1. A space high-speed spinning target ISAR three-dimensional imaging method based on time domain phase matching is characterized by comprising the following steps:

step 1: processing radar echo data; carrying out translation compensation on a radar echo of the linear frequency modulation signal, and estimating an angular velocity;

step 2: constructing a corresponding time domain coupling term by using the radar echo data in the step 1 and carrying out conjugate multiplication;

and step 3: and (3) performing parameter extraction and coordinate reconstruction by using results of the different matching parameters in the step (2) after the time-domain coupling term is processed to finally obtain the ISAR image.

2. The ISAR three-dimensional imaging method based on time domain phase matching is characterized in that the step 1 of processing radar echo data specifically comprises the following steps: firstly, the radar echo of the linear frequency modulation signal is subjected to slope removal processing, then translational motion compensation is carried out on the radar echo, and finally the rotation angular velocity is estimated.

3. The ISAR three-dimensional imaging method for the spatially high-speed spinning target based on the time domain phase matching as claimed in claim 2, wherein the step 1 is specifically to compensate the residual video phase and the echo envelope slant term after the rotating speed of the target is much less than the pulse repetition frequency PRF of the radar, and then the range is slow time radar echoTransformation of data to the range-slow time domain by a pulse compression method is represented by equation (1) s₁(r,t_m) (ii) a Wherein T is_pGamma, lambda refers to pulse width, linear modulation frequency, wavelength; t is t_mIs the slow time, r is the distance direction after the fast time transformation; n is the number of scattering points on the target;

wherein R is_i(t_m) Caused by the rotation of the target, which reflects the micromotion state of the scattering point;

in the ISAR imaging process of the high-speed spinning target, an angle alpha between a rotating axis vector and a radar sight line is assumed to be constant in observation time; thus R in formula (1)_i(t_m) Is written as

R_ir(t_m)＝z_icosα+ρ_isinαsin(θ_i+ωt_m) (2)

Performing 0.2 max global threshold operation on the signal (1) in the distance slow time domain, and performing inverse Fourier transform (IFFT) on the distance to the fast time slow time domain to obtain the signal

The second phase term of the formula (3) is a coupling term of a fast time and a slow time; if the second phase of a scattering point is eliminated by completely matching the coupling term and then the second phase is compressed in azimuth, the first phase can make the echo in the range slow time domainThere is an envelope-invariant component within the range gate.

4. The ISAR three-dimensional imaging method based on the time-domain phase matching is characterized in that the step 2 specifically comprises the following steps:

step 2.1: constructing a signal which is in a sinusoidal envelope along the slow time within the distance slow time;

step 2.2: performing inverse Fourier transform along the distance direction by using the sinusoidal signal of the step 2.1, and converting the inverse Fourier transform into a fast-time and slow-time domain;

step 2.3: then, performing conjugate multiplication on the time domain phases of the radar echo signal and the reference signal;

step 2.4: when the amplitude and the initial phase of the constructed sinusoidal parameter and one sinusoidal envelope in the echo are the same, the coupling phase term is inhibited, and the phases are matched;

step 2.5: and then, performing distance Fourier transform on the processed signal to obtain a component with unchanged envelope, namely, an echo component which is in a sinusoidal envelope along slow time in the original radar echo is changed into an echo component with unchanged envelope.

5. The ISAR three-dimensional imaging method based on the time-domain phase matching is characterized in that the step 2 specifically comprises the following steps:

wherein s is_mf(r,t_m) Is as follows; a sinusoidal envelope signal constructed in the range-slow time domain;

structure z₀A sine of 0, i.e. located at the center of the range gate in the range slow time plane;

performing a distance-oriented IFFT by equation (4) can obtain the fast-time slow-time coupling term of the required configuration:

wherein the content of the first and second substances,is the scattering point echo data in the time domain,is the conjugate expression form of the reference signal in the time domain, j is an imaginary unit, A_iIs the back-scattering coefficient of the object,in order to be a fast time,is the projected height of the plane of rotation, z₀For the height of the parameter match to be,

the result of conjugate multiplication of the formula (3) and the formula (5) is that the step is time domain phase matching:

6. the ISAR three-dimensional imaging method based on the time-domain phase matching is characterized in that the parameter extraction in the step 3 specifically comprises the following steps:

step C3.1: traversing different rotation radiuses and initial phases to construct a time domain coupling term;

step C3.2: and C3.1, performing conjugate multiplication on the time domain coupling term and the time domain echo, and extracting a peak parameter based on a processed echo summation result.

7. The ISAR three-dimensional imaging method based on the time-domain phase matching is characterized in that the coordinate reconstruction in the step 3 specifically comprises the following steps:

step Z3.1: after conjugate multiplication of time domain coupling terms, carrying out azimuth Fourier transform,

step Z3.2: then accumulating the echo in each range gate along slow time;

step Z3.3: a three-dimensional matrix is obtained based on steps 3.1 and 3.2, i.e. each range gate r corresponds to a plane traversed by the two-dimensional parameters.

8. The ISAR three-dimensional imaging method for the spatially high-speed spinning target based on the time-domain phase matching as claimed in claim 6 or 7, wherein the step 3 is specifically performed when there is a set of parametersθ₀＝θ_iThen, the distance compression of equation (6) can be obtained:

equation (7) shows that when the matched parameter radius and phase are identical to the parameters of a sinusoidal envelope in the echo, a distance is compressed to obtain a parameter located at r-z_i-z₀The envelope-invariant component of (a); wherein s is_u(r,ρ₀,θ₀,t_m) Echo T obtained by distance compression after time domain conjugate multiplication_pIs the pulse repetition period, z_iIs the projection height of the ith scattering point, z₀For the height of the parameter match to be,radius of rotation, p, of the projection of the jth scattering point₀Radius of rotation, θ, matched for parameter_jIs the initial phase of the jth scattering point, θ₀Phase for parameter matching, ω is the angular velocity of rotation of the target, t_mIs a slow time;

therefore, two-dimensional parameter matching is carried out on the echo, and each group of parameters can obtain a matched s_u(r,ρ₀,θ₀,t_m) The echo amplitude value in each range gate where the echo is located in the accumulation formula (7) is used as a matched reference value;

through the two-dimensional traversal parameters, each range gate corresponds to a matched peak plane calculated by the above formula (4-8).

9. The ISAR three-dimensional imaging method based on time domain phase matching is characterized in that the step 3 is concretely, as known from the IFFT characteristic, after the product of the fitness value and the number M of the range gates, the total number of the pixels with constant envelope is obtained, wherein the value of the fitness value represents the range gates; for the maximum value max (S) in each range gate fitness_fitness(r,ρ_extract,θ_extract) Select a threshold of 0.8 x the number of orientation gates to determine S_fitness(r,ρ₀,θ₀) Whether scattering points exist on the surface;

s after threshold operation_fitness(r,ρ₀,θ₀) Extracting a peak value on a plane, and extracting selection radius and phase information of scattering points; the height information is the size r of the distance door; wherein c is the speed of light and B is the bandwidth of the chirp signal;

θ_real＝θ_extract (11)

wherein Z is_realFor the height of the scattering point matched, p_realRadius of rotation, θ, for matched scattering points_realThe true phase of the matched scattering point is obtained.

Background

From the existing three-dimensional ISAR imaging method of the spatial high-speed spinning target, most of the three-dimensional ISAR imaging methods are based on parameter searching. And the imaging of the high-speed spinning target needs to obtain three unknown parameters, namely the height of a rotating plane where a scattering point is located, the rotating radius and the initial phase.

The prior art uses a slicing method to design matched filter banks at different heights. The method is an algorithm based on parameter traversal, and the algorithm has the defects of large calculation consumption and long calculation time, and has great influence on ISAR imaging with real-time requirements.

In the prior art, the three-dimensional parameter traversal process is used for integrating along the sine envelope of the echo, the calculated amount of the method is also large, and the ISAR imaging required by real-time performance is greatly influenced.

In the prior art, a PSO method is used for carrying out rapid parameter search on parameters of a sinusoidal envelope, and a Clean technology is used for eliminating extracted components. In the case of echo aliasing, the use of Clean technology greatly affects the accuracy of imaging. Low signal-to-noise ratios also affect the accuracy of the imaging.

Disclosure of Invention

The invention provides a time domain phase matching-based ISAR (inverse synthetic aperture radar) three-dimensional imaging method for a space high-speed spinning target, which is used for solving the defects that the existing parameter estimation method has overlarge calculated amount, overlarge requirement on priori knowledge (such as information of phase, height and the like), a quick search method is complex and has insufficient environmental adaptability and the like.

The invention is realized by the following technical scheme:

a space high-speed spinning target ISAR three-dimensional imaging method based on time domain phase matching is characterized by comprising the following steps:

step 1: processing radar echo data; carrying out translation compensation on a radar echo of the linear frequency modulation signal, and estimating an angular velocity;

step 2: constructing a corresponding time domain coupling term by using the radar echo data in the step 1 and carrying out conjugate multiplication;

and step 3: and (3) performing parameter extraction and coordinate reconstruction by using results of the different matching parameters in the step (2) after the time-domain coupling term is processed to finally obtain the ISAR image.

Further, the processing of the radar echo data in the step 1 specifically includes: firstly, the radar echo of the linear frequency modulation signal is subjected to slope removal processing, then translational motion compensation is carried out on the radar echo, and finally the rotation angular velocity is estimated.

Further, in step 1, specifically, when the rotation speed of the target is much less than the pulse repetition frequency PRF of the radar, after compensating the residual video phase and the echo envelope slant term, the range slow time radar echo transforms the data to the range slow time domain by the pulse compression method, which is expressed as formula (1) s₁(r,t_m) (ii) a Wherein T is_pGamma, lambda refers to pulse width, linear modulation frequency, wavelength; t is t_mIs the slow time, r is the distance direction after the fast time transformation; n is the number of scattering points on the target;

wherein R is_i(t_m) Caused by the rotation of the target, which reflects the micromotion state of the scattering point;

in the ISAR imaging process of the high-speed spinning target, an angle alpha between a rotating axis vector and a radar sight line is assumed to be constant in observation time; thus R in formula (1)_i(t_m) Is written as

R_ir(t_m)＝z_i cosα+ρ_i sinαsin(θ_i+ωt_m) (2)

Performing 0.2 max global threshold operation on the signal (1) in the distance slow time domain, and performing inverse Fourier transform (IFFT) on the distance to the fast time slow time domain to obtain the signal

The second phase term of the formula (3) is a coupling term of a fast time and a slow time; if the perfect matching coupling term cancels the phase of the second term of a scattering point,then the azimuth compression is carried out on the echo, and the first phase term can enable the echo to be in a slow distance time domainThere is an envelope-invariant component within the range gate.

Further, the step 2 specifically includes the following steps:

step 2.1: constructing a signal which is in a sinusoidal envelope along the slow time within the distance slow time;

step 2.2: performing inverse Fourier transform along the distance direction by using the sinusoidal signal of the step 2.1, and converting the inverse Fourier transform into a fast-time and slow-time domain;

step 2.3: then, performing conjugate multiplication on the time domain phases of the radar echo signal and the reference signal;

step 2.4: when the amplitude and the initial phase of the constructed sinusoidal parameter and one sinusoidal envelope in the echo are the same, the coupling phase term is inhibited, and the phases are matched;

step 2.5: and then, performing distance Fourier transform on the processed signal to obtain a component with unchanged envelope, namely, an echo component which is in a sinusoidal envelope along slow time in the original radar echo is changed into an echo component with unchanged envelope.

Further, the step 2 specifically includes the following steps:

wherein s is_mf(r,t_m) Is as follows; a sinusoidal envelope signal constructed in the range-slow time domain;

structure z₀A sine of 0, i.e. located at the center of the range gate in the range slow time plane;

performing a distance-oriented IFFT by equation (4) can obtain the fast-time slow-time coupling term of the required configuration:

wherein the content of the first and second substances,is the scattering point echo data in the time domain,is the conjugate expression form of the reference signal in the time domain, j is an imaginary unit, A_iIs the back-scattering coefficient of the object,in order to be a fast time,is the projected height of the plane of rotation, z₀For the height of the parameter match to be,

the result of conjugate multiplication of the formula (3) and the formula (5) is that the step is time domain phase matching:

further, the parameter extraction in step 3 specifically includes the following steps:

step C3.1: traversing different rotation radiuses and initial phases to construct a time domain coupling term;

step C3.2: and C3.1, performing conjugate multiplication on the time domain coupling term and the time domain echo, and extracting a peak parameter based on a processed echo summation result.

Further, the coordinate reconstruction in step 3 specifically includes the following steps:

step Z3.1: after conjugate multiplication of time domain coupling terms, carrying out azimuth Fourier transform,

step Z3.2: then accumulating the echo in each range gate along slow time;

step Z3.3: a three-dimensional matrix is obtained based on steps 3.1 and 3.2, i.e. each range gate r corresponds to a plane traversed by the two-dimensional parameters.

Further, theStep 3 is specifically that when there is a group of parametersThen, the distance compression of equation (6) can be obtained:

equation (7) shows that when the matched parameter radius and phase are identical to the parameters of a sinusoidal envelope in the echo, a distance is compressed to obtain a parameter located at r-z_i-z₀The envelope-invariant component of (a); wherein s is_u(r,ρ₀,θ₀,t_m) Echo T obtained by distance compression after time domain conjugate multiplication_pIs the pulse repetition period, z_iIs the projection height of the ith scattering point, z₀For the height of the parameter match to be,radius of rotation, p, of the projection of the jth scattering point₀Radius of rotation, θ, matched for parameter_jIs the initial phase of the jth scattering point, θ₀Phase for parameter matching, ω is the angular velocity of rotation of the target, t_mIs a slow time;

therefore, two-dimensional parameter matching is carried out on the echo, and each group of parameters can obtain a matched s_u(r,ρ₀,θ₀,t_m) The echo amplitude value in each range gate where the echo is located in the accumulation formula (7) is used as a matched reference value;

through the two-dimensional traversal parameters, each range gate corresponds to a matched peak plane calculated by the above formula (4-8).

Further, the step 3 is specifically that, as can be seen from the IFFT characteristics, after multiplying the value of the fitness by the number M of range gates, the envelope is not changedThe total number of the pixel points, wherein the value of the fitness represents that the pixel points are within the range gate; for the maximum value max (S) in each range gate fitness_fitness(r,ρ_extract,θ_extract) Select a threshold of 0.8 x the number of orientation gates to determine S_fitness(r,ρ₀,θ₀) Whether scattering points exist on the surface;

s after threshold operation_fitness(r,ρ₀,θ₀) Extracting a peak value on a plane, and extracting selection radius and phase information of scattering points; the height information is the size r of the distance door; wherein c is the speed of light and B is the bandwidth of the chirp signal;

θ_real＝θ_extract (11)

wherein Z is_realFor the height of the scattering point matched, p_realRadius of rotation, θ, for matched scattering points_realThe true phase of the matched scattering point is obtained.

The invention has the beneficial effects that:

the method directly processes the coupling terms in the time domain, and can complete the matching of scattering points with the same radius and phase through one-time two-dimensional parameter traversal. The height information is determined by the distance gate whose matching degree exceeds the threshold. The space debris can be imaged, and high-resolution imaging can be realized under the conditions of low signal-to-noise ratio and sparsity.

The method can complete the determination of the three-dimensional parameters by utilizing the matching idea and two-dimensional parameter matching, so the imaging accuracy is higher and the efficiency is higher; compared with the traditional three-dimensional parameter traversal method and the slicing method, the efficiency is higher.

The ISAR three-dimensional imaging of the space high-speed spinning target has important significance for recognition, posture judgment and key motion stage capture of the space debris target.

Drawings

FIG. 1 is an ISAR imaging model of the invention

FIG. 2 is a flow chart of the method of the present invention.

FIG. 3 is a graph of simulated scattering point model and echo data of the present invention, wherein (a) three-dimensional scattering point model distribution, (b) echoes consisting of distance slow time multi-component sinusoids, and (c) echoes after global thresholding.

Fig. 4 is a graph of the maximum match value (gate 512 x 0.8) for the fitness for each range gate of the present invention.

Fig. 5 is a fitness plan view of the range gate meeting the threshold condition according to the present invention, wherein (a) is the matching plane corresponding to the 513 th range gate meeting the threshold condition, (b) is the matching plane corresponding to the 518 th range gate meeting the threshold condition, and (c) is the matching plane corresponding to the 523 th range gate meeting the threshold condition.

FIG. 6 is a graph of ISAR imaging results of reconstructed scattering points of the present invention.

FIG. 7 is a diagram of the variance and root mean square error calculations for parameter estimates in a complex environment, where (a) the variance and root mean square error for parameter estimates at different signal-to-noise ratios, and (b) the variance and root mean square error for parameter estimates at different sparseness levels, in accordance with the present invention.

FIG. 8 is a range-compressed echo plot of a group target of the present invention, wherein (a) range slow time echoes and (b) echoes after a global thresholding.

Fig. 9 is a graph of the maximum matching value for each range gate at different rotational speeds according to the present invention, in which (a) the value of the maximum matching degree of the ftness corresponding to the range gate (gate 512 x 0.8) when the rotational angular speed is 3Hz, and (b) the value of the maximum matching degree of the ftness corresponding to the range gate (gate 512 x 0.8) when the rotational angular speed is 5 Hz.

FIG. 10 is a fitness plan view of a range gate satisfying a threshold condition when the rotational angular velocity of the present invention is 3Hz, wherein, (a) the 467 th range gate that meets the threshold condition at the time of the 3Hz rotation angular velocity, (b) the 482 th range gate that meets the threshold condition at the time of the 3Hz rotation angular velocity, (c) the 498 th range gate that meets the threshold condition at the time of the 3Hz rotation angular velocity, (d) the 537 th range gate that meets the threshold condition at the time of the 3Hz rotation angular velocity, (e) the 538 th range gate that meets the threshold condition at the time of the 3Hz rotation angular velocity, (f) the 559 th range gate that meets the threshold condition at the time of the 3Hz rotation angular velocity, (g) the 571 th range gate that meets the threshold condition at the time of the 3Hz rotation angular velocity, (h) the 582 th range gate that meets the threshold condition at the time of the 3Hz rotation angular velocity, and (i) the 583 th range gate that meets the threshold condition at the time of the 3Hz rotation angular velocity.

Fig. 11 is a fitness plan view corresponding to the range gate satisfying the threshold condition when the rotational angular velocity is 5Hz according to the present invention, wherein (a) is the 498 th range gate satisfying the threshold condition when the rotational angular velocity is 5Hz, (b) is the 513 th range gate satisfying the threshold condition when the rotational angular velocity is 5Hz, (c) is the 525 th range gate satisfying the threshold condition when the rotational angular velocity is 5Hz, (d) is the 537 th range gate satisfying the threshold condition when the rotational angular velocity is 5Hz, (e) is the 538 th range gate satisfying the threshold condition when the rotational angular velocity is 5Hz, (f) is the 582 th range gate satisfying the threshold condition when the rotational angular velocity is 5Hz, and (g) is the 583 th range gate satisfying the threshold condition when the rotational angular velocity is 5 Hz.

FIG. 12 is a three-dimensional ISAR reconstruction of the swarm objects of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

A space high-speed spinning target ISAR three-dimensional imaging method based on time domain phase matching comprises the following steps:

step 1: processing radar echo data; carrying out translation compensation on a radar echo of the linear frequency modulation signal, and estimating an angular velocity;

step 2: constructing a corresponding time domain coupling term by using the radar echo data in the step 1 and carrying out conjugate multiplication;

and step 3: and (3) performing parameter extraction and coordinate reconstruction by using results of the different matching parameters in the step (2) after the time-domain coupling term is processed to finally obtain the ISAR image.

Further, the processing of the radar echo data in the step 1 specifically includes: firstly, the radar echo of the linear frequency modulation signal is subjected to slope removal processing, then translational motion compensation is carried out on the radar echo, and finally the rotation angular velocity is estimated.

Further, in step 1, specifically, when the rotation speed of the target is much less than the pulse repetition frequency PRF of the radar, after compensating the residual video phase and the echo envelope slant term, the range slow time radar echo transforms the data to the range slow time domain by the pulse compression method, which is expressed as formula (1) s₁(r,t_m) (ii) a Wherein T is_pGamma, lambda refers to pulse width, linear modulation frequency, wavelength; t is t_mIs the slow time, r is the distance direction after the fast time transformation; n is the number of scattering points on the target;

wherein R is_i(t_m) Caused by the rotation of the target, which reflects the micromotion state of the scattering point;

in the ISAR imaging process of the high-speed spinning target, an angle alpha between a rotating axis vector and a radar sight line is assumed to be constant in observation time; thus R in formula (1)_i(t_m) Is written as

R_ir(t_m)＝z_i cosα+ρ_i sinαsin(θ_i+ωt_m) (2)

Performing 0.2 max global threshold operation on the signal (1) in the distance slow time domain, and performing inverse Fourier transform (IFFT) on the distance to the fast time slow time domain to obtain the signal

The second phase term of the formula (3) is a coupling term of a fast time and a slow time; if the second phase of a scattering point is eliminated by completely matching the coupling term and then the second phase is compressed in azimuth, the first phase can make the echo in the range slow time domainThere is an envelope-invariant component within the range gate.

Further, the step 2 specifically includes the following steps:

step 2.1: constructing a signal which is in a sinusoidal envelope along the slow time within the distance slow time;

step 2.2: performing inverse Fourier transform along the distance direction by using the sinusoidal signal of the step 2.1, and converting the inverse Fourier transform into a fast-time and slow-time domain;

step 2.3: then, performing conjugate multiplication on the time domain phases of the radar echo signal and the reference signal;

step 2.4: when the amplitude and the initial phase of the constructed sinusoidal parameter and one sinusoidal envelope in the echo are the same, the coupling phase term is inhibited, and the phases are matched;

step 2.5: and then, performing distance Fourier transform on the processed signal to obtain a component with unchanged envelope, namely, an echo component which is in a sinusoidal envelope along slow time in the original radar echo is changed into an echo component with unchanged envelope.

Further, the step 2 specifically includes the following steps:

wherein s is_mf(r,t_m) Is as follows; a sinusoidal envelope signal constructed in the range-slow time domain;

structure z₀Sine of 0, i.e. sine position in the distance slow time planeAt a distance from the center of the door;

performing a distance-oriented IFFT by equation (4) can obtain the fast-time slow-time coupling term of the required configuration:

wherein the content of the first and second substances,is the scattering point echo data in the time domain,is the conjugate expression form of the reference signal in the time domain, j is an imaginary unit, A_iIs the back-scattering coefficient of the object,in order to be a fast time,is the projected height of the plane of rotation, z₀For the height of the parameter match to be,

the result of conjugate multiplication of the formula (3) and the formula (5) is that the step is time domain phase matching:

further, the parameter extraction in step 3 specifically includes the following steps:

step C3.1: traversing different rotation radiuses and initial phases to construct a time domain coupling term;

step C3.2: and C3.1, performing conjugate multiplication on the time domain coupling term and the time domain echo, and extracting a peak parameter based on a processed echo summation result.

Further, the coordinate reconstruction in step 3 specifically includes the following steps:

step Z3.1: after conjugate multiplication of time domain coupling terms, carrying out azimuth Fourier transform,

step Z3.2: then accumulating the echo in each range gate along slow time;

step Z3.3: a three-dimensional matrix is obtained based on steps 3.1 and 3.2, i.e. each range gate r corresponds to a plane traversed by the two-dimensional parameters.

Further, the step 3 is specifically that when a group of parameters exists, the parameters includeThen, the distance compression is performed on the formula (6) to obtain

Equation (7) shows that when the matched parameter radius and one of the phase echoes are identical to the parameter of the sinusoidal envelope, a distance is compressed to obtain a distance positioned at r-z_i-z₀The envelope-invariant component of (a); wherein s is_u(r,ρ₀,θ₀,t_m) Echo T obtained by distance compression after time domain conjugate multiplication_pIs the pulse repetition period, z_iIs the projection height of the ith scattering point, z₀For the height of the parameter match to be,radius of rotation, p, of the projection of the jth scattering point₀Radius of rotation, θ, matched for parameter_jIs the initial phase of the jth scattering point, θ₀Phase for parameter matching, ω is the angular velocity of rotation of the target, t_mIs a slow time;

therefore, two-dimensional parameter matching is carried out on the echo, and each group of parameters can obtain a matched s_u(r,ρ₀,θ₀,t_m) The echo amplitude value in each range gate where the echo is located in the accumulation formula (7) is used as a matched reference value;

through the two-dimensional traversal parameters, each range gate corresponds to a matched peak plane through the above calculation.

Further, the step 3 is specifically that, according to the characteristics of IFFT, after multiplying the value of the fitness by the number M of range gates, the total number of unchanged pixel points is enveloped, where the value of the fitness represents in the range gates; for the maximum value max (S) in each range gate fitness_fitness(r,ρ_extract,θ_extract) Select a threshold of 0.8 x the number of orientation gates to determine S_fitness(r,ρ₀,θ₀) Whether scattering points exist on the surface;

s after threshold operation_fitness(r,ρ₀,θ₀) Extracting a peak value on a plane, and extracting selection radius and phase information of scattering points; the height information is the size r of the distance door. Wherein c is the speed of light and B is the bandwidth of the chirp signal;

θ_real＝θ_extract (11)。

based on the algorithm verification of computer simulation, a radar working in an X wave band is adopted, the corresponding carrier frequency is 10GHz, the bandwidth is 2GH, the pulse repetition frequency is 400Hz, the pulse width is 50 mus, the azimuth gate number is 512, and the distance gate number is 1024. The rotational angular velocity of the target was 5Hz, and 9 scattering points were observed in FIG. 3 (a).

The simulation of the target ISAR echo is shown in FIG. 3(b), the thresholded echo is shown in FIG. 3(c), and the optimal matching value corresponding to each range gate after the target time domain phase matching is shown in FIG. 4. The two-dimensional matching planes corresponding to three range gates that satisfy the threshold condition are shown in fig. 5. The coordinates can be reconstructed by extracting the scattering points from the peaks as shown in fig. 6.

The calculation error and the mean square error at different signal-to-noise ratios are shown in fig. 7 (a).

The calculation error and the mean square error in the case of different data loss are shown in fig. 7 (b).

The simulation of the multi-target ISAR echo is shown in FIG. 8(a), the thresholded echo is shown in FIG. 8(b), and the two-dimensional matching plane corresponding to the range gate satisfying the threshold condition after the target time domain phase matching is shown in FIG. 9. The matching plane of each range gate satisfying the condition is shown in fig. 10 and 10 a. The reconstruction of the group object is shown in fig. 10 b.