A microwave staring correlation imaging method based on reflective polarization conversion metasurface

Abstract

The present invention discloses a microwave staring correlation imaging method based on a reflective polarization conversion metasurface, comprising: arranging a microwave random radiation linear polarization antenna array in the antenna beam coverage area to form a linear polarization space-time two-dimensional random radiation field; using a receiver cross-polarization receiving antenna located at a set transceiver angle to receive a cross-polarization scattered echo signal formed by the interaction between the reflective polarization conversion metasurface structure attached to the surface of the target of interest to be imaged and the linear polarization space-time two-dimensional random radiation field; based on a correlation imaging model, collecting the scattered echo signal with a set cross-polarization reflection coefficient, and performing correlation processing with a preset linear polarization space-time two-dimensional random radiation field, and inverting to obtain the target image. This method can effectively suppress background clutter and sidelobe leakage of the transceiver antenna in the microwave staring correlation imaging experiment, and realize effective verification of the imaging mechanism.

Description

Technical Field

[0001] The present invention relates to the technical field of staring correlation imaging, and in particular to a microwave staring correlation imaging method based on a reflective polarization conversion metasurface. Background Art

[0002] Metamaterials usually refer to artificially designed composite materials with periodic structures. Such materials often have some electromagnetic properties that natural materials do not have. People can flexibly design electromagnetic metamaterials according to actual needs, thereby achieving effective control of propagation characteristics such as electromagnetic wave amplitude, propagation direction, phase and polarization.

[0003] Polarization is one of the most important characteristics of electromagnetic waves, which refers to the trajectory direction of the electric field vector along the propagation direction of the electromagnetic wave. Polarization characteristics have a wide range of applications both in military defense and in daily life, so it is very important to manipulate the polarization of electromagnetic waves. The most traditional method to achieve polarization control is to rely on the anisotropic properties of the material's own structure, but devices made of traditional materials are large and not easy to integrate, so it is difficult to apply them to practical systems. In addition, the narrow working frequency band, low efficiency, and high loss also make the polarization control effect not obvious, and the emergence of metamaterials overcomes the problems brought by traditional materials. By rationally designing the metamaterial structure, the equivalent electromagnetic parameters in each direction are different, and finally the polarization state of the electromagnetic wave can be flexibly controlled.

[0004] Microwave staring correlation imaging has the characteristics of high-resolution imaging because it breaks through the limitations of the antenna aperture of the traditional real aperture radar imaging system. However, in the experimental process, due to the sidelobe leakage problem caused by the background clutter and the incomplete isolation of the transmitting and receiving antennas, the echo information received by the receiving antenna is mixed with background scattered echoes and leakage waves, which is very cumbersome to handle and has a great impact on the verification of the imaging quality and the effectiveness of the imaging mechanism. Summary of the invention

[0005] The purpose of the present invention is to provide a microwave staring correlation imaging method based on a reflective polarization conversion metasurface, which can effectively suppress background clutter and sidelobe leakage of transceiver antennas in microwave staring correlation imaging experiments, and provide a feasible way to improve imaging quality and realize effective verification of imaging mechanism.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A microwave staring correlation imaging method based on a reflective polarization conversion metasurface comprises:

[0008] Arrange microwave random radiation linear polarization antenna arrays to form linear polarization space-time two-dimensional random radiation fields within the antenna beam coverage area;

[0009] The receiver cross-polarization receiving antenna located at the set receiving and transmitting angle is used to receive the cross-polarization scattered echo signal formed by the interaction between the reflective polarization conversion metasurface structure attached to the surface of the target to be imaged and the linearly polarized two-dimensional random radiation field in time and space;

[0010] Based on the correlation imaging model, the scattered echo signal with set cross-polarization reflection coefficient is collected, and the correlation processing is carried out with the preset linear polarization two-dimensional random radiation field in time and space to invert the target image.

[0011] It can be seen from the technical solution provided by the present invention that by applying a reflective polarization conversion metasurface on the surface of the target of interest to be imaged and using a cross-polarized receiving antenna to receive the echo, the co-polarization background clutter and leakage waves can be effectively filtered out, and better inversion imaging results can be obtained using the traditional microwave staring correlation imaging method. The present invention realizes high-resolution imaging of the target under the reflective polarization conversion metasurface; in addition, the echo signal received under the reflective polarization conversion metasurface is used as the effective information of the target, and the new imaging mechanism can be verified, which has further value for scientific research. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0013] Figure 1 A flow chart of a microwave staring correlation imaging method based on a reflective polarization conversion metasurface provided in an embodiment of the present invention;

[0014] Figure 2 A schematic diagram of an imaging scene of a microwave staring correlation imaging method based on a reflective polarization conversion metasurface provided in an embodiment of the present invention;

[0015] Figure 3 A schematic diagram of a reflective polarization conversion metasurface attached to an I-shaped imaging target surface provided by an embodiment of the present invention;

[0016] Figure 4 A schematic diagram of a reflective polarization conversion metasurface unit provided in an embodiment of the present invention;

[0017] Figure 5 A schematic diagram of the variation of the co-polarization reflection coefficient Rxx and the cross-polarization reflection coefficient Rxy with frequency when an electromagnetic wave is incident on a vertically reflective polarization conversion metasurface provided by an embodiment of the present invention;

[0018] Figure 6 A schematic diagram showing how the cross-polarization reflection coefficient of a reflective polarization conversion metasurface varies with frequency at different incident electromagnetic wave angles provided by an embodiment of the present invention;

[0019] Figure 7 A schematic diagram of the variation of the co-polarization reflection coefficient Rxx and the cross-polarization reflection coefficient Rxy with frequency when an electromagnetic wave vertical reflection polarization conversion metasurface unit provided by an embodiment of the present invention is incident;

[0020] Figure 8 A schematic diagram of a target image inverted by a wave staring correlation imaging method with and without a reflective polarization conversion metasurface attached to an I-shaped imaging target surface provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0021] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings 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 protection scope of the present invention.

[0022] First, the terms that may be used in this article are explained as follows:

[0023] The terms "include", "comprises", "contains", "has" or other descriptions with similar semantics should be interpreted as non-exclusive inclusion. For example, including certain technical feature elements (such as raw materials, components, ingredients, carriers, dosage forms, materials, dimensions, parts, components, mechanisms, devices, steps, procedures, methods, reaction conditions, processing conditions, parameters, algorithms, signals, data, products or products, etc.) should be interpreted as including not only certain technical feature elements explicitly listed, but also other technical feature elements known in the art that are not explicitly listed.

[0024] The term "consisting of..." means excluding any technical feature elements not explicitly listed. If this term is used in a claim, it will make the claim closed, so that it does not contain technical feature elements other than the technical feature elements explicitly listed, except for the conventional impurities related to them. If this term only appears in a clause of a claim, it only limits the elements explicitly listed in the clause, and the elements recorded in other clauses are not excluded from the overall claim.

[0025] The following is a detailed description of a microwave staring correlation imaging method based on a reflective polarization conversion metasurface provided by the present invention. The contents not described in detail in the embodiments of the present invention belong to the prior art known to professional and technical personnel in the field. If no specific conditions are specified in the embodiments of the present invention, the conventional conditions in the field or the conditions recommended by the manufacturer shall be followed. The instruments used in the embodiments of the present invention, for which the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0026] like Figure 1 As shown, a microwave staring correlation imaging method based on a reflective polarization conversion metasurface mainly includes the following steps:

[0027] Step 1: Arrange a microwave random radiation linear polarization antenna array to form a linear polarization space-time two-dimensional random radiation field within the antenna beam coverage area.

[0028] Step 2: Use the cross-polarization receiving antenna of the receiver located at the set receiving and transmitting angle to receive the cross-polarization scattered echo signal formed by the interaction between the reflective polarization conversion metasurface structure attached to the surface of the target of interest to be imaged and the linearly polarized two-dimensional random radiation field in space and time.

[0029] In an embodiment of the present invention, the reflective polarization conversion metasurface structure attached to the surface of the target of interest to be imaged is composed of periodically and closely arranged metasurface units, and the size of the metasurface unit is a subwavelength size of the working wavelength. Exemplarily, the metasurface unit includes: a dielectric substrate and a metal patch arranged on the top surface and the metal plate arranged on the bottom surface of the dielectric substrate respectively; the metal patch is composed of two coupled rectangular metal rings, each rectangular metal ring is etched with two identical notches on two sides perpendicular to each other, and the notches of two different rectangular metal rings are on different sides, together forming an open-loop resonator; the incident linearly polarized electromagnetic field resonates with each metasurface unit, and the net dominant current induced on the metasurface is perpendicular to the direction of the electric field vector of the incident linear polarization, forming a reflected cross-polarization scattering field.

[0030] Step 3: Based on the correlation imaging model, the scattered echo signal with the set cross-polarization reflection coefficient is collected, and the signal is correlated with the preset linear polarization space-time two-dimensional random radiation field to obtain the target image through inversion.

[0031] In the above scheme of the embodiment of the present invention:

[0032] 1) The microwave random radiation antenna array and the receiver antenna adopt different polarizations. The metasurface structure converts the co-polarized electromagnetic waves emitted by the microwave random radiation antenna array into cross-polarized electromagnetic waves received by the receiver antenna.

[0033] 2) A reflective polarization conversion metasurface structure is attached to the surface of the imaging target. When a linearly polarized incident wave is irradiated onto the metasurface, the specific structure of the designed metasurface will always make the incident field encounter a side with an etched notch and a side without an etched notch. Since there is a phase difference between the surface currents on the notched side and the non-notched side, the net current perpendicular to the direction of the incident electric field is the largest at resonance, resulting in good cross-polarization conversion.

[0034] 3) The size of the metasurface unit is comparable to the working wavelength within the working frequency band, and the structural symmetry of the open-ring resonator on the metal plane, with its wide polarization conversion bandwidth and stable incident angle of the incident wave, will greatly increase the amount of effective information obtained during the imaging experiment, which is of great help in verifying the effectiveness of the imaging quality and the imaging mechanism.

[0035] 4) Within the working frequency band of the reflective polarization conversion metasurface, when a linearly polarized electromagnetic wave in the air is incident on the top surface of the metasurface structure, each metasurface unit resonates, and the net dominant current induced on the metasurface is perpendicular to the direction of the electric field vector of the incident linear polarization, thereby generating a reflected cross-polarization electric field and realizing the conversion of the polarization angle.

[0036] In order to more clearly demonstrate the technical solution and technical effects provided by the present invention, Figure 2 The scene shown uses a specific embodiment to describe in detail a microwave staring correlation imaging method based on a reflective polarization conversion metasurface provided by an embodiment of the present invention.

[0037] 1. Lay out a microwave random radiation linear polarization antenna array.

[0038] In the embodiment of the present invention, the microwave random radiation linear polarization antenna array includes M linear polarization antenna units. Figure 2 middle represents the direction of electromagnetic wave propagation, represents the magnetic field vector, represents the electric field vector; the i-th linear polarization antenna unit transmits mutually orthogonal random signals as At time t, the linearly polarized two-dimensional random radiation field in space and time that irradiates the antenna beam coverage area is formed. Characterized by:

[0039]

[0040] in, represents the phase center position vector of the i-th linear polarization antenna element; is the antenna beam coverage area (i.e. Figure 2The position vector of the jth discrete grid resolution unit in the imaging area shown in the figure, j = 1, ..., Ω, Ω = P × Q is the number of resolution unit grids for spatial discretization in the antenna beam coverage area, P is the number of grids in the X direction, and Q is the number of grids in the Y direction; Ω includes the number of resolution unit grids Ω' of the target area to be imaged and the number of resolution unit grids Ω", of the background area, Ω = Ω'∪Ω"; F i (.) represents the directional pattern function of the i-th linear polarization antenna unit. The information in the brackets is the unit direction vector. is the radiation pattern of the i-th linear polarization antenna element, for Relative to is the unit vector in the spatial direction; c is the speed of light.

[0041] 2. Attach a reflective polarization conversion metasurface structure to the surface of the target of interest to be imaged.

[0042] In the embodiment of the present invention, the object of interest to be imaged is Figure 3 Taking the I-shape shown as an example, the reflective polarization conversion metasurface is applied to the surface of the I-shaped imaging target. The overall dimensions of the metasurface applied to the I-shaped imaging target include: the length * width * thickness dimensions of the upper and lower 'I' shapes are 308mm*70mm*2.4mm, and the length * width * thickness dimensions of the middle '|' shape are 238mm*70mm*2.4mm.

[0043] In the embodiment of the present invention, the metasurface unit includes: a dielectric substrate and a metal patch arranged on the top surface of the dielectric substrate and a metal plate arranged on the bottom surface. The metal patch on the bottom surface of the dielectric substrate is a 0.035 mm thick copper foil. The dielectric substrate used is FR-4, which has a relative dielectric constant of 4.4, a loss tangent of 0.02, and a substrate thickness of 2.4 mm. The metal patch is composed of two coupled rectangular metal rings, such as Figure 4 As shown, it can be specifically two symmetrical rectangular rings placed inside and outside with two identical notches etched on the vertical sides, and the notch of the outer rectangular ring and the notch of the inner rectangular ring are not on the same side. The structural parameters are that the length and width of the outer rectangular ring are both L=6mm, the notch is at the center of the two vertical sides of the rectangular ring, and the length is d=1mm. The length and width of the inner rectangular ring are both m=3mm, the notch is at the center of the two vertical sides of the rectangular ring, and the length is g=0.5mm. The notch of the outer rectangular ring and the notch of the inner rectangular ring are not on the same side. The metasurface units are closely arranged along the x and y directions at a period of W=6mm to form a metasurface array.

[0044] In the embodiment of the present invention, the frequency band of the electromagnetic waves emitted by the microwave random radiation linear polarization antenna array is 2GHz-12GHz vertically polarized waves, and accordingly, an imaging target with a reflective polarization conversion metasurface structure and a horn antenna for receiving 2GHz-12GHz horizontally polarized waves are attached.

[0045] 3. The linearly polarized two-dimensional random radiation field in space-time interacts with the target applied to the metasurface, forming a cross-polarized backscattering field through the polarization conversion of the electromagnetic field.

[0046] In the embodiment of the present invention, the reflective polarization conversion metasurface structure interacts with the linearly polarized two-dimensional random radiation field in space-time, and forms a cross-polarization scattering field at the phase center of the cross-polarization receiving antenna of the receiver located at the set transmitting and receiving angle through the polarization conversion of the electromagnetic field. It is expressed as:

[0047]

[0048] in, represents the radiation field irradiated on the target of interest to be imaged with the reflective polarization conversion metasurface structure, t represents the time, are the position vector and backscatter coefficient of the kth imaging target resolution unit, Ω' represents the number of resolution unit grids of the target area of ​​interest to be imaged, Represents the phase center position vector of the receiver's cross-polarization receiving antenna.

[0049] In the embodiment of the present invention, the total electromagnetic field E at the phase center of the cross-polarized receiving antenna of the receiver at the set receiving and transmitting angle is sca (t) includes: cross-polarization scattered field Co-polarized scattered field in the background area and the co-polarized electromagnetic field generated by the sidelobe leakage of the transmitting and receiving antennas Total electromagnetic field E sca (t) is expressed as:

[0050]

[0051] in, represents the radiation field irradiated on the background area, t represents the time; M represents the number of linearly polarized antenna units of the microwave random radiation linearly polarized antenna array, It means that the i-th linear polarization antenna unit transmits mutually orthogonal random signals. represents the phase center position vector of the i-th linear polarization antenna unit, c is the speed of light; k = 1, ..., Ω', Ω' represents the number of resolution unit grids of the target area of ​​interest to be imaged, are the position vector and backscattering coefficient of the kth imaging target resolution unit, respectively. represents the phase center position vector of the receiver’s cross-polarization receiving antenna, for Relative to The spatial direction unit vector; l=1,...,Ω”,Ω” represents the number of resolution unit grids in the background area, are the position vector and backscattering coefficient of the lth resolution unit in the background area respectively.

[0052] 4. The cross-polarization backscattered echo is synchronously received by the cross-polarization receiving antenna of the receiver located at the set transmitting and receiving angle.

[0053] In an embodiment of the present invention, the set receiving and transmitting angle at which the cross-polarization receiving antenna of the receiver is located is a wide receiving and transmitting angle. The method for determining the wide receiving and transmitting angle includes: connecting the transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver to a vector network analyzer respectively, and gradually opening the angle between the transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver relative to the reflective polarization conversion metasurface structure. The vector network analyzer scans the cross-polarization reflection coefficient of each frequency point in the working frequency band, and selects the angle variation range that keeps the cross-polarization reflection coefficient above the set value (for example, -3dB) as the wide receiving and transmitting angle of the transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver.

[0054] In the embodiment of the present invention, the cross-polarization receiving antenna of the receiver located at the set receiving and transmitting angle receives the cross-polarization scattered field signal, that is, the cross-polarization scattered echo signal The background clutter scattered field of the same polarization and receiving leakage wave electromagnetic fields are effectively suppressed; the received cross-polarization scattered echo signal It is expressed as:

[0055]

[0056] in, is the radiation pattern received by the receiver’s cross-polarized receiving antenna, is the position vector of the kth imaging target resolution unit Phase center position vector relative to the receiving antenna The spatial direction unit vector of are the position vector and backscattering coefficient of the kth imaging target resolution unit, respectively. for Relative to The spatial direction unit vector of M represents the number of linearly polarized antenna units in the microwave random radiation linearly polarized antenna array. It indicates that the i-th linear polarization antenna unit transmits mutually orthogonal random signals, t indicates the time, Represents the phase center position vector of the i-th linearly polarized antenna element.

[0057] 5. Based on the correlation imaging model, the scattered echo signal with high cross-polarization reflection coefficient in the working frequency band of the metasurface is collected, and the correlation processing and image inversion are carried out with the preset linear polarization space-time two-dimensional random radiation field.

[0058] 1. Collect scattered echo signals with high cross-polarization reflection coefficient within the working frequency band of the metasurface.

[0059] In an embodiment of the present invention, the working frequency band for setting the cross-polarization reflection coefficient is determined in the following manner: the transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver are respectively connected to the vector network analyzer, the transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver are placed together (i.e., in the same position), and the reflective polarization conversion metasurface structure is vertically illuminated. The vector network analyzer scans the cross-polarization reflection coefficient of each frequency point in the frequency band, and selects the frequency band with a cross-polarization reflection coefficient greater than a set value (for example, -3dB) as the working frequency band for setting the cross-polarization reflection coefficient.

[0060] like Figure 2 As shown, the imaging target with the reflective polarization conversion metasurface structure is placed on the xoy plane, each transmitting unit of the microwave random radiation source array is fixed and tilted 2m above the left of the imaging area, the receiver is fixed above the right of the transmitting antenna, the transmitting and receiving antennas are 2m apart at the same height, and are connected to a two-port vector network analyzer. The angle between the incident electromagnetic wave and the reflected electromagnetic wave is 30°. For the cross-polarization reflection coefficient, the placement direction of the receiving antenna is perpendicular to that of the transmitting antenna. The transmitting antenna transmits a linearly polarized electromagnetic wave in the frequency band of 2GHz-12GHz to the metasurface structure. After being reflected by the polarization conversion of the metasurface structure, the cross-polarization reflection signal can be displayed on the vector network analyzer.

[0061] like Figure 5 As shown, when the electromagnetic wave is incident on the vertical reflection polarization conversion metasurface, the frequency band in which the metasurface array converts the linearly polarized incident wave into the cross-polarized reflected wave with the highest efficiency is 7.5 to 9.5 GHz. In this frequency band, the co-polarization reflection coefficient Rxx is less than -15 dB, while the cross-polarization reflection coefficient Rxy is greater than -3 dB.

[0062] like Figure 6 As shown, in Figure 2 In the imaging scene shown, when the angle θ between the incident electromagnetic wave and the normal of the polarization conversion metasurface changes from 0° to 45°, the amplitude of the cross-polarization reflection coefficient in the working frequency band of 7.5 GHz-9.5 GHz hardly changes, indicating that the structure used in the present invention has high stability and robustness.

[0063] like Figure 7 As shown in the figure, in the frequency band 2-12GHz, when the electromagnetic wave is incident vertically on the polarization conversion metasurface unit, the co-polarization reflection coefficient and the cross-polarization reflection coefficient change with frequency. It can be clearly seen from the figure that in the 5-10.8GHz frequency band, the co-polarization reflection coefficient is small, while the cross-polarization reflection coefficient is greater than -3dB, accounting for 73% of the entire bandwidth, indicating the effectiveness of the imaging system.

[0064] 2. Correlation processing and inversion imaging.

[0065] In the embodiment of the present invention, the association processing and inversion imaging method includes: at different sampling times t, the collected scattered echo signals with set cross-polarization reflection coefficients are collected. The preset linear polarization space-time two-dimensional random radiation field at the corresponding time Perform association processing and invert to obtain the image of the target of interest It is expressed as: where ζ{·} represents the association processing algorithm.

[0066] like Figure 8 As shown in the figure, (a) and (b) are the inversion images of the I-shaped imaging target surface with the reflective polarization conversion metasurface attached, and the inversion images of the I-shaped imaging target surface without the reflective polarization conversion metasurface attached. Figure 8 It can be seen from the simulation results shown that: applying a reflective polarization conversion metasurface on the surface of the I-shaped imaging target and using a cross-polarized receiving antenna to receive the echo can effectively filter out the co-polarized background clutter and leakage waves, and using the traditional microwave staring correlation imaging method can obtain better inversion imaging results, while no reflective polarization conversion metasurface is applied to the surface of the I-shaped imaging target, and using a co-polarized receiving antenna to receive the echo, the traditional microwave staring correlation imaging method does not have a good inversion imaging result. It can be seen that the present invention achieves high-resolution imaging of the target under the reflective polarization conversion metasurface. In addition, the echo signal received under the reflective polarization conversion metasurface is used as the effective information of the target, and the new imaging mechanism can also be verified, which has further value for scientific research.

[0067] It should be noted that the numerical values ​​of various parameters involved in the text description of the present invention and the drawings are only examples and do not constitute limitations; in actual applications, users can adjust the numerical values ​​of various parameters according to actual conditions or experience.

[0068] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A microwave staring correlation imaging method based on reflective polarization conversion metasurface, It is characterized in that include: Arrange microwave random radiation linear polarization antenna arrays to form linear polarization space-time two-dimensional random radiation fields within the antenna beam coverage area; The receiver cross-polarization receiving antenna located at the set receiving and transmitting angle is used to receive the cross-polarization scattered echo signal formed by the interaction between the reflective polarization conversion metasurface structure attached to the surface of the target to be imaged and the linearly polarized two-dimensional random radiation field in time and space; Based on the correlation imaging model, the scattered echo signal with the set cross-polarization reflection coefficient is collected, and the correlation processing is performed with the preset linear polarization time-space two-dimensional random radiation field to invert the target image; The reflective polarization conversion metasurface structure interacts with the linearly polarized two-dimensional random radiation field in space-time, and forms a cross-polarization scattering field at the phase center of the cross-polarization receiving antenna of the receiver located at the set transmitting and receiving angle through the polarization conversion of the electromagnetic field. It is expressed as: in, represents the radiation field irradiated on the target of interest to be imaged with the reflective polarization conversion metasurface structure, t represents the time, are the position vector and backscatter coefficient of the kth imaging target resolution unit, Ω' represents the number of resolution unit grids of the target area of ​​interest to be imaged, Represents the phase center position vector of the receiver's cross-polarization receiving antenna; The cross-polarization receiving antenna of the receiver located at the set receiving and transmitting angle receives the cross-polarization scattered field signal, that is, the cross-polarization scattered echo signal It is expressed as: in, is the radiation pattern received by the receiver’s cross-polarized receiving antenna, is the position vector of the kth imaging target resolution unit Phase center position vector relative to the receiving antenna The spatial direction unit vector of are the position vector and backscatter coefficient of the kth imaging target resolution unit, respectively. i (.) represents the directional pattern function of the i-th linear polarization antenna element, for Relative to The spatial direction unit vector of M represents the number of linearly polarized antenna units in the microwave random radiation linearly polarized antenna array. It indicates that the i-th linear polarization antenna unit transmits mutually orthogonal random signals, t indicates the time, Represents the phase center position vector of the i-th linearly polarized antenna element.

2. According to the microwave staring correlation imaging method based on the reflective polarization conversion metasurface according to claim 1, It is characterized in that The microwave random radiation linear polarization antenna array includes M linear polarization antenna units, and the i-th linear polarization antenna unit transmits mutually orthogonal random signals: At time t, the linearly polarized two-dimensional random radiation field in space and time that irradiates the antenna beam coverage area is formed. Characterized by: in, represents the phase center position vector of the i-th linear polarization antenna element; is the position vector of the jth discrete grid resolution unit in the antenna beam coverage area, j=1,...,Ω, Ω=P×Q is the number of resolution unit grids for spatial discretization in the antenna beam coverage area, P is the number of grids in the X direction, and Q is the number of grids in the Y direction; Ω includes the number of resolution unit grids Ω' of the target area to be imaged and the number of resolution unit grids Ω", of the background area, Ω=Ω'∪Ω"; is the radiation pattern of the i-th linear polarization antenna unit, F i (.) represents the directional pattern function of the i-th linear polarization antenna element, for Relative to is the unit vector in the spatial direction; c is the speed of light.

3. According to the microwave staring correlation imaging method based on the reflective polarization conversion metasurface of claim 1, It is characterized in that The reflective polarization conversion metasurface structure attached to the surface of the target of interest to be imaged is composed of periodically and closely arranged metasurface units, and the size of the metasurface unit is a sub-wavelength size of the working wavelength.

4. According to claim 3, a microwave staring correlation imaging method based on a reflective polarization conversion metasurface, It is characterized in that The metasurface unit comprises: a dielectric substrate and a metal patch arranged on the top surface and the metal plate arranged on the bottom surface of the dielectric substrate respectively; the metal patch consists of two coupled rectangular metal rings, each rectangular metal ring is etched with two identical notches on two sides perpendicular to each other, and the notches of two different rectangular metal rings are on different sides, together forming an open-loop resonator; the incident linearly polarized electromagnetic field resonates with each metasurface unit, and the net dominant current induced on the metasurface is perpendicular to the direction of the electric field vector of the incident linear polarization, forming a reflected cross-polarization scattering field.

5. According to claim 1, a microwave staring correlation imaging method based on a reflective polarization conversion metasurface, It is characterized in that The set receiving and transmitting angle at which the cross-polarized receiving antenna of the receiver is located is a wide receiving and transmitting angle, and the wide receiving and transmitting angle is determined in the following manner: The transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver are respectively connected to the vector network analyzer, and the angles of the transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver relative to the reflective polarization conversion metasurface structure are gradually opened. The vector network analyzer scans the cross-polarization reflection coefficient of each frequency point in the working frequency band, and selects the angle variation range that keeps the cross-polarization reflection coefficient above the set value as the wide transmitting and receiving angle of the transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver.

6. According to claim 1, a microwave staring correlation imaging method based on a reflective polarization conversion metasurface, It is characterized in that The working frequency band for setting the cross-polarization reflection coefficient is determined in the following way: The transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver are respectively connected to the vector network analyzer, the transmitting antenna of the linear polarization antenna unit and the cross-polarization receiving antenna of the receiver are placed together, and the reflective polarization conversion metasurface structure is vertically illuminated. The vector network analyzer scans the cross-polarization reflection coefficient of each frequency point in the frequency band, and selects the frequency band with a cross-polarization reflection coefficient greater than a set value as the working frequency band for setting the cross-polarization reflection coefficient.

7. According to claim 1, a microwave staring correlation imaging method based on a reflective polarization conversion metasurface, It is characterized in that The total electromagnetic field E at the phase center of the receiver's cross-polarized receiving antenna at the set transmit / receive angle sca (t) includes: cross-polarization scattered field Co-polarized scattered field in the background area and the co-polarized electromagnetic field generated by the sidelobe leakage of the transmitting and receiving antennas Total electromagnetic field E sca (t) is expressed as: in, represents the radiation field irradiated on the background area, t represents the time; M represents the number of linearly polarized antenna units of the microwave random radiation linearly polarized antenna array, It means that the i-th linear polarization antenna unit transmits mutually orthogonal random signals. represents the phase center position vector of the i-th linear polarization antenna unit, c is the speed of light; k = 1, ..., Ω', Ω' represents the number of resolution unit grids of the target area of ​​interest to be imaged, are the position vector and backscattering coefficient of the kth imaging target resolution unit, respectively. represents the phase center position vector of the receiver’s cross-polarization receiving antenna, F i (.) represents the directional pattern function of the i-th linear polarization antenna element, for Relative to The spatial direction unit vector; l=1,...,Ω”,Ω” represents the number of resolution unit grids in the background area, are the position vector and backscattering coefficient of the lth resolution unit in the background area respectively.

8. According to claim 1 or 6, a microwave staring correlation imaging method based on a reflective polarization conversion metasurface, It is characterized in that The method of collecting the scattered echo signal with the set cross-polarization reflection coefficient based on the correlation imaging model and performing correlation processing with the preset linear polarization space-time two-dimensional random radiation field to invert the target image includes: At different sampling times t, the scattered echo signals with set cross-polarization reflection coefficients collected are The preset linear polarization space-time two-dimensional random radiation field at the corresponding time Perform association processing and invert to obtain the image of the target of interest It is expressed as: where ζ{·} represents the association processing algorithm.

Images