Electromagnetic vector high-resolution imaging method based on wave front nonlinear modulation

Abstract

The application relates to an electromagnetic vector high-resolution imaging method based on wave front nonlinear modulation, and the method comprises the following steps: S1, placing a wave front nonlinear modulation system on one side of an antenna system; S2, calibrating equivalent frequency responses of the wave front nonlinear modulation system under different states; S3, after a known pulse signal is reflected by a target and passes through the wave front nonlinear modulation system, the echo signal is received by a receiving antenna at a corresponding observation point; S4, if the state index is greater than the total number of states of the wave front nonlinear modulation system, S5 is executed, otherwise, the index is updated, and the step S3 is returned; S5, combining the echo signal, the known pulse signal and the equivalent frequency response, target inversion is carried out to obtain the radar reflection cross section of each target and the position image of each target. Compared with the prior art, the application has the advantages of improving the angle resolution and reducing the antenna size requirement.

Description

Technical Field

[0001] This invention relates to the technical field of electromagnetic vector high-resolution imaging, and in particular to an electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation. Background Technology

[0002] Electromagnetic vector high-resolution imaging is an important method for geographic remote sensing and target detection, with resolution being a crucial technical indicator. Generally, antenna aperture determines angular resolution, while the transmitted signal bandwidth determines range resolution. Range resolution can be improved by increasing parameters such as the transmitted signal bandwidth. However, for angular resolution, since beamwidth is inversely proportional to the radar antenna size, a larger antenna aperture is required to achieve higher angular resolution, i.e., a narrower main beamwidth. Taking radar imaging as an example, large physical aperture antenna technology, synthetic aperture technology, and very long baseline technology are all effective methods to improve resolution. While these methods can improve the resolution capability of antenna systems to some extent, they still struggle to solve the problem of fine resolution of approximately parallel incoming signals from multiple targets at the same frequency, and they are also costly. The shortcomings can be summarized as follows:

[0003] 1. Angular resolution depends on antenna aperture. For high-resolution imaging, an excessively large antenna aperture is required, making it difficult to implement in special application scenarios such as airborne, spaceborne, and missile-borne environments;

[0004] 2. In certain imaging modes, such as microwave staring imaging and forward-looking imaging, there is no relative motion between the imaging scene and the radar platform or no effective Doppler information, making it difficult to achieve two-dimensional high-resolution images.

[0005] 3. It cannot achieve the resolution of multiple targets at equal intervals within the main beam range. Summary of the Invention

[0006] The purpose of this invention is to provide an electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation in order to improve the accuracy of magnetic vector high-resolution imaging.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A high-resolution electromagnetic vector imaging method based on wavefront nonlinear modulation, the method comprising:

[0009] S1. Place a wavefront nonlinear modulation system on one side of the antenna system, and determine a reference point for the incident angle of the incident wave in front of the wavefront nonlinear modulation system in the direction of the incoming wave. When the antenna system has L receiving antennas, determine the observation point after the incident wave, corresponding to each receiving antenna of the antenna system, passes through the wavefront nonlinear modulation system. There are L observation points, and the wavefront nonlinear modulation system has N states. The state index of the wavefront nonlinear modulation system is initialized to j=1; where the incident angle and the two-dimensional space angle are the same angle.

[0010] S2. Calibrate and measure the equivalent frequency response of the wavefront nonlinear modulation system under different states:

[0011]

[0012] Where l represents the l-th observation point, f represents the incident frequency, and θ i This represents the i-th two-dimensional spatial angle in the discretization.

[0013] S3. The transmitting antenna of the antenna system transmits a known pulse signal p(t). The wavefront nonlinear modulation system is set to state j. After the known pulse signal is reflected by the target, it passes through the wavefront nonlinear modulation system and is received by the receiving antenna at the corresponding observation point, thus obtaining the echo signal. l represents the l-th receiving antenna;

[0014] S4. If the state index j is greater than the total number of states N of the wavefront nonlinear modulation system, then execute S5; otherwise, update the index j = j + 1 and return to S3.

[0015] S5. Collect all echo signals from the L receiving antennas in the N states. By combining the known pulse signal p(t) and equivalent frequency response, target inversion is performed using signal processing methods to obtain the radar cross-section of each target and the position image of each target.

[0016] Furthermore, the specific steps of the calibration measurement are as follows:

[0017] The simulation involves a signal reflected from a target entering a wavefront nonlinear modulation system. The system then discretizes the incident angle of the signal, obtaining discretized two-dimensional spatial angles θ1, θ2, ..., θ M Then, calculate the angle at the i-th discretized state in state j. electric field strength and The ratio of the electric field intensity of the incident plane wave component is used to obtain the equivalent frequency response in state j. Then, by switching other system states and corresponding discretized angles, the equivalent frequency responses of different discretized two-dimensional spatial angles in different states are obtained.

[0018] Wherein, the wavefront nonlinear modulation system satisfies:

[0019] When signals with different two-dimensional spatial angles pass through the medium in a wavefront nonlinear modulation system, the wavefront changes. Simultaneously, for the discretized two-dimensional spatial angles θ1, θ2, ..., θ... M And N system states, let Represents θ i The frequency response vector of an angle, representing two different discretized two-dimensional spatial angles θ. i The corresponding frequency response vectors are linearly independent;

[0020] In a wavefront nonlinear modulation system, each of the N states can be adjusted to another state, and repeated state adjustments are supported.

[0021] Furthermore, it is known that after the pulse signal is reflected by the target, it passes through the wavefront nonlinear modulation system and is received by the receiving antenna at the corresponding observation point to obtain the echo signal. The specific steps are as follows:

[0022] After the pulse signal is reflected by the target, it enters the wavefront nonlinear modulation system for modulation, based on the spectrum of the echo signal, the equivalent frequency response, and the reference point of the incident wave angle. The relationship between the spectrum of the echo signal at the location, and the reference point of the incident wave angle. The expression for the echo signal at a given location with respect to the radar cross-section is used to discretize the incident angle within the beam, resulting in the incident angle θ being discretized into: θ1, θ2, ..., θ M The echo signal was obtained.

[0023] Furthermore, the spectrum of the echo signal, the equivalent frequency response, and the reference point of the incident wave angle. The relationship between the frequencies of the echo signals at each location is as follows:

[0024]

[0025] in, Let represent the equivalent frequency response of the wavefront nonlinear modulation system's state j when the l-th receiving antenna is used as the observation point. R represents the spectrum of the echo signal from the l-th receiving antenna when the wavefront nonlinear modulation system is in state j. j (f, θ) is the reference point for the incident angle of the incident wave when the wavefront nonlinear modulation system is in state j. The spectrum of the echo signal at point θ, where θ is the incident angle and Θ is the set of possible incident angles.

[0026] Furthermore, the echo signal is subjected to Fourier transform to obtain the spectrum of the echo signal, and the incident wave angle reference point is used. The echo signal at that point is transformed using Fourier transform to obtain the reference point of the incident wave angle. The spectrum of the echo signal at that location.

[0027] Furthermore, the reference point for the incident wave angle. The expression for the echo signal at a certain point with respect to the radar cross-section is:

[0028]

[0029] Where, r j (t,θ i Let be the reference point for the incident angle of the incident wave corresponding to the discretized two-dimensional spatial angle under state j of the wavefront nonlinear modulation system. echo signal at that location, Let represent the radar cross-section of the target at a distance d, discretized in the i-th two-dimensional spatial angular direction under state j of the wavefront nonlinear modulation system, and let c represent the speed of light.

[0030] Furthermore, the echo signal for:

[0031]

[0032] Where M represents the total number of angles in the discretized two-dimensional space. Let represent the equivalent frequency response of the state j of the wavefront nonlinear modulation system in the i-th two-dimensional spatial angular direction when the l-th receiving antenna is used as the observation point.

[0033] Furthermore, the total number of discretized two-dimensional spatial angles is determined based on the performance of the wavefront nonlinear modulation system and the beamwidth corresponding to the transmitting antenna of the antenna system.

[0034] Furthermore, the known pulse signal is directly applied to the target without passing through the wavefront nonlinear modulation system or after passing through a closed wavefront nonlinear modulation system.

[0035] Furthermore, the step of target inversion using signal processing methods includes: processing the echoes received by each antenna under different states. Combining the transmitted waveform p(t) and the equivalent frequency response Construct a problem model, and then solve the problem model using an algorithm.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] This invention employs a wavefront nonlinear modulation system with adjustable states. By switching the system's states, it enables target observation under different modulation states and angles. Based on the echo signals of different states, it calculates the position images of each target, surpassing the angular resolution determined by the beamwidth of the receiving antenna, thus achieving an improved angular resolution while reducing the requirements for antenna size. Furthermore, by combining changes in state and angle, it enables the differentiation of targets at the same distance but in different directions. Attached Figure Description

[0038] Figure 1 This is a flowchart of the present invention;

[0039] Figure 2 This is a two-dimensional schematic diagram of the wavefront nonlinear modulation system of the present invention modulating an incident plane wave;

[0040] Figure 3 The actual radar cross-section of stationary targets to be imaged at equal distances within the beam;

[0041] Figure 4 The frequency response of the wavefront nonlinear modulation system at five angles under one state is obtained from the simulation.

[0042] Figure 5 The frequency response of the wavefront nonlinear modulation system at five angles under another state obtained from simulation;

[0043] Figure 6 This represents the radar cross-section obtained by this method. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0045] This invention proposes a high-resolution electromagnetic vector imaging method based on wavefront nonlinear modulation. The flowchart of the method is as follows: Figure 1 As shown. The wavefront of this invention refers to the equiphase surface of a single-frequency electromagnetic wave. Taking a plane wave incident at an angle θ and with a frequency of f as an example, its position... At point t, the electric field strength at time t is expressed as:

[0046]

[0047] Where a(f,θ) is the amplitude. Let φ(f,θ) be the wave vector of the plane wave (which has a one-to-one correspondence with θ when the propagation medium and f are known), where i is the imaginary unit, and φ(f,θ) is its initial phase. Without loss of generality, θ here can be a one-dimensional / two-dimensional angle. In this invention, θ is a two-dimensional angle.

[0048] When a single-frequency plane wave is incident simultaneously from various angles, the position in free space... The electric field strength at a certain point is observed; here, the receiving antenna is abstracted as the observation point. And temporarily ignore the antenna pattern characteristics. Based on the linearity and superposition of Maxwell's equations, the observed values ​​are the superposition of the plane wave electric field intensities at various angles, as shown in equation (1):

[0049]

[0050] Here, Θ represents the set of all potential incident angles. Therefore, the problem of electromagnetic vector imaging can be simply abstracted as... beg The problem.

[0051] Currently, most imaging methods based on electromagnetic vectors are extensions of the above equation. For classic real aperture radar, when there is only one channel, the isophase characteristics of the wavefront cannot be utilized. Therefore, high-resolution imaging can only be achieved by reducing the beamwidth and suppressing the amplitude of the outer plane wave of the beam, which can be expressed as the following equation (2):

[0052]

[0053] Among them, E e (f,θ) represents the antenna radiation pattern. Here, due to E e (f,θ) is a time-invariant quantity, and it cannot distinguish the wavefronts of plane waves incident at different angles within the beamwidth. If E e (f,θ) is replaced by a quantity that is stable within a single pulse period but different during different pulse periods. By repeatedly transmitting the same pulse, multiple different observations can be obtained, thus increasing the amount of information that can be acquired.

[0054] Based on the above principles, this invention defines wavefront nonlinear modulation as the modulation of the physical properties of the medium within a region (relative permittivity ∈ R). r relative permeability μ r The change in the state of the plane wave causes its wavefront to change as it passes through the medium at different angles. Furthermore, the modulation effect on the wavefront of the plane wave incident at different angles is not linearly related under multiple state changes; the definition of this modulation effect is provided below. (Reference) Figure 2A two-dimensional schematic diagram of a wavefront nonlinear modulation system modulating an incident plane wave. The dashed box represents the wavefront nonlinear modulation system, and a specific region within it is characterized by physical properties (relative permittivity ∈ R). r relative permeability μ r Variable media composition, Let be the reference point before the incident wave reaches the system (i.e., the location unaffected by this system). Let be the observation point after the incident wave passes through the system. Since the attenuation constant and phase shift constant of the medium are ∈ r ,μ r The function of the electromagnetic wave, and the attenuation and phase shift during propagation, can be expressed as integrals of the attenuation constant and phase shift constant over the propagation path. Therefore, when an incident plane wave passes through this system, the result of its wavefront modulation is reflected in... The amplitude and phase of the electric field intensity at the point change accordingly. θ in the figure is a one-dimensional angle. Without loss of generality, the following theory still applies when it is extended to a two-dimensional spatial angle.

[0055] When the physical properties of the medium within the system are in the j-th state, the effect of wavefront nonlinear modulation for a plane wave incident at angle θ can be defined as follows (3):

[0056]

[0057] in, In this state The electric field intensity of the incident plane wave component at that location. In this state The electric field strength at each location is in the complex form of the electric field strength.

[0058] At this point, considering plane waves incident at all angles, and combining formulas (2) and (3), we can obtain... The observed value is:

[0059]

[0060] The above single-frequency plane wave resolution is extended, that is, from the perspective of the signal, when the reference point... When selected, the l-th observation point is denoted as A wavefront nonlinear modulation system can be considered as a spatial filter, whose frequency response is the observation point. A function of state j, frequency f, and incident angle θ, i.e. And abbreviated as

[0061] When the wavefront nonlinear modulation system is in the j-th state, the incident angle θ reaches... The signal is represented as r j (t,θ), its spectrum is Rj (f,θ), The received signal is represented as Its spectrum is Because, under far-field conditions, the incoming wave at each angle can be decomposed by Fourier transform into a superposition of single-frequency plane waves. Therefore, we have and here This is a Fourier transform. Therefore, after introducing wavefront nonlinear modulation, Spectrum of the signal received by the receiving antenna Frequency response of wavefront nonlinear modulation system The spectrum R of the incident signal at angle θ j (f,θ) has the following relationship:

[0062]

[0063] The wavefront nonlinear modulation system of the present invention satisfies:

[0064] (1) The state is adjustable and repeatable.

[0065] (2) For the discretized angles θ1, θ2, ..., θ M And N system states, let Represents θ i The frequency response vector of an angle, where any two angles corresponding and They should be linearly independent.

[0066] Based on the above theory, the method of the present invention includes the following steps:

[0067] S1. Place a wavefront nonlinear modulation system on one side of the antenna system, and determine a reference point for the incident angle of the incident wave in front of the wavefront nonlinear modulation system in the direction of the incoming wave. When the antenna system has L receiving antennas, determine the observation point after the incident wave, corresponding to each receiving antenna of the antenna system, passes through the wavefront nonlinear modulation system. There are L observation points, and the wavefront nonlinear modulation system has N states. The state index of the wavefront nonlinear modulation system is initialized to j=1; where the incident angle and the two-dimensional space angle are the same angle.

[0068] S2. Calibrate and measure the equivalent frequency response of the wavefront nonlinear modulation system under different states:

[0069]

[0070] Where l represents the l-th observation point, f represents the incident frequency, and θ iThis represents the i-th two-dimensional spatial angle in the discretization.

[0071] S3. The transmitting antenna of the antenna system transmits a known pulse signal p(t). The wavefront nonlinear modulation system is set to state j. After the known pulse signal is reflected by the target, it passes through the wavefront nonlinear modulation system and is received by the receiving antenna at the corresponding observation point, thus obtaining the echo signal. l represents the l-th receiving antenna;

[0072] S4. If the state index j is greater than the total number of states N of the wavefront nonlinear modulation system, then execute S5; otherwise, update the index j = j + 1 and return to S3.

[0073] S5. Collect all echo signals from the L receiving antennas in the N states. By combining the known pulse signal p(t) and equivalent frequency response, target inversion is performed using signal processing methods to obtain the radar cross-section of each target and the position image of each target.

[0074] In S1 and S2, a system capable of wavefront nonlinear modulation is placed in front of the antenna system, and a point is selected in front of the wavefront nonlinear modulation system. As a reference point for the incident wave angle, when there are L receiving antennas (channels), the position of the receiving antennas can be used to determine the angle. Based on the antenna beamwidth and the performance of the wavefront nonlinear modulation system, the in-beam angles are discretized into M parts as two-dimensional spatial angles θ1,…,θ2. M Calibration measurement of the equivalent frequency response of a wavefront nonlinear modulation system. That is, the amplitude and phase changes caused by the propagation of an electromagnetic wave with frequency f incident at an angle θ in this system, which can be simplified as: The system has N switchable states, therefore 1 ≤ j ≤ N, 1 ≤ i ≤ M, and 1 ≤ l ≤ L. (Measured...) It serves as prior information for subsequent use.

[0075] The specific steps for calibration measurement are as follows:

[0076] The simulation involves a signal reflected from a target entering a wavefront nonlinear modulation system. The system then discretizes the incident angle of the signal, obtaining discretized two-dimensional spatial angles θ1, θ2, ..., θ M Then, calculate the angle at the i-th discretized state in state j. electric field strength and The ratio of the electric field intensity of the incident plane wave component is used to obtain the equivalent frequency response in state j. Then, by switching other system states and corresponding discretized angles, the equivalent frequency responses of different discretized two-dimensional spatial angles in different states are obtained. As shown in Equation 3.

[0077] From S3 to S5, when the wavefront nonlinear modulation system is in the j-th state, it is located at... Spectrum of the signal received by the receiving antenna Frequency response of wavefront nonlinear modulation system Incident at angle θ signal spectrum R j The relationship between (f,θ) is: in

[0078] It is known that after a pulse signal is reflected by the target, it passes through a wavefront nonlinear modulation system and is received by a receiving antenna at the corresponding observation point, thus obtaining an echo signal. The specific steps are as follows:

[0079] After the pulse signal is reflected by the target, it enters the wavefront nonlinear modulation system for modulation, based on the spectrum of the echo signal, the equivalent frequency response, and the reference point of the incident wave angle. The relationship between the spectrum of the echo signal at the location, and the reference point of the incident wave angle. The expression for the echo signal at a given location with respect to the radar cross-section is used to discretize the incident angle within the beam, resulting in the incident angle θ being discretized into: θ1, θ2, ..., θ M The echo signal was obtained.

[0080] The spectrum of the echo signal, the equivalent frequency response, and the reference point of the incident wave angle. The relationship between the frequencies of the echo signals at each location is as follows:

[0081]

[0082] in, Let represent the equivalent frequency response of the wavefront nonlinear modulation system's state j when the l-th receiving antenna is used as the observation point. R represents the spectrum of the echo signal at the l-th observation point in state j. j (f,θ) is the reference point for the incident angle of the incident wave in state j. The spectrum of the echo signal at point θ, where θ is the incident angle and Θ is the set of possible incident angles.

[0083] The echo signal is subjected to Fourier transform to obtain the spectrum of the echo signal, and the incident wave angle reference point. The echo signal at that point is transformed using Fourier transform to obtain the reference point of the incident wave angle. The spectrum of the echo signal at that location.

[0084] Reference point of incident wave angle The expression for the echo signal at a certain point with respect to the radar cross-section is:

[0085]

[0086] Where, r j (t,θ i () represents the reference point for the incident wave angle corresponding to the discretized i-th two-dimensional spatial angle in state j. The echo signal at that location, considering the possibility of relative motion between the radar system and the target in a real scenario, Let represent the radar cross-section of the target at a distance d in the discretized two-dimensional spatial angular direction under state j, , and represent the quantity to be estimated, where c represents the speed of light.

[0087] echo signal for:

[0088]

[0089] Where M represents the total number of angles in the discretized two-dimensional space. Let represent the equivalent frequency response of the state j of the l-th receiving antenna in the i-th two-dimensional spatial angular direction.

[0090] All echo signals in N states Combining p(t) and Target inversion is performed using signal processing methods to obtain the estimated target RCS value:

[0091]

[0092] in, The signal processing method mainly includes: processing the echoes received by each antenna under different states. Combining the transmitted waveform p(t) and the equivalent frequency response The process involves processing to obtain the target distribution interval and some estimated information. Determining the target interval reduces the solution range. The estimated information is then combined with signal data to construct an imaging model. The model is solved using common matrix, optimization, and statistical algorithms. The matrix, optimization, and statistical algorithms can include the least squares method.

[0093] Considering the possibility of relative motion between the radar system and the target in real-world scenarios, and that the initial target distribution is sufficient for imaging requirements, therefore here... express That is, when the first transmission pulse begins imaging, θ i The target's RCS is at a directional distance of d.

[0094] This invention proposes for the first time a high-resolution electromagnetic vector imaging method based on wavefront nonlinear modulation. This method introduces controllable wavefront nonlinear modulation into the received electromagnetic vector and achieves target observation under different modulation states through state switching. The proposed electromagnetic vector high-resolution imaging method surpasses the angular resolution determined by the beamwidth of the receiving antenna, achieving a significant improvement in angular resolution. In other words, while achieving high resolution, it reduces the requirements for antenna size, thus providing a high-resolution imaging solution for various scenarios where antenna size is limited.

[0095] The following is a simulation experiment: The antenna in the simulation is a Ku-band standard gain horn, with a main beamwidth of 40 degrees in the azimuth direction (0 degrees from the beam center, and the beam coverage range is [-20, 20] degrees; elevation angles are not considered here). There are one point target each at azimuth angles of -6, -3, 0, 3, and 6 degrees. These targets are all located at equal distances of 300 meters. The true RCS of the five targets at these angles is as follows: Figure 3 As shown.

[0096] Since there is only one receiving antenna, its position is set as follows: Equivalent frequency response data of wavefront nonlinear modulation system at 5 incident angles Generated by the electromagnetic simulation software CST, a total of 14 states were simulated. Here, the frequency response of two states is plotted, as shown below. Figure 4 As shown in Figure 5, it can be seen that the frequency response of the wavefront nonlinear modulation system is different at different angles in a single state. The transmitted signal is:

[0097]

[0098] Where T p The value is 1µs, and f1, f2, and f3 are 14, 15, and 16 GHz respectively. At different θ i They are all linearly independent.

[0099] This invention combines 14 states Solve using signal processing algorithms, such as Figure 6 As shown in the figure, the resolution of five targets at different angles was achieved, and the calculated amplitude is very close to the actual amplitude. In the case of real aperture radar imaging, these five targets are all equidistant targets within the beam and cannot be resolved.

[0100] Therefore, this simulation verifies the correctness and effectiveness of the present invention.

[0101] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A high-resolution electromagnetic vector imaging method based on wavefront nonlinear modulation, characterized in that the method... include: S1. Place a wavefront nonlinear modulation system on one side of the antenna system, and determine a reference point for the incident angle of the incident wave in front of the wavefront nonlinear modulation system in the direction of the incoming wave. The receiving antenna of the antenna system is L At each time point, the observation point after the incident wave, corresponding one-to-one with each receiving antenna of the antenna system, passes through the wavefront nonlinear modulation system is determined. The observation point is L There are a total of [number] wavefront nonlinear modulation systems. N The state index of the wavefront nonlinear modulation system is initialized with several states. The incident angle and the two-dimensional spatial angle are the same angle. S2. Calibrate and measure the equivalent frequency response of the wavefront nonlinear modulation system under different states: in l Indicates the first l One observation point, f Indicates the incident frequency, The first discretized part represents the discretized... i A two-dimensional spatial angle; S3, The transmitting antenna of the antenna system transmits a known pulse signal. Set the wavefront nonlinear modulation system as j Given a known pulse signal, after being reflected by the target, it passes through a wavefront nonlinear modulation system and is received by a receiving antenna at the corresponding observation point, resulting in an echo signal. , l Indicates the first l One receiving antenna; S4, if the state index j Greater than the total number of states of the wavefront nonlinear modulation system N If yes, execute S5; otherwise, update the index. And return to S3; S5, will L The received antennas All echo signals in each state Combined with known pulse signals By combining the equivalent frequency response with signal processing methods, target inversion is performed to obtain the radar cross-section of each target and the position image of each target. The specific steps for the calibration measurement are as follows: The simulation involves a signal reflected from a target entering a wavefront nonlinear modulation system. The system then discretizes the incident angle of the signal to obtain a discretized two-dimensional spatial angle. Then calculate In the state, the first i From a discretization perspective electric field strength and The ratio of the electric field intensity of the incident plane wave component is given by the following ratio: The equivalent frequency response under each state is obtained by switching other system states and corresponding discretized angles, thus obtaining the equivalent frequency response of different discretized two-dimensional spatial angles under different states. ; Wherein, the wavefront nonlinear modulation system satisfies: When signals with different two-dimensional spatial angles pass through the medium in a wavefront nonlinear modulation system, the wavefront changes. Simultaneously, for the discretized two-dimensional spatial angle... ,as well as A system state, let express The frequency response vector of an angle, two different discretized two-dimensional spatial angles. The corresponding frequency response vectors are linearly independent; Wavefront nonlinear modulation system N Each state can be adjusted to another state, and repeated state adjustments are supported.

2. The electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation according to claim 1, characterized in that, It is known that after a pulse signal is reflected by the target, it passes through a wavefront nonlinear modulation system and is received by a receiving antenna at the corresponding observation point, thus obtaining an echo signal. The specific steps are as follows: After the pulse signal is reflected by the target, it enters the wavefront nonlinear modulation system for modulation, based on the spectrum of the echo signal, the equivalent frequency response, and the reference point of the incident wave angle. The relationship between the spectrum of the echo signal at the location, and the reference point of the incident wave angle. The expression for the echo signal at a certain point with respect to the radar cross-section is used to discretize the incident angle within the beam, thus representing the incident angle. Discretized as: The echo signal was obtained. .

3. The electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation according to claim 2, characterized in that, The spectrum of the echo signal, the equivalent frequency response, and the reference point of the incident wave angle. The relationship between the frequencies of the echo signals at each location is as follows: in, Indicates the first l The state of the wavefront nonlinear modulation system when each receiving antenna is used as an observation point j The equivalent frequency response, Indicates the first l Each receiving antenna is in the state of the wavefront nonlinear modulation system. j The spectrum of the time echo signal, The wavefront nonlinear modulation system is in state j Time-incident wave incident angle reference point The spectrum of the echo signal at that location, The angle of incidence, Let be the set of incident angles.

4. The electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation according to claim 3, characterized in that, The echo signal is subjected to Fourier transform to obtain the spectrum of the echo signal, and the incident wave incident angle reference point. The echo signal at that point is transformed using Fourier transform to obtain the reference point of the incident wave angle. The spectrum of the echo signal at that location.

5. The electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation according to claim 4, characterized in that, Reference point of incident wave angle The expression for the echo signal at a certain point with respect to the radar cross-section is: in, State of the wavefront nonlinear modulation system j The first discretization i Reference point for the incident wave angle corresponding to each two-dimensional spatial angle echo signal at that location, Represents the state of the wavefront nonlinear modulation system j The first discretization i The two-dimensional spatial angular directions, with a distance of... d The radar cross-section of the target. It represents the speed of light.

6. The electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation according to claim 5, characterized in that, echo signal for: in, M This represents the total number of angles in the discretized two-dimensional space. Indicates the first l The state of the wavefront nonlinear modulation system when each receiving antenna is used as an observation point j The i Equivalent frequency response in two-dimensional spatial angular directions.

7. The electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation according to claim 6, characterized in that, The total number of discretized two-dimensional spatial angles is determined based on the performance of the wavefront nonlinear modulation system and the beamwidth corresponding to the transmitting antenna of the antenna system.

8. The electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation according to claim 1, characterized in that, The known pulse signal is directly applied to the target without passing through the wavefront nonlinear modulation system or after passing through a closed wavefront nonlinear modulation system.

9. The electromagnetic vector high-resolution imaging method based on wavefront nonlinear modulation according to claim 1, characterized in that, The step of target inversion using signal processing methods includes: processing the echoes received by each antenna under different states... Combined with the transmitted waveform and equivalent frequency response Construct a problem model, and then solve the problem model using an algorithm.

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