High-resolution ultra-wide imaging method and system based on intra-pulse multiple beams

Abstract

The invention discloses an intra-pulse multi-beam-based high-resolution ultra-wide imaging method and system, and the method comprises the steps: carrying out the filtering processing of each sub-pulse echo signal, and obtaining each sub-mapping-band echo signal; processing each sub-surveying-and-mapping-band echo signal to obtain an output signal of each receiving channel; according to the time-varying weighting coefficient of each receiving channel and the output signal of each receiving channel, obtaining a signal after DBF processing of each receiving channel; processing the signal processed by the DBF of each receiving channel to obtain each sub-swath signal; performing two-dimensional focusing processing on each sub-swath signal to obtain an SAR image of each sub-swath area; and carrying out splicing processing on the SAR image of each sub-swath area in the distance direction to obtain a high-resolution super-large-breadth SAR image. According to the invention, the problem that a traditional satellite-borne SAR system is difficult to realize high-resolution and ultra-large-breadth imaging at the same time is effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of signal processing, and in particular relates to a high-resolution ultra-wide-width imaging method and system based on intrapulse multi-beam. Background Art

[0002] In recent years, with the increasing demand for spatial resolution and imaging width in applications such as earth environment monitoring, the traditional classic single-channel SAR system cannot meet both high resolution and wide width due to the limitation of the minimum antenna area, and the amount of received data corresponding to a large area will also increase dramatically, which will bring huge storage and processing burdens to the payload and satellite platform, and bring new challenges to engineering applications. The traditional elevation multi-beam (MEB) technology achieves ultra-wide width by irradiating multiple sub-survey band areas simultaneously during each burst period, but there is serious mutual interference between multiple receiving sub-beams, and the system performance such as noise equivalent backscatter coefficient (NESZ) and range ambiguity ratio (RASR) will be seriously deteriorated, which seriously hinders practical engineering applications.

[0003] Traditional spaceborne SAR systems have difficulty achieving both high-resolution and ultra-wideband imaging. Summary of the invention

[0004] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and provide a high-resolution and ultra-wide-width imaging method and system based on intrapulse multi-beam, which effectively solves the problem that traditional satellite-borne SAR systems are difficult to achieve high-resolution and ultra-wide-width imaging at the same time, and can effectively reduce the amount of effective data collected and recorded by the payload without losing the imaging width.

[0005] The object of the present invention is achieved through the following technical solutions: a high-resolution ultra-wide-band imaging method based on intra-pulse multi-beam, comprising: emitting a plurality of different sub-pulses in the same pulse repetition period, each sub-pulse irradiating a sub-mapping band corresponding to each sub-pulse to obtain each sub-pulse echo signal; filtering each sub-pulse echo signal to obtain each sub-mapping band echo signal; converting each sub-mapping band echo signal to the range frequency domain and performing matched filtering to obtain the output signal of each receiving channel; obtaining the signal of each receiving channel after DBF processing in azimuth according to the time-varying weighting coefficient of each receiving channel and the output signal of each receiving channel; converting the signal of each receiving channel after DBF processing in azimuth to the range Doppler domain and performing unambiguous signal reconstruction to obtain the reconstructed signal, i.e., each sub-mapping band signal; performing two-dimensional focusing processing on each sub-mapping band signal to obtain the SAR image of each sub-mapping band area; splicing the SAR image of each sub-mapping band area in the range direction to obtain a high-resolution ultra-wide-band SAR image.

[0006] In the above-mentioned high-resolution ultra-wide imaging method based on intrapulse multi-beam, the echo signal of each sub-mapping band is obtained by the following formula:

[0007]

[0008] Among them, s tk (τ) is the kth sub-survey band echo signal, τ is the fast time, T p is the pulse width, f k is the carrier frequency of the kth sub-beam, K r is the modulation frequency of the LFM signal, T pk is the transmission delay of the kth sub-beam, and k is the sequence number of the sub-beam.

[0009] In the above-mentioned high-resolution ultra-wide imaging method based on intrapulse multi-beam, the output signal of each receiving channel is obtained by the following formula:

[0010]

[0011] Among them, s rn,m (τ) is the output signal of the nth receiving channel in the azimuth direction in the elevation direction, τ is the fast time, T pk is the transmission delay of the kth sub-beam, f k is the carrier frequency of the kth sub-beam, is the distance from the radiation center of the phased array antenna to the scattering target in the kth sub-surveying band, d n is the distance between the nth receiving channel and the reference receiving channel, θ k represents the normal deviation angle corresponding to the target in the kth sub-surveying zone, α k is the kth sub-survey band echo, λ k is the wavelength of the beam corresponding to the kth sub-band, σ k is the backscattering coefficient of the kth sub-survey band, and c is the speed of light.

[0012] In the above-mentioned high-resolution ultra-wide imaging method based on intrapulse multi-beam, the time-varying weighting coefficient of each receiving channel is obtained by the following formula:

[0013]

[0014] in, is the time-varying weighting coefficient of the nth receiving channel, τ is the fast time, d n is the distance between the nth receiving channel and the reference receiving channel, λ k is the wavelength of the beam corresponding to the kth sub-band, θ k (τ i ) is τ i The normal deviation angle corresponding to the target in the kth sub-surveying band at the moment, τi is the time corresponding to the i-th sampling point, i is the serial number of the sampling point, N r is the total number of sampling points in the distance direction, τ start is the sampling start time of the echo signal of the SAR system in the first sub-surveying band, H is the platform height, F r is the range sampling frequency, β is the normal installation angle of the SAR antenna, and c is the speed of light.

[0015] In the above-mentioned high-resolution ultra-wide imaging method based on intra-pulse multi-beam, the signal after DBF processing of each receiving channel in azimuth is obtained by the following formula:

[0016]

[0017] Among them, R m,DBF (τ) is the signal after DBF processing of the mth receiving channel in pitch direction, τ is the fast time, is the time-varying weighting coefficient of the nth receiving channel in the elevation direction, s rn,m (τ) is the output signal of the nth receiving channel in the elevation direction in the mth receiving channel in the azimuth direction, m is the azimuth channel number, and M is the total number of azimuth channels.

[0018] In the above-mentioned high-resolution ultra-wide imaging method based on intrapulse multi-beam, the reconstructed signal is obtained by the following formula:

[0019]

[0020] Among them, R out is the reconstructed signal, R m,DBF (f a ) is the signal after DBF processing of the mth receiving channel in the elevation direction after conversion to the range Doppler domain, P m (f a ) is the reconstruction filter corresponding to the mth receiving channel in azimuth, f a is the azimuth frequency, m is the azimuth channel number, and M is the total number of azimuth channels.

[0021] A high-resolution ultra-wideband imaging system based on intra-pulse multi-beams comprises: a first module for transmitting a plurality of different sub-pulses in the same pulse repetition period, each sub-pulse irradiating a sub-mapping band corresponding to each sub-pulse to obtain each sub-pulse echo signal; a second module for filtering each sub-pulse echo signal through a bandpass filter to obtain each sub-mapping band echo signal; a third module for converting each sub-mapping band echo signal into a range frequency domain for matched filtering to obtain an output signal of each receiving channel; a fourth module for obtaining a DBF-processed signal of each receiving channel according to a time-varying weighting coefficient of each receiving channel and the output signal of each receiving channel; a fifth module for converting the DBF-processed signal of each receiving channel into a range Doppler domain and then performing unambiguous signal reconstruction to obtain a reconstructed signal, i.e., each sub-mapping band signal; a sixth module for performing two-dimensional focusing processing on each sub-mapping band signal to obtain a SAR image of each sub-mapping band area; and a seventh module for performing splicing processing on the SAR image of each sub-mapping band area in the range direction to obtain a high-resolution ultra-wideband SAR image.

[0022] In the above-mentioned high-resolution ultra-wide imaging system based on intrapulse multi-beam, the echo signal of each sub-mapping band is obtained by the following formula:

[0023]

[0024] Among them, s tk (τ) is the kth sub-survey band echo signal, τ is the fast time, T p is the pulse width, f k is the carrier frequency of the kth sub-beam, K r is the modulation frequency of the LFM signal, T pk is the transmission delay of the kth sub-beam, and k is the sequence number of the sub-beam.

[0025] In the above-mentioned high-resolution ultra-wide imaging system based on intrapulse multi-beam, the output signal of each receiving channel is obtained by the following formula:

[0026]

[0027] Among them, s rn,m (τ) is the output signal of the nth receiving channel in the azimuth direction in the elevation direction, τ is the fast time, T pk is the transmission delay of the kth sub-beam, f k is the carrier frequency of the kth sub-beam, is the distance from the radiation center of the phased array antenna to the scattering target in the kth sub-surveying band, d n is the distance between the nth receiving channel and the reference receiving channel, θ krepresents the normal deviation angle corresponding to the target in the kth sub-surveying zone, α k is the kth sub-survey band echo, λ k is the wavelength of the beam corresponding to the kth sub-band, σ k is the backscattering coefficient of the kth sub-survey band, and c is the speed of light.

[0028] In the above-mentioned high-resolution ultra-wide imaging system based on intrapulse multi-beam, the time-varying weighting coefficient of each receiving channel is obtained by the following formula:

[0029]

[0030] in, is the time-varying weighting coefficient of the nth receiving channel, τ is the fast time, d n is the distance between the nth receiving channel and the reference receiving channel, λ k is the wavelength of the beam corresponding to the kth sub-band, θ k (τ i ) is τ i The normal deviation angle corresponding to the target in the kth sub-surveying band at the moment, τ i is the time corresponding to the i-th sampling point, i is the serial number of the sampling point, N r is the total number of sampling points in the distance direction, τ start is the sampling start time of the echo signal of the SAR system in the first sub-surveying band, H is the platform height, F r is the range sampling frequency, β is the normal installation angle of the SAR antenna, and c is the speed of light.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The present invention solves the problem that traditional spaceborne SAR systems are difficult to achieve high-resolution and ultra-wideband imaging at the same time, and can effectively reduce the amount of data collected and recorded by the payload without losing the imaging width. The method can be applied to SAR satellite high-resolution and wide-bandwidth earth observation tasks, making the system's quality factor exceed 200, which has important practical application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0034] Figure 1 It is a geometrical schematic diagram of high-resolution ultra-wide imaging based on intrapulse multi-beam provided by an embodiment of the present invention;

[0035] Figure 2 It is a flowchart of high-resolution ultra-wide imaging signal processing based on intrapulse multi-beam provided by an embodiment of the present invention;

[0036] Figure 3 4 are timing diagrams of the Burst modes provided in the embodiments of the present invention;

[0037] Figure 4 4 is a schematic diagram of NESZ of four Burst modes provided by an embodiment of the present invention;

[0038] Figure 5 4 is a schematic diagram of RASR in four Burst modes provided by an embodiment of the present invention;

[0039] Figure 6 4 is a schematic diagram of AASR in four Burst modes provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0040] Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to be able to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, in the absence of conflict, the embodiments of the present invention and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0041] The two-dimensional multi-channel system architecture can provide additional spatial degrees of freedom in azimuth and elevation for high-resolution ultra-wideband imaging, and the intra-pulse multi-beam technology can effectively reduce the amount of data without losing the imaging width, but the prerequisite is that the mutual interference between different sub-beams can be effectively suppressed. Combining the intra-pulse multi-beam technology on the basis of the two-dimensional multi-channel system architecture can make the system's quality factor Q (Q = width km / resolution m) exceed 200, but it is necessary to solve the intra-pulse multi-beam imaging and signal processing problems under the two-dimensional multi-channel system architecture, laying an important application foundation for the high-resolution ultra-wideband earth observation mission of SAR satellites.

[0042] like Figure 2 As shown, the high-resolution ultra-wide imaging method based on intrapulse multi-beam includes:

[0043] In the same pulse repetition period, K different sub-pulses are emitted, and each sub-pulse illuminates a sub-scanning band corresponding to each sub-pulse to obtain each sub-pulse echo signal; wherein the total width in the range direction is divided into K sub-scanning bands; K is a positive integer;

[0044] Each sub-pulse echo signal is filtered through a bandpass filter to obtain each sub-surveying band echo signal;

[0045] The echo signal of each sub-surveying band is converted into the range frequency domain and matched filtering is performed to obtain the output signal of each receiving channel;

[0046] Obtaining a signal after DBF processing of each receiving channel in azimuth according to a time-varying weighting coefficient of each receiving channel and an output signal of each receiving channel;

[0047] After converting the signal processed by DBF in each receiving channel in the azimuth direction into the range Doppler domain, an unambiguous signal reconstruction process is performed to obtain the reconstructed signal, i.e., the signal of each sub-surveying band;

[0048] Perform two-dimensional focusing processing on the signal of each sub-surveying band to obtain the SAR image of each sub-surveying band area;

[0049] The SAR images of each sub-surveying zone are spliced ​​in the range direction to obtain high-resolution and ultra-wideband SAR images.

[0050] Specifically, the method comprises the following steps:

[0051] Step 1: modulate different sub-pulse LFM (Linear Frequency Modulation) signals to carrier frequencies with different center frequencies within the same pulse repetition period (PRT).

[0052] Assume that the phased array antenna of the two-dimensional multi-channel SAR system is divided into M and N sub-apertures in the azimuth and range directions, respectively. K different sub-pulses are transmitted in the same pulse repetition period. Each sub-pulse corresponds to a transmit sub-beam. The LFM signals in different sub-beams are modulated onto carriers with different center frequencies and illuminate a sub-scanning strip. The total width in the range direction is divided into K (K≤M) sub-scanning strips. The geometric diagram is shown in Figure 1 shown.

[0053] Step 2: Filter each sub-pulse echo signal through a bandpass filter to obtain each sub-surveying band echo signal.

[0054] The echo signal received in the range direction is filtered through a bandpass filter, and the echo of the kth sub-beam transmission signal can be expressed as:

[0055]

[0056] Among them, s tk (τ) is the kth sub-survey band echo signal, τ is the fast time, T p is the pulse width, f k is the carrier frequency of the kth sub-beam, K ris the modulation frequency of the LFM signal, T pk =(k-1)·(T p +Δτ p ) is the transmission delay of the kth sub-beam, Δτ p is the time interval between each transmitted sub-beam.

[0057] Step 3: Convert the echo signal of each sub-surveying band into the range frequency domain and perform matched filtering to obtain the output signal of each receiving channel.

[0058] After bandpass filtering, amplification, down-conversion, sampling, and range-direction matched filtering, the output signal of the nth receiving channel in the azimuth direction can be abbreviated as

[0059]

[0060]

[0061] in, Defined as the distance from the radiation center of the phased array antenna to the scattering target P in the kth sub-surveying band. n is the distance between the nth receiving channel and the reference receiving channel. k represents the normal deviation angle corresponding to the target in the kth sub-surveying zone, α k is the kth sub-survey band echo, λ k is the wavelength of the beam corresponding to the kth sub-band, σ k is the backscattering coefficient of the kth sub-survey band, and c is the speed of light.

[0062] Step 4: After matched filtering, perform real-time weighted processing and phase mismatch calibration on each receiving channel in the pitch direction.

[0063] The time-varying weighting coefficient of the nth receiving channel in the elevation direction can be expressed as

[0064]

[0065] Among them, the normal deviation angle corresponding to the scattering target in the kth sub-surveying band can be expressed as

[0066]

[0067] where τ start It is represented as the sampling start time of the echo signal of the SAR system in the first sub-surveying band, F r is the distance sampling frequency, N r is the total number of sampling points in the range direction, H is the platform height, β is the normal installation angle of the SAR antenna, and λ k is the wavelength of the beam corresponding to the kth sub-band, θ k (τi ) is τ i The normal deviation angle corresponding to the target in the kth sub-surveying band at the moment, τ i is the time corresponding to the i-th sampling point, i is the i-th sampling point, and c is the speed of light.

[0068] The above time-varying weighting coefficients are multiplied with the signals of each receiving channel, and the phase error is corrected by the mutual interference method. Then, after the phase error is corrected, the output of the echo signal of the kth sub-surveying band after DBF processing can be written as

[0069]

[0070] Among them, R m,DBF (τ) is the signal after DBF processing of the mth receiving channel in pitch direction, τ is the fast time, is the time-varying weighting coefficient of the nth receiving channel in the elevation direction, s rn,m (τ) is the output signal of the nth receiving channel in the elevation direction in the mth receiving channel in the azimuth direction, m is the azimuth channel number, and M is the total number of azimuth channels.

[0071] Step 5: After DBF processing in range, the signals of each receiving channel in azimuth are converted to the range Doppler domain and then unambiguous signal reconstruction is performed.

[0072] After DBF processing in range, the echo signals of the M receiving channels in azimuth are processed by FFT and converted to the range Doppler domain. Then, the echo signal of the kth sub-surveying band is reconstructed using the traditional reconstruction filter P m (f a ) performs azimuth-unambiguous signal reconstruction processing on the M receiving channels in azimuth, and the reconstructed signal can be expressed as

[0073]

[0074] Among them, R out is the reconstructed signal, R m,DBF (f a ) is the signal after DBF processing of the mth receiving channel in the elevation direction after conversion to the range Doppler domain, P m (f a ) is the reconstruction filter corresponding to the mth receiving channel in azimuth, f a is the azimuth frequency, m is the azimuth channel number, and M is the total number of azimuth channels. Step 6: Perform two-dimensional focusing processing on each sub-mapping band signal to obtain the SAR image of the kth sub-mapping band area.

[0075] The traditional two-dimensional focusing processing algorithm is used to focus the echo signal of the k-th sub-mapping band to obtain a well-focused SAR image.

[0076] Step 7: The k sub-surveying swath area SAR images are stitched in the range direction to obtain a high-resolution ultra-wideband SAR image.

[0077] The SAR images of k sub-surveying swaths are focused and spliced ​​in the range direction to obtain high-resolution and ultra-wideband SAR images.

[0078] In summary, the specific process of high-resolution ultra-wideband imaging signal processing proposed by the present invention is as follows: Figure 2 As shown, it mainly includes the above seven steps, which is suitable for the spaceborne SAR system under the two-dimensional multi-channel system architecture, and has the ability to significantly improve the high-resolution and ultra-wideband imaging performance of future SAR systems.

[0079] In order to fully illustrate the effectiveness of the present invention, a system design solution embodiment in strip mode is given, and the specific parameters of the embodiment are shown in Table 1. Four independent Bursts are designed within the range of the lower viewing angle [10.2°, 48.2°]. Each Burst contains three sub-beams covering three consecutive sub-surveying bands. The width of each sub-surveying band is 66km, and the total width of each Burst is 200km. Figure 3 , Figure 4 , Figure 5 and Figure 6 The system performance evaluation results of 1m / 200km (resolution / width) are given, including system sensitivity and fuzzy ratio. Figure 3 This is the timing diagram of the 4 Burst modes. Figure 4 For 4 NESZ in Burst mode, Figure 5 There are 4 Burst mode RASRs. Figure 6 The above comparative analysis shows that in each group of Burst, the azimuth ambiguity ratio (AASR) is lower than -28.07dB, the range ambiguity ratio (RASR) is lower than -31.95dB, and the system sensitivity (NESZ) is lower than -20.0dB, which can meet the actual engineering application.

[0080] Table 1. Main system parameters of simulation test.

[0081] parameter Numeric Center carrier frequency 8.4 / 9.6 / 10.8GHz Platform height 750km Antenna physical dimensions 18.85m(A)×1.87m(R) Antenna installation angle 32.5° Bottom viewing angle 10.2°～48.2° Number of channels 10(A)×8(R) Sub pulse width 30us Number of sub-pulses 3 Sub-pulse interval 5us Signal bandwidth 500 / 330 / 250 / 210MHz Sampling frequency 600 / 396 / 300 / 252MHz PRF 780~980Hz Peak Power 16600W System loss 3.5dB Duty Cycle 7.02％～8.84％ Imaging Mode Stripe Mode

[0082] The present embodiment also provides a high-resolution ultra-wideband imaging system based on intra-pulse multi-beam, which includes: a first module, which is used to transmit a plurality of different sub-pulses in the same pulse repetition period, each sub-pulse irradiating a sub-mapping band corresponding to each sub-pulse to obtain each sub-pulse echo signal; a second module, which is used to filter each sub-pulse echo signal through a bandpass filter to obtain each sub-mapping band echo signal; a third module, which is used to convert each sub-mapping band echo signal into a range frequency domain and perform matched filtering to obtain an output signal of each receiving channel; a fourth module, which is used to obtain a DBF-processed signal of each receiving channel according to a time-varying weighting coefficient of each receiving channel and the output signal of each receiving channel; a fifth module, which is used to convert the DBF-processed signal of each receiving channel into a range Doppler domain and then perform unambiguous signal reconstruction to obtain a reconstructed signal, i.e., each sub-mapping band signal; a sixth module, which is used to perform two-dimensional focusing processing on each sub-mapping band signal to obtain a SAR image of each sub-mapping band area; and a seventh module, which is used to perform splicing processing on the SAR image of each sub-mapping band area in the range direction to obtain a high-resolution ultra-wideband SAR image.

[0083] This embodiment fully combines the advantages of intra-pulse beam pointing and digital beam forming technology on the basis of a two-dimensional multi-channel system architecture, so that the quality factor Q of the system reaches more than 200, effectively solving the problem that traditional satellite-borne SAR systems are difficult to achieve high-resolution and ultra-wideband imaging at the same time. At the same time, it can effectively reduce the amount of effective data collected and recorded by the payload without losing the imaging width, greatly reducing the storage burden of large-scale collection and recording data of the satellite platform.

[0084] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A high-resolution ultra-wideband imaging method based on intrapulse multi-beam, characterized in that include: A plurality of different sub-pulses are emitted in the same pulse repetition period, and each sub-pulse illuminates a sub-mapping band corresponding to each sub-pulse to obtain an echo signal of each sub-pulse; Filter each sub-pulse echo signal to obtain each sub-surveying band echo signal; The echo signal of each sub-surveying band is converted into the range frequency domain and matched filtering is performed to obtain the output signal of each receiving channel; Obtaining a signal after DBF processing of each receiving channel in azimuth according to a time-varying weighting coefficient of each receiving channel and an output signal of each receiving channel; After converting the signal processed by DBF in each receiving channel in the azimuth direction into the range Doppler domain, an unambiguous signal reconstruction process is performed to obtain the reconstructed signal, i.e., the signal of each sub-surveying band; Perform two-dimensional focusing processing on the signal of each sub-surveying band to obtain the SAR image of each sub-surveying band area; The SAR images of each sub-surveying zone are spliced ​​in the range direction to obtain high-resolution and ultra-wideband SAR images.

2. The high-resolution ultra-wide imaging method based on intrapulse multi-beam according to claim 1, characterized in that: The echo signal of each sub-surveying band is obtained by the following formula: Among them, s tk (τ) is the kth sub-survey band echo signal, τ is the fast time, T p is the pulse width, f k is the carrier frequency of the kth sub-beam, K r is the modulation frequency of the LFM signal, T pk is the transmission delay of the kth sub-beam, and k is the sequence number of the sub-beam.

3. The high-resolution ultra-wide imaging method based on intrapulse multi-beam according to claim 1, characterized in that: The output signal of each receiving channel is obtained by the following formula: Among them, s rn,m (τ) is the output signal of the nth receiving channel in the azimuth direction in the elevation direction, τ is the fast time, T pk is the transmission delay of the kth sub-beam, f k is the carrier frequency of the kth sub-beam, is the distance from the radiation center of the phased array antenna to the scattering target in the kth sub-surveying band, d n is the distance between the nth receiving channel and the reference receiving channel, θ k represents the normal deviation angle corresponding to the target in the kth sub-surveying zone, α k is the kth sub-survey band echo, λ k is the wavelength of the beam corresponding to the kth sub-band, σ k is the backscattering coefficient of the kth sub-survey band, and c is the speed of light.

4. The high-resolution ultra-wide imaging method based on intrapulse multi-beam according to claim 1, characterized in that: The time-varying weighting coefficient of each receiving channel is obtained by the following formula: in, is the time-varying weighting coefficient of the nth receiving channel, τ is the fast time, d n is the distance between the nth receiving channel and the reference receiving channel, λ k is the wavelength of the beam corresponding to the kth sub-band, θ k (τ i ) is τ i The normal deviation angle corresponding to the target in the kth sub-surveying band at the moment, τ i is the time corresponding to the i-th sampling point, i is the serial number of the sampling point, N r is the total number of sampling points in the distance direction, τ start is the sampling start time of the echo signal of the SAR system in the first sub-surveying band, H is the platform height, F r is the range sampling frequency, β is the normal installation angle of the SAR antenna, and c is the speed of light.

5. The high-resolution ultra-wide imaging method based on intrapulse multi-beam according to claim 1, characterized in that: The signal after DBF processing of each receiving channel in azimuth is obtained by the following formula: Among them, R m,DBF (τ) is the signal after DBF processing of the mth receiving channel in pitch direction, τ is the fast time, is the time-varying weighting coefficient of the nth receiving channel in the elevation direction, s rn,m (τ) is the output signal of the nth receiving channel in the elevation direction in the mth receiving channel in the azimuth direction, m is the azimuth channel number, and M is the total number of azimuth channels.

6. The high-resolution ultra-wide imaging method based on intrapulse multi-beam according to claim 1, characterized in that: The reconstructed signal is obtained by the following formula: Among them, R out is the reconstructed signal, R m,DBF (f a ) is the signal after DBF processing of the mth receiving channel in the elevation direction after conversion to the range Doppler domain, P m (f a ) is the reconstruction filter corresponding to the mth receiving channel in azimuth, f a is the azimuth frequency, m is the azimuth channel number, and M is the total number of azimuth channels.

7. A high-resolution ultra-wideband imaging system based on intrapulse multi-beam, characterized in that include: The first module is used to transmit a plurality of different sub-pulses in the same pulse repetition period, each sub-pulse irradiates a sub-mapping band corresponding to each sub-pulse to obtain an echo signal of each sub-pulse; The second module is used to filter each sub-pulse echo signal through a bandpass filter to obtain each sub-surveying band echo signal; The third module is used to convert the echo signal of each sub-surveying band into the range frequency domain and perform matched filtering to obtain the output signal of each receiving channel; A fourth module is used to obtain a DBF-processed signal of each receiving channel according to a time-varying weighting coefficient of each receiving channel and an output signal of each receiving channel; The fifth module is used to convert the signal after DBF processing of each receiving channel into the range Doppler domain and then perform unambiguous signal reconstruction processing to obtain the reconstructed signal, that is, the signal of each sub-surveying band; The sixth module is used to perform two-dimensional focusing processing on the signal of each sub-surveying band to obtain a SAR image of each sub-surveying band area; The seventh module is used to stitch the SAR images of each sub-surveying zone in the range direction to obtain a high-resolution and ultra-wideband SAR image.

8. The high-resolution ultra-wideband imaging system based on intrapulse multi-beam according to claim 7, characterized in that: The echo signal of each sub-surveying band is obtained by the following formula: Among them, s tk (τ) is the kth sub-survey band echo signal, τ is the fast time, T p is the pulse width, f k is the carrier frequency of the kth sub-beam, K r is the modulation frequency of the LFM signal, T pk is the transmission delay of the kth sub-beam, and k is the sequence number of the sub-beam.

9. The high-resolution ultra-wide imaging system based on intrapulse multi-beam according to claim 7, characterized in that: The output signal of each receiving channel is obtained by the following formula: Among them, s rn,m (τ) is the output signal of the nth receiving channel in the azimuth direction in the elevation direction, τ is the fast time, T pk is the transmission delay of the kth sub-beam, f k is the carrier frequency of the kth sub-beam, is the distance from the radiation center of the phased array antenna to the scattering target in the kth sub-surveying band, d n is the distance between the nth receiving channel and the reference receiving channel, θ k represents the normal deviation angle corresponding to the target in the kth sub-surveying zone, α k is the kth sub-survey band echo, λ k is the wavelength of the beam corresponding to the kth sub-band, σ k is the backscattering coefficient of the kth sub-survey band, and c is the speed of light.

10. The high-resolution ultra-wide imaging system based on intrapulse multi-beam according to claim 7, characterized in that: The time-varying weighting coefficient of each receiving channel is obtained by the following formula: in, is the time-varying weighting coefficient of the nth receiving channel, τ is the fast time, d n is the distance between the nth receiving channel and the reference receiving channel, λ k is the wavelength of the beam corresponding to the kth sub-band, θ k (τ i ) is τ i The normal deviation angle corresponding to the target in the kth sub-surveying band at the moment, τ i is the time corresponding to the i-th sampling point, i is the serial number of the sampling point, N r is the total number of sampling points in the distance direction, τ start is the sampling start time of the echo signal of the SAR system in the first sub-surveying band, H is the platform height, F r is the range sampling frequency, β is the normal installation angle of the SAR antenna, and c is the speed of light.

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