CN112859057A

CN112859057A - MIMO radar device and method for operating a MIMO radar device

Info

Publication number: CN112859057A
Application number: CN202011362972.7A
Authority: CN
Inventors: G·哈科拜恩; J·哈施
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-11-27
Filing date: 2020-11-27
Publication date: 2021-05-28
Also published as: DE102019218337A1

Abstract

The present invention relates to a MIMO radar apparatus having a plurality of transmitting 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 by means of a respective frequency shift on the basis of the primary ramp, wherein the transmit antenna is configured to transmit the respective transmit ramp. The invention also relates to a method for operating a MIMO radar apparatus.

Description

MIMO radar device and method for operating a MIMO radar device

Technical Field

The present invention relates to a Multiple-Input-Multiple-Output (MIMO) radar device and a method for operating a MIMO radar device.

Background

In order to provide a safety function and a comfort function, a radar system is used in a motor vehicle to measure a distance, a relative speed, and an angle of an object (e.g., a vehicle) and an obstacle. A Multiple Input Multiple Output (MIMO) apparatus having a plurality of transmission antennas and a plurality of reception antennas is known. This enables particularly accurate angle measurement, since the antenna aperture (i.e. the antenna area) which is important for angle measurement is actually enlarged (virtualll). The transmit antennas transmit signals independently of each other, the signals being separated in the receive channel. Due to the different distances from the transmitting antennas to the corresponding receiving antennas, a substantial aperture enlargement is obtained. In terms of computation, it is possible to proceed as if there is only one transmit antenna, wherein the number of receive antennas is multiplied, thereby resulting in a larger antenna aperture.

The signals may be separated in the frequency domain by a frequency-division multiplexing (FDM) method, in which different transmit antennas occupy different frequency ranges at the same point in time. Thereby reducing the available bandwidth per transmit channel. Since the distance separation capability of the radar system is proportional to its bandwidth, the distance separation capability is reduced.

The signals can also be separated in the time domain, where the antennas transmit sequentially in a time-division multiplexing (TDM) method. However, measuring time is increased by sequential measurements. Furthermore, during the increased measurement time, the object may have moved significantly, which reduces the accuracy of the measurement. Furthermore, the time interval between two sequential measurements of the respective transmit antenna increases, which may result in a decrease of the maximum uniquely measurable speed range.

The above implementation is independent of the modulation method used. Typical transmission frequencies are 24GHz or 77GHz, with the maximum bandwidth that can be occupied being up to 5GHz, but usually significantly lower. A typical bandwidth is about 0.5 GHz.

Modern radar systems for motor vehicles usually use FMCW modulation (english: Frequency Modulated Continuous Wave). Where multiple linear frequency ramps with the same or different slopes are experienced (durchlaufen). The frequency 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, an additive or subtractive component is included that passes through the doppler frequency, which is proportional to the relative velocity. In order to separate the distance information and the velocity information of a plurality of targets, a relatively complex method is required in which the results of different slopes are considered for use with the results of earlier measurement cycles.

Newer systems rely on FMCW modulation with a faster ramp, i.e., fast chirp modulation, whereby the doppler shift within the ramp can be ignored. The obtained distance information is to a large extent unique and unambiguous; the doppler shift can then be determined by observing the temporal development of the phase of the complex range signal. The distance determination and the velocity determination are made independently of one another, wherein a two-dimensional fourier transformation is generally used.

An exemplary radar sensor for a motor vehicle is known from DE 102016221947 a 1.

In order to extend the fast chirp radar system in the MIMO method to improve angle estimation, it is necessary to separate signals of transmission antennas. This is usually achieved by the TDM method, but reduces the ambiguity (Eindeutigkeit) of the doppler shift due to undersampling (Unterabtastung).

Current FMCW radar systems and fast chirp radar systems always broadcast (fast) a single frequency ramp and therefore do not produce a ramp extending in parallel. The available time-frequency resources are therefore only conditionally utilized.

Disclosure of Invention

The invention provides a MIMO radar apparatus having the features of the invention and a method for operating a MIMO radar apparatus having the features of the invention.

Preferred embodiments are the subject of corresponding further embodiments.

According to a first aspect, the invention relates to a MIMO radar device having a plurality of transmit antennas for emitting 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 with a respective frequency shift for each transmit antenna on the basis of the primary ramp. The transmit antennas are configured to transmit corresponding transmit ramps.

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, a transmit ramp is generated for each transmit antenna by means of a corresponding frequency shift. Transmitting the transmit ramp through a transmit antenna.

THE ADVANTAGES OF THE PRESENT INVENTION

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

At the same time, the overhead required for generating the transmit ramp and demodulating the radar signal at the receiver can be avoided by using a primary ramp or "genesis ramp". Therefore, a pure time division multiplexing method or a frequency division multiplexing method is not involved. The limitations of the conventional TDM scheme and FDM scheme can be avoided. A large number of transmit antennas may be used in MIMO operation without significantly degrading range resolution compared to conventional FDM.

The main advantages of the proposed MIMO radar concept are: multiple transmit antennas are used without drastically reducing the uniquely measurable speed range here, as is the case in conventional TDM schemes. In order to operate the transmitting antenna by means of a conventional TDM scheme without reducing the speed range which can be measured uniquely, a significantly steeper slope must be selected. The resulting beat frequency (Beatfrequenz) increases with the slope of the ramp, requiring a faster analog-to-digital converter and, in general, producing an inordinate amount of data. Furthermore, the ratio of ramp duration to time of flight deteriorates excessively, which leads to a reduction in the effective bandwidth and signal-to-noise ratio. Thus, the MIMO radar concept according to the present invention is much more efficient than the conventional TDM scheme.

An additional advantage of the MIMO radar concept described above is the coherence between the signals of the transmit channels. Under conventional TDM, a time offset is generated between measurements of the transmission channel. If the radar target moves during the measurement, it results in a velocity dependent phase component that affects the MIMO based angle estimation. To prevent this, the phase component must be compensated, which can only be done with limited quality. Similarly, distance-dependent phase components are generated in FDM because the transmission channels have different carrier frequencies. For most practical designs, the angle estimation may therefore be affected. The MIMO radar concept according to the invention uses transmit ramps that preferably have the same carrier frequency and a significantly lower time offset. For moving objects, therefore, a significantly smaller phase shift results between the signals of the transmit antennas, which can be ignored or compensated for significantly more easily.

Compared to existing radar systems, MIMO radar devices can achieve significant performance advantages. The receiver circuit can be realized particularly efficiently when it is realized as a highly integrated circuit by: an individualized receive path with an analog-to-digital converter is obtained for the intermediate frequency receive path for each transmit signal.

A temporally moving ramp may be generated by a special association between the time offset at which the primary ramp starts and the fixed frequency shift. It is very advantageous to use a transmit ramp without frequency offset and a minimum time offset, since this enables maximum coherence between the transmit channels.

A particular implementation of the MIMO radar apparatus according to the invention allows designing the transmit carrier and intermodulation products (intermodulation products) by individually selecting the frequency shifts of the individual transmit channels, whereby a received signal with high spectral purity can be generated despite the use of non-ideal modulators in the transmit branches.

Compared to TDM, the MIMO radar apparatus according to the present invention enables slower ramps and lower beat frequencies, and longer times to reach the target, thus achieving better signal-to-noise ratio and better bandwidth utilization, i.e. a more favorable ratio of time-of-flight to ramp duration.

According to one embodiment of the MIMO radar device, the time offset of temporally adjacent transmit ramps is smaller than the ramp duration of the transmit ramps. Therefore, the transmit ramp is slightly offset.

According to one embodiment of the MIMO radar device, the ramp generator is designed to generate transmission ramps that are not equidistant in time or slightly offset in frequency by a frequency shift.

According to one embodiment of the MIMO radar device, the ramp generator is designed to generate temporally equidistant transmit ramps by equidistant frequency shifts.

According to one embodiment of the MIMO radar device, the ramp generator is designed to generate transmit ramps having the same center frequency. This can be achieved, for example, by special setting of the frequency shift of the transmit ramp, which is proportional to the time shift of the transmit ramp. In particular transmission ramps with non-equidistant frequency shifts can be generated.

According to one embodiment of the MIMO radar device, the ramp generator is designed to generate the transmit ramp as a time-offset part of the primary ramp. The frequency shift is thus coupled with the time shift.

According to one embodiment of the MIMO radar device, the ramp generator is designed to generate transmit ramps with equidistant frequency shifts.

According to one embodiment of the MIMO radar device, the ramp generator is designed to generate transmission ramps that are equidistant in time. It may also be provided that the ramp generator generates transmission ramps which are not equidistant in time.

According to one embodiment, the MIMO radar device is based on any method with a linear ramp, for example, the FMCW method or the fast chirp method.

According to one embodiment, the MIMO radar device can determine the distance, speed and/or angle of a plurality of reflecting objects by receiving and evaluating the transmission signals reflected at the objects.

According to one embodiment, the MIMO radar device has a receiving device which is designed to receive the transmitted and reflected radar radiation and to mix it with a primary ramp in order to generate and output a measurement signal. Thus, the resulting beat frequency is produced offset in time and frequency. The signals of the different transmit antennas can therefore be separated uniquely and unambiguously by means of a frequency offset. The signals of all transmit antennas can be effectively detected and sampled by means of the receive channel of each receive antenna by: each transmit channel uses an analog-to-digital converter (ADC) with a correspondingly higher data rate. Alternatively, each transmit channel may be demodulated separately at the receiver, for which purpose an own path is provided for each transmit channel in each receive channel.

According to one embodiment of the MIMO radar device, the receiver arrangement also has an analog/digital converter for sampling the measurement signals, wherein the analog/digital converter samples the signals of all transmission channels.

According to one embodiment of the MIMO radar device, the transmit ramp has the same frequency progression between a predefined minimum frequency and a predefined maximum frequency. In particular, it may relate to linear frequency ramps extending in parallel.

According to one embodiment, the MIMO radar device has a fixed-frequency oscillator, which is designed to set the frequency offset of temporally adjacent transmit ramps. The ramp generator may comprise, inter alia, such a fixed frequency oscillator. The transmit ramp of the transmit antenna may be generated from the primary ramp by means of a fixed frequency oscillator and a switch. Here, the use of a fixed frequency oscillator for generating the frequency offset is particularly advantageous, since the fixed frequency oscillator can be implemented easily and with low phase noise. MIMO radar devices are particularly advantageous in terms of hardware overhead and phase noise.

According to one embodiment of the MIMO radar device, the ramp generator also has a switch in order to set the start and end times of the transmit ramp.

According to one embodiment of the MIMO radar device, the ramp generator is designed to generate a primary ramp in the high-frequency range.

According to one embodiment of the MIMO radar device, the ramp generator comprises an I-Q modulator which is designed to generate the signal ramp on the basis of the primary ramp.

According to one embodiment of the MIMO radar device, the ramp generator is also designed to generate a transmit ramp from the primary ramp by a frequency shift to a higher or lower frequency.

According to one embodiment of the MIMO radar device, the ramp generator is further designed to generate one of the transmission ramps as part of a primary ramp without a frequency shift.

According to one embodiment of the MIMO radar device, the ramp generator is also designed to generate a plurality of primary ramps one after the other in time and to generate corresponding transmit ramps for the transmit antennas. The generation of the transmit ramp may thus comprise a combination of a primary ramp based multiplexing with a known multiplexing method. For example, two transmit ramps may be generated from each primary ramp. In this way two further transmit ramps are generated by the next primary ramp. Thus, multiplexing is performed not only by means of beat frequencies but also by TDM.

According to one embodiment of the method for operating a MIMO radar system, the transmitted and reflected radar radiation is also received and mixed with a primary ramp in order to generate and output a measurement signal.

Drawings

The figures show:

fig. 1 shows a schematic block diagram of a MIMO radar apparatus according to an embodiment of the present invention;

fig. 2 shows a schematic block diagram of a MIMO radar apparatus according to another embodiment of the invention;

fig. 3 shows a schematic illustration of a primary ramp and the resulting transmit ramp;

fig. 4 shows a schematic block diagram of a MIMO radar apparatus according to another embodiment of the invention;

fig. 5 shows a schematic illustration of a time-frequency diagram of a primary ramp and a resulting transmit ramp;

FIG. 6 shows a schematic illustration of a qualitative spectrum of a received signal;

fig. 7 shows a schematic illustration of an intermediate frequency receive path for use in a MIMO radar apparatus according to an embodiment of the present invention;

FIG. 8 shows an exemplary frequency dependence of amplitude at a receiver;

fig. 9 shows a flow diagram of a method for operating a MIMO radar apparatus according to an embodiment of the invention.

Throughout the drawings, identical or functionally identical elements and devices are provided with the same reference numerals.

Detailed Description

Fig. 1 shows a schematic block diagram of a MIMO radar apparatus 1a having a plurality of transmission antennas 21 to 2n, where n denotes a natural number greater than 1. The MIMO radar apparatus 1a further includes a ramp generator 3a that generates a primary ramp. The ramp generator 3a generates one transmission ramp for each of the transmission 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 respective transmit ramps. The MIMO radar device 1a also comprises a receiving means or receiving antenna 4a which receives the transmitted radar radiation reflected on the object and then mixes it with the primary ramp in order to generate and output a measurement signal.

The ramp generator 3a includes a fixed frequency oscillator 31 which sets the frequency offset of temporally adjacent transmit ramps. The number of fixed frequency oscillators corresponds to the number of transmission channels. The ramp generator 3a also has a switch 32 to adjust the starting and ending times of the transmit ramp. The ramp generator 3a may generate the primary ramp in the baseband and then mix it up (hochmischen) into the high-frequency range, or may generate the primary ramp directly in the high-frequency range.

The MIMO radar apparatus 1a may be configured as a fast chirp radar system having independent distance analysis processing and velocity analysis processing and having a reception antenna 4a and a plurality of transmission antennas 21 to 2 n. However, according to other embodiments, it may relate to different MIMO radar apparatuses 1a, in particular with a different number of receive antennas and transmit antennas, which use a frequency ramp as the transmit signal.

The multiplexing method used by the MIMO radar apparatus 1a can be understood as an extension of the fast chirp method. Next, a fast chirp method for a transmission antenna is first described, and then extended in a MIMO scheme by a multiplexing method according to the present invention.

A radar signal (chirp signal) having a frequency at which an increase (step) is made is sequentially generated and transmitted by a transmitting device. The transmitted signal is reflected and received by objects in the environment. The received signal consists of temporally shifted (also frequency shifted in the case of moving objects), superimposed reflections. The reflections are brought into the low frequency range by mixing with a transmit ramp, where the frequency of each reflection corresponds to the distance to the object that made the reflection. Low pass filtering is then performed in order to suppress reflections of distant objects which are at a distance outside the field of view of the radar sensor. The low-pass filtered analog signal is sampled by means of an analog/digital converter. For measurements with independent distance and speed analysis processes, this procedure is repeated for a plurality of ramps one after the other. Here, the distance analysis process is performed by frequency estimation within each ramp, while the velocity estimation is performed by analyzing the phase change process across the ramps.

The distance analysis process and the velocity analysis process may be performed by means of two-dimensional fourier transform. The fourier transform provides a distance profile on each ramp, while the fourier transform provides a velocity profile across the ramps. After the two-dimensional fourier transformation, a two-dimensional radar image is produced, where there is a local maximum for each target.

In the case where the MIMO radar apparatus 1a is configured as a fast chirp radar, radar signals are transmitted by the plurality of transmission antennas 21 to 2n, whereby improved angle estimation can be achieved. In contrast to conventional time division multiplexing, the transmission ramps or frequency ramps of the different transmission channels or transmission antennas 21 to 2n are only slightly offset in time and extend in parallel. 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.

Preferably, the time offset between adjacent transmit ramps is greater than the time delay of the farthest target, i.e., the time delay at the maximum distance of the system design (in: maximum time-of-flight). Since the maximum time delay in a typical automotive radar is significantly less than the ramp duration that is usually used, this approach allows the transmit ramps to be arranged closer in time to one another.

Fig. 2 shows a schematic block diagram of the MIMO radar apparatus 1 b. The ramp generator 3b includes a primary ramp generator 31, a high-frequency modulator 33, a switch 32, and a frequency shift device 34. A ramp generator 31, in particular a fixed frequency oscillator, generates the primary ramp. After processing 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 further shifted by the frequency shifting means 34 at least by the maximum beat frequency and transmitted as a second transmission ramp by the second transmission antenna 22. According to other embodiments, other transmit antennas may be provided.

The transmitted radar radiation is reflected at the target 5 and received by the receiving antenna 41 of the receiving device 4 b. The receiving means 4b further comprise mixing means 42, an analog/digital converter 43 and analysis processing means 44. The mixing means 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 an analog/digital converter 43 and subjected to analysis processing by an analysis processing device 44.

Fig. 3 shows a schematic illustration of the primary ramp P for four transmit channels and the resulting transmit ramps R1 to R4. In general, N transmit ramps may be set for N transmit channels, where N is arbitrary. Therefore, the present invention is not limited to a specific number. In an exemplary embodiment, a bandwidth having a bandwidth of B + N is first generated_TxΔf_TXB is the bandwidth of the transmission ramps R1 to R4 of each transmission channel, N_TxIs the number of transmitting antennas 21 to 2n, and Δ f_TXIs the desired frequency spacing between channels. It should be designed to be larger than the maximum possible beat frequency. In fig. 3, a base on 4 transmit ramps (N) is exemplarily shown_Tx4) according to the invention. The duration for the primary ramp is given by:

T_genesis＝T_chirp+(N_Tx-1)·Δf_Tx·T_chirp/B

wherein, T_chirpIs the duration of the transmit ramps R1 through R4.

The transmission ramps R1 to R4 of the different transmission channels 21 to 2n can thus be generated by a single, slightly longer primary ramp P. For this purpose, a mixer, i.e. a frequency shifting device 34, is required for each transmission channel 21 to 2n, which mixer is to be used initiallyThe corresponding segment frequency shift Δ f of the step slope P_TXMultiples of (a). The generation of the primary ramp P can take place in the baseband, so that the transmit ramps R1 to R4 generated in the baseband are then highly mixed, but the primary ramp P can also be generated directly in the high-frequency range.

Furthermore, instead of the multiples, the frequency shifts can also be chosen arbitrarily, in particular with regard to the advantageous properties with regard to intermodulation products.

Fig. 4 shows a schematic block diagram of a MIMO radar apparatus 1c according to another embodiment of the present invention. In this case, a single primary ramp P is first generated by means of a primary ramp generator 31, for example by means of a phase-locked loop (PLL) or a direct digital frequency synthesizer (DDS), and by means of an oscillator 35. This may already occur in the target frequency band or at lower frequencies by means of a subsequent frequency multiplication. Then, in the transmission branch with n channels, the primary ramp P is shifted in frequency and switched on for a defined period of time (anschalten). This is achieved by means of the I-Q modulator 36 and the steering signal:

I_i＝cos(2π·Δf_TX,it),

Q_i＝sin(2π·Δf_TX,it).

wherein in an implementation with equidistant frequency offset Δ f_TX,i＝[0，Δf_TX，2Δf_TX，3Δf_TX，...]. The advantage of this division is that the transmit ramp for the different transmit channels 21 to 2n is identical and that only an additional fixed frequency is individually modulated for each transmit channel 21 to 2 n. A single primary ramp P is generated, from which the transmit ramps or signals of the transmit antennas 21 to 2n are generated. Compared with modulation

Additional modulation of a fixed frequency_TXThe modulation achieved by ramp generation usually has a much higher bandwidth and therefore the fixed frequency modulation is much simpler (i.e. the best choice of lower frequency and frequency generated by the I-Q signal) in order not to generate any unwanted secondary emissions in the implementation e.g. by means of DDS.The phase noise of the signals of the different transmission channels 21 to 2n is also largely the same, since the transmission signals are generated by the same primary ramp P.

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

f_TX1＝f_Genesis(t)+1·Δf_TX,

f_TX2＝f_Genesis(t)+2·Δf_TX,

f_TX3＝f_Genesis(t)+4·Δf_TX,

f_TX4＝f_Genesis(t)+5·Δf_TX.

here, 3. DELTA.f is avoided_TXAs will be explained in more detail below.

Receiving antennas 411 to 41m, mixing means or I-Q modulators 42 are also provided.

FIG. 5 shows the primary ramp P (i.e., f)_Genesis(t)) and the transmission ramp f generated thereby_TX1To f_TX4Schematic illustration of a time (t) -frequency (f) diagram of (a). For example, elucidating the fourth transmit ramp f_TX4At the start time t_start,4And an end time t_stop,4。

Furthermore, it can be provided that the transmission frequency f is generated by the primary ramp P without additional modulation_TX1But loses the advantages of heterodyne Radars (heterodyne-Radars) in which no direct mixing to baseband is done in the receiver, but to an intermediate frequency.

The transmission frequency can in principle be selected freely, i.e. as long as no beat overlap occurs in the receiving channel, i.e. the frequency spacing between the transmission frequencies is sufficiently large, the transmission frequency does not have to overlap the frequency grid Δ f_TXAnd (4) combining.

One advantageous configuration consists in: the frequency offset is selected such that beat frequency overlap due to strong harmonics is also avoided.

This results in the start of the transmit ramp being t_start,1...t_start,4And the end time is 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 transmit branch, by means of which the high-frequency signals at the transmit antennas TX1 to TX4 can be switched on and off.

In principle, the switch 32 may also be integrated with the modulator or output stage (Endstufe) in order to achieve an optimal isolation, for example by switching off the fixed frequency modulated signal.

As in fig. 3 or 5, the transmission signal may be generated from the primary ramp P by a positive or negative frequency shift, i.e. above or below the primary ramp P.

In the receiving means 4, the demodulation of the received signal is performed by mixing with the primary ramp P. This results in the reception signals of all transmission channels appearing in the baseband in the form of frequency division multiplexing. In the case of equidistant design, the frequency offset between the channels is equal to n Δ f_TXWhere n denotes an index of a transmission channel. This makes it possible to detect the signals of all transmission channels by means of correspondingly designed reception paths and fast analog/digital converters. The signal can then advantageously be processed by means of fourier transform analysis. Alternatively, the receive channels generated by the different transmit channels 21 to 2n may be digitally filtered, demodulated and processed separately.

A schematic illustration of the qualitative spectrum of the received signal is shown in fig. 6. The amplitude a at the receiver output is shown, which is shifted in frequency f due to the different signals of the different transmit antennas 21 to 2 n. The frequency difference between the primary ramp and the received signal decreases with signal propagation time because the closer an object is at a distance, the closer the signal is to the transmitted transmit frequency. The frequency difference decreases with greater distance and hence longer signal propagation time. For example, the offset frequency If is found at a distance of zero_TX1A decreasing intermediate frequency is obtained with increasing distance and a lower amplitude a is obtained according to the radar equation. In fig. 6, the offset frequency If is plotted for i-1 to 4 and some multiples_TXi. Optionally avoiding offset frequency 3 · Δ f_TXSince it is often present in practical circuits and it is often difficult to suppress the harmonics.

To this end, fig. 7 shows a schematic illustration of an intermediate frequency reception path with a mixer 42, a low-pass filter 45 and an analog/digital converter 43. In this implementation of the receiving path with a second mixing stage for converting the intermediate frequency signal into the DC range, an amplitude correction of the distance-dependent receiving amplitude is effected by means of the low-pass filter 45.

In this case, a low-pass filter 45 connected upstream of the a-D converter can also be integrated into the analog/digital converter 43 and, for example, be combined with an anti-aliasing filter there.

Fig. 8 shows the amplitude a at the receiver in relation to the frequency f. A variation process 11 of a digital anti-aliasing filter, a variation process 12 of an analog low-pass filter and a variation process 10 based on the reception spectrum of a transmitting antenna are shown.

Fig. 9 shows a flow chart of a method for operating a MIMO radar apparatus.

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

In method step S2, a transmission ramp is generated for each transmission antenna 21 to 2n, wherein the time offset of temporally adjacent transmission ramps is smaller than the ramp duration of the transmission ramp.

In a further method step S3, the transmit ramp is transmitted via a transmit antenna.

In method step S4, the reflected radar radiation emitted by the transmitting antenna as a transmitting ramp is received and mixed with the primary ramp in order to generate and output a measurement signal.

Claims

1. A MIMO radar apparatus (1 a; 1 b; 1c) having:

a plurality of transmit antennas (21-2n) for transmitting radar radiation; and

a ramp generator (3 a; 3 b; 3c) which is designed to generate a primary ramp (P), wherein the ramp generator (3 a; 3 b; 3c) is also designed to generate a respective transmission ramp (R1-R4) for each transmission antenna (21-2n) by means of a respective frequency shift on the basis of the primary ramp (P);

wherein the transmit antennas (21-2n) are configured to transmit respective transmit ramps (R1-R4).

2. The MIMO radar apparatus (1 a; 1 b; 1c) according to claim 1, further having a receiving device (4 a; 4b) configured to receive the transmitted and reflected radar radiation and to mix it with the primary ramp (P) in order to generate and output a measurement signal.

3. The MIMO radar apparatus (1 a; 1 b; 1c) according to claim 1 or 2, wherein the ramp generator (3 a; 3 b; 3c) is configured to generate a transmit ramp as follows: the transmit ramps have the same center frequency and have a time offset.

4. The MIMO radar apparatus (1 a; 1 b; 1c) according to any one of claims 1 to 3, wherein the ramp generator (3 a; 3 b; 3c) is configured to generate transmit ramps (R1-R4) that are not equidistant in time or shifted in frequency by a frequency shift.

5. The MIMO radar apparatus (1 a; 1 b; 1c) according to any one of claims 1 to 3, wherein the ramp generator (3 a; 3 b; 3c) is configured to generate temporally equidistant transmit ramps by equidistant frequency shifts.

6. The MIMO radar apparatus (1 a; 1 b; 1c) according to any one of the preceding claims, wherein the ramp generator (3 a; 3 b; 3c) is configured to generate the transmit ramp (R1-R4) as a time-shifted portion of the primary ramp (P).

7. The MIMO radar apparatus (1 a; 1 b; 1c) according to any of the preceding claims, wherein the ramp generator (3 a; 3 b; 3c) is configured to separately mix each transmit channel assigned to a respective transmit antenna (21-2n) into baseband and sample the transmit channel.

8. The MIMO radar apparatus (1 a; 1 b; 1c) according to any of the preceding claims, wherein the ramp generator (3 a; 3 b; 3c) is further configured to generate the transmit ramp (R1-R4) from the primary ramp by frequency shifting to a higher or lower frequency.

9. The MIMO radar apparatus (1 a; 1 b; 1c) according to any of the preceding claims, wherein the ramp generator (3 a; 3 b; 3c) is further configured to generate one of the transmit ramps (R1-R4) as part of a primary ramp without a frequency shift.

10. The MIMO radar apparatus (1 a; 1 b; 1c) according to any one of the preceding claims, wherein the ramp generator (3 a; 3 b; 3c) is further configured for generating a plurality of primary ramps (P) successive in time to each other and for generating respective transmit ramps for the transmit antennas (21-21 n).

11. A method for operating a MIMO radar device (1 a; 1 b; 1c), wherein the MIMO radar device (1 a; 1 b; 1c) has a plurality of transmit antennas (21-2n), has the following steps:

generating (S1) a primary ramp (P);

generating (S2) a transmit ramp (R1-R4) for each transmit antenna (21-2n) by means of a respective frequency shift; and is

Transmitting (S3) the transmit ramp (R1-R4) through the transmit antenna (21-2 n).