Radar system and method for operating a radar system

Abstract

A radar system comprises a global reference oscillator which is designed to produce a global reference signal, and comprises a plurality of radar devices which are coupled to the global reference oscillator. At least one of the radar devices comprises a local reference oscillator which is designed to produce a local reference signal. At least one of the radar devices comprises a synchronization unit which is designed to actuate the local reference oscillator in order to synchronize the local reference oscillator with the global reference oscillator using the global reference signal.

Description

[0001] Description

[0002] title

[0003] Radar system and method for operating a radar system

[0004] The present invention relates to a radar system and a method for operating a radar system.

[0005] State of the art

[0006] A radar sensor emits a signal that is reflected by objects in the radar channel. In monostatic mode, the reflected signal is received by the same radar sensor and evaluated to determine the range, speed, and angle of the radar target relative to the radar sensor. In bistatic mode, the reflected radar signal can also be received by a second, spatially separated radar sensor.

[0007] The actual distance or angle to the radar target can be calculated based on the known distance between the radar sensors. If the system is to operate coherently, i.e., with a fixed phase relationship between the two radar sensors, the transmitted signals must be synchronized. This can be achieved by physically distributing a common local oscillator (LO) signal.

[0008] Without such LO signal distribution, the transmitted signals from the radar sensors are neither temporally nor phase-correlated. When generating signals using a variable oscillator and a sweep phase-locked loop (PLL), the starting times of the ramps, such as in frequency-modulated continuous wave (FMCW) radar, are also not precisely unambiguous.

[0009] The timing error of the frequency ramps and the sampling times of the analog-to-digital converters in the receiver and the uncorrelated phase noise in bistatic measurements thus limit the performance of the system, for example with regard to the range.

[0010] From WO 2017 / 118621 A1 a method is known in which the phase reference is to be restored from the bistatic radar signals by means of signal processing.

[0011] Disclosure of the invention

[0012] The invention provides a radar system and a method for operating a radar system having the features of the independent patent claims.

[0013] Preferred embodiments are the subject of the respective subclaims.

[0014] According to a first aspect, the invention relates to a radar system comprising a global reference oscillator configured to generate a global reference signal, and comprising a plurality of radar devices coupled to the global reference oscillator. At least one of the radar devices comprises a local reference oscillator configured to generate a local reference signal. At least one of the radar devices comprises a synchronization device configured to control the local reference oscillator in order to synchronize the local reference oscillator with the global reference oscillator using the global reference signal.

[0015] According to a second aspect, the invention relates to a method for operating a radar system having a plurality of radar devices, wherein at least one of the radar devices has a local reference oscillator configured to generate a local reference signal. A global reference signal is generated by a global reference oscillator. The local reference oscillator of the at least one radar device is synchronized with the global reference oscillator using the global reference signal.

[0016] Advantages of the invention In order to operate a cooperative radar system, ie a network with several radar devices, the radar devices must be coupled or synchronized with each other.

[0017] To avoid synchronization using dedicated lines for transmitting clock, trigger and local oscillator (LO) signals and at the same time to maintain good performance despite uncorrelated phase noise, the local reference oscillators are synchronized with a global reference oscillator using a global reference signal.

[0018] The individual radar devices are designed in such a way that, when used in the cooperative radar system, a simpler synchronization of the radar devices is possible without LO signal distribution by means of additional synchronization and LO lines or additional algorithms.

[0019] To synchronize radar devices as simply as possible, the clocks of all local signal-generating or signal-processing components of the radar devices, e.g., transmitters, receivers, analog-to-digital converters, or digital signal processors, can be derived from the local reference signal. This makes it sufficient to synchronize the local reference signal with the global reference signal.

[0020] In the context of this invention, “synchronization” can be understood as an adjustment in phase and / or amplitude.

[0021] According to one embodiment of the radar system, the global reference oscillator is arranged externally to the radar devices of the radar system. In this embodiment, each radar device can have a local reference oscillator, which is synchronized with the external global reference oscillator. Advantageously, all radar devices can thus be constructed identically. According to a further embodiment of the radar system, the global reference oscillator is a local reference oscillator of one of the radar devices. This excellent radar device does not require a synchronization device. All other radar devices can have a synchronization device to synchronize their respective local reference oscillators with the global reference oscillator, i.e., the local reference oscillator of the excellent radar device. Advantageously, no separate global reference oscillator is required in this embodiment.

[0022] According to a further embodiment of the radar system, at least one of the radar devices comprises a transmitter-receiver device and a high-frequency local oscillator. The high-frequency local oscillator generates a high-frequency local oscillator signal using the local reference signal and outputs the high-frequency local oscillator signal to the transmitter-receiver device. By coupling the high-frequency local oscillator to the local reference oscillator, the transmitter-receiver devices of the radar devices are also synchronized.

[0023] According to a further embodiment of the radar system, the high-frequency local oscillator is operated at a constant frequency, i.e., with a fixed-frequency carrier, for example, using a phase-locked loop. The high-frequency local oscillator signal of the reference oscillator can also be divided into temporal segments, each with a different frequency that remains constant within the temporal segment. This allows for low or at least partially coherent phase noise to be achieved.

[0024] According to a further embodiment of the radar system, the transmitter-receiver device comprises an IQ mixer. The high-frequency local oscillator is configured to output the high-frequency local oscillator signal to the IQ mixer.

[0025] According to a further embodiment of the radar system, the transmitter-receiver device comprises a chirp generator for generating a chirp signal, wherein the chirp generator comprises an IQ mixer and a digital-to-analog converter or a direct digital synthesis (DDS) device. The high-frequency local oscillator outputs the high-frequency local oscillator signal to the IQ mixer. The digital-to-analog converter or the DDS device controls the IQ mixer using the local reference signal. The DDS device or the digital-to-analog converter has two channels for this purpose, one for the I path and one for the Q path. This allows chirps, including frequency and phase offsets, to be modulated onto the RF carrier.

[0026] According to a further embodiment of the radar system, the high-frequency local oscillator comprises a phase-locked loop device and an IQ mixer. The IQ mixer is arranged in a feedback path of the phase-locked loop device. The local reference oscillator outputs the local reference signal to the phase-locked loop device. The IQ mixer is controlled as a function of the local reference signal. Digital-to-analog converters or a DDS device can be provided for this purpose, which use the reference signal as a clock source and control the IQ mixer. This allows a frequency detuning to be imposed.

[0027] According to a further embodiment of the radar system, the local reference oscillator generates a comparison time signal. The synchronization device compares the comparison time signal with a reference time signal generated from the global reference signal in order to synchronize the local reference oscillator with the global reference oscillator. The local reference oscillator can derive the comparison time signal, for example, using a counter unit or a time-to-digital converter (TDC).

[0028] According to a further embodiment of the radar system, the local reference oscillator generates a comparison frequency signal. The synchronization device compares the comparison frequency signal with a reference frequency signal generated from the global reference signal in order to synchronize the local reference oscillator with the global reference oscillator. The comparison frequency signal can be obtained, for example, by frequency division. By the synchronization device synchronizing the frequency of the local reference signal to a constant frequency, it can be achieved that the phase noise is very low or at least partially coherent. The oscillator can only be influenced within a small range by the synchronization device. This allows the design of the local reference oscillator with high stability and low phase noise. The modulation of the radar signal is generated digitally in a subsequent step.

[0029] Further advantages, features and details of the invention will become apparent from the following description, in which various embodiments are described in detail with reference to the drawing.

[0030] Short description of the drawings

[0031] They show:

[0032] Figure 1 shows a radar system according to an embodiment of the invention;

[0033] Figure 2 shows a reception path of the radar system illustrated in Figure 1;

[0034] Figure 3 shows a radar system according to a further embodiment of the

[0035] Invention;

[0036] Figure 4 shows a radar system according to a further embodiment of the invention;

[0037] Figure 5 shows a radar system according to a further embodiment of the invention; and

[0038] Figure 6 shows a flowchart of a method for operating a radar system according to one embodiment of the invention. In all figures, identical or functionally identical elements and devices are provided with the same reference numerals. The numbering of method steps serves the purpose of clarity and is generally not intended to imply a specific chronological order. In particular, multiple method steps can be performed simultaneously.

[0039] Description of the embodiments

[0040] Figure 1 shows a radar system 1a. The radar system 1a has a global reference oscillator 2, which generates a global reference signal. The global reference signal can include a reference time or a reference frequency.

[0041] The global reference signal is provided to a plurality of radar devices 3a-1 to 3a-n. However, the invention is not limited to a specific number of radar devices 3a-1 to 3a-n.

[0042] Each of the radar devices 3a-1 to 3a-n is coupled to the global reference oscillator 2 via a respective synchronization interface 6 for receiving the global reference signal.

[0043] A control device 5 serves to control a local reference oscillator 4 of the corresponding radar device 3a-1 to 3a-n in order to synchronize the local reference oscillator 4 with the global reference oscillator 2. The control device 5 and the synchronization interface 6 thus form a synchronization device.

[0044] The reference oscillator 4 generates a local reference signal. The control device 5 generates a control signal for the local reference oscillator 4 by comparing the global reference signal with the local reference signal.

[0045] The local reference oscillator 4 is thereby influenced so that it runs synchronously with the global reference oscillator 2. Since all radar devices 3a-1 to 3a-n have access to the global reference oscillator 2, the local reference signals are synchronous.

[0046] The local reference oscillator 4 can, for example, generate a reference signal which has a substantially constant frequency at least within predetermined time periods.

[0047] In the following, only one radar device 3a-1 is described, while the other radar devices 3a-2 to 3a-n may be identical or substantially identical in design.

[0048] The radar device 3a-1 has a transmitter-receiver device 9a and a high-frequency local oscillator 7a.

[0049] The high-frequency local oscillator 7a has a high-frequency source 8, which generates a high-frequency local oscillator signal using the local reference signal. The high-frequency source 8 can, in particular, be a fixed-frequency or temporarily fixed-frequency (e.g., in the case of step-like signals) high-frequency source, for example, at 20 GHz.

[0050] The high-frequency local oscillator 7a outputs the high-frequency local oscillator signal to the transmitter-receiver device 9a. Optionally, the radar device 3a-1 can have a plurality of transmitter-receiver devices 9a, with the high-frequency local oscillator 7a providing the high-frequency local oscillator signal to the transmitter-receiver devices via lines 16.

[0051] An exemplary transmitter-receiver device 9a is described below. The transmitter-receiver device 9a includes a frequency multiplier 10 for transforming the high-frequency local oscillator signal into the desired frequency band, e.g., at 80 GHz.

[0052] The transmitter-receiver device 9a further comprises a transmission path 20a and a reception path 19a. The transmission path 20a comprises a splitter 11, which splits the transformed high-frequency local oscillator signal, the resulting signals being phase-shifted by 90 degrees. Furthermore, the transmission path 20a comprises an IQ mixer 12. The signal generated by the IQ mixer 12 is amplified by an amplifier 13 and transmitted via antenna elements (not shown).

[0053] In further embodiments, a regular mixer is used instead of the IQ mixer 12.

[0054] The transmitter-receiver device 9a further comprises a first digital-to-analog converter 14 and a second digital-to-analog converter 15, which receive the local reference signal provided by the local reference oscillator 4, use the local reference signal or a signal derived therefrom as a sampling clock, and accordingly control the I-path or the Q-path of the I-Q mixer 12. Since the local reference oscillator 4 is coupled to the global reference oscillator 2, the transmission signals are also synchronous.

[0055] Figure 2 shows the reception path 19a of the radar system 1a illustrated in Figure 1. The reception path 19a also includes a splitter 21, an I / Q mixer 22, and an amplifier 23. Furthermore, the reception path includes analog-to-digital converters 51 and 52 coupled to the I path and Q path, respectively.

[0056] Optionally, the transmitter-receiver device 9a comprises additional transmission paths 20a and reception paths 19a, which can be identical or different. The high-frequency local oscillator signal transformed by the frequency multiplier 10 is provided to the additional transmission paths 20a and reception paths 19a via corresponding lines 17.

[0057] While both transmission paths 20a and reception paths 19a are shown in Figure 1, in further embodiments either only transmission paths 20a or reception paths 19a may be present.

[0058] Furthermore, the radar device 3a-1 may comprise other digital components 18, such as analog-to-digital converters, which are also provided with the local reference signal generated by the local reference oscillator 4, and use the local reference signal or a signal derived therefrom as a clock.

[0059] According to one embodiment of the radar system 1a illustrated in Figure 1, the local reference oscillator 4 generates a comparison time signal, for example, using a counter unit or a time-to-digital converter (TDC). The control device 5 of the synchronization device 5, 6 compares the comparison time signal with a reference time signal generated from the global reference signal in order to synchronize the local reference oscillator 4 with the global reference oscillator 2.

[0060] According to a further embodiment of the radar system 1a illustrated in Figure 1, the local reference oscillator 4 generates a comparison frequency signal. The control device 5 of the synchronization device 5, 6 compares the comparison frequency signal with a reference frequency signal generated from the global reference signal in order to synchronize the local reference oscillator 4 with the global reference oscillator 2.

[0061] In the embodiment of the radar system 1a shown in Figure 1, the global reference oscillator 2 is arranged externally to the radar devices 3a-1 to 3a-n of the radar system 1a. However, it can also be provided that the global reference oscillator 2 is a local reference oscillator 4 of one of the radar devices 3a-1 to 3a-n. This radar device 3a-1 to 3a-n then does not require a synchronization device 5, 6.

[0062] Because the carrier has a fixed frequency, which is coupled to the global reference oscillator 2 via the local reference oscillator 4, the start phase is static. Since the modulation is generated by digital-to-analog converters 14, 15 or DDS devices 31, the start phase of the modulations can be fixed and is also static.

[0063] The fixed-frequency RF carrier architecture allows signal generation to be optimized for low phase noise.

[0064] Figure 3 shows another radar system 1b. The radar system 1b differs from the radar system 1a shown in Figures 1 and 2 in that, instead of the first digital-to-analog converter 14 and the second digital-to-analog converter 15, a direct digital synthesis (DDS) device 31 is provided. The DDS device has two channels, one for the I path and one for the Q path. Otherwise, the radar system 1b can correspond to the radar system 1a shown in Figures 1 and 2, so the description of the other components need not be repeated here.

[0065] Figure 4 shows a further radar system 1c, which differs from the radar systems 1a, 1b shown in Figures 1 to 3 in the structure of the transmitter-receiver device 9c.

[0066] The transmitter-receiver device 9c accordingly has a chirp generator 41 for generating a chirp signal, wherein the chirp generator 41 has a splitter 42 which, as described above, splits the received signal into two signals shifted by 90° in phase with respect to one another.

[0067] Furthermore, the chirp generator 41 comprises an IQ mixer 43 and a DDS device 45. The DDS device 45 receives the local reference signal from the local reference oscillator 4 and controls the IQ mixer 43 using the local reference signal.

[0068] Optionally, the chirp generator 41 further comprises a high-pass filter or a band-pass filter 44 to filter the signal output from the IQ mixer 43.

[0069] The transmission path 20c comprises a modulator 46 and an amplifier 13, wherein the modulator 46 modulates the signal received from the chirp generator 41 and the amplifier 13 amplifies the signal output by the modulator 46 and outputs it to antenna elements (not shown) for transmitting the radar radiation.

[0070] Modulator 46 can be, for example, a digital phase shifter and / or variable gain amplifier (VGA). Modulator 46 in transmit path 20c allows additional phase modulation and / or amplitude modulation of transmit paths 20c relative to each other and can also be coupled to local reference oscillator 4.

[0071] The receive path 19c can be configured analogously to the transmit path 20c. The receive path 19c can correspond to a conventional receive path. It can be implemented either as a real receive path or as an IQ receive path.

[0072] In this embodiment, chirps including frequency offsets can be modulated onto the RF carrier using the chirp generator 41.

[0073] Figure 5 shows another radar system 1d. The radar system 1d differs from the radar systems 1a to 1c shown in Figures 1 to 4 in the structure of the high-frequency local oscillator 7d.

[0074] The high-frequency local oscillator 7d has a phase-locked loop device 51 and an I / Q mixer 54. The phase-locked loop device 51 generates an output signal as a function of the local reference signal, which is provided to a high-frequency source 52 that generates the high-frequency local oscillator signal.

[0075] The IQ mixer 54 is arranged in a feedback path of the phase-locked loop device 51. For this purpose, the high-frequency local oscillator signal generated by the high-frequency source 52 is first transformed into a desired frequency band by a frequency divider 56 and then divided by a splitter 55, with the resulting signals being phase-shifted by 90 degrees. The two signals are provided to the IQ mixer 54. The output signal of the IQ mixer 54 is provided to the phase-locked loop device 51.

[0076] The local reference oscillator 4 provides the local reference signal to a digital-to-analog converter or DDS device 53, with an output signal being provided to the IQ mixer 54.

[0077] The IQ mixer 54 in the feedback path of the phase-locked loop device 51 can impose a frequency detuning by means of the digital-to-analog converter or the DDS device 53. Since the digital-to-analog converter or the DDS device 53 is also coupled to the local reference oscillator 4, this source is also synchronous to other components.

[0078] In the radar systems 1a to 1d described above, the respective configuration can ensure that the high-frequency local oscillator signal has low or (partially) coherent phase noise (e.g., through the use of fixed-frequency oscillators), and that a stable state of the relative phases of different radar devices is achieved, particularly within a measurement, e.g., even during a frequency hop. This is particularly advantageous for a bistatic measurement with distributed radar devices.

[0079] The embodiments shown can also be combined. In particular, the high-frequency local oscillator 7d shown in Figure 5 can also be used in one of the radar systems 1a to 1c of Figures 1 to 4. The high-frequency local oscillator 7d can replace a ramp generator comprising the frequency multiplier 10, the splitter 42, the IQ mixer 43, the bandpass filter 44, and the DDS device 45.

[0080] Figure 6 shows a flowchart of a method for operating a radar system with a plurality of radar devices. In particular, the radar system can be one of the radar systems 1a to 1d described above. At least one of the radar devices has a local reference oscillator configured to generate a local reference signal.

[0081] In a first step S1, a global reference signal is generated by a global reference oscillator. The global reference oscillator can be arranged externally to the radar devices of the radar system. The global reference oscillator can also be a local reference oscillator of one of the radar devices. In a second step S2, the local reference oscillator of the at least one radar device is synchronized with the global reference oscillator using the global reference signal.

[0082] At least one of the radar devices can comprise a transmitter-receiver device and a high-frequency local oscillator. The high-frequency local oscillator generates a high-frequency local oscillator signal using the local reference signal and outputs the high-frequency local oscillator signal to the transmitter-receiver device. The high-frequency local oscillator can be an oscillator operating at a (at least partially) constant frequency.

[0083] The transmitter-receiver device may further comprise an IQ mixer for each transmit / receive channel, which is coupled to the high-frequency local oscillator.

[0084] Furthermore, the transmitter-receiver device can have a chirp generator for generating a chirp signal, wherein the chirp generator has an IQ mixer and a DDS device. The high-frequency local oscillator outputs the high-frequency local oscillator signal to the IQ mixer. The DDS device controls the IQ mixer using the local reference signal.

[0085] The high-frequency local oscillator may also include a phase-locked loop device and an IQ mixer. The IQ mixer is arranged in a feedback path of the phase-locked loop device. The local reference oscillator outputs the local reference signal to the phase-locked loop device and to the digital-to-analog converters or DDS devices that drive the IQ mixer.

[0086] The local reference oscillator can generate a comparison time signal or a comparison frequency signal. The synchronization device compares the comparison time signal or the comparison frequency signal with a reference time signal or reference frequency signal generated from the global reference signal in order to synchronize the local reference oscillator with the global reference oscillator.

Claims

Claims 1 . Radar system (1 a to 1 d) comprising: a global reference oscillator (2) configured to generate a global reference signal; and a plurality of radar devices (3a-1 to 3a-n; 3b-1 to 3b-n; 3c-1 to 3c-n; 3d-1 to 3d-n) coupled to the global reference oscillator (2); wherein at least one of the radar devices (3a-1 to 3a-n; 3b-1 to 3b-n; 3c-1 to 3c-n; 3d-1 to 3d-n) has a local reference oscillator (4) configured to generate a local reference signal; and wherein at least one of the radar devices (3a-1 to 3a-n; 3b-1 to 3b-n; 3c-1 to 3c-n; 3d-1 to 3d-n) has a synchronization device (5, 6) which is designed to control the local reference oscillator (4) in order to synchronize the local reference oscillator (4) with the global reference oscillator (2) using the global reference signal.

2. Radar system (1a to 1d) according to claim 1, wherein at least one of the radar devices (3a-1 to 3a-n; 3b-1 to 3b-n; 3c-1 to 3c-n; 3d-1 to 3d-n) comprises a transmitter-receiver device (9a to 9c) and a high-frequency local oscillator (7a; 7d); wherein the high-frequency local oscillator (7a; 7d) is designed to generate a high-frequency local oscillator signal using the local reference signal and to output it to the transmitter-receiver device (9a to 9c).

3. Radar system (1 a to 1 d) according to claim 2, wherein the high-frequency local oscillator (7a; 7d) is a frequency converter which operates at an at least partially constant Frequency driven oscillator is 4. Radar system (1 a; 1 b) according to claim 2 or 3, wherein the transmitter-receiver device (9 a; 9 b) comprises an IQ mixer (12), and wherein the high-frequency local oscillator (7 a; 7 d) is designed to output the high-frequency local oscillator signal to the IQ mixer (12).

5. Radar system (1c) according to claim 2 or 3, wherein the transmitter-receiver device (9c) has a chirp generator (41) for generating a chirp signal, wherein the chirp generator (41) has an IQ mixer (43) and digital-to-analog converters or a direct digital synthesis, DDS, device (45); wherein the high-frequency local oscillator (7a; 7d) is designed to output the high-frequency local oscillator signal to the IQ mixer (43); and wherein the digital-to-analog converters or the DDS device (45) are designed to control the IQ mixer (43) using the local reference signal.

6. Radar system (1d) according to one of the preceding claims, wherein the high-frequency local oscillator (7d) comprises a phase-locked loop device (51) and an IQ mixer (54); wherein the transmitter-receiver device (9c) comprises digital-to-analog converters or a direct digital synthesis, DDS, device (45); wherein the IQ mixer (54) is arranged in a feedback path of the phase-locked loop device (51); and wherein the local reference oscillator (4) is designed to output the local reference signal to the phase-locked loop device (51) and the digital-to-analog converters or the DDS device (45), wherein output signals of the digital-to-analog converters or the DDS device (45) control the I -Q mixer (54).

7. Radar system (1a to 1d) according to one of the preceding claims, wherein the local reference oscillator (4) is configured to generate a comparison time signal; and wherein the synchronization device (5, 6) is configured to compare the comparison time signal with a reference time signal generated from the global reference signal in order to synchronize the local reference oscillator (4) with the global reference oscillator (2).

8. Radar system (1a to 1d) according to one of the preceding claims, wherein the local reference oscillator (4) is configured to generate a comparison frequency signal; and wherein the synchronization device (5, 6) is configured to compare the comparison frequency signal with a reference frequency signal generated from the global reference signal in order to synchronize the local reference oscillator (4) with the global reference oscillator (2).

9. Radar system (1 a to 1 d) according to one of the preceding claims, wherein the local reference oscillator (4) is an oscillator operated at a frequency that is at least partially constant.

10. A method for operating a radar system (1 a to 1 d) with a plurality of radar devices (3a-1 to 3a-n; 3b-1 to 3b-n; 3c-1 to 3d-n), wherein at least one of the radar devices (3a-1 to 3a-n; 3b-1 to 3b-n; 3c-1 to 3c-n; 3d-1 to 3d-n) has a local reference oscillator (4) which is designed to generate a local reference signal, comprising the steps: Generating (S1) a global reference signal by a global reference oscillator (2); and Synchronizing (S2) the local reference oscillator (4) of the at least one radar device (3a-1 to 3a-n; 3b-1 to 3b-n; 3c-1 to 3c-n; 3d-1 to 3d-n) with the global reference oscillator (2) using the global reference signal.

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