CN102176018B - Doppler wave beam sharpening rapid imaging method of mechanical scanning radar - Google Patents

Doppler wave beam sharpening rapid imaging method of mechanical scanning radar Download PDF

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CN102176018B
CN102176018B CN 201110062109 CN201110062109A CN102176018B CN 102176018 B CN102176018 B CN 102176018B CN 201110062109 CN201110062109 CN 201110062109 CN 201110062109 A CN201110062109 A CN 201110062109A CN 102176018 B CN102176018 B CN 102176018B
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frequency
matrix
doppler
orientation
radar
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CN102176018A (en
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李明
左磊
吴艳
王亚军
张晓伟
张鹏
罗小云
李响
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Xidian University
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Abstract

The invention discloses a Doppler wave beam sharpening rapid imaging method of a mechanical scanning radar, which mainly solves the problem that the prior art cannot be applied to a mechanical scanning radar. The method comprises the following steps of: firstly determining a pulse accumulation number M and a sharpening ratio N, arranging echoes after the pulse compression into a distance-direction matrix according to a receiving order; taking out two small matrixes which has directional length of 2*M and are mutually overlapped M from the matrix according to the receiving order; respectively performing the Doppler central estimation on the two small matrixes; using two Doppler centers to compute an interpolation frequency point; meanwhile, using the latter Doppler centre to perform the directional Doppler central compensation on the latter small matrix; then performing the directional FFT (Fast Fourier Transform), using the interpolation frequency point to extract a sub-image from the data behind the FFT, splicing the sub-image according to the receiving order to obtain a large image. Compared with the traditional DBS (direct broadcasting by satellite) imaging method, the Doppler wave beam sharpening rapid imaging method has low computation, and low requirement on the radar performance, and can be applied to the traditional mechanical scanning radar DBS imaging.

Description

The Doppler beam sharpening fast imaging method of mechanical scanning radar
Technical field
The invention belongs to the signal processing technology field, relate to radar imagery, can be used for the quick with great visual angle ground surface imaging of scope of real-time.
Background technology
Fixed ground target in the airborne radar wave beam irradiated region is because the orientation difference causes its sight line also different from the angle of the velocity vector of radar, and namely their relative carrier aircrafts have different radial velocities and produce different Doppler shifts.Doppler beam sharpening DBS becomes some narrow beamlet with the permanent echo beam splitting in the same wave beam, because different beamlet has different position angles, corresponding different Doppler frequencies, therefore can by Doppler frequency separately with different position angles separately, effectively improve radar bearing to resolution.
In the Doppler beam sharpened imaging algorithm, there is following relation:
Δ f d N = f r M
Δ f in the formula dBe the doppler bandwidth at certain scan angle place, f rBe pulse repetition rate, M is pulse accumulation number, and N is the sharpening ratio.
Because doppler bandwidth Δ f dChange with scan angle, for guaranteeing that resolution is consistent, sharpening should remain unchanged than N is common.So how to coordinate pulse repetition rate f r, coherent accumulation number M, and antenna rotation rate are the keys of Doppler beam sharpening Image Mosaics under the scanning work.For Phased Array Radar Antenna, scanning speed and the residence time control ratio of its antenna beam are easier to, and can guarantee has constant sharpening ratio under the different scanning angle.But to the mechanical scanning antenna, antenna scanning is continuous working, owing to reasons such as machinery inertials, is difficult for realizing non-uniform rotation.During coherent accumulation, pulse repetition rate and pulse accumulation number all are to keep constant in theory.But keep sharpening than constant, have one among both at least with the position segmentation step transition of scanning ripple.
Guarantee that sharpening has two kinds of thinkings usually than constant under the antenna uniform speed scanning:
Thinking one: fixed pulse accumulation number M makes pulse repetition rate f rChange with scanning angle;
Thinking two: fixed pulse repetition frequency f r, pulse accumulation number M is changed with scanning angle.
Contrast is above to guarantee that sharpening is than two kinds of constant thinkings: thinking one, and M is constant for pulse accumulation number, and namely the wave filter number in the relevant narrow band filter group is fixed.At this moment, f rNeed with bandwidth deltaf f in scan angle variation and the main beam dBe consistent, thereby so that in any case, bank of filters always is filled in Δ f dThinking two, f rConstant, pulse accumulation number M changes with scan angle, thereby guarantees that frequency resolution is constant.Thinking one often adopts f in engineering reality rStaged transition is to having relatively high expectations of Antenna Design; M changes in the thinking two, processing is made troubles to signal: signal often adopts DFT to realize coherent accumulation in processing, when using DFT here, the input data length is that M changes, and the length of exporting data should equal sharpening than N, the DFT that counts for difference, need to extract the twiddle factor table, programming is trouble, and implementation efficiency is low, is unfavorable for real-time implementation.
According to above two kinds of thinkings, at present commonly used have two kinds of methods: one by one beam sharpening method and f rInterior omnidistance FFT beam sharpening method.
Comparative maturity on these two kinds of theoretical methods, but concerning most of mechanical scanning radar, still relatively more difficult on Project Realization.In order to solve this difficult problem, the someone has proposed at pulse repetition rate f rConstant, coherent accumulation number M also keeps the sharpening pre-filtering method more constant than N under the constant prerequisite.The method is before FFT echo to be carried out filtering and down-sampled, but designs a bandwidth with Δ f dThe wave filter that changes and have good stopband characteristic and a linear phase characteristic is very difficult in engineering.
Summary of the invention
The present invention is directed to present DBS formation method and can not be applied to this shortcoming of mechanical scanning radar, proposed a kind of Doppler beam sharpening fast imaging method of mechanical scanning radar, the speed of processing to improve signal realizes the real time imagery function on the engineering.
For achieving the above object, performing step of the present invention comprises as follows:
(1) utilize known mechanical scanning radar running parameter, calculate constant radar pulse accumulation number M:
M = Δθ v θ · f r
Wherein, v θBe antenna rotation rate, Δ θ is beam angle, f rIt is radar pulse repetition frequency;
(2) according to the radar pulse of gained accumulation number M and known mechanical scanning radar running parameter, the sharpening of calculating Doppler beam sharpening is than N:
N = Δf dl · M f r
Wherein, Δ f DlThe doppler bandwidth at minimum place, expression antenna scanning angle;
The radar return that (3) will constantly receive after pulse compression as the distance to, sequentially line up the range-azimuth matrix by reception, record simultaneously the radar return number that receives, when the radar return number that receives reaches 3*M, be 3*M with an orientation to length, the sliding window that distance equates to sampling number to length and radar return distance, reading out data in the range-azimuth matrix of having lined up;
(4) small distance of the 1st to 2*M radar return in the data that read out being lined up-position and orientation matrix A, the small distance that M+1 is lined up to 3*M radar return-position and orientation matrix B, to A and these two range-azimuth matrixes of B respectively the uses energy equalization carry out the Doppler center and estimate, obtain the Doppler center f of small distance-position and orientation matrix A D1And the Doppler center f of small distance-position and orientation matrix B D2
(5) according to two estimated Doppler center f D1And f D2, determine interpolation frequency point set f n:
5a)
Figure BDA0000050303030000031
N=1,2 ... N, N are even numbers;
5b)
Figure BDA0000050303030000032
N=1,2 ... N, N are odd numbers;
(6) according to estimated Doppler center f D2Small distance-position and orientation matrix B is carried out the orientation to the compensation of Doppler center, make the centre frequency of Data in Azimuth Direction move on to 0 frequency place;
(7) data after the compensation of Doppler center are carried out the orientation to FFT, with the settling signal energy accumulation, the range-azimuth matrix after Doppler center compensation this moment has become distance-frequency matrix, and its frequency range is :-f r/ 2 to f r/ 2;
(8) from distance-frequency matrix, extract and be positioned at interpolation frequency point set f nData on institute's respective frequencies, it is consistent to angular resolution to obtain a width of cloth orientation, and the consistent subgraph of data transfer rate;
(9) with the subgraph that obtains by the order that obtains along frequency to directly splicing, obtain the with great visual angle image of scope of a width of cloth;
(10) wait for that radar receives M radar return data again after, will slide the windowsill orientation to downslide M, reading out data again, execution in step (11);
(11) repeating step (4) is to step (10).
The present invention has following advantage:
The present invention has improved again the antenna scanning speed that allows, thereby has reduced the possibility of image distorted because recycling radar return data had both guaranteed that the target in the wave beam irradiated region had enough and identical accumulation; Because the present invention adopts fixing coherent accumulation number M, use FFT energy accumulation is carried out to echo data in the orientation, thereby greatly improved the speed of Radar Signal Processing simultaneously; In addition because the present invention adopts constant radar pulse repetition frequency f r, with the designing requirement of reduction to antenna system, thereby conveniently install the Doppler beam sharpening function additional in existing mechanical scanning radar.
Experimental result shows that the present invention can be applied on the mechanical scanning radar, and can access the ground image of comparatively desirable with great visual angle scope.
Description of drawings
Fig. 1 is the Doppler beam sharpening fast imaging process flow diagram of mechanical scanning radar of the present invention;
Fig. 2 is to the real time imagery in certain city figure as a result with Doppler beam sharpening of the present invention.
Embodiment
With reference to Fig. 1, specific implementation process of the present invention is as follows:
Step 1. is calculated constant radar pulse accumulation number.
Mechanical scanning radar is installed on the aircraft that flies at a constant speed, can obtains antenna rotation rate v θ, radar beam width Delta θ and radar pulse repetition frequency f r, utilize these mechanical scanning radar running parameters, calculate constant radar pulse accumulation number M:
M = Δθ v θ · f r .
Step 2. calculate Doppler beam sharpening the sharpening ratio.
Because the doppler bandwidth Δ f of antenna dIncrease with the antenna scanning angle increases, so the doppler bandwidth Δ f of antenna dInterior frequency is counted also to be increased thereupon, in order to obtain the consistent subgraph of data transfer rate, adopts the doppler bandwidth Δ f at minimum place, antenna scanning angle among the present invention DlInterior frequency is counted as the unified sharpening ratio of Doppler beam sharpening, according to radar pulse repetition frequency f r, the doppler bandwidth Δ f at the minimum place of radar pulse accumulation number M and antenna scanning angle Dl, calculate Doppler beam sharpening sharpening than N:
N = Δf dl · M f r .
Step 3. reading out data.
With the radar return that constantly receives after pulse compression as distance to, sequentially line up the range-azimuth matrix by reception, record simultaneously the radar return number that receives, when the radar return number that receives reaches 3*M, be 3*M with an orientation to length, the sliding window that distance equates to sampling number to length and radar return distance, reading out data in the range-azimuth matrix of having lined up.
Step 4. Doppler center is estimated.
The small distance that the 1st to 2*M radar return in the data that read out lined up-position and orientation matrix A, the small distance that M+1 is lined up to 3*M radar return-position and orientation matrix B, to A and these two range-azimuth matrixes of B respectively the uses energy equalization carry out the Doppler center and estimate, obtain the Doppler center f of small distance-position and orientation matrix A D1And the Doppler center f of small distance-position and orientation matrix B D2
Step 5. is determined interpolation frequency point set f n
Two estimated Doppler center f D1And f D2Poor, be exactly the doppler bandwidth of the echo data of small distance-position and orientation matrix A and B lap, in this bandwidth range, extract equably sharpening and form interpolation frequency point set f than N frequency values n, this interpolation frequency point set f nOdevity according to N frequency values is calculated by following two kinds of formula:
5a)
Figure BDA0000050303030000051
N=1,2 ... N, N are even numbers;
5b) N=1,2 ... N, N are odd numbers.
The compensation of step 6. Doppler center.
Because estimated Doppler center f D2That the orientation of small distance-position and orientation matrix B is to the Doppler center, so when compensating at the Doppler center, each Data in Azimuth Direction of small distance-position and orientation matrix B be multiply by respectively Doppler center penalty function: exp (j2 π f D2K/f r), k=0,1,2M-1, just can make the centre frequency that compensates rear data move on to 0 frequency and locate, with corresponding Data in Azimuth Direction among the data replacement small distance-position and orientation matrix B after compensating, the centre frequency of each Data in Azimuth Direction among small distance-position and orientation matrix B is positioned at 0 frequency place at this moment.
Step 7. orientation is to FFT.
Each Data in Azimuth Direction to the small distance after the compensation of Doppler center-position and orientation matrix B carries out respectively FFT, replace corresponding Data in Azimuth Direction with the data behind the FFT, range-azimuth matrix B after Doppler center compensation this moment has become distance-frequency matrix, and its frequency range is :-f r/ 2 to f r/ 2, this step has also realized the signal energy accumulation simultaneously.
Step 8. extracts subgraph.
Successively from interpolation frequency point set f nMiddle reading frequency value is the frequency resolution of matrix when the frequency values that reads
Figure BDA0000050303030000061
Integral multiple the time, directly extract data corresponding to this frequency in the distance-frequency matrix, otherwise, in distance-frequency matrix, adopt the method for linear interpolation to extract data corresponding to this frequency; By ascending one-tenth arranged sequentially one width of cloth subgraph of frequency, this subgraph orientation is consistent to angular resolution, and data transfer rate is consistent with the data that extract.
The splicing of step 9. subgraph.
The subgraph that obtains take the first width of cloth subgraph as benchmark image, along frequency to directly arranging, is obtained the with great visual angle image of scope of a width of cloth by the order that obtains.
Step 10. will be slided the windowsill orientation to downslide M after waiting for that radar receives M radar return data again, reading out data again, execution in step (11).
Step 11. is along with the flight of aircraft and the rotation of antenna, and successional variation has occured the irradiation area of radar antenna on ground, and repeating step (4) obtains the subgraph in antenna irradiation zone this moment to step (10).
Effect of the present invention can further specify by following experiment:
1, experimental situation and content
Experimental situation: MATLAB 7.5.0, Intel (R) Pentium (R) 2CPU 3.0GHz, Window XPProfessional.
Experiment content: with the echo data of airborne mechanical scanning radar admission, under simulated environment, use the present invention and carry out imaging.
2, experimental result
Application the present invention carries out fast imaging to the echo data of airborne mechanical scanning radar admission, obtains the with great visual angle ground image of scope of a width of cloth, and the result as shown in Figure 2.
As seen from Figure 2 airport, city and around landforms etc., image quality is better, illustrates that the present invention can be applied to mechanical scanning radar.

Claims (4)

1. the Doppler beam sharpening fast imaging method of a mechanical scanning radar comprises the steps:
(1) utilize known mechanical scanning radar running parameter, calculate constant radar pulse accumulation number M:
M = Δθ v θ · f r
Wherein, v θBe antenna rotation rate, Δ θ is beam angle, f rIt is radar pulse repetition frequency;
(2) according to the radar pulse of gained accumulation number M and known mechanical scanning radar running parameter, the sharpening of calculating Doppler beam sharpening is than N:
N = Δ f dl · M f r
Wherein, Δ f DlThe doppler bandwidth at minimum place, expression antenna scanning angle;
The radar return that (3) will constantly receive after pulse compression as the distance to, sequentially line up the range-azimuth matrix by reception, record simultaneously the radar return number that receives, when the radar return number that receives reaches 3*M, be 3*M with an orientation to length, the sliding window that distance equates to sampling number to length and radar return distance, reading out data in the range-azimuth matrix of having lined up;
(4) small distance of the 1st to 2*M radar return in the data that read out being lined up-position and orientation matrix A, the small distance that M+1 is lined up to 3*M radar return-position and orientation matrix B, to A and these two range-azimuth matrixes of B respectively the uses energy equalization carry out the Doppler center and estimate, obtain the Doppler center f of small distance-position and orientation matrix A D1And the Doppler center f of small distance-position and orientation matrix B D2
(5) according to two estimated Doppler center f D1And f D2, determine interpolation frequency point set f n:
5a)
Figure FDA00002123970000013
N=1,2 ... N, N are even numbers;
5b)
Figure FDA00002123970000014
N=1,2 ... N, N are odd numbers;
(6) according to estimated Doppler center f D2Small distance-position and orientation matrix B is carried out the orientation to the compensation of Doppler center, make the centre frequency of Data in Azimuth Direction move on to 0 frequency place;
(7) data after the compensation of Doppler center are carried out the orientation to FFT, with the settling signal energy accumulation, the range-azimuth matrix after Doppler center compensation this moment has become distance-frequency matrix, and its frequency range is :-f r/ 2 to f r/ 2;
(8) from distance-frequency matrix, extract and be positioned at interpolation frequency point set f nData on institute's respective frequencies, it is consistent to angular resolution to obtain a width of cloth orientation, and the consistent subgraph of data transfer rate;
(9) with the subgraph that obtains by the order that obtains along frequency to directly splicing, obtain the with great visual angle image of scope of a width of cloth;
(10) wait for that radar receives M radar return data again after, will slide the windowsill orientation to downslide M, reading out data again, execution in step (11);
(11) repeating step (4) is to step (10).
2. described method according to claim 1, wherein step (6) is described according to estimated Doppler center f D2Small distance-position and orientation matrix B is carried out the orientation to Doppler center compensation, is that each Data in Azimuth Direction with small distance-position and orientation matrix B multiply by respectively Doppler center penalty function: exp (j2 π f D2K/f r), k=0,1 ... 2M-1 compensates one by one, replaces corresponding Data in Azimuth Direction with the data after the compensation, realizes the orientation of small distance-position and orientation matrix B is compensated to the Doppler center.
3. described method according to claim 1, wherein described the extracting from distance-frequency matrix of step (8) is positioned at interpolation frequency point set f nData on institute's respective frequencies are successively from interpolation frequency point set f nMiddle reading frequency value is the frequency resolution of matrix when the frequency values that reads
Figure FDA00002123970000021
Integral multiple the time, directly extract data corresponding to this frequency in the distance-frequency matrix, otherwise, in distance-frequency matrix, adopt the method for linear interpolation to extract data corresponding to this frequency; With the data that extract by ascending one-tenth arranged sequentially one width of cloth subgraph of frequency.
4. described method according to claim 1, wherein step (9) described with the subgraph that obtains by the order that obtains along frequency to directly splicing, that the subgraph that will obtain is take the first width of cloth subgraph as benchmark image, along frequency to directly arranging, obtain the with great visual angle image of scope of a width of cloth by the order that obtains.
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CN105182332B (en) * 2015-09-15 2018-01-19 上海无线电设备研究所 A kind of two dimensional beam sharpening method
CN105589071B (en) * 2015-12-11 2017-12-22 西安电子科技大学 Airborne radar high-resolution DBS imaging methods based on SPICE
CN106872969B (en) * 2017-03-22 2019-08-06 西安电子科技大学 Radar target angle estimation method based on MTD pulse accumulation and sliding processing
CN106970386B (en) * 2017-03-31 2019-09-03 西安电子科技大学 A kind of optimization method of Radar Doppler beam sharpening
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CN109613532B (en) * 2019-01-02 2020-11-10 电子科技大学 Airborne radar real-time Doppler beam sharpening super-resolution imaging method
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