MIMO radar device and method for operating an MIMO radar device

Abstract

The present invention relates to a MIMO radar device having a plurality of transmit antennas for transmitting radar radiation; and a ramp generator configured to generate a primary ramp, wherein the ramp generator is further configured to generate a respective transmit ramp for each transmit antenna based on the primary ramp by means of a respective frequency shift, and wherein the transmit antennas are configured to transmit the respective transmit ramps. The present invention also relates to a method for operating a MIMO radar device.

Description

Technical Field

[0001] The present invention relates to a Multiple-Input-Multiple-Output (MIMO) radar device and a method for operating an MIMO radar device. Background Art

[0002] In order to provide safety functions and comfort functions, radar systems are used in motor vehicles to measure the distance, relative speed and angle of objects (such as vehicles) and obstacles. Multiple-Input-Multiple-Output (MIMO) devices with multiple transmit antennas and multiple receive antennas are known. Thereby, particularly accurate angle measurement can be performed because the antenna aperture (i.e., the antenna area) important for angle measurement is actually enlarged. The transmit antennas emit signals independently of each other, and these signals are separated in the receive channel. Due to the different distances from the transmit antennas to the corresponding receive antennas, an actual aperture enlargement is obtained. In terms of calculation, it can be processed as if there were only one transmit antenna, where the number of receive antennas is multiplied, thereby obtaining a larger antenna aperture.

[0003] Signals can be separated in the frequency domain by a frequency-division multiplexing (FDM) method, where different transmit antennas occupy different frequency ranges at the same time point. However, this reduces the available bandwidth of each transmit channel. Since the range separation ability of a radar system is proportional to its bandwidth, the range separation ability is reduced.

[0004] Signals can also be separated in the time domain, where the antennas transmit sequentially by a time-division multiplexing (TDM) method. However, the measurement time is increased by sequential measurement. In addition, during the increased measurement time, the object may have moved significantly, which reduces the measurement accuracy. In addition, the time interval between two sequential measurements of the corresponding transmit antenna is increased, which may result in a reduction in the maximum uniquely measurable speed range.

[0005] The above implementations are independent of the modulation method used. Typical transmit frequencies are 24 GHz or 77 GHz, where the maximum available bandwidth can be up to 5 GHz, but is usually significantly lower. The typical bandwidth is about 0.5 GHz.

[0006] The radar systems of modern motor vehicles typically use FMCW modulation (Frequency Modulated Continuous Wave). Here, multiple linear frequency ramps with the same or different slopes are traversed. The mixing of the current transmitted signal and the received signal results in a low-frequency signal, the frequency of which is proportional to the distance. Additionally, it contains an addition or subtraction component via the Doppler frequency, which is proportional to the relative speed. In order to separate the distance information and speed information of multiple targets, a relatively complex method is required, in which the results of different ramps are considered for use together with the results of earlier measurement cycles.

[0007] Newer systems rely on FMCW modulation with faster ramps, namely fast chirp modulation, whereby the Doppler frequency shift within the ramp can be ignored. The obtained distance information is largely uniquely defined; then the Doppler frequency shift can be determined by observing the temporal development of the phase of the complex distance signal. Distance determination and speed determination are performed independently of each other, where typically a two-dimensional Fourier transform is used.

[0008] An exemplary radar sensor for a motor vehicle is known from DE 10 2016 221947 A1.

[0009] In order to expand a fast chirp radar system in a MIMO method to improve angle estimation, the signals of the transmit antennas must be separated. This is typically achieved by a TDM method, but the unambiguity of the Doppler frequency shift is reduced due to under-sampling.

[0010] Current FMCW radar systems and fast chirp radar systems always broadcast a single frequency ramp and thus do not generate parallel extended ramps. Therefore, the available time-frequency resources are only conditionally utilized. Summary of the Invention

[0011] The present invention provides a MIMO radar device having the features of the present invention and a method for operating a MIMO radar device having the features of the present invention.

[0012] Preferred embodiments are the subject of corresponding extended implementation schemes.

[0013] According to a first aspect, the present invention relates to a MIMO radar device having a plurality of transmit antennas for transmitting radar radiation and a ramp generator configured to generate a primary ramp, wherein the ramp generator is further configured to generate a corresponding transmit ramp for each transmit antenna based on the primary ramp with a corresponding frequency shift. The transmit antennas are configured to transmit the corresponding transmit ramps.

[0014] According to a second aspect, the invention relates to a method for operating a MIMO radar device, wherein the MIMO radar device has a plurality of transmit antennas. A primary ramp is generated. Furthermore, transmit ramps are generated for each transmit antenna by means of a respective frequency shift. The transmit ramps are transmitted via the transmit antennas.

[0015] Advantages of the invention

[0016] Since the frequency ramps overlap in time, i.e., are broadcast with a significantly smaller offset, the utilization efficiency of time-frequency resources is increased.

[0017] At the same time, by using the primary ramp or "Genesis ramp", it is possible to avoid increasing the overhead required for generating the transmit ramps and demodulating the radar signals at the receiver. Therefore, it does not involve a pure time-division multiplexing method or a frequency-division multiplexing method. Thus, the limitations of conventional TDM and FDM schemes can be avoided. Compared with traditional FDM, a large number of transmit antennas can be used in MIMO operation without significantly reducing the range resolution.

[0018] The main advantage of the proposed MIMO radar concept is that a plurality of transmit antennas are used, and in this case, the uniquely measurable velocity range is not reduced sharply as in the case of traditional TDM schemes. In order to operate the transmit antennas with a traditional TDM scheme without reducing the uniquely measurable velocity range, a significantly steeper ramp must be selected. The resulting beat frequency increases with the slope of the ramp, thus requiring a faster analog-to-digital converter and generally generating disproportionately more data. In addition, the ratio of the ramp duration to the flight time deteriorates disproportionately, which leads to a reduction in the effective bandwidth and the signal-to-noise ratio. Therefore, the MIMO radar concept according to the invention is much more efficient than conventional TDM schemes.

[0019] Another advantage of the above MIMO radar concept is the coherence between the signals of the transmit channels. In traditional TDM, a time offset is generated between the measurements of the transmit channels. If the radar target moves during the measurement, this leads to a velocity-dependent phase component that affects the MIMO-based angle estimation. To prevent this, this phase component must be compensated, which can only be done with limited quality. Similarly, in FDM, a range-dependent phase component is generated due to the different carrier frequencies of the transmit channels. For most practical designs, this may thus affect the angle estimation. The MIMO radar concept according to the invention uses transmit ramps that preferably have the same carrier frequency and a significantly lower time offset. Therefore, for a moving target, a significantly smaller phase shift is generated between the signals of the transmit antennas, which can be neglected or compensated much more easily.

[0020] Compared with existing radar systems, MIMO radar devices can achieve significant performance advantages. The receiver circuit can be implemented particularly effectively when it is implemented as a highly integrated circuit, in such a way that an individualized receiving path with an analog / digital converter is obtained for the intermediate frequency receiving path of each transmitted signal.

[0021] By a special correlation between the time offset at the start of the primary ramp and a fixed frequency shift, a time-shifted ramp can be generated. It is very advantageous to use a transmitted ramp without a frequency offset and a minimum time offset, because this enables maximum coherence between the transmission channels.

[0022] A special implementation of the MIMO radar device according to the invention allows the transmission carrier and intermodulation products to be designed by individually selecting the frequency shifts of the individual transmission channels. Thereby, despite the use of non-ideal modulators in the transmission branch, a received signal with high spectral purity can still be generated.

[0023] Compared with TDM, the MIMO radar device according to the invention can achieve slower ramps and lower beat frequencies, as well as a longer time to reach the target, thus achieving a better signal-to-noise ratio and better bandwidth utilization, i.e., a more favorable ratio of flight time to ramp duration.

[0024] According to an expansion scheme of the MIMO radar device, the time offset between temporally adjacent transmitted ramps is less than the ramp duration of the transmitted ramp. Thus, the transmitted ramps are slightly offset.

[0025] According to an expansion scheme of the MIMO radar device, the ramp generator is configured to generate transmitted ramps that are non-equidistant in time or slightly offset in frequency by means of a frequency shift.

[0026] According to an expansion scheme of the MIMO radar device, the ramp generator is configured to generate temporally equidistant transmitted ramps by means of an equidistant frequency shift.

[0027] According to an expansion scheme of the MIMO radar device, the ramp generator is configured to generate transmitted ramps having the same center frequency. For example, this can be achieved by a special setting of the frequency shift of the transmitted ramp, where the frequency shift of the transmitted ramp is proportional to the time offset of the transmitted ramp. In particular, transmitted ramps with non-equidistant frequency shifts can be generated.

[0028] According to an expansion scheme of the MIMO radar device, the ramp generator is configured to generate the transmitted ramp as a time-offset portion of the primary ramp. The frequency shift is thus coupled to the time offset.

[0029] According to an extended scheme of the MIMO radar device, the ramp generator is configured to generate transmit ramps with equally spaced frequency shifts.

[0030] According to an extended scheme of the MIMO radar device, the ramp generator is configured to generate transmit ramps that are equally spaced in time. However, it can also be arranged that the ramp generator generates transmit ramps that are not equally spaced in time.

[0031] According to an extended scheme, the MIMO radar device is based on any method with a linear ramp, such as the FMCW method or the fast linear frequency modulation method.

[0032] According to an extended scheme, the MIMO radar device can determine the distances, velocities, and / or angles of multiple reflecting objects by receiving and analyzing the transmitted signals reflected from the objects.

[0033] According to an extended scheme, the MIMO radar device has a receiving device that is configured to receive the transmitted and reflected radar radiation and mix it with a primary ramp to generate and output a measurement signal. Thus, the resulting beat frequency is generated offset in time and frequency. Therefore, the signals of different transmit antennas can be uniquely separated by the frequency offset. The signals of all transmit antennas can be effectively detected and sampled by means of the receiving channels of each receive antenna, in such a way that each transmit channel uses an analog-to-digital converter (ADC) with a correspondingly higher data rate. Alternatively, each transmit channel can be demodulated separately at the receiver, for which purpose a separate path is provided for each transmit channel in each receive channel.

[0034] According to an extended scheme of the MIMO radar device, the receiver device also has an analog-to-digital converter for sampling the measurement signal, wherein the analog-to-digital converter samples the signals of all transmit channels.

[0035] According to an extended scheme of the MIMO radar device, the transmit ramps have the same frequency variation between a pre-given minimum frequency and a pre-given maximum frequency. In particular, it can relate to linearly extending frequency ramps that are parallel.

[0036] According to an extended scheme, the MIMO radar device has a fixed-frequency oscillator that is configured to set the frequency offset of transmit ramps that are adjacent in time. The ramp generator can in particular include such a fixed-frequency oscillator. With the fixed-frequency oscillator and a switch, the transmit ramps of the transmit antennas can be generated from the primary ramp. Here, it is particularly advantageous to use the fixed-frequency oscillator to generate the frequency offset, because the fixed-frequency oscillator can be easily implemented with low phase noise. The MIMO radar device is particularly advantageous in terms of hardware overhead and phase noise.

[0037] According to an extended scheme of the MIMO radar device, the ramp generator further has a switch for setting the start time and end time of the transmission ramp.

[0038] According to an extended scheme of the MIMO radar device, the ramp generator is configured to generate a primary ramp in the high-frequency range.

[0039] According to an extended scheme of the MIMO radar device, the ramp generator includes an I-Q modulator configured to generate a signal ramp based on the primary ramp.

[0040] According to an extended scheme of the MIMO radar device, the ramp generator is further configured to generate a transmission ramp by frequency shifting the primary ramp to a higher or lower frequency.

[0041] According to an extended scheme of the MIMO radar device, the ramp generator is further configured to generate one of the transmission ramps as a part of the primary ramp without frequency shift.

[0042] According to an extended scheme of the MIMO radar device, the ramp generator is further configured to generate a plurality of primary ramps that are successive in time and to generate corresponding transmission ramps for the transmit antennas. The generation of the transmission ramps can thus include a combination of multiplexing based on the primary ramp and known multiplexing methods. For example, two transmission ramps can be generated from each primary ramp. In this way, another two transmission ramps are generated from the next primary ramp. Thus, multiplexing is performed not only by beat frequency but also by TDM.

[0043] According to an extended scheme of the method for operating a MIMO radar device, the transmitted and reflected radar radiation is also received and mixed with the primary ramp to generate and output a measurement signal. Description of the Drawings

[0044] The drawings show:

[0045] Figure 1 A schematic block diagram of a MIMO radar device showing an embodiment according to the present invention;

[0046] Figure 2 A schematic block diagram of a MIMO radar device showing another embodiment according to the present invention;

[0047] Figure 3 A schematic diagram showing the primary ramp and the resulting transmission ramps;

[0048] Figure 4 A schematic block diagram of a MIMO radar device showing another embodiment according to the present invention;

[0049] Figure 5Schematic diagram showing the time-frequency diagram of the primary ramp and the resulting transmit ramp;

[0050] Figure 6 Schematic diagram showing the qualitative spectrum of the received signal;

[0051] Figure 7 Schematic diagram showing the intermediate frequency receive path used in a MIMO radar device according to an embodiment of the present invention;

[0052] Figure 8 Schematic diagram showing an exemplary frequency-dependent relationship of the amplitude at the receiver;

[0053] Figure 9 Flowchart showing a method for operating a MIMO radar device according to an embodiment of the present invention.

[0054] In all the figures, identical or functionally identical elements and devices are provided with the same reference numerals. Detailed Description

[0055] Figure 1 Schematic block diagram showing a MIMO radar device 1a having a plurality of transmit antennas 21 to 2n, where n represents a natural number greater than 1. The MIMO radar device 1a further includes a ramp generator 3a that generates a primary ramp. The ramp generator 3a generates a transmit ramp for each of the transmit antennas 21 to 2n based on the primary ramp. The time offset between two adjacent transmit ramps is less than the ramp duration of the transmit ramp. The transmit antennas 21 to 2n transmit the corresponding transmit ramps. The MIMO radar device 1a further includes a receiving device or receiving antenna 4a that receives the radar radiation transmitted and reflected by the object and then mixes the radar radiation with the primary ramp to generate and output a measurement signal.

[0056] The ramp generator 3a includes a fixed-frequency oscillator 31 that sets the frequency offset of the transmit ramps adjacent in time. The number of fixed-frequency oscillators corresponds to the number of transmit channels. The ramp generator 3a further has a switch 32 for adjusting the start and end times of the transmit ramps. The ramp generator 3a can generate the primary ramp in the baseband and then upmix it to the high-frequency range, or can directly generate the primary ramp in the high-frequency range.

[0057] The MIMO radar device 1a can be configured as a fast chirp radar system having independent range analysis processing and velocity analysis processing and having a receiving antenna 4a and a plurality of transmitting antennas 21 to 2n. However, according to other embodiments, different MIMO radar devices 1a with different numbers of receiving and transmitting antennas in particular can be involved, which use a frequency ramp as the transmitted signal.

[0058] The multiplexing method used by the MIMO radar device 1a can be understood as an extended scheme of the fast chirp method. First, the fast chirp method for the transmitting antennas will be described, and then it will be extended in a MIMO scheme by means of the multiplexing method according to the invention.

[0059] The radar signals (chirp signals) with increasing frequency are generated and transmitted sequentially by the transmitting device. The transmitted signals are reflected and received by objects in the environment. The received signals consist of superposed reflections that are time-shifted (and also frequency-shifted in the case of moving objects). The reflections are brought into the low-frequency range by mixing with the transmit ramp, in which the frequency of each reflection corresponds to the distance to the reflecting object. Subsequently, low-pass filtering is performed in order to suppress the reflections of distant objects (which are at a certain distance outside the radar sensor's field of view). The low-pass filtered analog signal is sampled by means of an analog-to-digital converter. This process is repeated for a plurality of successive ramps for measurements with independent range analysis processing and velocity analysis processing. Here, the range analysis processing is performed by frequency estimation within each ramp, while the velocity estimation is performed by analyzing the phase change process across the ramps.

[0060] The range analysis processing and the velocity analysis processing can be performed by means of a two-dimensional Fourier transform. The Fourier transform provides the range curve on each ramp, while the Fourier transform across the ramps provides the velocity curve. After the two-dimensional Fourier transform, a two-dimensional radar image is generated, where there is a local maximum for each target.

[0061] In the case where the MIMO radar device 1a is configured as a fast chirp radar, the radar signals are transmitted by a plurality of transmitting antennas 21 to 2n, whereby improved angle estimation can be achieved. Contrary to conventional time division multiplexing, the transmit ramps or frequency ramps of different transmit channels or transmitting antennas 21 to 2n are only slightly offset in time and extend parallel to each other. The time offset between adjacent transmit ramps is not greater than the ramp duration of the transmit ramp, as is the case in conventional TDM.

[0062] Preferably, the time offset between adjacent transmission ramps is greater than the time delay of the farthest target, i.e., the time delay at the maximum distance of the system design (English: maximum time-of-flight). Since the maximum time delay in a typical automotive radar is significantly less than the ramp duration commonly used, this scheme allows the transmission ramps to be arranged closer to each other in time.

[0063] Figure 2 Fig. shows a schematic block diagram of the MIMO radar device 1b. The ramp generator 3b includes a primary ramp generator 31, a high-frequency modulator 33, a switch 32, and a frequency shift device 34. The ramp generator 31, especially a fixed-frequency oscillator, generates a primary ramp. After being processed by the high-frequency modulator 33, a first part of the primary ramp is selected by means of the switch 32 and transmitted as a first transmission ramp by the first transmission antenna 21. The primary ramp is shifted at least by the maximum beat frequency by the frequency shift device 34 and transmitted as a second transmission ramp by the second transmission antenna 22. According to other embodiments, other transmission antennas can be provided.

[0064] The transmitted radar radiation is reflected at the target 5 and received by the receiving antenna 41 of the receiving device 4b. The receiving device 4b also includes a mixing device 42, an analog / digital converter 43, and an analysis and processing device 44. The mixing device 42 mixes the received signal with the primary ramp provided by the high-frequency modulator 33. The signal thus obtained is converted into a digital signal by the analog / digital converter 43 and analyzed and processed by the analysis and processing device 44.

[0065] Figure 3 Fig. shows a schematic illustration of the primary ramp P for four transmission channels and the resulting transmission ramps R1 to R4. Generally, N transmission ramps can be provided for N transmission channels, where N is arbitrary. Therefore, the present invention is not limited to a specific number. In an exemplary embodiment, first, a primary ramp P with a bandwidth B + N Tx Δf TX is generated, where B is the bandwidth of the transmission ramps R1 to R4 of each transmission channel, N Tx is the number of transmission antennas 21 to 2n, and Δf TX is the desired frequency interval between channels. It should be designed to be greater than the maximum possible beat frequency. In Figure 3 , an exemplary embodiment based on 4 transmission ramps (N Tx = 4) according to the present invention is shown. For the duration of the primary ramp, it is obtained from the following:

[0066] T genesis = T chirp + (N Tx - 1)·Δf Tx·T chirp / B

[0067] where T chirp is the duration of the transmission ramps R1 to R4.

[0068] Thus, the transmission ramps R1 to R4 of the different transmission channels 21 to 2n can be generated from a single, slightly longer primary ramp P. For this purpose, each transmission channel 21 to 2n requires a mixer, i.e., a frequency shift device 34, which frequency shifts the corresponding segments of the primary ramp P by a multiple of Δf TX . Generation of the primary ramp P can be carried out in the baseband, such that the subsequently generated transmission ramps R1 to R4 in the baseband are then upmixed, but it is also possible to directly generate the primary ramp P in the high-frequency range.

[0069] Furthermore, instead of multiples, the frequency shift can also be arbitrarily selected, especially with regard to favorable properties with respect to intermodulation products.

[0070] Figure 4 Fig. shows a schematic block diagram of a MIMO radar device 1c according to another embodiment of the invention. Here, first a single primary ramp P is generated with the aid of a primary ramp generator 31, for example with the aid of a phase-locked loop (PLL) or a direct digital frequency synthesizer (DDS) and with the aid of an oscillator 35. This can already take place in the target frequency band, or at a lower frequency with subsequent frequency multiplication. Then, in the transmission branch with n channels, this primary ramp P is frequency-shifted and switched on for a defined period of time. This is achieved with the aid of an I-Q modulator 36 and a control signal:

[0071] I i = cos(2π·Δf TX,i t),

[0072] Q i = sin(2π·Δf TX,i t).

[0073] where, in an implementation with equidistant frequency offsets, Δf TX,i = [0, Δf TX , 2Δf TX , 3Δf TX ,...]. The advantage of this division is that the transmission ramps for the different transmission channels 21 to 2n are the same and only an additional fixed frequency is individually modulated for each transmission channel 21 to 2n. A single primary ramp P is generated, from which the transmission ramps or signals of the transmission antennas 21 to 2n are generated. Compared to modulation to an additional modulation of a fixed frequency Δf TX, Modulation achieved through ramp generation usually has a much higher bandwidth, so fixed-frequency modulation is much simpler (i.e., the lower frequency and the best choice of frequency for I-Q signal generation) so as not to generate any unwanted secondary emissions in an implementation using, for example, a DDS. The phase noise of the signals of different transmission channels 21 to 2n is also largely the same because the transmission signals are generated by the same primary ramp P.

[0074] Thus, for four transmission channels 21 to 2n, for example, four different frequency offsets are generated:

[0075] f TX1 =f Genesis (t)+1·Δf TX ,

[0076] f TX2 =f Genesis (t)+2·Δf TX ,

[0077] f TX3 =f Genesis (t)+4·Δf TX ,

[0078] f TX4 =f Genesis (t)+5·Δf TX .

[0079] Here, a frequency shift of 3·Δf TX is avoided, which will be elaborated in detail below.

[0080] Receiving antennas 411 to 41m and a mixing device or an I-Q modulator 42 are also provided.

[0081] Figure 5 A schematic diagram of the time (t)-frequency (f) diagram of the primary ramp P (i.e., f Genesis (t)) and the generated transmission ramps f TX1 to f TX4 is shown. For example, the start time t TX4 and the end time t start,4 of the fourth transmission ramp f stop,4 are illustrated.

[0082] In addition, it can be provided that the transmission frequency f TX1 is generated by the primary ramp P without additional modulation, but the advantages of heterodyne radars are lost, in which there is no direct mixing to the baseband in the receiver, but to an intermediate frequency.

[0083] In principle, the transmission frequency can be freely selected, i.e., as long as there is no beat frequency overlap in the receiving channel, that is, the frequency interval between the transmission frequencies is large enough, the transmission frequencies do not have to be combined with the frequency grid Δf TX Combined.

[0084] An advantageous design is that the frequency offset is selected such that beat frequency overlap caused by strong harmonics is also avoided.

[0085] This results in the start time of the transmission ramp being t start,1 ...t start,4 and the end time being t stop,1 ...t stop,4 . In order to be able to set the start time and the end time, a switch 33 is installed in the transmission branch, and with the aid of this switch, the high-frequency signals at the transmission antennas TX1 to TX4 can be switched on and off.

[0086] In principle, the switch 32 can also be integrated with the modulator or the output stage (Endstufe) in order to achieve optimal isolation, for example by cutting off the fixed-frequency modulation signal.

[0087] As in Figure 3 or Figure 5 , the transmission signal can be generated from the primary ramp P by positive or negative frequency shift, i.e., above or below the primary ramp P.

[0088] In the receiving device 4, the demodulation of the received signal is carried out by mixing with the primary ramp P. This results in the received signals of all transmission channels appearing in the baseband in the form of frequency division multiplexing. In the case of an equidistant design, the frequency offset between the channels is equal to nΔf TX , where n represents the index of the transmission channel. This enables the signals of all transmission channels to be detected with the aid of a correspondingly designed receiving path and a fast analog / digital converter. The signals can then be advantageously analyzed and processed with the aid of Fourier transform. Alternatively, the received channels generated by different transmission channels 21 to 2n can be digitally filtered, demodulated, and processed individually.

[0089] In Figure 6 a schematic diagram showing the qualitative spectrum of the received signal is shown. The amplitude A at the receiver output is shown, which is shifted in frequency f due to the different signals of the different transmission antennas 21 to 2n. The frequency difference between the primary ramp and the received signal decreases with the signal propagation time because the closer the object is, the closer the signal is to the transmitted transmission frequency. The frequency difference decreases with a greater distance and thus a longer signal propagation time. For example, at a distance of zero, the offset frequency If TX1 is obtained, and as the distance increases, a decreasing intermediate frequency is obtained, and according to the radar equation, a lower amplitude A is obtained. In Figure 6in which, offset frequencies If are plotted for i = 1 to 4 and some multiples TXi Optionally, the offset frequency 3·Δf is avoided TX since it often occurs in actual circuits and it is generally difficult to suppress said harmonics.

[0090] For this purpose Figure 7 A schematic diagram of an intermediate frequency reception path is shown, which has a mixer 42, a low-pass filter 45 and an analog-to-digital converter 43. In such an implementation of the reception path having a second mixing stage, amplitude correction of the distance-dependent reception amplitude is achieved by means of the low-pass filter 45, and the second mixing stage is used to convert the intermediate frequency signal into the DC range.

[0091] Here, the low-pass filter 45 connected upstream of the A-D converter can also be integrated into the analog-to-digital converter 43 and, for example, combined with the anti-aliasing filter there.

[0092] Figure 8 The correlation between the amplitude A and the frequency f at the receiver is shown. The course 11 of the digital anti-aliasing filter, the course 12 of the analog low-pass filter and the course 10 of the reception spectrum based on the transmitting antenna are shown.

[0093] Figure 9 A flow chart of a method for operating a MIMO radar device is shown.

[0094] In a first method step S1, a primary ramp is generated.

[0095] In method step S2, transmit ramps are generated for each of the transmit antennas 21 to 2n, wherein the time offset of temporally adjacent transmit ramps is less than the ramp duration of the transmit ramps.

[0096] In another method step S3, the transmit ramps are transmitted via the transmit antennas.

[0097] In method step S4, the reflected radar radiation transmitted as a transmit ramp via the transmit antennas is received and the radar radiation is mixed with the primary ramp in order to generate and output a measurement signal.

Claims

1. A MIMO radar device (1a; 1b; 1c), the MIMO radar device having: a plurality of transmitting antennas (21 - 2n) for transmitting radar radiation; and Ramp generators (3a; 3b; 3c), which are configured to generate a primary ramp (P), wherein, the ramp generator (3a; 3b; 3c) is further configured to generate respective transmission ramps (R1 - R4) for each transmitting antenna (21 - 2n) with a corresponding frequency shift based on the primary ramp (P); wherein the transmitting antennas (21 - 2n) are configured to transmit respective transmission ramps (R1 - R4), wherein the time offset between temporally adjacent transmission ramps is less than the ramp duration of the transmission ramps, wherein the MIMO radar device (1a; 1b; 1c) further has receiving means (4a; 4b) configured to receive the transmitted and reflected radar radiation and mix the radar radiation with the primary ramp (P) to generate and output a measurement signal.

2. The MIMO radar device (1a; 1b; 1c) according to claim 1, wherein, The ramp generator (3a; 3b; 3c) is configured to generate transmission ramps that have the same center frequency and have a time offset.

3. The MIMO radar device (1a; 1b; 1c) according to any one of claims 1 to 2, wherein, The ramp generator (3a; 3b; 3c) is configured to generate transmission ramps (R1 - R4) that are non - equidistant in time or frequency - shifted by frequency shifting.

4. The MIMO radar device (1a; 1b; 1c) according to any one of claims 1 to 2, wherein, The ramp generator (3a; 3b; 3c) is configured to generate temporally equidistant transmission ramps by equidistant frequency shifting.

5. The MIMO radar device (1a; 1b; 1c) according to any one of the above claims, wherein, The ramp generator (3a; 3b; 3c) is configured to generate the transmission ramps (R1 - R4) as a time - offset portion of the primary ramp (P).

6. The MIMO radar device (1a; 1b; 1c) according to any one of the above claims, wherein, The ramp generator (3a; 3b; 3c) is configured to separately mix each transmission channel assigned to a respective transmitting antenna (21 - 2n) into the baseband and sample the transmission channel.

7. The MIMO radar device (1a; 1b; 1c) according to any one of the above claims, wherein, The ramp generator (3a; 3b; 3c) is further configured to generate the transmission ramps (R1 - R4) from the primary ramp by frequency shifting to a higher or lower frequency.

8. The MIMO radar device (1a; 1b; 1c) according to any one of the above claims, wherein, The ramp generator (3a; 3b; 3c) is further configured to generate one of the transmission ramps (R1 - R4) as a portion of the primary ramp without frequency shift.

9. The MIMO radar device (1a; 1b; 1c) according to any one of the above claims, wherein, The ramp generator (3a; 3b; 3c) is further configured to generate a plurality of primary ramps (P) that are temporally successive to each other and to generate corresponding transmission ramps for the transmitting antennas (21 - 21n).

10. A method for operating a MIMO radar device (1a; 1b; 1c), wherein, The MIMO radar device (1a; 1b; 1c) has a plurality of transmitting antennas (21 - 2n), and the method has the following steps: generating (S1) a primary ramp (P); generating (S2) transmission ramps (R1 - R4) for each transmitting antenna (21 - 2n) with a corresponding frequency shift; and transmitting (S3) the transmission ramps (R1 - R4) through the transmitting antennas (21 - 2n), wherein the time offset between temporally adjacent transmission ramps is less than the ramp duration of the transmission ramps, wherein the MIMO radar device (1a; 1b; 1c) further has receiving means (4a; 4b), wherein the method has the following steps: Receive the transmitted and reflected radar radiation and mix the radar radiation with the primary ramp (P) in order to generate and output a measurement signal.

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