A radar dynamic echo simulation method for a coated electromagnetic regulation material target

Abstract

The application provides a radar dynamic echo simulation method of a target coated with electromagnetic modulation material, and steps are as follows: step one: obtaining electromagnetic scattering characteristic data of the target coated with the electromagnetic modulation material under different scattering states; step two: constructing an electromagnetic modulation signal model; step three: according to the electromagnetic modulation signal model, time domain splicing is performed on echo signals under different scattering states; and step four: target feature modulation effect analysis is performed based on target dynamic echo signals.The application starts from an electromagnetic characteristic model of the target coated with the electromagnetic modulation material, performs simulation analysis on target echoes, considers complex electromagnetic scattering characteristics of actual targets, makes the simulated echoes more reliable, converts static radar echoes of the electromagnetic modulation material under different scattering states into dynamic echoes by using the time domain splicing mode, has the advantages of low cost and short verification period, and can provide data support for target characteristic analysis, target detection and target identification of the target loaded with the electromagnetic modulation material.

Description

[Technical Field]

[0001] This invention is a radar dynamic echo simulation method for targets coated with electromagnetic control materials, belonging to the field of radar target characteristic technology. [Background Technology]

[0002] With the rapid development of metamaterials and electromagnetic control technologies, coating targets with electromagnetically modulated materials to alter their scattering characteristics has become a research hotspot in the field of radar target characteristics. Electromagnetically modulated materials integrate tunable elements based on traditional metamaterials, and by changing the impedance of these tunable elements, they achieve dynamic control over the amplitude, phase, polarization, and frequency of radar scattered signals, enabling precise control of the target's electromagnetic characteristics. This material-based target characteristic control technology offers advantages such as strong concealment, diverse control patterns, and precise control over target characteristics, making it of significant application value in the field of radar target characteristics. Therefore, it is urgent to study the radar target characteristics of targets coated with electromagnetically modulated materials.

[0003] When a radar emits an electromagnetic signal that strikes the target surface, the electromagnetic wave is reflected by the target and then received by the receiver. By extracting the target information contained in the echo signal, the radar can detect, locate, measure distances, and classify and identify the target. Therefore, obtaining radar echo signals has become the core of studying radar target characteristics.

[0004] However, current radar target echo characteristic analysis for targets coated with electromagnetically modulated materials mainly relies on experimental methods, with limited theoretical research. Furthermore, target electromagnetic characteristic modeling often employs point target models, neglecting the true electromagnetic scattering characteristics of complex targets, resulting in significant discrepancies with actual radar echo characteristics. Therefore, this invention proposes a radar dynamic echo simulation method for targets coated with electromagnetically modulated materials. Starting from the electromagnetic scattering characteristics of targets coated with electromagnetically modulated materials under different impedance conditions, this method performs time-domain stitching of echo signals under different scattering states based on the electromagnetic modulation signal, ultimately generating the dynamic echo of the radar target. Compared to existing electromagnetically modulated radar target echo simulation methods, this method, starting from the static scattering characteristics of the target after coating with electromagnetically modulated materials under different scattering states, has advantages such as a clear scattering mechanism and realistic simulation results. Compared to methods that directly obtain target echoes through anechoic chamber testing, it offers advantages such as low cost and short verification time. This method has significant engineering application value for the characteristic analysis, target detection, and target identification of radar targets loaded with electromagnetically modulated materials. [Summary of the Invention]

[0005] The technical problem this invention aims to solve is: to simulate and analyze the dynamic echo of a radar target after loading an electromagnetic modulation material, providing data support for analyzing the modulation effect of the electromagnetic modulation material on the radar target. The solution is as follows: first, calculate or perform static measurements in an anechoic chamber to obtain electromagnetic scattering data under different scattering states of the electromagnetic modulation material; then, based on the electromagnetic modulation signal model and time-domain stitching technology, purposefully slice and stitch the radar echo under different scattering states of the electromagnetic modulation material to study the modulation effect of the radar target echo characteristics and target features under the electromagnetic modulation material.

[0006] Specifically, this invention proposes a radar dynamic echo simulation method for targets coated with electromagnetic control materials, comprising the following steps:

[0007] Step 1: Obtain electromagnetic scattering characteristic data of the target after coating with electromagnetic control material under different scattering states;

[0008] Existing studies on radar echo characteristics of electromagnetically modulated materials often employ point models for analysis, neglecting the complex electromagnetic scattering characteristics of the target. This results in unclear scattering mechanisms and inaccurate actual control effects. This invention first studies the target characteristics of electromagnetically modulated materials under different scattering states. Currently, methods for obtaining electromagnetic characteristic data mainly include electromagnetic simulation calculations and anechoic chamber measurements. However, due to the development of electromagnetic calculation theory, target characteristic models obtained using simulation methods have achieved high accuracy. Therefore, considering all factors, this invention adopts electromagnetic simulation methods to obtain target scattering characteristic data.

[0009] Based on electromagnetic calculation theory, the scattering characteristics of targets coated with electromagnetic control materials are calculated. For most identification radars, the surveillance targets are electrically large, and the electromagnetic scattering characteristics of the targets can be modeled using a high-frequency prediction method. The total single-station scattering field of the target includes the primary scattering field, multiple scattering fields, and diffraction field. The algorithm model is as follows: Figure 1 As shown.

[0010] (1) The primary scattering field is calculated by the physical optics method (PO). The PO method is based on the Straton-Juran scattering field integral equation. Based on the principle of locality at high frequencies, it adopts the far-field approximation and the tangent plane approximation. The primary scattering field of the target can be expressed as:

[0011]

[0012] in, These are the scattering electric field and the scattering magnetic field, respectively, j 2 =-1, where imaginary unit is given, and k and η0 are the wave number and wave impedance in free space, respectively. The distance from the source point to the field point. Let be the position vector of the scatterer surface, and s' be the illuminated portion of the scatterer surface. It is the surface current density of the scattering body. Let be the unit vector of the scattering direction. Let be the unit vector of the incident direction.

[0013] (2) The multiple scattering characteristics of strong scattering structures such as dihedrals, trihedrals and various cavities are calculated using a hybrid geometric optics-physical optics (GO-PO) method. The specific process is to determine the illuminated surface elements by ray tracing, calculate the scattering contribution of the first surface element using the GO algorithm, and then use it as the incident wave of the next illuminated surface element. This process is iterated, and finally the PO algorithm is used to calculate the scattering field of the entire multiple coupling effect at the last active surface element.

[0014] A plane wave with arbitrary polarization can be represented by a set of components perpendicular to the incident plane (directions perpendicular to the incident plane) and components parallel to the incident plane. Therefore, the incident wave is... For the vertical polarization component of the incident wave, The unit direction vector representing vertical polarization. For the incident wave's horizontal polarization component, Let represent the unit direction vector of horizontal polarization, then the electric field of the reflected wave... for:

[0015]

[0016] The reflected field is taken as the incident field, and the scattered field is calculated using formula (4). The scattered field is then added to the primary scattered field, and the result is the magnitude of the secondary coupled scattered field. When the incident wave illuminates the second surface element after the reflected wave illuminates the second surface element, it does not leave the target surface but continues to illuminate other surface elements, which means that multiple coupling effects are generated. The calculation of the multiple scattered field is the same as the secondary coupled scattering analysis method, but the ray tracing process is added to determine all surface elements illuminated by the same ray from beginning to end.

[0017] For structures with surface discontinuities such as edges and corners, the incremental length diffraction theory (ILDC) is used to calculate the diffraction field of the target. The diffraction field can be expressed as:

[0018]

[0019] Among them, E d For the diffraction electric field, E i Let be the incident electric field, k be the wave number representing the phase change of the wave per unit length, k = 2π / λ, R be the distance from the incident field to the target, and dt be the edge element. The coefficients are the diagonal coefficients. The incident electric field component can be obtained by integrating the above equation along the edge of the wedge.

[0020] Therefore, the total scattered field of the target is the vector sum of the primary scattered field, the multiple scattered fields, and the diffracted field. Based on high-frequency theory, the scattered field of a target coated with electromagnetically controlled materials under different states can be calculated.

[0021] Step 2: Construct an electromagnetic modulation signal model;

[0022] By applying external excitation, electromagnetic modulation materials can control the amplitude, phase, and polarization of signals incident on the surface. The modulation modes can be divided into intra-pulse modulation (fast time dimension modulation) and inter-pulse modulation (slow time dimension modulation). The modulation forms mainly include periodic modulation and aperiodic modulation. Periodic / aperiodic modulation includes periodic / aperiodic amplitude modulation and periodic / aperiodic phase modulation. This invention provides a detailed analysis of commonly used periodic amplitude modulation models and aperiodic amplitude modulation models.

[0023] (1) Periodic amplitude modulation model

[0024] The periodic amplitude modulation model is mainly implemented using an Active Frequency Selective Surface (AFSS). By applying an external excitation source, the impedance characteristics of variable components on the AFSS surface are modulated, thereby changing the scattering characteristics of the AFSS surface. The amplitude of the radar wave reflection signal can be modulated using a periodic rectangular pulse train on the AFSS surface, and its modulation signal waveform is shown below. Figure 2 As shown.

[0025] Where x is defined as the amplitude coefficient, and the range of x is 0 < x < 1. When x = 1, it represents that the surface of the electromagnetically controlled material is in a state of total reflection, defined as a high scattering state; when x = 0, the surface of the electromagnetically controlled material is in a state of total absorption. The duty cycle of the periodic rectangular pulse signal is α, and the pulse width is αT. q The switching cycle is T. q The time-domain expression of the periodic amplitude modulation signal is:

[0026]

[0027] In the formula, t k t indicates fast time. m Representing slow time, rect(·) represents a rectangular pulse, and δ(·) represents an impulse pulse signal. For the convolution operator, T q This is called the inter-pulse modulation interval. Performing a Fourier transform on the time domain of the periodic amplitude modulated signal yields its spectrum as follows:

[0028]

[0029] Wherein, P(f k ,t m f is the spectrum of the modulated signal. k For a fast-time frequency variable, the amplitude coefficient A0 = (1-x)·α+x, and the amplitude coefficient A n = (1-x)·α·sinc(nα); sinc(·) is the Sinker function, expressed as sinc(x) = sin(πx) / πx; f q =1 / T q This is the inter-pulse modulation frequency.

[0030] (2) Aperiodic amplitude modulation model

[0031] Aperiodic amplitude modulation (AEM) modulates the incident electromagnetic wave aperiodically by generating a pseudo-random coded sequence, and its signal waveform is as follows: Figure 3 As shown. An aperiodic amplitude-modulated rectangular pulse is subjected to random coding a. n =Controlled by {1,x}, its time-domain expression is:

[0032]

[0033] In the formula, τ is the code length, N is the total number of codes, and the spectrum of the aperiodic amplitude modulation signal is expressed as:

[0034]

[0035] In the formula, the zero-order peak output amplitude of the spectrum is P(0,t). m )=(1-x)β / N+x, where β is the random code a n In the code, the number of times the code 1 occupies the entire code element,

[0036] Step 3: Based on the electromagnetic modulation signal model, time-domain splicing is performed on the echo signals under different scattering states;

[0037] Based on the correspondence between electromagnetic scattering data and target radar echoes, the electromagnetic scattering data of the target varying with frequency and angle, calculated using high-frequency algorithms, can be considered as baseband signal sampling data obtained by dechirp processing of the linear frequency modulated signal echo. Therefore, according to the electromagnetic modulation signal model, the low scattering state (signal amplitude coefficient x) and high scattering state (signal amplitude coefficient 1) in the model are correlated with the baseband signal obtained through electromagnetic calculations. Furthermore, based on digital signal processing techniques and the parameters of the modulation signal, the baseband echo signals of the high and low scattering states are intentionally spliced ​​in the time domain to obtain the dynamic echo of the radar target under electromagnetic modulation material. The specific implementation process is as follows: Figure 4 As shown.

[0038] Analyzing the radar's transmitted linear frequency modulated (LFM) signal, the transmitted signal can be represented as:

[0039]

[0040] Among them, f c K is the carrier frequency. r =B / T P Where B is the frequency modulation slope, and T is the signal bandwidth. p Where is the pulse width. The baseband echo signal can be represented as:

[0041]

[0042] Where M is the number of scattering centers of the target, σ i Let R be the radar cross section (RCS) of the i-th scattering center. i (t m Let ) represent the distance from the i-th scattering center of the target to the receiver, which varies with time t, and c represent the speed of light in free space. The difference in echo signals between the two different scattering states is mainly reflected in... They are respectively represented as Where, σ gi Let σ be the RCS of the i-th scattering center in the high scattering state. di Let RCS be the low-scattering state of the i-th scattering center, then the echo signal after time-domain stitching is:

[0043]

[0044] Among them, s gr (t k ,t m ), s dr (t k ,t m Γ(t) represents the echo signal in the high scattering state and the low scattering state, respectively. k ,t m (,0) represents the case where x=0 in the electromagnetic control signal.

[0045] In periodic amplitude modulation mode:

[0046] Under aperiodic amplitude modulation:

[0047] Step 4: Analyze the effect of target feature modulation based on the target dynamic echo signal;

[0048] By performing pulse compression and imaging processing on the electromagnetically modulated target echo signal obtained in step three, the electromagnetic modulation effect of the target features under different parameters can be analyzed in detail. This invention focuses on a detailed analysis of the modulated one-dimensional range profile (High-resolution Distance Profile, HRRP).

[0049] The range-direction pulse compression function is the complex conjugate of the transmitted signal. It can be represented as:

[0050]

[0051] Therefore, the frequency domain response of the modulated baseband echo signal formed by down-conversion of the modulated echo signal, after pulse compression, is:

[0052]

[0053] Where, Γ(f) k ,t m R(f,0) represents the modulation coefficient, determined by the selected modulation mode; k ,t m () represents the frequency domain response of the echo signal. The phase term is the conjugate of the frequency domain response of the transmitted signal. For video residue items, This is the obliquely placed envelope term.

[0054] For periodic amplitude modulation, the frequency response of the modulated baseband echo signal after pulse compression is:

[0055]

[0056] From the above formula, we can see that As the phase modulation term, the compressed output of the echo pulse after periodic amplitude modulation is a superposition of multiple discrete sinc peaks, where, when At the actual target location, the zeroth-order peak amplitude is when At that time, multiple levels of false targets were generated, and the distance interval between the false targets was ΔR = f q ·c / (2K r ).

[0057] For aperiodic amplitude modulation, the frequency response of the modulated baseband echo signal after pulse compression is:

[0058]

[0059] In the formula, As the modulation phase term, the echo pulse compression output after aperiodic amplitude modulation exhibits a linear superposition of a zero-order peak and a continuous Doppler frequency shift during pulse compression. The zero-order peak is located at the actual target position, and its amplitude is... The remaining continuous harmonic peaks are generated by frequency shift modulation, and their overall amplitude follows a sinc function distribution with a distance distribution range of ΔL = c / τ / K. r This produces a stripe effect that generates continuous clutter.

[0060] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0061] First, starting from the electromagnetic characteristic model of the target coated with electromagnetic control material, the target echo is simulated and analyzed. The complex electromagnetic scattering characteristics of the actual target are taken into account, making the simulated echo more reliable.

[0062] Secondly, this invention proposes to use time-domain stitching to convert static radar echoes under different scattering states of electromagnetically controlled materials into dynamic echoes, which has the advantages of low cost and short verification cycle, and can provide data support for target characteristic analysis, target detection and target recognition under electromagnetically controlled materials. [Attached Image Description]

[0063] Figure 1 This is a high-frequency electromagnetic scattering prediction model.

[0064] Figure 2 This is a periodic amplitude modulation signal model.

[0065] Figure 3 This is a waveform diagram of a non-periodic amplitude modulation signal.

[0066] Figure 4 This is a flowchart of the time-domain stitching process.

[0067] Figure 5 A flowchart for simulating the dynamic echo of a radar target under electromagnetic control materials.

[0068] Figure 6 HRRP images of a coated flat plate under high scattering and low scattering conditions.

[0069] Figure 7 This is a waveform diagram of a periodic amplitude modulation signal.

[0070] Figure 8 This is a graph showing the HRRP results for periodic amplitude modulation echo.

[0071] Figure 9 This is a waveform diagram of an aperiodic amplitude modulation signal.

[0072] Figure 10 This is a graph showing the HRRP results for aperiodic amplitude modulation echo.

Detailed Implementation Methods

[0073] This invention is applied in the field of radar target characteristics technology. By proposing a radar dynamic echo simulation method under the loading of electromagnetic control materials, this invention solves the problems of inaccurate research on the effect of loading electromagnetic control materials and difficulty in obtaining echoes in traditional methods.

[0074] To facilitate understanding of this invention, the following description will be provided in conjunction with the appendix to the specification. Figure 1-10 The present invention will be described more fully and in detail through the following embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0075] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0076] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0077] This invention relates to a method for simulating the dynamic radar echo of targets coated with electromagnetic control materials. The specific implementation flowchart is as follows: Figure 5 As shown, the steps are as follows:

[0078] Step 1: Obtain electromagnetic scattering characteristic data of the target after coating with electromagnetic control material under different scattering states;

[0079] This step mainly includes the design of electromagnetic control materials, the equivalent electromagnetic parameters of the materials, and the calculation of the target electromagnetic scattering characteristics of the materials under different scattering states. First, based on the design theory and foundation of AFSS materials, AFSS materials are mainly composed of active impedance surfaces, dielectric layers, and metal reflective layers. In the target frequency band, by changing the impedance value of the active impedance surface in the AFSS material, the material can switch between reflection and absorption states in the target frequency band. Since this invention mainly focuses on the simulation of dynamic echoes, the design of electromagnetic control materials will not be further introduced.

[0080] Then, based on the designed AFSS material, the material is equivalent to surface impedance using the equivalent circuit method. The coexistence of multiple scales—large electrical size of the target, small electrical size of the material's fine structure, and medium electrical size of the target component—poses a significant challenge to the accurate modeling of the target's electromagnetic scattering characteristics. Therefore, an equivalent electromagnetic parameter method is needed to convert the modulated material into surface impedance, providing material support for subsequent electromagnetic characteristic models. Specifically, the method involves: first, obtaining the surface reflection coefficient matrix for the electromagnetically modulated material unit model under different modulation states using an equivalent circuit model or full-wave simulation calculation method; then, calculating the equivalent surface impedance parameters based on the relationship between the reflection coefficient and the equivalent impedance, according to the calculated reflection coefficient matrix under different material states.

[0081] Finally, based on the equivalent impedance parameters of the material, the electromagnetic scattering characteristics of the target under different scattering states are calculated using a high-frequency algorithm. Electromagnetic calculation parameters are determined based on radar parameters, including the calculation frequency range, frequency bandwidth, frequency step size, angle range, and angle interval. Then, a high-frequency algorithm is used to simulate and calculate the scattering characteristics of the electromagnetically controlled material coated on the target under different scattering states. Based on the correspondence between the electromagnetic calculations and the radar signal echo, the baseband echoes of the controlled material under high and low scattering states are obtained.

[0082] The baseband echo in the high scattering state is represented as:

[0083]

[0084] The baseband echo in the low scattering state is represented as:

[0085]

[0086] Step 2: Construct an electromagnetic modulation signal model;

[0087] The electromagnetic modulation signals used in this invention are periodic amplitude modulation signals and aperiodic amplitude modulation signals.

[0088] The time-domain expression of the periodic amplitude modulation signal is:

[0089]

[0090] In the formula, rect(·) represents a rectangular pulse, and δ(·) is an impulse pulse signal. For the convolution operator, T q This is called the interpulse modulation interval.

[0091] Aperiodic amplitude modulation (AEM) modulates the incident electromagnetic wave aperiodically by generating a pseudo-random coded sequence, and its signal waveform is as follows: Figure 3 As shown. An aperiodic amplitude-modulated rectangular pulse is subjected to random coding a. n=Controlled by {1,x}, its time-domain expression is:

[0092]

[0093] Step 3: Based on the electromagnetic modulation signal model, time-domain splicing is performed on the echo signals under different scattering states;

[0094] Based on the electromagnetic modulation signal model, modulation signal parameters are set to generate an electromagnetic modulation signal. Then, based on time-domain slicing and stitching techniques, echo signals in high and low scattering states are stitched together in the fast time domain to obtain dynamic radar echo signals under different modulation signal models, which can be represented as:

[0095]

[0096] In the periodic amplitude modulation mode, it is Aperiodic amplitude modulation mode

[0097] Step 4: Analyze the effect of target feature modulation based on the target dynamic echo signal;

[0098] This step mainly includes baseband echo signal processing and target feature modulation effect analysis.

[0099] Based on radar signal processing technology, pulse compression processing can be performed on the baseband echo signal of the generated electromagnetic modulation material coated radar target to obtain a high-resolution one-dimensional range image of the radar.

[0100] For periodic amplitude modulation, the frequency response of the modulated baseband echo signal after pulse compression is:

[0101]

[0102] For aperiodic amplitude modulation, the frequency response of the modulated baseband echo signal after pulse compression is:

[0103]

[0104] A detailed analysis of the range-direction pulse compression output reveals the specific modulation effect on the target characteristics. The modulation pulse compression output shows that the echo pulse compression output after periodic amplitude modulation is a superposition of multiple symmetrical, discrete sinc peaks. Specifically, when... At the actual target location, the amplitude is when At that time, multiple orders of false targets were generated, and the distance interval between each order of false targets was ΔR = f q ·c / (2K r Specifically, if α = 0.5, the pulse compression result only has an odd number of terms, so the interval between spurious targets is ΔR = fq ·c / K r This produces a deceptive control effect; the echo pulse compression output after aperiodic amplitude modulation exhibits a linear superposition of a zero-order peak and a continuous Doppler frequency shift during pulse compression, where the zero-order peak is located at the true target position, and its amplitude is... The remaining continuous harmonic peaks are generated by frequency shift modulation, and their overall amplitude follows a sinc function distribution with a distance distribution range of ΔL = c / τ / K. r This produces a stripe effect that generates continuous clutter.

[0105] To demonstrate the effectiveness of this method, a set of simulation data was used to verify the invention.

[0106] At a frequency f = (9.5–10.5) GHz, a frequency interval Δf = 0.01 GHz, and an incident angle θ = 0°, Under the simulation condition of angular interval Δθ = 0.1°, electromagnetic simulation calculations were performed on a metal plate coated with AFSS material at two different resistance values: R = 1.5Ω and R = 120Ω. The plate size was (200*200*5) mm. Based on the relationship between electromagnetic calculation data and radar echo: the electromagnetic scattering data obtained by frequency scanning can be considered as the baseband signal sampling data obtained by Decirp processing of the linear frequency modulated signal echo. Radar baseband echo data under two different resistance values ​​were obtained, and their equivalent radar parameters are shown in Table 1. The normalized HRRP results for the two scattering states are as follows. Figure 6 As shown, the normalized HRRP indicates that...

[0107] Table 1 Radar Simulation Parameter Settings

[0108] <![CDATA[Carrier frequency f0]]> 10GHz Bandwidth B 1GHz <![CDATA[sampling frequency f s > 10MHz <![CDATA[Pulse width T p > 1us Pulse Repetition Frequency (PRF) 3000Hz Pulse count 101 Reference target distance 0km

[0109] Using R=1.5Ω and R=120Ω as two different amplitude modulation states, the echo signal was modulated using periodic and aperiodic encoding methods, respectively. The waveform of the periodic amplitude modulation signal is shown in the figure below. Figure 7 As shown. The modulation frequency of the periodic modulation signal is f. q =1MHz, duty cycle α=0.5, the normalized HRRP image in periodic modulation mode obtained by the method proposed in this invention is as follows: Figure 8 As shown.

[0110] Simulation results show that after range image pulse compression, the periodic amplitude modulated echo is composed of multiple discrete peaks superimposed and weighted on the range image. The overall amplitude envelope follows a sinc distribution, and the normalized amplitude at the real target is 0.636. Based on theoretical calculations, the normalized amplitude at the real target is... The discrete peak interval is ΔR = f q ·c / Kr =0.3(m), consistent with the theoretical analysis, verifying the effectiveness of the method proposed in this invention.

[0111] The waveform of the aperiodic modulation signal is as follows Figure 9 As shown, with a symbol width τ = 0.5 (μs), the HRRP image acquired in the aperiodic modulation mode is as follows. Figure 10 As shown.

[0112] The simulated HRRP results show that the output of the aperiodic modulated echo signal generated by the method proposed in this invention, after pulse compression, can be expressed as a linear superposition of the zero-order peak output and continuous distance-oriented spurious harmonic peaks. The normalized amplitude of the zero-order peak output is 0.607, and the theoretically calculated zero-order peak value is... The distance distribution range is ΔL = c / τ / K r =0.6(m), which is basically consistent with the theoretical analysis. This verifies the effectiveness of the method of the present invention.

Claims

1. A method for simulating the dynamic radar echo of a target coated with electromagnetic control material, characterized in that: Includes the following steps: Step 1: Obtain electromagnetic scattering characteristic data of the target after coating with electromagnetic control material under different scattering states; The electromagnetic scattering characteristics of the target are modeled using a high-frequency prediction method; the single-station scattering field of the target includes the primary scattering field, the multiple scattering field, and the diffraction field. Step 2: Construct an electromagnetic modulation signal model; By applying external excitation, electromagnetic modulation materials can regulate the amplitude, phase, and polarization of signals incident on the surface. The modulation modes are divided into intra-pulse modulation (i.e., fast-time modulation) and inter-pulse modulation (i.e., slow-time modulation). The modulation forms include periodic modulation and aperiodic modulation. Step 3: Based on the electromagnetic modulation signal model, time-domain splicing is performed on the echo signals under different scattering states; The low-scattering and high-scattering states in the electromagnetic control signal model are correlated with the baseband echo signals obtained by electromagnetic calculation after the electromagnetic control material is coated on the radar target under the low-scattering and high-scattering states. Based on digital signal processing technology and the parameters of the modulation signal, the baseband echo signals of the high and low-scattering states are spliced ​​in the time domain to obtain the dynamic echo signal of the radar target under the loading of electromagnetic control material. Step 4: Analyze the effect of target feature modulation based on the target dynamic echo signal; Matched filtering and imaging processing are performed on the electromagnetically modulated dynamic echo signal obtained in step three, and the electromagnetic control effect on the target features under different parameters is analyzed. In step two, the electromagnetic modulation signal model includes a periodic amplitude modulation model. The periodic amplitude modulation model is implemented using an active frequency selective surface (AFSS). The impedance characteristics of the variable components on the AFSS surface are controlled by an external excitation source. The amplitude of the radar wave reflected signal is controlled by a periodic rectangular pulse train on the AFSS surface. in, Defined as amplitude coefficient, The range of values ​​is ,when When the electromagnetically controlled material surface is in a state of total internal reflection, it is defined as a high scattering state. At that time, the surface of the electromagnetically controlled material is in a state of total absorption, and the duty cycle of the periodic rectangular pulse signal is... Pulse width is The switching cycle is The time-domain expression of the periodic amplitude modulation signal is: ； In the formula, Indicates a fast time. Indicates slow time. Represents a rectangular pulse. It is an impulse pulse signal. For convolution operators, This is called the inter-pulse modulation interval; performing a Fourier transform on the time domain of the periodic amplitude modulated signal yields the spectrum of the periodic amplitude modulated signal as follows: ； in, The spectrum of the modulated signal. For fast-time frequency variables, amplitude coefficients Amplitude coefficient ; The Sinking function is represented as: ; This refers to the inter-pulse modulation frequency; In step two, the electromagnetic modulation signal model also includes an aperiodic amplitude modulation model. The aperiodic amplitude modulation model modulates the incident electromagnetic wave aperiodically by generating a pseudo-random coded sequence; the aperiodic amplitude modulated signal is subject to random coding. Under the control of [the signal], the time-domain expression of the aperiodic amplitude modulation signal is: ； In the formula, Indicates a fast time. Indicates slow time. Represents a rectangular pulse. It is an impulse pulse signal. For convolution operators, Defined as amplitude coefficient, For code length, The total number of codes, For random coding, the spectrum of an aperiodic amplitude-modulated signal is represented as follows: ； In the formula, the zero-order peak output amplitude of the spectrum is ,in, For random encoding In the code, the number of times the code 1 occupies the entire code element, The sampling frequency.

2. The radar dynamic echo simulation method for a target coated with electromagnetic control material according to claim 1, characterized in that: In step one, the primary scattering field is calculated using the physical optics method PO, and is expressed as: ； ； in, , These are the scattering electric field and the scattering magnetic field, respectively. , The imaginary unit, and These represent the wave number and wave impedance in free space, respectively. The distance from the source point to the field point. , The position vector of the scatterer surface. The illuminated portion of the scattering surface. It is the surface current density of the scattering body. Let be the unit vector of the scattering direction. Let be the unit vector of the incident direction.

3. The radar dynamic echo simulation method for a target coated with electromagnetic control material according to claim 1 or 2, characterized in that: In step one, the multiple scattering field is calculated using a hybrid geometric optics-physical optics (GO-PO) method. Specifically, the illuminated surface elements are determined sequentially by ray tracing. The GO algorithm is used to calculate the scattering contribution of the first surface element. Then, the scattering contribution of the first surface element is used as the incident wave for the next illuminated surface element. This process is iterated, and finally, the PO algorithm is used to calculate the scattering field of the entire multiple coupling action at the last interacting surface element.

4. A radar dynamic echo simulation method for a target coated with electromagnetic control material according to claim 1 or 2, characterized in that: In step one, the diffraction field is represented as: ； in, For diffraction electric field, For the incident electric field, Wave number, representing the phase change of a wave per unit length. , Let λ be the wavelength of the electromagnetic wave, and R be the distance from the incident field to the target. For edge units, The coefficients are the diagonal coefficients. For the incident electric field component, It is the imaginary unit.

5. The radar dynamic echo simulation method for a target coated with electromagnetic control material according to claim 1, characterized in that: Step three includes analyzing the radar's transmitted linear frequency modulated (LFM) signal, which is represented as: ； in, Indicates a fast time. Indicates slow time. Represents a rectangular pulse. For carrier frequency, The imaginary unit, For frequency modulation slope, For signal bandwidth, The pulse width is denoted as ; the baseband echo signal is represented as: ； Where M is the number of scattering centers of the target, Let RCS be the radar cross-section of the i-th scattering center. Let be the distance from the i-th scattering center of the target to the receiver, which varies with slow time, and c be the speed of light in free space; the echo signal differs depending on the scattering state, as reflected in... , respectively represented as , ;in, Let RCS be the high scattering state of the i-th scattering center. Let RCS be the low-scattering state of the i-th scattering center, then the echo signal after time-domain stitching is: ； in, , These represent the echo signals under high scattering and low scattering states, respectively. For convolution operators, This refers to the case where x=0 in the electromagnetic control signal.

6. The radar dynamic echo simulation method for a target coated with electromagnetic control material according to claim 5, characterized in that: Step four includes pulse compression processing of the electromagnetically modulated dynamic echo signal to obtain the modulated one-dimensional range image HRRP, and analysis of the characteristics of the HRRP. The matched filter function is the complex conjugate of the transmitted signal. , represented as: ； Therefore, the frequency domain response of the modulated baseband echo signal after down-conversion and matched filtering is: ； in, The modulation coefficient; The frequency domain response of the echo signal. The phase term is the conjugate of the frequency domain response of the transmitted signal. For video residue items, This is the obliquely placed envelope term.

7. The radar dynamic echo simulation method for a target coated with electromagnetic control material according to claim 6, characterized in that: In step four, for periodic amplitude modulation, the frequency response of the modulated baseband echo signal after matched filtering is: ； As the phase modulation term, the compressed output of the echo pulse after periodic amplitude modulation is a superposition of multiple discrete sinc peaks, where, when At the actual target location, the zeroth-order peak amplitude is ;when At that time, multiple levels of false targets were generated, with the distance interval between the false targets being [missing information]. , The duty cycle of the periodic rectangular pulse signal is .

8. The radar dynamic echo simulation method for a target coated with electromagnetic control material according to claim 7, characterized in that: In step four, for aperiodic amplitude modulation, the frequency response of the modulated baseband echo signal after matched filtering is: ； In the formula, For code length, The total number of codes, For random encoding In the code, the number of times the code 1 occupies the entire code element, For fast-time frequency variables, Sampling frequency, As the modulation phase term, the echo pulse compression output after aperiodic amplitude modulation is characterized by a zero-order peak and a linear superposition of continuous Doppler frequency shift in matched filtering.

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