Radar dynamic echo simulation method for target coated with electromagnetic regulation and control material

Abstract

The invention provides a radar dynamic echo simulation method for a target coated with an electromagnetic regulation and control material. The radar dynamic echo simulation method comprises the following steps: step 1, acquiring electromagnetic scattering characteristic data of the target coated with the electromagnetic regulation and control material in different scattering states; 2, constructing an electromagnetic modulation signal model; step 3, according to an electromagnetic modulation signal model, carrying out time domain splicing on the echo signals in different scattering states; and 4, performing target characteristic regulation and control effect analysis based on the target dynamic echo signal. According to the method, simulation analysis is carried out on target echoes from an electromagnetic characteristic model of an electromagnetic regulation and control material coating target, and the complex electromagnetic scattering characteristics of an actual target are considered, so that the simulated echoes are more reliable; static radar echoes of the electromagnetic regulation and control material in different scattering states are converted into dynamic echoes in a time domain splicing mode, the method has the advantages of being low in cost and short in verification period, and data support can be provided for target characteristic analysis, target detection and target recognition under the condition that the electromagnetic regulation and control material is loaded.

Description

Technical Field

[0001] The present invention is a radar dynamic echo simulation method for a target coated with an electromagnetic modulation material, belonging to the technical field of radar target characteristics.

Background Art

[0002] With the rapid development of metamaterial technology and electromagnetic modulation technology, coating a target surface with an electromagnetic modulation material to change the scattering characteristics of the target has become one of the research hotspots in the field of radar target characteristics. The electromagnetic modulation material integrates adjustable elements on the basis of traditional metamaterials, and realizes the dynamic modulation of information such as the amplitude, phase, polarization, and frequency of the radar scattering signal by changing the impedance of the adjustable components, and can achieve precise modulation of the electromagnetic characteristics of the target. This technology based on material modulation of target characteristics has the advantages of strong concealment, diverse modulation styles, and can achieve precise modulation of target characteristics, and has important application value in the field of radar target characteristics. Therefore, it is urgent to study the radar target characteristics under the condition of a target coated with an electromagnetic modulation material.

[0003] The radar emits an electromagnetic signal that is incident on the target surface. After the electromagnetic wave is reflected by the target, it is received by the receiver. By extracting the target information contained in the echo signal, functions such as target detection, positioning, ranging, and classification and recognition are realized. Therefore, obtaining the radar echo signal becomes the core of studying radar target characteristics.

[0004] However, at present, the analysis of the radar target echo characteristics after coating a target with this electromagnetic modulation material mainly adopts the method of actual measurement, with less theoretical research. And when modeling the electromagnetic characteristics of the target, a point target model is mostly used, ignoring the true electromagnetic scattering characteristics of complex targets, which is quite different from the radar echo characteristics in the actual scenario. Therefore, the present invention proposes a radar dynamic echo simulation method for a target coated with an electromagnetic modulation material. Starting from the electromagnetic scattering characteristics of the target coated with the electromagnetic modulation material under different impedance conditions, the echo signals in different scattering states are spliced in the time domain based on the electromagnetic modulation signal, and finally the dynamic echo of the radar target is generated. Compared with the existing electromagnetic modulation radar target echo simulation methods, starting from the static scattering characteristics of the target coated with the electromagnetic modulation material in different scattering states, this method has the advantages of clear scattering mechanism and real simulation results. And compared with the method of directly obtaining the target echo through anechoic chamber testing, it also has the advantages of low cost and short verification time, and has important engineering application value for the characteristic analysis, target detection, and target recognition of a radar target loaded with an electromagnetic modulation material.

Summary of the Invention

[0005] The technical problem to be solved by the present invention is: after loading the electromagnetic modulation material, to simulate and analyze the dynamic echo of the radar target, and provide data support for analyzing the regulation effect of the loaded electromagnetic regulation material on the radar target. The solution is: first, calculate or perform static measurement in the anechoic chamber on the target characteristics under different scattering states of the electromagnetic regulation material to obtain the electromagnetic scattering data of the electromagnetic regulation material under different scattering states; then, based on the electromagnetic regulation signal model and the time-domain splicing technology, perform purposeful slicing and splicing on the radar echoes under different scattering states of the electromagnetic regulation material to realize the research on the radar target echo characteristics and the target feature regulation effect under the electromagnetic regulation material.

[0006] Specifically, the present invention provides a method for simulating the radar dynamic echo of a target coated with an electromagnetic regulation material, including the following steps:

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

[0008] Since the existing research on the radar echo characteristics of the loaded electromagnetic regulation material mostly uses the point model for analysis, ignoring the complex electromagnetic scattering characteristics of the target, there are problems such as unclear scattering mechanism and inaccurate actual regulation effect. The present invention first studies the target characteristics under different scattering states of the electromagnetic regulation material. At present, the methods for obtaining electromagnetic characteristic data mainly include electromagnetic simulation calculation and anechoic chamber measurement. However, due to the development of electromagnetic calculation theory, the target characteristic model obtained by the simulation method already has a high accuracy. Therefore, considering comprehensively, the present invention uses the electromagnetic simulation method to obtain the target scattering characteristic data.

[0009] According to the electromagnetic calculation theory, calculate the scattering characteristics of the target coated with the electromagnetic regulation material. For most identification radars, the monitored target belongs to electrically large size, and the high-frequency prediction method can be used to model the target electromagnetic scattering characteristics. The single-station total scattering field of the target includes the primary scattering field, the multiple scattering field and the diffraction field, and its algorithm model is as Figure 1 shown.

[0010] (1) The primary scattering field is calculated by the Physical Optics (PO) method. The PO method is based on the Stratton-Chu scattering field integral equation. Based on the high-frequency locality principle, using the far-field approximation and the tangent plane approximation, the primary scattering field of the target can be expressed as:

[0011]

[0012] Among them, are the scattered electric field and the scattered magnetic field respectively, j 2 =-1, which is the imaginary unit, k and η 0 are the wave number and the wave impedance in free space respectively, is the distance from the source point to the field point, is the surface position vector of the scatterer, and s' is the illuminated part of the surface of the scatterer. is the surface current density of the scatterer. is the unit vector in the scattering direction. is the unit vector in the incident direction.

[0013] (2) For the multiple scattering characteristics of strong scattering structures such as dihedral angles, trihedral angles, and various cavities, the hybrid geometric optics - physical optics method (GO - PO) is used for calculation. The specific process is to first determine the illuminated surface elements through ray tracing, calculate the scattering contribution of the first surface element using the GO algorithm, and then use it as the incident wave for the next illuminated surface element. Iterate in this way, and finally use the PO algorithm to calculate the scattering field of the entire multiple coupling effect at the last acting surface element.

[0014] A plane wave with any polarization can be represented by a set of components in the direction of vertical polarization (perpendicular to the incident plane) and parallel polarization (perpendicular to the incident plane). Then the incident wave is is the vertical polarization component of the incident wave. represents the unit direction vector of vertical polarization. is the horizontal polarization component of the incident wave. represents the unit direction vector of horizontal polarization. Then the electric field of the reflected wave is:

[0015]

[0016] Taking this reflected field as the incident field, and then using formula (4) to calculate the scattering field and accumulate it with the primary scattering field. The result is the magnitude of the secondary coupled scattering field. When the reflected wave after the incident wave irradiates the surface element illuminates the second surface element but does not leave the target surface, but continues to illuminate other surface elements, that is, multiple coupling effects occur. The calculation of the multiple scattering field is the same as the analysis method of the secondary coupled scattering, but the process of ray tracing is added to determine all the 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 is the diffraction electric field, E i is the incident electric field, k is the wave number, representing the phase change of the wave per unit length, k = 2π / λ, R is the distance from the incident field to the target, dt is the edge element, is the dyadic coefficient. is the incident electric field component, and the above formula can be integrated along the edge of the wedge.

[0020] Therefore, the total scattered field of the target is the vector sum of the first - order scattered field, the multiple - scattered field, and the diffraction field. According to the high - frequency theory, the scattered fields of targets coated with electromagnetic - regulation materials in different states can be calculated.

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

[0022] Through an external excitation, the electromagnetic modulation material can regulate the amplitude, phase, and polarization of the signal incident on its 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. In this invention, the common periodic amplitude modulation model and aperiodic amplitude modulation model are analyzed in detail.

[0023] (1) Periodic amplitude modulation model

[0024] The periodic amplitude modulation model is mainly realized by using an Active Frequency Selective Surface (AFSS). By applying an external excitation source, the impedance characteristics of the variable components on the AFSS surface are regulated to achieve changes in the scattering characteristics of the AFSS surface. The AFSS surface can use a periodic rectangular pulse train to regulate the amplitude of the radar - wave reflection signal, and its modulation signal waveform is as Figure 2 shown.

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

[0026]

[0027] In the formula, t k represents the fast time, t m represents the slow time, rect(·) represents a rectangular pulse, δ(·) is an impulse pulse signal, is the convolution operator, T q is called the inter - pulse modulation interval. Taking the Fourier transform of the time - domain of the periodic amplitude modulation signal, the spectrum of the periodic amplitude modulation signal is obtained as:

[0028]

[0029] Among them, P(f k ,t m ) is the spectrum of the modulation signal, f k is the frequency variable of the fast time, and the amplitude coefficient A 0 = (1 - x)·α + x, and the amplitude coefficient A n = (1 - x)·α·sinc(nα); sinc(·) is the sinc function, expressed as sinc(x) = sin(πx) / πx; f q = 1 / T q is the inter-pulse modulation frequency.

[0030] (2) Aperiodic amplitude modulation model

[0031] Aperiodic amplitude modulation performs aperiodic amplitude modulation on the incident electromagnetic wave by generating a pseudo-random coding sequence, and its signal waveform is as Figure 3 shown. The aperiodic amplitude modulation rectangular pulse is controlled by the random coding a n = {1, x}, and its time-domain expression is:

[0032]

[0033] In the formula, τ is the code length, N is the total number of codings, 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 number of codings 1 in the entire symbol in the random coding a n ,

[0036] Step 3: According to the electromagnetic modulation signal model, perform time-domain splicing on the echo signals in different scattering states;

[0037] According to the corresponding relationship between the electromagnetic calculation scattering data and the target radar echo, the electromagnetic scattering data of the target varying with frequency and angle calculated based on the high-frequency algorithm can be considered as the baseband signal sampling data obtained by processing the linear frequency modulation signal echo through dechirping. Therefore, according to the electromagnetic modulation signal model, the low scattering state (signal amplitude coefficient is x) and the high scattering state (signal amplitude coefficient is 1) in the model are corresponded to the baseband signal obtained by electromagnetic calculation, and according to the digital signal processing technology and the parameters of the modulation signal, purposeful time-domain splicing is performed on the baseband echo signals in the high and low scattering states, and the dynamic echo of the radar target under the loading of the electromagnetic control material can be obtained. The specific implementation process is as Figure 4 shown.

[0038] Analyze with the radar transmitting a linear frequency modulation (LFM) signal. The transmitted signal can be expressed as:

[0039]

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

[0041]

[0042] where M is the number of scattering centers of the target, σ i is the radar cross section (RCS) of the i-th scattering center of the target, R i (t m ) is the distance from the i-th scattering center of the target to the receiver, which changes with slow time, c is the propagation speed of light in free space. The echo signals in two different scattering states are different mainly reflected in are respectively expressed as where σ gi is the RCS of the i-th scattering center in the high-scattering state, σ di is the RCS of the i-th scattering center in the low-scattering state. Then the echo signal after time-domain splicing is:

[0043]

[0044] where s gr (t k , t m ) and s dr (t k , t m ) respectively represent the echo signals in the high-scattering state and the low-scattering state, Γ(t k , t m , 0) is the case of x = 0 in the electromagnetic control signal,

[0045] In the case of periodic amplitude modulation:

[0046] In the case of non-periodic amplitude modulation:

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

[0048] For the target echo signal obtained in Step 3 after electromagnetic modulation, pulse compression and imaging processing are performed, so that the electromagnetic regulation effects of target features under different parameters can be analyzed in detail. In the present invention, a detailed analysis is performed on the modulated one-dimensional range profile (HRRP).

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

[0050]

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

[0052]

[0053] where Γ(f k ,t m ,0) is the modulation coefficient, which is determined by the selected modulation mode; R(f k ,t m ) is the frequency-domain response of the echo signal, is the conjugate of the frequency-domain response of the transmitted signal, the phase term is the video residual term, is the oblique envelope term.

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

[0055]

[0056] It can be seen from the above formula that is the modulation phase term. The output of the echo pulse compression after periodic amplitude modulation is the superposition of multiple discrete sinc peaks. Among them, when it is at the true target, and the amplitude of the zero-order peak is When , multiple false targets are generated, and the distance interval between false targets is ΔR = f q ·c / (2K r ).

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

[0058]

[0059] In the formula, is the modulation phase term. After the echo pulse compressed output through non-periodic amplitude modulation, it shows a linear superposition of a zero-order peak and continuous Doppler frequency shift in pulse compression. Among them, 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 the overall amplitude follows a sinc function distribution. The range of distance distribution is ΔL = c / τ / K r , generating the control strip effect of 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 echo of the target is simulated and analyzed. Considering the complex electromagnetic scattering characteristics of the actual target, the simulated echo is more reliable;

[0062] Second, the present invention proposes to convert the static radar echo of the electromagnetic control material under different scattering states into a dynamic echo by means of time-domain splicing, which has the advantages of low cost and short verification period, and can provide data support for the analysis of target characteristics, target detection and target recognition under the loading of electromagnetic control materials.

Description of the Drawings

[0063] Figure 1 is the high-frequency electromagnetic scattering prediction algorithm model.

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

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

[0066] Figure 4 is the time-domain splicing flow chart.

[0067] Figure 5 is the simulation flow chart of the radar target dynamic echo under the loading of electromagnetic control materials.

[0068] Figure 6 are the HRRP images of the flat plate coated with materials in high-scattering state and low-scattering state.

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

[0070] Figure 8 is the HRRP result diagram of periodic amplitude modulation echo.

[0071] Figure 9 is the signal waveform diagram of non-periodic amplitude modulation.

[0072] Figure 10 is the HRRP result diagram of non-periodic amplitude modulation echo.

Specific Embodiments

[0073] The present invention is applied in the technical field of radar target characteristics. Through the radar dynamic echo simulation method under the loading of electromagnetic regulation materials proposed by the present invention, the problems of inaccurate research on the effect of loading electromagnetic regulation materials and difficult echo acquisition in the traditional method are solved.

[0074] To facilitate the understanding of the present invention, the following will describe the present invention more comprehensively and meticulously in conjunction with the Figures 1 - 10 accompanying drawings and embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

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

[0076] Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment, etc. used in the present invention can be obtained through the market or can be prepared by existing methods.

[0077] The present invention is a radar dynamic echo simulation method for a target coated with electromagnetic regulation materials. The specific implementation flowchart is as Figure 5 shown, and the steps are as follows:

[0078] Step 1: Obtain the electromagnetic scattering characteristic data of the target coated with electromagnetic regulation materials under different scattering states;

[0079] This step mainly includes the design of electromagnetic regulation materials, the equivalent of material electromagnetic parameters, and the calculation of the electromagnetic scattering characteristics of the target when the material is in different scattering states. First, according to the AFSS material design theory and basis, the AFSS material mainly consists of an active impedance surface, a dielectric layer, and a metal reflection layer. By changing the impedance value of the active impedance surface in the AFSS material in the target frequency band, the material can be switched between the reflection state and the wave absorption state in the target frequency band. Since the present invention mainly focuses on the simulation of dynamic echoes, no further introduction to the design of electromagnetic regulation materials will be made.

[0080] Then, based on the designed AFSS material, the equivalent circuit method is used to equivalent the material to surface impedance. Due to the coexistence of the electrically large size of the target, the electrically small size of the material's micro-structure, and the medium electrical size of the target component, it brings great challenges to accurately model the electromagnetic scattering characteristics of the target. Therefore, an electromagnetic parameter equivalent method is needed to equivalent the tuning material to surface impedance to provide material support for the subsequent electromagnetic characteristic model. The specific method is as follows: First, for the electromagnetic tuning material unit model in different modulation states, the surface reflection coefficient matrix is obtained through the equivalent circuit model or full-wave simulation calculation method. Then, based on the relationship between the reflection coefficient and the equivalent impedance, the equivalent surface impedance parameters are calculated according to the reflection coefficient matrix of the material in different states obtained by calculation.

[0081] Finally, according to the impedance parameters equivalent to the material, the electromagnetic scattering characteristics of the target in different scattering states of the material are calculated based on the high-frequency algorithm. Determine the electromagnetic calculation parameters according to the radar parameters, including the calculation frequency range, frequency bandwidth, frequency step size, angle range, angle interval, etc. Then, use the high-frequency algorithm to simulate and calculate the scattering characteristics of the electromagnetic tuning material coated on the target in different scattering states, and obtain the baseband echo of the tuning material in the high and low scattering states according to the corresponding relationship between the electromagnetic calculation and the radar signal echo.

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

[0083]

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

[0085]

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

[0087] The electromagnetic modulation signals applied in the present invention are periodic amplitude modulation signals and non-periodic amplitude modulation signals.

[0088] Among them, the time-domain expression of the periodic amplitude modulation signal is:

[0089]

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

[0091] The non-periodic amplitude modulation performs non-periodic amplitude modulation on the incident electromagnetic wave by generating a pseudo-random coding sequence, and its signal waveform is as Figure 3 shown. The non-periodic amplitude modulation rectangular pulse is affected by the random coding a nis controlled by {1, x}, and its time-domain expression is:

[0092]

[0093] Step 3: According to the electromagnetic modulation signal model, perform time-domain splicing on the echo signals in different scattering states;

[0094] Based on the electromagnetic modulation signal model, set the modulation signal parameters, generate the electromagnetic modulation signal, and based on the time-domain slicing and splicing technology, perform time-domain splicing on the echo signals in high and low scattering states in the fast time domain to obtain the radar dynamic echo signals under different modulation signal models, which can be expressed as:

[0095]

[0096] Among them, in the case of periodic amplitude modulation In the case of non-periodic amplitude modulation

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

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

[0099] According to the radar signal processing technology, perform pulse compression processing on the baseband echo signal of the radar target coated with the generated electromagnetic modulation material, and the high-resolution one-dimensional range image of the radar can be obtained.

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

[0101]

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

[0103]

[0104] Performing a detailed analysis on the pulse compression output result in the range direction, the specific modulation effect of the target features can be obtained. From the pulse compression output result of the modulation, it can be seen that: the pulse compression output of the echo after periodic amplitude modulation is the superposition of multiple symmetric sinc discrete peaks. Among them, when it is at the true target, and the amplitude is When multiple false targets are generated, and the distance interval between each order of false targets is ΔR = f q ·c / (2K r ), especially if α = 0.5, only odd terms exist in the pulse compression result, so the interval between false targets is ΔR = fq ·c / K r produces the effect of deceptive regulation; the compressed output of the echo pulse after non-periodic amplitude modulation shows a linear superposition of a zero-order peak and continuous Doppler frequency shift in pulse compression. Among them, the zero-order peak is located at the true target position, and the amplitude is The remaining continuous harmonic peaks are generated by frequency shift modulation, and the overall amplitude follows a sinc function distribution. The distance distribution range is ΔL = c / τ / K r produces the effect of a continuous clutter control strip.

[0105] To illustrate the effectiveness of this method, a set of simulation data is used to verify the present invention.

[0106] At a frequency f = (9.5 - 10.5) GHz, a frequency interval Δf = 0.01 GHz, an incident angle θ = 0°, an angular interval Δθ = 0.1° under the simulation conditions, electromagnetic simulation calculations of a metal-coated flat plate in two different resistance states of AFSS materials with R = 1.5 Ω and R = 120 Ω are carried out. The size of the flat plate is (200 * 200 * 5) mm, and based on the relationship between the electromagnetic calculation data and the radar echo: the electromagnetic scattering data obtained by frequency scanning can be considered as the sampled data of the baseband signal obtained by processing the linear frequency modulation signal echo through Dechirp. The radar baseband echo data in two different resistance states are obtained, and its equivalent radar parameters are shown in Table 1. The normalized HRRP results in two scattering states are as Figure 6 shown. It can be seen from the normalized HRRP that

[0107] Table 1 Radar simulation parameter settings

[0108] Radar parameters Set value <![CDATA[Carrier frequency f 0 > 10 GHz Bandwidth B 1 GHz <![CDATA[Sampling frequency f s > 10 MHz <![CDATA[Pulse width T p > 1 μs Pulse repetition frequency PRF 3000 Hz Number of pulses 101 Reference target distance 0 km

[0109] Taking the states of R = 1.5 Ω and R = 120 Ω as two different states of amplitude regulation, the echo signals are modulated respectively in the form of periodic coding and non-periodic coding. The waveform diagram of the periodic amplitude modulation signal is as Figure 7 shown. The modulation frequency of the periodic modulation signal is f q = 1 MHz, and the duty cycle α = 0.5. The normalized HRRP image in the periodic modulation mode obtained by using the method proposed in the present invention is as Figure 8 shown.

[0110] It can be seen from the simulation results that after the periodic amplitude modulation echo passes through the range image pulse compression processing, it is composed of the superposition and weighting of multiple discrete peaks on the range image. The overall amplitude envelope follows a sinc distribution, and the normalized amplitude at the true target is 0.636. According to the theoretical calculation, the normalized amplitude at the true target The discrete peak interval is ΔR = f q ·c / Kr = 0.3 (m), which is consistent with the theoretical analysis and verifies the effectiveness of the method proposed by the present invention.

[0111] The waveform diagram of the aperiodic modulation signal is as Figure 9 shown. The symbol width τ = 0.5 (μs). The HRRP image obtained under the aperiodic modulation mode is as Figure 10 shown.

[0112] It can be seen from the simulated HRRP results that the output result after pulse compression of the aperiodic modulation echo signal generated by the method proposed by the present invention can be expressed as the linear superposition of the zero-order peak output and the continuous range-direction false harmonic peaks. The normalized amplitude of the zero-order peak output is 0.607, and the theoretically calculated zero-order peak is The distance distribution range is ΔL = c / τ / K r = 0.6 (m), which is basically consistent with the theoretical analysis. The effectiveness of the method of the present invention is verified.

Claims

1. A radar dynamic echo simulation method for a target coated with an electromagnetic control material, characterized in that: The steps include: Step 1: Obtain target electromagnetic scattering characteristic data after the electromagnetic control material is coated under different scattering states; The high-frequency prediction method is used to model the electromagnetic scattering characteristics of the target; the single-station scattering field of the target includes the primary scattering field, multiple scattering field and diffraction field; Step 2: Construct electromagnetic modulation signal model; Through external excitation, electromagnetic modulation materials regulate the amplitude, phase and polarization of the signal incident on the surface. The regulation modes are divided into intra-pulse modulation, i.e. fast time modulation, and inter-pulse modulation, i.e. slow time modulation. The regulation forms include periodic modulation and non-periodic modulation. Step 3: Based on the electromagnetic modulation signal model, perform time domain splicing of echo signals of different scattering states; The low scattering state and high scattering state in the electromagnetic control signal model are matched with the baseband echo signal obtained by electromagnetic calculation after the radar target is coated with the electromagnetic control material in the low scattering state and the high scattering state, and the baseband echo signals in the high and low scattering states are spliced ​​in the time domain according to the digital signal processing technology and the parameters of the modulation signal to obtain the dynamic echo signal of the radar target loaded with the electromagnetic control material; Step 4: Analyze the target feature control effect based on the target dynamic echo signal; For the dynamic echo signal after electromagnetic modulation obtained in step three, matched filtering and imaging processing are performed, and the electromagnetic control effect of the target characteristics under different parameters is analyzed.

2. The radar dynamic echo simulation method of a target coated with an electromagnetic control material according to claim 1, characterized in that: In step 1, the primary scattered field is calculated by the physical optics method PO and is expressed as: in, are the scattered electric field and the scattered magnetic field, respectively, 2 = -1, j is an imaginary unit, k and η0 are the wave number and wave impedance in free space respectively, is the distance from the source point to the field point, is the position vector of the scatterer surface, s' is the illuminated surface of the scatterer, is the scatterer surface current density, is the unit vector of the scattering direction, is the unit vector of the incident direction.

3. The radar dynamic echo simulation method of a target coated with an electromagnetic control material according to claim 1 or 2, characterized in that: In step one, the multiple scattered fields are calculated using a hybrid geometric optics method-physical optics method GO-PO. The specific process is: the illuminated surface elements are determined in sequence through ray tracing, the scattering contribution of the first surface element is calculated using the GO algorithm, and then the scattering contribution of the first surface element is used as the incident wave for the next illuminated surface element, and this is iterated. Finally, the PO algorithm is used to calculate the scattering field of the entire multiple coupling effect at the last acting surface element.

4. The radar dynamic echo simulation method of a target coated with an electromagnetic control material according to claim 1 or 2, characterized in that: In step 1, the diffraction field is expressed as: Among them, E d is the diffracted electric field, E i is the incident electric field, k is the wave number, which indicates the phase change of the wave per unit length, k = 2π / λ, λ is the wavelength of the electromagnetic wave, R is the distance from the incident field to the target, dt is the edge unit, is the dyadic coefficient, is the incident electric field component, and j is an imaginary unit.

5. The radar dynamic echo simulation method of a target coated with an electromagnetic control material according to claim 1, characterized in that: In step 2, the electromagnetic modulation signal model includes a periodic amplitude modulation model; The periodic amplitude modulation model is implemented using active frequency selective surface AFSS. The impedance characteristics of the variable components on the AFSS surface are adjusted by an external excitation source. The AFSS surface uses a periodic rectangular pulse train to adjust the amplitude of the reflected signal of the radar wave. Where x is defined as the amplitude coefficient, and the value range of x is 0<x<1. When x=1, it means that the surface of the electromagnetic control material is in a full reflection state, which is defined as a high scattering state; when x=0, the surface of the electromagnetic control material is in a full absorption state, the duty cycle of the periodic rectangular pulse signal is α, and the pulse width is αT q , the switching period is T q , the time domain expression of the periodic amplitude modulation signal is: In the formula, t k Indicates fast time, t m represents slow time, rect(·) represents rectangular pulse, δ(·) is impulse pulse signal, is the convolution operator, T q It is called the inter-pulse modulation interval; the frequency spectrum of the periodic amplitude modulation signal is obtained by Fourier transforming the time domain of the periodic amplitude modulation signal as follows: Among them, P(f k ,t m ) is the spectrum of the modulated signal, f k is the frequency variable of the fast time, the amplitude coefficient A0=(1-x)·α+x, the amplitude coefficient A n =(1-x)·α·sinc(nα); sinc(·) is the sinc function, expressed as sinc(x)=sin(πx) / πx; f q =1 / T q is the pulse modulation frequency.

6. The radar dynamic echo simulation method of a target coated with an electromagnetic control material according to claim 5, characterized in that: In step 2, the electromagnetic modulation signal model also includes a non-periodic amplitude modulation model; The non-periodic amplitude modulation model performs non-periodic amplitude modulation on the incident electromagnetic wave by generating a pseudo-random coding sequence; The non-periodic amplitude modulated signal is randomly coded n ={1,x}, the time domain expression of the non-periodic amplitude modulation signal is: In the formula, t k Indicates fast time, t m represents slow time, rect(·) represents rectangular pulse, δ(·) is impulse pulse signal, is the convolution operator, x is defined as the amplitude coefficient, τ is the code length, N is the total number of codes, and the spectrum of the non-periodic amplitude modulated signal is expressed as: Where, 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 1s in the entire code element is encoded.

7. The radar dynamic echo simulation method of a target coated with an electromagnetic control material according to claim 1, characterized in that: In step three, the linear frequency modulation signal transmitted by the radar is analyzed, and the LFM signal is expressed as: Among them, t k Indicates fast time, t m represents slow time, rect(·) represents rectangular pulse, f c is the carrier frequency, j is the imaginary unit, K r =B / T P is the frequency modulation slope, B is the signal bandwidth, T p is the pulse width; the baseband echo signal is expressed as: Where M is the number of scattering centers of the target, σ i is the radar cross section RCS of the i-th scattering center, R i (t m ) is the distance from the target i-th scattering center to the receiver, which changes with slow time, and c is the propagation speed of light in free space; the echo signals of different scattering states are different, which is reflected in Respectively expressed as Among them, σ gi is the RCS of the i-th scattering center in the high scattering state, σ di is the RCS of the i-th scattering center in the low scattering state, then the echo signal after time domain splicing is: Among them, s gr (t k ,t m ),s dr (t k ,t m ) represent the echo signals of high scattering state and low scattering state respectively, is the convolution operator, Γ(t k ,t m ,0) is the case where x=0 in the electromagnetic control signal.

8. The radar dynamic echo simulation method of a target coated with an electromagnetic control material according to claim 7, characterized in that: In step 4, pulse compression processing is performed on the dynamic echo signal after electromagnetic modulation to obtain a modulated one-dimensional range image HRRP, and the characteristics of the HRRP are analyzed; The matched filter function is the complex conjugate of the transmitted signal It is expressed as: Therefore, the frequency domain response of the modulated baseband echo signal formed by down-conversion after matched filtering is: Among them, Γ(f k ,t m ,0) is the modulation coefficient; R(f k ,t m ) is the frequency domain response of the echo signal, S t * (f k ,t m ) is the conjugate of the frequency domain response of the transmitted signal, and the phase term is the video residual, is the oblique envelope term.

9. The radar dynamic echo simulation method of a target coated with an electromagnetic control material according to claim 8, characterized in that: In step 4, for periodic amplitude modulation, the frequency response of the modulated baseband echo signal after matched filtering is: is the modulation phase term. After periodic amplitude modulation, the echo pulse compression output is a superposition of multiple sinc discrete peaks. When is the real target, the zero-order peak amplitude is when When multiple false targets are generated, the distance interval between false targets is ΔR = f q ·c / (2K r ).

10. The radar dynamic echo simulation method of a target coated with an electromagnetic control material according to claim 9, characterized in that: In step 4, for non-periodic amplitude modulation, the frequency response of the modulated baseband echo signal after matched filtering is: In the formula, The phase term is modulated, and the echo pulse compression output after non-periodic amplitude modulation is a linear superposition of a zero-order peak and a continuous Doppler frequency shift in the matched filter.

Images