CN113900066A - Gate sidelobe suppression method for MIMO beamforming - Google Patents

Gate sidelobe suppression method for MIMO beamforming Download PDF

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CN113900066A
CN113900066A CN202111251447.2A CN202111251447A CN113900066A CN 113900066 A CN113900066 A CN 113900066A CN 202111251447 A CN202111251447 A CN 202111251447A CN 113900066 A CN113900066 A CN 113900066A
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echo signal
final
wave number
coherence factor
algorithm
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李超
杨冠
刘小军
方广有
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Aerospace Information Research Institute of CAS
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/28—Details of pulse systems
    • G01S7/285—Receivers
    • G01S7/292—Extracting wanted echo-signals
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/28—Details of pulse systems
    • G01S7/285—Receivers
    • G01S7/288—Coherent receivers
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section

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Abstract

The present disclosure provides a gate sidelobe suppression method for MIMO beamforming, comprising: s1: receiving an original scattering echo signal, selecting a transmitting array element, and analyzing an original echo signal corresponding to the transmitting array element; s2: transforming the original echo signals to a spatial frequency domain corresponding to the receiving array direction, and determining a corresponding spatial wave number spectrum; s3: performing wave field extrapolation on the spatial wave number spectrum by applying a PSM algorithm, performing phase compensation on residual phases related to the selected transmitting array elements to obtain an accurate explosion field function, and obtaining a primary target function and a coherent power term in a coherent factor algorithm; s4: reconstructing an original echo signal corresponding to the selected transmitting array element to obtain a virtual echo signal under a difference wave number; s5: calculating the virtual echo signal into a final incoherent power term in a coherence factor algorithm by referring to S2 and S3; and S6: and obtaining a coherence factor according to the obtained coherent power term and the final incoherent power term, and weighting and multiplying the coherence factor by the objective function to obtain a final objective imaging function result.

Description

Gate sidelobe suppression method for MIMO beamforming
Technical Field
The present disclosure relates to the field of radar technologies, and in particular, to a method for suppressing a gate side lobe for MIMO beamforming.
Background
Beamforming techniques are a common technique in array radars. A common radar imaging system generally realizes three-dimensional imaging based on a two-dimensional array, the resolution capability of the azimuth and the elevation direction depends on array parameters, and high resolution of the distance direction is realized by combining broadband signals. However, in the terahertz frequency band, the wavelength is very short, usually in the millimeter level or the submillimeter level, and is limited by the requirement of nyquist spatial sampling rate, the number of array elements required for designing a two-dimensional array is huge, and the cost of the terahertz device is relatively high, which results in high system cost under the existing conditions. A compromise scheme is that only a single transceiving array element is adopted to carry out two-dimensional space mechanical scanning, a three-dimensional focusing image can be obtained by combining a broadband signal, but the data acquisition time is too long, the real-time imaging application cannot be met, and most of the data acquisition time stays in a principle verification stage. The rise of the Multiple Input Multiple Output (MIMO) technology enables information of multiple spatial sampling rates to be obtained even if a small number of transceiving array elements are adopted, thereby greatly improving the data acquisition rate and reducing the system cost. However, most of the imaging methods based on such devices currently adopt Range Migration Algorithm (RMA) and Phase Shift Mapping (PSM) algorithms based on frequency-wave number domain to realize real-time imaging, and compared with a Back Projection (BP) Algorithm, the imaging speed of the algorithms is greatly increased, but the traditional wave number domain algorithms have high requirements on array space distribution, and limit the application thereof. The PSM imaging algorithm based on SIMO superposition makes up the disadvantages of the two algorithms, but due to channel splitting, the interval of the array elements of the virtual array is increased, and the side lobe of the point spread function is increased.
Therefore, it is an urgent technical problem to provide a more effective sidelobe suppression method.
Disclosure of Invention
Technical problem to be solved
In view of the above, the present disclosure provides a method for gate sidelobe suppression for MIMO beamforming to alleviate the deficiencies in the prior art.
(II) technical scheme
The present disclosure provides a gate sidelobe suppression method for MIMO beamforming, comprising: operation S1: receiving an original scattering echo signal obtained after a broadband signal is scattered by a target, selecting any one transmitting array element, and analyzing the original echo signal corresponding to the transmitting array element; operation S2: transforming the original echo signal to a spatial frequency domain corresponding to the receiving array direction, and determining a corresponding spatial wave number spectrum;
operation S3: performing wave field extrapolation on the spatial wave number spectrum by applying a PSM algorithm, performing phase compensation on residual phases related to the selected transmitting array elements to obtain an accurate explosion field function, and obtaining a preliminary target function and a coherent power term in a coherence factor algorithm; operation S4: reconstructing the original echo signal corresponding to the selected transmitting array element to obtain a virtual echo signal under a difference wave number; operation S5: calculating the virtual echo signal into a final incoherent power term in a coherence factor algorithm with reference to operations S2, S3; and operation S6: and obtaining a coherence factor according to the obtained coherent power term and the final incoherent power term, and performing weighted multiplication on the coherence factor and the objective function to obtain a final objective imaging function result.
In the embodiment of the disclosure, a linear array form is adopted in which the transmitting ends are arranged at two ends and the receiving ends are uniformly arranged in the middle, or the receiving ends are arranged at two ends and the transmitting ends are uniformly arranged in the middle.
In the disclosed embodiment, the final target imaging result uCF-PSM(x, z) is represented by
uCF-PSM(x，z)＝CF(x，z)·u(x，z) (23)；
Wherein, CF (x, z) is the final coherence factor, u (x, z) is the preliminary objective function, x is the imaging region azimuth coordinate grid point, and z is the imaging region distance coordinate grid point.
In the embodiment of the disclosure, the final coherence factor is coherent power | u (x, z) | in the coherence factor algorithm2With final incoherent power IpThe ratio of (x, z), expressed as:
Figure BDA0003321502770000021
in the embodiment of the present disclosure, original echo signal data reconstruction and virtual distance-direction wave number calculation are completed, all transmitting array elements are traversed, and the results are superimposed to obtain final incoherent power:
Figure BDA0003321502770000022
wherein NTX is the number of transmitting array elements, It(x, z) are sub-images associated with the selected transmit elements.
In the embodiment of the present disclosure, the preliminary target imaging function u (x, z) is comprehensively expressed as:
Figure BDA0003321502770000031
wherein u ist(x, z) is a sub-image related to the transmitting array element with the number t, s1(xrk) For the original receiving echo related to No. 1 transmitting array element, k is 2 pi f/c is the wave number corresponding to the transmitting frequency, kxrIs the azimuth wave number, kzIn the form of a distance to a wave number,
Figure BDA0003321502770000032
denotes with respect to kxrOne-dimensional inverse Fourier transform, FT of1D-xrIndicates about xrOne-dimensional fourier transform of (a).
In the disclosed embodiments, the incoherent power Ip(x, z) is expressed as:
Ip(x，z)＝∫[∫|∫s(xt，xr，k)exp(2jkR)dk|2dxr]dxt (16)。
(III) advantageous effects
As can be seen from the foregoing technical solutions, the method for suppressing gate sidelobe for MIMO beamforming according to the present disclosure has at least one or some of the following beneficial effects:
(1) the high efficiency of the frequency domain algorithm is utilized, the problems of limitation of array arrangement, data interpolation and rearrangement in the traditional RMA and the problems of array arrangement and data rearrangement in the PSM algorithm are solved, the advantages of the frequency domain algorithm are further exerted on the premise of ensuring the imaging effect, and the processing speed is increased; the super-resolution processing flow can be independent of the imaging flow, so that parallel processing can be realized, and only a small amount of calculation is increased; compared with the traditional CF algorithm based on the space domain BP, the method greatly improves the calculation efficiency.
(2) The position of the transmitter does not need to be assumed, so the method disclosed by the invention can be used for a one-dimensional MIMO imaging system with randomly distributed transmitters; according to reciprocity, the method is also applicable to the case of receivers with random distribution and transmitters with uniform distribution, and has wide applicability.
(3) Under the condition of maintaining the current working frequency and array arrangement, the power width of array dimension half-wave beams (3dB beam width defined as resolution) is reduced, the grid side lobe is suppressed, and super-resolution imaging is realized.
Drawings
Fig. 1 is a flowchart illustrating a method for suppressing a gate side lobe for MIMO beamforming according to an embodiment of the disclosure.
Fig. 2 is a schematic diagram of an embodiment of the present disclosure for arranging the wavenumbers k into a wavenumber square matrix.
Fig. 3 is a schematic diagram of a MIMO linear array arrangement according to an embodiment of the present disclosure.
Fig. 4a is a schematic diagram of a situation of a simulated target position according to an embodiment of the disclosure.
Fig. 4b is a schematic diagram of imaging results obtained without using the grid sidelobe suppression method for MIMO beamforming of the present disclosure.
Fig. 4c is a schematic diagram of an imaging result obtained by using the grid sidelobe suppression method for MIMO beamforming according to the present disclosure.
Detailed Description
The invention provides a grid side lobe suppression method for MIMO beam forming, which combines MIMO one-dimensional linear array beam forming and fan-shaped real beam scanning technologies and realizes target space three-dimensional imaging by stacking slices of two-dimensional pitching range images at different directions (X axes). The application of the MIMO array beam forming technology can greatly reduce the number of physical array elements, improve the data acquisition rate and reduce the system cost; and the fan-shaped real beam scanning system is adopted to simplify the imaging algorithm into two-dimensional imaging, so that quick imaging is easy to realize and the method accords with practical application scenes.
In the process of realizing the present disclosure, the inventor finds that when imaging is performed based on the RMA algorithm of the wavenumber domain, the transceiving array is required to be equal in length and uniform in spatial sampling so as to meet the nyquist frequency requirement of the wavenumber domain, and array zero padding and echo zero filling are required if the real aperture is not satisfied; redundancy of actually processed data is caused, and the imaging process involves wave number domain data rearrangement and interpolation, so that the imaging speed and accuracy are limited; when the MIMO-PSM algorithm based on the wave number domain is used for imaging, the requirement of the array by the RMA algorithm is consistent, interpolation in the RMA is replaced by wave field extrapolation in the imaging process, and wave number domain rearrangement still needs to be carried out; when the PSM algorithm based on SIMO superposition is used for imaging, the imaging speed is further improved, but the side lobe of the point spread function is higher, and the imaging effect is insufficient. In a common MIMO one-dimensional sparse linear array system with inter-transmitting/inter-transmitting ends, the above algorithms are affected by high side lobes to different degrees, and the imaging quality also improves the space; the super-resolution algorithm based on the Coherence Factor (CF) is realized by combining a BP algorithm in a spatial domain, is influenced by a high calculation amount, is applied to a wave number domain algorithm, and has a practical value for further improving the imaging quality through a suitable grid side lobe suppression method.
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings.
In an embodiment of the present disclosure, a method for suppressing a gate side lobe for MIMO beamforming is provided, as shown in fig. 1, where the method for suppressing a gate side lobe for MIMO beamforming includes:
operation S1: receiving an original scattering echo signal obtained after a broadband signal is scattered by a target, selecting any one transmitting array element, and analyzing the original echo signal corresponding to the transmitting array element;
operation S2: transforming the original echo signal to a spatial frequency domain corresponding to the receiving array direction, and determining a corresponding spatial wave number spectrum;
operation S3: performing wave field extrapolation on the space wave number spectrum by applying a PSM algorithm, performing phase compensation on residual phases related to the selected transmitting array elements to obtain an accurate explosion field function, and obtaining a target function and a coherent power term in a coherent factor;
operation S4: reconstructing the original echo signal corresponding to the selected transmitting array element to obtain a virtual echo signal under a difference wave number;
operation S5: calculating the virtual echo signal with reference to operations S2, S3 into a non-coherent power term in a coherence factor algorithm; and
operation S6: and obtaining a coherence factor according to the obtained coherent power item and the incoherent power item, and performing weighted multiplication on the coherence factor and the objective function to obtain a final objective imaging result.
Assuming that the distance of the plane in which the MIMO array is located at z-0, the transmit antenna is located at (x)t0) the receiving antenna is located at (x)rAnd 0). The array adopts transmitting antennas at two ends and receiving antennas in the middle, and the receiving antennas are uniformly arranged; or the transmission is in the middle and the reception is at both ends, and the transmission is uniformly arranged. Exciting the frequency stepping signal, wherein k is the wave number corresponding to different transmitting frequencies of the broadband signal, and the following operations are described by taking end-to-end transmission as an example to illustrate the grating side lobe suppression method:
in the embodiment of the present disclosure, when operation S1 is performed: receiving an original scattering echo signal obtained after a broadband signal is scattered by a target, selecting a transmitting array element, and analyzing an echo signal corresponding to the transmitting array element;
for example, if the No. 1 transmitting array element is selected, the coordinate of the No. 1 transmitting array element is matched
Figure BDA0003321502770000051
The relevant reflected echo signal is expressed as:
Figure BDA0003321502770000052
wherein R isT，RRCan be represented as:
Figure BDA0003321502770000053
wherein R isTFor transmitting the distance of the array element to the target point, RRFor receiving the distance, x, from the array element to the target pointrTo receive the spatial coordinates of the array elements, xtThe space coordinates of the transmitting array elements are obtained; rTNo longer following xtThe change is only related to the coordinates of the No. 1 transmitting array element.
In the embodiment of the present disclosure, when operation S2 is performed: converting the echo signals to a space frequency domain corresponding to the receiving array direction, and determining a corresponding space spectrum;
further, the formula (1) is arranged along xrPerforming Fourier transform, and transforming echo signal data to a frequency wave number domain to express that:
Figure BDA0003321502770000061
wherein F (k)xrK) denotes the phase exp (-jkR) associated with the accepted array element coordinatesR) The fourier transform of (a) can be expressed as:
Figure BDA0003321502770000062
the integral term in equation (4) can be solved by the stationary phase principle as:
Figure BDA0003321502770000063
further, bringing formula (5) into formula (3) can obtain:
Figure BDA0003321502770000064
the following wavenumber variable relationship can be defined by equation (6):
Figure BDA0003321502770000065
in the embodiment of the present disclosure, when operation S3 is performed: performing wave field extrapolation on the original echo space wave number spectrum of S2 by applying a PSM algorithm, performing phase compensation on residual phases related to the current transmitting array element to obtain an accurate explosion field function, and obtaining a target function and coherent power in a coherent factor;
from the wavenumber relationship defined in (7), "explosion field" in the frequency-wavenumber domain can be derived using bistatic MIMO data as follows:
Figure BDA0003321502770000066
further, the explosion field extrapolation property of the PSM algorithm means that for different distances zi＝z0，z1，…，zn-1The explosion field at z ═ 0 can be obtained by phase shift, and the specific operation is represented as:
U1(kx，zi，k)＝U1(kx，0，k)exp(jkzzi) (9)；
wherein exp (jk)zzi) Referred to as the phase shift factor along the propagation direction. Each y can then be derived based on a one-dimensional inverse Fourier transform in the wavenumber domaini"near-field" in range, if accurate field is to be obtained, the residual phase needs to be compensated
Figure BDA0003321502770000071
The operation can be expressed as
Figure BDA0003321502770000072
Then, according to the principle of the PSM algorithm, the image in the x-z coordinate system can be reconstructed at the "equivalent frequency" by integration of equation (10) to recover the "explosion field" at time t 0, where for convenience to represent the fourier transform, the wave number k can be replaced by the angular frequency ω, resulting in a preliminary objective function:
u1(x，zi，t)|t＝0＝∫U(x，zi，ω)·exp(jωt)dω (11)；
based on (11), u can be seen1(x，zi，t)|t＝0＝u1(x, z), therefore, for a single 2-D imaging, we can easily extend the SIMO case to the MIMO case, and the preliminary MIMO imaging function result expression is shown in equation (12):
Figure BDA0003321502770000073
in conclusion, the comprehensive expression of the PSM algorithm target function based on SIMO superposition can be obtained
Figure BDA0003321502770000074
Wherein u ist(x, z) is a sub-image related to the transmitting array element with the number t, s1(xrk) For the original receiving echo related to No. 1 transmitting array element, k is 2 pi f/c is the wave number corresponding to the transmitting frequency, kxrIs the azimuth wave number, kzIn the form of a distance to a wave number,
Figure BDA0003321502770000075
denotes with respect to kxrOne-dimensional inverse Fourier transform, FT of1D-xrIndicates about xrOne-dimensional fourier transform of (a).
According to the theory of Coherence Factor (CF), the CF factor can be expressed as a reflectance function coherent power | u (x, z). luminance2Incoherent power IpThe ratio of (x, z), i.e.:
Figure BDA0003321502770000081
in the CF grating sidelobe suppression algorithm of the traditional BP algorithm, a primary original two-dimensional image u (x, z) and incoherent power I can be usedp(x, z) is represented by
u(x，z)＝∫[∫∫s(xt，xr，k)exp(2jkR)dkdxr]dxt (15)；
Ip(x，z)＝∫[∫|∫s(xt，xr，k)exp(2jkR)dk|2dxr]dxt (16)；
Wherein the two-dimensional image described in equation (15) has been implemented in the wavenumber domain by the calculation procedure of equation (13).
In the embodiment of the present disclosure, when operation S4 is performed: reconstructing the echo signals related to the selected transmitting array element in the operation S1 through data rearrangement to obtain virtual echoes under the difference wave number;
in the application scenario of the MIMO array, the incoherent power I under the condition of taking the No. 1 transmitting array element as an example can be obtained1(x, z) expression:
I1(x，z)＝∫|∫s1(xr，k)exp(jk(RR+RT1)dk|2dxr (17)；
further, the complex signal can be rewritten into a double integral form according to a complex signal conjugation theory, and s can be obtained1(xrK) reduction to s in integration1(k1)
Figure BDA0003321502770000082
Definition kd＝k1-k2Is a difference wave number, where k1And k2Are identical, neglecting that for K1And k2The formula (18) has strong similarity with the standard BP algorithm expression (14). It can be seen that s is the same as in (18)1(k1)s1 *(k2) Depends only on (k)1-k2) Therefore, the idea of data rearrangement used in the MIMO wavenumber domain algorithm can be used for integral simplification. As shown in fig. 2, the wave number k is arranged as a wave number square matrix, each element representing the value of a difference wave number, according to (k)1-k2) With respect to the difference wave number kdRearranging s1(k1)s1 *(k2) Obtaining reconstructed virtual echo data E1(kd). Thus, for k1And k2Can be represented by kdIs calculated by a single integral, i.e.
Figure BDA0003321502770000083
Specifically, the wavenumber domain echo data s corresponding to each receiving array element1(xrK) are reconstructed as follows. The wave number k being N equally spaced samples, i.e. ki1，ki2，...，kiNSince k is sampled at equal intervals, the wavenumber difference relationship shown in fig. 2 indicates that each diagonal element pair has the same difference wavenumber (k)1-k2) With contributions, i.e. one and the same kdMay be different (k)1-k2) Combining; thus, will s1(k1)s1 *(k2) Arranged in the same manner as a data matrix, E1(kd) Is a weighted sum of all diagonal elements. Obtaining reconstructed data E1(kd) Thereafter, formula (19) may share the PSM algorithm implementation framework of formula (15), i.e., the comprehensive expression (13) of operations S2 and S3, with the only difference that the pseudo-distance is introduced to the wave number kzdTherefore, the compensation phase term is correspondingly changed, and the two sets of PSM algorithm imaging processes can be considered to correspond to and can be calculated in parallel. Defining virtual distance wavenumber kzdIs composed of
Figure BDA0003321502770000091
In the embodiment of the present disclosure, when operation S5 is performed: calculating the virtual echo of S4 according to the procedures of operation S2 and S3 to obtain a final incoherent power item in a coherence factor algorithm;
e is obtained by completing data reconstruction and calculating virtual distance to wave number1(kd) And kzdThereafter, I can be obtained according to the processing of operations S2 and S31(x, z). Specifically, mixing s1(xrK) and k are replaced by E1(xr，kd) And kdOperations S2 and S3 are performed again. Traversing all transmitting array elements to obtain It(x, z), the result is superimposed to obtain the final incoherent power:
Figure BDA0003321502770000092
referring to equation (13), the final coherence factor is CF (x, z), expressed as:
Figure BDA0003321502770000093
in the embodiment of the present disclosure, when operation S6 is performed: and calculating a coherence factor according to the coherent power and the incoherent power obtained in S3 and S5, and weighting and multiplying the coherence factor by the objective function in S3 to obtain a final objective imaging result.
Calculating according to the formula (14) to obtain a final coherence factor CF (x, z), and according to the coherence factor theory, in a coherent region (i.e., near the main beam), all aperture data are coherent, so the value is close to 1; in the incoherent region (i.e., the non-main beam region), all the aperture data is incoherent, and thus the value is less than 1. With CF (x, z) as the image weighting multiplier, the final reflectance function image can be represented as
uCF-PSM(x，z)＝CF(x，z)·u(x，z) (23)；
In the embodiment of the present disclosure, the feasibility of the above algorithm is subjected to simulation analysis by setting specific simulation parameters, which are specifically as follows:
1) setting simulation parameters as shown in table 1;
TABLE 1
Parameter(s) Size and breadth
Center of slant view 3.03m
Carrier frequency 100GHz
Bandwidth of 35GHz
Distance window 2.6m-3.4m
Number of transmitting antennas 6 are
Number of receiving antennas 39 are provided with
Transmitting antenna spacing 2.5mm
Spacing of receiving antennas 7.5mm
Array length 0.3m
2) A MIMO linear array setup is shown in fig. 3;
3) the situation of the simulated target position is shown in fig. 4a, the imaging result without the grid side lobe suppression method for MIMO beamforming is shown in fig. 4b, and the imaging result with the grid side lobe suppression method for MIMO beamforming is shown in fig. 4c, so that after the coherence factor processing, the side lobe with high energy around the target is suppressed, and the image obtains a larger dynamic range; the main lobe of the target is narrowed, and super-resolution is realized.
So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. Further, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by those of ordinary skill in the art.
From the above description, those skilled in the art should clearly recognize that the disclosed method for gate sidelobe suppression for MIMO beamforming is applicable.
In summary, the present disclosure provides a method for suppressing a grating side lobe for MIMO beamforming, which solves the problems of limitation of array arrangement and data interpolation and rearrangement in the conventional RMA and the problems of array arrangement and data rearrangement in the PSM algorithm, further exerts the advantages of the frequency domain algorithm on the premise of ensuring the imaging effect, and improves the processing speed; the super-resolution processing flow can be independent of the imaging flow, so that parallel processing can be realized, and only a small amount of calculation is increased; compared with the traditional CF algorithm based on the space domain BP, the method greatly improves the calculation efficiency. The location of the transmitter is not assumed. The algorithm can be used for a one-dimensional MIMO imaging system with arbitrarily distributed transmitters. From reciprocity, it is known that the algorithm will also be applicable to the case of receivers with arbitrary distribution and transmitters with uniform distribution, with wide applicability. Under the condition of maintaining the current working frequency and array arrangement, the power width of array dimension half-wave beams (3dB beam width defined as resolution) is reduced, the grid side lobe is suppressed, and super-resolution imaging is realized.
It should also be noted that directional terms, such as "upper", "lower", "front", "rear", "left", "right", and the like, used in the embodiments are only directions referring to the drawings, and are not intended to limit the scope of the present disclosure. Throughout the drawings, like elements are represented by like or similar reference numerals. Conventional structures or constructions will be omitted when they may obscure the understanding of the present disclosure. And the shapes and sizes of the respective components in the drawings do not reflect actual sizes and proportions, but merely illustrate the contents of the embodiments of the present disclosure.
The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify a corresponding element does not by itself connote any ordinal number of the element or any ordering of one element from another or the order of manufacture, and the use of the ordinal numbers is only used to distinguish one element having a certain name from another element having a same name.
In addition, unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be changed or rearranged as desired by the desired design. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims (7)

1. A method of gate sidelobe suppression for MIMO beamforming, comprising:
operation S1: receiving an original scattering echo signal obtained after a broadband signal is scattered by a target, selecting any one transmitting array element, and analyzing the original echo signal corresponding to the transmitting array element;
operation S2: transforming the original echo signal to a spatial frequency domain corresponding to the receiving array direction, and determining a corresponding spatial wave number spectrum;
operation S3: performing wave field extrapolation on the spatial wave number spectrum by applying a PSM algorithm, performing phase compensation on residual phases related to the selected transmitting array elements to obtain an accurate explosion field function, and obtaining a preliminary target function and a coherent power term in a coherence factor algorithm;
operation S4: reconstructing the original echo signal corresponding to the selected transmitting array element to obtain a virtual echo signal under a difference wave number;
operation S5: calculating the virtual echo signal into a final incoherent power term in a coherence factor algorithm with reference to operations S2, S3; and
operation S6: and obtaining a coherence factor according to the obtained coherent power term and the final incoherent power term, and performing weighted multiplication on the coherence factor and the objective function to obtain a final objective imaging function result.
2. The method of claim 1, wherein the method is implemented in a linear array form with transmitting ends at both ends and receiving ends at the middle, or with receiving ends at both ends and transmitting ends at the middle.
3. The method of claim 1, a final target imaging result u of the method for grating sidelobe suppression for MIMO beamformingCF-PSM(x, z) is represented by
uCF-PSM(x，z)＝CF(x，z)·u(x，z) (23)；
Wherein, CF (x, z) is the final coherence factor, u (x, z) is the preliminary objective function, x is the imaging region azimuth coordinate grid point, and z is the imaging region distance coordinate grid point.
4. The method of claim 3, wherein the final coherence factor is coherent power | u (x, z) | in a coherence factor algorithm2With final incoherent power IpThe ratio of (x, z), expressed as:
Figure FDA0003321502760000021
5. the method of claim 4, wherein the method for suppressing the grating sidelobe for MIMO beamforming is configured to complete original echo signal data reconstruction and virtual distance-to-wave number calculation, traverse all transmitting array elements, and obtain final incoherent power by superimposing the results:
Figure FDA0003321502760000022
wherein NTX is the number of transmitting array elements, It(x, z) are sub-images associated with the selected transmit elements.
6. The method of grating sidelobe suppression for MIMO beamforming according to claim 4, wherein the u (x, z) is a preliminary objective imaging function expressed comprehensively as:
Figure FDA0003321502760000023
wherein u ist(x, z) is a sub-image related to the transmitting array element with the number t, s1(xrK) is the original received echo associated with transmit array element number 1, k is the wave number corresponding to the transmit frequency, k is 2 pi f/cxrIs the azimuth wave number, kzIn the form of a distance to a wave number,
Figure FDA0003321502760000024
denotes with respect to kxrOne-dimensional inverse Fourier transform, FT of1D-xrIndicates about xrOne-dimensional fourier transform of (a).
7. The method of claim 4, non-coherent power I, for gate sidelobe suppression for MIMO beamformingp(x, z) is expressed as:
Ip(x，z)＝∫[∫|∫s(xt，xr，k)exp(2jkR)dk|2dxr]dxt (16)。
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