exemplary embodiment. The detection areas 7, 8 of the radars 3, 4 overlap, so that a

Overlap area 9 is given. The overlapping area 9 is bounded at an angle by the lines 7b, 8b. In the exemplary embodiment, an opening angle

Overlap area 9 about 70 °.

In their respective detection areas 7, 8, the radars 3, 4 can locate an object 10. In particular, the radar devices 3, 4 can each determine a distance R _{1 5} R ₂ , the object 10 of the respective radar device 3, 4, each a target angle · · ₂ , and a relative speed of the object 10 with respect to the motor vehicle 1 - these are measured variables The radar devices 3, 4. The target angles · 1, · ₂ are angles between each of a reference line 1 1, which passes through the corresponding radar device 3, 4, and a connecting line 12 which passes through the object 10 and the respective radar device 3, 4 ,

The radars 3, 4 can the respective target angle · 1, · ₂ after the

Measure phase monopulse method.

With reference to FIG. 2, the radar device 3-and analogously also the radar device 4-can have different partial regions A, B, C, D, E, F, G, H of the detection region 7

illuminate in succession. For example, a transmission lobe of a

Transmitting antenna electronically in the horizontal direction (azimuth direction) are pivoted, namely according to the phase array principle. At least one receiving antenna can in this case have a broad receiving characteristic in the horizontal direction, with which the entire detection area 7 is covered. Other configurations may alternatively narrow receive angle ranges in conjunction with wide

Realize transmission lobes. In FIG. 2, for the sake of clarity, only the subregions A to H of FIG

Detected area 7 of the first radar device 3 shown. Accordingly, the detection area 8 of the radar unit 4 is here also subdivided into a plurality of subregions, which are detected in succession by the second radar device 4. Although the further description refers only to the first radar device 3, the operation of the second radar device 4 corresponds to that of the first radar device 3.

In the operating mode or in a single measuring cycle, the subareas A to H are detected by the radar 3 in succession. In a single measurement cycle, the radar unit 3 transmits separately for each subarea A to H (ie per beam) a predetermined sequence of frequency-modulated signal pulses (chirps). In the operating mode, the partial areas A to H are thus illuminated one after the other in time, and objects located in the partial areas A to H are detected. In front of everyone

Measuring cycle or before the initiation of the operating mode - i. in front of everyone

Illuminate all sections A to H - is the radar device 3 first in a test mode, as will be explained in more detail below.

Fig. 3 shows a schematic representation of the structure of a receiver 13 of a single radar device 3, 4. The receiver 13 comprises a first and a second receiving antenna 14, 15, the individual antennas or a group of

Antennas can be. The first receiving antenna 14 is via a first

Receive path or receiving channel 16 is coupled to a first down-converter 17, namely with its RF (Radio Frequency) input 18. An output 19 of the first down converter 17 is connected to the first baseband amplifier 101

Control device 5 coupled, with a first channel input 20. The output 19 of the down converter 17 may be coupled to the controller 5 via an analog-to-digital converter (not shown). Alternatively, such a converter may be integrated into the control device 5.

Accordingly, the second receiving antenna 15 is coupled via a second receiving path 21 to an RF input 22 of a second downmixer 23. An output 24 of the second downmixer 23 is coupled via a second baseband amplifier 102 to the control device 5, namely with its second channel input 25. Again, may be connected between the controller 5 and the second downmix 23, an analog-to-digital converter; Alternatively, such a transducer in the

Control device 5 to be integrated. In each case a low-noise amplifier (Low Noise Amplifier) can be integrated into the respective receive paths 16, 21.

A local oscillator 26 provides an oscillator signal or an LO (Local Oscillator) signal 27, namely at an output 28. With the oscillator signal 27 are the

Down mixer 17, 23 fed via respective LO inputs 29, 30. For this purpose, the oscillator signal 27 is divided symmetrically by means of a power divider 31.

The first and the second receiving antenna 14, 15 receive signals S EI, SE2- These are received signals. The signals S _E i, S _E 2 are the transmission signals reflected by an object. The received signals S EI _J SE2 are determined by the respective

Down mixer 17, 23 mixed down, namely in the baseband. At their respective outputs 19, 24, the downconverters 17, 23 output baseband signals SBI, SB2. These baseband signals SBI, SB2 are then amplified by the two baseband amplifiers 101, 102, analog-to-digital converted by a converter and processed by the control device 5. The control device 5 determines on the basis of

Baseband signals SBI, SB2, the already mentioned measures of the radar 3, 4, namely the distance R _{1 5} R ₂ , the relative speed, as well as the target angle oci,

0C2-

The angle information of the received signals SEI, S _E 2 is determined in the control device 5 from a difference between the phases of the baseband signals SBI, SB2. However, the output phase of the down-converters 17, 23 and the baseband amplifiers 101, 102 is not determined solely by the signals S _E i, S _E 2 of the two reception paths 16, 21, but is additionally also from the operating temperature and the

Variations in the production parameters of the down-converters 17, 23 and the baseband amplifiers 101, 102 and their integration into a housing dependent.

The target angle oci, 0C ₂ is determined depending on a phase shift between the respective phases of the baseband signals SBI, SB2.

In order to ensure a determination of the target angle · 1, · ₂ , as well as the distance R _{1 5} R ₂ and the relative speed with the highest accuracy, the receiver 13 on test means 32. The test means 32 are designed to generate a local test signal S _P and to couple the same test signal S _{P into} both the first and the second reception paths 16, 21 symmetrically. The local test signal S _P is single-sideband modulated. The control device 5 generates a first pilot signal Sp _iot i at a first pilot _output 33; at a second pilot output 34, it generates a second pilot signal S _Pi | _0t 2- The first pilot signal S _Pi | _0t i is preferably a harmonic signal, namely in particular a square wave signal. The first pilot signal S _Pi | _0t i may have a predetermined fundamental frequency, which is, for example, in a value range of 10 Hz to 1 MHz. The second pilot signal S _Pi iot2 is a same signal and with respect to the first pilot signal Sp _iot i phase-shifted by 90 °. Also, the second pilot signal S _Pi iot2 is thus a rectangular signal. The two pilot signals S _P ii _ot , S _Pi iot2 can be generated, for example, by means of a small oscillator in the control device 5.

The test means 32 comprise an up-converter 35, which is designed for single sideband modulation and thus is a single-sideband mixer. A first input 36 of the up-converter 35 is coupled to the first pilot output 32 while a second input 37 of the up-converter 35 is coupled to the second pilot output 34. By means of the up-converter 35, the two pilot signals S _P ii _ot , S _Pi iot2 are mixed upwards and superimposed, namely to the local test signal S _P. The high-frequency local test signal S _P has such a fundamental frequency, which corresponds to the average frequency of the transmission signals of the radar 3, 4. The local test signal S _P is - as already stated - in the first and in the second

Receiving path 16, 21 symmetrically coupled. For this purpose, the test means 32 comprise a symmetrical power divider 38, which divides the local test signal S _P. The power of the test signal S _{P is} halved. The test signal S _P is in the respective

Receive path 16, 21 coupled by means of a directional coupler 39, 40. The directional couplers 39, 40 are the same structure.

The local oscillator 26 is a common oscillator for the down-converters 17, 23 and the up-converter 35. It is controlled by the control device 5. The oscillator 26 is, for example, a voltage-controlled oscillator (voltage control oscillator), which generates the oscillator signal 27 at a frequency which is dependent on the amplitude of a DC voltage provided to the oscillator 26 by the control device 5.

A part of the power of the oscillator signal 27 is coupled out for the up-converter 35, namely for example by means of a directional coupler 41. With this tapped oscillator signal 27 of the up-mixer 35 is fed, namely at its LO input 42. This decoupled for the up-converter 35 part of Power of the oscillator signal 27 is preferably a very small part, namely for example -20dBm. It is unnecessary, an additional amplifier for the LO input 42, as well as for that oscillator signal 27, with which the down-converters 17, 23 are fed. The pilot signals S _Pi | _{In fact, 0t} i, S _Pi iot2 are generated with correspondingly higher power.

Thus, the local test signal S _P in the first receive path 16 on the one hand and in the second receive path 21 on the other hand coupled. The test signal S _P is thus mixed by the first down mixer 17 on the one hand and the second downwards mixing he 23 on the other hand downwards, namely in the baseband. The first down-converter 17 outputs a first test signal Sn from the test signal S _P , while the second down-converter 23 outputs a second test signal S _T 2. The test signals Sn, ST2 are received by the control device 5, namely at the respective channel inputs 20, 25.

As already stated, the radar device 3, 4 is in the test mode, before each measurement cycle or before the initiation of each operating mode. In this test mode, the control device 5 first checks the reception paths 16, 21 for their functionality. The control device 5 generates the pilot signals S _Pi | _0t i, S _Pi | _0t 2 and checks whether the test signals Sn, S _T 2 are present at the respective channel inputs 20, 25 or not. If the test signals Sn, S _T 2 can be detected by the control device 5, the two receiving paths 16, 21 and the downmixers 17, 23 are functional.

It should be noted at this point that the test signal S _{P is} a separate or independent signal from a transmission signal of the radar device.

Depending on the test signals Sn, S _T 2, the control device 5 also determines a correction variable for a correction of the measured variables. Namely, the controller 5 may calculate a phase difference between the phase of the first test signal Sn and the phase of the second test signal S _T 2 as a correction quantity. This phase difference is then used by the control device 5 for a correction of the measured variables, in particular the target angle oci, 0C2. Because the phase difference is the differences in the propagation and phase characteristics of the two receive paths 16, 21 and the down mixer 17, 23, the baseband amplifier 101, 102 and possibly other components of the receiver 13 again. Thus, possibly existing Inaccuracies or deviations from a nominal dimension are taken into account in the determination of the measured variables.

Instead of the pilot signals S _Pi | _0t i, S _Pi iot2 and thus the local test signal S _P in one

Test mode of the radar 3, 4 to produce the same signal S _Pi | _0t i, S _Pi | _0t 2, S _P are also permanently generated by the control device 5, namely during the operation of the radar 3, 4. Then, the pilot signal S _Pi | results continuously _0t i, Spüot2 corresponding frequency component in the respective baseband signals SBI, SB2- Since this frequency is known, it can then be suppressed by the controller 5 - for example by a notch filter.

The pilot signals S _Pi | _0t i, S _Pi iot2 are rectangular signals in the embodiment. These pilot signals S _P ii _ot , S _Pi iot2 are fed to the up-converter 35, which then provides the high-frequency local test signal S _P. The test signal S _P is down-converted in the two receiving channels by the down-converters 17, 23 and amplified by the baseband amplifiers 101, 102.

In the present case, the interest is directed to the determination of the target angle or

Azimuthwinkels α as a function of the phase difference between the phases of the received signals S _E i, S _E2 . As already stated, the control device 5 determines a correction variable for the correction of the target angle oc; the correction quantity is the phase difference between the phase shift in the first receiving channel and the phase shift in the second receiving channel. This phase difference is in

Essentially caused by the down-converters 17, 23, as well as by the baseband amplifiers 101, 102. While the down-converters 17, 23 have substantially constant phase characteristics over the frequency range of the baseband, and therefore no phase difference variations are expected over the entire baseband, the baseband amplifiers 101, 102 cause a baseband frequency dependent phase error. The baseband amplifiers 101, 102 thus cause a phase shift between the phases of the received signals SEI, S _E 2, which is dependent on the frequency. The frequency-dependent

Phase shift is due to the gain characteristic of the baseband amplifiers 101, 102. FIG. 6 shows on the one hand a gain characteristic V and on the other hand a phase characteristic of the baseband amplifiers 101, 102, each as a function of the frequency f. As is apparent from Fig. 6, a gain characteristic V which increases by 20 dB per frequency decade (in the logarithmic progression) was selected. Thus, the decreasing power of the received signals S _E i, S _E 2 becomes increasing distance of the object compensated. As further from FIG. 6

As can be seen, cause the baseband amplifier 1 01, 1 02 a frequency-dependent phase shift of the amplified baseband signals S _B i, S _B 2-

For this reason, the control means 5 determines the correction quantity for the correction of the target angle θ as a frequency-dependent correction quantity. Namely, a frequency-dependent phase difference 6 (f) is determined as a correction quantity. These

Phase difference 6 (f) gives the frequency dependent difference between the

Phase shift in the first receiving channel and the phase shift in the second receiving channel again. For determining the frequency-dependent phase difference 6 (f), the rectangular shape of the pilot signals S _Pi | _0t i, S _Pi iot2 particularly advantageous. Then the test signal S _P namely has a plurality of frequency components or

Harmonics that occur in addition to the fundamental frequency. In addition to the fundamental frequency, even odd integer multiples of the fundamental frequency occur. An exemplary frequency spectrum of the test signal S _P is shown in FIG. 7. The carrier frequency of the tester signal S _P is denoted by ft in FIG. In addition to the carrier frequency ft are also more frequency components or sidebands can be seen. Because the two pilot signals SpüoH, S _Pi | _0t 2 are 90 _{° out of} phase with each other, have the harmonics

(2n-1) -ft of these pilot signals S _Pi | _0t i and S _Pi | _0t 2 always has a phase difference of (2n-1) -90 °. Thus, the harmonics have a phase difference of +/- 90 °, and a corresponding sideband suppression, which is required for phase calibration, remains ensured, namely due to the single-sideband modulation. As can be seen from FIG. 7, with increasing index n, the lower (left) and upper (right) sidebands are alternately suppressed, starting from the carrier frequency ft.

The control device 5 evaluates now to determine the frequency-dependent

Phase difference (6 (f)), the test signals Sn, S _T 2 not only at the fundamental frequency, but also harmonics of these test signals Sn, ST2 are evaluated. By evaluating the harmonics is a frequency-dependent calibration of

Phase difference of the two receiving channels made or it can also phase inequalities between the two baseband amplifiers 101, 1 02 calibrated at the harmonic frequency points. The correction quantity (6 (f)) is thus determined not only for the fundamental frequency but also for the (at least odd) integer multiples of the fundamental frequency, ie for the harmonics of the test signals

Sn, ST2 4 shows a schematic representation of a general structure (HF layout) of the up-converter 35 in microstrip technology. The up-converter 35 is a so-called rat race mixer with diodes (not shown). At the LO input 42, the oscillator signal 27 is applied. The oscillator signal 27 is using a

Power divider 43 halves and propagates to a first port 44 of a first annular coupler 45 on the one hand and to a first port 46 of a second annular coupler 47 on the other. From the first entrance 36 of the

Upmixer 35, the first pilot signal S _Pi | is propagated ₀ ti toward a second port 48 of the coupler 45. Accordingly, the second pilot signal S _Pi iot2 propagates from the second input 37 to a second port 49 of the second coupler 47. The first pilot signal S _Pi | _0t i and the oscillator signal 27 on the one hand and the second pilot signal S _Pi iot2 and the oscillator signal 27 on the other hand overlap and the respective

Superpositions extend to a 90 ° hybrid coupler 50. There these superpositions overlap, so that the local test signal S _{P is} output.

5 also shows, in a schematic representation, the general structure (HF layout) of the receiver 13. A ground surface is designated 51 in FIG. Two mounting surfaces 52, 53 are provided, on which the first down-mixer 17 and the second down-mixer 23 are mounted, respectively. In FIG. 5, respective microstrip lines can be seen, which form the first and second receiving paths 16, 21, respectively. These lines are on the one hand with terminals 54, 55 for the

Receive antennas 14, 15 are coupled and on the other hand led to the mounting surfaces 52, 53 to be connected there to the respective down-converters 17, 23. The local test signal S _P is coupled via the power divider 38 in microstrip technology and via the respective directional couplers 39, 40 in the receiving paths 16, 21. Also, the power divider 31 is provided in microstrip technology and coupled via a microstrip line 56 to the first downmixer 17 on the one hand and via a further microstrip line 57 to the second downmixer 23.

The directional couplers 39, 40 are constructed identically. The power divider 38 is a symmetrical power divider, so that the power of the local test signal S _{P is} halved.

Claims

claims

1 . Driver assistance device (2) for a vehicle (1) which has a radar device (3, 4) for determining at least one measured variable (oci, furnace, Ri, R ₂ ) relating to an external vehicle object (10), wherein the radar device (3, 4) comprises:

at least a first and a second receiving antenna (14, 15) each for receiving signals (S _E i, S _E 2),

a first down-converter (17) coupled to the first receive antenna (14) via a first receive path (16) and a second down-converter (23) coupled to the second receive antenna (15) via a second receive path (21) each for down-converting the received signals ( S _E i, S _E2 ) into respective baseband signals (S _B i, S _B 2), - a control device (5) for receiving the baseband signals (S _B i, S _B 2) and for determining the at least one measured variable (oci, ofe , Ri, R ₂ ) based on the baseband signals (S _B i, S _B2 ) and

Test means (32) for generating a local test signal (S _P ) and for coupling selbigen test signal (S _P ) in the first receiving path (16) on the one hand and in the second receiving path (21) on the other hand, so that the control device (5) by the first down mixer (17) down-converted test signal (S _P) as a first test signal (Sn) on the one hand and by the second downconverter (23) down-converted test signal (S _P) as a second test signal (S _T 2) on the other hand receives,

wherein the control device (5) is designed to determine from the test signals (Sn, S _T 2) a correction variable (6 (f)) for the correction of the measured variable (oci, 0C2, Ri, R ₂ ),

characterized in that

the control device (5) is designed to use the test signals (Sn, S _T 2) to determine the correction variable (6 (f)) as a frequency-dependent variable.

2. driver assistance device (2) according to claim 1,

characterized in that the frequency-dependent correction quantity is a phase difference (6 (f)) between a phase of the first test signal (Sn) and a phase of the second test signal (S _T 2).

3. driver assistance device (2) according to claim 1 or 2,

characterized in that

the measurand (oci, ο ^, Ri, R ₂ ) is a target angle (oci, 0C2) which is an angle between a reference line (1 1) passing through the radar (3, 4) and a connecting line (12) through the radar device (3, 4) and the object (10).

4. driver assistance device (2) according to one of the preceding claims,

characterized in that

the control device (5) is designed to determine the

frequency-dependent correction variable (6 (f)) to evaluate the test signals (Sn, S _T 2) at integer multiples of a fundamental frequency of the test signals (Sn, S _T 2).

5. driver assistance device (2) according to one of the preceding claims,

characterized in that

the test signal (S _P ) is single-sideband modulated.

6. driver assistance device (2) according to one of the preceding claims,

characterized in that

the control device (5) is designed to transmit to the test means (32) a first pilot signal (S _Pi | _0t i) and to the first pilot signal (SPN _O H) by 90 °

phase-shifted second pilot signal from which the test signal (S _P ) can be generated.

7. driver assistance device (2) according to claim 6,

characterized in that

the pilot signals (SRI _O H, _P n _ol2 ) are square wave _signals .

8. driver assistance device (2) according to one of the preceding claims, characterized in that

the radar apparatus (3, 4) comprises a first baseband amplifier coupled to the first downmixer (17) and a second baseband amplifier coupled to the second downmixer (23) for amplifying the baseband signals (S _B i, S _B 2), preferably the baseband amplifiers

have frequency-dependent gain characteristic, which by one

Increase slope factor per frequency decade, which is in a range of 17 dB to 20 dB, in particular 20 dB.

9. driver assistance device (2) according to one of the preceding claims,

characterized in that

the test means (32) comprises an up-converter (35) for generating the local

Test signal (S _P ) whose output is coupled to the first receiving path (16) on the one hand and with the second receiving path (21) on the other.

10. driver assistance device (2) according to claim 9,

characterized in that

the radar device (3, 4) has a local oscillator (26) common to the first and second downmixers (17, 23) and to the upmixer (35) for providing an oscillator signal (27).

1 1. Driver assistance device (2) according to claim 10,

characterized in that

the local oscillator (26) is coupled via a directional coupler or a power divider (41) to an input (42) of the up-converter (35), the directional coupler or the power divider (41) being designed to divide a portion of -25 dB to - 15 dB from a power of the oscillator signal (27) for the

To tap upwards mixer (35).

12. driver assistance device (2) according to one of the preceding claims,

characterized in that

the control device (5) is designed, on the one hand, based on the first test signal (Sn) on the one hand and / or on the other hand, on the basis of the second test signal (S _T 2), on the other hand Receive path (16) and / or the second receive path (21) to its

Functionality to check out.

13. Driver assistance device (2) according to one of the preceding claims,

characterized in that

the test signal (S _P ) can be generated in a test mode of the radar device (3, 4), in which the radar device (3, 4) has no transmission signals for determining the

Measurement (oci, ο ^, Ri, R ₂ ) sends.

14. Vehicle (1), in particular motor vehicle, with a driver assistance device (2) according to one of the preceding claims.

15. A method for operating a radar device (3, 4) in a vehicle (1), wherein by the radar device (3, 4) at least one on a vehicle external object (10) related measure (oci, ο ^, Ri, R ₂ ) is determined, with the steps:

Receiving signals (S _E i, S _E2 ) by at least a first and a second receiving antenna (14, 15),

Downmixing of the received signals (S _E i, S _E2 ) in respective baseband signals (S _B i, S _B2 ) by a first down-converter (17) coupled to the first receiving antenna (14) via a first receiving path (16) on the one hand and with the second

Receiving antenna (15) via a second receiving path (21) coupled second down mixer (23) on the other.

Receiving the baseband signals (S _B i, S _B2 ) and determining the at least one measured variable (oci, 02, Ri, R ₂ ) based on the baseband signals (S _B i, S _B2 ) by a control device (5) and

Generating a local test signal (S _P ) and coupling the local test signal (S _P ) into the first receive path (16) and the second receive path (21), such that the control device (5) mixes the signal down through the first down converter (17) Test signal (S _P ) as a first test signal (Sn) on the one hand and the test signal (S _P ) mixed down by the second down-converter (23) as a second test signal (S _T2 ) on the other hand, wherein the control device (5) from the test signals (Sn, S _T2 ) a

Correction variable (6 (f)) for the correction of the measured variable (od, furnace, R ₁ , R ₂ ) determined, characterized in that

the correction quantity (6 (f)) is determined as a frequency-dependent variable by the control device (5) on the basis of the test signals (Sn, S _T2 ).