WO2023057538A1

WO2023057538A1 - Calibration device arrangement for an automotive radar device, calibration device and calibration method

Info

Publication number: WO2023057538A1
Application number: PCT/EP2022/077757
Authority: WO
Inventors: Milan Kvicera; Michal Mandlik; Vladimir Brazda
Original assignee: Valeo Schalter Und Sensoren Gmbh
Priority date: 2021-10-08
Filing date: 2022-10-06
Publication date: 2023-04-13
Also published as: DE102021126142A1

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) and calibration objects (6) positioned spaced apart on the holding unit (5). Upon radar wave emission from the radar device (2) to the calibration objects (6) a phase between individual back signals emittable from the calibration objects (6) is changeable so that a direction of arrival (13) of received back signals is changeable. The received back signals are analyzable using a fast Fourier transformation (FFT) algorithm. A peak location of each back signal in the FFT spectrum is directly correspondable to the direction of arrival (13) and distinguishable in relation to the direction of arrival (13) so that a calibration of the radar device (2) is performable.

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 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.

EP 3 816 654 A1 discloses a radar device and a radar system with which an improved angle resolution by sufficient calibration can be provided. The radar device itself comprises an array antenna including a plurality of reception antennas.

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

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

A first 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 holding unit positioned at a predefined distance to the automotive radar device. The 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 predefined positions on the holding unit. For example, the two calibration objects can be placed at two different positions in a height direction of the calibration device, meaning they can be placed at different positions in a vertical direction to the automotive radar 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. If the calibration objects are placed at different positions in height direction, for example, at each calibration object a radar wave emitted by the radar device is receivable at a different elevation angle in relation to the automotive radar device.

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. Preferably 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. At least one, preferably each, calibration object receives the emitted radar wave and sends a signal back to the radar device.

Upon simultaneous radar wave emission from the automotive radar device to preferably all calibration objects a phase between individual back signals emittable from the calibration objects and receivable by the radar device is changeable so that a direction of arrival of the received back signals is changeable. Preferably, the phase between the individual back signals is continuously changed over time, meaning that the calibration objects continuously perform a phase shift between the back signals. In other words, the calibration objects perform an array of calibration objects so that due to the phase change artificial back signals are created that mimic or imitate a specific direction of origin. The direction of origin is not static but changes with time, wherein it changes simultaneously with the change of the phase change. The reason for this is that the phase change leads to the imitated direction of arrival. The change in phase and the change in direction are, hence, related to each other and the direction of arrival is a direct consequence of the changeable phase between the individual back signals. If the phase change between the individual back signals is changed continuously, the direction of arrival of the artificially created back signals also changes continuously. In other words, by changing the phase an electronic sweep over preferably all possible directions of arrival of back signals to the radar device is performed, wherein the possible directions are preferably only limited by the positions of the calibration objects on the holding unit and their orientation towards the radar device.

The received back signals are analysable using a fast Fourier transformation (FFT) algorithm. 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 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 received back signal in the FFT spectrum is directly correspondable to the direction of arrival and distinguishable in relation to the direction of arrival so that a calibration of the radar device is performable. If the different calibration objects are positioned at different positions in the height direction of the calibration device, a calibration for elevation angles of the radar device is performable.

In other words, each back signal is located at a specific location within the FFT spectrum after its transformation. Therefore, one peak within the calculated FFT spectrum, which can be represented by a FFT plot, is identifiable. This peak is connectable to a direction of arrival. Upon analyzing multiple peaks in the FFT plot that are each correlated to a specific direction of arrival and under consideration of information on the calibration objects, for example the applied phase change, preferably the position of the calibration objects on the holding unit and the distance of the holding unit to the radar device, calibration parameters for the radar device can be calculated. This allows performing a direct calibration of the radar device for, in this example, elevation angles. The calibration is based on the idea, that artificially created back signals from multiple directions are received by the radar device and used as calibration measurements. Since the back signals are correlated to the direction of arrival, the radar measurement for each direction of arrival can be analyzed and, for example, checked for conformance with the artificially created direction of arrival. Alternative, by analyzing the peak positions correlated to respective directions of arrival, internal settings of the radar device are directly adjustable because each peak position is unambiguously linked to the respective direction of arrival so that internal settings for this direction of arrival can be adapted to the respective peak position, for example.

If the calibration objects are positioned at different positions in horizontal direction or transverse direction of the calibration device, the radar device and the vehicle, calibration for azimuth 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. 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 a 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 phase and direction changes can be performed completely electronically and relatively fast so that, for example, within a very short time interval of, for example, only one second various directions of arrival can be simulated. Therefore, for example, a full calibration scan for all possible elevation angles and/or azimuth angles of the radar device (depending on the arrangement of the calibration objects in relation to the radar device) can be performed in a short time interval. A speed of a calibration procedure for an automotive radar device is, hence, increased significantly, particularly compared to state of the art procedures. Therefore, the described calibration device arrangement is particularly fast and works without any mechanical or manual movement of calibration objects or the whole holding unit.

An embodiment comprises that the calibration object is an artificial target. The back signal to the automotive radar device preferably 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. By changing a phase difference between the back signals of the multiple artificial targets, a common artificial target is created that moves out of different directions towards the radar device, while the direction of movement is moving at least between the artificial targets that are positioned at the ends of the holding unit. In the example with the calibration objects positioned at different positions in height direction, these are the calibration objects positioned at the very top and bottom in height direction.

The back signals imitating one specific direction of movement and, hence, direction of arrival, are located at a defined peak location in the FFT spectrum. 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 direction of arrival, which is in this case the direction of movement of the artificial target towards the radar device. By varying, for example, the phase between the two or more artificial targets three times, three different directions of arrival are imitated which are each positioned at defined different peak locations within the FFT spectrum and can hence be identified and directly correlated to the respective direction of arrival. This allows for clear and easy identification of multiple and preferably continuously changed directions of arrival within the received back signal data of 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 direction of arrival is assignable to an individual segment of a range axis of the range-Doppler plot wherein the individual segments differ from one another depending on the direction of arrival. 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. 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. 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, preferably by taking into account the defined properties of the artificial target, its position on the holding unit, the current setting of the phases 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 embodiment comprises that the calibration objects are antennas which form a phased array. In other words, the various calibration objects form an electronically scanned array which creates a beam of, for example, radio waves that can be electronically steered to point in different directions without moving the antennas themselves. This is achieved by performing the described phase changes between the individuals back signals of the multiple antennas. Antennas in this context are very economic and allow for an easy realization of the calibration device arrangement.

Another embodiment comprises that an amplitude of one of the antennas differs from an amplitude of an adjacent antenna of the phased array. By additionally changing the amplitude of the back signals, a higher signal-to-noise ratio can be achieved so that, for example, unwanted background noise can be reduced. The background noise can, for example, origin from parts of the holding unit that are located adjacent to the individual calibration objects on which the emitted radar wave is reflected. The positions of the background noise in, for example, the FFT spectrum can overlay with the peaks corresponding to the different directions of arrival of the back signals. Due to the amplitude change, the peaks corresponding to the different directions of arrival can be separated from the background noise. This can result in an easier analysis of the FFT spectrum in order to do the calibration.

Furthermore, an embodiment comprises that by applying the FFT algorithm on the back signals a range plot is generatable in which each direction of arrival is assignable to an individual segment of a range axis of the range plot wherein the individual segments differ from one another depending on the direction of arrival. 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, the antennas form the phased array so that all the received back signals which are correlated to a specific direction of arrival can still be corresponded to a respective peak within the FFT spectrum that is specific for the respective specific direction of arrival, as they are differentiable by the range segment on the range axis. Two back signals with different directions of arrival correspond, hence, to peaks in different segments of the range axis of the FFT spectrum while two back signals with the same direction of arrival correspond to a common peak located at the same segment of the range axis. Therefore, by using antennas as calibration objects, fast and easy calibration of the radar device is possible. Besides, there is an embodiment comprising that the holding unit comprises a basic element on which the at least two calibration objects are positioned. The basic element is arranged vertically or horizontally to the radar device. Preferably, it is arranged parallel to a vertical or a horizontal direction in relation to the automotive radar device. This means that the at least two calibration objects can be either positioned at different positions in the height direction, as already mentioned above. Alternatively, they can be positioned in the transverse direction of the calibration device, meaning they are positioned in a horizontal plane with regard to the automotive radar device and, hence, horizontally. By arranging them parallel to the vertical direction, a calibration for elevation angles is possible, whereas if they are arranged in the horizontal direction a calibration for azimuth angles of the radar device is performable. Depending on what kind of radar device needs to be calibrated, a corresponding basic element can be chosen. Therefore, the described calibration device arrangement is diverse usable.

Moreover, a preferred embodiment comprises that the holding unit comprises a cross element arranged perpendicular to the basic element. At least two of the calibration objects are positioned on the cross element. This means that if, for example, only three calibration objects are used, calibration for both angels is possible if two of the calibration objects are positioned on, for example, the basic element, whereas one of these two is also positioned on the cross element together with the third calibration object. At the same time by performing, for example, first a phase shift sweep in the vertical direction and afterwards in the horizontal direction, in principle, calibration both for elevation and azimuth angles is possible with the described calibration device arrangement without any manual movement of the calibration objects.

Preferably, in another embodiment the basic element and/or the cross element are straight or at least partially curved, preferably circular curved. The basic element is preferably 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 and/or cross 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. Multiple different arrangements of the holding unit and the calibration objects are, hence, possible in order to achieve the described phased array. Depending on the geometry chosen, meaning if it is a straight or at least partially curved basic element and/or cross element, different basic settings are included and used for detailed analysis of the received data. However, especially a curved basic element and and/or cross element allow for constant distances between the calibration objects and the radar device which can facilitate the necessary calculation steps.

Another embodiment comprises that the holding unit apart from the calibration objects is 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 might not be distinguishable from the background noise.

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 described alignment of the calibration objects in height direction and transverse direction, only electronic sweeps achieved by continuously changing the phase between adjacent calibration objects is necessary to get a full three dimensional calibration. For example first the phases between the calibration objects in height direction are changed and afterwards the phases between the calibration objects in transverse direction. It would be particularly advantageous, if there was a sufficient number of calibration objects on the basic element and the cross element of the holding unit so that precise phased arrays were provided and no manual movement of the calibration device was necessary in order to get enough data to do the calibration for elevation angles and, for example, afterwards for azimuth angles.

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.

Another aspect of the invention relates to a calibration device. The calibration device comprises a holding unit and at least two calibration objects positioned spaced apart from each other at defined positions 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. The calibration device comprises a 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 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, wherein a phase between the emitted back signals is changed in time, preferably continuously, so that a direction of arrival of the back signals received by the automotive radar device is changed in time as well, preferably continuously; analyzing the received back signals using a fast Fourier transformation algorithm; and performing of the calibration of the automotive radar device considering that a peak location of each received back signal in the fast Fourier transformation spectrum corresponds directly to the direction of arrival and is distinguishable in relation to the direction of arrival. The individual embodiments as well as combinations of the individual embodiments of the above-described calibration device arrangement apply, if appliable, as well for the calibration method. Therein show:

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

Fig. 2 a schematic drawing of the directions of arrival of received back signals; and

Fig. 3 a schematic representation of a range-Doppler plot.

Fig. 1 shows a vehicle 1 with wheels 10 wherein the vehicle 1 comprises 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 holding unit 5 and at least two calibration objects 6. The calibration objects 6 are positioned spaced apart from each other at defined positions on the holding unit 5. The height direction 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. In the example shown in Fig. 1 , the calibration objects 6 are positioned at different positions in height direction of the calibration device 4.

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 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 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 the basic principle of the calibration device arrangement 3. Upon simultaneous radar signal emission from the automotive radar device 2 to at least one and preferably all calibration objects 6, a phase between the individual back signals emittable from the calibration objects 6 and receivable by the radar device 2 is changeable. This results in a changing of a direction of arrival 13, which is here sketched as areas with a specific orientation, as well. In other words, an electronic sweep is performed by changing the phases between the individual back signals emitted by the individual calibration objects 6 so that artificial signals indicating different directions of origin throughout for example all elevation angles 11 are performable without changing manually an actual position of the individual calibration objects 6. The direction of origin is an example for another expression for the direction of arrival 13. The change in direction of arrival 13 is indicated by two-headed arrows 14.

The individual calibration objects 6 can be artificial targets, wherein the back signal to the automotive radar device 2 then preferably mimics a movement, meaning a moving object. Alternatively, the calibration objects 6 can be antennas which together form a phased array. Additionally to the described phase change between the individual back signals, it is possible to change an amplitude, meaning that an amplitude of one of the antennas differs from an amplitude of an adjacent antenna of the phased array. By doing so, a signal-to- noise ratio of the receiving back signals can be increased.

In Fig. 2 different steps taking place in order to perform the calibration of the automotive radar device 2 are indicated. 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, wherein a phase between the emitted back signals is changed so that a direction of arrival of the back signals received by the automotive radar device is changed. 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 received back signal in the FFT spectrum corresponds directly to the direction of arrival and is distinguishable in relation to the direction of arrival. Afterwards in an additional step, the determined calibration data can be transmitted from the calculation device 7 to the automotive radar device 2.

Furthermore, Fig. 2 shows an embodiment to calibrate for azimuth angles 12 of the radar device 2. If the holding unit 5 comprises a basic element 20 on which the at least two calibration objects are positioned, it is possible to arrange the basic element 20 for example in the horizontal directions of the radar device 2, meaning for example parallel to the y-direction.

It is furthermore possible to have a cross-like structure as holding unit 5 by adding a cross element to the basic element 20 resulting in an embodiment in which the calibration objects 6 are both aligned in the vertical and horizontal direction (y.- and z-direction) of the automotive radar device 2 (not shown in Fig. 2). The basic element 20 and/or the cross element can be straight or at least partially curved, preferably they are at least partially circular curved. For example, the embodiment sketched in Fig. 2 shows such a basic element 20 with an at least partially curved structure in the horizontal direction of the automotive radar device 2 so that calibration for azimuth angles 12 is performable.

In between the individual calibration objects, the holding unit 5, preferably the basic element 20 and/ or the cross element, are at least partially covered by a radar frequency absorber 21. 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 the back signals of one common direction of arrival 13 create a value peak 19 within the range-Doppler plot 15. Here, four different value peaks 19 are shown because four different directions of arrival 13 are assumed. 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 direction of arrival 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 corresponding to different directions of arrival 13.

In summary, an automotive radar calibration method without any mechanical movement is shown. To fully get rid of mechanical movement, a set of artificial targets, meaning multiple calibration objects 6, with a minimum of two calibration objects 6, are for example positioned separated in azimuth angle 12 or elevation angle 11 . Considering that we have a set of artificial targets, there are already techniques that can be employed to continuously change the phase between these targets. Such a technique, for example, one resulting in changing the phase between individual back signals, is used. Utilizing electronic sweep of the direction of arrival 13 that can be, for example, based on changing the phase and amplitude of adjacent antennas in an antenna array, achieves this. As an example, artificial targets distributed along azimuth angle 12 would then easily enable to directly obtain the corresponding calibration vectors within a fraction of time needed for a conventional physical sweep of an arm with a corner reflector. There may be multiple artificial targets in parallel or separately at different ranges or Doppler bins. As a consequence, a detailed investigation of radar performance across the FFT spectrum including various azimuth angles 12 would be possible.

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 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 on the holding unit (5), wherein upon simultaneous radar wave emission from the automotive radar device (2) to the calibration objects (6) a phase between individual back signals emittable from the calibration objects (6) and receivable by the automotive radar device (2) is changeable so that a direction of arrival (13) of the received back signals is changeable, wherein the received back signals are analyzable using a fast Fourier transformation algorithm, wherein a peak location of a received back signal in the fast Fourier transformation spectrum is directly correspondable to the direction of arrival (13) and distinguishable in relation to the direction of arrival (13) so that a calibration of the automotive radar device (2) is performable. Calibration device arrangement (3) according to claim 1 , wherein the calibration object (6) is an artificial target, wherein the back signal to the automotive radar device (2) is located at a defined peak location in the fast Fourier transformation spectrum. 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 the back signal with a respective direction of arrival (13) is assignable to a respective individual segment (17) of a range axis (16) of the range- Doppler plot (15) wherein the individual segments (17) differ from one another depending on the direction of arrival (13). Calibration device arrangement (3) according to claim 1 , wherein the calibration objects (6) are antennas which form a phased array. Calibration device arrangement (3) according to claim 4, wherein an amplitude of one of the antennas differs from an amplitude of an adjacent antenna of the phased array. Calibration device arrangement (3) according to any of the claims 4 or 5, wherein by applying the fast Fourier transformation algorithm on the back signals a range plot is generatable in which each direction of arrival (13) 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 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 arranged vertically or horizontally in relation to the automotive radar device (2). Calibration device arrangement (3) according to claim 7, wherein the holding unit (5) comprises a cross element arranged perpendicular to the basic element (20), wherein at least two of the calibration objects (6) are positions on the cross element. Calibration device arrangement (3) according to any of the claims 7 or 8, wherein the basic element (20) and/or the cross element are straight or at least partially curved, preferably circular curved. Calibration device arrangement (3) according to any of the preceding claims, wherein the holding unit (5) apart from the calibration objects (6) is at least partially covered by a radar frequency absorber (21 ). 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. Calibration device (4) comprising a holding unit (5) and at least two calibration objects (6) positioned spaced apart from each other at defined positions 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 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 on the holding unit (5), wherein the method comprises the following steps:

- simultaneous radar wave emission (S1 ) from the automotive radar device (2) to the 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), wherein a phase between the emitted back signals is changed in time so that a direction of arrival (13) of the back signals received by the automotive radar device (2) is changed in time;

- 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; and

- performing (S5) of the calibration of the automotive radar device (2) considering that a peak location of a received back signal in the fast Fourier transformation spectrum is directly correspondable to the direction of arrival (13) and distinguishable in relation to the direction of arrival (13).