A radar signal processing method

Abstract

The present invention belongs to the field of radar signal processing technology, and specifically relates to a radar signal processing method, which adopts a broadband linear frequency modulation continuous wave as a transmitting signal, receives an echo signal from a detection target, and mixes the two to obtain a difference frequency signal. For the difference frequency signal, a compensation frequency item is determined by a preset analysis rule, and frequency compensation is performed to solve the problems of distance migration and parameter estimation accuracy reduction caused by the high-speed movement of the target. In addition, the corresponding compensation processing is completed in a linear manner in the digital domain, including the steps of calculating the compensation coefficient and clutter suppression. In addition, through simulation verification, the method can effectively correct the target distance unit under set parameters, such as a signal carrier frequency of 35GHz, a transmission bandwidth of 600MHz, etc., and significantly improve the radar's detection capability for high-speed targets.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing, and in particular relates to a radar signal processing method. Background Art

[0002] With the application of high-speed targets such as modern fighter jets, hypersonic aircraft, cruise missiles, high-speed submarines, satellites, space debris, etc., there is an urgent need for accurate detection of such high-speed targets.

[0003] An important development trend of radar target detection is to detect the position and motion state of high-speed targets more accurately, especially in the two dimensions of distance and speed. Traditional radar signal processing methods are usually based on narrowband signals. Due to bandwidth limitations, it is difficult to accurately distinguish multiple high-speed targets at close range, and it can no longer meet the needs of modern radars for high-speed target detection. Therefore, modern radars mostly use large-bandwidth signals to achieve high resolution of targets in the distance dimension, while further reducing the impact of surface clutter represented by ground clutter and sea clutter.

[0004] However, since the radar range resolution unit is small at this time, high-speed moving targets often cross one or more range units (i.e., range migration) during the coherent accumulation time. If targeted compensation is not performed, the target energy will be spread across multiple range units and cannot be effectively accumulated, thereby reducing the system's detection capability and parameter estimation accuracy for such targets. At the same time, traditional compensation methods usually require complex calculations, high requirements for computing resources and time, and are not suitable for real-time systems. Summary of the invention

[0005] The purpose of the present invention is to provide a radar signal processing method to solve the problem in the prior art that it is difficult for a radar based on a narrowband signal to perform range migration compensation and effective energy accumulation for a high-speed target in a real-time manner.

[0006] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0007] The present invention provides a radar signal processing method, the method comprising:

[0008] The radar sends a transmission signal to the detection target and receives an echo signal from the detection target;

[0009] Mixing the echo signal and the transmission signal to obtain a difference frequency signal, wherein the phase of the difference frequency signal is related to the distance and motion state of the detection target;

[0010] Determine the compensation frequency item of the difference frequency signal based on a preset analysis rule; wherein the compensation frequency item includes the compensation distance frequency, the distance velocity Doppler frequency and the frequency related to the number of snapshots, and the compensation frequency modulation item frequency;

[0011] According to the compensation frequency item, frequency compensation is performed on the digital signal obtained by pre-converting the difference frequency signal in the single echo snapshot;

[0012] Determine the distance and speed information of the detected target according to the compensated digital signal;

[0013] The step of performing frequency compensation on a digital signal obtained by converting the difference frequency signal in a single echo snapshot according to the compensation frequency term includes:

[0014] Determine the compensation coefficient according to the compensation frequency term and calculate the compensation distance frequency and range velocity Doppler frequency The frequency associated with the number of snapshots ;

[0015] And calculate the compensation frequency modulation term Frequency ;

[0016] The frequency and the frequency The compensation coefficient is set to filter and amplify the difference frequency signal in the single echo snapshot, and then perform A / D conversion to obtain a digital signal. In the digital domain, the digital signal is multiplied by the compensation coefficient to complete frequency compensation.

[0017] Furthermore, the transmission signal adopts a broadband linear frequency modulation continuous wave, including a signal amplitude , FM signal starting frequency , frequency modulation period , and the initial phase ; The echo signal contains the distance from the detection target to the radar , Speed ​​of Light , consider the influence of the receiving antenna and the coefficient of radio wave propagation attenuation .

[0018] Further, mixing the echo signal and the transmit signal to obtain a difference frequency signal includes:

[0019] The echo signal is mixed with the transmission signal by a mixer to obtain a difference frequency signal containing the distance and speed information of the detected target;

[0020] exist In a repetitive cycle, the phase of the difference frequency signal is recorded and analyzed to extract parameters related to the distance and motion state of the detected target, including radar parameters and detected target parameters.

[0021] Further, mixing the echo signal and the transmit signal to obtain a difference frequency signal further comprises:

[0022] (1) Calculated in The phase of the difference frequency signal within a repetition period , the expression is:

[0023] ;

[0024] in, For the The relative distance between the detected target and the radar during a repetition cycle;

[0025] (2) Calculate the phase frequency corresponding to the difference frequency signal , the expression is:

[0026] ,in ;

[0027] in, represents the Doppler frequency, represents the distance frequency, Indicates the range velocity Doppler frequency; Indicates frequency modulation item.

[0028] Further, the determining the compensation frequency term of the difference frequency signal based on a preset analysis rule includes:

[0029] According to the phase frequency of the difference frequency signal The relationship between radar parameters and detection target parameters is analyzed to identify the Doppler frequency, range frequency, range-speed Doppler frequency and compensation frequency term in the frequency modulation term.

[0030] Further, determining the distance and speed information of the detection target according to the compensated digital signal includes:

[0031] Perform spectrum analysis on the compensated digital signal to obtain a frequency domain signal;

[0032] According to the characteristics of the frequency domain signal, the distance and speed information of the detected target are extracted.

[0033] The beneficial effects of the present invention are:

[0034] The radar signal processing method provided by the present invention transmits a broadband linear frequency modulation continuous wave LFMCW, receives an echo signal, mixes the two, and then filters, amplifies, and A / D converts them into digital signals, and then compensates them. After compensation, the target is corrected in distance, which solves the problem of target energy diffusion and reduced distance accuracy in radar detection of high-speed targets, and the related processing is all linear operation, with high real-time performance, which improves the radar's detection capability of high-speed targets and parameter estimation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of a flow chart of a radar signal processing method provided in an embodiment of the present application;

[0036] Figure 2 A schematic diagram of another flow chart of a radar signal processing method provided in an embodiment of the present application;

[0037] Figure 3 It is a simulation diagram of a hypothetical signal before compensation in the simulation case part of the embodiment of the present application;

[0038] Figure 4 It is a simulation diagram of a hypothetical signal after compensation in the simulation case part of the embodiment of the present application;

[0039] Figure 5 It is a three-dimensional echo diagram in the simulation case part of the embodiment of the present application;

[0040] Figure 6 It is an echo distance diagram in the simulation case part of the embodiment of the present application;

[0041] Figure 7 This is a simulation diagram of uncompensated filtering in a part of multiple echoes in a simulation case of an embodiment of the present application;

[0042] Figure 8 This is a simulation diagram of filtering and compensation in multiple echoes in a simulation case of an embodiment of the present application;

[0043] Fig. 9 This is a simulation diagram of filtering and compensation in a single snapshot of a simulation case of an embodiment of the present application;

[0044] Fig.10 This is an enlarged view of the local simulation of filtering and compensation in a single snapshot of a simulation case of an embodiment of the present application. DETAILED DESCRIPTION

[0045] The present application is further described in detail below in conjunction with the accompanying drawings. It is necessary to point out here that the following specific implementation methods are only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Technical personnel in this field can make some non-essential improvements and adjustments to the present application based on the above application content.

[0046] Example 1

[0047] like Figure 1-2 As shown, this embodiment proposes a radar signal processing method, the method comprising the following steps:

[0048] S1. The radar sends a transmission signal to the detection target and receives an echo signal from the detection target;

[0049] S2, mixing the echo signal and the transmission signal to obtain a difference frequency signal, the phase of which is related to the distance and motion state of the detection target;

[0050] S3, determining the compensation frequency item of the difference frequency signal based on a preset analysis rule; wherein the compensation frequency item includes the compensation distance frequency, the distance velocity Doppler frequency and the frequency related to the number of snapshots, and the compensation frequency modulation item frequency;

[0051] S4, performing frequency compensation on the digital signal obtained by pre-converting the difference frequency signal in the single echo snapshot according to the compensation frequency item;

[0052] S5. Determine the distance and speed information of the detected target according to the compensated digital signal.

[0053] Specifically, the transmission signal uses a broadband linear frequency modulated continuous wave, including the signal amplitude , FM signal starting frequency , frequency modulation period , and the initial phase ; The echo signal contains the distance from the detected target to the radar , Speed ​​of Light , consider the influence of the receiving antenna and the coefficient of radio wave propagation attenuation .

[0054] In some embodiments, the radar uses a wideband linear frequency modulated continuous wave LFMCW as a transmitting signal, that is, ,in is the signal amplitude, is the starting frequency of the FM signal, is the frequency modulation period, is the initial phase, ;

[0055] Radar receives echo signal , the echo signal is the reflected wave received by the antenna after the transmitted signal encounters the target, then ,in, , is the distance from the target to the radar, is the speed of light, To consider the influence of the receiving antenna and the attenuation coefficient of radio wave propagation. The instantaneous phase of the signal is .

[0056] Specifically, the echo signal and the transmission signal are mixed to obtain a difference frequency signal, including:

[0057] (1) Use a mixer to mix the echo signal with the transmitted signal to obtain a difference frequency signal containing the distance and speed information of the detected target;

[0058] (2) In In a repetitive cycle, the phase of the difference frequency signal is recorded and analyzed to extract parameters related to the distance and motion state of the detected target, including radar parameters and detected target parameters.

[0059] In some embodiments, the received signal is mixed with the transmitted LFMCW signal to obtain a difference frequency signal, and the phase of the difference frequency signal is . It can be seen from this that when the time interval When is a constant, the signal is a sinusoidal signal, and its frequency is proportional to the time interval (i.e., the distance to the target ). When the target moves relative to the radar, the frequency of the difference frequency signal also changes. In order to detect the distance and speed information of the target, the above formula is processed as follows:

[0060] If the target moves radially relative to the radar, let the radial velocity be , the direction away from the radar is positive, then, where for The distance from the target to the radar at time . Therefore, the phase of the difference frequency signal can be modified to .

[0061] From the form, there are two independent variables, one is , and the other is , is any value greater than , and Restricted to The value is between Take a certain integer value to ensure. So the two expressions are consistent and there is no contradiction. When processing data, a repetition cycle of data is often used as a processing unit. Therefore, all the independent variables in the above formula are replaced by Indicates more appropriate.

[0062] Specifically, mixing the echo signal and the transmission signal to obtain a difference frequency signal also includes:

[0063] (1) Calculated in The phase of the difference frequency signal within a repetition period , the expression is:

[0064] ;

[0065] in, For the When the target is detected during a repetition cycle, the relative distance between the target and the radar is ;

[0066] (2) Calculate the phase frequency of the corresponding difference frequency signal , the expression is:

[0067] ,in ;

[0068] in, represents the Doppler frequency, represents the distance frequency, Indicates the range velocity Doppler frequency; Indicates frequency modulation item.

[0069] Specifically, the compensation frequency term of the difference frequency signal is determined based on a preset analysis rule, including: The relationship between radar parameters and detection target parameters is analyzed to identify the Doppler frequency, range frequency, range-speed Doppler frequency and compensation frequency term in the frequency modulation term.

[0070] In some embodiments, based on the phase and frequency of the difference frequency signal, it can be seen that it is specifically a linear frequency modulation signal, and its starting frequency , FM slope , which has certain relationship with radar parameters and target parameters, including:

[0071] (1) Doppler frequency The frequency modulated signal Produced on the target movement;

[0072] (2) Distance frequency Distance to target and radar and FM slope When the target motion velocity is high, There will be obvious unit motion in different echo snapshots;

[0073] (3) can be rewritten as , from which we can see that the range velocity Doppler frequency is the distance frequency The magnitude of the target motion is related to the distance of the moving target from the radar. and speed related, requiring compensation;

[0074] (4) Frequency modulation slope With target speed and the frequency modulation slope of the transmitted signal This term means that the de-sloped echo signal is also a linear frequency modulation signal and needs to be compensated.

[0075] Theoretically, the target speed needs to be obtained for compensation, which is usually verified by multiple assumptions and grading. Based on the above relationship, the compensation method is given, including:

[0076] (1) The Doppler frequency is only related to the target speed and frequency band. The terminal motion model can be considered as a CV model. This term is a constant in a single snapshot.

[0077] (2) The distance frequency is , that is, the range velocity Doppler frequency ,Include and Two items, the second of which It depends on variables such as the number of snapshots and needs to be compensated. Assuming the FM slope and frequency modulation period It is a fixed value in the same working mode;

[0078] (3) Range velocity Doppler frequency It can also be decomposed into and Two items, the second of which It is related to the number of snaps and needs to be compensated;

[0079] (4) The frequency modulation term is , when the target speed is very small, that is , can be ignored, but for the high frequency modulation slope commonly used in modern radars, it cannot be ignored and needs to be compensated.

[0080] Specifically, according to the compensation frequency term, frequency compensation is performed on the digital signal obtained by converting the difference frequency signal in the single echo snapshot, including:

[0081] (1) Determine the compensation coefficient based on the compensation frequency term and calculate the compensation distance frequency and range velocity Doppler frequency The frequency associated with the number of snapshots ;

[0082] as well as,

[0083] (2) Calculate the compensation frequency modulation term Frequency ;

[0084] (3) Frequency and frequency Set as compensation coefficient;

[0085] (4) Filter and amplify the difference frequency signal in the single echo snapshot, and then perform A / D conversion to obtain a digital signal;

[0086] (5) In the digital domain, multiply the digital signal by the compensation coefficient to complete frequency compensation.

[0087] Specifically, the distance and speed information of the detected target is determined according to the compensated digital signal, including:

[0088] (1) Perform spectrum analysis on the compensated digital signal to obtain a frequency domain signal;

[0089] (2) Based on the characteristics of the frequency domain signal, the distance and speed information of the detected target is extracted.

[0090] In order to more clearly illustrate the present invention and its advantages, the following will combine the performance simulation of signal compensation based on the above signal processing method.

[0091] For example, Figure 3 and Figure 4 The simulation diagram (including before and after simulation) is used to verify the principle of the compensation method. The parameters in the simulation are: assuming that the signal carrier frequency is 35GHz, the transmission bandwidth is 600MHz, the frequency modulation period is 80us, and the target speed is about 1700m / s. In order to better demonstrate, only white noise is considered in the simulation, and ground clutter is not considered. In order to avoid falling into the speed blind zone due to speed ambiguity, blind speed is avoided by staggered repetition frequency.

[0092] In the radar parameters, the distance resolution unit is 0.25 meters. The target moves 0.14 meters in a single frequency modulation cycle, and the distance in two adjacent frequency modulation cycles reaches 0.28 meters, which exceeds the distance resolution unit and there is distance movement. That is, in the results before compensation, the distance units corresponding to the targets in each echo are not in the same position.

[0093] Perform spectrum analysis (FFT) on the de-skewed signal, that is, perform compensation. It can be clearly seen from the compensated results that the distance units corresponding to the targets in each echo are corrected to the same position.

[0094] Figure 5 and Figure 6 For the echo simulation diagram, the simulation is performed according to the working parameters (power, gain, etc.) and target parameters (RCS, etc.) of the radar system design. On the basis that the simulation parameters are the same as the simulation parameters of the principle verification of the compensation method, the σ =0.3m / s related ground clutter; it can be seen that RCS=0.001m 2 Small targets will be energetically submerged in the powerful ground clutter spectrum and cannot be effectively detected without special processing.

[0095] Figure 7 and Figure 8 This is a simulation comparison diagram of filtering and filtering plus compensation in multiple echoes. After MTI filtering, the target echo can be distinguished from the clutter, but the target has obvious range movement; after compensation, the range unit corresponding to the target is corrected to the same position.

[0096] Fig. 9 and Fig.10 This is a simulation comparison diagram of filtering and filtering plus compensation in a single snapshot. In theory, due to the phenomenon of high-speed target moving in distance over time, if no compensation is given, the MTI filter improvement factor will deteriorate because the target crosses the distance unit. After compensation, the target is corrected in distance, and MTI will obtain a relatively good improvement factor at this time.

[0097] From the comparison results, it can be seen that the target signal-to-noise ratio after filtering and compensation processing is improved by 9dB compared with filtering processing alone, and the target signal-to-noise ratio reaches about 24dB, which fully meets the detection requirements.

[0098] According to the above embodiments, the compensation processing in the present invention is all linear processing in the digital domain, and vector multiplication can be completed in the FPGA, and the compensation coefficients can be pre-calculated and normalized to the window function coefficients that suppress the range side lobes, with low complexity.

[0099] It can be understood that according to the performance simulation case provided by the present invention and the simulation results, the signal processing method of the present invention has the following advantages:

[0100] (1) Improve distance resolution:

[0101] In the simulation case, high-precision detection of high-speed targets was achieved by setting parameters such as signal carrier frequency 35GHz and transmission bandwidth 600MHz. In two adjacent frequency modulation cycles, the target movement distance exceeded the distance resolution unit (0.25 meters), and there was distance migration. However, after compensation processing, the distance units corresponding to the targets in each echo were corrected to the same position, significantly improving the distance resolution.

[0102] (2) Effectively suppress ground clutter:

[0103] The simulation considers the correlated ground clutter of σ=0.3m / s. For a small target with RCS=0.001m², its echo will be submerged in the powerful ground clutter spectrum in terms of energy. However, after MTI filtering and compensation, the target echo can be effectively distinguished from the clutter, and the range unit corresponding to the target is corrected to the same position, indicating that the signal processing method in the present invention has excellent ground clutter suppression capability.

[0104] (3) Solving the distance migration problem:

[0105] During the radar detection process of high-speed targets, the echo signal will produce distance migration in adjacent frequency modulation cycles due to the high speed of the target. The present invention effectively solves this problem through compensation processing, so that the target is accurately corrected in distance.

[0106] (4) Improve velocity resolution:

[0107] Although the simulation case does not directly mention the improvement of velocity resolution, the method of the present invention uses wideband linear frequency modulated continuous wave (LFMCW) as the transmission signal and improves the distance resolution through compensation processing, which indirectly helps to improve the velocity resolution. Because the velocity resolution is related to the bandwidth and coherent accumulation time of the radar signal, the method of the present invention improves the utilization efficiency of the coherent accumulation time by optimizing the signal processing process.

[0108] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments can still be modified, or some of the technical features can be replaced by equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A radar signal processing method, characterized in that: The method comprises: The radar sends a transmission signal to the detection target and receives an echo signal from the detection target; Mixing the echo signal and the transmission signal to obtain a difference frequency signal, wherein the phase of the difference frequency signal is related to the distance and motion state of the detection target; Determine the compensation frequency item of the difference frequency signal based on a preset analysis rule; wherein the compensation frequency item includes the compensation distance frequency, the distance velocity Doppler frequency and the frequency related to the number of snapshots, and the compensation frequency modulation item frequency; According to the compensation frequency item, frequency compensation is performed on the digital signal obtained by pre-converting the difference frequency signal in the single echo snapshot; Determine the distance and speed information of the detected target according to the compensated digital signal; The step of performing frequency compensation on a digital signal obtained by converting the difference frequency signal in a single echo snapshot according to the compensation frequency term includes: Determine the compensation coefficient according to the compensation frequency term and calculate the compensation distance frequency and range velocity Doppler frequency The frequency associated with the number of snapshots ; And calculate the compensation frequency modulation term Frequency ; The frequency and the frequency The compensation coefficient is set to filter and amplify the difference frequency signal in the single echo snapshot, and then perform A / D conversion to obtain a digital signal. In the digital domain, the digital signal is multiplied by the compensation coefficient to complete frequency compensation.

2. A radar signal processing method according to claim 1, characterized in that: The transmission signal adopts a broadband linear frequency modulation continuous wave, including signal amplitude , FM signal starting frequency , frequency modulation period , and the initial phase ; The echo signal contains the distance from the detection target to the radar , Speed ​​of Light , consider the influence of the receiving antenna and the coefficient of radio wave propagation attenuation .

3. A radar signal processing method according to claim 2, characterized in that: Mixing the echo signal and the transmit signal to obtain a difference frequency signal, comprising: The echo signal is mixed with the transmission signal by a mixer to obtain a difference frequency signal containing the distance and speed information of the detected target; Within n repetition cycles, the phase of the difference frequency signal is recorded and analyzed to extract parameters related to the distance and motion state of the detected target, including radar parameters and detected target parameters.

4. A radar signal processing method according to claim 3, characterized in that: Mixing the echo signal and the transmit signal to obtain a difference frequency signal also includes: (1) Calculated in The phase of the difference frequency signal within a repetition period , the expression is: ； in, For the The relative distance between the detected target and the radar during a repetition cycle; (2) Calculate the phase frequency corresponding to the difference frequency signal , the expression is: ,in ; in, represents the Doppler frequency, represents the distance frequency, Indicates the range velocity Doppler frequency; Indicates frequency modulation item.

5. A radar signal processing method according to claim 4, characterized in that: The determining of the compensation frequency term of the difference frequency signal based on a preset analysis rule comprises: According to the phase frequency of the difference frequency signal The relationship between radar parameters and detection target parameters is analyzed to identify the Doppler frequency, range frequency, range-speed Doppler frequency and compensation frequency term in the frequency modulation term.

6. A radar signal processing method according to claim 1, characterized in that: Determining the distance and speed information of the detection target according to the compensated digital signal includes: Perform spectrum analysis on the compensated digital signal to obtain a frequency domain signal; According to the characteristics of the frequency domain signal, the distance and speed information of the detected target are extracted.

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