WO2023057497A1

WO2023057497A1 - Calibration device arrangement for an automotive radar device, calibration device and calibration method

Info

Publication number: WO2023057497A1
Application number: PCT/EP2022/077666
Authority: WO
Inventors: Milan Kvicera; Ondrej STEJSKAL; Michal Mandlik
Original assignee: Valeo Schalter Und Sensoren Gmbh
Priority date: 2021-10-08
Filing date: 2022-10-05
Publication date: 2023-04-13
Also published as: CN118159868A; JP2024537868A; DE102021126144A1; EP4413392A1

Abstract

The invention relates to a calibration device arrangement (3), a calibration device (4) and a calibration method. The calibration device arrangement (3) comprises an automotive radar device (2) and a calibration device (4) comprising a holding unit (5) positioned at a distance (8) to the radar device (2) and calibration objects (6) positioned spaced apart in a first direction of the calibration device (4). Upon radar wave emission from the radar device (2) to all calibration objects (6), back signals receivable by the radar device (2) are analyzable using a fast Fourier transformation (FFT) algorithm. A peak location of each transformed back signal in the FFT spectrum is distinguishable and correspondable to the involved calibration object (6) so that a calibration of the radar device (2) for elevation and azimuth angles (11, 12) is performable while moving the holding unit (5) in a second direction perpendicular to the first direction.

Description

Calibration device arrangement for an automotive radar device, calibration device and calibration method

The invention relates to a calibration device arrangement for an automotive radar device. The invention furthermore relates to a calibration device as comprised by such a calibration device arrangement and a calibration method for an automotive radar device performed with such a calibration device arrangement.

A vehicle can comprise a radar device as a detection system to determine a distance, an angle or a velocity of an object in the surroundings of the vehicle in relation to the radar device. The radar device typically comprises a transmitter producing electromagnetic waves in the radio or microwave domain, a transmitting antenna, a receiving antenna, a receiver and a processor. Radio waves transmitted by the radar device are reflected by the object in the surroundings of the vehicle. The back signal, meaning the reflected radio waves, is received by the radar device and gives information about the object’s location and speed. The word “radar” is an abbreviation and stands for radio detection and ranging.

The data on the object in the surroundings of the vehicle provided by the radar device can, for example, be used by a driver assistance system such as a lane assistant. However, in order to provide reliable radar data for the driver assistance system, the radar device needs to be calibrated accurately.

US 2017/0212215 A1 shows a method and apparatus for determining misalignment of a radar sensor unit mounted to a vehicle by means of a test station with well-defined targets. Based on received radar waves reflected on the targets, a presence, location and distance of the targets to the radar sensor unit can be determined and compared with actual locations and distances of the targets in order to provide data to calibrate the radar device. The targets are corner reflectors positioned at known distances to the radar sensor unit.

It is the object of the invention to provide a solution by means of which a duration of a calibration procedure for an automotive radar device is reduced.

This object is solved by the subject matters of the independent claims.

One aspect of the invention relates to a calibration device arrangement for an automotive radar device. The calibration device arrangement comprises the automotive radar device and a calibration device. The automotive radar device is, for example, a radar sensor mounted to a vehicle. Alternatively, the automotive radar device is a standalone device that is preferably configured to be mounted to the vehicle. The vehicle is preferably a motor vehicle, for example a car, bus or truck. The vehicle can be considered as a component of the calibration device arrangement as well. The automotive radar device is, for example, positioned in a front or a back section of the vehicle facing a surrounding area of the vehicle. The automotive radar device can be positioned in front or behind a bumper of the vehicle. The vehicle and/or the standalone automotive radar device stands still during the calibration of the automotive radar device.

The calibration device comprises a movable holding unit. The movable holding unit is positioned at a predefined distance to the automotive radar device. The movable holding unit is preferably placed at a distance of about 1 meter away from a part of the vehicle where the automotive radar device is positioned. Alternatively, a smaller distance of, for example, 0.2 meter, 0.5 meter, 0.7 meter, 0.8 meter or 0.9 meter or any distance between these values is possible. Alternatively, a greater distance can be chosen, for example, 1 .2 meter, 1 .5 meter, 2 meter, 3 meter, 4 meter or 5 meter or any distance between these values. In other words, the movable holding unit can be placed closer than 1 meter or further away from the automotive radar device. However, in case it is placed in a near field zone of the antennas of the radar device, meaning the transmitting and/or receiving antenna of the radar device, a correction algorithm can be applied to data measured by the radar device in order to perform a correction that is necessary due to the placement of the holding unit in the near field zone of the radar device.

Furthermore, the calibration device comprises at least two calibration objects. The at least two calibration objects are positioned spaced apart from each other at defined positions in a first direction of the calibration device on the holding unit. Preferably, the first direction is a height direction of the calibration device. Preferably, the height direction of the calibration device corresponds to a height direction of the vehicle with the radar device. The height direction of the calibration device is preferably as well a height direction of the automotive radar device. The individual calibration objects are fixed to the holding unit. In other words, the position of each calibration object on the holding unit and preferably as well in relation to the radar device is known during the calibration process. Alternatively or additionally to being fixed to the holding unit, the calibration objects can be movable along the holding unit, for example, by a step motor of the holding unit. Preferably, displacement of the two calibration objects relative to each other, for example due to movement of the holding unit in relation to the vehicle, is prevented.

Preferably in the beginning, the calibration device is adjusted to a height of the radar device so that a first calibration object in height direction is positioned directly opposite the radar device. This means that a direct theoretical connection line between, for example, a center point of the radar device and the first calibration object is parallel to a ground on which both the vehicle with the radar device and the calibration device are positioned.

Upon simultaneous radar wave emission from the automotive radar device to all calibration objects, individual back signals from the calibration objects receivable by the automotive radar device are preferably analyzable using a fast Fourier transformation (FFT) algorithm. The radar device emits waves in the radio wave range, particularly in the microwave range, wherein the radio waves emitted are referred to as radar waves. All calibration objects, hence, receive the radar wave that was emitted at a specific point in time. The radar device, for example, can emit radar waves over a defined area that extends, for example, both in a length and height direction of the radar device and the vehicle, meaning an area that extends over azimuth and elevation angles in relation to the radar device. Each calibration object receives the emitted radar wave and sends a signal back to the radar device. However, each calibration object preferably does not simply reflect the emitted radio wave but creates an individual back signal. The individual back signal is preferably a modified signal based on a reflection of the received radar wave that comprises an individual signature of the calibration object. The back signal is hence different for every calibration object.

Once, the back signals are received by the radar device, they are analyzed in order to perform the calibration of the radar device. In order to do so, the FFT algorithm can be used. The FFT algorithm computes, for example, a discrete FFT of each back signal. By applying the FFT algorithm, each received back signal is transformed from its original domain, which is for example wavelength, to a representation of the corresponding back signal in a frequency domain. By doing this for all back signals, a representation of the back signals in a FFT spectrum is created. A peak location of each transformed individual back signal in the FFT spectrum is distinguishable and corresponds directly to the involved calibration object. In other words, a peak location of each transformed individual back signal in the FFT spectrum is directly correspondable to the involved calibration object. This means that each back signal is located at a specific location within the FFT spectrum after its transformation. The involved calibration object is the calibration object that emitted the respective back signal.

Various peaks within the calculated FFT spectrum, which can be represented by a FFT plot, are identifiable. Each of these peaks is connectable to one of the at least two calibration objects. This means that a distance between the respective calibration object and the radar device and/or a relative velocity of a calibration object can be calculated upon analyzing the peak in the FFT plot that is connected to the respective calibration object. In order to do this calculation, information on the structure of the back signal, meaning on specifications of the respective calibration object, the position of the respective calibration object on the holding unit as well as the distance of the holding unit to the radar device are, for example, considered. The information on the structure of the back signal comprises, for example, a rule according to which the individual part of the back signal that provides a link to the calibration object is created. This allows performing a direct calibration of the radar device for the positions of the calibration objects in the first direction. If these positions are in height direction, calibration for elevation angles is performable.

The necessary calculating steps can be performed by a calculation device, which is, for example, an individual device such as a laptop or a stationary computer. Alternatively, the radar device can comprise the calculation device. The calculation device comprises a processing unit.

Furthermore, while moving the holding unit at the predefined distance between a starting position and an ending position in a second direction perpendicular to the first direction, calibration of the radar device for positions in the first direction at positions between the starting and the ending position in the second direction is possible. In other words, calibrations for positions in the first direction are performed at changing positions in the second direction. The position in second direction changes due to the preferably continuing movement in the second direction between the starting and ending position. Preferably, the starting and ending position are located on a horizontal plane of the automotive radar device, which is perpendicular to the height direction. In this example, calibration of the radar device for azimuth angles is performable as well. The horizontal plane extends in length and transverse direction of the radar device and the vehicle. The horizontal plane is vertically aligned, meaning perpendicular, to the height direction. The starting position and the ending position are defined locations, preferably at opposite edges of a field of view or coverage area of the radar device in the second direction. The field of view or coverage area can be spatially confined by the mounting of the radar device to the vehicle. In other words, calibration for elevation angles is performed along the movement between the starting and ending position so that it is performed at different azimuth angles. If this is continued for at least multiple azimuth angles, a detailed calibration for a three dimensional radar device mounted to the vehicle is possible.

Azimuth and elevation angles refer to a horizontal coordinate system that uses a sphere centered on the radar device. Angles in plane, meaning different angles in relation to the radio device in the horizontal plane, are referred to as azimuth angles. Angles vertical to the horizontally aligned azimuth angles are referred to as elevation angles or alternatively altitude angle. In other words, the calibration for elevation angle means that a calibration vertically to the radar device is performed whereas the calibration for azimuth angle is a calibration in the horizontal plane in relation to the automotive radar device.

The movement of the holding unit between the starting position and the ending position is preferably a continuous movement, wherein during this movement the simultaneous radar wave emission to the calibration objects takes place. This means that only the movement between the starting position and the ending position, meaning preferably a transverse movement of the calibration device, is necessary in order to provide a full calibration of the radar device in all possible emission directions towards the surroundings of the vehicle. However, there is no direct movement in the first direction, meaning in vertical or height direction of the calibration device, necessary in order to calibrate the radar device for at least two elevation angles due to the preferably vertically positioned calibration objects. This results in a fast calibration procedure because calibration data for all elevation angles is measured at the same time. The duration of a calibration procedure for an automotive radar device is, thus, reduced. Besides, the described calibration device arrangement is independent of manual support, especially when the movement between the starting position and the ending position is automatic, for example performed by a moving unit of the calibration device.

In the following examples for embodiments of this aspect of the invention, it is assumed, that the calibration objects are positioned at different positions in height direction on the holding unit. Alternatively, the calibration objects can be positioned at different positions in transverse direction of the calibration device, which is preferably a transverse direction of the vehicle and/or the radar device. The transverse direction is preferably perpendicular to the length and height direction of the radar device and/or the vehicle. The movement between the starting and ending position is then in height direction. This results in a calibration for azimuth angles first followed by a calibration for azimuth directions at different elevation angles along the movement in height direction.

An embodiment comprises that the calibration object is an artificial target. The back signal to the automotive radar device mimics a moving object. An artificial target is a device that receives the emitted radar wave and sends back a back signal that comprises a specific signal segment indicating that the artificial target is currently moving. The artificial target is, hence, no classical corner reflector. Since the artificial target imitates a movement of a target, for example, a Doppler frequency is comprised by the back signal. The back signal is located at a defined peak location in the FFT spectrum due to defined properties of the artificial target. In other words, the artificial target allows for the distinguishable and directly correspondable relation between the peak location of the individual back signal in the FFT spectrum and the respective calibration object, which is in this case the artificial target. By choosing, for example, two or more artificial targets positioned on the holding unit after applying the FFT algorithm, the back signal of each artificial target will be located at the defined peak location within the FFT spectrum and can hence be identified and directly correlated to the artificial target it was sent out by. This allows for clear and easy identification of each individual calibration object within the received back signal data of the radar device.

Alternatively or additionally in an example, the calibration object could be a target that is actually moving towards the radar device from a direction corresponding to the position of the calibration object on the holding unit. In this case, for example, a path guiding element is comprised by the calibration device in order to move the target towards the radar device.

A further embodiment comprises that by applying the FFT algorithm on the back signals a range-Doppler plot is generatable. In the generated range-Doppler plot, each back signal is assignable to an individual segment of a range axis of the range-Doppler plot wherein the individual segments differ from one another. On one axis of the range-Doppler plot, range, meaning distance, is plotted. On another axis, for example, Doppler frequency is plotted. In this context, a range is used to describe a distance between the predefined calibration object and the radar device, which could be in this embodiment the distance of the artificial target to the automotive radar device. However, this distance does not have to refer to the actual distance since the artificial target generates a specific back signal that is not just a reflection of the emitted radar wave. Alternatively or additionally, the artificial target can comprise a cable providing a back signal representing a reflection of the emitted radar wave. However, the artificial target is then a passive artificial target. This means that the actual distance between the artificial target and the radar device first has to be determined, for example by the calculation device, for example by taking into account the defined properties of the artificial target, its position on the holding unit and the distance of the holding unit to the radar device. However, the determined range of the peak location is evaluated to calculate respective data required for the calibration of the automotive radar device. The artificial target is, hence, a reasonable calibration object for the calibration device arrangement.

An alternative embodiment comprises that the calibration object is an antenna with a delay line of a delay line length. The delay line length is different for each calibration object of the at least two calibration objects. This means that the holding unit holds several individual antennas, which can be distinguished by their different delay line lengths. A delay line can be realized by a cable length of an antenna cable of the respective antenna. The use of antennas as calibration objects is based on the observation that first the emitted radar wave is received by the antenna, then it is passed through the internal antenna electronics, so that the delay line length has influence on the back signal that is sent back from the antenna to the radar device. The internal antenna electronics can, for example, comprise only a cable. Hereby, each antenna emits a different back signal since the delay lines all have different delay line lengths. The back signals are, thus, time delayed in relation to the back signals from antennas with a longer delay line length. The antenna is a cost-effective calibration object. Moreover, the antenna acts as a static object in the surroundings of the radar device, which reduces necessary calculation steps as no Doppler frequency is observed during the calibration of the radar device.

Furthermore, an embodiment comprises that by applying the FFT algorithm on the back signals a range plot is generatable in which each back signal is assignable to an individual segment of a range axis of the range plot wherein the individual segments differ from one another. Due to antennas as calibration objects, no moving object is mimicked which results in a representation of the back signals in a range plot instead of a range-Doppler plot. However, each antenna has a specific delay line length so that all the received back signals can still be corresponded to specific peaks within the FFT spectrum, as they are differentiable by the range segment on the range axis. The back signal of the antenna with the shortest delay line is typically positioned in the FFT spectrum at the smallest range values, meaning in a smallest range segment, compared to the back signals of antennas with longer delay line lengths. Therefore, by using antennas as calibration objects, fast and easy calibration of the radar device is possible. The calculations for the calibration are at least based, for example, on the known delay line length of the respective antenna, the measured range of the peak value corresponding to the respective antenna, the position of the antenna on the holding unit and the distance of the holding unit to the radar device.

Alternatively or additionally, instead of artificial targets or antennas with delay lines, the calibration objects may be corner reflectors that have different predefined distances to the radar device. This is achieved, if, for example, the corner reflectors are vertically aligned on a pole so that each corner reflector has a different distance to the radar device and can thus be distinguished in range as described above.

Besides, an embodiment comprises that each antenna is electronically connected to a splitter, preferably via a band-pass filter, a frequency mixer and/or an amplifier. The splitter is a power splitter, which can, for example, be referred to as directional coupler. The splitter is intended to copy and/or replicate the signal received by the antenna, meaning the signal due to receiving of the radar wave. The copy can then, for example, be stored for later analysis by the calculation device. This is advantageous because if the calibration device is moving between the starting position and the ending position, continuously radar waves are received by the multiple antennas of the calibration device. All the corresponding data are then saved and stored so that, for example, after receiving the back signal by the automotive radar device both the received back signal as well as information on the emitted radar waves are all available. The stored data can be used, for example, by the calibration device to determine calibration values for the radar device. The band-pass filter, the frequency mixer and/or the amplifier are used to provide a signal that is easily and with cost-effective equipment further processed. For example, the mixer is used for down-conversion and later up-conversion of the signal. In other words, these electronic components provide a reasonable signal preparation. Instead of the splitter, an on- and off-switch could be used. However, the splitter has the advantage that is directly allows for parallel measurements.

Alternatively, at least one calibration object, preferably multiple calibration objects, is an artificial target while the at least one other calibration object, preferably multiple other calibration objects, is an antenna.

Moreover, an embodiment comprises that the holding unit comprises a basic element. On the basic element the at least two calibration objects are positioned. The basic element is movable in the first direction, preferably in height direction, between a basic position and an elevated position. In order to allow for the movement between the basic position and the elevated position, a height adjustment device can be comprised by the holding unit. The height adjustment device is for example a manually operable device comprised by the holding unit. The height adjustment device can be, for example, a telescopically extendable stick. Preferably, the stick is connected to the basic element on which the calibration objects are placed. An extension of the stick can alternatively or additionally be performed by an electronic motor, preferably upon manual or electronic activation of the electric motor. In each position between the basic and elevated position, the radar wave emission from the automotive radar device is receivable by the at least two calibration objects. If, for example, the calibration device comprises exactly two calibration objects at two different positions in height direction of the calibration device, these two calibration objects can be moved upwards or downwards at least in one further position. This means that if the measurements for calibration are repeated at different height positions of the basic element, calibration data from multiple specific height locations, meaning for multiple specific elevation angels, can be received. Therefore, it is, for example, possible to have few calibration objects while still performing a locally detailed calibration.

It is possible to perform the calibration for azimuth angles at one height setting of the basic element and afterwards to change the height setting and repeating the movement between the starting position and the ending position for the changed height setting and so on until a sufficiently detailed calibration for elevations angels is achieved.

Another embodiment comprises that the basic element is movable between the basic position and the elevated position in predefined steps. Preferably, each step corresponds to a shift in elevation angle by 5 degrees. This means that preferably by each step the angle between the automotive radar device and the respective calibration object is increased or decreased by 5 degrees. While movement of the basic elements upwards in height direction, it is stopped after every 5 degrees elevation angle to, for example, repeat at this height the horizontal movement between the starting and ending position. This means that, for example, if the first calibration object is placed at an elevation angle of 0 degrees and other calibration objects at 10 and 20 degrees, after the upwards movement of the basic element, the calibration objects are positioned at elevation angles of 5, 15 and 25 degrees. Preferably, at the end values or data from every fifth degree of elevation angle is provided. This results in a thorough calibration procedure without needing a big amount of calibration objects. Therefore, the calibration device arrangement is cost-effective since although the number of calibration objects might be limited to two, three, four or five, it is possible to get detailed data in height direction or another first allowing for a detailed and thorough calibration for elevation angles of alternatively azimuth angles.

According to another embodiment, the basic element is straight and arranged parallel to the first direction. Preferably, it is arranged parallel to a vertical direction of the automotive radar device. The basic element can, for example, be a stick with no curves or edges. However, the different calibration objects are differentiable due to the use of artificial targets and/or antennas. Such a straight basic element is easy to produce and to adjust.

In a different embodiment, the basic element is at least between the positions of the at least two calibration objects curved. Preferably, it is at least in these parts of the basic element circular curved. In this embodiment, the different calibration objects have, for example, all the same distance to the radar device because they are aligned on the curved basic element, which is curved in a way that the radar device is positioned at a center point of a circle segment formed by the curved basic element. With such a basic element, every calibration object receives the simultaneously emitted radar wave from the automotive radar device at the same time, so that no time correction measurements are necessary to determine which received signals correspond to one specific position during the movement between the starting position and the ending position.

Moreover, there is an embodiment comprising that the automotive radar device is a three- dimensional radar. The three-dimensional radar can emit simultaneously radar waves in all three directions, meaning vertically and horizontally. Usually, to calibrate such a three- dimensional radar, many different calibration steps have to be performed. However, due to the alignment of the calibration objects in the first direction, preferably in height direction, only a sweep in the second direction, preferably in horizontal direction, meaning in the transverse direction, is necessary in order to get data for all areas in the field of view or coverage area of the three-dimensional radar device. It would be particularly advantageous, if there was a sufficient number of calibration objects on the holding unit so that no movement in first direction, preferably height direction, was necessary in order to get enough data to do the calibration for the elevation angles. This is, for example, the case, if for every 5 degrees elevation (or alternatively or additionally azimuth) angle a calibration object is positioned on the holding unit.

In another embodiment, an automotive radar device is a near field radar or a high definition radar. This allows for relatively close calibration distances of for example 1 meter, while still maintaining radar data of sufficient quality to perform the calibration.

The holding unit apart from the calibration objects can be at least partially covered by a radar frequency absorber. A radar frequency absorbing material covers, hence, preferably all parts of the calibration device facing the radar device except for the calibration objects. This reduces background noise signals, which are for example visible by respective signals in the FFT spectrum and can, for example, result an enlarged signal peak area within the range-Doppler plot or the range plot. By using the radar frequency absorber material around the calibration objects, background noise can be drastically reduced, which results in more precise results especially in overlap segments of the range axis where actual peaks due to the back signals are not distinguishable from the background noise. Another aspect of the invention relates to a calibration device. The calibration device comprises a movable holding unit and at least two calibration objects positioned spaced apart from each other at defined positions in a first direction of the calibration device on the holding unit. The calibration device is designed for the calibration device arrangement as described above. Features of the calibration device as described by an embodiment or a combination of embodiments of the above-described calibration device arrangement are considered to be embodiments of the inventive calibration device.

Another aspect of the invention relates to a calibration method for an automotive radar device performed with a calibration device arrangement as described above. The calibration device arrangement comprises the automotive radar device and a calibration device comprising a movable holding unit positioned at a predefined distance to the automotive radar device and at least two calibration objects positioned spaced apart from each other at defined positions in a first direction of the calibration device on the holding unit. The method comprises the following steps: simultaneous radar wave emission from the automotive radar device to all calibration objects; by the calibration objects, receiving of the radar signal and emission of individual back signals to the automotive radar device; receiving of the individual back signals by the automotive radar device; analyzing the received back signals using a FFT algorithm; performing of the calibration of the automotive radar device for the defined positions in the first direction considering that a peak location of each transformed individual back signal in the FFT spectrum is distinguishable and directly correspondable to the involved calibration object; moving the holding unit at the predefined distance between a starting position and an ending position in a second direction perpendicular to the first direction while repeating the steps above to perform the calibration for the defined positions in the first direction at positions between the starting position and the ending position in the second direction. If the position on the holding unit are in height direction: performing of the calibration of the automotive radar device for elevation angles considering that a peak location of each transformed individual back signal in the FFT spectrum is distinguishable and directly correspondable to the involved calibration object; moving the holding unit at the predefined distance between a starting position and an ending position in a horizontal plane of the radar device; and repeating the steps above to perform the calibration for azimuth angles of the automotive radar device. The individual embodiments as well as combinations of the individual embodiments of the above-described calibration device arrangement apply, if applicable, as well for the calibration method.

The figures show in:

Fig. 1 a schematic drawing of a calibration device arrangement;

Fig. 2 a schematic top view of the calibration device arrangement;

Fig. 3 a schematic representation of a range-Doppler plot; and Fig. 4 a schematic representation of electronic connections within a calibration device.

Fig. 1 shows a vehicle 1 comprising an automotive radar device 2. The automotive radar device 2 is supposed to be calibrated. In order to do so, a calibration device arrangement 3 is shown. The calibration device arrangement 3 comprises the radar device 2 and a calibration device 4. The calibration device arrangement 3 can also comprise the vehicle

1.

The calibration device 4 comprises a movable holding unit 5 and at least two calibration objects 6. The calibration objects 6 are positioned spaced apart from each other at defined positions in a first direction of the calibration device 4 on the holding unit 5. The first direction is in this example a height direction of the calibration device 4 which corresponds to a z-direction. The height direction of the calibration device 4 corresponds in this embodiment to a height direction of the vehicle 1 and the automotive radar device

2. The exemplarily sketched calibration device 4 comprises in total four different calibration objects 6. Alternatively, it could comprise two, three, five or even more calibration objects 6, for example up to ten or twenty calibration objects 6.

The calibration device arrangement 3 furthermore comprises a calculation device 7, which can be located externally from the vehicle 1 and/or the calibration device 4. It is possible that the calculation device 7 is comprised by the automotive radar device 2 itself, so that all calculations related to the calibration are performed directly within the automotive radar device 2. Alternatively or additionally, the calculation device 7 can be an individual device, for example, a laptop, a tablet, a smartphone or a stationary computer.

The movable holding unit 5 is positioned at a predefined distance 8 to the radar device 2. The predefined distance 8 is, for example, about 1 meter.

The calibration device 4 comprises a height adjustment device 9 which is designed to move the holding unit 5 upwards or downwards in height direction, meaning in z-direction. The calibration device 4 is also horizontally movable with the help of at least one wheel 10. Alternatively, the calibration device 4 is movable on a rail (not shown here). In this case, the calibration device 4 can be designed as an arm-like device. Preferably, there are at least 2 wheels, preferably 4 wheels, located at a lower part in z-direction of the calibration device 4 in order to allow for movement in x- and y-direction. The x- and y- direction correspond to a longitudinal and transverse direction of the calibration device 4, the radar device 2 and/or the vehicle 1 .

During calibration typically different calibrations for different elevation angles 11 are performed. The elevation angles 11 are represented by a two-headed arrow in Fig. 1 .

Fig. 2 shows a schematic top view of the calibration device arrangement 3. Due to the wheels 10 of the calibration device 4, it is movable between different positions in a second direction perpendicular to the first direction. In this example, the second direction is a transverse direction in relation to the calibration device 4, meaning in y-direction. In Fig. 2 an azimuth angle 12, which is another typical angle for calibration of a radar device 2, is sketched with a two-headed arrow. The movement in transverse direction is possible between a starting position 13 and an ending position 14 which are here exemplary sketched. In other words, the calibration device 4 is movable between the starting position 13 and the ending position in a horizontal plane of the radar device 2, wherein the horizontal plane is a x-y-plane. During the movement in the horizontal plane, the predefined distance 8 remains preferably constant, so that the movement of the calibration device 4 follows a path that resembles a circle segment.

In Fig. 2 different steps taking place in order to perform the calibration of the automotive radar device 2 are indicated. It is possible that the calibration procedure described in the following is recorded continuously but processing steps performed on the recorded data are performed afterwards, for example, offline by the calculation device 7.

In a preferably first step S1 , the automotive radar device 2 emits simultaneously a radar wave to all calibration objects 6. All the calibration objects 6 receive in a step S2, for example, the emitted radar wave and emit individual back signals to the automotive radar device 2. In a step S3, the individual back signals are preferably received by the automotive radar device 2. Afterwards, data can be provided for the calculation device 7 which analyzes, for example in a step S4, the received back signals by using a fast Fourier transformation (FFT) algorithm. In a step S5, the calibration of the automotive radar device 2 for elevation angles 11 can be performed. This is done by considering that a peak location of each transformed individual back signal in the FFT spectrum is distinguishable and directly correspondable to the involved calibration object 6. More generally, in step S5 the calibration of the automotive radar device 2 is performed for the defined positions in the first direction considering that a peak location of each transformed individual back signals in the fast Fourier transformation spectrum is distinguishable and directly correspondable to the involved calibration object 6. In a step S6, the holding unit 5 is preferably moved between the starting position 13 and the ending position 14. During this movement, the previous steps S1 to S5 are repeated continuously to perform calibration for different azimuth angles 12. More generally, the holding unit 5 is moved between the starting position 13 and the ending position 14 in the second direction while repeating the steps above to perform the calibration for the defined positions in the first direction at positions between the starting position 13 and the ending position 14 in the second direction. Afterwards in an additional step S7, the determined calibration data can be transmitted from the calculation device 7 to the automotive radar device 2.

The calibration object 6 can be, for example, an artificial target. An artificial target can mimic a moving object by sending respective back signals that mimic a movement relative to the automotive radar device 2 upon receiving the radar wave. The mimicked relative movement is, for example, a movement of the calibration object 6 towards or away from the radar device 2. The back signal of the artificial target is located at a predefined peak location in the FFT spectrum. This is the case because the artificial target has well-defined properties meaning that this information can be derived, for example, from a frequency information within the back signal that was sent out by the artificial target. By applying the FFT algorithm on the back signals received from the artificial targets, a range-Doppler plot 15 is generated. A simplified example of a range-Doppler plot 15 is shown in Fig. 3.

Fig. 3 shows that each back signal creates a value peak 19 within the range-Doppler plot 15. Here, four different value peaks 19 are shown because of the four different calibration objects 6 shown in Figs. 1 and 2. On the x-axis of Fig. 3, a range axis 16 is sketched. The y-axis is a frequency axis 18, which could, for example, display a Doppler-frequency or a velocity of the mimicked moving object. On the range axis 16, different individual segments 17 are shown. In other words, the range axis 16 is divided into adjacent sections, which can alternatively be referred to as range-Doppler bins. Each back signal is now assignable to an individual segment 17 of the range axis 16 of the range-Doppler plot 15 wherein the individual segments 17 differ from one another. Here it is shown that each peak area is clearly distinguishable from one another so that there is no overlap in range between the back signals.

Alternatively or additionally, the calibration object 6 can be an antenna. In Fig. 4 the calibration device 4 with antennas as calibration object 6 is sketched. The holding unit 5 comprises a basic element 20 on which the at least two calibration objects 6 are positioned. The basic element 20 can be straight and arranged parallel to a vertical direction (z-direction) of the automotive radar device 2. Alternatively and as sketched here, the basic element 20 is at least between the positions of the calibration object 6 curved. Preferably, it is circularly curved.

The height adjustment device 9, which is comprised by the holding element 5, is arranged to move the basic element 20 in height direction (z-direction) between a basic position and an elevated position (not sketched). The direction of this movement is sketched with a two-headed arrow 21. In each position in height direction (z-direction), the radar wave emission from the radar device 2 is receivable by the at least two calibration objects 6. Preferably, the height adjustment device 9 moves the basic element 20 in predefined steps. Preferably, the steps correspond to a shift in elevation angle 11 of 5 degrees. This means that an angle between the radar device 2 and the respective calibration object 6 is increased by 5 degrees by each step.

It is furthermore shown that each antenna is connected to a splitter 28. The splitter 28 allows for a continual measurement of received radar waves during the horizontal movement of the calibration device 4. Furthermore, the antennas are typically connected to a band-pass filter 24, a frequency mixer 25 and an amplifier 26. Furthermore, each antenna is connected to a delay line 22 with a delay line length 23. The delay line length 23 is different for each calibration object 6 of the at least two calibration objects 6. This means that, for example, the cable length of each antenna cable between the antenna itself and the splitter 28 is different for every antenna. This is visualized with a varying number of cable loops. Fig. 4 shows furthermore a reference antenna at the very bottom in z- direction of the calibration objects 6. A reference signal is received by the reference antenna which is typically in a frequency range of 77 to 81 gigahertz (GHz). After the frequency mixer 25, a signal between 8 and 12 GHz is sent to the splitter 28. Alternatively, the reference signal is in another frequency range and/or is not converted to a lower frequency compared to the original reference signal. Furthermore, a local oscillator 27 is provided to provide a reference signal for the measurements.

For antennas instead of artificial targets a plot similar to Fig. 3 is calculatable. Instead of a range-Doppler plot 15, a simple range plot is generated in which each back signal is assignable to an individual segment 17 of a range axis 16 of the range plot wherein the individual segments 17 differ from one another. The range plot can as well be referred to as range-Doppler plot 15.

The automotive radar device 2 is three-dimensional radar wherein it can be a near field radar or a high definition radar.

Alternatively or additionally to the example in Fig. 1 , 2 and 4, the calibration objects 6 can be positioned at different positions in transverse direction (y-direction) of the calibration device 4, which is preferably a transverse direction of the vehicle 1 and/or the radar device 2 (not shown). The transverse direction is preferably perpendicular to the length and height direction of the radar device 2 and/or the vehicle 1 . The movement between the starting position 13 and ending position 14 is then in height direction. This results in a calibration for azimuth angles 12 first followed by a calibration for azimuth angles 12 at different elevation angles 11 along the movement in height direction.

In summary, the invention relates to a simultaneous calibration of an automotive radar device 2 at arbitrary cuts in field of view. By using the method described above, a significant reduce of mechanical movement needed for precise calibration of the automotive radar device 2 is achieved. This is based on the idea that usually for radar calibration for azimuth angles 12 a mechanical rotation of a radar target, for example, a color reflector or a rotation of the radar device 2 itself by the target is static is used. In this way, calibration data can be obtained. However, this approach becomes tedious when calibration for elevation angles 11 is required as well as in this way repetitions of this rotational movement would have to be repeated in every elevation angle 11 of interest. Apart from technical issues related to precise setting of the particular elevation and the consistency of the subsequent measurements, the time needed for such calibrations is becoming unrealistic considering such calibrations at the end of line production of the vehicle 1 and/or at a workshop.

With an advantage, the fact that the arbitrary range-Doppler bins, meaning the value peaks 19, in the FFT spectrum can be used to cover the calibration data easily enables the simultaneously measured calibration device 4 for multiple cuts in the radar devices 2 field of view in the following way. For example, a set of artificial targets with defined properties can be placed vertically, for example on a circle, to represent different elevation angles 11 with respect to the radar device 2. These artificial targets are used as calibration objects 6. By having each calibration object 6 at a different range bin, meaning at a different segment 17 on the range axis 16 of a range plot, using only one sweep over azimuth angles 12 or equivalently one rotation of the radar device 2 calibration data for all the selected elevation angles 11 are obtained. Similarly, different Doppler bins can be used as well, meaning peak values 19 at different segments 17 on the range axis 16 of a range-Doppler plot 15. The advantage of using different range bins is that a simple receiver and transmitter can represent the artificial target with different connected delay lines, for example, simple cables of different lengths (delay line lengths 23).

A circular structure holding antennas could be vertical and then all range bins would have to be searched in the spectrum and input manually. However, antennas with delay lines 22 are used as respective calibration objects 6, for example, resulting in one peak value 19 of an antenna each ten range bins within FFT spectrum meaning within the range plot if the antennas are positioned spaced apart in a way that their positions’ elevation angles 11 differ by 10 degrees. In this case, the corresponding back signals are easily distinguishable after applying the FFT algorithm on the back signals.

The basic element 20 preferably comprises a vertical part to adjust for radar height above ground. The whole set of antennas can be manually moved in height direction meaning for different elevation angles 11 with defined steps. For example, first measurements can be performed at 0, 10 and 20 degrees of elevation angle 11 and then by moving up 5 degrees measuring another set at 5, 15 and 25 degrees. Steps and spacings are adjusted based on testing a mechanical dimension. In principle, only one mechanical movement between the basic position and the elevated position is needed to obtain calibration data for multiple elevation angles 11 .

Claims

Claims Calibration device arrangement (3) for an automotive radar device (2), wherein the calibration device arrangement (3) comprises the automotive radar device (2) and a calibration device (4) comprising a movable holding unit (5) positioned at a predefined distance (8) to the automotive radar device (2) and at least two calibration objects (6) positioned spaced apart from each other at defined positions in a first direction of the calibration device (4) on the holding unit (5), wherein upon simultaneous radar wave emission from the automotive radar device (2) to all calibration objects (6) individual back signals from the calibration objects (6) receivable by the automotive radar device (2) are analyzable using a fast Fourier transformation algorithm, wherein a peak location of each transformed individual back signal in the fast Fourier transformation spectrum is distinguishable and directly correspondable to the involved calibration object (6) so that a calibration of the automotive radar device (2) for elevation angles (1 1 ) and azimuth angles (12) is performable while moving the holding unit (5) at the predefined distance (8) between a starting position (13) and an ending position (14) in a second direction perpendicular to the first direction. Calibration device arrangement (3) according to claim 1 , wherein the calibration object (6) is an artificial target wherein the back signal to the radar device (2) mimics a moving object and is located at a defined peak location in the fast Fourier transformation spectrum due to defied properties of the artificial target. Calibration device arrangement (3) according to claim 2, wherein by applying the fast Fourier transformation algorithm on the back signals a range-Doppler plot (15) is generatable in which each back signal is assignable to an individual segment (17) of a range axis (16) of the range-Doppler (15) plot wherein the individual segments (17) differ from one another. Calibration device arrangement (3) according to claim 1 , wherein the calibration object (6) is an antenna with a delay line (22) of a delay line length (23), wherein the delay line length (23) is different for each calibration object (6) of the at least two calibration objects (6). Calibration device arrangement (3) according to claim 4, wherein by applying the fast Fourier transformation algorithm on the back signals a range plot is generatable in which each back signal is assignable to an individual segment (17) of a range axis (16) of the range plot wherein the individual segments (17) differ from one another. Calibration device arrangement (3) according to any of the claims 4 or 5, wherein each antenna is electronically connected to a splitter (28), preferably via a bandpass filter (24), a frequency mixer (25) and/or an amplifier (26). Calibration device arrangement (3) according to any of the preceding claims, wherein the holding unit (5) comprises a basic element (20) on which the at least two calibration objects (6) are positioned, wherein the basic element (20) is movable in the first direction between a basic position and an elevated position, wherein in each position the radar wave emission from the automotive radar device (2) is receivable by the at least two calibration objects (6). Calibration device arrangement (3) according to claim 7, wherein the basic element (20) is movable between the basic position and the elevated position in predefined steps, preferably in steps corresponding to a shift in elevation angle (11) and/or azimuth angle (12) by 5 degrees. Calibration device arrangement (3) according to any of the claims 7 or 8, wherein the basic element (20) is straight and arranged parallel to the first direction. Calibration device arrangement (3) according to any of the claims 7 or 8, wherein the basic element (20) is at least between the positions of the at least two calibration objects (6) curved, preferably circular curved. Calibration device arrangement (3) according to any of the preceding claims, wherein the automotive radar device (2) is a three-dimensional radar. Calibration device arrangement (3) according to any of the preceding claims, wherein the automotive radar device (2) is a near field radar or a high definition radar. 17 Calibration device (4) comprising a movable holding unit (5) and at least two calibration objects (6) positioned spaced apart from each other at defined positions in a first direction of the calibration device (4) on the holding unit (5), wherein the calibration device (4) is comprisable by a calibration device arrangement (3) according to any of the preceding claims. Calibration method for an automotive radar device (2) performed with a calibration device arrangement (3) comprising the automotive radar device (2) and a calibration device (4) comprising a movable holding unit (5) positioned at a predefined distance (8) to the automotive radar device (2) and at least two calibration objects (6) positioned spaced apart from each other at defined positions in a first direction of the calibration device (4) on the holding unit (5), wherein the method comprises the following steps:

- simultaneous radar wave emission (S1 ) from the automotive radar device (2) to all calibration objects (6);

- by the calibration objects (6), receiving (S2) of the radar wave and emission of individual back signals to the automotive radar device (2);

- receiving (S3) of the individual back signals by the automotive radar device (2);

- analyzing (S4) the received back signals using a fast Fourier transformation algorithm;

- performing (S5) of the calibration of the automotive radar device (2) for the defined positions in the first direction considering that a peak location of each transformed individual back signal in the fast Fourier transformation spectrum is distinguishable and directly correspondable to the involved calibration object (6);

- moving (S6) the holding unit (5) at the predefined distance (8) between a starting position (13) and an ending position (14) in a second direction perpendicular to the first direction while repeating the steps above (S1to S5) to perform the calibration for the defined positions in the first direction at positions between the starting position (13) and the ending position (14) in the second direction.