An ultra-wideband impulse SAR standing wave suppression method and device

Abstract

The application provides an ultra-wideband impulse SAR standing wave suppression method and device, relates to the field of radars, and comprises the following steps: obtaining echo data through ultra-wideband impulse SAR scanning and performing data preprocessing; performing two-dimensional SAR imaging by using the preprocessed echo data to obtain a two-dimensional SAR image with a standing wave; selecting a mismatch frequency range according to a standing wave signal frequency model and actual antenna parameters, and removing in the distance spectrum of the two-dimensional SAR image; extrapolating the removed frequency components by using an energy-weighted least square method to obtain a complete distance spectrum; and transforming the obtained distance spectrum back to an image domain after a certain amplitude weighting to obtain a two-dimensional SAR image after standing wave suppression. The application discards mismatch frequency components in the distance spectrum of the two-dimensional SAR image, realizes the suppression of mismatch signal components, and solves the spectrum leakage and distance resolution loss caused by the removal of the frequency components through spectrum extrapolation.

Description

Technical Field

[0001] This invention relates to the field of radar technology, and specifically to a method and apparatus for suppressing standing waves in ultra-wideband impulse SAR. Background Technology

[0002] Impulse radar, as a typical ultra-wideband radar system, achieves extremely high range resolution by emitting narrow pulse signals on the order of nanoseconds or even picoseconds, thus providing a technological foundation for high-precision imaging with synthetic aperture radar. However, according to antenna impedance matching theory, the input impedance of an antenna is a complex frequency function. When radiating a wideband signal, the real and imaginary parts of the impedance change drastically with frequency, making it difficult to achieve full-band matching with a single circuit. This leads to a deterioration of standing wave characteristics, resulting in a secondary signal with a similar frequency component following the main signal at a fixed distance, causing ringing, false targets, etc., affecting subsequent signal processing processes such as target detection and identification.

[0003] In terms of hardware, resistor loading technology is often used to extend the operating bandwidth of antennas. This involves intentionally connecting a resistor in series or parallel at an appropriate location on the antenna (such as the middle or end of the vibrator) to actively and controllably dissipate some energy, thereby altering the antenna's performance parameters. However, this method inevitably leads to energy loss. For transmitting antennas, this means a higher power amplifier is needed to achieve the same radiated power; for receiving antennas, this means a decrease in the signal-to-noise ratio.

[0004] In signal processing, there is only a limited amount of research on radar standing wave suppression, and these studies are all based on time-domain models of standing wave signals, assuming that the standing wave signal is identical to the main signal except for its amplitude. However, in reality, ultra-wideband signals only have mismatches in a portion of the frequency bands, and the frequency components of the standing wave signal are not entirely identical to the main signal, leading to mismatches in existing models. Summary of the Invention

[0005] To address the above technical problems, this invention provides an ultra-wideband impulse SAR standing wave suppression method and apparatus, which can effectively suppress the effects of standing waves in two-dimensional SAR images. This invention suppresses mismatched signal components by discarding mismatched frequency components from the range spectrum of the two-dimensional SAR image, and then solves the spectral leakage and range resolution loss caused by removing frequency components through spectral extrapolation. The specific technical solution is as follows:

[0006] A method for suppressing standing waves in ultra-wideband impulse SAR includes the following steps:

[0007] Step 1: Acquire echo data through ultra-wideband impulse SAR scanning and perform data preprocessing;

[0008] Step 2: Use the preprocessed echo data to perform two-dimensional SAR imaging to obtain a two-dimensional SAR image with standing waves;

[0009] Step 3: Select the mismatched frequency range based on the standing wave signal frequency model and the actual antenna parameters, and remove it in the range spectrum of the two-dimensional SAR image;

[0010] Step 4: Extrapolate the removed frequency components using the energy-weighted least squares method to obtain the complete distance spectrum;

[0011] Step 5: Perform a certain amplitude weighting on the extrapolated distance spectrum and transform it back to the image domain to obtain a two-dimensional SAR image with standing wave suppression.

[0012] Preferably, in step 1, an impulse SAR system is used to scan the scene to be imaged to acquire raw echo data. ,in Indicates distance in terms of time. Indicates azimuth in slow time; preprocess the echo data by using Hilbert transform to convert the signal from a real signal to a complex signal:

[0013] .

[0014] Preferably, in step 2, a temporal imaging algorithm is used for two-dimensional imaging, specifically as follows:

[0015] ;

[0016] in, Indicates the first Radar echo signals from each location, This represents the total number of directional points. It is the azimuth and imaging point Two-way delay between; It is a two-dimensional SAR imaging result with standing waves.

[0017] Preferably, in step 3, a frequency model of the standing wave signal is first established, and the collected echo is represented as the superposition of the ideal signal and the standing wave signal, with the following spectral expression:

[0018] ;

[0019] in, For ideal conditions, there is no standing wave signal. The spectrum, Here is the spectrum of the standing wave signal, where The time-domain delay between the standing wave signal and the ideal signal. This indicates the amplitude of the standing wave signal at different frequency components;

[0020] antenna operating frequency The range spectrum is obtained by performing a Fourier transform on the range direction of the two-dimensional SAR imaging results, and this frequency band is then set to zero.

[0021] ;

[0022] The obtained distance spectrum .

[0023] Preferably, in step 4, the distance spectrum The result of a certain orientation is represented as a vector. The measured spectrum as energy-weighted least squares is expressed as:

[0024] ;

[0025] in, For the spectrum to be extrapolated, The special Fourier transform matrix is ​​represented as:

[0026] ;

[0027] ;

[0028] in, It is the set of numbers corresponding to the selected frequency. This represents the total number of points in the directional direction.

[0029] Preferably, step 4 further includes: employing a time-domain energy-weighted spectral extrapolation method, the spectral extrapolation process being expressed as:

[0030] ;

[0031] ;

[0032] in, Indicates the extrapolated solution. This forms a diagonal weight matrix, and Let represent the standard inner product in Hilbert space; according to the projection theorem, we derive:

[0033] ;

[0034] This yields the range spectrum of an ideal two-dimensional SAR image without standing waves.

[0035] Preferably, in step 5, the average amplitude ratio of the original spectrum to the extrapolated spectrum is first calculated:

[0036] ;

[0037] The range spectrum of the two-dimensional SAR image to be obtained is obtained by weighting based on this ratio:

[0038] ;

[0039] Finally, the two-dimensional SAR image after standing wave suppression is obtained by inverse Fourier transform:

[0040] .

[0041] An ultra-wideband impulse SAR standing wave suppression device includes:

[0042] The data acquisition module acquires echo data through ultra-wideband impulse SAR scanning and performs data preprocessing.

[0043] The imaging module uses preprocessed echo data to perform two-dimensional SAR imaging, obtaining a two-dimensional SAR image with standing waves.

[0044] The removal module selects the mismatched frequency range based on the standing wave signal frequency model and the actual antenna parameters, and removes it in the range spectrum of the two-dimensional SAR image;

[0045] The extrapolation module uses the energy-weighted least squares method to extrapolate the removed frequency components to obtain the complete distance spectrum;

[0046] The result generation module performs a certain amplitude weighting on the extrapolated distance spectrum and then transforms it back into the image domain to obtain a two-dimensional SAR image with standing wave suppression.

[0047] An electronic device includes: one or more processors; and a memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method.

[0048] A computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, cause the processor to implement the method described thereon.

[0049] The present invention has the following beneficial effects:

[0050] Existing methods using resistor loading at the antenna end result in energy loss, reduced antenna gain, and consequently, a deteriorated signal-to-noise ratio (SNR). In contrast, this method achieves standing wave (SWR) suppression through signal processing, suppressing SWR without increasing hardware overhead or incurring energy loss. This is particularly important for applications such as through-wall detection, where the signal is significantly attenuated after penetrating the wall at least twice during detection, resulting in weak echo signals and a very low SNR. Therefore, this energy-loss-free SWR suppression method is especially crucial.

[0051] Currently, there are few existing standing wave suppression methods based on signal processing techniques. The existing methods do not consider the different impedance matching conditions at different frequencies when mathematically modeling the standing wave signal, and can only be applied under ideal conditions. In addition, compared with other methods that start from the raw radar echo data, this method processes directly on the two-dimensional SAR image, which greatly reduces the amount of data. Moreover, the spectrum extrapolation method used does not involve complex matrix operations, so the computation speed is relatively high. Attached Figure Description

[0052] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0054] The purpose of this invention is to provide a method for suppressing standing waves in ultra-wideband impulse SAR, the specific process of which is as follows:

[0055] Step 1: Acquire echo data through ultra-wideband impulse SAR scanning and perform data preprocessing;

[0056] Step 2: Use the preprocessed echo data to perform two-dimensional SAR imaging to obtain a two-dimensional SAR image with standing waves;

[0057] Step 3: Select the mismatched frequency range based on the standing wave signal frequency model and the actual antenna parameters, and remove it in the range spectrum of the two-dimensional SAR image;

[0058] Step 4: Extrapolate the removed frequency components using the energy-weighted least squares method to obtain the complete distance spectrum;

[0059] Step 5: Perform a certain amplitude weighting on the extrapolated distance spectrum and transform it back to the image domain to obtain a two-dimensional SAR image with standing wave suppression.

[0060] Step 1, the acquisition of echo data and data preprocessing via ultra-wideband impulse SAR scanning, includes the following steps: using an impulse SAR system to scan the scene to be imaged to acquire raw echo data. ,in Indicates distance in terms of time. This indicates the azimuth direction in slow time. The echo data is preprocessed by using a Hilbert transform to convert the signal from a real signal to a complex signal:

[0061] ;

[0062] Step 2, using the preprocessed complex signal for two-dimensional SAR imaging, includes the following steps: Since the signal transmitted by impulse SAR is an ultra-wideband signal with a large instantaneous bandwidth, it is difficult to estimate the Doppler frequency, and commonly used frequency domain imaging algorithms have large errors. Therefore, this invention uses a time domain imaging algorithm, such as the back projection algorithm, for two-dimensional imaging:

[0063] ;

[0064] in, Indicates the first Radar echo signals from each location, This represents the total number of directional points. It is the azimuth and imaging point Two-way delay between them. It is a two-dimensional SAR imaging result with standing waves.

[0065] In step 3, the mismatched frequency range is selected and removed based on the standing wave signal frequency model and the actual antenna parameters. This includes the following steps: First, the frequency model of the standing wave signal is established. The collected echo can be represented as the superposition of the ideal signal and the standing wave signal, and its spectral expression is:

[0066] ;

[0067] in, For ideal conditions, there is no standing wave signal. The spectrum, Here is the spectrum of the standing wave signal, where The time-domain delay between the standing wave signal and the ideal signal. It represents the amplitude of the standing wave signal at different frequency components, reflecting the degree of matching of the antenna with different frequencies of the ultra-wideband signal.

[0068] According to the antenna's performance specifications, we can know... In general, the impedance characteristics of an antenna are relatively stable within its operating frequency band, and its response to different frequency components of the signal is relatively consistent. However, outside the operating frequency band, its phase response undergoes drastic and nonlinear changes, which disrupts the phase relationship between different frequency components of the signal, further aggravating waveform distortion. The operating frequency of the antenna can be obtained by consulting its performance specifications. The range spectrum is obtained by performing a Fourier transform on the range direction of the 2D SAR imaging results, and this frequency band is then set to zero.

[0069] ;

[0070] The obtained distance spectrum Most of the mismatched frequency components have been suppressed, but this direct frequency truncation method leads to spectral leakage and resolution loss.

[0071] Step 4, which involves extrapolating the removed frequency components using the energy-weighted least squares method, mainly includes, since in this invention, each azimuth direction of the two-dimensional SAR image can be processed independently, taking the range spectrum from step 3. The result of a certain orientation is represented as a vector. The measured spectrum as energy-weighted least squares is expressed as:

[0072] ;

[0073] in, The spectrum to be extrapolated is the spectrum of the ideal signal. The special Fourier transform matrix can be represented as:

[0074] ;

[0075] ;

[0076] in, It is the set of numbers corresponding to the selected frequency. This represents the total number of points in the directional direction.

[0077] To obtain the complete spectrum, this invention employs a spectrum extrapolation method based on time-domain energy weighting. This spectrum extrapolation process can be expressed as:

[0078] ;

[0079] ;

[0080] in, Indicates the extrapolated solution. This forms a diagonal weight matrix, and This represents the standard inner product in Hilbert space. (Formula) Ensure extrapolation results Compared with the original spectrum Similarity, which indicates Most of the information in the formula is preserved. The constraints in the formula... This also ensures that most of the energy in the mismatched spectrum is effectively filtered out.

[0081] According to the projection theorem, we can derive:

[0082] ;

[0083] Thus, the range spectrum of an ideal two-dimensional SAR image without standing waves was obtained by extrapolation of the spectrum.

[0084] In step 5, the extrapolated range spectrum is subjected to a certain amplitude weighting and then transformed back into the image domain to obtain the VSWR-suppressed 2D SAR image. This mainly includes the following steps: Since the extrapolated spectrum inevitably has an overall deviation in amplitude from the original spectrum, the average amplitude ratio between the original spectrum and the extrapolated spectrum must be calculated first.

[0085] ;

[0086] The range spectrum of the two-dimensional SAR image to be obtained is obtained by weighting based on this ratio:

[0087] ;

[0088] Finally, the two-dimensional SAR image after standing wave suppression is obtained by inverse Fourier transform:

[0089] .

[0090] The present invention also provides an ultra-wideband impulse SAR standing wave suppression device, comprising:

[0091] The data acquisition module acquires echo data through ultra-wideband impulse SAR scanning and performs data preprocessing.

[0092] The imaging module uses preprocessed echo data to perform two-dimensional SAR imaging, obtaining a two-dimensional SAR image with standing waves.

[0093] The removal module selects the mismatched frequency range based on the standing wave signal frequency model and the actual antenna parameters, and removes it in the range spectrum of the two-dimensional SAR image;

[0094] The extrapolation module uses the energy-weighted least squares method to extrapolate the removed frequency components to obtain the complete distance spectrum;

[0095] The result generation module performs a certain amplitude weighting on the extrapolated distance spectrum and then transforms it back into the image domain to obtain a two-dimensional SAR image with standing wave suppression.

[0096] The present invention also provides an electronic device, comprising: one or more processors; and a memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method.

[0097] The present invention also provides a computer-readable storage medium having executable instructions stored thereon, which, when executed by a processor, cause the processor to implement the method described thereon.

[0098] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0099] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0100] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0101] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0102] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0103] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for suppressing standing waves in ultra-wideband impulse SAR, characterized in that, Includes the following steps: Step 1: Acquire echo data through ultra-wideband impulse SAR scanning and perform data preprocessing; Step 2: Use the preprocessed echo data to perform two-dimensional SAR imaging to obtain a two-dimensional SAR image with standing waves; Step 3: Select the mismatched frequency range based on the standing wave signal frequency model and the actual antenna parameters, and remove it in the range spectrum of the two-dimensional SAR image; Step 4: Extrapolate the removed frequency components using the energy-weighted least squares method to obtain the complete distance spectrum; Step 5: Perform a certain amplitude weighting on the extrapolated range spectrum and transform it back to the image domain to obtain the two-dimensional SAR image after standing wave suppression; In step 3, the frequency model of the standing wave signal is first established. The collected echo is represented as the superposition of the ideal signal and the standing wave signal, and its spectral expression is: ； in, For ideal conditions, there is no standing wave signal. The spectrum, Here is the spectrum of the standing wave signal, where The time-domain delay between the standing wave signal and the ideal signal. This indicates the amplitude of the standing wave signal at different frequency components; antenna operating frequency The range spectrum is obtained by performing a Fourier transform on the range direction of the two-dimensional SAR imaging results, and the frequency bands are then... The spectrum is set to zero: ； In step 4, the distance spectrum The result of a certain orientation is represented as a vector. The measured spectrum as energy-weighted least squares is expressed as: ； in For the spectrum to be extrapolated, The special Fourier transform matrix is ​​represented as: ； ； in It is the set of numbers corresponding to the selected frequency. This represents the total number of points in the distance direction; Step 4 further includes: The spectrum extrapolation process is represented as: ； ； in, Indicates the extrapolated solution. This forms a diagonal weight matrix, and Let represent the standard inner product in Hilbert space; according to the projection theorem, we derive: ； This yields the range spectrum of an ideal two-dimensional SAR image without standing waves; In step 5, first calculate the average amplitude ratio between the original spectrum and the extrapolated spectrum: ； The range spectrum of the two-dimensional SAR image to be obtained is obtained by weighting based on this ratio: ； Finally, the two-dimensional SAR image after standing wave suppression is obtained by inverse Fourier transform: 。 2. The ultra-wideband impulse SAR standing wave suppression method according to claim 1, characterized in that, In step 1, an impulse SAR system is used to scan the scene to be imaged to acquire raw echo data. ,in Indicates distance in terms of time. Indicates direction in slow time; The echo data is preprocessed by using the Hilbert transform to convert the signal from a real signal to a complex signal: 。 3. The ultra-wideband impulse SAR standing wave suppression method according to claim 2, characterized in that, In step 2, a time-domain imaging algorithm is used for two-dimensional imaging, specifically as follows: ； in, Indicates the first Radar echo signals from each location, This represents the total number of directional points. It is the azimuth and imaging point Two-way delay between; It is a two-dimensional SAR imaging result with standing waves.

4. An ultra-wideband impulse SAR standing wave suppression device, used to implement the method of claim 1, characterized in that, include: The data acquisition module acquires echo data through ultra-wideband impulse SAR scanning and performs data preprocessing. The imaging module uses preprocessed echo data to perform two-dimensional SAR imaging, obtaining a two-dimensional SAR image with standing waves. The removal module selects the mismatched frequency range based on the standing wave signal frequency model and the actual antenna parameters, and removes it in the range spectrum of the two-dimensional SAR image; The extrapolation module uses the energy-weighted least squares method to extrapolate the removed frequency components to obtain the complete distance spectrum; The result generation module performs a certain amplitude weighting on the extrapolated distance spectrum and then transforms it back into the image domain to obtain a two-dimensional SAR image with standing wave suppression.

5. An electronic device, characterized in that, include: One or more processors; A memory for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors cause the one or more processors to implement the method of any one of claims 1 to 3.

6. A computer-readable storage medium, characterized in that, It stores executable instructions that, when executed by a processor, cause the processor to implement the method described in any one of claims 1 to 3.

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