Subband Synthetic Imaging Method and Device for Ultra-Wideband Stepped Frequency Modulation SAR

Abstract

This application relates to the field of SAR imaging technology, and provides a sub-band synthetic imaging method and apparatus for ultra-wideband stepped-frequency-modulated SAR. The method extracts sub-band errors from ultra-wideband stepped-frequency-modulated SAR using self-closed-loop data, and constructs range-direction matched filters for each sub-band using the extracted sub-band errors. Then, the constructed range-direction matched filters are used to perform range-direction pulse compression on the echo data of each sub-band to complete separate imaging of each sub-band. Simultaneously, residual constant-phase errors between sub-bands are estimated using prominent points within the imaging scene. Finally, the estimated residual constant-phase errors between sub-bands are used to compensate for the imaging results of each sub-band, and the compensated sub-band imaging results are then superimposed to obtain the SAR sub-band synthetic imaging result. This method can effectively improve error compensation accuracy, achieve high-quality stepped-frequency-modulated SAR imaging, and requires no iterative operations during error extraction, resulting in high execution efficiency.

Description

Technical Field

[0001] This application relates to the field of synthetic aperture radar (SAR) imaging technology, and in particular to a subband synthetic imaging method and apparatus for ultra-wideband stepped frequency modulated SAR. Background Technology

[0002] Resolution is one of the important evaluation indicators of SAR images. High resolution means that SAR images contain richer details, which is beneficial for SAR image interpretation and target detection and identification. The range resolution of SAR depends on the bandwidth of the transmitted signal. Stepped frequency modulation (FM) technology is one of the means to achieve a large bandwidth transmitted signal. It transmits several linear frequency modulated signals with different carrier frequencies in sequence, and then synthesizes them through digital processing to achieve an equivalent large bandwidth, thereby improving the range resolution.

[0003] The key to achieving stepped frequency modulated SAR imaging lies in two aspects: first, the synthesis of different subbands; and second, error compensation within and between subbands.

[0004] There are two main types of subband synthesis methods for stepped frequency modulated SAR: one is to synthesize the subband first and then image, and the other is to image first and then synthesize the subband in the image domain. The subband synthesis method is further divided into two approaches: one is a time-domain broadband synthesis method, which reconstructs the time-domain broadband signal through steps such as upsampling, frequency shifting, phase compensation, time shifting, and time-domain stitching; the other is a frequency-domain broadband synthesis method, which synthesizes different subband signals in the frequency domain through steps such as frequency-domain matched filtering, removing overlapping spectra, frequency shifting, and frequency-domain stitching to reconstruct the broadband spectrum of the target signal. When the slant range offset in a pulse train is not negligible, the method of synthesizing the subband first and then image cannot avoid the problem of spatially varying slant range error compensation; while the method of image first imaging and then image-domain subband synthesis, based on overall azimuth time shift alignment of the image, can effectively avoid spatially varying slant range error compensation.

[0005] A proposed subband synthesis method for spaceborne frequency-stepped SAR has been developed, employing a time-domain algorithm to image each subband separately and then stitching the subband images together in the range-frequency domain. However, this method does not consider intra- and inter-subband errors. For high-resolution frequency-stepped SAR systems, on the one hand, within a single subband, it is difficult to guarantee absolutely linear phase and a flat amplitude-frequency response for a large-bandwidth signal; on the other hand, due to differences in receiving channels, amplitude-phase errors and time delay errors inevitably exist between subbands. If subband synthesis is performed directly, these errors will be directly coupled into the synthesized broadband spectrum, leading to spectral distortion. This manifests in the final imaging result as range-oriented main lobe broadening, asymmetrical sidelobe lifting, and the appearance of grating lobes, severely affecting imaging quality.

[0006] In the field of stepped frequency modulated SAR error compensation technology, current methods mainly fall into two categories. One category uses external or internal calibration techniques to extract and compensate for inter-subband errors, while the other estimates and compensates for inter-subband errors based on echo data. Related technologies propose methods using external calibration techniques, utilizing calibration objects such as corner reflectors deployed within the imaging scene to extract and compensate for inter-channel amplitude and phase errors in the radar system. However, this type of external calibration method highly depends on the precise placement of calibration objects and ideal reflection characteristics. In practical applications, it is subject to multiple limitations due to terrain conditions, deployment costs, equipment accuracy, and complex electromagnetic environments, thus lacking universal applicability. Related technologies also propose using internal calibration techniques, constructing three calibration loops to monitor and extract errors in the complete signal link from transmission to reception. However, this requires designing complex hardware calibration loops, increasing system complexity and cost, and the accuracy and stability of the calibration loops themselves introduce new uncertainties. Related technologies have further proposed a method for estimating inter-subband errors based on echo data, which uses the spectral overlap between adjacent subbands to estimate and compensate for amplitude and phase errors. However, this method can lead to error accumulation and is heavily dependent on the signal-to-noise ratio of the data. Summary of the Invention

[0007] In view of this, the present application provides a subband synthetic imaging method and apparatus for ultra-wideband stepped frequency modulated SAR, in order to solve the problem that the error estimation accuracy is insufficient and thus the imaging accuracy is low in the prior art when performing subband synthetic imaging of stepped frequency modulated SAR.

[0008] A first aspect of this application provides a sub-band synthetic imaging method for ultra-wideband stepped frequency modulated SAR, comprising:

[0009] The sub-band errors of ultra-wideband stepped frequency modulated SAR are extracted using self-closed-loop data; each sub-band error includes intra-sub-band phase error, inter-sub-band delay error and constant phase error, as well as intra-sub-band and inter-sub-band amplitude errors.

[0010] Construct range-guided matched filters for each sub-band based on the extracted sub-band errors;

[0011] Range-directed pulse compression is performed on the echo data of each sub-band using a range-directed matched filter to complete the imaging of each sub-band separately;

[0012] Estimating inter-subband residual constant phase error using prominent points within the imaging scene;

[0013] The residual constant phase error between sub-bands is used to compensate for the imaging results of each sub-band, and the compensated imaging results of each sub-band are superimposed to obtain the SAR sub-band synthetic imaging result.

[0014] A second aspect of this application provides a sub-band synthetic imaging device for ultra-wideband stepped frequency modulated SAR, comprising:

[0015] The extraction module is configured to extract sub-band errors of ultra-wideband stepped frequency modulated SAR using self-closed-loop data; wherein each sub-band error includes sub-band phase error, inter-sub-band delay error and constant phase error, as well as sub-band and inter-sub-band amplitude errors.

[0016] The construction module is configured to construct each sub-band range-directed matched filter based on the extracted sub-band error;

[0017] The imaging module is configured to use a range-matched filter to perform range pulse compression on the echo data of each sub-band separately in order to complete the imaging of each sub-band separately;

[0018] The estimation module is configured to estimate the inter-subband residual constant phase error using prominent points within the imaging scene;

[0019] The compensation module is configured to compensate for the imaging results of each sub-band using the residual constant phase error between sub-bands, and then superimpose the compensated imaging results of each sub-band to obtain the SAR sub-band synthetic imaging result.

[0020] A third aspect of this application provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the above-described method.

[0021] A fourth aspect of this application provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the above-described method.

[0022] The beneficial effects of this application embodiment compared with the prior art are as follows: This application embodiment extracts the sub-band errors of ultra-wideband stepped frequency modulated SAR using self-closed-loop data, and constructs range-direction matched filters for each sub-band using the extracted sub-band errors; then, the constructed range-direction matched filters are used to perform range-direction pulse compression on the echo data of each sub-band to complete the imaging of each sub-band separately; simultaneously, the residual constant phase error between sub-bands is estimated using prominent points in the imaging scene; finally, the estimated residual constant phase error between sub-bands is used to compensate for the imaging results of each sub-band, and the compensated imaging results of each sub-band are superimposed to obtain the SAR sub-band composite imaging result. This method can effectively improve the error compensation accuracy, achieve high-quality stepped frequency modulated SAR imaging, and does not require iterative operations in the error extraction process, resulting in high execution efficiency. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart illustrating a subband synthetic imaging method for ultra-wideband stepped frequency modulated SAR provided in an embodiment of this application.

[0025] Figure 2 This is a flowchart illustrating the method for extracting the sub-band phase error of an ultra-wideband stepped frequency modulated SAR target sub-band using self-closed-loop data, as provided in an embodiment of this application.

[0026] Figure 3 This is a flowchart illustrating the method for extracting inter-subband delay error and constant phase error of an ultra-wideband stepped frequency modulated SAR target subband using self-closed-loop data, as provided in the embodiments of this application.

[0027] Figure 4 This is a flowchart illustrating the method for extracting intra-subband and inter-subband amplitude errors of an ultra-wideband stepped frequency modulated SAR target subband using self-closed-loop data, as provided in an embodiment of this application.

[0028] Figure 5 This is a flowchart illustrating a method for estimating inter-subband residual constant phase error using prominent points within an imaging scene, as provided in an embodiment of this application.

[0029] Figure 6 This is a flowchart illustrating another subband synthetic imaging method for ultra-wideband stepped frequency modulated SAR provided in this application embodiment.

[0030] Figure 7 This is a schematic diagram of the subband synthetic imaging results provided in the embodiments of this application.

[0031] Figure 8 This is a partial comparison image of the imaging results provided in the embodiments of this application.

[0032] Figure 9 This is a schematic diagram of a subband synthetic imaging device for ultra-wideband stepped frequency modulated SAR provided in an embodiment of this application.

[0033] Figure 10 This is a schematic diagram of the electronic device provided in the embodiments of this application. Detailed Implementation

[0034] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application may also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted so as not to obscure the description of this application with unnecessary detail.

[0035] The following will describe in detail, with reference to the accompanying drawings, a subband synthetic imaging method and apparatus for ultra-wideband stepped frequency modulated SAR according to embodiments of this application.

[0036] As mentioned above, the error estimation accuracy of existing step-frequency modulated SAR subband synthetic imaging is insufficient, resulting in low imaging accuracy.

[0037] Specifically, most existing stepped frequency modulated SAR subband synthesis imaging methods achieve subband synthesis in the echo or image domain, and extract or estimate inter-subband errors through system calibration techniques or echo data-based methods. The limitations of these methods are:

[0038] 1) The error model is imperfect and does not fully consider the impact of non-ideal factors within the sub-band: Current step-frequency SAR error compensation technology mainly focuses on the amplitude and phase errors between sub-bands. As the bandwidth of the sub-band signal increases, the errors introduced by amplitude imbalance and phase non-linearity within the sub-band cannot be ignored.

[0039] 2) The calibration technology is highly dependent, and its engineering applicability and cost are limited: External calibration requires the deployment of artificial calibration bodies such as corner reflectors in the observation scene, which is costly and inflexible; internal calibration does not require external equipment, but it relies on the complex calibration loop inside the system, which not only increases the complexity of the system hardware and the design difficulty, but the drift and non-ideality of the calibration loop itself may also introduce additional system errors.

[0040] 3) Data-driven methods lack robustness and have low computational efficiency: Error estimation methods based on echo data (such as using subband spectrum overlap, genetic algorithms, or image contrast optimization) rely on the spectrum overlap assumption, and the estimation accuracy drops sharply when the signal-to-noise ratio in the overlap area is low; most methods require multiple iterations for searching or optimization, resulting in a heavy computational burden.

[0041] In view of this, this application provides a sub-band synthetic imaging method for ultra-wideband stepped frequency modulated SAR. It utilizes the self-closed-loop test signal built into the radar system to obtain the initial error characteristics of the system, achieving preliminary extraction of intra-sub-band and inter-sub-band errors. Using the extraction results, range-direction matched filters are constructed for each sub-band, and each sub-band is imaged separately. Highlighted points are selected in the imaging results to estimate the residual constant phase error between sub-bands. The residual errors are compensated, and sub-band synthesis is performed in the image domain to obtain the final stepped frequency modulated SAR sub-band synthetic imaging result.

[0042] Figure 1 This is a schematic flowchart of a subband synthetic imaging method for ultra-wideband stepped frequency modulated SAR provided in an embodiment of this application. Figure 1 As shown, the method includes the following steps:

[0043] In step S101, the sub-band errors of the ultra-wideband stepped frequency modulated SAR are extracted using self-closed-loop data.

[0044] Each sub-band error includes sub-band phase error, sub-band delay error, constant phase error, and sub-band amplitude error.

[0045] In step S102, a range-directed matched filter for each sub-band is constructed based on the extracted sub-band error.

[0046] In step S103, a range-matched filter is used to perform range pulse compression on the echo data of each sub-band to complete the imaging of each sub-band.

[0047] In step S104, the residual constant phase error between subbands is estimated using prominent points within the imaging scene.

[0048] In step S105, the residual constant phase error between sub-bands is used to compensate for the imaging results of each sub-band, and the compensated imaging results of each sub-band are superimposed to obtain the SAR sub-band synthetic imaging result.

[0049] In some embodiments of this application, the method may be executed by a server or by a terminal device with certain processing capabilities.

[0050] In some embodiments of this application, sub-band errors of an ultra-wideband stepped frequency modulated SAR can be extracted using self-closed-loop data. Here, self-closed-loop data refers to data acquired when the SAR is operating in self-closed-loop mode. Self-closed-loop mode is typically used for SAR echo simulator self-testing, including simulator channel error calibration, stability testing, and system status checks.

[0051] In some embodiments of this application, range-matched filters for each sub-band can be constructed based on the extracted sub-band errors, and the constructed range-matched filters can be used to perform range pulse compression on the echo data of each sub-band to complete the imaging of each sub-band separately.

[0052] In some implementations, conventional time-domain or frequency-domain imaging algorithms can be used to process the echo data of each sub-band. During the imaging process, the range-directed matched filter constructed in the above steps can be used to perform range-directed pulse compression on the echo data of each sub-band to compensate for amplitude, phase, and delay errors within and between sub-bands.

[0053] Furthermore, prominent points within the imaging scene can be used to estimate the inter-subband residual constant phase error. Prominent points, also known as salient points or strong scattering points, are scattering centers with high echo amplitude in SAR or Inverse Synthetic Aperture Radar (ISAR) imaging. Their amplitude fluctuations are relatively small, while noise and clutter amplitude fluctuations are larger. The inter-subband residual constant phase error can be estimated using prominent points based on linear regression or optimization methods.

[0054] In some embodiments of this application, the estimated inter-subband residual constant phase error can be used to compensate for the imaging results of each subband, and the compensated imaging results of each subband can be superimposed to obtain the SAR subband synthetic imaging result.

[0055] According to the technical solution provided in this application, the errors of each sub-band of ultra-wideband stepped frequency modulated SAR are extracted using self-closed-loop data, and the extracted sub-band errors are used to construct range-matched filters for each sub-band. Then, the constructed range-matched filters are used to perform range pulse compression on the echo data of each sub-band to complete the imaging of each sub-band separately. At the same time, the residual constant phase error between sub-bands is estimated using prominent points in the imaging scene. Finally, the estimated residual constant phase error between sub-bands is used to compensate for the imaging results of each sub-band, and the compensated imaging results of each sub-band are superimposed to obtain the SAR sub-band composite imaging result. This method can effectively improve the error compensation accuracy, achieve high-quality stepped frequency modulated SAR imaging, and does not require iterative operations in the error extraction process, resulting in high execution efficiency.

[0056] In some embodiments of this application, the Phase Gradient Autofocus (PGA) algorithm can be used to process the self-closed-loop data of each sub-band channel to extract the range phase error within the sub-band. In some embodiments, other methods can also be used to estimate the phase error within the sub-band, and no limitation is made here. The following description uses the PGA algorithm to extract the phase error within the sub-band as an example.

[0057] Figure 2This is a flowchart illustrating a method for extracting intra-subband phase error of an ultra-wideband stepped frequency modulated SAR target subband using self-closed-loop data, as provided in an embodiment of this application. Figure 2 As shown, the method includes the following steps:

[0058] In step S201, N frames of self-closed-loop data of the target subband are acquired.

[0059] Where N is a positive integer greater than 1.

[0060] In step S202, the range-direction matched filtering of each frame of self-closed-loop data in the target subband is performed using an ideal matched filter to obtain N range compressed signals.

[0061] In step S203, the distance gate where the amplitude peak is located is located in each distance compression signal.

[0062] In step S204, a window is added centered on the distance gate obtained from the positioning, and a data segment is extracted.

[0063] In step S205, the truncated data segments are subjected to Fourier transform, complex multiplication, and phase taking operations in sequence to obtain the frequency domain phase error gradient corresponding to each frame of self-closed-loop data.

[0064] In step S206, the average phase error gradient is obtained by averaging the frequency domain phase error gradient corresponding to each frame of self-closed-loop data.

[0065] In step S207, the average phase error gradient is accumulated to obtain the sub-band phase error of the target sub-band.

[0066] The target subband is any subband of the ultra-wideband stepped frequency modulated SAR.

[0067] In some embodiments of this application, when extracting the sub-band phase error of the frequency-modulated SAR target sub-band, N frames of self-closed-loop data of the target sub-band can be obtained first, and range-direction matched filtering can be performed on each frame of self-closed-loop data of the target sub-band using an ideal matched filter to obtain N range compressed signals.

[0068] Then, the range gates containing the amplitude peaks in each range compression signal are located. Next, a window is added centered on the located range gates, data segments are extracted, and Fourier transform, complex multiplication, and phase taking operations are performed on the extracted data segments in sequence to obtain the frequency domain phase error gradient corresponding to each frame of self-closed-loop data.

[0069] The steps of performing Fourier transform, complex multiplication, and phase taking on the truncated data segment can be as follows: using the formula... Calculate the distance-to-fast time The corresponding frequency domain phase error gradient of the self-closed-loop data; The target sub-band number, For range frequency, To obtain the phase function, This indicates the Fourier transform operation. For the extracted data segment, The symbol for complex multiplication is . This represents the frequency domain sampling interval.

[0070] Next, the average phase error gradient in the frequency domain corresponding to each frame of self-closed-loop data is calculated to obtain the average phase error gradient. Finally, the average phase error gradients are summed to obtain the sub-band phase error of the target sub-band.

[0071] In other words, assuming there are K sub-bands in total, where K is a positive integer greater than 1, for each of the sub-bands... If we take this as the target subband, we can first use an ideal matched filter to filter the subband. Self-closed-loop data Range-directed matched filtering is performed to obtain the range-compressed signal. . It is a positive integer less than or equal to K.

[0072] Then The distance to the peak of the mid-position amplitude gate Add a window centered on it to extract data segments. Then follow The frequency domain phase error gradient is estimated through Fourier transform, complex multiplication, and phase taking operations. .

[0073] Multiple frames of self-closed-loop data can be collected, and the above operation can be repeated to obtain the frequency domain phase error gradient of each frame of signal. These gradients can then be averaged to obtain the average phase gradient. Then, the average phase gradients of each phase gradient are calculated. Accumulate the data to reconstruct the subband. In-band phase error .

[0074] Figure 3 This is a flowchart illustrating the method for extracting inter-subband delay error and constant phase error of an ultra-wideband stepped frequency modulated SAR target subband using self-closed-loop data, as provided in an embodiment of this application. Figure 3 As shown, the method includes the following steps:

[0075] In step S301, the spectral phase of the target subband closed-loop data after distance pulse compression is extracted.

[0076] In step S302, the least squares method is used to linearly fit the spectral phase of the target subband closed-loop data after range pulse compression along the range frequency to obtain a first-order fitting polynomial.

[0077] In step S303, the relative delay error and relative constant phase error of the target sub-band are determined based on the coefficients of the first-order fitting polynomial, using the first sub-band of the ultra-wideband stepped frequency modulated SAR as a reference.

[0078] The target subband is any subband of the ultra-wideband stepped frequency modulated SAR.

[0079] The first-order fitting polynomial is ; The spectral phase of the target subband closed-loop data after range pulse compression. The target sub-band number, For range frequency, The coefficients of the linear term, The constant term is used; the relative delay error of the target subband is... ; The linear term coefficients of the first sub-band are given; the relative constant phase error of the target sub-band is... ; This is the constant term for the first sub-band.

[0080] In some embodiments of this application, when extracting the inter-subband delay error and constant phase error of the frequency-modulated SAR target subband, the spectral phase of the target subband closed-loop data after range pulse compression can be extracted first. Then, the least squares method is used to linearly fit the spectral phase of the target subband closed-loop data after range pulse compression along the range frequency to obtain a first-order fitting polynomial. Finally, taking the first subband of the ultra-wideband stepped frequency-modulated SAR as a reference, the relative delay error and relative constant phase error of the target subband are determined based on the coefficients of the first-order fitting polynomial.

[0081] In other words, the spectral phase of each sub-band self-closed-loop data after pulse compression can be extracted first. Then, the least squares method is used to linearly fit it along the frequency along the range direction. The fitting process can be expressed as follows: .

[0082] Finally, using sub-band 1 as a reference, based on the fitting coefficients... , , and Subbands can be calculated relative delay error and relative constant phase error .

[0083] Figure 4 This is a flowchart illustrating the method for extracting intra-subband and inter-subband amplitude errors of an ultra-wideband stepped frequency modulated SAR target subband using self-closed-loop data, as provided in an embodiment of this application. Figure 4 As shown, the method includes the following steps:

[0084] In step S401, the spectral amplitude of each sub-band closed-loop data after pulse compression is extracted.

[0085] In step S402, the average spectral amplitude of the first subband of the ultra-wideband stepped frequency modulated SAR is determined as the reference amplitude.

[0086] In step S403, the error value between the spectral amplitude of the target sub-band and the reference amplitude is determined to be the amplitude error within and between sub-bands of the target sub-band.

[0087] In some embodiments of this application, when extracting the intra-subband and inter-subband amplitude errors of a frequency-modulated SAR target subband, the spectral amplitude of the closed-loop data range pulse after compression of each subband can be extracted first. Then, the average spectral amplitude of the first subband of the ultra-wideband stepped frequency-modulated SAR can be determined as the reference amplitude. Finally, the error value between the spectral amplitude of the target subband and the reference amplitude is determined as the intra-subband and inter-subband amplitude errors of the target subband.

[0088] In other words, the spectral amplitude of each sub-band self-closed-loop data after pulse compression can be extracted. (Unit: decibels (dB)). Then take the average amplitude of the sub-band 1 spectrum. (dB) is used as a reference amplitude to extract the amplitude error of each sub-band. (dB) is used to subsequently compensate for amplitude unevenness within each sub-band and amplitude imbalance between sub-bands.

[0089] In some embodiments of this application, the sub-band phase error extracted based on the above steps can be used. Inter-subband delay error and constant phase error , And amplitude errors within and between sub-bands. Construct range pulse compression filters for each subband.

[0090] Any subband The range-directed matched filter can be expressed as: ;in, For children The distance-directed matched filter, For range-direction frequency, symbol Represents the power exponent. For children The amplitude error within and between sub-bands, Indicates exponentiation. It is the symbol for imaginary numbers. For children Sub-band phase error, For children Subband delay error, For children The constant phase error, To adjust the frequency of the transmitted signal.

[0091] Although range-matched filters are used to perform range pulse compression on the echo data of each sub-band during imaging, compensating for amplitude, phase, and delay errors within and between sub-bands, different power-ups cause changes in the initial phase of the channel frequency response. Therefore, even after error compensation using self-closed-loop data extraction, residual constant phase errors still exist between sub-bands. Thus, embodiments of this application utilize a method based on prominent points to further estimate and compensate for residual constant phase errors between sub-bands.

[0092] Figure 5 This is a flowchart illustrating a method for estimating inter-subband residual constant phase error using prominent points within an imaging scene, as provided in an embodiment of this application. Figure 5 As shown, the method includes the following steps:

[0093] In step S501, any prominent point within the imaging scene is acquired.

[0094] In step S502, the local region where the prominent point is located is extracted from the imaging results of each sub-band, and an inverse fast Fourier transform is performed in the local region to obtain the range-direction spectral phase of the prominent point in each sub-band.

[0095] In step S503, the distance-direction spectral phase of the prominent points in each sub-band is linearly regressed to obtain a first-order regression polynomial.

[0096] In step S504, the first-order coefficients in the first-order regression polynomials corresponding to each sub-band are weighted and averaged to obtain the common first-order coefficients.

[0097] In step S505, the first-order regression polynomials corresponding to each sub-band are refitted using the common first-order coefficients to obtain the updated first-order regression polynomial constant term.

[0098] In step S506, the difference between the constant term of the updated first-order regression polynomial of the target subband and the constant term of the updated first-order regression polynomial of the first subband of the ultra-wideband stepped frequency modulated SAR is determined as the inter-subband residual constant phase error of the target subband.

[0099] The common first-order coefficients are expressed by the formula. Calculated; For common first-order coefficients, This represents the target sub-band number, where the target sub-band can be any sub-band. For the number of sub-bands, For children The first-order coefficients of the first-order regression polynomial, For children The weighting coefficients.

[0100] The constant term of the first-order regression polynomial after the target subband update is expressed by the formula. Calculated; For children The updated constant term of the first-order regression polynomial, For children The first-order regressive polynomial, For range-direction frequency.

[0101] In some embodiments of this application, the residual constant phase error between sub-bands can be estimated using a linear regression method based on prominent points within the imaging scene. In this case, any prominent point within the imaging scene can be obtained first, and a local region containing the prominent point can be extracted from the imaging results of each sub-band. An inverse fast Fourier transform is then performed in the local region to obtain the range-direction spectral phase of the prominent point in each sub-band.

[0102] Then, linear regression is performed on the distance-direction spectral phase of the prominent points in each sub-band to obtain a first-order regression polynomial. The first-order coefficients in the first-order regression polynomials corresponding to each sub-band are weighted and averaged to obtain common first-order coefficients. Furthermore, the common first-order coefficients can be used to refit the first-order regression polynomials corresponding to each sub-band to obtain the updated constant term of the first-order regression polynomial.

[0103] Finally, it can be determined that the difference between the constant term of the first-order regression polynomial after the target subband update and the constant term of the first-order regression polynomial after the first subband update of the ultra-wideband stepped frequency modulated SAR is the inter-subband residual constant phase error of the target subband.

[0104] In other words, any prominent point in the imaging scene can be selected, and for each sub-band imaging result, a local region containing the same prominent point can be cropped, and a range-directed IFFT can be performed on each local region to obtain the sub-band. The range-direction spectral phase of the central special point .right Perform linear regression to obtain .

[0105] Since only constant phase error exists between each sub-band, and the focal points are aligned, the first-order coefficients of the linear fitting of each sub-band should be consistent. Using the first-order coefficient consistency constraint, a weighted average is taken to obtain the common first-order coefficients. .

[0106] For each sub-band data, fix the linear coefficients. By re-estimating the constant term of the linear fit, we can obtain... By calculating the sub-band jump estimate, the relative constant phase error can be obtained. .

[0107] In some embodiments of this application, compensating for each sub-band imaging result using inter-sub-band residual constant phase error may include: zero-padding each sub-band imaging result in the range direction in the frequency domain to achieve range-direction... Doubling the sampling rate; Number of sub-bands; use the formula Range-direction frequency shift and inter-subband residual constant phase error compensation are performed on the upsampled sub-band imaging results to obtain the compensated sub-band imaging results; among which... For the compensated sub-band Imaging results, sub-band For any sub-band, Subband after upsampling Imaging results, Indicates exponentiation. It is the symbol for imaginary numbers. The center frequency spacing between adjacent sub-bands For distance to fast time, For direction, slow time, Let k be the inter-subband residual constant phase error. The compensated subband imaging results are coherently superimposed in the two-dimensional time domain to obtain the SAR subband composite imaging result. .

[0108] In other words, the imaging results of each sub-band can first be zero-padded in the frequency domain along the range direction, with the number of zero-padded points being... To achieve distance Double-sampling. Among them, This represents the number of distance-oriented sampling points for a single sub-band. Sub-band Upsampled imaging results To express.

[0109] Then, the results of upsampling each sub-band are compensated for range-direction frequency shift and residual constant phase error to obtain... Finally, the subbands are coherently superimposed in the two-dimensional time domain to obtain... This is the final subband synthetic imaging result.

[0110] Understandably, when compensating for residual constant phase error between sub-bands using sub-band residual constant phase error, the execution order of the upsampling step and the residual constant phase error compensation step can be interchanged. That is, one can first perform range-direction frequency shift and inter-sub-band residual constant phase error compensation on the imaging results of each sub-band, and then perform frequency domain zero-padding on the compensation results to achieve range-direction frequency shift compensation. Double the sampling.

[0111] In addition, range-direction frequency shifting can also be achieved using frequency-domain circular shifting or other methods. Alternatively, subband synthesis can be achieved using frequency-domain coherent superposition.

[0112] Figure 6 This is a schematic flowchart of another subband synthetic imaging method for ultra-wideband stepped frequency modulated SAR provided in an embodiment of this application. Figure 6 As shown, for any two subbands of an ultra-wideband stepped frequency modulated SAR: subband 1 and subband 2, error compensation and imaging processing can be performed respectively.

[0113] The error compensation and imaging processing for sub-band 1 can be performed as follows: First, sub-band 1 self-closed-loop data is acquired; then, errors are extracted from this sub-band 1 self-closed-loop data, including phase error extraction, amplitude error extraction, and delay error extraction; finally, a sub-band 1 matched filter is constructed based on the extracted errors. Simultaneously, the sub-band 1 echo signal can also be acquired. Based on the constructed sub-band 1 matched filter, the range migration algorithm is used to perform imaging processing on the sub-band 1 echo signal to obtain the sub-band 1 imaging result.

[0114] The same processing method can be used to perform error compensation and imaging processing on sub-band 2 to obtain the imaging results of sub-band 2.

[0115] Then, residual constant phase error can be extracted using the imaging results of sub-band 1 and sub-band 2. Based on the extracted results, range-direction frequency shift and constant phase error compensation can be performed on the imaging results of sub-band 1 and sub-band 2, respectively. Finally, the compensation results are coherently superimposed to obtain the sub-band synthetic imaging result.

[0116] Specifically, the imaging results of sub-band 1 and sub-band 2 can be subjected to range upsampling separately before range-direction frequency shift and constant phase error compensation. Alternatively, range upsampling can be performed separately after range-direction frequency shift and constant phase error compensation is applied to the imaging results of sub-band 1 and sub-band 2.

[0117] The technical solution provided in this application comprehensively considers various errors within and between sub-bands in stepped frequency modulated SAR, and can effectively achieve high-quality stepped frequency modulated SAR imaging; it performs joint error estimation based on self-closed-loop data and special points, and performs error compensation in two steps during and after sub-band imaging, which can effectively improve the accuracy of error compensation; no iterative operation is required in the error extraction process, resulting in high execution efficiency.

[0118] To verify the technical effect of the technical solution provided in the embodiments of this application, the following experiment was designed: An experiment was conducted using airborne four-subband stepped frequency-modulated SAR echo data, and the processed subband synthetic imaging results are shown in Figure 7. Figure 7 Taking the two local areas marked by the red box in the middle as examples, a comparison is made between the single subband and the subband synthesis results, as shown in Figure 8.

[0119] Figure 8The horizontal direction represents the range. The two images on the left show the single-subband imaging results, and the two images on the right show the subband composite imaging results. Measurements show that the 3dB main lobe width in the range direction for the middle corner reflector in the lower left image is 8.2 cm, and the same corner reflector in the lower right image has a 3dB main lobe width of 2.1 cm, achieving a fourfold improvement in range resolution. These results demonstrate the effectiveness of the subband composite imaging method for ultra-wideband stepped frequency modulated SAR proposed in this application.

[0120] All of the above-mentioned optional technical solutions can be combined in any way to form the optional embodiments of this application, and will not be described in detail here.

[0121] The following are embodiments of the apparatus described in this application, which can be used to execute the embodiments of the method described in this application. For details not disclosed in the apparatus embodiments of this application, please refer to the embodiments of the method described in this application.

[0122] Figure 9 This is a schematic diagram of a subband synthetic imaging device for ultra-wideband stepped frequency modulated SAR provided in an embodiment of this application. Figure 9 As shown, the device includes:

[0123] The extraction module 901 is configured to extract sub-band errors of ultra-wideband stepped frequency modulated synthetic aperture radar (SAR) using self-closed-loop data; wherein each sub-band error includes intra-sub-band phase error, inter-sub-band delay error and constant phase error, as well as intra-sub-band and inter-sub-band amplitude errors.

[0124] Construction module 902 is configured to construct each sub-band range-directed matched filter based on the extracted sub-band error;

[0125] Imaging module 903 is configured to use a range-matched filter to perform range-direction pulse compression on the echo data of each sub-band to complete imaging of each sub-band separately.

[0126] The estimation module 904 is configured to estimate the inter-subband residual constant phase error using prominent points within the imaging scene.

[0127] The compensation module 905 is configured to compensate for the imaging results of each sub-band using the residual constant phase error between sub-bands, and to superimpose the compensated imaging results of each sub-band to obtain the SAR sub-band synthetic imaging result.

[0128] According to the technical solution provided in this application, the errors of each sub-band of ultra-wideband stepped frequency modulated SAR are extracted using self-closed-loop data, and the extracted sub-band errors are used to construct range-matched filters for each sub-band. Then, the constructed range-matched filters are used to perform range pulse compression on the echo data of each sub-band to complete the imaging of each sub-band separately. At the same time, the residual constant phase error between sub-bands is estimated using prominent points in the imaging scene. Finally, the estimated residual constant phase error between sub-bands is used to compensate for the imaging results of each sub-band, and the compensated imaging results of each sub-band are superimposed to obtain the SAR sub-band composite imaging result. This method can effectively improve the error compensation accuracy, achieve high-quality stepped frequency modulated SAR imaging, and does not require iterative operations in the error extraction process, resulting in high execution efficiency.

[0129] In some implementations, the sub-band phase error of an ultra-wideband stepped frequency modulated SAR target sub-band is extracted using self-closed-loop data, including: acquiring N frames of self-closed-loop data of the target sub-band; N being a positive integer greater than 1; performing range-direction matched filtering on each frame of self-closed-loop data of the target sub-band using an ideal matched filter to obtain N range compressed signals; locating the range gate where the amplitude peak is located in each range compressed signal; adding a window centered on the located range gate and extracting data segments; performing Fourier transform, complex multiplication, and phase taking operations on the extracted data segments sequentially to obtain the frequency domain phase error gradient corresponding to each frame of self-closed-loop data; averaging the frequency domain phase error gradients corresponding to each frame of self-closed-loop data to obtain the average phase error gradient; and summing the average phase error gradients to obtain the sub-band phase error of the target sub-band; wherein, the target sub-band is any sub-band self-closed-loop data of an ultra-wideband stepped frequency modulated SAR.

[0130] In some implementations, the inter-subband delay error and constant phase error of the target subband of the ultra-wideband stepped frequency modulated SAR are extracted using self-closed-loop data. This includes: extracting the spectral phase of the target subband closed-loop data after range pulse compression; linearly fitting the spectral phase of the target subband closed-loop data along the range direction frequency using the least squares method to obtain a first-order fitting polynomial; and determining the relative delay error and relative constant phase error of the target subband based on the coefficients of the first-order fitting polynomial, using the first subband of the ultra-wideband stepped frequency modulated SAR as a reference. Wherein, the target subband is any subband of the ultra-wideband stepped frequency modulated SAR; the first-order fitting polynomial is... ; The spectral phase of the target subband closed-loop data after range pulse compression. The target sub-band number, For range frequency, The coefficients of the linear term, The constant term is used; the relative delay error of the target subband is... ; The linear term coefficients of the first sub-band are given; the relative constant phase error of the target sub-band is... ; This is the constant term for the first sub-band.

[0131] In some implementations, the intra-subband and inter-subband amplitude errors of the target subband of the ultra-wideband stepped frequency modulated SAR are extracted using self-closed-loop data, including: extracting the spectral amplitude of each subband after range pulse compression; determining the average spectral amplitude of the first subband of the ultra-wideband stepped frequency modulated SAR as the reference amplitude; and determining the error value between the spectral amplitude of the target subband and the reference amplitude as the intra-subband and inter-subband amplitude errors of the target subband; wherein, the target subband is any subband of the ultra-wideband stepped frequency modulated SAR.

[0132] In some implementations, any sub-band The range-directed matched filter is: ;in, For children The distance-directed matched filter, It is a positive integer. For range-direction frequency, symbol Represents the power exponent. For children The amplitude error within and between sub-bands, Indicates exponentiation. It is the symbol for imaginary numbers. For children Sub-band phase error, For children Subband delay error, For children The constant phase error, To adjust the frequency of the transmitted signal.

[0133] In some implementations, the inter-subband residual constant phase error is estimated using prominent points within the imaging scene, including: acquiring any prominent point within the imaging scene; extracting local regions where the prominent points are located from the imaging results of each sub-band, performing inverse fast Fourier transform in the local regions to obtain the range spectral phase of the prominent points in each sub-band; performing linear regression on the range spectral phase of the prominent points in each sub-band to obtain a first-order regression polynomial; weighting the first-order coefficients in the first-order regression polynomials corresponding to each sub-band to obtain common first-order coefficients; refitting the first-order regression polynomials corresponding to each sub-band using the common first-order coefficients to obtain updated first-order regression polynomial constant terms; determining the difference between the updated first-order regression polynomial constant term of the target sub-band and the updated first-order regression polynomial constant term of the first sub-band of the ultra-wideband stepped frequency modulated SAR as the inter-subband residual constant phase error of the target sub-band; wherein, the common first-order coefficients are obtained using the formula... Calculated; For common first-order coefficients, This represents the target sub-band number, where the target sub-band can be any sub-band. For the number of sub-bands, For children The first-order coefficients of the first-order regression polynomial, For children The weighting coefficients; the constant term of the first-order regression polynomial after the target subband update is expressed by the formula. Calculated; For children The updated constant term of the first-order regression polynomial, For children The first-order regressive polynomial, For range-direction frequency.

[0134] In some implementations, the residual constant phase error between sub-bands is used to compensate for the imaging results of each sub-band, including: zero-padding the imaging results of each sub-band in the range direction in the frequency domain to achieve range-direction zero-padding. Doubling the sampling rate; Number of sub-bands; use the formula Range-direction frequency shift and inter-subband residual constant phase error compensation are performed on the upsampled sub-band imaging results to obtain the compensated sub-band imaging results; among which... For the compensated sub-band Imaging results, sub-band For any sub-band, Subband after upsampling Imaging results, Indicates exponentiation. It is the symbol for imaginary numbers. The center frequency spacing between adjacent sub-bands For distance to fast time, For direction, slow time, Let k be the inter-subband residual constant phase error. The compensated subband imaging results are coherently superimposed in the two-dimensional time domain to obtain the SAR subband composite imaging result. .

[0135] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0136] Figure 10 This is a schematic diagram of the electronic device provided in an embodiment of this application. For example... Figure 10As shown, the electronic device 10 of this embodiment includes: a processor 1001, a memory 1002, and a computer program 1003 stored in the memory 1002 and executable on the processor 1001. When the processor 1001 executes the computer program 1003, it implements the steps in the various method embodiments described above. Alternatively, when the processor 1001 executes the computer program 1003, it implements the functions of each module / unit in the various device embodiments described above.

[0137] Electronic device 10 may be a desktop computer, laptop, handheld computer, cloud server, or other electronic device. Electronic device 10 may include, but is not limited to, a processor 1001 and a memory 1002. Those skilled in the art will understand that... Figure 10 This is merely an example of electronic device 10 and does not constitute a limitation on electronic device 10. It may include more or fewer components than shown, or different components.

[0138] The processor 1001 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0139] The memory 1002 can be an internal storage unit of the electronic device 10, such as a hard disk or RAM of the electronic device 10. The memory 1002 can also be an external storage device of the electronic device 10, such as a plug-in hard disk, Smart Media Card (SMC), Secure Digital (SD) card, FlashCard, etc., equipped on the electronic device 10. The memory 1002 can also include both internal and external storage units of the electronic device 10. The memory 1002 is used to store computer programs and other programs and data required by the electronic device.

[0140] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0141] If an integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program may include computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. A computer-readable medium may include: any entity or device capable of carrying computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0142] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A sub-band synthetic imaging method for ultra-wideband stepped frequency modulated SAR, characterized in that, include: The sub-band errors of ultra-wideband stepped frequency modulated synthetic aperture radar (SAR) are extracted using self-closed-loop data; each sub-band error includes intra-sub-band phase error, inter-sub-band delay error, constant phase error, and intra-sub-band and inter-sub-band amplitude errors. Construct range-guided matched filters for each sub-band based on the extracted sub-band errors; The range-matched filter is used to perform range pulse compression on the echo data of each sub-band to complete the imaging of each sub-band separately; Estimating inter-subband residual constant phase error using prominent points within the imaging scene; The residual constant phase error between sub-bands is used to compensate for the imaging results of each sub-band, and the compensated imaging results of each sub-band are superimposed to obtain the SAR sub-band composite imaging result; Among them, estimating the inter-subband residual constant phase error using prominent points within the imaging scene includes: Acquire any prominent point within the imaging scene; In each sub-band imaging result, a local region where the prominent point is located is extracted, and an inverse fast Fourier transform is performed in the local region to obtain the range-direction spectral phase of the prominent point in each sub-band. A first-order regression polynomial is obtained by performing linear regression on the distance-direction spectral phase of prominent points in each sub-band. The common first-order coefficients are obtained by taking a weighted average of the first-order coefficients in the first-order regression polynomials corresponding to each sub-band. The first-order regression polynomials corresponding to each sub-band are refitted using the common first-order coefficients to obtain the updated first-order regression polynomial constant term. The difference between the constant term of the first-order regression polynomial after the target subband update and the constant term of the first-order regression polynomial after the first subband update of the ultra-wideband stepped frequency modulated SAR is determined as the inter-subband residual constant phase error of the target subband. The common first-order coefficients are expressed by the formula: Calculated; The common first-order coefficients, This represents the target sub-band number, where the target sub-band can be any sub-band. For the number of sub-bands, For children The first-order coefficients of the first-order regression polynomial, For children Weighting coefficients; The constant term of the first-order regression polynomial after the target subband update is expressed by the formula. Calculated; For children The updated constant term of the first-order regression polynomial, For children The first-order regressive polynomial, For range-direction frequency.

2. The sub-band synthetic imaging method for ultra-wideband stepped frequency modulated SAR according to claim 1, characterized in that, The sub-band phase error of an ultra-wideband stepped frequency modulated SAR target sub-band is extracted using self-closed-loop data, including: Obtain N frames of self-closed-loop data from the target subband; N is a positive integer greater than 1. By using an ideal matched filter to perform range-direction matched filtering on each frame of self-closed-loop data in the target subband, N range compressed signals are obtained. Locate the distance gate where the amplitude peak is located in each distance compression signal; Add a window centered on the distance gate obtained from the positioning, and extract the data segment; The extracted data segments are subjected to Fourier transform, complex multiplication, and phase take-off operations in sequence to obtain the frequency domain phase error gradient corresponding to each frame of self-closed-loop data. The average phase error gradient is obtained by averaging the frequency domain phase error gradient corresponding to each frame of self-closed-loop data. The average phase error gradient is accumulated to obtain the sub-band phase error of the target sub-band; The target subband is any subband of self-closed-loop data from ultra-wideband stepped frequency modulated SAR.

3. The sub-band synthetic imaging method for ultra-wideband stepped frequency modulated SAR according to claim 1, characterized in that, The inter-subband delay error and constant phase error of ultra-wideband stepped frequency modulated SAR target subbands are extracted using self-closed-loop data, including: Extracting the spectral phase of the target subband closed-loop data after range pulse compression; The least squares method was used to linearly fit the spectrum phase of the target subband closed-loop data after range pulse compression along the range frequency to obtain a first-order fitting polynomial. Using the first sub-band of the ultra-wideband stepped frequency modulated SAR as a reference, the relative delay error and relative constant phase error of the target sub-band are determined based on the coefficients of the first-order fitting polynomial. Among them, the target subband is any subband of the ultra-wideband stepped frequency modulated SAR; The first-order fitting polynomial is: ; The spectral phase of the target subband closed-loop data after range pulse compression. The target sub-band number, For range frequency, The coefficients of the linear term, For constant terms; The relative delay error of the target sub-band is ; The coefficients of the linear terms in the first sub-band; The relative constant phase error of the target subband is ; This is the constant term for the first sub-band.

4. The sub-band synthetic imaging method for ultra-wideband stepped frequency modulated SAR according to claim 1, characterized in that, The intra-subband and inter-subband amplitude errors of ultra-wideband stepped frequency modulated SAR target subbands are extracted using self-closed-loop data, including: Extract the spectral amplitude of each subband closed-loop data after pulse compression; The average spectral amplitude of the first subband of the ultra-wideband stepped frequency modulated SAR is determined as the reference amplitude; The error value between the spectral amplitude of the target sub-band and the reference amplitude is determined to be the amplitude error within and between the sub-bands of the target sub-band; The target subband is any subband of the ultra-wideband stepped frequency modulated SAR.

5. The sub-band synthetic imaging method for ultra-wideband stepped frequency modulated SAR according to claim 1, characterized in that, Any subband The range-directed matched filter is: ;in, For children The distance-directed matched filter, It is a positive integer. For range-direction frequency, symbol Represents the power exponent. For children The amplitude error within and between sub-bands, Indicates exponentiation. It is the symbol for imaginary numbers. For children Sub-band phase error, For children Subband delay error, For children The constant phase error, To adjust the frequency of the transmitted signal.

6. The sub-band synthetic imaging method for ultra-wideband stepped frequency modulated SAR according to claim 1, characterized in that, The sub-band imaging results are compensated using the inter-sub-band residual constant phase error, including: The imaging results of each sub-band are zero-padded in the frequency domain in the range direction to achieve range-direction zeroing. Doubling the sampling rate; Number of sub-bands; Use formula Range-direction frequency shift and inter-subband residual constant phase error compensation are performed on the upsampled sub-band imaging results to obtain the compensated sub-band imaging results; among which... For the compensated sub-band Imaging results, sub-band For any sub-band, Subband after upsampling Imaging results, Indicates exponentiation. It is the symbol for imaginary numbers. The center frequency spacing between adjacent sub-bands For distance to fast time, For direction, slow time, The inter-subband residual constant phase error is denoted as k. The compensated sub-band imaging results are coherently superimposed in the two-dimensional time domain to obtain the SAR sub-band composite imaging result. .

7. A sub-band synthetic imaging device for ultra-wideband stepped frequency modulated SAR, characterized in that, include: The extraction module is configured to extract sub-band errors of ultra-wideband stepped frequency modulated synthetic aperture radar (SAR) using self-closed-loop data; wherein each sub-band error includes intra-sub-band phase error, inter-sub-band delay error and constant phase error, as well as intra-sub-band and inter-sub-band amplitude errors. The construction module is configured to construct each sub-band range-directed matched filter based on the extracted sub-band error; The imaging module is configured to use the range-matched filter to perform range pulse compression on the echo data of each sub-band, so as to complete the imaging of each sub-band separately; The estimation module is configured to estimate the inter-subband residual constant phase error using prominent points within the imaging scene; The compensation module is configured to compensate for the imaging results of each sub-band using the residual constant phase error between sub-bands, and to superimpose the compensated imaging results of each sub-band to obtain the SAR sub-band composite imaging result; Among them, estimating the inter-subband residual constant phase error using prominent points within the imaging scene includes: Acquire any prominent point within the imaging scene; In each sub-band imaging result, a local region where the prominent point is located is extracted, and an inverse fast Fourier transform is performed in the local region to obtain the range-direction spectral phase of the prominent point in each sub-band. A first-order regression polynomial is obtained by performing linear regression on the distance-direction spectral phase of prominent points in each sub-band. The common first-order coefficients are obtained by taking a weighted average of the first-order coefficients in the first-order regression polynomials corresponding to each sub-band. The first-order regression polynomials corresponding to each sub-band are refitted using the common first-order coefficients to obtain the updated first-order regression polynomial constant term. The difference between the constant term of the first-order regression polynomial after the target subband update and the constant term of the first-order regression polynomial after the first subband update of the ultra-wideband stepped frequency modulated SAR is determined as the inter-subband residual constant phase error of the target subband. The common first-order coefficients are expressed by the formula: Calculated; The common first-order coefficients, This represents the target sub-band number, where the target sub-band can be any sub-band. For the number of sub-bands, For children The first-order coefficients of the first-order regression polynomial, For children Weighting coefficients; The constant term of the first-order regression polynomial after the target subband update is expressed by the formula. Calculated; For children The updated constant term of the first-order regression polynomial, For children The first-order regressive polynomial, For range-direction frequency.

8. 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 computer program, it implements the steps of the method as described in any one of claims 1 to 6.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1 to 6.

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