Single-channel bistatic radar clutter cancellation method, device and equipment

Abstract

The invention provides a single-channel bistatic radar clutter cancellation method, device and equipment. The method comprises the following steps: acquiring a radar echo signal of a target area; the radar echo signal comprises a moving target signal and a static ground clutter signal; performing range direction processing on the radar echo signal to obtain a range direction processing signal; performing focusing processing based on global orientation resampling on the distance direction processing signal to obtain a first image domain signal; the global orientation resampling is focusing processing on the whole target area; performing focusing processing based on block azimuth resampling on the distance direction processing signal to obtain a second image domain signal; block orientation resampling is focusing processing performed on divided sub-blocks of a target area; performing cancellation processing on the first image domain signal and the second image domain signal to obtain a final moving target signal; the moving target final signal is a moving target signal without clutter. The separation effect of moving target signals and clutters is improved, and the engineering practicability of the scheme is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of radar clutter suppression, and in particular to a single-channel bistatic radar clutter cancellation method. Background Art

[0002] In the field of modern radar detection, there is a growing demand for detecting and imaging moving targets, especially in complex scenarios. Bistatic Forward-looking Synthetic Aperture Radar (BFSAR) technology, with its ability to achieve high-precision SAR focused imaging of the area directly in front of the receiver, has shown great application potential in key areas such as traffic control and battlefield surveillance. However, a major challenge facing BFSAR systems in practical applications is clutter interference. Clutter signals generated by stationary objects can seriously interfere with the detection and imaging quality of moving target signals. Clutter cancellation technology, as a key means to address this problem, aims to effectively remove clutter from echo signals through specific algorithms, thereby improving the detection sensitivity and imaging accuracy of moving target signals. Therefore, how to efficiently and accurately implement clutter cancellation in BFSAR systems has become a technical problem that needs to be urgently addressed in the current field of radar signal processing.

[0003] To address the above technical issues, existing technologies have proposed a variety of clutter suppression and cancellation schemes, which can be mainly summarized into two categories: single-channel clutter suppression methods and multi-channel clutter cancellation methods. Single-channel clutter suppression methods rely on the spectral differences between clutter and moving target signals, filtering out clutter by designing specific filter structures. Multi-channel clutter cancellation methods, on the other hand, utilize multi-path echo signals collected by multiple antennas and achieve separation of clutter and moving target signals through space-time adaptive processing technology. Among them, multi-channel clutter cancellation methods are considered one of the effective ways to solve the BFSAR clutter problem due to their high clutter suppression performance.

[0004] Although the existing technology provides certain solutions for clutter cancellation in the BFSAR system, there are still many deficiencies. Specifically, the clutter suppression method based on a single channel is limited by the two-dimensional spatio-variability characteristics of the clutter spectrum, that is, the wide distribution of clutter in the time domain and Doppler domain, making it difficult to effectively separate the moving target signal from the clutter, thus limiting the application effect of this method in the BFSAR system. On the other hand, although the clutter cancellation method based on multiple channels can theoretically overcome the limitations of the single-channel method, its implementation depends on the installation and arrangement of multiple antennas, which poses strict requirements on the physical structure of the radar system, especially difficult to implement on platforms with limited space (such as fighter jets, missiles). In addition, the acquisition and processing of multi-channel signals bring a huge computational burden, resulting in a decrease in the real-time performance of the system and making it difficult to meet the rapid response requirements in practical applications. Therefore, developing a clutter cancellation technology that can effectively cope with clutter interference in the BFSAR system and has good engineering practicability has become a key problem that urgently needs to be solved in the current radar signal processing field. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the present invention provides a clutter cancellation method, device and equipment for a single-channel bistatic radar.

[0006] The technical problems to be solved by the present invention are realized through the following technical solutions:

[0007] In a first aspect, the present invention provides a clutter cancellation method for a single-channel bistatic radar, which is applied to a single-antenna receiving device and includes:

[0008] Obtain the radar echo signal of the target area; the radar echo signal includes: a moving target signal and a stationary ground clutter signal;

[0009] Perform range-direction processing on the radar echo signal to obtain a range-direction processed signal;

[0010] Perform focusing processing based on global azimuth resampling on the range-direction processed signal to obtain a first image-domain signal; global azimuth resampling is the focusing processing performed on the entire target area;

[0011] Perform focusing processing based on block azimuth resampling on the range-direction processed signal to obtain a second image-domain signal; block azimuth resampling is the focusing processing performed on the divided blocks of the target area;

[0012] Perform cancellation processing on the first image-domain signal and the second image-domain signal to obtain the final moving target signal; the final moving target signal is a moving target signal without clutter.

[0013] Optionally, performing range-direction processing on the radar echo signal to obtain a range-direction processed signal includes:

[0014] Perform a fast Fourier transform in the range direction on the above-mentioned radar echo signal to obtain a first echo transform signal;

[0015] Perform a matched filtering process on the first echo transform signal to obtain a second echo transform signal;

[0016] Perform a wedge transform on the second echo transform signal to obtain a third echo transform signal;

[0017] Perform an inverse fast Fourier transform in the range direction on the third echo transform signal to obtain a range direction processed signal.

[0018] Optionally, performing a matched filtering process on the first echo transform signal to obtain a second echo transform signal includes:

[0019] Multiply the first echo transform signal by a reference matched filtering function to obtain a second echo transform signal.

[0020] Optionally, performing a focusing process based on global azimuth resampling on the range direction processed signal to obtain a first image domain signal includes:

[0021] Obtain a first preset chirp phase filter, a first preset azimuth resampling filter, and a first preset azimuth matching filter; the first preset chirp phase filter, the first preset azimuth resampling filter, and the first preset azimuth matching filter are determined under a second-order space-variant scenario using the motion parameters of a single-antenna receiving device and a transmitting device and the global center reference point of the target area;

[0022] Multiply the first preset chirp phase filter and the range direction processed signal in sequence and perform a fast Fourier transform in the azimuth direction to obtain a first azimuth frequency domain signal;

[0023] Multiply the first azimuth frequency domain signal and the first preset azimuth resampling filter in sequence and perform an inverse Fourier transform in the azimuth direction to obtain a first azimuth time domain signal;

[0024] Multiply the first azimuth time domain signal and the first preset azimuth matching filter in sequence and perform a fast Fourier transform in the azimuth direction to obtain a first image domain signal.

[0025] Optionally, performing a focusing process based on block azimuth resampling on the range direction processed signal to obtain a second image domain signal includes:

[0026] Obtain a second preset frequency modulation phase filter, a second preset azimuth resampling filter, and a second preset azimuth matching filter; the second preset frequency modulation phase filter, the second preset azimuth resampling filter, and the second preset azimuth matching filter are determined using the motion parameters of the single-antenna receiving device and the transmitting device, and the central reference point of the target area sub-block, in a first-order space-variant sub-block scenario; the target area sub-block is an area block obtained by splitting the target area according to a preset division rule;

[0027] Multiply the second preset frequency modulation phase filter and the range processing signal in sequence, and perform a fast Fourier transform in the azimuth direction to obtain a plurality of second azimuth frequency domain signals;

[0028] Multiply each second azimuth frequency domain signal and the second preset azimuth resampling filter in sequence, and perform an inverse Fourier transform in the azimuth direction to obtain a plurality of second azimuth time domain signals;

[0029] Multiply each second azimuth time domain signal and the second preset azimuth matching filter in sequence, and perform a fast Fourier transform in the azimuth direction to obtain a plurality of second image domain sub-signals;

[0030] Stitch the plurality of second image domain sub-signals to obtain a second image domain signal.

[0031] Optionally, perform cancellation processing on the first image domain signal and the second image domain signal to obtain a final moving target signal, including:

[0032] Subtract the second image domain signal from the first image domain signal to obtain a final moving target signal.

[0033] Optionally, the final moving target signal is expressed as:

[0034]

[0035] S CC represents the final moving target signal, S NCS,1 represents the first image domain signal, S NCS,2 represents the second image domain signal, W a represents the azimuth frequency domain rectangular window function, f a represents the azimuth frequency domain variable, f p,1 represents the azimuth focusing position of the target after global azimuth resampling focusing processing, j represents the imaginary unit, R0 represents the round-trip distance of the target at t a =0, L0 represents the remaining phase related to R0, t a represents the azimuth time domain variable, Δγ a,1 represents the remaining azimuth chirp rate of the first image domain signal after global azimuth resampling focusing processing, f p,2Denotes the azimuth focusing position of the second image domain signal after the focusing process of block azimuth resampling, Δγ a,2 Denotes the remaining azimuth chirp rate of the second image domain signal after the focusing process of block azimuth resampling, T a Denotes the synthetic aperture time, and exp(·) denotes the exponential function.

[0036] In a second aspect, the present invention provides a single-channel bistatic radar clutter cancellation device. The single-channel bistatic radar clutter cancellation device includes: an acquisition unit, a processing unit, and a signal cancellation unit;

[0037] The acquisition unit is configured to: acquire the radar echo signal of the target area; the radar echo signal includes: a moving target signal and a stationary ground clutter signal;

[0038] The processing unit is configured to: perform range direction processing on the radar echo signal to obtain a range direction processed signal;

[0039] The processing unit is further configured to: perform a focusing process based on global azimuth resampling on the range direction processed signal to obtain a first image domain signal; the global azimuth resampling is a focusing process performed on the entire target area;

[0040] The processing unit is further configured to: perform a focusing process based on block azimuth resampling on the range direction processed signal to obtain a second image domain signal; the block azimuth resampling is a focusing process performed on the divided blocks of the target area;

[0041] The signal cancellation unit is configured to: perform a cancellation process on the first image domain signal and the second image domain signal to obtain a final moving target signal; the final moving target signal is a moving target signal without clutter.

[0042] In a third aspect, the present invention provides a single-channel bistatic radar clutter cancellation device, including: a processor, a storage medium, and a bus. The storage medium stores machine-readable instructions executable by the processor. When the single-channel bistatic radar clutter cancellation device runs, the processor communicates with the storage medium through the bus, and the processor executes the machine-readable instructions to perform the steps of the single-channel bistatic radar clutter cancellation method according to any one of the above first aspects.

[0043] The present invention provides a clutter cancellation method, apparatus, and device for a single-channel bistatic radar. Among them, a clutter cancellation method for a single-channel bistatic radar, which is applied to a single-antenna receiving device, includes: obtaining a radar echo signal of a target area; the radar echo signal includes: a moving target signal and a stationary ground clutter signal; performing range-direction processing on the radar echo signal to obtain a range-direction processed signal; performing focusing processing based on global azimuth resampling on the range-direction processed signal to obtain a first image-domain signal; global azimuth resampling is a focusing process performed on the entire target area; performing focusing processing based on block azimuth resampling on the range-direction processed signal to obtain a second image-domain signal; block azimuth resampling is a focusing process performed on the divided blocks of the target area; performing cancellation processing on the first image-domain signal and the second image-domain signal to obtain a final moving target signal; the final moving target signal is a moving target signal without clutter. In the present invention, first, since the global and block azimuth resampling processes have different effects on the characteristics of the radar echo signal, such as phase, frequency, and chirp rate, there are differences in characteristics between the first image-domain signal and the second image-domain signal. This difference provides a basis for subsequent cancellation processing, that is, since the clutter still has feature consistency after being respectively processed by global and block azimuth resampling, while the target signal will have different feature manifestations under these two processing methods due to its own movement and other factors. Therefore, in the cancellation processing, the clutter part will cancel each other out in the two signals, while the moving target signal is retained due to the feature difference, improving the separation effect between the moving target signal and the clutter. Further, although this solution also involves signal processing, it does not depend on the installation and arrangement of multiple antennas. Instead, it realizes clutter cancellation by performing different processes (global and block azimuth resampling processes) on the radar echo signal of a single antenna, avoiding the physical structure limitation problem caused by the installation of multiple antennas and the problem of large computational complexity in processing the multi-dimensional echo signals obtained by multiple antennas, improving the real-time performance of system processing, making the method of the present invention more feasible on platforms with limited space or sensitive to computational complexity, and enhancing the engineering practicability of the solution.

[0044] The following will further elaborate on the present invention in conjunction with the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic flow chart of a clutter cancellation method for a single-channel bistatic radar provided by an embodiment of the present invention;

[0046] Figure 2 Exemplarily shows a schematic diagram of the spatial geometric configuration of the transceiver platform;

[0047] Figure 3 Exemplarily shows a schematic diagram of the phase error of the first-order fitted azimuth chirp rate and the phase error of the second-order fitted azimuth chirp rate;

[0048] Figure 4 The process schematic diagram of the block focusing and splicing process is exemplarily shown;

[0049] Figure 5 The comparison result diagram before and after clutter cancellation using the method of the present invention is exemplarily shown;

[0050] Figure 6 The structural schematic diagram of a single-channel bistatic radar clutter cancellation device provided by an embodiment of the present invention;

[0051] Figure 7 The structural schematic diagram of a single-channel bistatic radar clutter cancellation device provided by an embodiment of the present invention. Specific embodiments

[0052] The present invention will be further described in detail below in conjunction with specific embodiments, but the implementation manners of the present invention are not limited thereto.

[0053] In order to improve the separation effect of moving target signals and clutter and improve the real-time performance of system processing and calculation, an embodiment of the present invention provides a single-channel bistatic radar clutter cancellation method. Figure 1 The flow schematic diagram of a single-channel bistatic radar clutter cancellation method provided by an embodiment of the present invention. As Figure 1 shown, it includes:

[0054] S101. Obtain the radar echo signal of the target area.

[0055] The radar echo signal includes: moving target signals and stationary ground clutter signals.

[0056] Figure 2 The schematic diagram of the spatial geometric configuration of the transceiver platform is exemplarily shown. As Figure 2 shown,

[0057] The transmitter irradiates the target area, and the forward-looking receiver (single-antenna receiving device) records the radar echo scattered by the target scene. A Cartesian right-handed coordinate system is established with the nadir point O of the receiver as the origin. The ground is the X-Y plane, and the position of the transmitter is P t (x t ,y t ,h t ), x t ,y t ,h t respectively represent the abscissa, ordinate and vertical coordinate of the transmitter position, and the nadir point of the transmitter is O￠(x t ,y t ,0), x t ,y t, 0 represents the abscissa, ordinate, and vertical coordinate of the point under the transmitter respectively; the velocity of the transmitter is defined as v t (v tx , v ty , 0), v tx , v ty , 0 are the lateral velocity, longitudinal velocity, and vertical velocity of the transmitter respectively; the velocity and acceleration of the receiver are v r (0, v ry , v rz ) and a r (a rx , a ry , a rz ). 0, v ry , v rz represent the lateral velocity, longitudinal velocity, and vertical velocity of the receiver respectively, and a rx , a ry , a rz represent the lateral acceleration, longitudinal acceleration, and vertical acceleration of the receiver. For any moving target M at an arbitrary position in the scene, at the moment of the synthetic aperture center, it is located at (x m , y m , 0), and its velocity is v m (v mx , v my , 0). The center point C(0, y c , 0) of the scene irradiated by the beam is used as the reference point. Then the two-way distance history R(t a ) of any ground moving target can be expressed as:

[0058]

[0059] where t a is the azimuth variable. It can be seen that the two-way distance history shows a double-square root form, which is not conducive to the derivation of the signal analytical formula. The present invention proposes a distance model suitable for the BFSAR configuration when the receiver has both three-axis acceleration and descent velocity, which can be written as:

[0060]

[0061] Furthermore, operations such as changing the expansion order of the Taylor series in the derivation processes of the slant range history model and the filtering function, for example, increasing the Taylor approximation order in formula (2) and then performing the derivation, can also achieve the same effect as the method proposed in the present invention.

[0062] where

[0063]

[0064] where

[0065]

[0066] Among them, R0 is the two-way distance of the moving target at time t a = 0. It can be seen that the imaging parameters b1, b2, and b3 are all determined by the positions and motion states of the moving target and the platform. It can be seen that when the speed v of the moving target m = 0, the distance model shown in formula (2) can also represent the two-way distance history of a stationary target.

[0067] The transmitter radar emits a chirp signal, and the scene echo signal (radar echo signal) s received by the receiver echo (t, t a ) can be expressed as:

[0068]

[0069] Among them, t is the distance time-domain variable, and the corresponding distance frequency-domain variable is f r . γ is the chirp rate of the transmitted signal, c is the speed of light, λ is the carrier wavelength of the transmitted signal, and its corresponding carrier frequency is f c . w r (·) and w a (·) are the distance time-domain rectangular window function and the azimuth time-domain rectangular window function of the transmitter signal, respectively.

[0070] S102. Perform range-direction processing on the radar echo signal to obtain a range-direction processed signal.

[0071] Optionally, S102 includes:

[0072] Perform a range-direction fast Fourier transform on the aforementioned radar echo signal to obtain a first echo transform signal;

[0073] Perform matched filtering processing on the first echo transform signal to obtain a second echo transform signal;

[0074] Perform a wedge transform on the second echo transform signal to obtain a third echo transform signal;

[0075] Perform an inverse range-direction fast Fourier transform on the third echo transform signal to obtain a range-direction processed signal.

[0076] Optionally, performing matched filtering processing on the first echo transform signal to obtain a second echo transform signal includes:

[0077] Multiply the first echo transform signal by a reference matched filtering function to obtain a second echo transform signal.

[0078] Next, perform a range-direction fast Fourier transform on the original echo signal. Using the stationary phase method, the corresponding range frequency-domain signal (first echo transform signal) S1(fr ,t a ) The expression is as follows:

[0079]

[0080] Among them, W r (f r ) is the distance envelope function of the distance spectrum, and f τ = f c + f r , representing the instantaneous distance frequency domain variable.

[0081] The reference matched filtering function can be set as:

[0082]

[0083] Among them, b 10 , b 20 and b 30 are the values of b1, b2, and b3 with respect to the reference point C, respectively.

[0084] Multiplying Equation (6) and Equation (7) gives the expression of the signal (the second echo transformation signal) S2(f r ,t a ) after matched filtering as:

[0085]

[0086] Among them:

[0087]

[0088] Then, performing the Keystone transform on S2(f r ,t a ), the Keystone transform can be written as:

[0089]

[0090] The signal after the Keystone transform (the third echo transformation signal) can be written as:

[0091]

[0092] Since f r << f c , there is:

[0093]

[0094] Therefore, Equation (11) can be expressed as:

[0095]

[0096] In Equation (13), the first exponential term represents the range to the focusing position and the residual range migration, and the second exponential term represents the azimuth modulation term. In BFSAR, the residual range migration term and the cubic azimuth modulation term can usually be ignored, while the quadratic azimuth modulation term has a large spatial variation and cannot be ignored. Therefore, performing an inverse FFT in the range direction on S3(f r ,t a ) to the time domain, the expression for the range-direction processed signal can be obtained as:

[0097]

[0098] where f m =-Δb1 / λ, γ a =-2Δb2 / λ. f m represents the focusing frequency of the target, and γ a represents the azimuth chirp rate of the signal. In Equation (14), the first exponential term represents the range constant phase and can be ignored; the second exponential term represents the azimuth focusing position; the third exponential term represents the quadratic azimuth modulation term, which is the key to the focusing process.

[0099] For the convenience of subsequent derivation, f m is decomposed into the Doppler frequency position component and the Doppler frequency velocity component. Combining Equations (3), (4), and (9), we can obtain:

[0100]

[0101] where f n represents the Doppler frequency position component, and f v represents the Doppler frequency velocity component.

[0102]

[0103] S103. Perform focusing processing on the range-direction processed signal based on global azimuth resampling to obtain the first image-domain signal.

[0104] Among them, global azimuth resampling is the focusing processing performed on the entire target area.

[0105] Optionally, S103 includes: obtaining a first preset frequency modulation phase filter, a first preset azimuth resampling filter, and a first preset azimuth matching filter; the first preset frequency modulation phase filter, the first preset azimuth resampling filter, and the first preset azimuth matching filter are determined using the motion parameters of the single-antenna receiving device and transmitting device and the global center reference point of the target area in a second-order spatially variant scenario;

[0106] Multiply the first preset frequency modulation phase filter and the range-direction processed signal in sequence and perform a fast Fourier transform in the azimuth direction to obtain the first azimuth frequency-domain signal;

[0107] Multiply the first azimuth frequency-domain signal and the first preset azimuth resampling filter in sequence, and then perform an inverse Fourier transform in the azimuth direction to obtain the first azimuth time-domain signal;

[0108] Multiply the first azimuth time-domain signal and the first preset azimuth matching filter in sequence, and then perform a fast Fourier transform in the azimuth direction to obtain the first image-domain signal.

[0109] Analyze the quadratic azimuth modulation term in formula (14) for s4(t, t m ). The variation of the azimuth modulation frequency γ a along the azimuth frequency can be approximated by polynomial fitting, but it will introduce a phase error, which can be expressed as:

[0110]

[0111] where Δγ a represents the polynomial fitting error of the azimuth modulation frequency along the azimuth frequency. The phase error caused by the polynomial fitting approximation corresponding to any target in the scene can be calculated according to formula (19). The phase errors of the first-order fitting azimuth modulation frequency and the second-order fitting azimuth modulation frequency are as Figure 3 shown. The allowable upper limit of the phase error is π / 4. Therefore, the azimuth modulation frequency γ a needs to be approximated by a second-order polynomial to meet the requirements. According to the above analysis, assume that the azimuth modulation frequency γ a is approximated as γ a1 , which can be written as:

[0112]

[0113] where E1, E2, and F are the first fitting coefficient, the second fitting coefficient, and the third fitting coefficient respectively, and G(R0) is the fitting function that varies with range for K a . For simplicity, G(R0) is denoted as G. A set of γ a1 , f n , f vWith the R0 sequence values, the values of E1, E2, F, and G can be obtained through numerical fitting. This process can refer to the literature "X. Wang et al., 'Fast Universal Azimuth Signal Modeling for Maneuvering-Platform BFSAR Imaging,' in IEEE Transactions on Geoscience and Remote Sensing, vol. 62, pp. 1-17, 2024, Art no. 5215617, doi: 10.1109 / TGRS.2024.3420944".

[0114] Based on the above analysis, the focusing process based on global azimuth resampling is given below:

[0115] First, a to-be-determined chirp phase needs to be introduced in the azimuth time domain, that is, the first preset chirp phase filter H UFM,1 (t m ):

[0116]

[0117] The range processing signal corresponding to formula (14) is multiplied by the first preset chirp phase filter corresponding to formula (21), and then transformed to the azimuth frequency domain (performing fast Fourier transform in the azimuth direction), and the phase expression of the first azimuth frequency domain signal can be obtained:

[0118]

[0119] Among them, f a is the frequency domain variable corresponding to t m . Then, an azimuth resampling factor (the first preset azimuth resampling filter) is introduced. The first preset azimuth resampling filter can be written as:

[0120]

[0121] Among them, Y2, Y3, q2, q3, and q4 are azimuth resampling parameters. Using these parameters to perform azimuth resampling on the signal can correct the space-variant. The azimuth frequency domain signal with the introduced azimuth resampling factor is subjected to inverse Fourier transform, and by combining formula (15) and formula (20), the first azimuth time domain signal Φ6(t m ) can be obtained:

[0122]

[0123] Among them:

[0124]

[0125]

[0126] The signal phase Φ6(t m ), the first item is related to t m The irrelevant constant term does not affect the focus of the signal and can be ignored. The second term represents the focus position of the target in the azimuth frequency domain. The third, fourth and fifth terms are the focus position offsets caused by the azimuth resampling operation, which are related to f n and f v The sixth term is the distance-variant term of the azimuth frequency modulation. For a certain distance unit, its value is constant and can be compensated by matching filtering. The seventh and eighth terms are the first-order and second-order space-variant terms of the azimuth frequency modulation, respectively. The ninth term is the relationship between the azimuth frequency modulation and the target velocity Doppler f. v The relevant components of f v The sign of is determined. It can be seen that to eliminate the null-variant terms of the target focus position and azimuth modulation frequency, it is necessary to set:

[0127] J i =0, i=2,3,4,6,7; (34)

[0128] From equation (34), the azimuth resampling parameters can be obtained as:

[0129]

[0130] After the influence of the above-mentioned space-varying and Doppler frequency velocity components is eliminated, a first preset azimuth matching filter can be constructed to perform azimuth focusing. The first preset azimuth matching filter H AM (t m ) can be written as:

[0131]

[0132] The first azimuth time domain signal corresponding to the phase shown in formula (24) is multiplied by the first preset azimuth matched filter shown in formula (36), and then the multiplication result is subjected to azimuth fast Fourier transform. After the signal is transformed into the azimuth frequency domain, the focusing result (first image domain signal) can be obtained. The first image domain signal S NCS,1 (f a ) can be expressed as:

[0133]

[0134] in:

[0135] f p,1 =ε(f n +f v );(38)

[0136]

[0137] Δγ a,1 = L1f v ;(40)

[0138]

[0139] It can be seen that after global azimuth resampling, the azimuth focusing position of the moving target changes from f m to f p,1 , where ε is its broadening coefficient. At the same time, the space-variant terms related to f n are eliminated. For the ground stationary target, f v = 0. Therefore, the clutter energy in the echo signal corresponding to the ground stationary target is effectively concentrated, which is beneficial to subsequent clutter cancellation operations. However, due to the lack of consideration of the terms related to f v in the azimuth chirp rate, there is a slight defocusing in the focusing result of the moving target signal energy, but it can be ignored.

[0140] So far, the first image domain signal S NCS,1 is obtained.

[0141] In addition, it should be noted that the first preset azimuth matching filter can also be re-derived and designed, that is, splitting or combining the expression of the filter, which can achieve the same effect as the algorithm proposed in this patent. In addition, in the focusing processing part, when the signal parameters vary slightly spatially, changing the focusing processing based on global azimuth resampling to the conventional range-Doppler algorithm can also achieve the focusing processing, or modifying the undetermined chirp phase and azimuth resampling factor given in the present invention, that is, adjusting the order of azimuth resampling, can achieve the same effect as the method proposed in the present invention.

[0142] S104. Perform focusing processing on the range-direction processed signal based on block azimuth resampling to obtain a second image domain signal.

[0143] Among them, block azimuth resampling is the focusing processing performed on the sub-blocks divided from the target area.

[0144] Optionally, S104 specifically includes:

[0145] Obtain a second preset chirp phase filter, a second preset azimuth resampling filter, and a second preset azimuth matching filter; the second preset chirp phase filter, the second preset azimuth resampling filter, and the second preset azimuth matching filter are determined in the first-order space-variant sub-block scenario by using the motion parameters of the single-antenna receiving device and the transmitting device and the central reference point of the target area sub-block; the target area sub-block is the area block obtained by splitting the target area according to the preset division rule;

[0146] Multiply the second preset FM phase filter and the range processed signal in sequence and then perform azimuth fast Fourier transform to obtain multiple second azimuth frequency domain signals;

[0147] Multiply each second azimuth frequency domain signal and the second preset azimuth resampling filter in sequence and then perform inverse azimuth Fourier transform to obtain multiple second azimuth time domain signals;

[0148] Multiply each second azimuth time domain signal and the second preset azimuth matched filter in sequence and then perform azimuth fast Fourier transform to obtain multiple second image domain sub-signals;

[0149] Stitch multiple second image domain sub-signals to obtain a second image domain signal.

[0150] It can be seen from Figure 3 that although globally the phase error of the first-order fitted azimuth FM rate exceeds π / 4, within the vicinity of azimuth frequency 0, the phase error of the first-order fitted azimuth FM rate remains within π / 4. Therefore, the idea of azimuth block focusing and then stitching can be used to keep the phase error of the first-order fitted azimuth FM rate within π / 4 within each azimuth sub-block. After sub-block focusing processing, sub-block stitching can be performed to obtain another focusing result.

[0151] In addition, it should be noted that the preset division rule can be target region blocks obtained by dividing the target region according to a preset division size. Figure 4 An exemplary schematic diagram of the process of block focusing and then stitching is shown, Figure 4 Taking the number of blocks as 2 as an example, the aforementioned reference point C is respectively set as reference point 1 and reference point 2, and then focusing processing based on block azimuth resampling is respectively performed to obtain a focusing processed image according to reference point 1 and a focusing processed image according to reference point 2, as shown in Figure 4 the upper left and upper right figures in the middle. Due to the spatially variant characteristic of the azimuth FM rate of the range processed signal, the focusing effect of the block azimuth resampling processing is worse for regions farther away from the reference point. Therefore, after the focusing processing based on block azimuth resampling, the regions within the sub-blocks of each second image domain sub-signal are well focused, while the regions outside the sub-blocks are poorly focused. Therefore, corresponding sub-blocks are respectively cropped from each second image domain sub-signal, and then these sub-blocks are stitched in sequence to obtain an image with good global focusing of the entire target region. The focusing processing based on block azimuth resampling is specifically as follows:

[0152] Assume that the second-order spatial variation is negligible within each azimuth sub-block, and the azimuth FM rate γ a can be approximated by a first-order polynomial. Let the azimuth FM rate γ a be approximated as γ a2 , which can be written as:

[0153] γ a2 = E1·f n + F·f v + G; (43)

[0154] Here, E1, F, and G are fitting coefficients, with the same meanings as in the previous step. For how to obtain the values of E1, F, and G, please refer to the literature "X. Wang et al., 'Fast Universal Azimuth Signal Modeling for Maneuvering-Platform BFSAR Imaging,' in IEEE Transactions on Geoscience and Remote Sensing, vol. 62, pp. 1-17, 2024, Art no. 5215617, doi: 10.1109 / TGRS.2024.3420944". Repeat the multi-parameter azimuth resampling process in step S103:

[0155] First, it is necessary to introduce a to-be-determined frequency modulation phase in the azimuth time domain, that is, the second preset frequency modulation phase filter H UFM,2 (t m ):

[0156]

[0157] Multiply the range processing signal corresponding to formula (14) by the second preset frequency modulation phase filter of formula (44), and then transform it to the azimuth frequency domain (perform fast Fourier transform in the azimuth direction), and the phase expression Φ7(f a ) of the second azimuth frequency domain signal can be obtained as:

[0158]

[0159] Among them, f a is the frequency domain variable corresponding to t[[ID=3^4]] m . Then, introduce the second preset azimuth resampling filter, and the processed result H NCS,2 (f a ) can be written as:

[0160]

[0161] Among them, Y2, q2, and q3 are the parameters of azimuth resampling. Perform the inverse Fourier transform on the azimuth frequency domain signal introduced with the azimuth resampling factor, and combine formula (15) and formula (43) to obtain the phase expression Φ8(t m ) of the second azimuth time domain signal:

[0162]

[0163] Wherein:

[0164]

[0165]

[0166] Among them, J0, J1, and J5 have been given in step S103.

[0167] To eliminate the cross terms of the null variation and f n and f v Let K2, K3, and K6 be equal to zero to establish an equation. The expressions of the azimuth resampling parameters Y2, q2, and q3 are the same as those listed in Equation (35).

[0168] Then, a second preset azimuth matching filter as shown in Equation (36) can be constructed and multiplied by the second azimuth time-domain signal Φ8(t m ) to perform azimuth focusing.

[0169] Finally, after performing an azimuth fast Fourier transform to transform the signal into the azimuth frequency domain, the focusing result (the second image domain sub-signal) can be obtained. The second image domain sub-signal can be expressed as:

[0170]

[0171] Wherein:

[0172]

[0173]

[0174] By selecting different sub-block center reference points and performing the above-mentioned block azimuth resampling processing respectively, a series of second image domain sub-signals can be obtained. Then, these second image domain sub-signals are stitched together to obtain the second image domain signal. Since the targets of these second image domain sub-signals are fully focused in the sub-blocks, the cropping and stitching operations only remove the signals outside the sub-blocks, and the signals inside the sub-blocks will not be affected. Therefore, the second image domain signal can also be represented by S NCS,2 is represented. Thus, the second image domain signal S NCS,2 is obtained.

[0175] S105. Cancel the first image domain signal and the second image domain signal to obtain the final moving target signal.

[0176] Among them, the final moving target signal is a moving target signal without clutter.

[0177] Optionally, S105 may specifically include:

[0178] Subtract the first image domain signal from the second image domain signal to obtain the final moving target signal.

[0179] Perform a cancellation operation on the first image domain signal and the second image domain signal. This process can be expressed as:

[0180]

[0181] S CC represents the final moving target signal, S NCS,1 represents the first image domain signal, S NCS,2 represents the second image domain signal, W a represents the azimuth frequency domain rectangular window function, f a represents the azimuth frequency domain variable, f p,1 represents the azimuth focusing position of the target after global azimuth resampling focusing processing. j represents the imaginary unit, and R0 represents the two-way distance of the target at t a = 0. The remaining phase related to R0 is represented by L0, and t a represents the azimuth time domain variable, Δγ a,1 represents the remaining azimuth chirp rate of the first image domain signal after global azimuth resampling focusing processing, f p,2 represents the azimuth focusing position of the second image domain signal after block azimuth resampling focusing processing, Δγ a,2 represents the remaining azimuth chirp rate of the second image domain signal after block azimuth resampling focusing processing, T a represents the synthetic aperture time, and exp(·) represents the exponential function.

[0182] Furthermore, the azimuth time domain variable and the azimuth frequency domain variable are fixed and are only determined by the sampling time of the received signal of the receiver and the pulse repetition frequency of the transmitter.

[0183] For a stationary target, there is f v = 0. Therefore, we have:

[0184]

[0185] Since azimuth blocks are performed in the focusing processing based on azimuth resampling, Δγ a,2 can be regarded as 0. Therefore, for a stationary target, S NCS,1 - S NCS,2 = 0, and the clutter corresponding to the stationary target is completely cancelled.

[0186] For a moving target, f v ≠ 0, and we have:

[0187]

[0188] Therefore, for moving targets, S NCS,1 -S NCS,2 ≠0, the moving targets will not be canceled, and due to different focusing positions, each moving target will leave two signal points in S CC . At the same time, Δγ a,1 and Δγ a,2 are usually small, and the two signal points formed by the moving target signals can be considered to have completed coarse aggregation and can be used for moving target detection.

[0189] In summary, in the obtained signal S CC after clutter cancellation, the clutter is eliminated, the moving target signals are retained, and can be used for moving target detection.

[0190] To verify the effectiveness of a single-channel bistatic radar clutter cancellation method provided by an embodiment of the present invention, a simulation experiment was also carried out. The experimental data used the radar echo data of a certain area, and the radar echo data included moving target signals and stationary ground clutter. Figure 5 Exemplarily, a comparison result graph before and after clutter cancellation using the method of the present invention is shown. As Figure 5 shown. The dashed line (green) represents the azimuth profile of the focusing result using global azimuth resampling before clutter cancellation. It can be seen that the moving target signals are completely masked by the clutter. The signal after clutter cancellation by the method of the present invention is shown as the solid line (orange). The moving target signals form two focused spikes, while the clutter is significantly suppressed, verifying the effectiveness of the proposed method.

[0191] The single-channel bistatic radar clutter cancellation method proposed by the present invention, in a single-channel configuration, using a set of transceiver antenna equipment, in the echo signal of BFSAR, can suppress the ground clutter signal in the echo signal of a complex imaging scene containing moving targets, retain the moving target signals and make the moving target signals appear in coarse focus, improve the signal-to-clutter ratio of the signal, and facilitate the detection of moving targets. Therefore, the present invention can detect moving targets in the area directly in front of the receiving radar and can be used in fields such as traffic monitoring and battlefield reconnaissance.

[0192] In addition, not limited to the application of airborne BFSAR, in the BFSAR applications carried on platforms such as unmanned aerial vehicles, missiles, and satellites, using the method proposed by the present invention can suppress the clutter in the echo signal, thus facilitating the detection of moving targets, and is beneficial to the extraction, identification, and positioning of moving targets in the monitoring area, and has broad application prospects in military, civilian, remote sensing and other fields.

[0193] An embodiment of the present invention provides a clutter cancellation method for a single-channel bistatic radar, which is applied to a single-antenna receiving device and includes: obtaining a radar echo signal of a target area; the radar echo signal includes: a moving target signal and a stationary ground clutter signal; performing range-direction processing on the radar echo signal to obtain a range-direction processed signal; performing focusing processing based on global azimuth resampling on the range-direction processed signal to obtain a first image-domain signal; global azimuth resampling is a focusing process performed on the entire target area; performing focusing processing based on block azimuth resampling on the range-direction processed signal to obtain a second image-domain signal; block azimuth resampling is a focusing process performed on the divided blocks of the target area; performing cancellation processing on the first image-domain signal and the second image-domain signal to obtain a final moving target signal; the final moving target signal is a moving target signal without clutter. In the present invention, first, since the global and block azimuth resampling processes have different effects on the characteristics of the radar echo signal such as phase, frequency, and chirp rate, there are differences in characteristics between the first image-domain signal and the second image-domain signal. This difference provides a basis for subsequent cancellation processing, that is, since the clutter still has characteristic consistency after passing through the global and block azimuth resampling processes respectively, while the target signal will have different characteristic manifestations under these two processing methods due to its own movement and other factors. Therefore, in the cancellation processing, the clutter part will cancel each other out in the two signals, while the moving target signal is retained due to the characteristic difference, improving the separation effect between the moving target signal and the clutter. Further, although this solution also involves signal processing, it does not depend on the installation and arrangement of multiple antennas, but realizes clutter cancellation by performing different processing (global and block azimuth resampling processing) on the radar echo signal of a single antenna, avoiding the physical structure limitation problem caused by the installation of multiple antennas and the problem of huge computational complexity in processing the multi-dimensional echo signals obtained by multiple antennas, improving the real-time performance of system processing, making the method of the present invention more feasible on platforms with limited space or sensitive to computational complexity, and enhancing the engineering practicability of the solution.

[0194] The method provided by the embodiment of the present invention can be applied to an electronic device. Specifically, the electronic device can be: a desktop computer, a portable computer, a smart mobile terminal, a server, etc., which is not limited in the embodiment of the present invention.

[0195] Based on the same inventive concept, an embodiment of the present invention also provides a clutter cancellation device for a single-channel bistatic radar. Figure 6 It is a schematic structural diagram of a clutter cancellation device for a single-channel bistatic radar provided by an embodiment of the present invention. As Figure 6 shown, it includes: an acquisition unit 601, a processing unit 602, and a signal cancellation unit 603;

[0196] The acquisition unit 601 is configured to: acquire the radar echo signal of the target area; the radar echo signal includes: moving target signals and stationary clutter signals;

[0197] The processing unit 602 is configured to: perform range direction processing on the radar echo signal to obtain a range direction processed signal;

[0198] The processing unit 602 is further configured to: perform focusing processing on the range direction processed signal based on global azimuth resampling to obtain a first image domain signal; the global azimuth resampling is a focusing process performed on the entire target area;

[0199] The processing unit 602 is further configured to: perform focusing processing on the range direction processed signal based on block azimuth resampling to obtain a second image domain signal; the block azimuth resampling is a focusing process performed on the divided blocks of the target area;

[0200] The signal cancellation unit 603 is configured to: perform cancellation processing on the first image domain signal and the second image domain signal to obtain a final moving target signal; the final moving target signal is a moving target signal without clutter.

[0201] Figure 7 The figure is a schematic structural diagram of a single-channel bistatic radar clutter cancellation device provided by an embodiment of the present invention, including: a processor 710, a storage medium 720, and a bus 730. The storage medium 720 stores machine-readable instructions executable by the processor 710. When the single-channel bistatic radar clutter cancellation device runs, the processor 710 communicates with the storage medium 720 through the bus 730, and the processor 710 executes the machine-readable instructions to perform the steps of the above method embodiment. The specific implementation manners and technical effects are similar and will not be elaborated here.

[0202] The storage medium may include a random access memory (RAM), or may also include a non-volatile memory (NVM), such as at least one disk memory. Optionally, the storage medium may also be at least one storage device located far from the aforementioned processor.

[0203] The above-mentioned processor may be a general-purpose processor, including a Central Processing Unit (CPU), a Network Processor (NP), etc.; it may also be a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field-Programmable Gate Array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components.

[0204] It should be noted that the terms "first", "second", etc. are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. On the contrary, they are only examples of devices and methods consistent with some aspects of the present invention.

[0205] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0206] Although the present invention has been described in connection with various embodiments herein, however, in the process of implementing the claimed invention, those skilled in the art can understand and implement other variations of the above-described disclosed embodiments by viewing the drawings and the disclosure. In the description of the present invention, the term "including" does not exclude other components or steps, the term "a" or "one" does not exclude a plurality of cases, and the meaning of "a plurality" is two or more, unless otherwise specifically defined. In addition, certain measures are described in different embodiments, but this does not mean that these measures cannot be combined to produce good results.

[0207] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A clutter cancellation method for a single-channel bistatic radar, which is applied to a single-antenna receiving device, is characterized in that Including: Obtaining the radar echo signal of the target area; The radar echo signal includes: moving target signal and stationary ground clutter signal; Performing range direction processing on the radar echo signal to obtain a range direction processed signal; Performing focusing processing based on global azimuth resampling on the range direction processed signal to obtain a first image domain signal; the global azimuth resampling is the focusing processing performed on the entire target area; Performing focusing processing based on block azimuth resampling on the range direction processed signal to obtain a second image domain signal; the block azimuth resampling is the focusing processing performed on the divided blocks of the target area; Performing cancellation processing on the first image domain signal and the second image domain signal to obtain a final moving target signal; the final moving target signal is a moving target signal without clutter.

2. The clutter cancellation method for a single-channel bistatic radar according to claim 1, wherein The performing range direction processing on the radar echo signal to obtain a range direction processed signal includes: Performing range direction fast Fourier transform on the radar echo signal to obtain a first echo transform signal; Performing matched filtering processing on the first echo transform signal to obtain a second echo transform signal; Performing wedge transform on the second echo transform signal to obtain a third echo transform signal; Performing inverse range direction fast Fourier transform on the third echo transform signal to obtain the range direction processed signal.

3. The single-channel bistatic radar clutter cancellation method according to claim 2, wherein The performing matched filtering processing on the first echo transform signal to obtain a second echo transform signal includes: Multiplying the first echo transform signal by a reference matched filtering function to obtain the second echo transform signal.

4. The clutter cancellation method for a single-channel bistatic radar according to claim 1, wherein The performing focusing processing based on global azimuth resampling on the range direction processed signal to obtain a first image domain signal includes: Obtaining a first preset frequency modulation phase filter, a first preset azimuth resampling filter, and a first preset azimuth matching filter; the first preset frequency modulation phase filter, the first preset azimuth resampling filter, and the first preset azimuth matching filter are determined in a second-order space-variant scenario using the motion parameters of the single-antenna receiving device and transmitting device and the global center reference point of the target area; Performing multiplication processing and azimuth direction fast Fourier transform on the first preset frequency modulation phase filter and the range direction processed signal in sequence to obtain a first azimuth frequency domain signal; Performing multiplication processing and inverse azimuth direction Fourier transform on the first azimuth frequency domain signal and the first preset azimuth resampling filter in sequence to obtain a first azimuth time domain signal; Performing multiplication processing and azimuth direction fast Fourier transform on the first azimuth time domain signal and the first preset azimuth matching filter in sequence to obtain the first image domain signal.

5. The clutter cancellation method for a single-channel bistatic radar according to claim 1, characterized in that, The performing focusing processing based on block azimuth resampling on the range direction processed signal to obtain a second image domain signal includes: Obtain a second preset frequency modulation phase filter, a second preset azimuth resampling filter, and a second preset azimuth matching filter; the second preset frequency modulation phase filter, the second preset azimuth resampling filter, and the second preset azimuth matching filter are determined in a first-order space-variant sub-block scenario by using the motion parameters of the single-antenna receiving device and transmitting device and the central reference point of the target area sub-block; the target area sub-block is an area block obtained by splitting the target area according to a preset splitting rule; Multiply the second preset frequency modulation phase filter and the range-direction processed signal in sequence and then perform azimuth fast Fourier transform to obtain a plurality of second azimuth frequency domain signals; Multiply each of the second azimuth frequency domain signals and the second preset azimuth resampling filter in sequence and then perform inverse azimuth Fourier transform to obtain a plurality of second azimuth time domain signals; Multiply each of the second azimuth time domain signals and the second preset azimuth matching filter in sequence and then perform azimuth fast Fourier transform to obtain a plurality of second image domain sub-signals; Perform splicing processing on the plurality of second image domain sub-signals to obtain the second image domain signal.

6. The single-channel bistatic radar clutter cancellation method according to claim 1, wherein The canceling process of the first image domain signal and the second image domain signal to obtain the final moving target signal includes: Perform a subtraction process on the first image domain signal and the second image domain signal to obtain the final moving target signal.

7. The clutter cancellation method for a single-channel bistatic radar according to claim 1, characterized in that, The final moving target signal is expressed as: S CC represents the final signal of the moving target, S NCS,1 represents the first image domain signal, S NCS,2 represents the second image domain signal, W a represents the azimuth frequency domain rectangular window function, f a represents the azimuth frequency domain variable, f p,1 represents the azimuth focusing position of the target after global azimuth resampling focusing processing, j represents the imaginary unit, and R0 represents the two-way distance of the target at t a = 0 moment, L0 represents the residual phase related to R0, t a represents the azimuth time domain variable, Δγ a,1 represents the remaining azimuth chirp rate of the first image domain signal after global azimuth resampling focusing processing, f p,2 represents the azimuth focusing position of the second image domain signal after block azimuth resampling focusing processing, Δγ a,2 represents the remaining azimuth chirp rate of the second image domain signal after block azimuth resampling focusing processing, T a represents the synthetic aperture time, and exp(·) represents the exponential function.

8. A single-channel dual-base radar clutter cancellation device, characterized in that, The single-channel bistatic radar clutter cancellation device includes: an acquisition unit, a processing unit, and a signal cancellation unit; The acquisition unit is used to: acquire the radar echo signal of the target area; the radar echo signal includes: a moving target signal and a stationary ground clutter signal; The processing unit is used to: perform range-direction processing on the radar echo signal to obtain a range-direction processed signal; The processing unit is further used to: perform focusing processing based on global azimuth resampling on the range-direction processed signal to obtain a first image domain signal; the global azimuth resampling is a focusing process performed on the entire target area; The processing unit is further used to: perform focusing processing based on block azimuth resampling on the range-direction processed signal to obtain a second image domain signal; the block azimuth resampling is a focusing process performed on the divided sub-blocks of the target area; The signal cancellation unit is used to: perform cancellation processing on the first image domain signal and the second image domain signal to obtain a final moving target signal; the final moving target signal is a moving target signal without clutter.

9. A single-channel dual-base radar clutter cancellation device, characterized in that, Including: A processor, a storage medium, and a bus, the storage medium stores machine-readable instructions executable by the processor, when the single-channel bistatic radar clutter cancellation device runs, the processor communicates with the storage medium through the bus, and the processor executes the machine-readable instructions to perform the steps of the single-channel bistatic radar clutter cancellation method according to any one of claims 1-7.

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