Method for calculating and evaluating characteristics of target radar echo correlation domain covered by plasma

Abstract

The application discloses a kind of plasma covering target radar echo correlation domain characteristic calculation and evaluation method, comprising: based on the iterative update calculation formula of electric field and magnetic field of electromagnetic wave propagation in plasma, the electric field and magnetic field intensity of reflected electromagnetic wave of plasma covering target are calculated;Based on the electric field and magnetic field intensity of reflected electromagnetic wave, the reflection coefficient of plasma covering target is obtained, the reflection coefficient is coupled into radar signal frequency domain expression, so as to obtain the frequency domain radar echo signal of plasma covering target;Using frequency domain matching filtering method, combined with fast inverse fourier transform, the correlation domain echo signal of plasma covering target is obtained, and the evaluation method of correlation domain stealth performance of plasma to radar echo is proposed.

Description

Technical Field

[0001] This invention belongs to the field of radar detection and electromagnetic calculation technology, and relates to a method for calculating and evaluating the correlation domain characteristics of radar echoes from targets covered by plasma. Background Technology

[0002] When hypersonic vehicles fly at speeds exceeding 15 Mach or even 25 Mach, and their reentry capsule re-enters the atmosphere, the high-speed vehicle platform experiences intense friction with the air during flight. This causes the temperature at the vehicle's nose to reach several thousand degrees Celsius, resulting in the dissociation and ionization of air molecules and the generation of plasma. When ground-based radar detects targets covered by plasma, the radar echo characteristics of plasma-covered targets differ from those of conventional radar. Furthermore, when plasma is used for plasma stealth, it coats the surface of a metal plate, causing the radar echo of plasma-covered targets to differ from that of uncoated targets.

[0003] The correlation domain characteristics of radar echoes from targets covered by plasma play a crucial role in radar detection, and the peak value of the correlation domain is closely related to the radar target detection capability. However, existing methods for calculating radar echoes from targets covered by plasma do not consider methods for calculating the correlation domain characteristics of broadband radar signals in real research contexts. This makes it impossible to effectively assess the influence of plasma on the correlation domain characteristics, thus seriously affecting research on radar detection of targets covered by plasma and the effectiveness analysis of plasma stealth technology. Summary of the Invention

[0004] The purpose of this invention is to provide a method for calculating and evaluating the correlation domain characteristics of radar echoes from targets covered by plasma, in order to solve the problem that existing radar signal calculation models under plasma neglect the calculation and evaluation of the correlation domain characteristics of radar signals under plasma coverage, resulting in the inability to evaluate the impact of plasma on radar detection and stealth characteristics.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for calculating and evaluating the correlation domain characteristics of radar echoes from targets covered by plasma, comprising:

[0007] Based on the iterative calculation formulas for the electric and magnetic fields of electromagnetic waves propagating in plasma, the electric and magnetic field strengths of electromagnetic waves reflected by the plasma-covered target are calculated.

[0008] The reflection coefficient of the plasma-covered target is obtained by measuring the electric and magnetic field strengths of the reflected electromagnetic wave. The reflection coefficient of the plasma-covered target is then coupled into the frequency domain expression of the radar signal to obtain the frequency domain radar echo signal of the plasma-covered target.

[0009] By using a frequency-domain matched filter and combining it with a fast inverse Fourier transform, the correlation domain echo signal of the plasma covering the target is calculated, and the correlation domain stealth effectiveness of the plasma on the radar echo is evaluated based on a new variable, namely the stealth coefficient.

[0010] The beneficial effects of this invention are as follows: Based on the iterative calculation formulas of the electric and magnetic fields of electromagnetic waves propagating in plasma, the reflection coefficient of the plasma-covered target to electromagnetic signals is calculated. The reflection coefficient is coupled into the frequency domain expression of the linear frequency modulated signal, and a frequency domain matched filtering method combined with fast inverse Fourier transform is used to obtain the correlation domain echo signal of the plasma-covered target. Furthermore, a method for evaluating the correlation domain stealth effectiveness of plasma to radar echoes is proposed, effectively solving the problem that existing radar echo calculation methods cannot effectively calculate and evaluate the correlation domain echo characteristics of plasma-covered targets. Moreover, this calculation method couples the influence of broadband dispersion effect on the correlation domain characteristics of radar echoes, resulting in more accurate analysis results. This lays the foundation for the radar detection of plasma-covered targets and the application research of plasma stealth technology. Attached Figure Description

[0011] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0012] Figure 1 This is a flowchart of the method for calculating and evaluating the correlation domain characteristics of radar echoes of plasma-covered targets according to an embodiment of the present invention.

[0013] Figure 2 The electron density in this embodiment of the invention is 4 × 10⁻⁶. 16 / m 3 Time-domain diagram of radar signals reflected by targets not covered by plasma.

[0014] Figure 3 The electron density in this embodiment of the invention is 4 × 10⁻⁶. 16 / m 3 Time-domain diagram of radar signals reflected by targets covered by plasma.

[0015] Figure 4 The electron density in this embodiment of the invention is 4 × 10⁻⁶. 16 / m 3 Correlation domain diagram of radar signals reflected by targets not covered by plasma.

[0016] Figure 5 The electron density in this embodiment of the invention is 4 × 10⁻⁶. 16 / m3 Correlation domain diagram of radar signals reflected by targets covered by plasma.

[0017] Figure 6 The results are calculated based on the correlation domain characteristics of radar echoes from plasma-covered targets under different flow field parameters, considering and not considering envelope distortion effects. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] An embodiment of the present invention provides a method for calculating and evaluating the correlation domain characteristics of radar echoes from plasma-covered targets, comprising:

[0020] Step 1: Based on the propagation characteristics of electromagnetic waves in plasma, and using iterative calculation formulas for electric and magnetic fields, calculate the electric and magnetic field strengths of the electromagnetic waves reflected by the plasma covering the target to form a plasma sheath. The specific steps are as follows:

[0021] First, based on the unconditionally stable finite-difference time-domain method, the electric field E from n to n+1 / 2 steps can be obtained. x E y and magnetic field H z The iterative calculation formula is as follows:

[0022]

[0023]

[0024]

[0025] Where n is the time step, i and j are the coordinates of the spatial grid, Δt is the time step size, Δx and Δy are the spatial step sizes, and ε is the dielectric constant.

[0026] This represents the electric field intensity component in the x-direction at the spatial location (i+1 / 2, j) at time step n+1 / 2. This represents the electric field intensity component in the x-direction at the spatial position (i+1 / 2, j) at time step n. This represents the component of the magnetic field strength in the z-direction at the spatial position (i+1 / 2, j+1 / 2) at time step n. This represents the component of the magnetic field strength in the z-direction at the spatial position (i+1 / 2, j-1 / 2) at time step n. This represents the x-direction current density component at spatial location (i+1 / 2, j) at time step n. This represents the x-direction current density component at the spatial location (i+1 / 2, j) at time step n+1 / 2.

[0027] This represents the electric field intensity component in the y-direction at the spatial location (i, j+1 / 2) at time step n+1 / 2. This represents the electric field intensity component in the y-direction at the spatial position (i, j+1 / 2) at time step n. This represents the component of the magnetic field strength in the z-direction at the spatial location (i+1 / 2, j+1 / 2) at time step n+1 / 2. This represents the component of the magnetic field strength in the z-direction at the spatial location (i-1 / 2, j+1 / 2) at time step n+1 / 2. Let represent the y-direction current density component at spatial position (i, j+1 / 2) at time step n. This represents the y-direction current density component at the spatial location (i, j+1 / 2) at time step n+1 / 2.

[0028] This represents the electric field intensity component in the x-direction at the spatial position (i+1 / 2, j+1) at time step n. This represents the electric field intensity component in the y-direction at the spatial location (i+1, j+1 / 2) at time step n+1 / 2.

[0029] Secondly, the current density in step n+1 / 2 and They are respectively:

[0030]

[0031]

[0032] in, and Describes the electric field at step n+1 / 2. and Represents the current density over n steps; variable σ 0 It can be written as:

[0033]

[0034] ω p ν is the plasma frequency, and v is the collision frequency.

[0035] United and The above and Substituting the iterative formula into the above text and The iterative formula yields:

[0036]

[0037]

[0038] in It can be solved directly, while Can be combined The solution is obtained by using the chasing method.

[0039] Step 2: Based on the electric and magnetic field strengths of the reflected electromagnetic waves, calculate the reflection coefficient of the plasma-covered target. Couple the reflection coefficient of the plasma-covered target into the frequency domain expression of the radar signal to obtain the frequency domain radar echo signal of the plasma-covered target. The specific steps are as follows:

[0040] First, calculate the broadband field strength E of the incident electromagnetic wave in the frequency domain. i (f) and the broadband field strength frequency domain calculation results of the reflected electromagnetic wave E r (f), the reflection coefficient R(f) of the plasma-covered target is obtained by comparison:

[0041] R(f)=E i (f) / E r (f);

[0042] Where f represents frequency, E i (f) is the Fourier transform result of the incident electromagnetic wave, E r (f) is the Fourier transform result of the reflected electromagnetic wave.

[0043] Secondly, the frequency domain expression y(f) of the radar signal without coupled plasma effects is written as:

[0044]

[0045] The plasma frequency domain reflection coefficient R(f) is coupled into the analytical expression of the radar signal in the frequency domain, thereby calculating the frequency domain radar echo signal y of the target covered by plasma. plasma (f):

[0046]

[0047] Among them, T p K is the pulse width, K is the frequency modulation, and t0 is the time delay.

[0048] Step 3: Using a frequency-domain matched filter and combined with a fast inverse Fourier transform, calculate the plasma-covered target correlation domain echo signal and establish a new variable, namely the stealth coefficient. Then, construct a method for evaluating the correlation domain stealth effectiveness of plasma against radar echoes. The specific steps are as follows:

[0049] First, the frequency domain matched filter is written as follows:

[0050]

[0051] Secondly, by using the frequency domain matched filtering method, and then combining it with the fast inverse Fourier transform, the correlation domain echo signal y of the plasma-covered target can be obtained. plasma,cor (t):

[0052]

[0053] Finally, a new evaluation variable, Stealth_factor, is proposed to evaluate the correlation domain stealth effectiveness of plasma against radar echoes.

[0054] Stealth_factor = 10 * log10(P) plasma / P noplasma )

[0055] Among them, P plasma The peak energy level when there is plasma, P noplasma It represents the peak energy level without plasma.

[0056] In this invention, the larger the stealth factor (Stealth_factor), the stronger the amplitude attenuation of the radar echo correlation domain, and the more significant the stealth effect of plasma covering the target on radar detection.

[0057] Two examples are used to illustrate the method for calculating and evaluating the correlation domain characteristics of radar echoes from plasma-covered targets according to embodiments of the present invention.

[0058] Example 1

[0059] The results of the correlation domain characteristics calculation of radar echoes from targets covered by plasma were obtained. The simulation parameters were: signal pulse width 100μs, bandwidth 60MHz, carrier frequency 2GHz, and plasma electron density 4×10⁻⁶. 16 / m 3 At that time, the time-domain waveform and correlation-domain waveform of the radar signal reflected by the target not covered by plasma are as follows: Figure 2 and Figure 4 As shown, the time-domain waveform and correlation-domain waveform of the radar signal reflected by the target covered by plasma are as follows: Figure 3 and Figure 5As shown in the figure. The simulation results show that, due to the effect of plasma, the radar echo exhibits amplitude attenuation and envelope distortion in the time domain. This envelope distortion is caused by the dispersive properties of the plasma. (Comparison) Figure 4 and Figure 5 The peak value of the radar echo correlation domain of the plasma-covered target decreased significantly, demonstrating that the embodiments of the present invention can accurately calculate the radar echo correlation domain characteristics of the plasma-covered target.

[0060] Example 2

[0061] The results of the correlation domain characteristics of radar echoes from targets covered by plasma under different flow field parameters are calculated. The simulation parameters are: carrier frequency 2 GHz, collision frequency 0.1–30 GHz, and electron density 1 × 10⁻⁶. 16 / m 3 5×10 16 / m 3 and 1×10 17 / m 3 The stealth coefficients under different flow field conditions, considering the envelope distortion effect caused by dispersion and without considering envelope distortion, are as follows: Figure 6 As shown in the figure. It can be seen from the figure that when the electron density is equal to 1×10... 17 / m 3 Under strong absorption conditions, curves exhibiting envelope distortion differ from those without. Therefore, envelope distortion cannot be ignored when studying plasma stealth technology or radar detection of hypersonic vehicles covered by a plasma sheath. The method for calculating the correlation domain characteristics of radar echoes from plasma-covered targets in this invention covers the envelope distortion effect caused by dispersion, thus enabling accurate and effective calculation and evaluation of the correlation domain characteristics of radar echoes from plasma-covered targets.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for calculating and evaluating the correlation domain characteristics of radar echoes from targets covered by plasma, characterized in that, include: Based on the iterative calculation formulas for the electric and magnetic fields of electromagnetic waves propagating in plasma, the electric and magnetic field strengths of electromagnetic waves reflected by the plasma-covered target are calculated. The reflection coefficient of the plasma-covered target is obtained by measuring the electric and magnetic field strengths of the reflected electromagnetic wave. The reflection coefficient of the plasma-covered target is then coupled into the frequency domain expression of the radar signal to obtain the frequency domain radar echo signal of the plasma-covered target. Using a frequency domain matched filter and combining it with a fast inverse Fourier transform, the correlation domain echo signal of the plasma-covered target is calculated, and the correlation domain stealth effectiveness of the plasma on the radar echo is evaluated based on a new variable, namely the stealth coefficient. The reflection coefficient and frequency domain radar echo signal of the plasma-covered target are calculated according to the following steps: First, by comparing the electric field strength of the reflected electromagnetic wave with that of the incident wave, the reflection coefficient R(f) of the plasma-covered target is obtained: R(f)=E i (f) / E r (f); Among them, E i (f) is the frequency domain calculation result of the broadband field strength of the incident electromagnetic wave, that is, the Fourier transform result of the incident electromagnetic wave, E r (f) is the frequency domain calculation result of the broadband field strength of the reflected electromagnetic wave, that is, the Fourier transform result of the reflected electromagnetic wave, where f represents the frequency. Secondly, the frequency domain expression y(f) of the radar signal without coupled plasma effects is written as: Among them, T p K is the pulse width, K is the frequency modulation, and t0 is the time delay; The plasma frequency domain reflection coefficient R(f) is coupled into the analytical expression of the radar signal frequency domain to calculate the frequency domain radar echo signal y of the plasma-covered target. plasma (f): The plasma-covered target correlation domain echo signal and stealth effectiveness are calculated and evaluated using the following method: First, the frequency domain matched filter is written as follows: Secondly, the frequency domain matched filtering method combined with the fast inverse Fourier transform is used to obtain the plasma-covered target correlation domain echo signal y. plasma,cor (t): Finally, a new evaluation variable, the stealth coefficient Stealth_factor, is established to assess the correlation domain stealth effectiveness of plasma against radar echoes: Stealth_factor=10*log10(P plasma / P noplasma ) Among them, P plasma The peak energy magnitude when there is plasma, P noplasma It is the peak energy level without plasma; The larger the Stealth_factor, the stronger the amplitude attenuation of the radar echo correlation domain, and the more significant the stealth effect of plasma covering targets on radar detection.

2. The method for calculating and evaluating the correlation domain characteristics of radar echoes from plasma-covered targets according to claim 1, characterized in that, The electric and magnetic field strengths of the electromagnetic waves reflected by the plasma-covered target are calculated according to the following steps: First, based on the unconditionally stable finite-difference time-domain method, the electric field E from step n to n+1 / 2 is... x and E y and magnetic field H z Iteration formula: Where n is the time step, and i and j are the coordinates of the spatial grid; This represents the electric field intensity component in the x-direction at the spatial location (i+1 / 2, j) at time step n+1 / 2. This represents the electric field intensity component in the x-direction at the spatial position (i+1 / 2, j) at time step n. This represents the component of the magnetic field strength in the z-direction at the spatial position (i+1 / 2, j+1 / 2) at time step n. This represents the component of the magnetic field strength in the z-direction at the spatial position (i+1 / 2, j-1 / 2) at time step n. This represents the x-direction current density component at the spatial location (i+1 / 2, j) at time step n. This represents the x-direction current density component at the spatial location (i+1 / 2, j) at time step n+1 / 2; This represents the electric field intensity component in the y-direction at the spatial location (i, j+1 / 2) at time step n+1 / 2. This represents the electric field intensity component in the y-direction at the spatial position (i, j+1 / 2) at time step n. This represents the component of the magnetic field strength in the z-direction at the spatial location (i+1 / 2, j+1 / 2) at time step n+1 / 2. This represents the component of the magnetic field strength in the z-direction at the spatial location (i-1 / 2, j+1 / 2) at time step n+1 / 2. Let represent the y-direction current density component at spatial position (i, j+1 / 2) at time step n. This represents the y-direction current density component at the spatial location (i, j+1 / 2) at time step n+1 / 2; This represents the electric field intensity component in the x-direction at the spatial position (i+1 / 2, j+1) at time step n. This represents the electric field intensity component in the y-direction at the spatial location (i+1, j+1 / 2) at time step n+1 / 2; Δt is the time step, Δx and Δy are the spatial steps, and ε is the dielectric constant; Secondly, the current density in step n+1 / 2 and They are respectively: and Describes the electric field at step n+1 / 2. and This represents the current density over n steps; variable σ 0 writing: Where ω p Where is the plasma frequency, and v is the collision frequency; The above and Substituting the iterative formula into the above text and The iterative formula is used to derive the following formula: in Solve directly. Combination The solution is obtained by using the chasing method.

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