Sparse expansion target imaging method based on metasurface microwave correlated imaging system

Abstract

The invention relates to a sparse expansion target imaging method based on a metasurface microwave correlated imaging system. The sparse expansion target imaging method comprises the following steps of S1, constructing the metasurface microwave correlated imaging system, S2, modulating and transmitting a signal, S3, setting an imaging plane space, S4, constructing a signal model, S5, constructing an imaging equation, S6, carrying out structured recombination on a reference matrix block, and S7, calculating an imaging reconstruction algorithm and solving. The method has the advantage of good imaging effect.

Description

Technical Field

[0001] The present invention belongs to the technical field of target imaging, and in particular relates to a sparse extended target imaging method based on a metasurface microwave correlation imaging system. Background Art

[0002] Microwave correlation imaging is one of the new radar imaging technologies. It can break through the limitation of antenna aperture on imaging resolution and has the advantages of forward-looking, staring, and quick-shot imaging. The rapid development of metasurface technology in recent years has provided a new approach for microwave correlation imaging. In reality, the sparse expansion characteristics of targets are widely present in the fields of speech signal processing, medical image processing, and radar image processing. The design of imaging reconstruction algorithm is the core link of metasurface microwave correlation imaging.

[0003] At present, there are many theories and algorithms for sparse point target reconstruction based on microwave correlation imaging systems, but there are relatively few theories and algorithms for sparse extended targets. Domestic and foreign research mainly uses orthogonal matching pursuit (OMP) and sparse Bayesian learning (SBL) methods to solve microwave correlation imaging problems. However, these two existing methods do not take into account the correlation within the sparse extended target, and intend to use the sparse point target imaging framework to solve the sparse extended target imaging problem. There are defects such as low imaging accuracy and long imaging time for sparse extended targets. Therefore, designing a new reconstruction method for sparse extended target imaging has important practical value. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a sparse extended target imaging method based on a metasurface microwave correlation imaging system with good imaging effect.

[0005] The technical solution of the present invention is as follows: A sparse extended target imaging method based on a metasurface microwave correlation imaging system comprises the following steps: Step S1: construct a metasurface microwave correlation imaging system consisting of a transmitting antenna, a reflective two-bit phase modulation metasurface, and a receiving antenna; Step S2: modulate the transmission signal of the transmitting antenna and transmit it to the target through space transmission. The transmission signal is received by the receiving antenna after scattering. Step S3: setting an imaging plane directly in front of the reflective two-bit phase modulation metasurface, wherein the imaging plane is evenly divided into square grids of the same size, and the scattering point is located at the grid center of the imaging plane, and the normal line of the reflective two-bit phase modulation metasurface passes through the plane center of the imaging plane; Step S4: Construct a signal model to obtain the reflected signal and reference signal ; Step S5: Construct the imaging equation to obtain the received signal vector Sr and the reference matrix ; Step S6: The reference matrix block is restructured to finally obtain a new reference matrix containing the imaging block structure information. , create a structure information index Sindex Recording a new reference matrix Each atom in the reference matrix The index in ; Step S7: Computational imaging reconstruction algorithm solution, the specific steps are as follows: Input: Receive signal Sr , the reference matrix , the block sparsity of the signal K , structure information index Sindex ; Output: Reconstructed scene scattering intensity ; Step S71: BOMP algorithm initialization: setting the number of block iterations k =0, residual r= Sr , select the atomic set Φ k is an empty set, restore the index set Λ k is an empty set; Step S72: Iteration step, k Iterations; (1) Finding residuals r With reference matrix S The most matching relevant block D j In all relevant blocks D j The index in is as follows: ; (2) Record related blocks D j Zhongzheng Atoms in the New Reference Matrix Index set in J k , increase the recovery index set , increase the support set ; (3) Least squares reconstruction of target signal ,in Representation Matrix of pseudo-rebellion; (4) Update residual ; (5) Determine whether the number of cycles reaches the set number of cycles or the residual norm is less than the set threshold. If it is satisfied, stop. If not, continue iterating. Step S73: restore the index set Λk , structure information index Sindex and , the scattering coefficient of the reconstructed space is matched with the index to obtain the target microwave correlation imaging result.

[0006] Furthermore, the specific process of constructing the signal model in step S4 is: Assume that the number of units of the reflective two-bit phase modulation metasurface is N , the number of grids in the imaging plane is L , the start time of the transmitter signal is t , the transmitted signal is S(t) , the transmitting antenna to the reflective two-bit phase modulation metasurface n Unit distance , No. n Units to The distance of the imaging grid , No. The distance from the imaging unit to the receiving antenna , assuming that the signal irradiated by the transmitting antenna on the metamaterial surface is a plane wave, that is, the amplitude of the signal received by each metamaterial unit is equal, and the transmitted signal propagates to the metasurface n The incident signal of a unit It is expressed as: ; in c Represents the speed of light, metamaterials n The output signal of each unit It is expressed as: ; in is the random phase shift of the two-bit metamaterial unit, The value is 0 or π , j is an imaginary unit, all metamaterials N The unit emits signals to the imaging grid space point The superposition of the incident signal It is expressed as: ; After acting on the target, from the grid space point The outgoing signal It is expressed as: ; in Represents spatial grid points The target scattering coefficient is the signal received by the receiving antenna. Sr(t) The superposition of the outgoing signals from all grid points is expressed as: ; Select random frequency hopping signal as the transmission signal, then the transmission signal S(t) The specific form is: ; in is the signal amplitude, is the center frequency, is the minimum frequency hopping interval, c is the frequency hopping control code, that is, the total delay of the receiving antenna receiving the signal : ; The receiving antenna receives the signal Sr(t) It is expressed as: ; No. Reference signal of imaging grid points It is expressed as: .

[0007] Furthermore, the specific process of constructing the imaging equation in step S5 is: The transmitted signal selected from the random frequency hopping signal S(t) Discretize, design random frequency hopping signal and random coding sequence configuration timing, perform single-point sampling in each coding time, one coding number represents one measurement, assuming the coding number is M , the microwave correlation imaging equations are constructed as follows: ; in Representative M The received signal under coding, Representative M Encoded L The reference signal of the grid, For the L The scattering intensity of the grid target, For the L The microwave correlation imaging equation matrix is ​​expressed as follows: Sr = S· +n in Sr is the received signal vector, S is the reference matrix, is the target scattering coefficient vector, n is the additive noise vector.

[0008] Furthermore, the specific steps of structurally reorganizing the reference matrix block in step S6 are: SS301, divide the scene D into several square imaging blocks D = {D1, ...D M}; S302, placing the atoms corresponding to the reference matrix S together in columns according to the neighbor characteristics of the imaging grid structure in the two-dimensional square block; S303: Obtain a new reference matrix containing imaging block structure information , create a structure information index Sindex Recording a new reference matrix Each atom in the reference matrix The index in .

[0009] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention constructs the constraint of block reconstruction through step S7. The selection of atoms in the orthogonal matching pursuit algorithm depends on the level of overall correlation strength of the block, ensuring that the neighborhood information of the point target can also be reconstructed, increasing the probability of target center being reconstructed, reducing the possibility of interference by strong scattering points, and improving the robustness of the algorithm.

[0010] 2. The present invention adopts a positive correlation atom addition strategy through step S7, so that only atoms showing positive correlation can be added into the reconstructed support set. This strategy is consistent with the principle of microwave correlation imaging, and while improving the accuracy, it reduces the algorithm calculation amount and shortens the imaging time. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a schematic diagram of the supersurface microwave correlation imaging system of the present invention; Figure 2 is a flow chart of the imaging equation reconstruction algorithm of the present invention; Figure 3 is a target scene graph of an embodiment of the present invention; Figure 4 The embodiment of the present invention provides a target scene imaging reconstruction result map; DETAILED DESCRIPTION

[0012] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0013] like Figure 1-4 As shown, a sparse extended target imaging method based on a metasurface microwave correlation imaging system comprises the following specific steps: The steps include: Step S1: construct a metasurface microwave correlation imaging system consisting of a transmitting antenna, a reflective two-bit phase modulation metasurface, and a receiving antenna, wherein each metamaterial unit on the reflective two-bit phase modulation metasurface is evenly distributed in a plane, and the spacing between adjacent units is half a wavelength; Step S2: The transmitting antenna transmits a random frequency hopping signal, which is incident on a reflective two-bit phase modulation metasurface with a random phase modulation, generating a random radiation field that is not correlated in space and time. After being modulated, the signal is transmitted through space and acts on the target. The signal at the target is scattered and then received by the receiving antenna. Step S3: setting an imaging plane directly in front of the reflective two-bit phase modulation metasurface, wherein the imaging plane is evenly divided into square grids of the same size, and the scattering point is located at the grid center of the imaging plane, and the normal line of the reflective two-bit phase modulation metasurface passes through the plane center of the imaging plane; Step S4: Construct a signal model to obtain the reflected signal and reference signal ; The specific process of constructing the signal model in step S4 is: Assume that the number of units of the reflective two-bit phase modulation metasurface is N , the number of grids in the imaging plane is L , the start time of the transmitter signal is t , the transmitted signal is S(t) , the transmitting antenna to the reflective two-bit phase modulation metasurface n Unit distance , No. n Units to The distance of the imaging grid , No. The distance from the imaging unit to the receiving antenna , assuming that the signal irradiated by the transmitting antenna on the metamaterial surface is a plane wave, that is, the amplitude of the signal received by each metamaterial unit is equal, and the transmitted signal propagates to the metasurface n The incident signal of a unit It is expressed as: ; in c Represents the speed of light, metamaterials n The output signal of each unit It is expressed as: ; in is the random phase shift of the two-bit metamaterial unit, The value is 0 or π , j is an imaginary unit, all metamaterials N The unit emits signals to the imaging grid space point The superposition of the incident signal It is expressed as: ; After acting on the target, from the grid space point The outgoing signal It is expressed as: ; in Represents spatial grid points The target scattering coefficient is the signal received by the receiving antenna. Sr(t) The superposition of the outgoing signals from all grid points is expressed as: ; Select random frequency hopping signal as the transmission signal, then the transmission signal S(t) The specific form is: ; in is the signal amplitude, is the center frequency, is the minimum frequency hopping interval, c is the frequency hopping control code, that is, the total delay of the receiving antenna receiving the signal : ; The receiving antenna receives the signal Sr(t) It is expressed as: ; No. Reference signal of imaging grid points It is expressed as: ; Step S5: Construct the imaging equation to obtain the received signal vector Sr and the reference matrix ; The specific process of constructing the imaging equation in step S5 is: The transmitted signal selected from the random frequency hopping signal S(t) Discretize, design random frequency hopping signal and random coding sequence configuration timing, perform single-point sampling in each coding time, one coding number represents one measurement, assuming the coding number is M , the microwave correlation imaging equations are constructed as follows: ; in Representative M The received signal under coding, Representative M Encoded L The reference signal of the grid, For the L The scattering intensity of the grid target, For the L The microwave correlation imaging equation matrix is ​​expressed as follows: Sr = S· +n in Sr is the received signal vector, S is the reference matrix, is the target scattering coefficient vector, n is the additive noise vector; Step S6: The reference matrix block is restructured to finally obtain a new reference matrix containing the imaging block structure information. , create a structure information index Sindex Recording a new reference matrix Each atom in the reference matrix The index in ; The specific steps of structurally reorganizing the reference matrix block in step S6 are: S301, divide the scene D into several square imaging blocks D={D1,...D M}; S302, placing the atoms corresponding to the reference matrix S together in columns according to the neighbor characteristics of the imaging grid structure in the two-dimensional square block; S303: Obtain a new reference matrix containing imaging block structure information , create a structure information index Sindex Recording a new measurement matrix The index of each atom in the reference matrix S; Step S7: Calculate the imaging reconstruction algorithm to solve the imaging equation. The present invention provides an improved block orthogonal matching pursuit (BOMP) algorithm to solve the imaging equation, as shown in the attached figure. Figure 2 The flowchart shown, the specific steps of the improved block orthogonal matching pursuit (BOMP) algorithm are as follows: Input: Receive signal Sr , the reference matrix , the block sparsity of the signal K , structure information index Sindex ; Output: Reconstructed scene scattering intensity ; Step S71: BOMP algorithm initialization: setting the number of block iterations k =0, residual r= Sr , select the atomic set Φ k is an empty set, restore the index set Λ k is an empty set; Step S72: Iteration step, k Iterations; (1) Finding residuals r With reference matrix S The most matching relevant block D j In all relevant blocks D j The index in is as follows: ; (2) Record related blocks D j Zhongzheng Atoms in the New Reference Matrix Index set in J k , increase the recovery index set , increase the support set ; (3) Least squares reconstruction of target signal ,in Representation Matrix of pseudo-rebellion; (4) Update residual ; (5) Determine whether the number of cycles reaches the set number of cycles or the residual norm is less than the set threshold. If it is satisfied, stop. If not, continue iterating. Step S73: restore the index set Λ k , structure information index Sindex and , the scattering coefficient of the reconstructed space is matched with the index to obtain the target microwave correlation imaging result.

[0014] The target scene of the experiment is "cyber". Figure 3 The imaging reconstruction results of the improved block orthogonal matching pursuit (BOMP) algorithm are shown in the attached figure. Figure 4 ,The analysis results show that the sparse extended target imaging method based on ,metasurface microwave correlation imaging system proposed in this paper presents good ,imaging effect.

[0015] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A sparse extended target imaging method based on a metasurface microwave correlation imaging system, characterized in that: The steps include: Step S1: construct a metasurface microwave correlation imaging system consisting of a transmitting antenna, a reflective two-bit phase modulation metasurface, and a receiving antenna; Step S2: modulate the transmission signal of the transmitting antenna and transmit it to the target through space transmission. The transmission signal is received by the receiving antenna after scattering. Step S3: setting an imaging plane directly in front of the reflective two-bit phase modulation metasurface, wherein the imaging plane is evenly divided into square grids of the same size, and the scattering point is located at the grid center of the imaging plane, and the normal line of the reflective two-bit phase modulation metasurface passes through the plane center of the imaging plane; Step S4: Construct a signal model to obtain the reflected signal and reference signal ; Step S5: Construct the imaging equation to obtain the received signal vector Sr and the reference matrix ; Step S6: The reference matrix block is restructured to finally obtain a new reference matrix containing the imaging block structure information. , create a structure information index Sindex Recording a new reference matrix Each atom in the reference matrix The index in ; Step S7: Computational imaging reconstruction algorithm solution, the specific steps are as follows: Input: Receive signal Sr , the reference matrix , the block sparsity of the signal K , structure information index Sindex ; Output: Reconstructed scene scattering intensity ; Step S71: BOMP algorithm initialization: setting the number of block iterations k =0, residual r= Sr , select the atomic set Φ k is an empty set, restore the index set Λ k is an empty set; Step S72: Iteration step, k Iterations; (1) Finding residuals r With reference matrix S The most matching relevant block D j In all relevant blocks D j The index in is as follows: ; (2) Record related blocks D j Zhongzheng Atoms in the New Reference Matrix Index set in J k , increase the recovery index set , increase the support set ; (3) Least squares reconstruction of target signal ,in Representation Matrix of pseudo-rebellion; (4) Update residual ; (5) Determine whether the number of cycles reaches the set number of cycles or the residual norm is less than the set threshold. If it is satisfied, stop. If not, continue iterating. Step S73: restore the index set Λ k , structure information index Sindex and , the scattering coefficient of the reconstructed space is matched with the index to obtain the target microwave correlation imaging result.

2. According to claim 1, a sparse extended target imaging method based on a metasurface microwave correlation imaging system is characterized in that: The specific process of constructing the signal model in step S4 is: Assume that the number of units of the reflective two-bit phase modulation metasurface is N , the number of grids in the imaging plane is L , the start time of the transmitter signal is t , the transmitted signal is S(t) , the transmitting antenna to the reflective two-bit phase modulation metasurface n Unit distance , No. n Units to The distance of the imaging grid , No. The distance from the imaging unit to the receiving antenna , assuming that the signal irradiated by the transmitting antenna on the metamaterial surface is a plane wave, that is, the amplitude of the signal received by each metamaterial unit is equal, and the transmitted signal propagates to the metasurface n The incident signal of a unit It is expressed as: ; in c Represents the speed of light, metamaterials n The output signal of each unit It is expressed as: ； in is the random phase shift of the two-bit metamaterial unit, The value is 0 or π , j is an imaginary unit, all metamaterials N The unit emits signals to the imaging grid space point The superposition of the incident signal It is expressed as: ； After acting on the target, from the grid space point The outgoing signal It is expressed as: ； in Represents spatial grid points The target scattering coefficient is the signal received by the receiving antenna. Sr(t) The superposition of the outgoing signals from all grid points is expressed as: ； Select random frequency hopping signal as the transmission signal, then the transmission signal S(t) The specific form is: ； in is the signal amplitude, is the center frequency, is the minimum frequency hopping interval, c is the frequency hopping control code, that is, the total delay of the receiving antenna receiving the signal : ； The receiving antenna receives the signal Sr(t) It is expressed as: ； No. Reference signal of imaging grid points It is expressed as: 。 3. The sparse extended target imaging method based on the metasurface microwave correlation imaging system according to claim 2 is characterized in that: The specific process of constructing the imaging equation in step S5 is: The transmitted signal selected from the random frequency hopping signal S(t) Discretize, design random frequency hopping signal and random coding sequence configuration timing, perform single-point sampling in each coding time, one coding number represents one measurement, assuming the coding number is M , the microwave correlation imaging equations are constructed as follows: ； in Representative M The received signal under coding, Representative M Encoded L The reference signal of the grid, For the L The scattering intensity of the grid target, For the L The grid noise, the microwave correlation imaging equation matrix is ​​expressed as follows: Sr=S· +n; in Sr is the received signal vector, S is the reference matrix, is the target scattering coefficient vector, n is the additive noise vector.

4. The sparse extended target imaging method based on the metasurface microwave correlation imaging system according to claim 1 is characterized in that: The specific steps of structurally reorganizing the reference matrix block in step S6 are: S301, divide the scene D into several square imaging blocks D={D1,...D M }; S302, placing the atoms corresponding to the reference matrix S together in columns according to the neighbor characteristics of the imaging grid structure in the two-dimensional square block; S303: Obtain a new reference matrix containing imaging block structure information , create a structure information index Sindex Recording a new reference matrix Each atom in the reference matrix The index in .

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