Fast analysis method based on local coupling time-domain iterative physical optics method

Abstract

The application discloses a kind of fast analysis methods of time-domain iterative physical optics method based on local coupling, first to target modeling, and with triangle face element subdivision to fit target surface appearance;Set incident wave as modulated Gaussian pulse, time discrete sampling is carried out to incident wave;Secondly, whether the source triangle meets local condition and the time delay between source and field triangle meets within the duration of echo, the coupling effect of all source triangles that meet the above conditions to field triangle is calculated, the coupling effect of all is accumulated to obtain the induced current of each discrete surface element surface;Finally, the far zone scattering field of each surface element is calculated by induced current and is accumulated, and the echo response of target is obtained;The echo response is carried out discrete fourier transformation to obtain the echo frequency domain response of target, which is divided by the frequency domain response of incident wave to obtain the wideband RCS of target.The method reduces unnecessary coupling source iteration, improves the efficiency of algorithm under the condition of meeting accuracy.

Description

Technical Field

[0001] This invention belongs to the field of target electromagnetic scattering characteristic calculation technology, specifically involving a method for rapidly analyzing the electromagnetic scattering characteristics of electrically large targets by using a local coupling method to reduce the computational load of iterations. Background Technology

[0002] Frequency domain methods are suitable for electromagnetic problems with few frequency points and small bandwidths. However, in real-world scenarios, radar emits time-domain signals with a certain bandwidth. Furthermore, compared to frequency domain methods, time-domain methods can obtain wideband target information through Fast Fourier Transform. Time-domain methods can fully explore the target's time-domain information without requiring calculation of the target's RCS at individual frequency points, thus improving computational efficiency. Time-domain methods include time-domain numerical methods and time-domain high-frequency methods. Among these, time-domain numerical methods offer high computational accuracy and can study targets with complex shapes and intricate structures. However, when used to analyze electrically large targets, the required computational memory and time increase. Time-domain high-frequency methods, on the other hand, are fast and require less memory, making them effective methods for studying electrically large targets. Among some high-frequency methods, time-domain iterative physical optics has the advantages of high computational accuracy and fast iterative convergence, and is widely used to calculate the electromagnetic scattering of strongly coupled targets such as cavities and dihedrals.

[0003] The traditional TDIPO method requires current iteration on all bright area elements, resulting in a computational complexity of O(N). 2 As the number of facets increases, the computational load becomes unbearable. To improve the computational speed of this method, this invention introduces a local coupling acceleration technique. The local coupling method uses ray tracing to find the iterative coupling local region for each facet, reducing global coupling to local regions and effectively reducing the number of facets in the iteration. Summary of the Invention

[0004] This invention proposes a fast analysis method based on local coupling and time-domain iterative physical optics, which reduces unnecessary iterations of coupling sources and improves the efficiency of the algorithm while meeting accuracy requirements.

[0005] The technical solution to achieve the objective of this invention is as follows: Firstly, this invention provides a rapid analysis method based on local coupling using a time-domain iterative physical optics method, comprising the following steps:

[0006] Step 1: Construct a model of the electrically large target, set parameters, and divide the target into triangular facets. Output the node numbers and coordinate information of the triangular facets. Read the target information, preprocess the facets, and record the bouncing intersection facets of each facet.

[0007] Step 2: Select the incident pulse as a modulated Gaussian pulse, set the signal sampling parameters, and perform discrete sampling on the signal; perform discrete Fourier transform on the discrete time-domain signal to obtain the discrete frequency-domain response sequence;

[0008] Step 3: Using the intersecting surface element information obtained from ray tracing in Step 1, determine the local region corresponding to each field triangle, determine whether all source triangles are in the local region, and remove source triangles that are not in the local region; calculate whether the time delay between the source triangles and field triangles in the local region is within the echo duration, and remove source triangles that do not meet the condition; accumulate the coupling effect of all source triangles that meet the condition to obtain the final induced current on the surface of each discrete surface element.

[0009] Step 4: Calculate the far-field scattering field of each surface element based on its induced current and accumulate the results to obtain the target's echo response; perform a discrete Fourier transform on the echo response to obtain its frequency domain response; divide the echo response by the corresponding frequency domain response of the incident wave to obtain the broadband RCS.

[0010] Furthermore, in step 1, a model of the electrically large target is constructed in the FEKO software.

[0011] Furthermore, in step 1, the face elements are preprocessed, including occlusion detection and ray tracing.

[0012] Furthermore, in step 3, intersecting triangles are found through ray tracing. The local region of each field triangle iteration is determined by a cube with a side length of 15 to 20 wavelengths centered on this intersecting triangle element to eliminate source triangles not in this region.

[0013] Furthermore, the method of using a cube with a side length of 15 to 20 wavelengths centered on the intersecting triangular facets to eliminate source triangles not located in this region is as follows:

[0014] A series of ray tubes simulates the bouncing reflection of electromagnetic waves, with the ray tubes starting from the center point of each surface element. Starting point; using ray tracing, record the direction of each bounce of the ray tube and its intersection with the target; find the previous triangle element of the bounced field triangle element, and only retain the source triangles in the local area around this triangle. Due to the coupling effect, source triangles not in this region are eliminated; the local region is set as a cube with a side length of 15 to 20 wavelengths, and the wavelength is calculated from the highest cutoff frequency of the incident wave.

[0015] Furthermore, in step 3, the time delay between the field and the source triangle and the duration of the echo are calculated to eliminate source triangles whose time delay is not within the echo duration at any given time, as detailed below:

[0016] Setting the target origin as the reference point, the initial time of the impulse response is set as follows when using the TDIPO algorithm:

[0017]

[0018] In the above formula, and Here, R is the coordinates of the center points of the surface element and the source element, R is the distance between their center points, and c is the speed of light. It is the direction of the incident wave. It is the direction of observation. This refers to the time delay between any field and source triangular elements; since the calculation is based on a single-station RCS, at this time... The duration of the echo pulse is:

[0019]

[0020] In the above formula, t p It is the effective width of the modulated Gaussian pulse, t p << L / c, where L is the actual size of the target, so at any time t only a portion of the target surface will be illuminated; when calculating the time-domain response of the target, it is only necessary to calculate the coupling between the field and source triangular elements that satisfy the following conditions:

[0021]

[0022] The above formula effectively reduces the amount of calculation and avoids coupling calculation between all surface elements; combined with the coupling method of local region, the coupling effect of all source triangles that satisfy the local conditions and formula (3) is accumulated to obtain the induced current of the field triangle.

[0023] In a second aspect, the present invention provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the steps of the method described in the first aspect.

[0024] Thirdly, the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method described in the first aspect.

[0025] Fourthly, the present invention provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the method described in the first aspect.

[0026] Compared with the traditional TDIPO method, the present invention has the following significant advantages: (1) The traditional TDIPO method requires iterating all surface elements to consider the coupling effect between target surfaces, which has high computational complexity and is very time-consuming. The present invention introduces a local coupling method to restrict global coupling to a local region, reducing the coupling effect of a large number of radiation sources with small impact and reducing computational complexity. (2) By calculating the time delay between the field and the source surface elements and the echo duration, unnecessary coupling calculations of source surface elements at any time are reduced, further reducing the computation time. Attached Figure Description

[0027] Figure 1 This is a flowchart of the method for rapid analysis of the electromagnetic scattering characteristics of electrically large targets based on the time-domain iterative physical optics method with local coupling in this invention.

[0028] Figure 2 This is a schematic diagram of the local coupling method in this invention.

[0029] Figure 3 This is a diagram of a dihedral model with a side length of 1 meter in an embodiment of the present invention.

[0030] Figure 4 This is the time-domain waveform of the incident pulse in an embodiment of the present invention.

[0031] Figure 5 This is the time-domain echo response of the dihedral angle in an embodiment of the present invention.

[0032] Figure 6 This is a comparison chart of the single-station RCS results of the time-frequency domain IPO and MLFMA algorithms in an embodiment of the present invention.

[0033] Figure 7 The single-station RCS result diagrams for local regions of different sizes are set for the TDIPO method based on local coupling in the embodiments of the present invention. Detailed Implementation

[0034] This invention proposes a fast analysis method based on local coupling using the temporal iterative physical optics method. For electrically large targets, the traditional TDIPO method is computationally slow. This method, building upon TDIPO, introduces a ray tracing mechanism to find the local region with the greatest coupling effect for each surface element, thus limiting the global coupling effect to a local region and reducing computational complexity.

[0035] Figure 1 This is a flowchart of the fast analysis method for the electromagnetic scattering characteristics of electrically large targets based on the time-domain iterative physical optics method with local coupling, as described in this invention. To improve the efficiency of the algorithm and reduce computational load, the traditional TDIPO method for analyzing the electromagnetic scattering characteristics of electrically large targets is used.

[0036] A fast analysis method based on local coupling and time-domain iterative physical optics, with the following specific steps:

[0037] Step 1: In FEKO software, model the target of the Open University and set the meshing size. Mesh the target to obtain the node numbers and coordinate information of discrete triangular facets. The algorithm reads the target information, performs occlusion detection and ray tracing, and records the bouncing intersection facets of each facet.

[0038] Step 2: Set the incident wave as a modulated Gaussian pulse E(t), set the signal sampling interval to satisfy the Narquist sampling criterion, and perform discrete sampling on the signal to obtain the discrete time-domain signal E. i (t); for E i (t) Performing a discrete Fourier transform yields the discrete frequency domain response sequence E. i (f);

[0039] Step 3: Record the intersecting surface elements through ray tracing in Step 1, and determine that the local coupling region of each surface element is a cube with a side length of 15 to 20 wavelengths centered on this surface element. Remove the source triangles that are not in this local region.

[0040] When the target is an ideal conductor, the TDIPO current iteration formula is:

[0041]

[0042] Where PV represents the principal value integral. Represents the coordinates of the source point. Represents the coordinates of the field point. s is the normal vector of the field element, and s' is the integration variable. It is the initial current. and These are the iteration currents of the nth and (n+1)th orders, respectively.

[0043] When calculating the discrete echo at each moment, the time delay and echo duration are calculated, and it is determined whether the time delay between the field and source triangular elements is within the echo duration. Source elements that do not meet the condition are eliminated. The coupling effect of all source elements in the local region whose time delay is within the echo duration is accumulated, and finally the induced current of the field element at any moment is obtained by equation (4).

[0044] Step 4: Calculate and sum the far-field scattering fields of each surface element to obtain the echo response E at each discrete time point. s (t); for E s The frequency domain response E is obtained by performing a discrete Fourier transform on (t). s (f); E s (f) and Ei (f) Dividing by the corresponding time interval yields the target broadband RCS: RCS(f) = E s (f) / E i (f).

[0045] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0046] Example

[0047] The fast analysis method based on local coupling time-domain iterative physical optics in this embodiment has the following steps:

[0048] Step 1: Combining Figure 3 First, the dihedral model is modeled in FEKO software, using triangular facets with a side length of λ / 8 to subdivide the dihedral. Second, the algorithm reads the node numbers and coordinate information of the target's triangular facets. Finally, the target is then...

[0049] 1) Occlusion detection

[0050] The three nodes of a triangular element are evaluated. If all three nodes are in the shadow area, the element is considered to be occluded, and these triangular elements are removed.

[0051] 2) Ray Tracing

[0052] A series of ray tubes are used to simulate electromagnetic waves incident on a target. The midpoint of each surface element is the initial position of the ray tube incident on the target. The ray tubes will bounce and reflect multiple times on the target. Calculate and record the surface elements where each ray tube intersects.

[0053] Step 2: Referring to the embodiment, the incident wave is set as a modulated Gaussian pulse, and the time-domain waveform is as follows. Figure 4 The center frequency is set to 2.5 GHz, and the bandwidth is 3 GHz. The pulse width τ = 4 / B ≈ 1.3 ns, and t0 = 0.8τ ≈ 1.07 ns. Therefore, the time-domain form of this pulse function is:

[0054]

[0055] Discrete sampling and discrete Fourier transform of (5) yield the discrete frequency domain form E of the incident wave. i (f).

[0056] Step 3: Using the intersecting surface element information obtained from ray tracing in Step 1, determine the local region corresponding to each field triangle, eliminate the coupling effects of all source triangles not located within the local region, and limit the global coupling effects to the more influential local regions. Combined with... Figure 2 As shown, Figure 2The colors in the diagram represent the normalized coupling strength of each facet to the red facet. Using the ray tracing described in step 1, the bounce path through the red facet ray tube is found to be ABCD. From the color intensity distribution in the diagram, it can be seen that point B is the location of the previous triangular facet that bounces to point C (the red facet), and its coupling strength to the red facet is the greatest, decreasing from point B outwards. Therefore, we can eliminate many facets far from point B with less influence, replacing the global coupling with only the most influential local region within the white dashed box in the diagram. This method greatly reduces the computational load. In the specific implementation, the side lengths of the local regions are set to 5λ, 7λ, 10λ, 15λ, and 20λ, where λ is the wavelength.

[0057] The time delay and echo duration between the field and the source triangle are calculated. Finally, only the coupling effects of the source triangles within the local region and whose time delay is within the duration are retained. The final induced current of each surface element is obtained by summing all couplings that satisfy the conditions.

[0058] Step 4: The far-field scattering field of each discrete surface element can be used to substitute the final induced current into the following equation:

[0059]

[0060] in This represents the far-field scattering field, where r is the distance to the far-field region and η is the wave impedance. and These are the scattering direction and the incident direction, respectively. The final induced current is obtained by summing the scattered fields of all discrete surface elements to obtain the target echo time-domain response E at any given time. s (t). For E s The echo frequency domain response E is obtained by performing a discrete Fourier transform on (t). s (f). The broadband RCS can then be obtained using the following formula:

[0061] RCS(f) = E s (f) / E i (f) (7)

[0062] Figure 3 It is a dihedral model with a side length of 1 meter and 135112 unknowns. The incident wave is a modulated Gaussian pulse with f0 of 2.5 GHz and B of 3 GHz. The incident angle is θ. i =45°, The polarization mode is HH polarization. The time-domain electromagnetic scattering characteristics of the dihedral angle are analyzed using the TDIPO method and the locally coupled TDIPO method. In the locally coupled method, the wavelength is calculated based on the highest cutoff frequency of 10 GHz. Figure 4, Figure 5 These are the time-domain waveforms of the incident wave and the echo, respectively. Figure 6 and Figure 7 This is a comparison of the single-station RCS results for different algorithms and local regions of different sizes. TD-LIPO represents the locally coupled TDIPO algorithm proposed in this paper. Table 1 compares the computation time and accuracy of algorithms for local regions of different sizes.

[0063] Table 1

[0064]

[0065]

[0066] like Figure 6 As shown, the curves for IPO, TDIPO, and the MLFMA curve in the business software FEKO are almost identical. This proves the validity of IPO and TDIPO. Figure 7 As shown in Table 1, compared with the MLFMA algorithm, the TD-LIPO method exhibits the largest error when the local region's side length is 5 wavelengths. The error decreases as the side length increases. As shown in Table 1, the TDIPO method consumes 15064 seconds, indicating very low computational efficiency. While a side length of 5 wavelengths effectively reduces computation and increases the speed by 7.2 times compared to TDIPO, its larger error leads to unreliable results. However, when the side length is set to 15 wavelengths, the time is reduced by 3.9 times within an acceptable error range, demonstrating the effectiveness and efficiency of the local method in this invention. Therefore, we generally set the size of the local region to 15–20 wavelengths to achieve a balance between time and computational accuracy.

Claims

1. A fast analysis method based on local coupling in the time-domain iterative physical optics method, characterized in that, The steps are as follows: Step 1: Construct a model of the electrically large target, set parameters, and divide the target into triangular facets. Output the node numbers and coordinate information of the triangular facets. Read the target information, preprocess the face elements, and record the bouncing intersecting face elements of each face element; Step 2: Select the incident pulse as a modulated Gaussian pulse, set the signal sampling parameters, and perform discrete sampling on the signal; Discrete frequency domain response sequences are obtained by performing a discrete Fourier transform on discrete time-domain signals. Step 3: Using the intersecting surface element information obtained from ray tracing in Step 1, determine the local region corresponding to each field triangle, determine whether all source triangles are in the local region, and remove source triangles that are not in the local region; calculate whether the time delay between the source triangles and field triangles in the local region is within the echo duration, and remove source triangles that do not meet the condition; accumulate the coupling effect of all source triangles that meet the condition to obtain the final induced current on the surface of each discrete surface element. By calculating the time delay between the field and the source triangle, and the duration of the echo, source triangles whose time delay is not within the echo duration at any given time are eliminated, as follows: Setting the target origin as the reference point, the initial time of the impulse response is set as follows when using the TDIPO algorithm: (1) In the above formula, and These are the coordinates of the center points of the surface element and the source surface element. It is the distance between their center points. It's the speed of light. It is the direction of the incident wave. It is the direction of observation. This refers to the time delay between any field and source triangular elements; since the calculation is based on a single-station RCS, at this time... The duration of the echo pulse is: (2) In the above formula It is the effective width of the modulated Gaussian pulse. , Given the actual size of the target, when calculating the time-domain response of the target, it is only necessary to calculate the coupling between the field and source triangular elements that satisfy the following conditions: (3) By combining the coupling method of the local region, the coupling effect of all source triangles that satisfy the local conditions and formula (3) is accumulated to obtain the induced current of the field triangle; Step 4: Calculate the far-field scattering field of each surface element based on its induced current and accumulate the results to obtain the target's echo response; perform a discrete Fourier transform on the echo response to obtain its frequency domain response; divide the echo response by the corresponding frequency domain response of the incident wave to obtain the broadband RCS.

2. The fast analysis method based on local coupling in time-domain iterative physical optics according to claim 1, characterized in that, Models of electrically large targets are constructed in FEKO software.

3. The fast analysis method based on local coupling in time-domain iterative physical optics according to claim 1, characterized in that, Step 1 involves preprocessing the face elements, including occlusion detection and ray tracing.

4. The fast analysis method based on local coupling in time-domain iterative physical optics according to claim 1, characterized in that, In step 3, intersecting triangles are found through ray tracing. The local region of each field triangle iteration is determined by a cube with a side length of 15 to 20 wavelengths centered on the intersecting triangle element to eliminate source triangles not in this region.

5. The fast analysis method based on local coupling in time-domain iterative physical optics according to claim 4, characterized in that, The method of using a cube with a side length of 15 to 20 wavelengths centered on the intersecting triangular elements to eliminate source triangles not located in this region is as follows: The bouncing reflection of electromagnetic waves is simulated using a ray tube, with the ray tube starting from the center point of each surface element. Departure; using ray tracing, record the direction of each bounce of the ray tube and its intersection with the target; Find the previous triangle element of the bouncing triangle element, and only retain the source triangles in the local region surrounding this triangle. Due to the coupling effect, source triangles not in this region are eliminated; the local region is set as a cube with a side length of 15 to 20 wavelengths, and the wavelength is calculated from the highest cutoff frequency of the incident wave.

6. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the method as described in any one of claims 1-5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the steps of the method as described in any one of claims 1-5.

8. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method described in any one of claims 1-5.

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