Spherical wave correction radar cross section near-field measurement method, system, device and medium

Abstract

This invention discloses a method, system, device, and medium for near-field measurement of radar cross section (RCS) using spherical wave correction, relating to the field of radar target scattering characteristic measurement technology. The invention includes: acquiring the near-field echo signal of the target through near-field measurement; effectively filtering dynamically changing background noise using preprocessing techniques; performing amplitude and phase correction on the echo data using spherical wave correction and probe compensation methods; generating a two-dimensional ISAR image of the target using a post-projection imaging algorithm; extracting the equivalent scattering center of the target from the ISAR image based on the CLEAN algorithm and constructing a scattering center model; inverting and extrapolating the far-field RCS of the target using the equivalent scattering center model, and calibrating using a calibration body to obtain the absolute RCS value. This invention can effectively eliminate the influence of near-field spherical wave distortion and probe modulation, achieving high-precision, low-cost near-field RCS measurement.

Description

Technical Field

[0001] This invention relates to the field of radar target scattering characteristic measurement technology, specifically to a method, system, device, and medium for near-field measurement of spherical wave-corrected radar cross section. Background Technology

[0002] With the rapid development of radar detection technology, the design and performance evaluation of stealth targets have become a key research focus in modern military and civilian fields. Radar cross section (RCS), as a crucial physical parameter for measuring a target's electromagnetic scattering capability, is of great significance for the characteristic analysis, structural optimization, and performance verification of stealth targets. Traditional RCS measurement methods mainly include far-field measurement and compact field measurement. Far-field measurement requires open areas, is greatly affected by the environment, and suffers from severe signal attenuation, making it difficult to meet the high-precision measurement requirements of electrically large targets. Compact field measurement, although conducted in a microwave anechoic chamber, requires extremely high precision in the reflective surface processing, resulting in high system costs, and the fixed bistatic measurement angle limits its applicability.

[0003] In recent years, near-field RCS measurement methods based on inverse synthetic aperture radar (ISAR) imaging have gradually gained attention. This method acquires target echo data by performing broadband frequency and wide-angle scanning of the target in the near-field region, reconstructs the target's two-dimensional scattering distribution using ISAR imaging technology, and then obtains the target's far-field RCS through extrapolation algorithms. However, existing near-field ISAR-RCS measurement methods still have the following technical shortcomings: Under near-field conditions, the electromagnetic waves emitted by the antenna are spherical waves rather than plane waves, resulting in significant differences in the amplitude and phase of the echo signal compared to the ideal far-field condition. Existing methods often lack precise correction for the spherical wave effect, impacting the focusing quality of subsequent ISAR imaging and the accuracy of RCS extrapolation. The radiation patterns of actual transmitting and receiving antennas (probes) are not ideally omnidirectional or uniform, and their gain modulation of incident / scattered signals at different angles will introduce systematic measurement errors. Summary of the Invention

[0004] The purpose of this invention is to provide a method, system, device, and medium for near-field measurement of spherical wave-corrected radar cross section, in order to solve the problems mentioned in the background art.

[0005] According to a first aspect of the present invention, in order to achieve the above-mentioned objective, the present invention provides the following technical solution: a near-field measurement method for spherical wave-corrected radar cross section, comprising the following steps: Collect complex electromagnetic scattering echo data, background noise echo data, and standard scatterer echo data of the target under test in a near-field test environment to construct an echo dataset; Phase center calibration, background cancellation, and gate function processing are performed on the echo data in the echo dataset to obtain preprocessed echo data. For the preprocessed echo data, the post-projection BP algorithm is used to correct the phase and amplitude, forming the inverse synthetic aperture radar (ISAR) scattering distribution map of the target. The CLEAN algorithm is used to extract the spatial location of the target scattering center and its corresponding complex amplitude information from the ISAR scattering distribution image, and an equivalent scattering center model is constructed. Based on the extracted spatial location of the scattering center and the complex amplitude, the scattering contribution of the target under far-field conditions is coherently superimposed to obtain the relative RCS angular spectrum result of the target. The obtained relative RCS angular spectrum result is introduced into the theoretical RCS value of the standard scatterer, and the relative RCS angular spectrum is calibrated to obtain the absolute RCS angular spectrum result of the target under test.

[0006] Furthermore, complex electromagnetic scattering echo data, background noise echo data, and standard scatterer echo data of the target under test were collected in a near-field testing environment, as detailed below: In a near-field testing environment, the transmitting and receiving antennas are arranged to form a quasi-monostation measurement configuration. Without placing the target under test, based on the quasi-single-station measurement configuration and the turntable rotation capability, scanning is performed within a preset frequency range and observation angle range to collect background noise echo data; After the target is placed in the measurement area, the target is electromagnetically irradiated frequency by frequency within the preset frequency range. At the same time, the observation angle is changed by rotating the turntable to form multi-frequency and multi-angle echo data of the target. At various frequency points and observation angles, the scattered echo signals of the target under test are collected and coherently demodulated to obtain complex electromagnetic scattered echo data. The standard scatterer is placed on the turntable, and its scattered echo signal is collected under the same conditions to obtain the calibration body echo data. Background noise echo data, target echo data, and calibration body echo data are organized and stored according to frequency and angle dimensions to form a multi-frequency, multi-angle echo dataset.

[0007] Furthermore, phase center calibration, background cancellation, and gate function processing are performed on the echo data in the echo dataset to obtain preprocessed echo data, as follows: Using the one-dimensional range image of a standard metal sphere, the phase shift of the echo signal is calculated, and phase compensation is performed on the original echo data to correct the phase center shift. The specific compensation formula is as follows: In the formula, This is the frequency domain echo signal after phase compensation; The equivalent distance error (m) caused by the phase center offset is the radial distance offset calculated by the deviation between the peak position of the measured one-dimensional range image of the standard metal sphere and the theoretical position. In the frequency domain, the target echo data and the background echo data of the empty anechoic chamber are subtracted by complex values ​​to eliminate the influence of inherent system noise and environmental background scattering. By setting a fixed start and end distance range, the effective scattered echo of the target is intercepted, and stray signals in non-target areas are suppressed. Based on the precise distance from the target's equivalent scattering center to each near-field scanning point The amplitude and phase differences between spherical waves and plane waves are calculated, and amplitude and phase compensation is performed on the collected near-field complex scattering data to correct the non-planar wavefront error caused by spherical wave illumination. Acquire the normalized complex radiation patterns of the transmitting and receiving probes within the measurement frequency band and scanning angle range. and Divide the near-field scattering data at each scan point by the product of the radiation patterns at that point. This is to eliminate the modulation effect of the non-ideal radiation and reception characteristics of the actual probe on the measurement data.

[0008] Furthermore, the phase and amplitude are corrected using the post-projection BP algorithm on the preprocessed echo data to form the inverse synthetic aperture radar (ISAR) scattering distribution map of the target, as follows: The preprocessed complex electromagnetic scattering echo data is decomposed into range and azimuth directions, and data representations in the frequency dimension and observation angle dimension are established respectively. The range wavenumber K is frequency-shifted by an amount equal to the initial beam. This makes the integration region become ( At this point, the echo data becomes ; Perform an inverse Fourier transform on the range echo data after frequency shifting to obtain the complex range image of the target in the range direction; Phase compensation is performed on the range echo data to correct the phase deviation introduced by range frequency shift processing; For near-field measurement conditions, spherical wave phase compensation is performed on the azimuth echo data to eliminate the azimuth phase distortion caused by spherical wave propagation; After completing the range and azimuth phase compensation, the echo signals of all imaging grid points are coherently superimposed to form the ISAR scattering distribution image of the target.

[0009] Furthermore, the CLEAN algorithm is used to extract the spatial location of the target scattering center and its corresponding complex amplitude information from the ISAR scattering distribution image, and an equivalent scattering center model is constructed, as follows: The obtained ISAR scattering distribution image is used as the initial ISAR image, and the point with the maximum electromagnetic property intensity value is found in the initial ISAR image. Record the electromagnetic characteristic intensity value at that point. and position coordinates ( ); Calculate the comparison value after the nth iteration. This comparison value is the logarithmic representation of the ratio of the maximum complex amplitude of the current ISAR image to the maximum complex amplitude of the initial ISAR image, specifically expressed as: Comparison value = 10 ; Based on the calculated comparison value, it is determined whether the comparison value is less than the set cutoff threshold. If it is, the process of obtaining the target equivalent scattering center model stops; otherwise, the process continues to the next step. At the location of the maximum electromagnetic characteristic strength value ( At the location of the maximum electromagnetic characteristic intensity value, the electromagnetic characteristic intensity value is convolved with the point spread function to obtain an ISAR image of the scattering center after imaging alone, and then subtracted from the current ISAR image to obtain the next generation ISAR image.

[0010] Furthermore, based on the extracted spatial location and complex amplitude of the scattering center, the scattering contribution of the target under far-field conditions is coherently superimposed to obtain the relative RCS angular spectrum result of the target, as follows: Based on the equivalent scattering center model, a set of equivalent scattering centers extracted by the CLEAN algorithm is obtained, including the position coordinates of each scattering center. and each scattering center at frequency k and azimuth angle Electromagnetic property strength value ; All extracted equivalent scattering centers are coherently superimposed under far-field conditions to obtain the target at any wavenumber k and azimuth angle. Far-field scattering field below: Where N is the total number of scattering centers; Based on far-field scattering Calculate the radar cross section (RCS) of the target at the corresponding frequency and angle: In the formula, This represents the far-field scattered electric field. The electric field of the incident plane wave.

[0011] Furthermore, the obtained relative RCS angular spectrum results are incorporated into the theoretical RCS value of the standard scatterer, and the relative RCS angular spectrum is calibrated to obtain the absolute RCS angular spectrum results of the measured target, as follows: Based on the obtained complex electromagnetic scattering echo data of the standard scatterer, imaging processing, scattering center modeling, and far-field RCS extrapolation are performed to obtain the relative RCS angular spectrum of the standard scatterer at different frequencies and observation angles. Based on the geometric dimensions and electromagnetic properties of the standard scatterer, calculate its theoretical absolute radar cross section value at the corresponding frequency and observation angle, and establish the theoretical RCS angular spectrum of the standard scatterer. The amplitude of the obtained standard scatterer relative RCS angular spectrum is compared with the theoretical absolute RCS angular spectrum at the same frequency and observation angle to estimate the amplitude response characteristics of the measurement system at different frequencies and observation angles. Based on the amplitude response characteristics, a system amplitude calibration factor matrix or continuous calibration function with frequency and observation angle as independent variables is constructed to characterize the amplitude non-uniformity characteristics of the measurement system under wide bandwidth and large angle conditions. Based on the constructed system amplitude calibration function, the amplitude of the relative RCS angle spectrum is corrected under the corresponding frequency point and observation angle conditions, the mapping relationship between the relative RCS and the absolute RCS is established, and the absolute RCS angle spectrum result of the measured target is obtained.

[0012] According to a second aspect of the present invention, the present invention provides a near-field measurement system for spherical wave-corrected radar cross section, used to implement the near-field measurement method for spherical wave-corrected radar cross section described in the first aspect, comprising: The dataset construction module is used to collect complex electromagnetic scattering echo data, background noise echo data and standard scatterer echo data of the target under test in a near-field test environment, and construct an echo dataset. The data preprocessing module is used to perform phase center calibration, background cancellation, and gate function processing on the echo data in the echo dataset to obtain preprocessed echo data. The imaging module is used to perform phase and amplitude correction on the preprocessed echo data using the post-projection BP algorithm to form an inverse synthetic aperture radar (ISAR) scattering distribution map of the target under test. The model building module is used to extract the spatial location of the target scattering center and its corresponding complex amplitude information from the ISAR scattering distribution image using the CLEAN algorithm, and to build an equivalent scattering center model. The extrapolation module is used to coherently superimpose the scattering contribution of the target under far-field conditions based on the extracted spatial location of the scattering center and the complex amplitude, so as to obtain the relative RCS angular spectrum result of the target. The amplitude calibration module is used to input the obtained relative RCS angle spectrum result into the theoretical RCS value of the standard scatterer, perform amplitude calibration on the relative RCS angle spectrum, and obtain the absolute RCS angle spectrum result of the target under test.

[0013] According to a third aspect of the present invention, the present invention provides a terminal device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that the memory stores the computer program capable of running on the processor, and when the processor loads and executes the computer program, it employs the spherical wave-corrected radar cross section near-field measurement method described in the first aspect.

[0014] According to a fourth aspect of the present invention, the present invention provides a storage medium comprising computer-executable instructions, wherein the computer-executable instructions, when executed by a computer processor, are used to perform a near-field measurement method for spherical wave-corrected radar cross section as described in the first aspect.

[0015] The present invention has at least the following beneficial effects: 1. This invention accurately calculates the actual distance from the equivalent scattering center of the target to each near-field scanning point, and performs amplitude and phase compensation on the acquired near-field complex scattering data, effectively eliminating the non-planar wavefront error caused by spherical wave propagation. Based on this, combined with a post-projection imaging algorithm and azimuth spherical wave phase compensation, the focusing quality of the reconstructed ISAR image under near-field conditions is significantly improved, laying a reliable foundation for the accurate extraction of the target scattering center.

[0016] 2. This invention comprehensively employs multiple preprocessing and post-processing techniques, including phase center calibration, frequency domain background cancellation, time domain gate function truncation, and CLEAN algorithm iterative sidelobe suppression, to form a full-link clutter filtering mechanism from the raw echo to the ISAR image. This method not only eliminates fixed background scattering in the anechoic chamber but also effectively suppresses dynamically changing noise interference and sidelobe crosstalk, significantly improving the signal-to-noise ratio and extraction reliability of weak scattering centers. It is particularly suitable for the fine measurement of low-scattering characteristic targets.

[0017] 3. This invention utilizes the amplitude comparison of the relative RCS angular spectrum of a standard scatterer under the same measurement conditions with its theoretical absolute RCS value at each frequency point and observation angle to construct a system amplitude calibration function or calibration factor matrix. This calibration strategy can comprehensively reflect the amplitude inconsistency characteristics of the measurement system over a wide frequency band and a large angle range, thereby performing refined amplitude correction on the relative RCS angular spectrum of the measured target, ultimately obtaining high-fidelity absolute RCS angular spectrum results, overcoming the shortcomings of traditional single-point calibration methods such as low accuracy and poor frequency band adaptability.

[0018] 4. This invention introduces normalized complex radiation patterns for both the transmitting and receiving probes. During the data preprocessing stage, the scattering data at each scanning point is divided by the product of the corresponding probe radiation pattern, fundamentally eliminating the non-uniform modulation effect of probe radiation and receiving characteristics. This compensation strategy significantly improves the amplitude consistency and phase fidelity of measurement data across the entire frequency band and angle range, avoiding systematic measurement errors introduced by the probe radiation pattern.

[0019] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart illustrating the overall process of the measurement method described in Embodiment 1 of the present invention. Figure 2 This is a flowchart of the CLEAN algorithm described in Embodiment 1 of the present invention; Figure 3 This is a scattering center image of the measurement method described in Embodiment 1 of the present invention; Figure 4 This is a comparison chart of the extrapolated RCS and the far-field simulated RCS in Embodiment 1 of the present invention; Figure 5 This is a comparison diagram of the RCS polar coordinates in Embodiment 1 of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] Example 1: This embodiment utilizes a stepped frequency signal as the transmitted waveform. By scanning the target in the near-field region at multiple frequencies and angles, multi-frequency and multi-angle scattering echo data of the target is acquired. Preprocessing of the echo data is performed using a phase center calibration algorithm, background cancellation technology, and time-domain gate function processing to effectively eliminate system errors, coupling noise, and dynamically changing background interference. Based on the preprocessed echo data, combined with spherical wave correction and probe compensation methods, a back projection algorithm is used to reconstruct a high-resolution ISAR scattering distribution image of the target in two-dimensional space. The CLEAN algorithm is used to extract the spatial location of the target scattering center and its corresponding complex amplitude information from the ISAR image, effectively suppressing sidelobe interference caused by truncation effects. Based on the extracted spatial location of the scattering center and complex amplitude, the scattering contribution of the target under far-field conditions is coherently superimposed, and the relative RCS angle spectrum of the target is extrapolated. By introducing the analytical RCS theoretical value of a standard metal sphere, the relative RCS angle spectrum is amplitude-calibrated, establishing a mapping relationship between the measurement results and the absolute RCS, ultimately obtaining a high-precision target absolute RCS angle spectrum result.

[0024] Please see Figure 1 This invention provides a technical solution: a near-field measurement method for spherical wave-corrected radar cross section, comprising the following steps: S1: Collect complex electromagnetic scattering echo data, background noise echo data, and standard scatterer echo data of the target under near-field testing conditions to construct an echo dataset, as detailed below: Step S11: Arrange the transmitting antenna and receiving antenna in a near-field test environment so that the transmitting antenna and receiving antenna form a pseudo-monostation measurement configuration; Step S12: Under the condition that the target under test is not placed or the equivalent scatterer is removed, based on the pseudo-single-station measurement configuration and the turntable rotation capability, control the test system to scan within the preset frequency range and observation angle range, and collect the background noise echo data corresponding to the test environment; Step S13: After the target under test is placed in the measurement area, based on the pseudo-single-station measurement configuration and the turntable rotation capability, the test system is controlled to perform frequency-by-frequency electromagnetic irradiation on the target under test within the preset frequency range. At the same time, the observation angle of the target under test relative to the antenna is changed by rotating the turntable to form multi-frequency and multi-angle measurement. Step S14: Under the conditions of each frequency point and each observation angle, based on the quasi-monostation measurement configuration and the turntable rotation capability, the scattered echo signal of the target under test is collected, and the scattered echo signal is coherently demodulated to obtain complex electromagnetic scattered echo data at the corresponding frequency and observation angle; at the same time, a standard scatterer (calibration sphere) is placed on the turntable, and its scattered echo signal is collected under the same frequency and angle conditions for subsequent amplitude calibration; Step S15: Organize and store the background noise echo data, the target echo data, and the calibration body echo data according to the frequency dimension and the angle dimension to form a multi-frequency, multi-angle echo dataset for subsequent processing; This embodiment utilizes a quasi-monostation measurement architecture and a turntable collaborative scanning system to achieve systematic acquisition of target multi-frequency and multi-angle scattering echo data under near-field conditions, including background noise, target echo, and calibration body echo data, thus constructing a complete frequency-angle domain measurement dataset. S2: Perform phase center calibration, background cancellation, and gate function processing on the echo data in the echo dataset to obtain preprocessed echo data, as detailed below: Step S21: Using the one-dimensional distance image of a standard metal sphere, calculate the phase offset of the echo signal, and perform phase compensation on the original echo data to correct the phase center offset introduced by cables, amplifiers, and probe units in the test system. The specific compensation formula is as follows: Step S22: Perform complex subtraction between the target echo and the background echo in the anechoic chamber in the frequency domain to eliminate the influence of inherent system noise and environmental background scattering. Step S23: By setting a fixed start and end distance range, the effective scattered echo of the target is intercepted, while the clutter signals in non-target areas are suppressed, thereby improving the signal-to-noise ratio and spatial resolution of subsequent ISAR imaging; Step S24: Based on the precise distance from the target's equivalent scattering center to each near-field scanning point The amplitude and phase differences between spherical waves and plane waves are calculated, and amplitude compensation (multiplying by) is performed on the acquired near-field complex scattering data. ) and phase compensation (introducing phase factor) To correct the non-planar wavefront error caused by spherical wave illumination; Step S25: Obtain the normalized complex radiation pattern of the transmitting and receiving probes within the measurement frequency band and scanning angle range. and Divide the near-field scattering data at each scan point by the product of the radiation patterns at that point. v, to eliminate the modulation effect of the non-ideal radiation and receiving characteristics of the actual probe on the measurement data; This embodiment completes echo preprocessing through one-dimensional range image phase calibration, frequency domain background cancellation, and time domain gating techniques; combined with spherical wave amplitude-phase compensation and probe pattern correction, it effectively suppresses system bias and environmental interference, and significantly improves the accuracy of ISAR imaging and RCS inversion. S3: For the preprocessed echo data, the post-projection BP algorithm is used to correct the phase and amplitude, forming the inverse synthetic aperture radar (ISAR) scattering distribution map of the target, as follows: Step S31: Decompose the preprocessed complex scattered echo data according to the range and azimuth directions, and establish data representations in the frequency dimension and the observation angle dimension respectively; Step S32: To meet the integration interval requirements of IFFT, the range wavenumber K is frequency-shifted by an amount equal to the initial beam. This makes the integration region become ( At this point, the echo data becomes... ; Step S33: Perform inverse Fourier transform (IFFT) on the range echo data after frequency shift processing to obtain the complex range image of the target in the range direction; Step S34: Perform phase compensation on the range echo data to correct the phase deviation introduced by the range frequency shift processing; Step S35: For near-field measurement conditions, perform spherical wave phase compensation on the azimuth echo data to eliminate azimuth phase distortion caused by spherical wave propagation; Step S36: After completing the range and azimuth phase compensation, coherently superimpose the echo signals of all imaging grid points to form the ISAR scattering distribution image of the target.

[0025] This embodiment achieves range pulse compression through frequency-shifted IFFT, and combines near-field spherical wave phase correction with azimuth coherent superposition to construct a high-resolution ISAR image, thereby realizing visualization of the target's two-dimensional scattering distribution. S4: The CLEAN algorithm is used to extract the spatial location of the target scattering center and its corresponding complex amplitude information from the ISAR scattering distribution image, and an equivalent scattering center model is constructed, as follows: Step S41: In the initial ISAR image (The ISAR image generated by the nth iteration of the thickening process is) Find the point with the maximum electromagnetic property strength (where n is the number of iterations). Record the electromagnetic characteristic intensity value at that point. and location ( ) Step S42: Calculate the comparison value of the nth iteration, where the formula for calculating the comparison value after the nth iteration is: Comparison value = 10 Step S43: Determine if the comparison value is less than the set cutoff threshold. If yes, stop obtaining the target equivalent scattering center model; otherwise, continue to step S44. Step S44: At the location of the maximum electromagnetic characteristic strength value ( On the electromagnetic property strength value ISAR image obtained by convolving with PSF to obtain the maximum electromagnetic property intensity point and imaging it separately. Then subtract it from the initial image to obtain the next-generation ISAR image. Then proceed to step S41; This embodiment uses the CLEAN algorithm to iteratively extract the target equivalent scattering center. By successively identifying and removing the strongest scattering points and point spread function convolutions in the image until the remaining energy is lower than the preset cutoff threshold, a high-fidelity equivalent scattering center model for far-field RCS extrapolation is finally constructed. S5: Based on the extracted spatial location and complex amplitude of the scattering center, the scattering contribution of the target under far-field conditions is coherently superimposed to obtain the relative RCS angular spectrum result of the target, as follows: Step S51: Obtain the set of equivalent scattering centers extracted by the CLEAN algorithm, and the location of each scattering center. and each scattering center at frequency k and azimuth angle Electromagnetic property strength value ; Step S52: Coherently superimpose all extracted equivalent scattering centers under far-field conditions to obtain the target at any wavenumber k and azimuth angle. Far-field scattering field Where N is the total number of scattering centers.

[0026] Step S53: Based on far-field scattering Calculate the radar cross section (RCS) of the target at the corresponding frequency and angle: This embodiment obtains the target's far-field scattering field by coherently superimposing the equivalent scattering centers extracted by the CLEAN algorithm under far-field conditions. Then, based on the definition of radar cross section, the relative RCS angle spectrum of the target is calculated, realizing a high-precision mapping from near-field echo to far-field RCS. S6: The obtained relative RCS angular spectrum result is introduced into the theoretical RCS value of the standard scatterer, and the amplitude of the relative RCS angular spectrum is calibrated to obtain the absolute RCS angular spectrum result of the measured target, as follows: Step S61: Extract the standard scattering echo data corresponding to each frequency point and each observation angle from the complex electromagnetic scattering echo data of the standard scatterer obtained in step S14; based on the data processing flow consistent with the target under test, perform imaging processing, scattering center modeling and far-field RCS extrapolation on the standard scattering echo data to obtain the relative RCS angular spectrum of the standard scatterer at different frequencies and observation angles; Step S62: Based on the geometric dimensions and electromagnetic properties of the standard scatterer, calculate its theoretical absolute radar cross section value at the corresponding frequency and observation angle, and establish the theoretical RCS angular spectrum of the standard scatterer.

[0027] Step S63: Compare the amplitude of the standard scatterer relative RCS angular spectrum obtained in step S61 with the theoretical absolute RCS angular spectrum obtained in step S62 at the same frequency and observation angle to estimate the amplitude response characteristics of the measurement system at different frequencies and observation angles. Based on the amplitude response characteristics, a system amplitude calibration factor matrix or continuous calibration function with frequency and observation angle as independent variables is constructed to characterize the amplitude non-uniformity characteristics of the measurement system under wide bandwidth and large angle conditions. Step S64: Based on the system amplitude calibration function constructed in step S63, perform amplitude correction on the relative RCS angle spectrum of the target obtained in step S5 under the corresponding frequency point and observation angle conditions, establish the mapping relationship between relative RCS and absolute RCS, and obtain the absolute RCS angle spectrum result of the target.

[0028] Example 2: This embodiment provides a near-field measurement system for spherical wave-corrected radar cross section, used to implement the near-field measurement method for spherical wave-corrected radar cross section described in Embodiment 1, including: The dataset construction module is used to collect complex electromagnetic scattering echo data, background noise echo data and standard scatterer echo data of the target under test in a near-field test environment, and construct an echo dataset. The data preprocessing module is used to perform phase center calibration, background cancellation, and gate function processing on the echo data in the echo dataset to obtain preprocessed echo data. The imaging module is used to perform phase and amplitude correction on the preprocessed echo data using the post-projection BP algorithm to form an inverse synthetic aperture radar (ISAR) scattering distribution map of the target under test. The model building module is used to extract the spatial location of the target scattering center and its corresponding complex amplitude information from the ISAR scattering distribution image using the CLEAN algorithm, and to build an equivalent scattering center model. The extrapolation module is used to coherently superimpose the scattering contribution of the target under far-field conditions based on the extracted spatial location of the scattering center and the complex amplitude, so as to obtain the relative RCS angular spectrum result of the target. The amplitude calibration module is used to input the obtained relative RCS angle spectrum result into the theoretical RCS value of the standard scatterer, perform amplitude calibration on the relative RCS angle spectrum, and obtain the absolute RCS angle spectrum result of the target under test.

[0029] Example 3: The present invention provides a terminal device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. The memory stores the computer program capable of running on the processor. When the processor loads and executes the computer program, it employs the spherical wave-corrected radar cross section near-field measurement method described in Embodiment 1.

[0030] It should be noted that the terminal device can be a computer device such as a desktop computer, a laptop computer, or a cloud server, and the terminal device includes, but is not limited to, a processor and a memory. For example, the terminal device may also include input / output devices, network access devices, and buses.

[0031] Furthermore, the processor can be a central processing unit (CPU). Of course, depending on the actual use, other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), off-the-shelf programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. can also be used. The general-purpose processor can be a microprocessor or any conventional processor, etc., and this application does not limit it in this regard.

[0032] Example 4: The present invention provides a storage medium containing computer-executable instructions, which, when executed by a computer processor, are used to perform the near-field measurement method for spherical wave-corrected radar cross section described in Embodiment 1.

[0033] The computer program can be stored in a computer-readable medium. The computer program includes computer program code, which can be in the form of source code, object code, executable file, or certain middleware. The computer-readable medium includes any entity or device capable of carrying computer program code, recording media, USB flash drive, portable hard drive, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc. It should be noted that the computer-readable medium includes, but is not limited to, the above-mentioned components.

[0034] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0035] The foregoing has shown and described the basic principles, main features, and advantages of this application. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of the claims of this application.

Claims

1. A method of spherical wave corrected radar cross section near field measurement, characterized in that, Includes the following steps: Collect complex electromagnetic scattering echo data, background noise echo data, and standard scatterer echo data of the target under test in a near-field test environment to construct an echo dataset; Phase center calibration, background cancellation, and gate function processing are performed on the echo data in the echo dataset to obtain preprocessed echo data. For the preprocessed echo data, the post-projection BP algorithm is used to correct the phase and amplitude, forming the inverse synthetic aperture radar (ISAR) scattering distribution map of the target. The CLEAN algorithm is used to extract the spatial location of the target scattering center and its corresponding complex amplitude information from the ISAR scattering distribution image, and an equivalent scattering center model is constructed. Based on the extracted spatial location of the scattering center and the complex amplitude, the scattering contribution of the target under far-field conditions is coherently superimposed to obtain the relative RCS angular spectrum result of the target. The obtained relative RCS angular spectrum result is introduced into the theoretical RCS value of the standard scatterer, and the relative RCS angular spectrum is calibrated to obtain the absolute RCS angular spectrum result of the target under test.

2. The method of spherical wave correction for radar cross section near- field measurements according to claim 1, characterized in that: Complex electromagnetic scattering echo data, background noise echo data, and standard scatterer echo data of the target under test were collected in a near-field testing environment, as detailed below: In a near-field testing environment, the transmitting and receiving antennas are arranged to form a quasi-monostation measurement configuration. Without placing the target under test, based on the quasi-single-station measurement configuration and the turntable rotation capability, scanning is performed within a preset frequency range and observation angle range to collect background noise echo data; After the target is placed in the measurement area, the target is electromagnetically irradiated frequency by frequency within the preset frequency range. At the same time, the observation angle is changed by rotating the turntable to form multi-frequency and multi-angle echo data of the target. At various frequency points and observation angles, the scattered echo signals of the target under test are collected and coherently demodulated to obtain complex electromagnetic scattered echo data. The standard scatterer is placed on the turntable, and its scattered echo signal is collected under the same conditions to obtain the calibration body echo data. Background noise echo data, target echo data, and calibration body echo data are organized and stored according to frequency and angle dimensions to form a multi-frequency, multi-angle echo dataset.

3. The near-field measurement method for spherical wave corrected radar cross section according to claim 1, characterized in that: Phase center calibration, background cancellation, and gating function processing are performed on the echo data in the echo dataset to obtain preprocessed echo data, as follows: Using the one-dimensional range image of a standard metal sphere, the phase shift of the echo signal is calculated, and phase compensation is performed on the original echo data to correct the phase center shift. The specific compensation formula is as follows: In the formula, is the phase-compensated frequency-domain echo signal; Equivalent distance error (m) caused by phase center offset, i.e. the radial distance offset converted from the deviation of the peak position of the measured one-dimensional range image of the standard metal sphere from the theoretical position; In the frequency domain, the target echo data and the background echo data of the empty anechoic chamber are subtracted by complex values ​​to eliminate the influence of inherent system noise and environmental background scattering. By setting a fixed start and end distance range, the effective scattered echo of the target is intercepted, and stray signals in non-target areas are suppressed. Based on the precise distance from the target's equivalent scattering center to each near-field scanning point The amplitude and phase differences between spherical waves and plane waves are calculated, and amplitude and phase compensation is performed on the collected near-field complex scattering data to correct the non-planar wavefront error caused by spherical wave illumination. Acquire the normalized complex radiation patterns of the transmitting and receiving probes within the measurement frequency band and scanning angle range. and Divide the near-field scattering data at each scan point by the product of the radiation patterns at that point. This is to eliminate the modulation effect of the non-ideal radiation and reception characteristics of the actual probe on the measurement data.

4. The method of spherical wave correction for radar cross section near- field measurements of claim 1, wherein: For the preprocessed echo data, the post-projection backpropagation (BP) algorithm is used to correct the phase and amplitude, forming the inverse synthetic aperture radar (ISAR) scattering distribution map of the target, as shown below: The preprocessed complex electromagnetic scattering echo data is decomposed into range and azimuth directions, and data representations in the frequency dimension and observation angle dimension are established respectively. The distance direction wave number K is frequency shifted, and the shift is the initial beam , so that the integral region becomes ( ), and the echo data becomes ; Perform an inverse Fourier transform on the range echo data after frequency shifting to obtain the complex range image of the target in the range direction; Phase compensation is performed on the range echo data to correct the phase deviation introduced by range frequency shift processing; For near-field measurement conditions, spherical wave phase compensation is performed on the azimuth echo data to eliminate the azimuth phase distortion caused by spherical wave propagation; After completing the range and azimuth phase compensation, the echo signals of all imaging grid points are coherently superimposed to form the ISAR scattering distribution image of the target.

5. The spheric wave corrected radar cross section near field measurement method of claim 1, wherein: The CLEAN algorithm is used to extract the spatial location and corresponding complex amplitude information of the target scattering center from the ISAR scattering distribution image, and an equivalent scattering center model is constructed as follows: the obtained ISAR scattering distribution image is taken as an initial ISAR image, a point with a maximum electromagnetic property intensity value is found in the initial ISAR image , and an electromagnetic property intensity value of the point is recorded and a position coordinate ) Calculate the comparison value after the nth iteration. This comparison value is the logarithmic representation of the ratio of the maximum complex amplitude of the current ISAR image to the maximum complex amplitude of the initial ISAR image, specifically expressed as: Comparison value = 10 ; Based on the calculated comparison value, it is determined whether the comparison value is less than the set cutoff threshold. If it is, the process of obtaining the target equivalent scattering center model stops; otherwise, the process continues to the next step. At the location of the maximum electromagnetic characteristic strength value ( At the location of the maximum electromagnetic characteristic intensity value, the electromagnetic characteristic intensity value is convolved with the point spread function to obtain an ISAR image of the scattering center after imaging alone, and then subtracted from the current ISAR image to obtain the next generation ISAR image.

6. The near-field measurement method for spherical wave-corrected radar cross section according to claim 1, characterized in that: Based on the extracted spatial location and complex amplitude of the scattering center, the scattering contribution of the target under far-field conditions is coherently superimposed to obtain the relative RCS angular spectrum of the target, as follows: Based on the equivalent scattering center model, a set of equivalent scattering centers extracted by the CLEAN algorithm is obtained, including the position coordinates of each scattering center. and each scattering center at frequency k and azimuth angle Electromagnetic property strength value ; All the extracted equivalent scattering centers are coherently superimposed under far-field conditions to obtain the far-field scattering field of the measured target at any wave number k and azimuth angle under far-field conditions: Where N is the total number of scattering centers; Based on far field scattering field Computing the radar cross section, RCS, of the measured target at the corresponding frequency and angle: wherein is the far zone scattered electric field; is the incident plane wave electric field.

7. The spheric wave corrected radar cross section near-field measurement method of claim 1, wherein: The obtained relative RCS angular spectrum results are introduced into the theoretical RCS value of the standard scatterer, and the relative RCS angular spectrum is calibrated to obtain the absolute RCS angular spectrum results of the measured target, as follows: Based on the obtained complex electromagnetic scattering echo data of the standard scatterer, imaging processing, scattering center modeling, and far-field RCS extrapolation are performed to obtain the relative RCS angular spectrum of the standard scatterer at different frequencies and observation angles. Based on the geometric dimensions and electromagnetic properties of the standard scatterer, calculate its theoretical absolute radar cross section value at the corresponding frequency and observation angle, and establish the theoretical RCS angular spectrum of the standard scatterer. The amplitude of the obtained standard scatterer relative RCS angular spectrum is compared with the theoretical absolute RCS angular spectrum at the same frequency and observation angle to estimate the amplitude response characteristics of the measurement system at different frequencies and observation angles. Based on the amplitude response characteristics, a system amplitude calibration factor matrix or continuous calibration function with frequency and observation angle as independent variables is constructed to characterize the amplitude non-uniformity characteristics of the measurement system under wide bandwidth and large angle conditions. Based on the constructed system amplitude calibration function, the relative RCS angular spectrum is amplitude corrected under the corresponding frequency point and observation angle conditions, the mapping relationship between relative RCS and absolute RCS is established, and the absolute RCS angular spectrum result of the measured target is obtained.

8. A spherical wave corrected radar cross section near field measurement system for implementing the spherical wave corrected radar cross section near field measurement method of any one of claims 1 to 7, characterized in that, include: The dataset construction module is used to collect complex electromagnetic scattering echo data, background noise echo data and standard scatterer echo data of the target under test in a near-field test environment, and construct an echo dataset. The data preprocessing module is used to perform phase center calibration, background cancellation, and gate function processing on the echo data in the echo dataset to obtain preprocessed echo data. The imaging module is used to perform phase and amplitude correction on the preprocessed echo data using the post-projection BP algorithm to form an inverse synthetic aperture radar (ISAR) scattering distribution map of the target under test. The model building module is used to extract the spatial location of the target scattering center and its corresponding complex amplitude information from the ISAR scattering distribution image using the CLEAN algorithm, and to build an equivalent scattering center model. The extrapolation module is used to coherently superimpose the scattering contribution of the target under far-field conditions based on the extracted spatial location of the scattering center and the complex amplitude, so as to obtain the relative RCS angular spectrum result of the target. The amplitude calibration module is used to input the obtained relative RCS angle spectrum result into the theoretical RCS value of the standard scatterer, perform amplitude calibration on the relative RCS angle spectrum, and obtain the absolute RCS angle spectrum result of the target under test.

9. A terminal device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that, The memory stores a computer program that can run on a processor. When the processor loads and executes the computer program, it employs the spherical wave-corrected radar cross section near-field measurement method as described in any one of claims 1 to 7.

10. A storage medium containing computer-executable instructions, characterized in that, The computer-executable instructions, when executed by a computer processor, are used to perform the near-field measurement method for spherical wave-corrected radar cross section as described in any one of claims 1 to 7.

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