Simulated sheath target high-fidelity radar echo simulation method

Abstract

The invention belongs to the technical field of electronic system engineering, and discloses a high-fidelity radar echo simulation method for a simulated sheath target. The invention relates to setting a spatial position parameter of a sheath target and a position parameter of a radar; parameters of target fluctuation characteristics of the sheath are set, and particle swarm number and speed parameters are set; calculating RCS amplitude information and RCS phase information of each particle by adopting a POMC method based on incident plane construction and ray tracing; generating a radar echo of a single particle target by using the RCS amplitude information and the RCS phase information of each particle; and superposing all particle radar echoes in the particle swarm to complete sheath target radar echo simulation. According to the method, the spatial distribution of the plasma sheath is simulated by utilizing the speed difference of the particle swarm target, so that grid division of the space is avoided, and the calculation amount required by sheath target echo simulation is greatly reduced.

Description

Technical Field

[0001] The invention mainly relates to the technical field of electronic system engineering, and in particular to a high-fidelity radar echo simulation method for a simulated sheath target. Background Art

[0002] Airborne targets are one of the main detection targets of ground radars. The simulation of airborne targets is of great significance for the detection of hypersonic airborne vehicles and return capsules. Traditional radar target echo simulation is based on a point scattering model, which generates echo signals of complete targets by superimposing echo signals of multiple scattering points. Airborne targets will produce a plasma sheath at an altitude of 50 kilometers, and their target characteristics are different from those of conventional point targets.

[0003] The traditional sheath target modeling method is to model the non-uniform plasma sheath as multiple layers of uniform plasma thin layers, and use the layered medium to simulate the non-uniform medium method to calculate the parameters of the plasma sheath. At the same time, the propagation characteristics and transmission characteristics of linearly polarized and circularly polarized electromagnetic waves are simulated, and the loss model under polarization mismatch is analyzed. The main disadvantage of this method is that there is a frequency mismatch problem in the simulation of the plasma sheath model for radars in specific frequency bands.

[0004] The most widely used sheath target echo simulation method is the finite-difference time domain method (FDTD). This method calculates the RCS parameters of the plasma sheath by constructing a square grid in space. Since the calculation method is simple and easy to understand, it is widely used in commercial software. The main disadvantage of the finite-difference time domain method (FDTD) is that the high-precision parameter calculation requires the refinement of the grid, so the amount of calculation is too large. At the same time, this method has a high dependence on the dielectric constant, and the algorithm is difficult to converge, so it cannot be effectively used in actual engineering.

[0005] In order to solve the problem that the finite difference time domain method (FDTD) has high requirements for grid refinement and large amount of calculation, a simulated sheath target echo simulation method is designed. The sheath target is modeled as a particle swarm target with different velocity distributions, and the Doppler characteristics of the target velocity in the radar echo are used to simulate the spatial distribution of the sheath target, so as to achieve a highly realistic echo simulation of the sheath target. Summary of the invention

[0006] In view of the problem that the traditional time-domain finite-difference method has a large amount of calculation due to the refined grid division, the purpose of the present invention is to provide a high-fidelity radar echo simulation method for a simulated sheath target, which utilizes the velocity difference of a particle group target to simulate the spatial distribution of a plasma sheath, avoids grid division of the space, and greatly reduces the amount of calculation required for sheath target echo simulation.

[0007] To achieve the above object, the present invention provides a method for simulating high-fidelity radar echo of a simulated sheath target, comprising the following steps: Step 1: Set the spatial position parameters of the sheath target and the position parameters of the radar; Step 2: Setting the parameters of the sheath target fluctuation characteristics, the number of particle swarms and the speed parameters according to the spatial position parameters of the sheath target; Step 3: Calculate the RCS amplitude information and RCS phase information of each particle using the POMC method based on incident plane construction and ray tracing; Step 4: Generate the radar echo of a single particle target using the RCS amplitude information and RCS phase information of each particle; Step 5: Repeat steps 3 and 4 until the radar echoes of all particles in the particle swarm are calculated, and then superimpose the radar echoes of all particles in the particle swarm to complete the sheath target radar echo simulation.

[0008] Further, the POMC method in step 3 includes: S1: Construction of the incident plane. According to step 1, the spatial position parameters of the sheath target and the position parameters of the radar are set to determine the incident direction of the electromagnetic wave. After determining the incident direction of the electromagnetic wave, the incident plane of the sheath target is constructed. The incident plane is the illumination surface of the plasma composed of particle groups, and the normal vector perpendicular to the incident plane is and the incident electromagnetic wave vector satisfy ; S2: Ray tracing, the POMC method refines the sheath target into multiple subdivision units, and the impedance in the subdivision unit m is ; The angle of incidence of the ray in the next mesh element The relationship is .

[0009] Furthermore, the dielectric constant of each section unit is different, and rays will be refracted and reflected at the interface of section units with different dielectric constants; If the incident electromagnetic wave is vertically polarized, the relationship between the reflection coefficient R and the refraction coefficient T is ;

[0010] If the incident electromagnetic wave is horizontally polarized, the relationship between the reflection coefficient R and the refraction coefficient T is .

[0011] Furthermore, if the incident angle is greater than the critical angle , the ray is completely reflected, and the outgoing direction is completely opposite to the incident direction. The outgoing angle at the boundary of the profile unit can be calculated by the reverse tracing method, and the amplitude and phase information of the scattered field intensity can be calculated and recorded; The relationship between the amplitude of the scattered field intensity of the subdivision unit m and the phase attenuation of the scattered field intensity of the subdivision unit m+1 is: .

[0012] Furthermore, the simulated sheath target radar echo simulation method is to generate radar echoes of multiple particle targets with the same range unit but different radial velocities and superimpose them. The calculation formula is: .

[0013] The present invention provides a high-fidelity radar echo simulation method for a simulated sheath target, which overcomes the shortcomings of the prior art finite-difference time-domain (FDTD) method in terms of high requirements for grid refinement and large amount of calculation. The present invention uses the POMC method only to perform a fine segmentation on the target electromagnetic scattering model without performing layered processing on the plasma, and the implementation is simpler. The present invention uses particle group targets with different velocity distributions to simulate the spatial distribution of the plasma sheath, avoiding the spatial grid division of the traditional method, effectively reducing the amount of calculation, and making the simulation result more realistic. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a flow chart of a method for simulating high-fidelity radar echo of a simulated sheath target according to an embodiment of the present invention; Figure 2 is a graph showing the RCS amplitude distribution of a particle swarm involved in an embodiment of the present invention; Figure 3 is a diagram of the RCS phase distribution of a particle swarm involved in an embodiment of the present invention; Figure 4 is a simulation result of an echo at an azimuth angle of 0° according to an embodiment of the present invention; Figure 5 is the echo simulation result of the azimuth angle 20° involved in the embodiment of the present invention; Figure 6 This is the result of the echo simulation at an azimuth angle of 140° involved in the embodiment of the present invention.

[0015] Description of reference numerals: in: is the normal vector perpendicular to the incident plane; is the incident electromagnetic wave vector; m is the impedance in the section unit; is the dielectric constant of air; is the magnetic permeability of air; is the incident angle of the incident electromagnetic wave in the next subdivision unit; R is the reflection coefficient; T is the refraction coefficient; It is a uniform plasma medium; is the distance that the incident electromagnetic wave travels through the uniform plasma medium; is the wave number, which is specifically expressed as ; re is the real part of the incident electromagnetic wave vector; im is the imaginary part of the incident electromagnetic wave; Indicates the fluctuation of the amplitude of the baseband signal over time; k indicates the number of targets with different speeds; It is by and The amplitude information of the nth target is obtained, expressed as ; Expressed by Obtain the phase information of the nth target ; It represents the Doppler frequency shift caused by different radial velocities and is expressed as ; It indicates the speed that is not fully compensated when simulating the target pulse pressure for the nth time; Indicates the wavelength of the radar transmitted signal; Target position deviation after pulse pressure The relationship is expressed as ; is the frequency modulation slope of the transmitted linear frequency modulation signal, expressed as , is the signal bandwidth, is the pulse width; Target position offset With target speed The relationship is expressed as . DETAILED DESCRIPTION

[0016] The preferred mechanism and implementation method of the present invention are further described below in conjunction with the accompanying drawings and specific implementation methods.

[0017] RCS is the radar scattering surface.

[0018] like Figures 1 to 6 As shown, an embodiment of the present invention discloses a technical solution for a method for simulating high-fidelity radar echo of a simulated sheath target. The present invention involves setting the spatial position parameters of the sheath target and the position parameters of the radar; setting the parameters of the sheath target fluctuation characteristics, the number of particle swarms and the speed parameters; using the POMC method based on incident plane construction and ray tracing to calculate the RCS amplitude information and RCS phase information of each particle; using the RCS amplitude information and RCS phase information of each particle to generate a radar echo of a single particle target; superimposing all particle radar echoes in the particle swarm to complete the sheath target radar echo simulation. Example

[0019] Figure 1 The present invention is a flowchart of a method for simulating high-fidelity radar echo of a sheath target according to an embodiment of the present invention.

[0020] The method for simulating high-fidelity radar echo of a simulated sheath target in this embodiment comprises the following steps: Step 1: Set the spatial position parameters of the sheath target and the position parameters of the radar; Step 2: Setting the parameters of the sheath target fluctuation characteristics, the number of particle swarms and the speed parameters according to the spatial position parameters of the sheath target; Step 3: Calculate the RCS amplitude information and RCS phase information of each particle using the POMC method based on incident plane construction and ray tracing; Step 4: Generate the radar echo of a single particle target using the RCS amplitude information and RCS phase information of each particle; Step 5: Repeat steps 3 and 4 until the radar echoes of all particles in the particle swarm are calculated, and then superimpose the radar echoes of all particles in the particle swarm to complete the sheath target radar echo simulation. Example

[0021] This embodiment is basically the same as Embodiment 1, except that the POMC method comprises: S1: Incident plane construction: According to step 1, the spatial position parameters of the sheath target and the position parameters of the radar are set to determine the incident direction of the electromagnetic wave. After determining the incident direction of the electromagnetic wave, the incident plane of the sheath target is constructed. The incident plane is the illumination surface of the plasma composed of particle groups. The prerequisite for judging it as the illumination surface is that the normal vector is perpendicular to the incident plane. and the incident electromagnetic wave vector satisfy (Formula 1), that is, the angle of the vector exceeds 90°. In traditional physical optics, the impact of spatial occlusion on electromagnetic calculations must be considered. When this model is used, since the incident electromagnetic wave will be reflected, the occlusion is no longer considered. At the same time, the number of incident electromagnetic waves is determined according to the illumination plane. The number of incident electromagnetic waves in each cycle must be sufficient to ensure that each section unit can be calculated by the POMC algorithm. The incident plane is constructed according to the above conditions. After the incident plane is constructed, rays are generated according to the incident direction of the electromagnetic wave and the phase information is confirmed.

[0022] S2: Ray Tracing: The plasma sheath of the target in the air can be regarded as a lossy inhomogeneous medium, and the electromagnetic medium theory can be used to process the electromagnetic scattering characteristics of the target. Plasma is usually unevenly distributed in space. In traditional optical theory, the inhomogeneous plasma is mainly approximated as consisting of multiple layers of medium slices with different parameters, and each layer of medium slices is approximately considered to be uniformly distributed. When simulating electromagnetic waves in inhomogeneous media, the POMC algorithm does not need to treat plasma as multiple layers of medium slices. It only needs to refine the target electromagnetic model, so that the plasma in a single segmentation unit can be considered to be approximately uniformly distributed. The plasma in each segmentation unit is considered to be approximately uniformly distributed, and the medium parameters will also change. Assuming that the movement of rays in each segmentation unit is approximately regarded as the propagation of electromagnetic waves in a uniform plasma, this method can simplify the processing flow and has a smaller error than the multi-layer medium model.

[0023] The POMC method divides the sheath target into multiple subdivision units, and the impedance in the subdivision unit m is (Formula 2); is the dielectric constant of air, is the magnetic permeability of air. According to the law of refraction, the incident angle of the ray in the next subdivision unit can be determined based on the difference in impedance. The relationship is (Formula 3).

[0024] If the incident electromagnetic wave is vertically polarized, the reflection coefficient R and can be expressed as (Formula 4); If the incident electromagnetic wave is horizontally polarized, the reflection coefficient R and can be expressed as (Formula 5).

[0025] At the interface of media with different dielectric constants, rays will refract and reflect. Random simulation is used to analyze the refraction and reflection of the interface. The range of dielectric constant of the profile unit is ,exist A random number is randomly selected between . If it is less than the reflection coefficient obtained by formula 4 or formula 5, the ray will be reflected at the interface. The scattered field intensity is calculated according to the reflection coefficient. At the same time, the amplitude and phase information of the scattered field intensity are recorded to calculate the RCS of the target, and the cycle ends. If this value is greater than the reflection coefficient, refraction occurs at the interface of the profile unit. The refraction direction is calculated according to the law of refraction, and the field intensity is calculated according to the transmission coefficient. At the same time, the critical angle of refraction must also be considered. If the incident angle is greater than the critical angle The ray is completely reflected, and the outgoing direction is completely opposite to the incident unit. The outgoing angle at the model boundary can be calculated through the reverse tracing method, and the amplitude and phase information of the scattered field intensity can be calculated and recorded.

[0026] The dielectric constant of plasma is in complex form and has an imaginary part. When electromagnetic waves in space pass through plasma, their energy will be absorbed, resulting in loss. At the same time, the inhomogeneous characteristics of the plasma medium itself will cause different energy losses of reflected electromagnetic waves in different subdivision units, resulting in inconsistent amplitude and phase changes of the field strength. After optical calculation, the scattering characteristics of the target will also change. Therefore, when simulating the movement of particles under different paths, it is necessary to consider energy loss and phase change.

[0027] Given a uniform plasma medium , electromagnetic waves pass through the medium The attenuation of power and phase after distance can be expressed as (Formula 6), where is the wave number, which is specifically expressed as , re represents the real part, im represents the imaginary part. For finely divided section units, the plasma can be considered to be approximately uniformly distributed. Therefore, the amplitude and phase attenuation relationship from unit m to unit m+1 is (Formula 7).

[0028] High-fidelity radar echo simulation method for the sheath target simulated in step 4: After calculating the amplitude and phase changes of the outgoing echo of rays with different incident angles, the plasma sheath echo simulation also needs to obtain the distribution of the sheath in the spatial domain. According to the pulse compression theory, when there are targets with different radial velocities around the target, the target velocity is not fully compensated after the pulse compression, which will cause an offset in the distance dimension and form multiple peaks. Using this feature, the distribution of the plasma sheath is simulated by generating echoes of multiple targets with the same distance unit but different radial velocities. The specific relationship is shown in the following formula: (Formula 8); in It represents the fluctuation of the amplitude of the baseband signal over time, and k represents the number of targets with different speeds.

[0029] Assuming that the ray passes through m mesh elements, then The amplitude information of the nth target is obtained by the formula and is expressed as follows (Formula 9); Represents the phase information of the nth target obtained by (Equation 7) .

[0030] It represents the Doppler frequency deviation caused by different radial velocities. The specific relationship is: (Formula 10), where Indicates the speed that is not fully compensated when simulating the target pulse pressure for the nth time. Indicates the wavelength of the radar transmitted signal.

[0031] Target position deviation after pulse pressure The relationship is expressed as (Formula 11), is the frequency modulation slope of the transmitted linear frequency modulation signal, expressed as , is the signal bandwidth, Is the pulse width.

[0032] Target position offset With target speed The relationship is expressed as (Formula 12).

[0033] By superimposing multiple target echoes of different speeds in the same distance unit, the distribution of the plasma sheath around the target is simulated, and finally the simulation of the plasma sheath echo of the target in the air is realized.

[0034] Taking the X-band plasma sheath echo simulation as an example, the number of targets with different speeds is 137, the speed interval is 100m / s, and the radial speed range is -6800m / s to 6800m / s. The observation depression angle is 0°, the azimuth angle is 0° to 180°, the interval is 2°, and the bandwidth is 10MHz. The amplitude and phase of the RCS of each target at different observation angles are calculated using the method of (Equation 9). The calculation results are as follows: Figure 2 and Figure 3 As shown: At the same azimuth, the RCS amplitude and phase information of different targets are used to construct the original echo model of the target using (Equation 8). After pulse compression, the simulation results of the plasma sheath of the target in the air are obtained. When the azimuth changes, the simulation results are as follows: Figures 4 to 6 shown.

[0035] The present invention provides a high-fidelity radar echo simulation method for a simulated sheath target, which overcomes the shortcomings of the prior art finite-difference time-domain (FDTD) method in terms of high requirements for grid refinement and large amount of calculation. The present invention uses the POMC method only to perform a fine segmentation on the target electromagnetic scattering model without performing layered processing on the plasma, and the implementation is simpler. The present invention uses particle group targets with different velocity distributions to simulate the spatial distribution of the plasma sheath, avoiding the spatial grid division of the traditional method, effectively reducing the amount of calculation, and making the simulation result more realistic.

[0036] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent substitutions for some of the technical features therein. However, any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for simulating high-fidelity radar echo of a simulated sheath target, characterized in that: The following steps are involved: Step 1: Set the spatial position parameters of the sheath target and the position parameters of the radar; Step 2: Setting the parameters of the sheath target fluctuation characteristics, the number of particle swarms and the speed parameters according to the spatial position parameters of the sheath target; Step 3: Calculate the RCS amplitude information and RCS phase information of each particle using the POMC method based on incident plane construction and ray tracing; Step 4: Generate the radar echo of a single particle target using the RCS amplitude information and RCS phase information of each particle; Step 5: Repeat steps 3 and 4 until the radar echoes of all particles in the particle swarm are calculated, and then superimpose the radar echoes of all particles in the particle swarm to complete the sheath target radar echo simulation.

2. The method for simulating high-fidelity radar echo of a simulated sheath target according to claim 1, characterized in that: The POMC method in step 3 includes: S1: Construction of the incident plane. According to step 1, the spatial position parameters of the sheath target and the position parameters of the radar are set to determine the incident direction of the electromagnetic wave. After determining the incident direction of the electromagnetic wave, the incident plane of the sheath target is constructed. The incident plane is the illumination surface of the plasma composed of particle groups, and the normal vector perpendicular to the incident plane is and the incident electromagnetic wave vector satisfy ; S2: Ray tracing, the POMC method refines the sheath target into multiple subdivision units, and the impedance in the subdivision unit m is ; The angle of incidence of the ray in the next mesh element The relationship is .

3. The method for simulating high-fidelity radar echo of a simulated sheath target according to claim 2, characterized in that: The dielectric constant of each section unit is different, and rays will be refracted and reflected at the interface of section units with different dielectric constants; If the incident electromagnetic wave is vertically polarized, the relationship between the reflection coefficient R and the refraction coefficient T is ; If the incident electromagnetic wave is horizontally polarized, the relationship between the reflection coefficient R and the refraction coefficient T is .

4. The method for simulating high-fidelity radar echo of a simulated sheath target according to claim 3, characterized in that: If the incident angle is greater than the critical angle , the ray is completely reflected, and the outgoing direction is completely opposite to the incident direction. The outgoing angle at the boundary of the profile unit can be calculated by the reverse tracing method, and the amplitude and phase information of the scattered field intensity can be calculated and recorded; The relationship between the amplitude of the scattered field intensity of the subdivision unit m and the phase attenuation of the scattered field intensity of the subdivision unit m+1 is: .

5. The method for simulating high-fidelity radar echo of a simulated sheath target according to claim 4, characterized in that: The simulated sheath target radar echo simulation method is to generate radar echoes of multiple particle targets with the same range unit but different radial velocities and superimpose them. The calculation formula is: .

Images