CN112014807A - Self-adaptive clutter suppression method for frequency agile radar - Google Patents

Self-adaptive clutter suppression method for frequency agile radar Download PDF

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CN112014807A
CN112014807A CN202010824214.6A CN202010824214A CN112014807A CN 112014807 A CN112014807 A CN 112014807A CN 202010824214 A CN202010824214 A CN 202010824214A CN 112014807 A CN112014807 A CN 112014807A
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clutter
target
clu
doppler
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CN112014807B (en
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曹运合
刘帅
王徐华
吴春林
罗运华
卢毅
王从思
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Xidian University
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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
    • G01S7/36—Means for anti-jamming, e.g. ECCM, i.e. electronic counter-counter measures
    • 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
    • G01S7/414—Discriminating targets with respect to background clutter

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Abstract

The invention discloses a self-adaptive clutter suppression method of a frequency agile radar, which comprises the following steps: establishing a frequency agility signal model, constructing an echo data model of a frequency agility radar, and acquiring a sampling signal of a range gate where a target is located as an input signal to be processed; designing a generalized Doppler window function; designing a distance matching filter bank corresponding to the clutter Doppler channel; calculating a high-resolution one-dimensional range profile of the input signal to be processed on a clutter Doppler channel; constructing a clutter and noise covariance matrix; designing a clutter suppression filter bank corresponding to a target Doppler channel; and the clutter suppression filter bank is utilized to carry out clutter suppression and one-dimensional range profile generation on the input signal to be processed. The invention can utilize all the pulses transmitted in the frequency agile radar one-time CPI to realize clutter suppression and coherent processing, and has stronger adaptability, namely, the invention is suitable for the condition of clutter power spectrum broadening and different clutter fluctuation conditions.

Description

Self-adaptive clutter suppression method for frequency agile radar
Technical Field
The invention relates to the technical field of radar signal processing, in particular to a self-adaptive clutter suppression method for a frequency agile radar. The method is suitable for target one-dimensional imaging and detection of the frequency agile radar in a clutter environment.
Background
The radar countermeasure is an important component of the electronic countermeasure, and the frequency agility technology is an effective measure for realizing active anti-interference of the radar; in the frequency agility signal, the carrier frequency of each transmission pulse is agile in a wider range in a wider frequency band in a random or predetermined mode, has the characteristic of low interception probability, and can effectively inhibit various main amplitude lobe interference modes such as aiming mode, pressing mode, deception mode and the like.
Frequency agile radars are receiving much attention due to their excellent interference rejection and high resolution in the range dimension. However, due to the inconsistency of the carrier frequencies of the pulse transmission, the frequency agile radar is incompatible with the traditional radar Moving Target Detection (MTD) technology, so that the clutter suppression problem becomes a great obstacle for the frequency agile radar to be used in actual engineering.
At present, two coherent processing algorithms are suitable for the frequency agile radar in the clutter environment. The other method is that clutter suppression is realized by using a same-frequency pulse signal within a time of primary coherent processing, then bandwidth synthesis is realized by using a different-frequency pulse echo, and a target high-resolution one-dimensional range profile subjected to clutter suppression is output; the method has the defects that the degree of freedom provided by all pulses cannot be utilized during clutter suppression, so that the clutter suppression performance is limited, and if the clutter processing gain is kept high enough, a radar is required to transmit multiple groups of same-frequency pulses, so that the regularity of transmitted waveforms is increased, and the anti-interference performance of the frequency agile radar is reduced. The other method is to utilize all pulses transmitted in the primary CPI of the frequency agile radar to realize clutter suppression and bandwidth synthesis processing, the algorithm realizes different-frequency clutter suppression, the clutter suppression can be realized by using the degree of freedom provided by all the pulses in the primary CPI, the only example at present is that S.R.J.Axelsson of the Swedish national defense research institute published a subtrraction algorithm in the journal of IEEE Trans on GRS in 2007, the algorithm is a great progress of the clutter suppression of the frequency agile radar, the feasibility of the different-frequency clutter suppression is marked, but the algorithm can only play a good suppression role on completely static clutter, generally, due to the influence of wind speed, the power spectrum of the clutter has a certain spectral width, namely, a clutter scatterer cannot be completely static, and therefore, the application of the algorithm in practical engineering is greatly limited.
Disclosure of Invention
Aiming at the problems in the prior art, the invention aims to provide a self-adaptive clutter suppression method for a frequency agile radar, which can realize clutter suppression and coherent processing by using all pulses transmitted in one CPI of the frequency agile radar, and has stronger adaptability, namely, the method is suitable for the condition of clutter power spectrum broadening and different clutter fluctuation conditions.
In order to achieve the purpose, the invention is realized by adopting the following technical scheme.
A self-adaptive clutter suppression method of a frequency agile radar comprises the following steps:
step 1, establishing a frequency agility signal model, constructing an echo data model of a frequency agility radar under a clutter background, and sequentially performing down-conversion, low-pass filtering, pulse compression and target sampling on the echo data of the frequency agility radar to obtain a sampling signal of a range gate where a target is located as an input signal to be processed;
step 2, designing a generalized Doppler window function according to the frequency agility signal model, and expanding the Doppler coverage range of the clutter Doppler channel in the step 3;
step 3, designing a distance matching filter bank corresponding to a clutter Doppler channel according to the frequency agile radar model; calculating a high-resolution one-dimensional range profile of the input signal to be processed on a clutter Doppler channel through the range matching filter bank and the generalized Doppler window function, and estimating the range and amplitude information of a strong clutter scattering point according to the high-resolution one-dimensional range profile;
step 4, constructing a clutter and noise covariance matrix R according to the distance and amplitude information of the strong clutter scattering points;
step 5, designing a clutter suppression filter bank corresponding to a target Doppler channel according to the frequency agile signal model, the clutter covariance matrix R and the tracking speed of the target; and performing clutter suppression on the input signal to be processed by using the clutter suppression filter bank to obtain a target high-resolution one-dimensional range profile after clutter suppression, and completing the self-adaptive clutter suppression of the frequency agile radar.
Compared with the prior art, the invention has the beneficial effects that:
(1) compared with the method for realizing clutter suppression by using the same-frequency pulse signals in the time of the primary coherent processing, the method can realize clutter suppression by using the degrees of freedom provided by all pulses, so that the method has better theoretical performance of clutter suppression; the method realizes the suppression of the different-frequency clutter, does not need to transmit a plurality of same-frequency pulses within one coherent processing time, and can ensure that the transmitted signal has strong randomness to reduce the interception probability; in addition, the heterofrequency clutter suppression also means that the radar can be kept randomly agile within a large range without losing the high distance resolution performance of the frequency agile radar.
(2) Compared with the subtrection algorithm, the invention designs the generalized Doppler window function and the Doppler domain broadening method of the clutter suppression filter, so that the method can be suitable for the actual clutter environment, namely, the method is still effective under the condition that the clutter power spectrum has a certain spectrum width.
Drawings
The invention is described in further detail below with reference to the figures and specific embodiments.
FIG. 1 is a flow chart of an implementation of the present invention;
FIG. 2(a) is a graph comparing the velocity response of the generalized Doppler window function designed by the present invention with the result of a conventional rectangular window process;
FIG. 2(b) is a partial enlarged view of the 3dB main lobe of FIG. 2 (a);
FIG. 3(a) is a result graph of a high resolution one-dimensional range profile corresponding to a clutter Doppler channel generated using a generalized Doppler window function in the present invention;
FIG. 3(b) is a result graph of a high resolution one-dimensional range profile corresponding to a clutter Doppler channel obtained using a normal rectangular window function;
FIG. 4(a) is a range-Doppler two-dimensional response result graph of a clutter suppression filter designed according to the present invention;
FIG. 4(b) is a partial enlarged view of the stop band resulting from FIG. 4 (a);
FIG. 4(c) is an enlarged partial view of the pass band in the result of FIG. 4 (a);
FIG. 5(a) is a graph of the range response of a clutter suppression filter designed according to the present invention in a clutter Doppler channel;
FIG. 5(b) is a graph of the Doppler response of an embodiment of the present invention at a range bin within which the passband is located;
FIG. 6(a) is a graph of the results of a high resolution one-dimensional range profile of a target using a range-matched filter bank;
FIG. 6(b) is a diagram of the result of a high-resolution one-dimensional range profile of a target obtained using the clutter suppression filter bank of the present invention;
FIG. 7(a) is a graph of the method and subtrection algorithm of the present invention as a function of parameter σcComparing the clutter suppression performance curve with the clutter suppression performance curve when v changes;
FIG. 7(b) is a comparison graph of clutter suppression performance curves for the method and the subtrection algorithm of the present invention as a function of input signal-to-noise ratio and the parameter v.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention.
Referring to fig. 1, the adaptive clutter suppression method for a frequency agile radar provided by the present invention includes the following steps:
step 1, establishing a frequency agility signal model, constructing an echo data model of a frequency agility radar under a clutter background, and sequentially performing down-conversion, low-pass filtering, pulse compression and target sampling on the echo data of the frequency agility radar to obtain a sampling signal of a range gate where a target is located as an input signal to be processed;
establishing a frequency agility signal model: let a coherent processing time (CPI) be used to transmit N independent chirps with a pulse repetition interval of TrThe time width and the bandwidth of each pulse are respectively TpAnd BpFrequency agile interval of Δ f, fcAs the initial carrier frequency, the carrier frequency of each pulse can be respectively written as fc+niΔ f, wherein i ═ 0,1, …, N-1, NiEncoding the ith random frequency modulation. If M is the number of selectable frequency points, f isc+niΔf∈[fc,fc+MΔf]. Then, the ith transmit pulse signal can be written as:
Figure BDA0002635557960000051
where t is time, μ ═ Bp/TpFor chirp rate, rect (-) is a rectangular window function,
Figure BDA0002635557960000052
constructing an echo data model of the frequency agile radar under the clutter background: setting a radial velocity VtarThe target is captured and tracked by the radar, the target consists of K scattering points, and the initial distance between each target scattering point and the radar is respectively as follows: rtar(1),Rtar(2),…,Rtar(K) (ii) a Then, the distance of the kth scattering point with respect to the radar at time t is rtar(t,k)＝Rtar(k)-Vtart。
In a similar way, L clutter scattering points are arranged in the range gate where the target is located, and the initial distance between each clutter scattering point and the radar is respectively as follows: rclu(1),Rclu(2),…,Rclu(L), the speed of each clutter scattering point is respectively as follows: vclu(1),Vclu(2),…,Vclu(L), then the distance r of the ith clutter scattering point to the radar at time tclu(t,l)＝Rclu(l)-Vclu(l) t. ThatHowever, the received signal corresponding to the range gate can be written as:
Figure BDA0002635557960000053
wherein w (t) is a power of σw 2Of the receiver noise, gammatar(k) And gammaclu(l) The scattering coefficients of the kth target scattering point and the l clutter scattering point are respectively.
The received signal is subjected to a complete linear frequency modulation signal processing flow, namely, down conversion, low-pass filtering and pulse compression, and then is subjected to sampling processing, and the sampling signal of the ith echo pulse at a range gate where a target is located is obtained and written as:
s(i)＝star(i)+sclu(i)+w(i)
wherein
Figure BDA0002635557960000061
Figure BDA0002635557960000062
Defining the received signal vector as s ∈ C1×N，s＝[s(0),s(1),…,s(N-1)]Is provided with
s＝star+sclu+w
Wherein s istar＝[star(0),star(1),…,star(N-1)]A sample vector, s, representing the targetclu＝[sclu(0),sclu(1),…,sclu(N-1)]Sample vector representing clutter, w ═ w (0), w (1), …, w (N-1)]A vector of samples representing noise. The vector s serves as the input signal to be processed.
Step 2, designing a generalized Doppler window function according to the frequency agility signal model, and expanding the Doppler coverage range of the clutter Doppler channel in the step 3;
doppler window function generalized Doppler for broadening zero Doppler channelAnd (4) designing a generalized Doppler window function according to the Doppler phase term of target sampling data in the frequency agile radar echo model in the coverage range. Sampling data(s) from a targettar(i) Formula (V) to design a velocity V0The doppler phase vector corresponding to the clutter scattering point:
Figure BDA0002635557960000063
at the same time, a speed is designed to be V1Reference vector of (2):
Figure BDA0002635557960000064
and (3) setting the generalized Doppler window function as [ omega (0), omega (1), …, omega (N-1) ], and performing cross-correlation on the clutter Doppler phase vector and the reference vector on the basis of using the generalized Doppler window function to obtain a correlation function of the clutter Doppler phase vector and the reference vector:
Figure BDA0002635557960000071
wherein Δ V ═ V0-V1By [. alpha. ] representing a Hadamard product]HRepresenting a conjugate transpose.
And designing a generalized Doppler window function based on a traditional window function according to the expression form of the correlation function.
Since the generalized Doppler window function is used to broaden the Doppler coverage of the zero Doppler channel, the function is suitably designed based on a large main lobe width window function, such as Blackman window, Kaiser window, etc. Illustratively, the original Blackman window function (Blackman window) is:
Figure BDA0002635557960000072
the generalized doppler window function based on the Blackman window design can be written as:
Figure BDA0002635557960000073
step 3, designing a distance matching filter bank corresponding to a clutter Doppler channel according to the frequency agility signal model; calculating a high-resolution one-dimensional range profile of the input signal to be processed on a clutter Doppler channel through the range matching filter bank and the generalized Doppler window function, and estimating the range and amplitude information of a strong clutter scattering point according to the high-resolution one-dimensional range profile;
the invention estimates the distance and amplitude information of strong clutter scattering points by generating a high-resolution one-dimensional range profile corresponding to a clutter Doppler channel to realize self-adaptive clutter suppression.
Specifically, a distance matching filter matrix corresponding to a doppler channel having a center velocity V is defined as ΦV∈CN ×MWherein
Figure BDA0002635557960000074
Figure BDA0002635557960000075
According to the matched filtering principle, the elements in the distance matched filter matrix are:
Figure BDA0002635557960000081
since clutter power spectrum generally obeys a 0-mean Gaussian distribution, Φ is defined0A distance matching filter matrix corresponding to the clutter Doppler channel, wherein the corresponding central speed is 0 m/s; the complex high-resolution one-dimensional range profile generated by the received signal vector s on the doppler channel is calculated according to the following formula:
Figure BDA0002635557960000082
then y iscluCorresponding high resolution one-dimensional range profile is
Figure BDA00026355579600000810
And | is a modulus operation.
For high-resolution one-dimensional range profile
Figure BDA0002635557960000083
Performing threshold detection, wherein clutter scattering points exceeding a preset detection threshold are strong clutter scattering points to obtain H strong clutter scattering points, and the distance and scattering coefficient estimation values of the H strong clutter scattering points are respectively
Figure BDA0002635557960000084
And
Figure BDA0002635557960000085
h＝1,2,…,H,H>1。
step 4, constructing a clutter and noise covariance matrix R according to the distance and amplitude information of the strong clutter scattering points;
the clutter and noise covariance matrix is used for enabling the clutter suppression filter to form the null at the position of a strong clutter scattering point, and the null broadening is carried out in a speed-distance two-dimensional mode simultaneously in consideration of clutter power spectrum expansion and estimation errors of distance information of the strong clutter scattering point so as to keep the robustness of clutter suppression.
Specifically, the broadening degree of the null of the clutter suppression filter in the velocity dimension is set to be D according to the current working environment of the radarVThe extent of broadening in the distance dimension is DR(ii) a Wherein DVGreater than clutter spectral width σc，DRThe distance resolution c/2 Mdelta f is larger than that of the frequency agile radar; setting the distance parameter of the h strong clutter scattering point
Figure BDA0002635557960000086
Velocity parameter Vclu(h)～N(0,DV 2) Then, define Rclu(h) And Vclu(h) Respectively is
Figure BDA0002635557960000087
And
Figure BDA0002635557960000088
comprises the following steps:
Figure BDA0002635557960000089
Figure BDA0002635557960000091
defining a clutter covariance matrix corresponding to the h-th strong clutter scattering point as Rh∈CN×NThe alpha row and beta column elements are [ R ]h]α,βAnd then:
when a is equal to β, then,
[Rh]α,β＝1
when a is not equal to β,
Figure BDA0002635557960000092
wherein n isαFor the alpha random frequency modulation coding, nβEncoding the beta random frequency modulation;
due to Rclu(h) And Vclu(h) Independent of each other, the above formula can be rewritten as:
Figure BDA0002635557960000093
the clutter covariance matrix R of the h-th strong clutter scattering point can be obtained based on the formulahEach element of (1).
Then, a clutter plus noise covariance matrix is defined as R ∈ CN×NThe method comprises the following steps:
Figure BDA0002635557960000094
wherein the content of the first and second substances,
Figure BDA0002635557960000095
is the distance estimation value of the h-th strong clutter scattering point, I belongs to CN×NIs an identity matrix.
Step 5, designing a clutter suppression filter bank corresponding to a target Doppler channel according to the frequency agile signal model, the clutter covariance matrix R and the tracking speed of the target; and performing clutter suppression on the input signal to be processed by using the clutter suppression filter bank to obtain a target high-resolution one-dimensional range profile after clutter suppression, and completing the self-adaptive clutter suppression of the frequency agile radar.
Setting the tracking speed of the target as
Figure BDA0002635557960000101
The estimate is given by the radar target tracking module. The distance matching filter matrix corresponding to the Doppler channel where the target is located is
Figure BDA0002635557960000102
Figure BDA0002635557960000103
Can be calculated by formula (I) in step 3.
Setting the clutter suppression filter matrix corresponding to the Doppler channel as
Figure BDA0002635557960000104
Figure BDA0002635557960000105
Figure BDA0002635557960000106
Calculated by the following formula:
Figure BDA0002635557960000107
Figure BDA0002635557960000108
the lagrange multiplier method shows that:
Figure BDA0002635557960000109
using clutter suppression filter matrices
Figure BDA00026355579600001010
Performing clutter suppression on an input signal s to be processed to obtain a target complex high-resolution one-dimensional range profile after clutter suppression:
Figure BDA00026355579600001011
and (3) obtaining a target high-resolution one-dimensional range profile after the frequency agile radar clutter is suppressed by taking the module value of each element:
Figure BDA00026355579600001012
in order to realize the self-adaptive clutter suppression of the frequency agility radar, firstly, a high-resolution one-dimensional range profile corresponding to a clutter Doppler channel is made by using a frequency agility signal echo and is used for estimating the range and amplitude information of a strong clutter scattering point; considering that the power spectrum of the actual clutter is extended, namely the radial velocity of the clutter randomly changes in a small range with 0 as the center, the method designs a generalized Doppler window function for extending the coverage range of a clutter Doppler channel in the clutter range imaging process. Secondly, designing a clutter and noise covariance matrix according to the distance and amplitude estimation information of strong clutter scattering points, and calculating a clutter suppression filter bank with a distance-Doppler two-dimensional characteristic according to the clutter and noise covariance matrix; the covariance matrix is used for enabling the clutter suppression filter to form a null at the position of a strong clutter scattering point (distance-Doppler two-dimension), and considering the distance estimation error of the strong clutter scattering point and the power spectrum expansion condition, the method can enable the null of the clutter suppression filter to be widened at the same time in the distance dimension and the speed dimension by adjusting the covariance matrix so as to enhance the robustness of the method. And finally, replacing the distance matching filter bank with the clutter suppression filter bank to obtain the clutter suppressed target high-resolution one-dimensional range profile.
The method can utilize all pulses transmitted by the frequency agile radar CPI once to realize clutter suppression, is still applicable under the condition of clutter power spectrum broadening, and solves the compatibility problem of frequency agile and clutter suppression on the basis of realizing different-frequency clutter suppression and considering the actual clutter characteristics.
Simulation experiment
To demonstrate the effectiveness of the present invention, the following simulation and comparative experiments were used for further illustration.
(1) Simulation conditions are as follows:
the waveform parameters of the frequency agile signal are set as follows: initial frequency fcThe number of transmission pulses N of one CPI is 256, the number of optional frequency points M is 128, and the pulse repetition interval T is 8GHzr100us, pulse width Tp100us, pulse bandwidth Bp10MHz, frequency agility interval Δ f 10MHz, receiver noise power σw 2Carrier frequency modulation coding n of 0dBi(i-0, 1, …, M-1) obeys a discrete uniform distribution over {0,1, …, M-1} and is independent of each other. In simulations 2-4, a fixed target scene is given, wherein the target velocity is 40m/s, the target consists of three scattering points, and the distance parameters are Rtar(1)＝1508m,Rtar(2)＝1509m,Rtar(3) 1510m, their respective scattering coefficients are γtar(1)＝1dB,γtar(2)＝3dB,γtar(3) 2 dB. The range gate of the target has three strong clutter scattering points and several weak clutter scattering points, the total power of the weak clutter echoes is consistent with that of the target echo, and the distance parameters of the three strong clutter scattering points are Rclu(1)＝1503m,Rclu(2)＝1507m,Rclu(3) 1509m, the scattering coefficients are respectively gammaclu(1)＝20dB,γclu(2)＝22dB,γclu(3) In order to simulate the clutter power spectrum spreading condition, the speed parameters of three strong clutter scattering points are set to be V respectivelyclu(1)＝0.169m/s,Vclu(2)＝-0.028m/s,Vclu(3) In simulation 5, the target scene is randomly set according to different scene parameters, which is 0.483 m/s.
(2) Simulation content and results:
simulation 1, simulating the characteristic of the generalized Doppler window function in step 2 of the method of the invention, and comparing the result with a common rectangular window function, wherein the Doppler response results of the two window functions are shown in FIG. 2(a), and FIG. 2(b) is a partial enlarged view of the 3dB main lobe in FIG. 2 (a); as can be seen from fig. 2(a), the generalized doppler window function can significantly increase the velocity coverage of the clutter doppler channel, and as can be seen from fig. 2(b), the 3dB doppler mainlobe width of the rectangular window is 0.60m/s, while the generalized doppler window function is 1.04 m/s.
Simulation 2, simulating the high-resolution one-dimensional range profile corresponding to the clutter Doppler channel generated in the step 3 of the method, and comparing the result with that when a common rectangular window function is used; the simulation results are shown in fig. 3, in which fig. 3(a) is a result obtained using a generalized doppler window function and fig. 3(b) is a result obtained using a general rectangular window function. As can be seen from fig. 3(a), when the generalized doppler window function is not used, the third strong clutter scattering point cannot be detected and information cannot be estimated from the clutter one-dimensional range profile, and then the strong clutter scattering point cannot be effectively suppressed; as can be seen from fig. 3(b), when the generalized doppler window function is used, three strong clutter scattering points can be detected, and the distance parameter estimates are:
Figure BDA0002635557960000121
Figure BDA0002635557960000122
the scattering coefficients are estimated as
Figure BDA0002635557960000123
Figure BDA0002635557960000124
Simulation 3, simulating the range-doppler two-dimensional response of the clutter suppression filter generated in step 5 of the method of the present invention, and the simulation result is shown in fig. 4(a), wherein fig. 4(b) is a partial enlarged view of the stop band in the result of fig. 4(a), and fig. 4(c) is a partial enlarged view of the pass band in the result of fig. 4 (a); as can be seen from fig. 4(a), 4(b), and 4(c), the clutter suppression filter designed by the method of the present invention has a two-dimensional characteristic, the clutter suppression filter forms a pass band on the doppler channel where the target is located, and forms nulls on the doppler channel where the clutter is located, and the null positions correspond to the scattering points of the strong waves. The range response of the clutter suppression filter in the clutter doppler channel and the doppler response of the range cell in the passband are shown in fig. 5(a) and 5(b), respectively; as can be seen from fig. 5(a) and 5(b), nulls are broadened in both the distance dimension and the velocity dimension, broadening in the distance dimension can reduce clutter suppression performance degradation caused by distance information estimation errors of strong clutter scattering points, and broadening in the velocity dimension can cope with the influence of clutter power spectrum expansion.
And 4, simulating the target high-resolution one-dimensional range profile generated after clutter suppression in the step 5 of the method, and comparing the target high-resolution one-dimensional range profile with a common coherent processing result, wherein the simulation result is shown in fig. 6, wherein fig. 6(a) is a result obtained by using a range matched filter bank, and fig. 6(b) is a result obtained by using the clutter suppression filter bank of the invention. As can be seen from fig. 6(a), in the one-dimensional range profile obtained by the conventional coherent processing, the target is submerged by the noise floor formed by the clutter; as can be seen from fig. 6(b), in the one-dimensional range profile obtained by the clutter suppression filter designed by the method of the present invention, the peaks formed by the three scattering points of the target are all visible, and the peak positions correctly correspond to the range parameters of the three target scattering points.
Simulation 5, simulating the performance of the method under different input signal-to-noise ratios, different clutter spectrum widths and different clutter fluctuation models, and comparing the result with a subtrection algorithm; wherein the input signal-to-noise ratio varies from-30 dB to-10 dB, and the clutter power spectrum obeys the spectral width sigmac(standard deviation) gaussian distribution varying from 0 to 0.5m/s, K distribution with different clutter fluctuation models obeying scale parameter α being 1, shape parameter v being 1, 2, 4 respectively;10000 Monte Carlo experiments were performed in each case, the simulation results are shown in FIG. 7, and the method of the present invention was simulated in FIG. 7(a) with the parameter σcAnd v is changed, the input signal-to-noise-and-noise ratio is fixed to-20 dB; in FIG. 7(b), the condition of the method of the present invention varying with the input signal-to-noise ratio and the parameter v is simulated, and the spectral width σ of the clutter power is setcFixed at 0.22 m/s. As can be seen from fig. 7(a), since the clutter spectrum spreading is not considered, the performance of the subtrraction algorithm is severely degraded as the clutter power spectrum width is increased; in the method, due to the use of a generalized Doppler window function and the broadening of clutter suppression filter null in a Doppler dimension, the method is still applicable to the condition of broadening of clutter power spectrum; comparing fig. 7(a) and 7(b), it can be seen that different clutter fluctuation models also have a certain influence on the performance of the algorithm, but the influence is small because the method of the present invention adopts the adaptive clutter suppression system, and has adaptability to different clutter fluctuation models.
Although the present invention has been described in detail in this specification with reference to specific embodiments and illustrative embodiments, it will be apparent to those skilled in the art that modifications and improvements can be made thereto based on the present invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims (8)

1. A self-adaptive clutter suppression method of a frequency agile radar is characterized by comprising the following steps:
step 1, establishing a frequency agility signal model, constructing an echo data model of a frequency agility radar under a clutter background, and sequentially performing down-conversion, low-pass filtering, pulse compression and target sampling on the echo data of the frequency agility radar to obtain a sampling signal of a range gate where a target is located as an input signal to be processed;
step 2, designing a generalized Doppler window function according to the frequency agility signal model, and expanding the Doppler coverage range of the clutter Doppler channel in the step 3;
step 3, designing a distance matching filter bank corresponding to a clutter Doppler channel according to the frequency agile radar model; calculating a high-resolution one-dimensional range profile of the input signal to be processed on a clutter Doppler channel through the range matching filter bank and the generalized Doppler window function, and estimating the range and amplitude information of a strong clutter scattering point according to the high-resolution one-dimensional range profile;
step 4, constructing a clutter and noise covariance matrix R according to the distance and amplitude information of the strong clutter scattering points;
step 5, designing a clutter suppression filter bank corresponding to a target Doppler channel according to the frequency agile signal model, the clutter covariance matrix R and the tracking speed of the target; and performing clutter suppression on the input signal to be processed by using the clutter suppression filter bank to obtain a target high-resolution one-dimensional range profile after clutter suppression, and completing the self-adaptive clutter suppression of the frequency agile radar.
2. The adaptive clutter suppression method for frequency agile radar according to claim 1, wherein the establishing a frequency agile signal model specifically comprises: setting N independent linear frequency modulation pulses to be transmitted within one-time coherent processing time, wherein the pulse repetition interval is TrThe time width and the bandwidth of each pulse are respectively TpAnd BpFrequency agile interval of Δ f, fcThe carrier frequency of each pulse is fc+niΔ f, wherein i ═ 0,1iEncoding the ith random frequency modulation;
if M is the number of selectable frequency points, f isc+niΔf∈[fc，fc+MΔf]Then, the ith transmission pulse signal is:
Figure FDA0002635557950000021
where t is time, μ ═ Bp/TpFor chirp rate, rect (-) is a rectangular window function,
Figure FDA0002635557950000022
3. the adaptive clutter suppression method for frequency agile radar according to claim 2, wherein the constructing the echo data model of the frequency agile radar in the clutter background is specifically:
first, let a radial velocity VtarThe target is captured and tracked by the radar, the target consists of K scattering points, and the initial distance between each target scattering point and the radar is respectively as follows: rtar(1)，Rtar(2)，...，Rtar(K) (ii) a Then, the distance of the kth scattering point with respect to the radar at time t is rtar(t，k)＝Rtar(k)-Vtart；
Secondly, it is established that there is last clutter scattering point in the range gate of target place, and the initial distance between each clutter scattering point and the radar is respectively: rclu(1)，Rclu(2)，...，Rclu(L), the speed of each clutter scattering point is respectively as follows: vclu(1)，Vclu(2)，...，Vclu(L), then the distance r of the ith clutter scattering point to the radar at time tclu(t，l)＝Rclu(l)-Vclu(l)t；
Finally, the received signal corresponding to the range gate where the target is located is:
Figure FDA0002635557950000023
wherein w (t) is a power of σw 2Of the receiver noise, gammatar(k) And gammaclu(l) The scattering coefficients of the kth target scattering point and the l clutter scattering point are respectively;
the sampling signal of the ith echo pulse at the range gate where the target is located is:
s(i)＝star(i)+sclu(i)+w(i)
wherein
Figure FDA0002635557950000031
Figure FDA0002635557950000032
The total target sampling signal, i.e. the input signal to be processed, is then:
s＝star+sclu+w
wherein s istar＝[star(0)，star(1)，...，star(N-1)]A sample vector, s, representing the targetclu＝[sclu(0)，sclu(1)，...，sclu(N-1)]A sampling vector representing clutter, w ═ w (0), w (1), w (N-1)]A vector of samples representing noise.
4. The adaptive clutter suppression method for frequency agile radar according to claim 2, wherein the generalized doppler window function is designed according to a frequency agile signal model, specifically:
2.1, designing a velocity V from the Doppler phase term of the target sampling data expression0The doppler phase vector corresponding to the clutter scattering point:
Figure FDA0002635557950000033
at the same time, a speed is designed to be V1Reference vector of (2):
Figure FDA0002635557950000034
2.2, the generalized doppler window function is ω ═ ω (0), ω (1),.., ω (N-1) ], and the clutter doppler phase vector and the reference vector are cross-correlated on the basis of using the generalized doppler window function to obtain a correlation function of the two:
Figure FDA0002635557950000035
wherein Δ V ═ V0-V1By [. alpha. ] representing a Hadamard product]HRepresents a conjugate transpose;
2.3, designing a generalized Doppler window function based on a traditional window function according to the representation form of the correlation function;
wherein, the traditional window function is a Blackman window function or a Kaiser window function.
5. The adaptive clutter suppression method of frequency agile radar according to claim 4, wherein the designing of the range matched filter bank of the clutter doppler channel specifically comprises:
defining a distance-matched filter matrix corresponding to the Doppler channel with a center velocity V as phiV∈CN×MWherein
Figure FDA0002635557950000041
Figure FDA0002635557950000042
According to the matched filtering principle, the elements in the distance matched filter matrix are:
Figure FDA0002635557950000043
6. the adaptive clutter suppression method of frequency agile radar according to claim 5, wherein the computing the high resolution one-dimensional range profile of the input signal to be processed on the clutter doppler channel and estimating the range and amplitude information of the strong clutter scattering point according to the computed high resolution one-dimensional range profile is specifically:
first, due to clutter powerThe spectra are usually obeyed to a 0-mean Gaussian distribution, defining phi0A distance matching filter matrix corresponding to the clutter Doppler channel, wherein the corresponding central speed is 0 m/s; the complex high-resolution one-dimensional range profile generated by the target sampling data s on the clutter Doppler channel is calculated according to the following formula:
Figure FDA0002635557950000044
then y iscluCorresponding high resolution one-dimensional range profile is
Figure FDA0002635557950000045
| · | is the modulo operation;
then, for the high resolution one-dimensional range profile
Figure FDA0002635557950000046
Performing threshold detection, wherein clutter scattering points exceeding a preset detection threshold are strong clutter scattering points to obtain H strong clutter scattering points, and the distance and scattering coefficient estimation values of the H strong clutter scattering points are respectively
Figure FDA0002635557950000047
And
Figure FDA0002635557950000048
7. the adaptive clutter suppression method of frequency agile radar according to claim 1, wherein said constructing a clutter plus noise covariance matrix according to the distance and amplitude information of said strong clutter scattering points comprises the steps of:
4.1 setting the broadening degree of the null of the clutter suppression filter in the velocity dimension to DVThe extent of broadening in the distance dimension is DR(ii) a Wherein DVGreater than clutter spectral width σc，DRThe distance resolution c/2 Mdelta f is larger than that of the frequency agile radar; setting the distance of the h strong clutter scattering pointParameter(s)
Figure FDA0002635557950000051
Velocity parameter Vclu(h)～N(0，DV 2) Then, define Rclu(h) And Vclu(h) Respectively is
Figure FDA0002635557950000052
And
Figure FDA0002635557950000053
comprises the following steps:
Figure FDA0002635557950000054
Figure FDA0002635557950000055
where Δ f is a frequency agile interval, fcIs an initial carrier frequency, and M is the number of selectable frequency points;
4.2 define the clutter covariance matrix corresponding to the h-th strong clutter scattering point as Rh∈CN×NThe alpha row and beta column elements are [ R ]h]α，βAnd then:
when a is equal to β, then,
[Rh]α，β＝1；
when a is not equal to β,
Figure FDA0002635557950000056
wherein n isαFor the alpha random frequency modulation coding, nβEncoding the beta random frequency modulation;
due to Rclu(h) And Vclu(h) Independent of each other, the above formula can be rewritten as:
Figure FDA0002635557950000061
the clutter covariance matrix R of the h-th strong clutter scattering point can be obtained based on the formulahEach of the elements of (a);
4.3, defining a clutter and noise covariance matrix as R epsilon CN×NThe method comprises the following steps:
Figure FDA0002635557950000062
wherein the content of the first and second substances,
Figure FDA0002635557950000063
is the distance estimation value of the h-th strong clutter scattering point, I belongs to CN×NIs an identity matrix, σw 2Is the noise power of the receiver.
8. The method of claim 5, wherein step 5 comprises the sub-steps of:
5.1, setting the tracking speed of the target as
Figure FDA0002635557950000064
The distance matching filter matrix corresponding to the Doppler channel where the target is located is
Figure FDA0002635557950000065
Figure FDA0002635557950000066
Can be obtained by the calculation formula of the elements in the distance matching filter matrix corresponding to the Doppler channel with the central speed V in the step 3;
5.2, setting a clutter suppression filter matrix corresponding to the Doppler channel where the target is positioned as
Figure FDA0002635557950000067
Figure FDA0002635557950000068
Figure FDA0002635557950000069
Calculated by the following formula:
Figure FDA00026355579500000610
Figure FDA00026355579500000611
the method can be obtained by a Lagrange multiplier method:
Figure FDA00026355579500000612
5.3 using clutter suppression filter matrices
Figure FDA00026355579500000613
Performing clutter suppression on an input signal s to be processed to obtain a target complex high-resolution one-dimensional range profile after clutter suppression:
Figure FDA0002635557950000071
to thetatarThe module value of each element in the method can obtain a target high-resolution one-dimensional range profile after the frequency agile radar clutter is suppressed:
Figure FDA0002635557950000072
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CN109061589B (en) * 2018-07-06 2022-08-26 西安电子科技大学 Target motion parameter estimation method of random frequency hopping radar

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CN112731301B (en) * 2020-12-29 2023-06-09 北京环境特性研究所 Interference suppression method and device for disc-shaped clutter simulation measurement
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