High-speed moving target identification method based on bistatic broadband radar

Abstract

The invention discloses a high-speed moving target identification method based on a bistatic broadband radar, relates to the technical field of radar signal processing, and aims at solving the problems that when a high-speed moving target is detected in the prior art, an echo signal of the target is influenced by a remarkable Doppler effect, an intra-pulse modulation phenomenon is generated, and broadening and distortion of an echo waveform are caused. In order to solve the problem that target identification accuracy is low due to the fact that in-pulse modulation of a moving target, target dynamic scattering characteristics at different moments are obtained through a dynamic time-varying bistatic geometrical relationship, and frequency domain multiplication is carried out on the target dynamic scattering characteristics and echoes after in-pulse modulation of the moving target to obtain a target echo result. In this way, the phenomenon of intra-pulse modulation caused by the fact that echo signals of the target are affected by the remarkable Doppler effect is avoided. According to the method, the echo simulation result of the high-speed moving target and the one-dimensional range profile of the target under the complex geometric background can be accurately obtained. And the accuracy of target identification is improved.

Description

Technical Field

[0001] The present application relates to the field of radar signal processing technology, and specifically to a method for identifying high-speed moving targets based on a dual-base broadband radar. Background Art

[0002] Bistatic radars offer enhanced anti-interference capabilities and concealment, reducing the risk of enemy detection or destruction. Furthermore, the bistatic structure facilitates complex reconnaissance modes such as passive reception and multi-base coordination, effectively enhancing target detection and identification capabilities. In terms of target identification, due to the geometric differences in the transmit and receive paths, bistatic radars provide richer scattering signature information, enhancing detection capabilities for stealthy targets. Therefore, bistatic radars are becoming a key development direction for the next generation of high-performance radar systems.

[0003] Compared to narrowband radar, wideband radar's high-resolution performance allows it to detect targets differently than point targets, more accurately distinguishing the target's individual scattering points and enabling target identification. Therefore, research on target characteristic modulation based on extended targets can facilitate more accurate target identification, with radar echo simulation being a key component of radar system testing and radar signal processing technology research. Unlike point targets, wideband radar target echoes require convolution of the target echo with a sequence of scattering characteristic data characterized at different times. Because this step is computationally complex, a frequency-domain point multiplication can be used to obtain an echo modulated by the scattering characteristics.

[0004] In bistatic radar systems, especially those based on space-based platforms, the transmitter and receiver are located on different orbits or platforms, resulting in complex system geometry and high relative speeds. When detecting high-speed moving targets, such as aircraft, the target's echo signal is significantly affected by the Doppler effect, resulting in intra-pulse modulation, broadening and distortion of the echo waveform, and thus low target recognition accuracy. Summary of the Invention

[0005] The present invention aims to address the problem that when detecting high-speed moving targets, the target's echo signal is significantly affected by the Doppler effect, resulting in intra-pulse modulation, causing broadening and distortion of the echo waveform. This in turn leads to low target recognition accuracy. The present invention provides a high-speed moving target recognition method based on a bistatic broadband radar.

[0006] The technical solution adopted by the present invention to solve the above technical problems is:

[0007] The method for identifying high-speed moving targets based on a bistatic broadband radar includes the following steps:

[0008] Step 1: Based on the coordinates of the transmitting station, receiving station, and target in the geodetic coordinate system and combined with the geometric characteristics of the bistatic radar, the incident angle, scattering angle, and bistatic angle of the radio wave are obtained;

[0009] Step 2: Set the velocity and acceleration vectors of the transmitting station, receiving station, and target, and obtain the distance history equation between the transmitting station and the target, and the distance history equation between the receiving station and the target based on the velocity and acceleration vectors of the transmitting station, receiving station, and target;

[0010] Step 3: Obtain the equivalent motion equation based on the distance history equation between the transmitting station and the target and the distance history equation between the receiving station and the target;

[0011] Step 4: The transmitting station transmits the LFM signal and combines the LFM signal with the equivalent motion equation to obtain the frequency domain echo model;

[0012] Step 5: Obtain the incident angle, scattering angle, and bistatic angle at different frequencies, as well as the corresponding RCS data. Multiply the RCS data by the frequency domain echo model frequency by frequency to obtain the target echo.

[0013] Step 6: Perform inverse Fourier transform on the target echo to obtain the time domain output of the target echo;

[0014] Step 7: Pulse compress the target echo to obtain the HRRP image;

[0015] Step 8: Repeat steps 1 to 7 to obtain the time domain output and HRRP image of the target echo under different pulses, that is, the target recognition result.

[0016] Furthermore, the specific steps of step 1 are:

[0017] Step 11: Use the transformation matrix from the geodetic coordinate system to the geocentric rectangular coordinate system to transform the coordinates of the transmitting station, receiving station, and target into the geocentric rectangular coordinate system:

[0018] Step 12: Obtain the transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system, and subtract the coordinates of the target in the geocentric rectangular coordinate system from the coordinates of the transmitting station. Multiply the result of the subtraction by the transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system to obtain the coordinates of the target in the transmitting station coordinate system.

[0019] Step 13: Subtract the coordinates of the target in the geocentric rectangular coordinate system from the coordinates of the receiving station. Multiply the result of the subtraction by the transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system to obtain the coordinates of the receiving station in the transmitting station coordinate system.

[0020] Step 14: Obtain the transformation matrix from the transmitting station coordinate system to the target coordinate system, and multiply the coordinates of the target in the transmitting station coordinate system and the coordinates of the receiving station in the transmitting station coordinate system by the transformation matrix from the transmitting station coordinate system to the target coordinate system to obtain the coordinates of the transmitting station in the target coordinate system and the coordinates of the receiving station in the target coordinate system;

[0021] Step 15: Using the coordinates of the transmitting station in the target coordinate system and the coordinates of the receiving station in the target coordinate system, and combining the angular geometric relationship, the incident angle, scattering angle and bistatic angle of the radio wave are obtained.

[0022] Furthermore, the transformation matrix from the geodetic coordinate system to the geocentric rectangular coordinate system in step 11 is expressed as:

[0023]

[0024] Among them, (U, V, W) is the geocentric rectangular coordinate system, (L, B, H) represents the latitude and longitude, and N is an intermediate variable. a is the major radius of the Earth, e 2 is the square of the first eccentricity.

[0025] Furthermore, the transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system in step 12 is expressed as:

[0026]

[0027] Among them, (L gt ,B gt ,H gt ) is the latitude and longitude parameter of the radar transmitting station, B t is the transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system.

[0028] Furthermore, the coordinates of the target in the transmitting station coordinate system and the coordinates of the receiving station in the transmitting station coordinate system in step 12 are expressed as:

[0029]

[0030] Among them, (x t ,y t ,z t ) are the coordinates of the target or receiving station in the transmitting station coordinate system, (x, y, z) are the coordinates of the transmitting station in the geocentric rectangular coordinate system, and (x0, y0, z0) are the coordinates of the target or receiving station in the geocentric rectangular coordinate system.

[0031] Furthermore, the transformation matrix from the transmitting station coordinate system to the target coordinate system is expressed as:

[0032]

[0033] where (ψ, θ, φ) are the yaw, pitch and roll angles of the target-mounted gyroscope in real-time, respectively, B bg is the transformation matrix from the launch station coordinate system to the target coordinate system.

[0034] Further, the distance history equation of the launch station and the target is represented as:

[0035]

[0036] where v is the velocity vector of the target, a is the acceleration vector of the target, v T is the velocity vector of the launch station, a T is the acceleration vector of the launch station, R TP0 is the initial distance vector between the launch station and the target, t m is the slow time.

[0037] Further, the distance history equation of the launch station and the target is represented as:

[0038]

[0039] where R RP0 is the initial distance vector between the launch station and the target.

[0040] Further, the equivalent motion equation is represented as:

[0041]

[0042] C T1 = 2R TP0 (v-v T )

[0043] C T2 = 2R TP0 (a-a T )+(v-v T ) 2

[0044] C R1 = 2R RP0 (v-v R )

[0045] C R2 = 2R RP0 (a-a R )+(v-v R ) 2

[0046] where R0, v0, a0 are the distance, velocity and acceleration of the target relative to the radar after the equivalent, respectively, C T1 , CT2 , C R1 , C R2 is an intermediate variable.

[0047] Further, the frequency domain echo model is expressed as:

[0048]

[0049] B e = K e T p

[0050]

[0051] v m = v0 + a0t m

[0052]

[0053] wherein T p is the pulse width, f c is the center frequency, K e , f e , B e , r m , v m , lambda m , lambda v , lambda a , rho v , zeta m are intermediate variables, gamma is the frequency modulation rate, j is the imaginary unit, f is the frequency value, and c is the speed of light.

[0054] The beneficial effects of the present application are:

[0055] The present application obtains the dynamic scattering characteristics of the target at different times through dynamic time-varying bistatic geometry, and multiplies the echoes after the intra-pulse modulation of the moving target in the frequency domain to obtain the target echo result. In this way, the echo signal of the target is avoided from being significantly affected by the Doppler effect and producing intra-pulse modulation. The present application can accurately obtain the echo simulation result of the high-speed moving target in a complex geometry background and the one-dimensional range image of the target, and improves the accuracy of target recognition. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 is a schematic diagram of geometry coordinate system conversion under bistatic radar;

[0057] Figure 2 is a schematic diagram of target echo modulation model;

[0058] Figure 3 is a schematic diagram of incident angle and scattering angle varying with pulse;

[0059] Figure 4 Schematic diagram of bistatic angle changing with pulse;

[0060] Figure 5 Schematic diagram of radar target echo under different pulses;

[0061] Figure 6 Schematic diagram of target HRRP image under different pulses;

[0062] Figure 7 Comparison of HRRP images under different pulses. DETAILED DESCRIPTION

[0063] It should be noted that, unless there is any conflict, the various embodiments disclosed in this application can be combined with each other.

[0064] Specific implementation method 1: The high-speed moving target recognition method based on bistatic broadband radar described in this implementation method includes the following steps:

[0065] Step 1: Based on the coordinates of the transmitting station, receiving station, and target in the geodetic coordinate system and combined with the geometric characteristics of the bistatic radar, the incident angle, scattering angle, and bistatic angle of the radio wave are obtained;

[0066] Step 2: Set the velocity and acceleration vectors of the transmitting station, receiving station, and target, and obtain the distance history equation between the transmitting station and the target, and the distance history equation between the receiving station and the target based on the velocity and acceleration vectors of the transmitting station, receiving station, and target;

[0067] Step 3: Obtain the equivalent motion equation based on the distance history equation between the transmitting station and the target and the distance history equation between the receiving station and the target;

[0068] Step 4: The transmitting station transmits the LFM signal and combines the LFM signal with the equivalent motion equation to obtain the frequency domain echo model;

[0069] Step 5: Obtain the incident angle, scattering angle, and bistatic angle at different frequencies, as well as the corresponding RCS data. Multiply the RCS data by the frequency domain echo model frequency by frequency to obtain the target echo.

[0070] Step 6: Perform inverse Fourier transform on the target echo to obtain the time domain output of the target echo;

[0071] Step 7: Pulse compress the target echo to obtain the HRRP image;

[0072] Step 8: Repeat steps 1 to 7 to obtain the time domain output and HRRP image of the target echo under different pulses, that is, the target recognition result.

[0073] Step 1: First, set the coordinates of the transmitting station, receiving station, and target in the geodetic coordinate system. Based on the geometric characteristics of the bistatic radar, the time-varying angle of incidence, scattering angle, and bistatic angle are obtained. This is specifically divided into the following sub-steps:

[0074] (1) Using the conversion formula from the geodetic coordinate system to the geocentric rectangular coordinate system, the coordinates are converted to the geocentric rectangular coordinate system. The formula is:

[0075]

[0076] Among them, (U, V, W) is the geocentric rectangular coordinate system, (L, B, H) represents the latitude and longitude, The major radius of the Earth a = 6378245m, the square of the first eccentricity e 2 =0.0069342162297.

[0077] (2) Using the transformation matrix B from the geocentric rectangular coordinate system to the transmitting station coordinate system t for:

[0078]

[0079] Among them (L gt ,B gt ,H gt ) are the latitude and longitude parameters of the radar transmitting station, then the transformation process of the target and receiving station from the geocentric rectangular coordinate system to the transmitting station rectangular coordinate system is as follows:

[0080]

[0081] Among them, (x t ,y t ,z t ) are the coordinates of the target or receiving station in the transmitting station coordinate system, (x, y, z) are the coordinates of the transmitting station in the geocentric rectangular coordinate system, and (x0, y0, z0) are the coordinates of the target or receiving station in the geocentric rectangular coordinate system.

[0082] (3) Using the conversion formula B from the transmitting station coordinate system to the target coordinate system bg for:

[0083]

[0084] Where (ψ, θ, φ) are the yaw angle, pitch angle and roll angle recorded by the target's gyroscope in real time under actual measurement. According to the coordinates of the target and the receiving station in the transmitting station coordinate system obtained in (2) and the conversion formula B bg By multiplying them, we can get the coordinates of the receiving station and the transmitting station in the target coordinate system.

[0085] (4) Using the coordinates and angle geometric relationship in the target coordinate system to obtain the radio wave incident pitch angle φ t ∈[0,2π), azimuth angle θ t ∈[0,π) and the scattering pitch angle φ r , azimuth angle θ r and the bistatic angle β;

[0086] Repeat (2)-(4) to obtain the angle parameters under each pulse.

[0087] Step 2: Set the target's velocity and acceleration vectors to v and a; the transmitter's velocity and acceleration vectors to v T 、a T ; The velocity and acceleration vector of the receiving station is v R 、a R The distance history equations between the transmitting station, the receiving station and the target are calculated as R TP (t m ) and R RP (t m ), which can be expressed as:

[0088]

[0089] where R TP0 and R RP0 are the initial distance vectors between the transmitter and receiver and the target, respectively, t m For slow time.

[0090] In the process of converting the distance vector into a scalar, Taylor approximation is used to obtain the distance history equation of the target under dual base:

[0091]

[0092] C T1 =2R TP0 (vv T ),C T2 =2R TP0 (aa T )+(vv T ) 2 ,C R1 =2R RP0 (vv R ),C R2 =2R RP0 (aa R )+(vv R ) 2 ,

[0093] Then we can get:

[0094]

[0095] The results show that the distance history equation of a dual-base target can be equivalent to that of a uniformly accelerated target under a single base.

[0096] Step 3. Set the radar signal parameters: the frequency band is "Ku" band, that is, the starting frequency is 15GHz, the bandwidth is 3GHz, the frequency points are all the frequency points after sampling in the frequency band of 15-18GHz, and the pulse width T p is 0.5ms, the center frequency f c is 16.5GHz, and γ is 6×10 12 (f c 、T p ,γ), assuming that the LFM transmission signal is:

[0097]

[0098] Combined with the equivalent motion model, the baseband echo can be expressed as follows after approximation:

[0099]

[0100] Generally speaking, it is assumed that the envelope term ignores the quadratic term and the phase term ignores the cubic term, and their impact on the result can be ignored. The baseband echo can be approximately expressed as:

[0101]

[0102] in

[0103] to s r (t) Performing Fourier transform can obtain the echo signal expressed in the frequency domain as:

[0104]

[0105] After a series of mathematical operations, the final expression of the echo frequency domain is:

[0106]

[0107] In the formula B e =K e T p .

[0108] Step 4: Calculate the target echo signal and target one-dimensional range image obtained after modulation by the target scattering characteristics. This is specifically divided into the following sub-steps:

[0109] Get the radio wave incident pitch angle φ t ∈[0,2π), azimuth angle θ t ∈[0,π) and the scattering pitch angle φr , azimuth angle θ r , and use the radio wave incident pitch angle φ t ∈[0,2π), azimuth angle θ t ∈[0,π), and the scattering pitch angle φ r , azimuth angle θ r , we get the bistatic angle β;

[0110] According to the static target scattering characteristic data, the scattering angle under different pulses (scattering pitch angle φ r , azimuth angle θ r ), bistatic angle and RCS data H(β,φ,f) corresponding to the frequency point;

[0111] Multiplying the frequency domain echo model S(f) after intra-pulse modulation by the RSC data obtained from the table frequency-wise can be expressed as:

[0112] S r (f)=S(f)H(β,φ,f)

[0113] The modulated target echo S r (f) Pulse compression is performed to obtain the HRRP image, and the target echo is subjected to inverse Fourier transform to obtain the time domain output of the target echo, which can be expressed as:

[0114] s r (t) = F -1 {S r (f)}

[0115] The target recognition results are obtained using HRRP images and time domain output.

[0116] Repeat (1)-(3) to obtain the target echo time domain output and high-resolution one-dimensional range image under different pulses

[0117] Step 5: Output and visualize all recorded results, which is the final target echo simulation result.

[0118] It should be noted that the specific embodiments are merely explanations and illustrations of the technical solutions of the present invention and cannot be used to limit the scope of protection. Any minor changes made based on the claims and description of the present invention shall still fall within the scope of protection of the present invention.

Claims

1. High-speed moving target recognition method based on bistatic broadband radar, characterized by Including the following step; Step 1: Based on the coordinates of the transmitting station, receiving station, and target in the geodetic coordinate system and combined with the geometric characteristics of the bistatic radar, the incident angle, scattering angle, and bistatic angle of the radio wave are obtained; Step 2: Set the velocity and acceleration vectors of the transmitting station, receiving station, and target, and obtain the distance history equation between the transmitting station and the target, and the distance history equation between the receiving station and the target based on the velocity and acceleration vectors of the transmitting station, receiving station, and target; Step 3: Obtain the equivalent motion equation based on the distance history equation between the transmitting station and the target and the distance history equation between the receiving station and the target; Step 4: The transmitting station transmits the LFM signal and combines the LFM signal with the equivalent motion equation to obtain the frequency domain echo model; Step 5: Obtain the incident angle, scattering angle, and bistatic angle at different frequencies, as well as the corresponding RCS data. Multiply the RCS data by the frequency domain echo model frequency by frequency to obtain the target echo. Step 6: Perform inverse Fourier transform on the target echo to obtain the time domain output of the target echo; Step 7: Pulse compress the target echo to obtain the HRRP image; Step 8: Repeat steps 1 to 7 to obtain the time domain output and HRRP image of the target echo under different pulses, that is, the target recognition result.

2. The method for identifying high-speed moving targets based on a bistatic broadband radar according to claim 1 is characterized in that The specific steps of step 1 are: Step 11: Use the transformation matrix from the geodetic coordinate system to the geocentric rectangular coordinate system to transform the coordinates of the transmitting station, receiving station, and target into the geocentric rectangular coordinate system: Step 12: Obtain the transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system, and subtract the coordinates of the target in the geocentric rectangular coordinate system from the coordinates of the transmitting station. Multiply the result of the subtraction by the transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system to obtain the coordinates of the target in the transmitting station coordinate system. Step 13: Subtract the coordinates of the target in the geocentric rectangular coordinate system from the coordinates of the receiving station. Multiply the result of the subtraction by the transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system to obtain the coordinates of the receiving station in the transmitting station coordinate system. Step 14: Obtain the transformation matrix from the transmitting station coordinate system to the target coordinate system, and multiply the coordinates of the target in the transmitting station coordinate system and the coordinates of the receiving station in the transmitting station coordinate system by the transformation matrix from the transmitting station coordinate system to the target coordinate system to obtain the coordinates of the transmitting station in the target coordinate system and the coordinates of the receiving station in the target coordinate system; Step 15: Using the coordinates of the transmitting station in the target coordinate system and the coordinates of the receiving station in the target coordinate system, and combining the angular geometric relationship, the incident angle, scattering angle and bistatic angle of the radio wave are obtained.

3. The method for identifying high-speed moving targets based on a bistatic broadband radar according to claim 2 is characterized in that The transformation matrix from the geodetic coordinate system to the geocentric rectangular coordinate system in step 11 is expressed as: Among them, (U, V, W) is the geocentric rectangular coordinate system, (L, B, H) represents the latitude and longitude, and N is an intermediate variable. a is the major radius of the Earth, e 2 is the square of the first eccentricity.

4. The method for identifying high-speed moving targets based on a bistatic broadband radar according to claim 3 is characterized in that The transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system in step 12 is expressed as: Among them, (L gt ,B gt ,H gt ) are the latitude and longitude parameters of the radar transmitting station, B t is the transformation matrix from the geocentric rectangular coordinate system to the transmitting station coordinate system.

5. The method for identifying high-speed moving targets based on a bistatic broadband radar according to claim 4 is characterized in that In step 12, the coordinates of the target in the transmitting station coordinate system and the coordinates of the receiving station in the transmitting station coordinate system are expressed as follows: Among them, (x t ,y t ,z t ) are the coordinates of the target or receiving station in the transmitting station coordinate system, (x, y, z) are the coordinates of the transmitting station in the geocentric rectangular coordinate system, and (x0, y0, z0) are the coordinates of the target or receiving station in the geocentric rectangular coordinate system.

6. The method for identifying high-speed moving targets based on a bistatic broadband radar according to claim 5 is characterized in that The transformation matrix from the transmitting station coordinate system to the target coordinate system is expressed as: Among them, (ψ, θ, φ) are the yaw angle, pitch angle and roll angle recorded by the target's gyroscope in real time under actual measurement conditions, and B bg is the transformation matrix from the transmitting station coordinate system to the target coordinate system.

7. The method for identifying high-speed moving targets based on a bistatic broadband radar according to claim 6 is characterized in that The distance history equation between the transmitting station and the target is expressed as: Among them, v is the velocity vector of the target, a is the acceleration vector of the target, and v T is the velocity vector of the transmitting station, a T is the acceleration vector of the transmitting station, R TP0 is the initial distance vector between the transmitter and the target, t m For slow time.

8. The method for identifying high-speed moving targets based on a bistatic broadband radar according to claim 7 is characterized in that The distance history equation between the receiving station and the target is expressed as: Among them, R RP0 is the initial distance vector between the receiver and the target.

9. The method for identifying high-speed moving targets based on a bistatic broadband radar according to claim 8, characterized in that The equivalent motion equation is expressed as: C T1 =2R TP0 (v-v T ) C T2 =2R TP0 (a-a T )+(v-v T ) 2 C R1 =2R RP0 (v-v R ) C R2 =2R RP0 (a-a R )+(v-v R ) 2 Among them, R0, v0, a0 are the distance, velocity and acceleration of the target relative to the radar after equivalent, C T1 、C T2 、C R1 、C R2 is an intermediate variable.

10. The method for identifying high-speed moving targets based on a bistatic broadband radar according to claim 9, characterized in that The frequency domain echo model is expressed as: B e =K e T p v m =v0+a0t m Among them, T p is the pulse width, f c is the center frequency, K e 、f e 、B e 、r m 、v m ,λ m ,λ v ,λ a , ρ v ,ζ m is the intermediate variable, γ is the modulation frequency, j is the imaginary unit, f is the frequency value, and c is the speed of light.

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