A method for calculating target radar cross section based on complex impedance

Abstract

The present invention discloses a method for calculating a target's radar cross section based on complex impedance, which belongs to the field of electromagnetic scattering technology. The method comprises the following steps: 1. constructing a three-dimensional model of the target's outer surface and dividing the outer surface into regions; 2. measuring the complex impedance of each divided region using a vector network analyzer; 3. importing the three-dimensional model of the target's outer surface into electromagnetic simulation software, and assigning the complex impedance values ​​of the divided regions to the three-dimensional model of the outer surface in the electromagnetic simulation software; and 4. setting the propagation direction, polarization, frequency band, and angle of incidence of the incident electromagnetic wave in the electromagnetic simulation software, and using the electromagnetic simulation software to calculate the target's radar cross section. The present invention uses the target's complex impedance as a boundary condition, using complex impedance to replace the dielectric constant, magnetic permeability, and thickness parameters used in conventional calculations, thereby achieving the calculation of the target's radar cross section. The method does not require a large measurement site and can achieve complex impedance measurement in an outdoor environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic scattering, in particular to a method for calculating a target radar cross section based on complex impedance. Background Art

[0002] Measuring a target's radar cross section (RCS) typically requires an open field. For large targets like aircraft, this often requires a field tens of kilometers long. However, there are only a handful of sites worldwide suitable for measuring the RCS of large targets, limiting the use of direct methods for measuring the RCS of large targets.

[0003] The patent, published as CN107192990B and titled "Extrapolation Method for Measuring Radar Cross-Section Area," proposes deriving the RCS of a target at infinity (i.e., in the far field) by fitting the functional relationship between distance and RCS after multiple RCS measurements at different distances. While this method reduces the required site requirements for RCS measurement, it is not suitable for targets made of complex materials. Furthermore, the cost of constructing a large anechoic chamber required to measure larger targets using the extrapolation method is extremely high, comparable to the cost of building a conventional RCS measurement site.

[0004] At present, in the process of using electromagnetic simulation software to calculate the target radar scattering cross-section, the commonly used method is: input the electromagnetic parameters such as the dielectric constant, magnetic permeability, thickness, etc. of the target surface material into the three-dimensional model of the target, and use the electromagnetic simulation software to calculate the target radar scattering cross-section.

[0005] However, as time goes by, the actual target surface will undergo mechanical or chemical changes such as wear, scratches, and oxidation under the influence of external factors such as sunlight. The electromagnetic parameters of the target surface material will change, which is often inconsistent with the design stage, resulting in changes in the target radar scattering cross section. Therefore, the target radar scattering cross section calculated based on the electromagnetic parameters of the target surface material will deviate from the actual value.

[0006] For actual targets such as aircraft, the measurement equipment and testing environment for electromagnetic parameters such as the dielectric constant, magnetic permeability, and thickness of their surfaces require high standards, and the measurement is difficult. Summary of the Invention

[0007] In order to overcome the difficulties in measuring target electromagnetic parameters and the limitations of test sites, the present invention proposes a method for calculating target radar cross section based on complex impedance.

[0008] The technical solution adopted by the present invention to solve its technical problems is:

[0009] A method for calculating target radar cross section based on complex impedance, the steps are as follows:

[0010] Step 1: construct a three-dimensional model of the outer surface of the target and divide the outer surface into regions;

[0011] Step 2: Use a vector network analyzer to measure the complex impedance of each divided area;

[0012] Step 3: import the target outer surface three-dimensional model into the electromagnetic simulation software, and assign the complex impedance value of the divided area to the outer surface three-dimensional model of the electromagnetic simulation software;

[0013] Step 4: Set the propagation direction, polarization, frequency band, and incident angle of the incident electromagnetic wave in the electromagnetic simulation software, and use the electromagnetic simulation software to calculate the target radar scattering cross section.

[0014] Furthermore, step 1 includes:

[0015] First, establish a rectangular coordinate system

[0016] Set the vertex of the aircraft nose as the coordinate origin o, the direction of the aircraft nose on the horizontal plane where the coordinate origin o is located as the x-direction, any direction in the horizontal plane perpendicular to the x-direction and passing through the origin o as the y-direction, and the upward direction perpendicular to the xoy horizontal plane and passing through the origin o as the z-direction, to establish the oxyz rectangular coordinate system.

[0017] Secondly, draw the 3D model of the target's outer surface

[0018] Draw a three-dimensional model of the space where the outer surface of the target is located, so that each point on the outer surface of the target is in the established oxyz rectangular coordinate system.

[0019] Finally, divide the area according to the target outer surface material

[0020] The three-dimensional model built with the aircraft as the target is divided into areas according to the material of its outer surface, that is, the same material is one area.

[0021] Furthermore, step 2 includes the process of calibrating the vector network analyzer, selecting the antenna, setting the antenna position, and measuring the complex impedance of the target, as follows:

[0022] First, calibrate the vector network analyzer

[0023] Before the measurement begins, turn on the vector network analyzer and perform three calibrations on it. For the first calibration, connect the waveguide-to-coaxial converter to the vector network analyzer port, connect the waveguide end to the short-circuit plate, and perform the vector network analyzer calibration. For the second calibration, disconnect the waveguide end from the short-circuit plate, connect one end of the straight waveguide to the waveguide-to-coaxial converter, and connect the other end of the straight waveguide to the short-circuit plate for further calibration of the vector network analyzer. For the third calibration, disconnect the straight waveguide from the short-circuit plate, connect the waveguide load to the waveguide-to-coaxial converter, and perform the final calibration of the vector network analyzer.

[0024] Next, select the antenna and set the antenna position.

[0025] The antenna is used to transmit and receive electromagnetic waves. The frequency f of the transmitted and received electromagnetic waves is 2-18 GHz. The focal spot radius of the electromagnetic waves transmitted by the antenna is r. The antenna transmits the received electromagnetic waves to the vector network analyzer via a coaxial cable.

[0026] The vector network analyzer is connected to the antenna, processes the electromagnetic waves received by the antenna, and outputs the complex impedance;

[0027] The antenna is placed on one side of the measured target, the antenna port is opposite to the surface of the measured area and is located in the normal direction of the cross section of the surface of the measured area. The closest distance between the antenna port and the surface of the measured area is d, and the distance d is calculated by formula (1).

[0028] d=0.62*(8r 3 / λ) 1 / 2 (1)

[0029] In formula (1), λ is the wavelength of the electromagnetic wave transmitted and received by the antenna, and r is the focal spot radius of the electromagnetic wave transmitted by the antenna.

[0030] Finally, measure the complex impedance of the target

[0031] The antenna port is facing the surface of the area to be measured, and measurement is performed according to the divided areas to obtain the complex reflection coefficient Γ of the measured area. The complex impedance value Z of the measured area is calculated by formula (2).

[0032] Z=50*(1+Γ) / (1-Γ) (2)

[0033] In formula (2), Γ is the complex reflection coefficient of the measured area.

[0034] At this point, the target complex impedance value Z is obtained.

[0035] Furthermore, the electromagnetic simulation software is Feko software, or CST software, or HFSS software.

[0036] Furthermore, in step 4, when the electromagnetic simulation software is the Feko software, the process of calculating the target RCS is:

[0037] Set the relevant parameters of the electromagnetic simulation software; first, select the radar as single-station or dual-station mode. If the single-station radar mode is selected, the RCS calculation will be entered in the single-station calculation module; if the dual-station radar mode is selected, the RCS calculation will be entered in the dual-station calculation module; second, set the propagation direction, polarization, frequency band, and incident angle of the incident electromagnetic wave; finally, set the direction of the receiving radar under far-field conditions.

[0038] Calculation of target radar cross section: When the target electrical size is less than or equal to 100 times the wavelength of the incident electromagnetic wave λ, the moment method is used to calculate the target radar cross section; when the target electrical size is greater than 100 times the wavelength of the incident electromagnetic wave λ and less than 500 times the wavelength of the incident electromagnetic wave, the multi-layer fast multipole algorithm is used to calculate the target radar cross section; when the target electrical size is greater than or equal to 500 times the wavelength of the incident electromagnetic wave λ, the physical optics method is used to calculate the target radar cross section.

[0039] Furthermore, in step 4, when CST software is selected as the electromagnetic simulation software, the process of calculating the target RCS is:

[0040] First, set the propagation direction, polarization, frequency band, and angle of incidence of the incident electromagnetic wave. Second, start the CST software. Finally, select the radar as single-station or dual-station mode. If single-station radar mode is selected, the RCS calculation module will be entered in the single-station calculation module. If dual-station radar mode is selected, the RCS calculation module will be entered in the dual-station calculation module.

[0041] Furthermore, in step 4, when HFSS software is used as the electromagnetic simulation software, the process of calculating the target RCS is:

[0042] First, set the propagation direction, polarization, frequency band, and incident angle of the incident electromagnetic wave; second, set the far-field calculation range; finally, start the HFSS software to run the calculation.

[0043] The beneficial effects of the present invention are:

[0044] The present invention provides a method for calculating the radar cross section of a target based on complex impedance. The method uses the complex impedance of the target as a boundary condition and uses the complex impedance to replace the dielectric constant, magnetic permeability and thickness parameters in conventional calculations, thereby realizing the calculation of the radar cross section of the target.

[0045] The target radar cross section is calculated by measuring the complex impedance. No large measurement site is required and the site requirements are low to medium. Complex impedance measurement can be achieved under outdoor environmental conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The present invention will be further described below with reference to the accompanying drawings and examples.

[0047] Figure 1 Flowchart of the method of the present invention. DETAILED DESCRIPTION

[0048] Example

[0049] A method for calculating a target's radar cross section based on complex impedance is provided. A certain type of aircraft parked in an outdoor field is used as the target. Under outdoor environmental conditions, a vector network analyzer is used to measure electromagnetic parameters of various regions on the aircraft's exterior surface. The obtained complex impedance is used to calculate the aircraft's radar cross section. The specific process includes the following steps:

[0050] Step 1: Build a 3D model of the target's outer surface and divide the outer surface into regions:

[0051] First, establish a rectangular coordinate system:

[0052] Set the vertex of the aircraft nose as the coordinate origin o, the direction of the aircraft nose on the horizontal plane where the coordinate origin o is located as the x-direction, any direction in the horizontal plane perpendicular to the x-direction and passing through the origin o as the y-direction, and the upward direction perpendicular to the xoy horizontal plane and passing through the origin o as the z-direction, to establish the oxyz rectangular coordinate system.

[0053] Next, draw the 3D model of the target's outer surface:

[0054] Draw a three-dimensional model of the space where the outer surface of the target is located, so that each point on the outer surface of the target is in the established oxyz rectangular coordinate system.

[0055] Finally, divide the area according to the target outer surface material:

[0056] The three-dimensional model built with the aircraft as the target is divided into areas according to the material of its outer surface, that is, the same material is one area.

[0057] Step 2: Use a vector network analyzer to measure the complex impedance of each divided area;

[0058] First, calibrate the vector network analyzer:

[0059] Before measurements begin, turn on the vector network analyzer and perform three calibrations. For the first calibration, connect the waveguide-to-coaxial converter to the vector network analyzer port and connect the waveguide end to a shorting plate for vector network analyzer calibration. For the second calibration, disconnect the waveguide end from the shorting plate, connect one end of the straight waveguide to the waveguide-to-coaxial converter, and the other end to the shorting plate for further vector network analyzer calibration. For the third calibration, disconnect the straight waveguide from the shorting plate and connect the waveguide load to the waveguide-to-coaxial converter for the final vector network analyzer calibration.

[0060] Next, select the antenna and set the antenna position.

[0061] The antenna is used to transmit and receive electromagnetic waves. The frequency f of the transmitted and received electromagnetic waves is 2-18 GHz. The focal radius of the electromagnetic waves transmitted by the antenna is r. The antenna transmits the received electromagnetic waves to the vector network analyzer through a coaxial cable.

[0062] The vector network analyzer is connected to the antenna, processes the electromagnetic waves received by the antenna, and outputs the complex impedance.

[0063] The antenna is placed on one side of the target to be measured, with the antenna port facing the surface of the measured area and located in the normal direction of the cross section of the measured area. The closest distance between the antenna port and the surface of the measured area is d, which is calculated by formula (1).

[0064] d=0.62*(8r 3 / λ) 1 / 2 (1)

[0065] In formula (1), λ is the wavelength of the electromagnetic wave transmitted and received by the antenna, and r is the focal spot radius of the electromagnetic wave transmitted by the antenna.

[0066] Finally, measure the complex impedance of the target

[0067] The antenna port is facing the surface of the area to be measured, and the measurement is carried out according to the divided area to obtain the complex reflection coefficient Γ of the measured area. The complex impedance value Z of the measured area is calculated by formula (2).

[0068] Z=50*(1+Γ) / (1-Γ) (2)

[0069] In formula (2), Γ is the complex reflection coefficient of the measured area.

[0070] Step 3: Import the target outer surface 3D model into the electromagnetic simulation software, and assign the complex impedance value of the divided area to the outer surface 3D model of the electromagnetic simulation software:

[0071] The electromagnetic simulation software is Feko software, CST software, or HFSS software.

[0072] Step 4: Set the incident electromagnetic wave propagation direction, polarization, frequency band, and incident angle in the electromagnetic simulation software, and use the electromagnetic simulation software to calculate the target radar cross section:

[0073] When Feko software is selected, the process of calculating the target RCS is:

[0074] Set the relevant parameters of the electromagnetic simulation software. First, select the radar as either single-station or dual-station mode. If you select single-station radar mode, the RCS calculation will be performed in the single-station module; if you select dual-station radar mode, the RCS calculation will be performed in the dual-station module. Secondly, set the propagation direction, polarization, frequency band, and angle of incidence of the incident electromagnetic wave. Finally, set the direction of the receiving radar under far-field conditions.

[0075] Different methods are used to calculate the target radar cross section depending on the target electrical size. The specific method is: when the target electrical size is less than or equal to 100 times the wavelength of the incident electromagnetic wave, the moment method is used to calculate the target radar cross section; when the target electrical size is greater than 100 times the wavelength of the incident electromagnetic wave, but less than 500 times the wavelength of the incident electromagnetic wave, the multi-layer fast multipole algorithm is used to calculate the target radar cross section; when the target electrical size is greater than or equal to 500 times the wavelength of the incident electromagnetic wave, the physical optics method is used to calculate the target radar cross section.

[0076] When using CST software, the process for calculating the target RCS is:

[0077] First, set the propagation direction, polarization, frequency band, and angle of incidence of the incident electromagnetic wave. Second, start the CST software. Finally, select the radar as single-station or dual-station mode. If single-station radar mode is selected, the RCS calculation module will be entered in the single-station calculation module. If dual-station radar mode is selected, the RCS calculation module will be entered in the dual-station calculation module.

[0078] When HFSS software is selected, the process of calculating the target RCS is:

[0079] First, set the propagation direction, polarization, frequency band, and incident angle of the incident electromagnetic wave; second, set the far-field calculation range; finally, start the HFSS software to run the calculation.

[0080] At this point, the radar cross section of the measured target is obtained.

Claims

1. A method for calculating target radar cross section based on complex impedance, characterized in that: Here are the steps: Step 1: construct a three-dimensional model of the outer surface of the target and divide the outer surface into regions; Step 2: Use a vector network analyzer to measure the complex impedance of each divided area; Step 2 includes, first, calibrating the vector network analyzer: Before the measurement begins, the vector network analyzer is turned on and calibrated three times. For the first calibration, the waveguide-to-coaxial converter is connected to the vector network analyzer port, and the waveguide end is connected to a short-circuit plate to calibrate the vector network analyzer. For the second calibration, the waveguide end is disconnected from the short-circuit plate, one end of the straight waveguide is connected to the waveguide-to-coaxial converter, and the other end of the straight waveguide is connected to the short-circuit plate to further calibrate the vector network analyzer. For the third calibration, the straight waveguide is disconnected from the short-circuit plate, and the waveguide load is connected to the waveguide-to-coaxial converter to perform the final calibration of the vector network analyzer. Next, select the antenna and set the antenna position: The antenna is used to transmit and receive electromagnetic waves, the frequency f of the transmitted and received electromagnetic waves is 2-18 GHz, the focal spot radius of the electromagnetic waves transmitted by the antenna is r, and the antenna transmits the received electromagnetic waves to the vector network analyzer via a coaxial cable; The vector network analyzer is connected to the antenna, processes the electromagnetic waves received by the antenna, and outputs the complex impedance; The antenna is placed on one side of the measured target, the antenna port is opposite to the surface of the measured area, and is located in the normal direction of the cross section of the surface of the measured area. The closest distance between the antenna port and the surface of the measured area is d, and the distance d is calculated by formula (1); d=0.62*(8r 3 / λ) 1 / 2 (1) In formula (1), λ is the wavelength of the electromagnetic wave transmitted and received by the antenna, and r is the focal spot radius of the electromagnetic wave transmitted by the antenna; Finally, measure the complex impedance of the target: The antenna port is facing the surface of the area to be measured, and the measurement is carried out according to the divided area to obtain the complex reflection coefficient Γ of the measured area, and the complex impedance value Z of the measured area is calculated by formula (2); Z=50*(1+Γ) / (1-Γ) (2) In formula (2), Γ is the complex reflection coefficient of the measured area; At this point, the target complex impedance value Z is obtained; Step 3: Import the target outer surface 3D model into the electromagnetic simulation software and assign the complex impedance value of the divided area to the electromagnetic The outer surface three-dimensional model of the simulation software; the electromagnetic simulation software includes: Feko software, or CST software, or HFSS software; Step 4: Set the propagation direction, polarization, frequency band, and incident angle of the incident electromagnetic wave in the electromagnetic simulation software, calculate the target radar cross section using the electromagnetic simulation software, and select the calculation algorithm based on the target electrical size; Among them, the target electrical size selection calculation algorithm includes: When the electrical size is ≤100λ, the moment method is used; When 100λ<electrical size<500λ, the multi-layer fast multipole algorithm is used; When the electrical size is ≥500λ, the physical optics method is used; Step 5: Run the electromagnetic simulation software to output the target radar cross section.

2. The method for calculating target radar cross section based on complex impedance according to claim 1, wherein: In step 1, the process of constructing a three-dimensional model of the outer surface of the target and dividing the outer surface into regions includes the following steps: First, establish a rectangular coordinate system: Set the vertex of the aircraft nose as the coordinate origin o, the direction of the aircraft nose on the horizontal plane where the coordinate origin o is located as the x-direction, any direction in the horizontal plane perpendicular to the x-direction and passing through the origin o as the y-direction, and the upward direction perpendicular to the xoy horizontal plane and passing through the origin o as the z-direction, to establish the oxyz rectangular coordinate system; Next, draw the 3D model of the target's outer surface: Draw a three-dimensional model of the space where the outer surface of the target is located, so that each point on the outer surface of the target is in the established oxyz rectangular coordinate system; Finally, divide the area according to the target outer surface material: A three-dimensional model is built with an aircraft as the target, and the areas are divided according to the material of its outer surface.

3. The method for calculating target radar cross section based on complex impedance according to claim 1, wherein: Step 2 includes the process of calibrating the vector network analyzer, selecting the antenna, setting the antenna position, and measuring the complex impedance of the target.

4. The method for calculating target radar cross section based on complex impedance according to claim 1, wherein: In step 4, when the Feko software is selected as the electromagnetic simulation software, the process of calculating the target RCS is: Set the relevant parameters of the electromagnetic simulation software. First, select the radar as single-station or dual-station mode. If the single-station radar mode is selected, the RCS calculation will enter the single-station calculation module; if the dual-station radar mode is selected, the RCS calculation will enter the dual-station calculation module. Second, set the propagation direction, polarization, frequency band, and angle of incidence of the incident electromagnetic wave. Finally, set the direction of the receiving radar under far-field conditions. Calculation of target radar cross section: When the target electrical size is less than or equal to 100 times the wavelength of the incident electromagnetic wave λ, the moment method is used to calculate the target radar cross section; When the target electrical size is greater than 100 times the wavelength of the incident electromagnetic wave λ and less than 500 times the wavelength of the incident electromagnetic wave, the multi-layer fast multipole algorithm is used to calculate the target radar cross section; When the target electrical size is greater than or equal to 500 times the wavelength λ of the incident electromagnetic wave, the physical optics method is used to calculate the target radar cross section.

5. The method for calculating target radar cross section based on complex impedance according to claim 1, wherein: In step 4, when the CST software is selected as the electromagnetic simulation software, the process of calculating the target RCS is: First, set the propagation direction, polarization, frequency band, and incident angle of the incident electromagnetic wave; Secondly, start the CST software; Finally, select the radar as single-station or dual-station mode. If you select single-station radar mode, the RCS calculation will be performed in the single-station calculation module; if you select dual-station radar mode, the RCS calculation will be performed in the dual-station calculation module.

6. The method for calculating target radar cross section based on complex impedance according to claim 1, wherein: In step 4, when the electromagnetic simulation software is selected as the HFSS software, the process of calculating the target RCS is: First, set the propagation direction, polarization, frequency band, and incident angle of the incident electromagnetic wave; Secondly, set the calculation range of the far field; Finally, start the HFSS software to run the calculation.

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