A new radar moving target simulation method and equipment

Abstract

The present invention discloses a new radar moving target simulation method and device, which is different from the prior art mainly in that the instantaneous frequency of the signal is obtained by the instantaneous frequency measurement technology in the signal processing, the phase compensation factor is constructed by using the instantaneous frequency value, and the phase compensation factor is multiplied with the signal to complete the FIFO residual distance modulation. The method of the present invention enables the radar simulator to achieve millimeter-level distance stepping, and ensures that the phase of the transmitted signal remains continuous, thereby achieving an ideal simulation of the target velocity spectrum.

Description

Technical Field

[0001] The invention relates to a radar target simulation method and equipment based on DRFM, belonging to the field of radar testing. Background Art

[0002] In the field of automotive radar testing, automotive radar simulators based on fiber-optic delay technology can only achieve a distance step of 2 to 3 cm due to the limitations of the production process. And automotive radar simulators based on digital DRFM can only achieve a minimum distance step of 3 cm (corresponding to 5G sampling rate) due to the limitations of the ADC sampling rate. For these two simulators, at the moment of distance jump, the distance step amount is much larger than the wavelength, resulting in signal phase discontinuity, which ultimately causes target velocity spectrum distortion.

[0003] In the field of military radar simulation, linear frequency modulation signals based on pulse modulation are commonly used signals for military radars. At the moment of distance jump, the FPGA's FIFO delay distance step is much larger than the wavelength, resulting in signal phase discontinuity, which ultimately causes target velocity spectrum distortion.

[0004] The distortion of the velocity spectrum first manifests itself in the main lobe of the target, where the peak value will be reduced, directly leading to inaccurate target RCS simulation. In the application of synthetic aperture radar imaging, it directly causes inaccurate grayscale values ​​of the target image, affecting the quality of image simulation. Secondly, the side lobes deteriorate and rise as a whole, causing the side lobes of large targets to drown out small targets, affecting the radar's multi-target detection performance. Summary of the invention

[0005] According to the present invention, the DRFM technology is still used, and the following beneficial effects can be achieved only through digital signal processing:

[0006] 1. Enable the radar simulator to achieve millimeter-level distance stepping and ensure the phase continuity of the transmitted signal to achieve ideal simulation of the target velocity spectrum.

[0007] 2. It is not necessary to know the radar waveform information. It can adapt to most existing automotive radar waveforms, whether it is CW or a combination of stepped frequency and FMCW signals with multiple frequency modulation slopes, or a DDMA waveform used for MIMO. As long as it is a waveform that uses phase or frequency for ranging, it can adapt. At the same time, it can adapt to non-pure pulse delay ranging radars in military use.

[0008] 3. Since the compensated FIFO distance residual is expressed using fixed-point data and the decimal point position is defined by oneself, high precision can be achieved very easily, making the distance stepping amount much lower than the centimeter level of conventional digital FIFO, and easily achieving millimeter or even micron level distance stepping without any additional cost.

[0009] The present invention proposes a new radar moving target simulation method, wherein the method comprises: obtaining a frequency measurement value f[n] of an input signal x[n], and calculating a phase compensation factor y[n] in real time according to the frequency measurement value f[n], the formula is as follows

[0010]

[0011] Among them, j is an imaginary number, π is the circumference of a circle, and R Δ The distance R simulated by FIFO can be subtracted from the target distance R to be simulated. FIFO , c is the speed of light, n is the discrete time sequence number, and f[n] is the frequency measurement value of the signal. The target high-precision distance modulation is completed by aligning y[n] with the input signal x[n] in time and multiplying them.

[0012] Preferably, the signal may be an intermediate frequency signal, the method may include analog-to-digital conversion, and the frequency measurement value f[n] may be obtained by continuously and real-time instantaneous frequency measurement processing of the intermediate frequency signal after the analog-to-digital conversion, or may be given by the radar through an external voltage signal.

[0013] Preferably, the instantaneous frequency measurement process can be performed by a phase difference method.

[0014] Preferably, the method may further include: before obtaining the frequency measurement value f[n] of the signal, improving the signal-to-noise ratio of the signal by using channelization or other filtering techniques.

[0015] Preferably, the method may further include: performing image frequency suppression filtering when performing analog-to-digital conversion on a single-channel real signal.

[0016] The present invention also proposes a new radar moving target simulation device, wherein the device implements the radar target simulation method as described above.

[0017] According to the present invention, without knowing the radar emission waveform, the DRFM method can be used to complete the simulation of the ideal moving point target and simultaneously complete the distance stepping simulation at the millimeter level or even below the millimeter level. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a principle block diagram of the prior art;

[0019] Figure 2 It is a principle block diagram of the method of the present invention;

[0020] Figure 3 Schematic diagram of the compensation distance of the present invention.

[0021] Figure 4: Block diagram of the 77GHz band radar target simulator system. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0023] The embodiment of the method of the present invention is as follows:

[0024] According to the present invention, a new radar moving target simulation method is proposed, which can selectively retain the hardware and software framework of the existing DRFM simulator. Figure 1 Shown is a functional block diagram of the prior art DRFM simulator. Figure 2 FIG. 1 is a block diagram of the principle of the method of the present invention. Figure 2 The difference from the existing technical features is mainly reflected in the signal processing steps that include a residual distance compensation process for FIFO distance jumps. The processing steps are as follows: first, the instantaneous frequency is measured continuously in real time, and a phase compensation factor y[n] is constructed according to the frequency measurement result f[n], and then the phase compensation factor y[n] is used to compensate for the inherent delay of the system.

[0025] The multi-target simulation process of the prior art is as follows: the receiving antenna obtains the radar transmission signal, and the intermediate frequency signal (which can be a real signal or a complex signal) is obtained through the down-conversion module, and then enters the FPGA after being collected by the ADC. If it is a real signal, it is necessary to obtain the IQ complex signal x[n] after image frequency suppression filtering. If two ADCs are used to implement IQ sampling, the complex signal x[n] is directly obtained. The complex signal is then divided into multiple modulation branches, each of which modulates the distance and Doppler information of a target respectively. Finally, the parallel modulation branches of all targets are superimposed together, output to the up-conversion module through the DAC, and then radiated to the radar by the transmitting antenna to complete the multi-target simulation.

[0026] According to the present invention, the ADC data is collected in two paths, one of which is subjected to image frequency suppression filtering to obtain x[n]. If it is a complex signal, image frequency suppression filtering is not required, and x[n] is directly obtained; before x[n] is divided into multiple branches for target information modulation, a multiplication operation of inherent delay compensation is first performed, that is, a complex multiplication operation of x[n] and a phase compensation factor y[n] is performed. The calculation formula of the phase compensation factor y[n] is as follows:

[0027]

[0028] Among them, j is an imaginary number, π is the circumference of a circle, and R Δ The distance R simulated by FIFO can be subtracted from the target distance R to be simulated. FIFO, c is the speed of light, n is the discrete time serial number, corresponding to the number of FPGA operation clocks, and f[n] is the frequency value of the intermediate frequency signal measured in real time by the instantaneous frequency measurement module after the ADC. The target high-precision distance modulation is completed by aligning y[n] with the input signal x[n] in time and multiplying them, making the intermediate frequency signal phase continuous.

[0029] The applicable conditions of the embodiment of the method of the present invention are described below.

[0030] Since the method of the present invention measures the frequency of the signal in real time, calculates the phase compensation factor in real time, and realizes the compensation of the fixed delay of the system in real time, it works for radar signal waveforms that use frequency and phase to measure distance, including the following waveforms: frequency modulation continuous wave (FMCW), frequency shift keying FSK, point frequency continuous wave, fast sweep sawtooth wave, multiple frequency shift keying (MFSK), double group sawtooth wave, and any combination of waveforms in time, and is adaptable to the parameters of the above various waveforms, for example, for various FMCW signals with variable periods and variable frequency modulation slopes, and FSK signals with variable frequencies f1 and f2, and MFSK signals with various parameters, etc., the method of the present invention is applicable. For military radars, as long as the frequency modulation method is used in the pulse for ranging, the method of the present invention is applicable.

[0031] The feasibility of the method of the present invention is analyzed below.

[0032] The single-frequency CW waveform emitted by the radar can be expressed as: s(t) = e j2πft , where f is the signal frequency.

[0033] Assuming that the motion trajectory of the point target is uniform linear motion, the starting distance is R0, and the motion speed is v, its radial trajectory equation can be expressed as: R = R0 + vt

[0034] The round trip delay of the corresponding electromagnetic wave can be expressed as: τ(t) = 2R / c

[0035] The echo signal received by the radar can be expressed as: r(t) = s(t-τ(t)) = e j2πf(t-τ(t))

[0036] The radar transmit waveform s(t) and the receive waveform r(t) are mixed to obtain the intermediate frequency signal as follows

[0037]

[0038] Here, * represents the conjugation operation.

[0039] R is the ideal simulated target motion trajectory, R FIFO is the target motion trajectory generated by FIFO, R Δis the distance that needs to be compensated, and the three satisfy the formula R Δ =RR FIFO The relationship among the three is expressed as Figure 3 .

[0040] Target trajectory R under FIFO control FIFO It is a distance jump, and the distance simulation error is R in the figure Δ The calculation formula is as follows:

[0041]

[0042] mod() represents the remainder operation.

[0043] The following is the formula for the radar baseband signal generated by the simulator.

[0044] for Figure 1 In the traditional simulator algorithm structure shown in FIG, FIFO processing is performed at the intermediate frequency instead of at the radio frequency. Here, it is first assumed that the FIFO can achieve infinitesimal steps. The baseband echo obtained after the simulated signal is mixed by the radar is

[0045]

[0046] Where f is the instantaneous frequency of the RF signal.

[0047] where f IF is the instantaneous frequency of the FIFO intermediate frequency signal.

[0048] This is equivalent to equation (1). The first term is generated by the ideal FIFO, and the second term is generated by Doppler modulation. Unfortunately, the real FIFO cannot achieve infinitesimal continuous changes in distance, but follows Figure 3 R FIFO The distance changes. Therefore, the baseband echo formula in the actual system is:

[0049]

[0050] The first term is generated by FIFO processing, which will cause velocity spectrum distortion, and the second term is generated by Doppler modulation. In order to solve the velocity spectrum distortion problem, the structure of the new algorithm is as follows: Figure 4 As shown, the baseband echo formula of the new algorithm is as follows:

[0051]

[0052] Compared with formula (3), there is an additional intermediate term It is this term that makes it consistent with formula (1). The important point is: the intermediate frequency f IF It is obtained continuously through the method of instantaneous frequency measurement.

[0053] The new algorithm is processed point by point in real time in the FPGA. At the moment of phase compensation, it is necessary to add some delay alignment and the commonly used methods to keep the data rate consistent, which will not be repeated here.

[0054] Although the above formula is derived according to a single-point frequency signal, according to the formula content and algorithm structure, even if the frequency of the transmitted signal changes, since the compensation amount changes in real time with the change of frequency, it is applicable to common automotive radar waveforms, such as CW, FMCW, FSK, MFSK, DDM waveforms, etc., and military pulse linear frequency modulation signals.

[0055] Device embodiment 1 of the present invention: 24 GHz frequency band radar target simulator.

[0056] The block diagram of the 24GHz frequency band radar target simulator system is as follows: Figure 3 As shown. The device of the present invention includes: an antenna subsystem, a microwave subsystem and a signal processing subsystem. The antenna subsystem includes a receiving antenna and a transmitting antenna. The microwave subsystem includes a signal receiving module, a signal transmitting module and a frequency synthesis module. The signal processing subsystem can be one or more signal processing boards, and the devices included are mainly: high-speed ADC, FPGA, high-speed DAC. The FPGA in the signal processing subsystem completes all the steps of the method of the present invention, including an image frequency suppression filter module, an instantaneous frequency measurement module, a phase compensation factor calculation, a compensation multiplication module, as well as FIFO delay, Doppler modulation, modulation information calculation module, display and control module, etc. The display and control module mainly completes the communication with the user interface. The working process of the 24GHz frequency band radar target simulator device is as follows.

[0057] The receiving antenna of the 24GHz band radar target simulator device receives the RF signal of the 24GHz band, and after down-conversion, converts the signal to the intermediate frequency range of 100-450MHz, with an instantaneous bandwidth of 350MHz. The ADC module converts the intermediate frequency analog signal into a digital signal after 1GSPS sampling. The digital signal is divided into two paths. One path is converted into 4 parallel orthogonal signals after image suppression filtering. The data rate of each path is 250MSPS, and the sum of the 4 paths is x[n]; the other path is subjected to instantaneous frequency measurement to obtain the intermediate frequency instantaneous frequency measurement value f of the signal. IF[n]. Instantaneous frequency measurement can use a low-latency phase differential method to measure the frequency, and then filter it to improve the frequency measurement accuracy. It can also use channelization technology to first improve the signal-to-noise ratio, then use the phase differential method to measure the frequency, and finally perform smoothing filtering to improve the frequency measurement accuracy. In x[n], multiple branches are divided to perform target FIFO delay, which is traditional distance modulation, and then the phase compensation of the signal is performed to complete the distance modulation of the FIFO residual, that is, x[n] is multiplied by a phase compensation factor y[n]. The calculation formula of the phase compensation factor y[n] is as follows:

[0058]

[0059] Among them, j is an imaginary number, π is the circumference of a circle, ΔR is the distance value corresponding to the inherent delay of the DRFM simulator system, in meters, c is the speed of light, in meters per second, and n is the discrete time sequence number, corresponding to the number of FPGA operation clocks. Finally, the phase compensation factor y[n] is multiplied by x[n] to complete the compensation of the residual distance of the FIFO distance jump. The processing delays of the instantaneous frequency measurement branch and the image frequency suppression filter branch are inconsistent. The delay can be controlled through the FPGA to make its impact negligible. The signal after phase compensation is then Doppler modulated, that is, complex multiplication The final digital modulation signal for each target is generated, and the multiple modulation signals are superimposed together and sent to the DAC to be converted into an intermediate frequency analog signal, and finally up-converted and radiated by the transmitting antenna.

[0060] Device Example 2 of the Invention: 77 GHz Frequency Band 4 GHz Instantaneous Bandwidth Radar Target Simulator

[0061] The receiving antenna of the device receives the RF signal in the 77GHz frequency band, and after orthogonal down-conversion, the signal is converted to an IQ complex signal in the intermediate frequency range of -2GHz to 2GHz, with an instantaneous bandwidth of 4GHz. The up and down conversion local oscillator can be set arbitrarily in the range of 76GHz to 81GHz to achieve full frequency band coverage of 76GHz to 81GHz. After two-channel IQ ADC sampling with a sampling rate of 5GSPS per channel, the orthogonal intermediate frequency analog signal is converted into an orthogonal digital signal. The orthogonal digital signal is then divided into two paths. One path is converted into 20 parallel orthogonal signals x[n] through serial-to-parallel conversion, with a data rate of 250MSPS for each path; the other path is subjected to instantaneous frequency measurement to obtain the instantaneous frequency measurement value f[n] of the signal. Subsequent processing is similar to that of the 24GHz radar target simulator. The difference is that since the intermediate frequency of the baseband signal is zero, the Doppler modulated complex multiplied signal is where f c For the carrier frequency.

[0062] In summary, the present invention provides a new radar moving target simulation method and device. The above are only some embodiments of the present invention and are not intended to limit the protection scope of the present invention. In fact, the present invention has no restrictions on the frequency band and bandwidth of the radar. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A new DRFM radar moving target simulation method, characterized by: The method comprises: obtaining a frequency measurement value f[n] of an input signal x[n], and calculating a phase compensation factor y[n] in real time according to the frequency measurement value f[n], as follows: Among them, j is an imaginary number, π is the ratio of circumference to diameter, and R Δ The distance R simulated by FIFO can be subtracted from the target distance R to be simulated. FIFO , c is the speed of light, n is the discrete time sequence number, and f[n] is the instantaneous frequency measurement value of the signal. The target high-precision distance modulation is completed by aligning y[n] with the input signal x[n] in time and multiplying them together.

2. A new DRFM radar moving target simulation device, characterized in that: The device implements the radar target simulation method according to claim 1.

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