Radar sensor for a motor vehicle, method for operating a radar sensor and motor vehicle

Abstract

Radar sensor (14) for a motor vehicle (24), comprising:- an antenna arrangement (7) for transmitting and receiving radar signals,- a signal generating arrangement (15) for generating a radar signal to be transmitted via the antenna arrangement (7),- a mixer (9) for mixing the transmitted radar signal with a radar signal received by the antenna arrangement (7) after reflection of the transmitted radar signal from at least one object, to form a radar signal to be evaluated, and- an evaluation arrangement (10) for evaluating the radar signal to be evaluated to determine at least one item of object information relating to the at least one object, wherein the signal generating arrangement (15) has an oscillator (16) and a comb generator (17) for generating a frequency comb with a plurality of carrier frequencies (20) as a radar signal to be transmitted in continuous wave operation.

Description

[0001] The invention relates to a radar sensor for a motor vehicle, comprising: - an antenna arrangement for transmitting and receiving radar signals, - a signal generating arrangement for generating a radar signal to be transmitted via the antenna arrangement, - a mixer for mixing the transmitted radar signal with a radar signal received after reflection of the transmitted radar signal on at least one object with the antenna arrangement to form a radar signal to be evaluated, and - an evaluation arrangement for evaluating the radar signal to be evaluated in order to determine at least one item of object information relating to the at least one object.

[0002] The invention also relates to a method for operating a radar sensor and a motor vehicle.

[0003] Radar sensors are used in many modern applications. In particular, radar sensors are increasingly being used in automotive contexts, such as motor vehicles, whether for environmental detection or for capturing object information within an interior.

[0004] Today's automotive radar sensors use fast or slow FMCW (frequency modulated continuous wave) modulation, also known as modulated continuous wave radar. This involves varying a single carrier signal across a frequency range, a process also referred to as a "sweep." If the frequency changes quickly, for example, within a few microseconds, it is referred to as a fast FMCW radar. If the frequency changes in milliseconds, it is referred to as a slow FMCW radar. If such sweeps are repeated multiple times, usually as an ascending ramp, the fast FMCW radar is referred to as a chirp sequence radar. Fast and slow FMCW radar are common standards in the automotive sector.

[0005] Trends in the development of radar sensors for automotive applications are moving toward integrating as much of the radar sensor's electronics and high-frequency components as possible into small, fully integrated chips, thus requiring minimal peripheral circuitry. For example, analog-to-digital converters (ADCs) and processing units have been implemented together as SoCs (System on a Chip). These can also include communication interfaces (for example, to buses such as CAN, LIN, and Flexray, and / or Ethernet), volatile and non-volatile memory, as well as boot and functional software areas. The switch from gallium arsenite (GaN) to CMOS technology has significantly reduced the costs and power consumption of radar sensors.

[0006] However, implementing high-frequency circuitry in CMOS technology on a highly integrated chip is more complex due to problems related to noise, crosstalk, and sometimes large structures for the high-frequency components. In other words, storage devices, computing devices, and other digital structures are usually implemented in nanometer technology, while high-frequency components with sizes of 1 to 100 µm tend to require larger implementations. However, chip area is crucial in terms of cost and complexity, and large spacing between individual components, especially high-frequency components, is necessary to reduce crosstalk and interference on the chip. This complicates further miniaturization, effort reduction, and cost reduction in radar sensors for automotive applications.

[0007] US 5,793,309 A discloses a low-cost, short-range electromagnetic transceiver in which a low-frequency oscillator signal is used to charge a step recovery diode (SRD), which converts the stored charge into a very short pulse to perform frequency multiplication. The very short pulse is used to perform a pulse measurement.

[0008] DE 10 2021 131 166 A1 relates to the generation of a high-frequency FMCW radar from a low-frequency FMCW radar, wherein a frequency converter is used to convert a source signal with a first frequency into a source signal with a second frequency. For this purpose, it is proposed to generate several harmonic signals from the source signal with the first frequency using an amplifier circuit, after which a harmonic signal lying in the second frequency range of the second frequency is selected by a bandpass filter. The use of several different frequency bands in an FMCW radar is intended to improve resolution.

[0009] DE 10 2018 115 079 A1 discloses a radar arrangement intended to shorten the required measurement time. Instead of using sequentially generated frequencies (classic FSCW system (FSCW - frequency stepped continuous wave)) and evaluating them sequentially, it is proposed to use a frequency comb generator on both the transmitting unit and the receiving unit to generate a primary signal containing multiple frequency components and to achieve a mixing with the received signal on the receiving side such that the individual frequency components are retained for separate evaluation.

[0010] The invention is based on the object of providing a radar sensor which allows further miniaturization, cost reduction and reduction of the complexity of radar sensors by simplifying the circuit technology.

[0011] This object is achieved according to the invention by a radar sensor, a method, and a motor vehicle according to the independent claims. Advantageous embodiments are set out in the dependent claims.

[0012] In a radar sensor of the type mentioned at the outset, the invention provides that the signal generating arrangement has an oscillator and a comb generator for generating a frequency comb with a plurality of carrier frequencies as a radar signal to be transmitted in continuous wave operation.

[0013] It is therefore proposed to use an oscillator which, during an operating phase of the radar sensor as a continuous-wave radar, generates a fundamental signal with a fixed, predetermined fundamental signal frequency (base frequency) located in a baseband. The fundamental signal can be, for example, a sine signal or a cosine signal. Using the comb generator, a high-frequency radar signal to be transmitted in a radar band is generated from the fundamental signal. This high-frequency radar signal has a frequency comb, i.e., has several, in particular equidistant, carrier frequencies as frequency components, which also do not change during the operating phase of the radar sensor. After the transmitted radar signal is mixed with the subsequently received radar signal, the several carrier frequencies then coincide again, producing a common, low-frequency radar signal in the baseband that is to be evaluated.In other words, the multiple carriers overlap additively, including in terms of phase. The radar signal to be evaluated can be analyzed particularly advantageously using the same components as in an FMCW radar.

[0014] In other words, it is proposed to change the form of the radar signal to be transmitted, away from FMCW, by converting a single, unmodulated carrier (the fundamental signal frequency of the fundamental signal in the baseband) into a multi-carrier signal in preparation for transmission, without any change in frequency, i.e., frequency modulation. This is achieved by sending the fundamental signal to a comb generator for control in order to generate harmonics of the fundamental signal, resulting in a multi-carrier signal in the frequency spectrum, i.e., identical representations of the fundamental signal across a broad frequency range. The term "comb generator" originates from the fact that the spectral lines are equidistant, like a comb. A comb generator can also be referred to as a frequency multiplier.

[0015] It has been shown that the form of the radar signal to be transmitted used here for continuous-wave operation enables significantly simpler high-frequency circuit technology, while still allowing the object information, in particular certain object parameters such as distance, angle, and relative speed, to be determined using the same evaluation approaches and components. In other words, the circuit complexity is advantageously significantly reduced. While known FMCW radar sensors require complex frequency-variable signal generators with sometimes complex linearizations, charge pumps for power stabilization, and the like to cycle through an FMCW signal for each chirp in a time interval of a few µs and repeat it at least a thousand times, the present invention requires only one oscillator with a downstream comb generator.The oscillator for generating the basic signal can be designed extremely simply, thus saving costs and effort, since the requirements for frequency stability and phase noise are greatly reduced, as will be explained in more detail below.

[0016] Despite this significant simplification, the existing signal processing mechanisms for determining object information can still be used. No new programming, mental reconfiguration, or other additional evaluation techniques are required. In fact, using the transmitted radar signal with the frequency comb even leads to improvements in the quality of the received object information and the quality of the measurement process, since combining multiple carriers, in particular, results in very good signal-to-noise ratios.

[0017] Advantageously, a multi-carrier signal, i.e., a radar signal with multiple carrier frequencies / frequency components, is more robust against interference and / or measurement disturbances selective for frequencies and / or frequency ranges. If frequency components are canceled out by interference, diffraction, or refraction of the transmitted radar signal due to peripheral buildings, ground, uneven surfaces, and the like (destructive interference), sufficient frequency components of the transmitted radar signal with other frequencies exist where this cancellation does not occur or which are even amplified by in-phase or phase-similar superposition (constructive interference).

[0018] Combating interference from other radar systems in your own vehicle or from other road users is also much easier and more robust than with an FMCW radar sensor. If an FMCW radar sensor of another road user causes interference, this interference only occurs for a very short time. Due to the many carriers in the transmitted and received radar signal, which carry the same information, it is insignificant if a carrier frequency cannot be evaluated for a short time. This also applies to frequency dispersion in the transmission channel.

[0019] If broadband interference occurs, such as that caused by industrial facilities, high-voltage lines, or similar sources, greater robustness is also achieved by using multiple carrier frequencies. While the noise floor is higher, a broad spectrum makes it more likely that the interference will exceed the noise floor for individual carrier frequencies, thus allowing for analysis.

[0020] In general, it should be noted that the object information that can be determined is a distance of the object and / or a relative speed of the object and / or an object class and / or an angle at which the object is detected. This generally known object information and, if appropriate, other known object information, such as that frequently determined by radar, can also be determined within the scope of the present invention, in some cases even with improved quality.

[0021] Using the radar sensor according to the invention, object classification using radar can be simplified. The complex impulse response of the detected object, due to its shape, also generates a characteristic signature of the reflected, received radar signal. With an FMCW signal, a frequency-side singular sampling over time takes place for evaluation and classification, whereby the signal presents itself in a time-variant manner in the event of movement (self-motion and / or object movement). In contrast, when using a radar signal with multiple carriers, a characteristic representation of the object's radar signature is immediately available at every observation time. The same classification algorithms for object classification can be applied and work much more precisely because the relative movement does not lead to "smearing" of the impulse response, thus eliminating the need for smoothing by Kalman filtering.

[0022] The relative velocity of the object is also determined in the radar sensor according to the invention via the Doppler frequency shift. No changes to the evaluation process are required compared to FMCW radar. However, this does not require the evaluation of several hundred chirps, which involves integrating the signal components; instead, only the parallel evaluation of the individual carriers in one time step is necessary. Since each individual carrier of the multi-carrier signal contains the same Doppler shift, this is also integrated across all carrier frequencies. Thus, simultaneous transmission (and thus measurement) on multiple carrier frequencies enables faster evaluation.For example, if an FMCW radar with a system clock of 25 ms required the evaluation of a large number of individual chirps, meaning that the relative speed was only available after the end of the burst comprising the chirps, the relative speed can be determined much more quickly when object detection is carried out using multiple carrier frequencies. In the example of the 25 ms system clock mentioned above, but also with other known system clock lengths, it is even possible to determine the relative speed repeatedly within the system clock, for example to increase accuracy through statistical combination and / or for mutual plausibility checks, so that the system clock can be maintained and an improved evaluation is possible. It is of course also conceivable to determine the relative speed (or the object information in general, at least in part) more quickly ormore frequently so that vehicle systems of the motor vehicle can be informed earlier. In particular, such a vehicle system which uses the object information can be a vehicle system designed for at least partially automatic guidance of the motor vehicle, since faster or more frequent provision of object information offers an advantage, especially for time-critical, autonomous driving functions. Overall, it can therefore be said that the relative speed of the object continues to be determined via the Doppler shift, which becomes apparent when the received radar signal is downconverted to baseband, whereby the processing can still correspond to that of the FMCW radar. At the same time, however, there is the advantage that the Doppler shift is the same for all carriers and can be integrated per unit of time, so that a clearer, improved and faster determination is possible.

[0023] It should be noted at this point that the characteristics and / or the operating point of the comb generator can expediently be selected as a function of a maximum relative speed such that, at least up to the maximum relative speed, no shift of a carrier frequency to a neighboring carrier frequency occurs. In other words, the spacing between the individual carrier frequencies can be selected such that no intersymbol interference occurs at maximum Doppler shift, as would occur at the maximum relative speed. The maximum relative speed for a motor vehicle, for example, can be selected in the range of 200 to 400 km / h, in a specific example as 250 km / h. If a non-linearly operated component is used in the comb generator, this usually has a characteristic curve so that an operating point on this characteristic curve can be suitably selected.

[0024] The distance of the object from the radar sensor, and thus from the motor vehicle, is still calculated, as is well known, based on the signal propagation time. To locate the object, in particular to determine the angle at which the object is located, the methods generally known in the prior art, in particular the monopulse method and / or digital beamforming, can also be used, whereby, in particular, propagation time phase differences of individual receiving antenna elements can be evaluated. These procedures do not depend on the shape of the radar signal, but rather on the antenna characteristics and the number of antenna elements in the antenna array. Therefore, the methodology of an FMCW radar can be used equally well here as well.

[0025] Overall, it can be said that the determination of object information, i.e. object recognition, is largely identical to the procedure used with an FMCW radar, although the individual pieces of information can be determined at least in part more quickly and / or with higher quality.

[0026] In this case, similar to known FMCW radar sensors, the transmitted radar signal can also be fed to a detector unit in addition to the (receive) mixer, which measures the power of the transmitted radar signal and / or serves for signal monitoring and / or signal control. Measurement data from the detector unit can be used to implement adaptive gain control (AGC) and to prevent overloading of the analog-to-digital converter (ADC) in the receive path. Additionally or alternatively, radar cross sections can be determined if the ADC determines a receive level.

[0027] In summary, the modified radar signal shape and the specific signal processing, particularly the mixing of the received radar signal with the transmitted radar signal, provide a variety of advantages. The main advantage is the significant simplification of the high-frequency circuitry in the signal conditioning and signal transmission (TX) path. Phase noise, frequency jitter, and temperature stability play a minor role, resulting in a significantly simpler, smaller, and therefore more cost-effective implementation.

[0028] According to the invention, a static form of the radar signal to be transmitted in continuous-wave operation of the radar sensor is proposed, which is neither pulsed nor temporally modulated or modified in terms of frequency and / or amplitude. The radar signal to be transmitted has a frequency spectrum similar to a frequency comb, in which several carrier frequencies follow one another with a certain frequency spacing within a radar band. In other words, the radar signal to be transmitted (and thus also the transmitted one) comprises frequency-stable, unmodulated frequency components similar to a frequency comb. This radar signal is used to reduce the effort required for signal generation while maintaining the other components known from a conventional FMCW radar, in particular the antenna arrangement, the receiver mixer, which mixes the transmitted radar signal and the received radar signal, and the analog-to-digital converter in the signal reception path.

[0029] In particular, an advantageous embodiment of the radar sensor according to the invention can provide that at least the signal generation arrangement, the mixer and the evaluation arrangement are implemented as part of a single-chip system (System on a Chip - SoC), in particular as part of a CMOS chip.

[0030] The comb generator can be provided with a diode operating in the nonlinear characteristic range. Diodes are already known in frequency multipliers to generate harmonics of a fundamental signal, thus achieving spectral spreading.

[0031] However, in a particularly advantageous embodiment of the present invention, the comb generator comprises an amplifier operated in the non-linear range. The non-linear range is also referred to as the saturation range. If an amplifier is operated in saturation mode, i.e., in the non-linear operating range / characteristic range, not only is spectral spreading achieved, but signal amplification is also effected, in particular such that the amplifier's output signal already has a signal strength suitable for transmission. Additional amplifiers are then not required, so that the amplifier of the comb generator can be provided as the only amplifier in the signal transmission path. This ensures a further simple, less complex design, since the amplifier of the comb generator serves, on the one hand, to generate the frequency comb and, on the other hand, to amplify the signal, thus fulfilling a dual purpose.

[0032] The oscillator generates the fundamental signal waveform, for example, a sine signal and / or a cosine signal. Harmonics are generated by the nonlinearity of the high-frequency amplifier, which operates in saturated, overdriven, or nonlinear, mode. Depending on the nonlinearity of the comb generator's high-frequency amplifier's characteristic curve, broad frequency ranges with multiple frequency components identical to the fundamental signal waveform are generated. The spacing of the individual carrier frequencies also depends on the characteristic curve.

[0033] As with known FMCW radars and other radar concepts, the radar sensor described here also uses a specific radar band. Therefore, the signal generation arrangement can be provided with a bandpass filter to limit the transmitted radar signal to a predetermined radar band comprising several carrier frequencies. Particularly advantageously, even generally speaking, the transmitted radar signal can be generated in the radar band from 76 to 81 GHz or 77 to 81 GHz. Thus, a bandwidth of 5 or 4 GHz is available over which the carrier frequencies can be distributed.

[0034] It can be provided that the signal generation arrangement for generating the radar signal to be transmitted is designed with at least five, in particular at least ten, carrier frequencies. In this case, a maximum number of carrier frequencies can be used, which, as described above, avoids intersymbol interference up to a maximum relative speed. One embodiment is obtained, for example, with a radar band of 76 to 81 GHz and eighteen carrier frequencies used.

[0035] An advantageous development of the present invention can provide that the oscillator can be controlled and / or adjusted to change its frequency and / or the comb generator can be controlled and / or adjusted with regard to its characteristics, in particular an operating point on the non-linear characteristic curve of the amplifier, in particular the oscillator is designed as a voltage-controlled oscillator (VCO). In this way, it is possible to avoid interference from a similar radar sensor in the same motor vehicle and / or in another motor vehicle, or to react to such interference. If two or more radar sensors of the type described here are used in a motor vehicle and could interfere with one another, slightly different basic signal frequencies can be selected for them on the oscillator, thus avoiding interference. In less preferred embodiments, an adaptation can also be made with regard to the comb generator.However, interference can also be reduced, possibly even reactively, with respect to other sources of interference, such as the use of the radar sensor in other motor vehicles. For example, the radar sensor can be provided with a control unit that, when a disturbance condition is met, is designed to control the oscillator and / or the comb generator to reduce the interference.

[0036] Alternatively or additionally, in this context, the signal generation arrangement can also be provided with a coding unit for radar-sensor-specific marking of the signal to be transmitted, in particular by modulation. For example, the oscillator that generates the base signal can already incorporate unique codes into the radar signal, enabling unambiguous signal recognition by means of correlation in the presence of very strong interference, for example, from other radar systems.

[0037] Overall, combating interference from other radar systems, whether in your own vehicle or from other road users, is significantly simpler and more robust than with FCMW radars. If the same radar sensor in your own vehicle causes interference, interference can be effectively prevented, particularly by slightly adjusting the base signal. Alternatively, a different operating point for the comb generator can be selected, particularly on the amplifier's characteristic curve, which results in a different harmonic distribution. In the case of short-term interference from radar systems of other road users, the interference can be detected, enabling a dynamic response based on the interference condition.

[0038] In a method according to the invention for operating a radar sensor according to the invention, it is provided that - by means of the signal generating arrangement, a radar signal to be transmitted is generated as a frequency comb with several carrier frequencies, - the radar signal to be transmitted is transmitted by means of the antenna arrangement, and - the transmitted radar signal is forwarded to a mixer, - wherein the transmitted radar signal reflected by at least one object is received by the antenna arrangement, and - the received radar signal is fed to the mixer to generate a radar signal to be evaluated, - after which the radar signal to be evaluated is evaluated by the evaluation arrangement to determine object information describing the at least one object.

[0039] All statements regarding the radar sensor according to the invention can be applied analogously to the method according to the invention, and vice versa. Thus, the same advantages can be achieved.

[0040] Finally, the present invention also relates to a motor vehicle having at least one radar sensor according to the invention. The statements regarding the method and the radar sensor can also be applied to the motor vehicle.

[0041] In particular, in the case of potentially interfering radar sensors of the motor vehicle, it can be provided that different voltages are set at the VCOs and / or different operating points on the characteristic curve of the amplifier and / or different codes are applied to the basic signal by the oscillator.

[0042] Further advantages and details of the present invention will become apparent from the exemplary embodiments described below and from the drawings. In the drawings: Fig. 1 a functional schematic diagram of a state-of-the-art FMCW radar sensor, Fig. 2 a functional schematic diagram of a radar sensor according to the invention, Fig. 3 schematically shows a frequency spectrum of a radar signal to be transmitted, and Fig. 4 a motor vehicle according to the invention.

[0043] Fig. Figure 1 shows a schematic diagram of a prior art radar sensor 1 operating as a frequency-modulated continuous wave (FMCW) radar. The radar sensor 1 comprises a signal generation arrangement 2, which is shown here in a simplified manner. It includes an oscillator 3 in its signal transmission path, which is controlled to generate a fundamental signal with a frequency that increases linearly to a maximum value in a few microseconds, as indicated by the temporal frequency response 4. The oscillator 3, as a signal generator with variable frequency over a wide range, is a complex, expensive component. The fundamental signal is amplified by a linearly operated amplifier 5 and converted into a radar band, resulting in a chirp (see frequency response 6). This chirp is repeated identically multiple times, for example, more than a thousand times. The amplifier 5 is also an expensive, complex component, since exact linearity of the characteristic curve is required.The signal generating arrangement 2 comprises further complex and expensive components, not shown in detail here, including, for example, further linearization means, charge pumps and the like.

[0044] The chirp signal is transmitted via an antenna array 7 with antenna elements 8 for transmission and / or reception and is also forwarded to a mixer 9 (receiver mixer) as part of a receiver array 10, so that it can be mixed there with a received signal resulting from the transmitted chirp signal by reflection from at least one object and measured by the antenna array 7, to generate an evaluation signal in the baseband. This can be digitized by an analog-to-digital converter 11 (ADC) in order to be evaluated by an evaluation array 12, which can comprise at least one computing unit and implements evaluation algorithms for determining object information about the at least one object.

[0045] The emitted chirp signal can further be fed to a detector unit 13, where a power measurement and / or signal monitoring / signal control can take place.

[0046] Fig. Figure 2 shows a radar sensor 14 according to the invention for a motor vehicle, which is modified in the signal generation arrangement 15 compared to radar sensor 1 to use a different signal shape. For the sake of simplicity, technically identical components of radar sensor 1 that can also be used in radar sensor 14 are provided with the same reference numerals.

[0047] The signal transmission path of the signal generation arrangement 15 comprises an oscillator 16 and a comb generator 17, as well as optionally a bandpass filter 25. Using the oscillator 16 as a signal generator, a fundamental signal of a temporally fixed frequency is generated. The oscillator 16 can be designed as a VCO, so that the frequency can be varied at least within a small range. The fundamental signal can be, for example, a sine signal and / or a cosine signal. Since neither rapid, highly precise frequency changes are required, nor do phase noise, frequency jitter, and temperature stability play a major role, as will be explained below, the oscillator 16 can be designed extremely simply compared to the oscillator 3.

[0048] The fundamental signal in the baseband of radar sensor 14 is fed to the comb generator 17, which in this case comprises an amplifier 18 operating in the nonlinear range, i.e., the saturation range. The nonlinearity of amplifier 18 generates harmonics depending on the nonlinearity of the characteristic curve. This creates a multi-carrier signal in which the fundamental signal shape is present at several equidistant carrier frequencies. The spacing of the individual carrier frequencies also depends on the characteristic curve of amplifier 18.

[0049] Since amplifier 18 also provides signal amplification, the multi-carrier signal can be used directly as a high-frequency radar signal to be transmitted if all carrier frequencies lie within a radar band to be used. If carrier frequencies outside the radar band are generated in comb generator 17, the optional bandpass filter 25 can be used to select the carrier frequencies within the radar band. Radar sensor 14 is used in continuous-wave operation, meaning that during an operating phase, the radar signal to be transmitted is continuously transmitted at the same, fixed carrier frequencies.

[0050] Fig. Figure 3 schematically shows, by way of example, a possible frequency spectrum 19 of the radar signal to be transmitted, generated by the signal generation arrangement 15. Here, all equidistant carrier frequencies 20 lie within the radar band 21. In the present example, eighteen carrier frequencies 20 are used in the radar band from 76 to 81 GHz. Due to its appearance, such a frequency spectrum 19 or the corresponding radar signal to be transmitted is also referred to as a frequency comb.

[0051] In general, the spacing between the carrier frequencies 20 is always selected such that, up to a maximum relative speed, the Doppler shift does not cause a carrier frequency 20 to be shifted to the value of the adjacent carrier frequency 20 (intersymbol interference). In particular, a maximum number of carrier frequencies 20 can be selected with respect to the maximum relative speed. The maximum relative speed can be, for example, 200 to 500 km / h.

[0052] As can be seen, the circuit complexity for implementing the signal generation arrangement 15 is significantly reduced compared to the signal generation arrangement 2. Instead of complex frequency-variable signal generators and other components with complex linearization, charge pumps for power stabilization, and the like, only an oscillator 16 with an amplifier 18 driven in nonlinear saturation mode is required. The remaining components, in particular the antenna arrangement 7, the mixer 9, the analog-to-digital converter 11, and the evaluation arrangement 12, can be configured as in the radar sensor 1.

[0053] In the present case, at least the signal generating arrangement 15 and the receiving arrangement 10 are implemented as a single-chip system (SoC), thus forming a chip 22. Embodiments have also been proposed in which the antenna arrangement 7 is also integrated into the single-chip system, for example, in a multilayer structure. Such embodiments can also be applied to the radar sensor 14. CMOS technology is used here.

[0054] After the transmitted radar signal from radar sensor 14 is fed to mixer 9 to be mixed with the received radar signal, the multiple carrier frequencies coincide again in the baseband, so that the information they carry ultimately "adds up," resulting in values ​​with a low signal-to-noise ratio even in a single time step. This applies to both the phase and the Doppler shift. Because the complex impulse response of an object is present in every time step and no relative motion effects need to be corrected, faster and better object classification is possible. The multiple carriers also make the measurement more robust, for example, if destructive interference occurs for one carrier. Overall, phase noise, frequency stability, and temperature effects are therefore less relevant for high-quality radar measurements.

[0055] In addition to determining object classes through object classification, conventional object information can also be determined by radar sensor 14 as is generally known, in particular the distance of the object, the relative speed of the object, and the angle at which the object is detected. The latter is also possible using the monopulse method or digital beamforming using antenna array 7.

[0056] The distance to the object is also calculated based on the signal propagation time, which can be determined using the phase shift. With regard to the Doppler frequency shift, there is also the advantage that, since the Doppler shift is the same for each carrier frequency, they are, so to speak, integrated during mixing, which ensures a clear, quickly available Doppler signal. This also enables fast, accurate analysis.

[0057] Due to the rapid evaluation possible, at least part of the object information can also be provided more frequently, i.e. at shorter intervals, for example to a vehicle system for at least partially automatic guidance of the motor vehicle.

[0058] Because the base signal frequency of the oscillator 16 is easily adjustable, which can be controlled, for example, by a control unit 23 of the radar sensor, mutual interference can be reduced when multiple radar sensors 14 are used in a motor vehicle. It is also conceivable, upon detection of external interference, for example, upon fulfillment of an interference condition, to adjust the base signal frequency, particularly briefly, to reduce the interference. Alternatively or additionally, the operating point on the characteristic curve of the amplifier 18 can be adjusted. Finally, to reduce interference, it is also conceivable to apply unique codes to the base signal using the oscillator 16 or an additional component, which enable the signal to be recognized.

[0059] Fig.4 shows a schematic diagram of a motor vehicle 24 according to the invention. It can be seen that the motor vehicle 24 in the present case has two radar sensors 14 according to the invention directed towards the area in front of the motor vehicle 24, which in the present case also operate at different basic signal frequencies in order to avoid mutual disturbance and interference. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 5,793,309 A

[0007] DE 10 2021 131 166 A1

[0008] DE 10 2018 115 079 A1

[0009]

Claims

[1] Radar sensor (14) for a motor vehicle (24), comprising: - an antenna arrangement (7) for transmitting and receiving radar signals, - a signal generating arrangement (15) for generating a radar signal to be transmitted via the antenna arrangement (7), - a mixer (9) for mixing the transmitted radar signal with a radar signal received after reflection of the transmitted radar signal on at least one object with the antenna arrangement (7) to form a radar signal to be evaluated, and - an evaluation arrangement (10) for evaluating the radar signal to be evaluated in order to determine at least one item of object information relating to the at least one object, characterized by that the signal generating arrangement (15) has an oscillator (16) and a comb generator (17) for generating a frequency comb with a plurality of carrier frequencies (20) as a radar signal to be transmitted in continuous wave operation. [2] Radar sensor according to claim 1, characterized by that the comb generator (17) has an amplifier (18) operated in the non-linear range. [3] Radar sensor according to claim 2, characterized by that the amplifier (18) of the comb generator (17) is the only amplifier of the signal generating arrangement (15). [4] Radar sensor according to one of the preceding claims, characterized by that the signal generating arrangement (15) has a band filter (25) for limiting the radar signal to be transmitted to a predetermined radar band (21) comprising a plurality of carrier frequencies (20). [5] Radar sensor according to one of the preceding claims, characterized by that the signal generating arrangement (15) is designed to generate the radar signal to be transmitted with at least five, in particular at least ten, carrier frequencies (20) and / or in the radar band (31) from 76 to 81 GHz. [6] Radar sensor according to one of the preceding claims, characterized bythat the oscillator (16) can be controlled and / or adjusted to change its frequency and / or the comb generator (17) can be controlled and / or adjusted with regard to its characteristics, in particular the operating point on the non-linear characteristic curve of the amplifier (18), in particular the oscillator (16) is designed as a voltage-controlled oscillator (16). [7] Radar sensor according to claim 6, characterized by that the radar sensor (14) has a control unit (23) which, when a disturbance condition is fulfilled, is designed to control the oscillator (16) and / or the comb generator (17) to reduce the disturbance. [8] Radar sensor according to one of the preceding claims, characterized by that the signal generating arrangement (15) has a coding unit for radar sensor-specific marking of the radar signal to be transmitted, in particular by modulation. [9] Method for operating a radar sensor (14) according to one of the preceding claims, wherein a radar signal to be transmitted is generated as a frequency comb with a plurality of carrier frequencies (20) by means of the signal generation arrangement (15) and is transmitted by means of the antenna arrangement (7) and forwarded to a mixer (9), wherein the transmitted radar signal reflected by at least one object is received by the antenna arrangement (7) and the received radar signal is fed to the mixer (9) to generate a radar signal to be evaluated, after which the radar signal to be evaluated is evaluated by the evaluation arrangement (12) to determine object information describing the at least one object. [10] Motor vehicle (24) comprising a radar sensor (14) according to one of claims 1 to 8.

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