CN104635214A - Airborne forward-looking frequency diversity array radar distance fuzzy clutter suppression method - Google Patents

Abstract

The invention belongs to the technical field of radar clutter suppression, and particularly relates to an airborne forward-looking frequency diversity array radar distance fuzzy clutter suppression method. The method comprises the following specific steps: acquiring the echo space-time snapshot data xc of an airborne forward-looking frequency diversity array radar; determining the secondary distance dependence compensation vector of a non-fuzzy distance region and the secondary distance dependence compensation vector of a fuzzy distance region; acquiring a secondary distance dependence compensation vector in an airspace-Doppler combined frequency region; acquiring echo space-time snapshot data after secondary distance dependence compensation; performing space-time adaptive processing on the echo space-time snapshot data after secondary distance dependence compensation of the non-fuzzy distance region and the echo space-time snapshot data after secondary distance dependence compensation of the fuzzy distance region respectively.

Description

Air-borne Forward-looking frequency diversity array radar range ambiguity clutter suppression method

Technical field

The invention belongs to radar clutter suppression technology field, particularly the suppressing method of Air-borne Forward-looking frequency diversity array radar range ambiguity clutter, be mainly used in distinguishing unambiguous distance district clutter and fuzzy distance district clutter in spatial frequency domain.

Background technology

Space-time adaptive process (STAP) has important using value in airborne early warn ing radar, and it can be combined time and space information and detect target from clutter and interference.In airborne positive side-looking array radar, the coupled relation between the spatial domain frequency of clutter and Doppler frequency does not change with distance.But in the application of some special airborne radars (as forward sight array airborne radar, circular array airborne radar etc.), the distance invariability of clutter distribution is no longer set up, and the distribution of its clutter has serious distance dependencies.The distance dependencies of clutter will cause the degradation of STAP method performance.When appearance distance is fuzzy, target not only needs to compete with unambiguous distance clutter at a slow speed, and will be at war with fuzzy distance clutter, and Low SNR signal will be submerged in clutter completely.As shown in Figure 1, be airborne radar range ambiguity schematic diagram in prior art.With reference to Fig. 1, the clutter in unambiguous distance district and fuzzy distance district mixes in time domain, it should be noted that, the noise performance in these two regions but has very large difference.Therefore, traditional STAP method performance degradation under this harsh conditions.

Summary of the invention

The object of the invention is to the suppressing method proposing Air-borne Forward-looking frequency diversity array radar range ambiguity clutter, the present invention explores the controllable degrees of freedom in distance dimension of frequency diversity array (FDA), construct the signal model of FDA-STAP (frequency diversity array-space-time adaptive process), propose a kind of suppressing method of range ambiguity clutter.Adopt frequency diversity array, make array steering vector be the function of distance, therefore, the range information that it can be utilized to provide, realizes being separated of the clutter in unambiguous distance district and fuzzy distance district.Consider that steering vector can produce secondary range dependence, the present invention proposes a kind of secondary range and rely on compensation method.Distinguish unambiguous distance district clutter and fuzzy distance district clutter in spatial frequency domain, and secondary range dependence compensation is combined with traditional clutter spectrum compensation method, solve Range-dependent and range ambiguity problem simultaneously.

In order to realize above-mentioned technical purpose, the present invention adopts following technical scheme to be achieved.

The suppressing method of Air-borne Forward-looking frequency diversity array radar range ambiguity clutter comprises the following steps:

Step 1, utilizes each array element of frequency diversity array to transmit, utilizes the echoed signal that frequency diversity array received is corresponding; Fast beat of data x when the echo of acquisition Air-borne Forward-looking frequency diversity array radar is empty _c;

Step 2, determines that the secondary range in unambiguous distance district relies on compensation vector and is expressed as and the secondary range dependence compensation vector in fuzzy distance district is expressed as show that the secondary range in spatial domain-Doppler's Combined Frequency district relies on compensation vector wherein, represent Kronecker product, α is 1 or 2; 1 _kfor the column vector that N is capable, 1 _kin all elements be the array number that 1, N represents in frequency diversity array entirely;

Step 3, draws unambiguous distance district fast beat of data when secondary range relies on the sky of the echo after compensating with fuzzy distance district fast beat of data when secondary range relies on the sky of the echo after compensating wherein, ⊙ then represents Hadamard product;

Step 4, respectively to unambiguous distance district fast beat of data when secondary range relies on the sky of the echo after compensating with fuzzy distance district fast beat of data when secondary range relies on the sky of the echo after compensating carry out space-time adaptive process.

Feature of the present invention and further improvement are:

In step 1, fast beat of data x when the echo of Air-borne Forward-looking frequency diversity array radar is empty _cfor:

Wherein, M represents the range unit number of Air-borne Forward-looking frequency diversity array radar, m=1,2...M; N _arepresent the scattering point number in each range unit, i=1,2 ..., N _a; γ ^{{ i, m}}represent the complex scattering coefficients of i-th scattering point in m range unit, represent Kronecker product, ⊙ then represents Hadamard product; represent the normalization Doppler frequency of i-th scattering point in m range unit, represent the time domain steering vector that in m range unit, i-th scattering point is corresponding; f _r ^{{ m}}represent the normalized cumulant frequency of each scattering point in m range unit, s _r(f _r ^{{ m}}) represent the distance steering vector that in m range unit, each scattering point is corresponding; f _a ^{{ i, m}}represent the normalization direction frequency of i-th scattering point in m range unit, s _a(f _a ^{{ i, m}}) represent the direction steering vector that in m range unit, i-th scattering point is corresponding; f _s ^{{ i, m}}represent the normalization spatial frequency of i-th scattering point in m range unit, s _s(f _s ^{{ i, m}}) represent the full spatial domain steering vector that in m range unit, i-th scattering point is corresponding.

In step 2, for:

$h_{\mathrm{SRDC}}^{\left\{\mathrm{\α}\right\}}\left(f_c\right)={[1,e^{-j2\mathrm{\π}{f}_c},...,e^{-j2\mathrm{\π}{f}_c(N-1)}]}^T$

Wherein, the device of subscript T representing matrix or vector, Δ f represents the frequency increment of described frequency diversity array, and c represents the light velocity; When α=1, R _c=R ₁, R ₁for setpoint distance value; When α=2, R _c=R ₂=R ₁+ R _u, R _u=c/2f _r, f _rrepresent the pulse repetition rate that Air-borne Forward-looking frequency diversity array radar transmits.

The array element distance d of described frequency diversity array meets

$d\≤\frac{{\mathrm{\λ}}_0}{4}$

Wherein, λ ₀represent the carrier wavelength that the reference array element in frequency diversity array transmits.

Beneficial effect of the present invention is: 1) analyze and indicate the Range-dependent characteristic in spatial domain and the quadratic dependency of forward sight frequency diversity array radar space-time two-dimensional clutter; 2) propose a kind of new secondary range and rely on compensation method; 3) secondary range dependence compensation and traditional clutter spectrum compensation method are combined, thus restrained effectively range ambiguity clutter.4) because unambiguous distance district clutter and fuzzy distance district clutter can separate in spatial domain frequency field by forward sight frequency diversity array radar, therefore non-homogeneous clutter recognition performance can greatly be improved.

Accompanying drawing explanation

Fig. 1 is airborne radar range ambiguity schematic diagram in prior art;

Fig. 2 is the geometric model of Air-borne Forward-looking frequency diversity array radar of the present invention and the schematic diagram of echo reception flow process;

Fig. 3 is the relation schematic diagram of Air-borne Forward-looking frequency diversity array radar scattering point spatial frequency and Distance geometry angle in the present invention;

Fig. 4 is the clutter Spatial Doppler coupled relation schematic diagram of Air-borne Forward-looking frequency diversity array radar of the present invention when there is range ambiguity;

Fig. 5 a is the Spatial Doppler frequency couple relation clutter Spatial Doppler coupled relation schematic diagram obtained after adopting secondary proposed by the invention to rely on compensation to unambiguous distance district;

Fig. 5 b is the Spatial Doppler frequency couple relation clutter Spatial Doppler coupled relation schematic diagram obtained after adopting secondary proposed by the invention to rely on compensation to fuzzy distance district;

Fig. 6 is the schematic flow sheet of the suppressing method of Air-borne Forward-looking frequency diversity array radar range ambiguity clutter of the present invention;

Fig. 7 a is original clutter spectrum distribution schematic diagram when detecting moving target in emulation experiment in unambiguous distance district;

Fig. 7 b is the clutter spectrum distribution schematic diagram after secondary range dependence compensates utilizing the present invention to draw when moving target is detected in unambiguous distance district in emulation experiment;

Fig. 7 c is the clutter spectrum schematic diagram after carrying out traditional clutter spectrum compensation when moving target is detected in unambiguous distance district in emulation experiment;

Fig. 8 a is original clutter spectrum distribution schematic diagram when detecting moving target in emulation experiment in fuzzy distance district;

Fig. 8 b is the clutter spectrum distribution schematic diagram after secondary range dependence compensates utilizing the present invention to draw when moving target is detected in fuzzy distance district in emulation experiment;

Fig. 8 c is the clutter spectrum schematic diagram after carrying out traditional clutter spectrum compensation when moving target is detected in fuzzy distance district in emulation experiment.

Embodiment

Below in conjunction with accompanying drawing, the invention will be further described:

With reference to Fig. 2, be the geometric model of Air-borne Forward-looking frequency diversity array radar of the present invention and the schematic diagram of echo reception flow process.Carrier aircraft height (podium level) is H, and carrier aircraft speed is V, and the coherent pulse number of Air-borne Forward-looking frequency diversity array radar Received signal strength is K, and the coherent pulse that Air-borne Forward-looking frequency diversity array radar transmits is spaced apart T _r, the pulse repetition rate f that Air-borne Forward-looking frequency diversity array radar transmits _r=1/T _r.

In Air-borne Forward-looking frequency diversity array radar, the even linear array that frequency diversity array is made up of N number of omnidirectional array element, in frequency diversity array, array element distance is d.The carrier frequency f that in frequency diversity array, the n-th array element transmits _nfor:

f _n＝f ₀+(n-1)Δf,n＝1,2,…,N (1)

Wherein, f ₀for the reference frequency of described frequency diversity array, Δ f is the frequency increment of described frequency diversity array.Under above-mentioned prerequisite, the suppressing method of Air-borne Forward-looking frequency diversity array radar range ambiguity clutter of the present invention comprises the following steps:

Step 1, utilizes each array element of frequency diversity array to transmit, utilizes the echoed signal that frequency diversity array received is corresponding; Fast beat of data x when the echo of acquisition Air-borne Forward-looking frequency diversity array radar is empty _c.

Its concrete steps are:

Utilize each array element of frequency diversity array to transmit, utilize the echoed signal that frequency diversity array received is corresponding; In the embodiment of the present invention, described frequency diversity array is the even linear array with N number of array element, and the reference frequency (the 1st carrier frequency that array element transmits of described frequency diversity array) of described frequency diversity array is f ₀, the frequency increment of described frequency diversity array is Δ f.The waveform that any two array elements of frequency diversity array are launched is mutually orthogonal, and the signal that each array element of frequency diversity array is launched can effectively be separated in the echo data received.For obtaining enough signal gains, when frequency diversity array received signal, received beam being done to each transmitted waveform in echo data and is formed.This step also can be described as being launched by single array element, by full aperture array received.

For arbitrary ground scatter point, its to frequency diversity array n-th array element oblique distance be expressed as wherein, n=1,2 ..., N, θ represent the position angle of corresponding ground scattering point relative to frequency diversity array, represent the corresponding ground scattering point angle of pitch relative to frequency diversity array, R represents given reference oblique distance (being such as the ground scatter o'clock oblique distance to N number of array element), and d represents the array element distance in frequency diversity array.

The phase place ψ of the echoed signal received by frequency diversity array (full array aperture) after scattering that transmits of frequency diversity array n-th array element _nfor:

Wherein, c represents the light velocity, f _nrepresent the carrier frequency that in frequency diversity array, the n-th array element transmits.With the 1st array element in frequency diversity array for reference array element, then the phase difference ψ of the n-th array element and reference array element in frequency diversity array _nfor:

Wherein, f ₀represent the reference frequency of described frequency diversity array, Δ f represents the frequency increment of described frequency diversity array, λ ₀represent the carrier wavelength that the reference array element in frequency diversity array transmits, λ ₀=c/f ₀.From the content on the right side of the last equal sign of formula (3), Section 1 is the function of Distance geometry frequency increment, and Section 2 is identical with traditional phased array, and Section 3 is secondary modulation item.In fact, because carrier frequency is negligible compared with frequency increment, Section 3 can be left in the basket.As can be seen here, different from traditional phased array, the Δ ψ in formula (3) _nrelated with angle and distance.

For considering a problem conveniently, the present invention only considers the horizontal velocity of motion platform, then the normalization Doppler frequency f of the signal be reflected back by corresponding ground scatterer that transmits of frequency diversity array n-th array element _tfor:

Wherein, V represents carrier aircraft speed, f _rrepresent the pulse repetition rate that Air-borne Forward-looking frequency diversity array radar transmits.Find out according to formula (4), for the different array element of frequency diversity array, the normalization Doppler frequency slightly difference of its signal be reflected back by corresponding ground scatterer that transmits, but, under normal conditions, frequency increment again due to frequency diversity array is very little, and this difference can also be left in the basket.Then in embodiments of the present invention, the kth pulse echo signal x received by frequency diversity array (full array aperture) after scattering that transmits of frequency diversity array n-th array element _nkfor:

Wherein, γ _pfor with carrier frequency independently complex coefficient, γ _pfor the complex coefficient of setting.ζ _kfor

Then the echoed signal x of the corresponding scattering point of Air-borne Forward-looking frequency diversity array radar reception is:

Wherein, represent Kronecker product, ⊙ then represents Hadamard product; f _trepresent the normalization Doppler frequency of corresponding scattering point, f _srepresent the normalization spatial frequency of corresponding scattering point, f _rrepresent the normalized cumulant frequency of corresponding scattering point, f _arepresent the normalization direction frequency of corresponding scattering point.F _t, f _s, f _rand f _abe respectively:

f _s＝f _R+f _a；

S _trepresent time domain steering vector, s _tfor the column vector that K is capable, K represents the coherent pulse number of Air-borne Forward-looking frequency diversity array radar Received signal strength; s _rrepresent distance steering vector, s _rfor the column vector that N is capable, N represents the array number of frequency diversity array.S _arepresent direction steering vector, s _afor the column vector that N is capable.S _sthe full spatial domain steering vector synthesized by distance steering vector and direction steering vector, s _sfor the column vector that N is capable.S _t(f _t), s _r(f _r), s _a(f _a) and s _s(f _s) be respectively:

$s_t\left(f_t\right)={[1,e^{j2\mathrm{\π}{f}_t},...,e^{j2\mathrm{\π}{f}_t(K-1)}]}^T---(7.a)$

$s_R\left(f_R\right)={[1,e^{j2\mathrm{\π}{f}_R},...,e^{j2\mathrm{\π}{f}_R(N-1)}]}^T---(7.b)$

$s_a\left(f_a\right)={[1,e^{j2\mathrm{\π}{f}_a},...,e^{j2\mathrm{\π}{f}_a(N-1)}]}^T---(7.c)$

Wherein, the device of subscript T representing matrix or vector.Can find out, s _t(f _t) identical with the time domain steering vector of traditional phased-array radar, s _a(f _a) identical with the direction steering vector of traditional phased-array radar.But s _a(f _a) different from the full spatial domain steering vector of traditional phased-array radar, s _r(f _r) depend on the frequency increment Δ f of oblique distance R and described frequency diversity array.

In the embodiment of the present invention, the echoed signal of Air-borne Forward-looking frequency diversity array radar is formed by stacking by clutter scattering in equidistant ring, therefore, and fast beat of data x when the echo of Air-borne Forward-looking frequency diversity array radar is empty _cfor:

Wherein, M represents range unit number (fuzzy distance number), m=1,2...M; N _ato represent in each range unit independently scattering point number, i=1,2 ..., N _a.γ ^{{ i, m}}represent the complex scattering coefficients (for known quantity) of i-th scattering point in m range unit, represent Kronecker product, ⊙ then represents Hadamard product; f _t ^{{ i, m}}represent the normalization Doppler frequency of i-th scattering point in m range unit, s _t(f _t ^{{ i, m}}) represent the time domain steering vector that in m range unit, i-th scattering point is corresponding, s _t(f _t ^{{ i, m}}) be the capable column vector of K, K represents the coherent pulse number of Air-borne Forward-looking frequency diversity array radar Received signal strength.F _r ^{{ m}}represent the normalized cumulant frequency of each scattering point in m range unit, s _r(f _r ^{{ m}}) represent the distance steering vector that in m range unit, each scattering point is corresponding, s _r(f _r ^{{ m}}) be the capable column vector of N, N represents the array number of frequency diversity array.F _a ^{{ i, m}}represent the normalization direction frequency of i-th scattering point in m range unit, s _a(f _a ^{{ i, m}}) represent the direction steering vector that in m range unit, i-th scattering point is corresponding, s _a(f _a ^{{ i, m}}) be the capable column vector of N.F _s ^{{ i, m}}represent the normalization spatial frequency of i-th scattering point in m range unit, s _s(f _s ^{{ i, m}}) represent the full spatial domain steering vector that in m range unit, i-th scattering point is corresponding, s _s(f _s ^{{ i, m}}) be the capable column vector of N.

In the embodiment of the present invention, f _t ^{{ i, m}}, f _r ^{{ m}}, f _a ^{{ i, m}}and f _s ^{{ i, m}}expression formula be respectively:

Wherein, V represents carrier aircraft speed, f _rrepresent the pulse repetition rate that Air-borne Forward-looking frequency diversity array radar transmits, λ ₀represent the carrier wavelength that the reference array element in frequency diversity array transmits, λ ₀=c/f ₀, f ₀represent the reference frequency of described frequency diversity array; Δ f represents the frequency increment of described frequency diversity array, and c represents the light velocity, and d represents the array element distance in frequency diversity array.θ ^{{ i, m}}to represent in m range unit the position angle of i-th scattering point relative to frequency diversity array, to represent in m range unit the angle of pitch of i-th scattering point relative to frequency diversity array, R ^{{ m}}represent given reference oblique distance that each scattering point in m range unit is corresponding (be such as in m range unit arbitrary scattering point to the oblique distance of N number of array element).

In the embodiment of the present invention, s _t(f _t ^{{ i, m}}), s _r(f _r ^{{ m}}), s _a(f _a ^{{ i, m}}) and s _s(f _s ^{{ i, m}}) expression formula be respectively:

Wherein, the device of subscript T representing matrix or vector.

Step 2, determines that the secondary range in unambiguous distance district relies on compensation vector and is expressed as and the secondary range dependence compensation vector in fuzzy distance district is expressed as show that the secondary range in spatial domain-Doppler's Combined Frequency district relies on compensation vector

$h_{\mathrm{st}-\mathrm{SRDC}}^{\left\{\mathrm{\α}\right\}}\left(f_c\right)=1_K\⊗h_{\mathrm{SRDC}}^{\left(\mathrm{\α}\right)}\left(f_c\right)$

Wherein, represent Kronecker product, α=1,2; 1 _kfor the column vector that N is capable, 1 _kin all elements be 1 entirely.

Its concrete steps are:

For ground scatter point, full spatial domain steering vector comprises two parts: direction steering vector and distance steering vector.For Air-borne Forward-looking frequency diversity array radar, the direction steering vector of ground scatter point and the identical of traditional phased-array radar.It should be noted that, its distance steering vector is the function of Distance geometry frequency increment, by the normalization spatial frequency f of corresponding ground scattering point _sagain be rewritten as:

Distance and angle is depended on by formula (9) known spatial frequency.

With reference to Fig. 3, it is the relation schematic diagram of Air-borne Forward-looking frequency diversity array radar scattering point spatial frequency and Distance geometry angle in the present invention.As shown in Figure 3, solid line represents distance for R ₁wave front, represented by dotted arrows distance be R ₂wave front, R ₁and R ₂be set-point; R ₁-R ₂=Δ R.For given direction, in the present invention, the spatial frequency of the ground scatter point of Air-borne Forward-looking frequency diversity array radar changes with distance.

In the embodiment of the present invention, Air-borne Forward-looking frequency diversity array radar is about R ₁the normalization spatial frequency f of ground scatter point _s(R ₁) be expressed as

Air-borne Forward-looking frequency diversity array radar is about R ₂the normalization spatial frequency f of ground scatter point _s(R ₂) be expressed as

Then have:

$\mathrm{\Δ}{f}_s\left(\mathrm{\ΔR}\right)=f_s\left(R_1\right)-f_s\left(R_2\right)=f_R\left(R_1\right)-f_R\left(R_2\right)=-\frac{2\mathrm{\Δf\ΔR}}{c}---\left(12\right)$

It is poor that formula (12) gives the spatial frequency depending on chamfer distance difference Δ R when assigned direction and frequency increment.Therefore, a more thorny Range-dependent problem can be run in Air-borne Forward-looking frequency diversity array radar of the present invention, i.e. secondary Range-dependent problem.

When there is fuzzy distance, the spatial frequency difference of unambiguous distance and fuzzy distance can be expressed as follows:

$\mathrm{\Δ}{f}_s=f_s\left(R_1\right)-f_s\left(R_2\right)=f_s\left(R_1\right)-f_s(R_1+R_u)=-\frac{2\mathrm{\Δf}{R}_u}{c}---\left(13\right)$

Wherein, R ₂=R ₁+ R _u, R _u=c/2f _r, R _urepresent maximum unambiguous distance.R ₁for set-point.Although the clutter in unambiguous distance district and fuzzy distance district is inseparable in time domain, Air-borne Forward-looking frequency diversity array radar still can utilize spatial frequency difference Δ f _sthey are separated.This also demonstrates the superiority of frequency diversity array compared to traditional phased array.

In Air-borne Forward-looking frequency diversity array radar of the present invention, the angle Doppler frequency relational expression of the clutter that corresponding ground scattering point is corresponding is expressed as

Wherein, h is carrier aircraft height.Formula (14) indicates the oval coupled relation of clutter distribution.With reference to Fig. 4, be the clutter Spatial Doppler coupled relation schematic diagram of Air-borne Forward-looking frequency diversity array radar of the present invention when there is range ambiguity.In Fig. 4, transverse axis represents normalization Doppler frequency (standardization Doppler frequency), the longitudinal axis represents normalization spatial frequency (standardised space frequency), different lines represent different range units respectively, unit is m, A, B, C represent three different scattering points, and R represents oblique distance.Can find out, when oblique distance changes, oval coupled relation (clutter Spatial Doppler coupled relation) curve also can along with spatial domain frequency f _rchange and change.In addition, this ellipse can increase along with the increase of oblique distance.

Therefore, be different from traditional phased-array radar, the clutter of Air-borne Forward-looking frequency diversity array radar of the present invention is distributed in spatial domain frequency field can be changed with the change of oblique distance.Therefore, Air-borne Forward-looking frequency diversity array radar can realize being separated of unambiguous distance clutter and fuzzy distance clutter in spatial domain frequency field.It should be noted that, although frequency diversity array (FDA) provides additional information in spatial domain frequency field, also result in secondary range Dependence Problem.

Air-borne Forward-looking frequency diversity array radar of the present invention can provide additional information in spatial frequency domain, and a kind of effective range ambiguity clutter suppression method is discussed in the present invention.First, for overcoming secondary range dependency problem, proposing secondary range and relying on compensation method; Construct two groups of compensation vector respectively according to unambiguous distance district and fuzzy distance district, then realize range ambiguity clutter recognition in conjunction with traditional clutter spectrum compensation method.

Specifically, in embodiments of the present invention, for giving set a distance (range unit is identical), the secondary range in unambiguous distance district relies on compensation vector and is expressed as the secondary range in fuzzy distance district relies on compensation vector and is expressed as make α=1,2, then have:

$h_{\mathrm{SRDC}}^{\left\{\mathrm{\α}\right\}}\left(f_c\right)={[1,e^{-j2\mathrm{\π}{f}_c},...,e^{-j2\mathrm{\π}{f}_c(N-1)}]}^T---\left(15\right)$

Wherein, the device of subscript T representing matrix or vector, for the column vector that N is capable.F _crepresent compensating frequency, Δ f represents the frequency increment of described frequency diversity array, and c represents the light velocity, R _cit is corresponding oblique distance.When α=1, R _c=R ₁, when α=2, R _cfor fuzzy distance, R _c=R ₂=R ₁+ R _u, R _urepresent maximum unambiguous distance, R _u=c/2f _r, f _rrepresent the pulse repetition rate that Air-borne Forward-looking frequency diversity array radar transmits.

In the embodiment of the present invention, compensation vector the secondary range dependence of clutter can be compensated.Rely on after compensation deals through secondary range, clutter spectrum meets independent same distribution characteristic in spatial domain.

In the embodiment of the present invention, the secondary range in spatial domain-Doppler's Combined Frequency district relies on compensation vector for:

$h_{\mathrm{st}-\mathrm{SRDC}}^{\left\{\mathrm{\α}\right\}}\left(f_c\right)=1_K\⊗h_{\mathrm{SRDC}}^{\left(\mathrm{\α}\right)}\left(f_c\right)$

Wherein, represent Kronecker product, α=1,2; 1 _kfor the column vector that N is capable, 1 _kin all elements be 1 entirely.

Step 3, draws unambiguous distance district fast beat of data when secondary range relies on the sky of the echo after compensating with fuzzy distance district fast beat of data when secondary range relies on the sky of the echo after compensating wherein, ⊙ then represents Hadamard product.

Its concrete steps are:

In Air-borne Forward-looking frequency diversity array radar, time empty to the echo in unambiguous distance district and fuzzy distance district respectively, fast beat of data is carried out secondary range and is relied on and compensate, draw unambiguous distance district through secondary range rely on the echo after compensating empty time fast beat of data with fuzzy distance district fast beat of data when secondary range relies on the sky of the echo after compensating

Make α=1,2, then have:

Wherein, for the column vector that N is capable.F _crepresent compensating frequency, Δ f represents the frequency increment of described frequency diversity array, and c represents the light velocity, R _cit is corresponding oblique distance.When α=1, R _c=R ₁, when α=2, R _cfor fuzzy distance, R _c=R ₂=R ₁+ R _u, R _urepresent maximum unambiguous distance, R _u=c/2f _r, f _rrepresent the pulse repetition rate that Air-borne Forward-looking frequency diversity array radar transmits. the spatial domain steering vector after compensating,

for compensating spatial domain frequency accordingly:

As from the foregoing, the angle Doppler frequency relational expression of the clutter in formula (14) can be rewritten as follows:

Have when α=1:

Have when α=2:

With reference to Fig. 5 a, rely on the Spatial Doppler frequency couple relation clutter Spatial Doppler coupled relation schematic diagram obtained after compensating for adopting secondary proposed by the invention to unambiguous distance district; With reference to Fig. 5 b, rely on the Spatial Doppler frequency couple relation clutter Spatial Doppler coupled relation schematic diagram obtained after compensating for adopting secondary proposed by the invention to fuzzy distance district; In Fig. 5 a and Fig. 5 b, transverse axis represents normalization Doppler frequency (standardization Doppler frequency), and the longitudinal axis represents normalization spatial frequency (standardised space frequency), and different lines represent different range units respectively.From Fig. 5 a and Fig. 5 b, in the frequency field of spatial domain, the clutter in unambiguous distance district and fuzzy distance district can effectively be differentiated.As shown in Figure 5 a, from spatial frequency domain, the unambiguous distance district clutter distribution of Air-borne Forward-looking frequency diversity array radar will be aligned to center section, and fuzzy distance district can be aligned to both sides.Contrary, as shown in Fig. 5 (b), the clutter in unambiguous distance district is positioned at both sides, and fuzzy distance district clutter is positioned at the centre of spatial frequency domain.

In addition, in embodiments of the present invention, in order to ensure effective classification of unambiguous distance clutter and fuzzy distance clutter, the array element distance d of frequency diversity array of the present invention should meet

$d\≤\frac{{\mathrm{\λ}}_0}{4}---\left(22\right)$

Wherein, λ ₀represent the carrier wavelength that the reference array element in frequency diversity array transmits, λ ₀=c/f ₀, f ₀represent the reference frequency of described frequency diversity array.For without loss of generality, array element space d is generally 1/4th of wavelength, i.e. d=0.25 λ ₀.

Step 4, respectively to unambiguous distance district fast beat of data when secondary range relies on the sky of the echo after compensating with fuzzy distance district fast beat of data when secondary range relies on the sky of the echo after compensating carry out space-time adaptive process, fast beat of data when showing that the echo of fuzzy distance district after secondary range dependence compensates after the clutter recognition of fast beat of data and the correspondence when secondary range relies on the sky of the echo after compensating of the unambiguous distance district after corresponding clutter recognition is empty.

In step 4, the process of space-time adaptive process is known to the skilled person, and is not described in detail in this.

In a word, when there is range ambiguity, space-time adaptive process (STAP) performance of traditional phased-array radar can degradation.First, because range ambiguity causes clutter seriously non-stationary, make the sample needed for clutter covariance matrix estimation be difficult to obtain; Secondly, in non-working side geometry, because the compensation of unambiguous distance clutter and fuzzy distance clutter conditions each other, traditional clutter spectrum compensation method is caused to lose efficacy; Finally, range ambiguity causes Clutter Degrees of Freedom greatly to increase, and adds the burden of system clutter recognition.And in embodiments of the present invention, rely on after compensation (clutter spectrum compensation) through secondary range, Air-borne Forward-looking frequency diversity array radar achieves the separation of range ambiguity clutter in spatial domain frequency field, the clutter spectrum in unambiguous distance district and fuzzy distance district compensates and no longer conditions each other, and traditional clutter spectrum penalty method can be utilized to realize clutter and compensate and clutter recognition.With reference to Fig. 6, it is the schematic flow sheet of the suppressing method of Air-borne Forward-looking frequency diversity array radar range ambiguity clutter of the present invention.

Effect of the present invention can be further illustrated by once simulation result:

1) simulated conditions

Table 1 simulation parameter

In emulation experiment, the measuring distance in setting unambiguous distance district is 8000m, and the measuring distance in fuzzy distance district is 18000m.

2) content is emulated

Emulation experiment 1: target setting is in unambiguous distance district.With reference to Fig. 7 a, for detecting original clutter spectrum distribution schematic diagram during moving target in emulation experiment in unambiguous distance district; With reference to Fig. 7 b, rely on the clutter spectrum distribution schematic diagram after compensating for what utilize the present invention to draw when moving target is detected in unambiguous distance district in emulation experiment through secondary range; With reference to Fig. 7 c, it is the clutter spectrum schematic diagram after carrying out traditional clutter spectrum compensation when moving target is detected in unambiguous distance district in emulation experiment; In Fig. 7 a to Fig. 7 c, transverse axis represents normalization Doppler frequency, and the longitudinal axis represents normalization spatial frequency, and different gray-scale values represents different clutter spectrum amplitudes.As can be seen from Fig. 7 a to Fig. 7 c, in Air-borne Forward-looking frequency diversity array radar, unambiguous distance clutter and the fuzzy distance clutter of frequency zones, spatial domain can be distinguished.Because secondary range relies on, clutter seriously spreads in spatial frequency domain.Utilize the present invention carry out secondary range rely on compensate and clutter compensation after, without confusion region clutter being distributed as [-1/4,1/4] in spatial frequency domain, and fuzzy distance district clutter be distributed as [-1/2 ,-1/4] ∪ [1/4,1/2].Now, the target detection of fuzzy distance district clutter on unambiguous distance district there is no too large impact.

Emulation experiment 2: target setting is in fuzzy distance district.In fact, the distance dependencies of clutter is very little in the change of fuzzy distance district, but can have significant change in unambiguous distance district.With reference to Fig. 8 a, for detecting original clutter spectrum distribution schematic diagram during moving target in emulation experiment in fuzzy distance district; With reference to Fig. 8 b, rely on the clutter spectrum distribution schematic diagram after compensating for what utilize the present invention to draw when moving target is detected in fuzzy distance district in emulation experiment through secondary range; With reference to Fig. 8 c, it is the clutter spectrum schematic diagram after carrying out traditional clutter spectrum compensation when moving target is detected in fuzzy distance district in emulation experiment; In Fig. 8 a to Fig. 8 c, transverse axis represents normalization Doppler frequency, and the longitudinal axis represents normalization spatial frequency, and different gray-scale values represents different clutter spectrum amplitudes.As can be seen from Fig. 8 a to Fig. 8 c, after utilizing the present invention to compensate fuzzy distance district clutter, fuzzy distance district clutter be distributed as [-1/4,1/4], unambiguous distance district clutter be distributed as [-1/2,-1/4] ∪ [1/4,1/2], range ambiguity clutter also can distinguish in spatial frequency domain.It can thus be appreciated that the unambiguous distance clutter after secondary range dependence compensates and fuzzy distance clutter are separable.In conjunction with traditional clutter compensation method, clutter recognition performance can obviously be promoted.

In sum, Simulation experiments validate correctness of the present invention, reliability and validity.

Obviously, those skilled in the art can carry out various change and modification to the present invention and not depart from the spirit and scope of the present invention.Like this, if these amendments of the present invention and modification belong within the scope of the claims in the present invention and equivalent technologies thereof, then the present invention is also intended to comprise these change and modification.

Claims (4)

1. Air-borne Forward-looking frequency diversity array radar range ambiguity clutter suppression method, is characterized in that, comprise the following steps:

Step 1, utilizes each array element of frequency diversity array to transmit, utilizes the echoed signal that frequency diversity array received is corresponding; Fast beat of data x when the echo of acquisition Air-borne Forward-looking frequency diversity array radar is empty _c;

Step 2, determines that the secondary range in unambiguous distance district relies on compensation vector and is expressed as and the secondary range dependence compensation vector in fuzzy distance district is expressed as show that the secondary range in spatial domain-Doppler's Combined Frequency district relies on compensation vector wherein, represent Kronecker product, α is 1 or 2; 1 _kfor the column vector that N is capable, 1 _kin all elements be the array number that 1, N represents in frequency diversity array entirely;

Step 3, draws unambiguous distance district fast beat of data when secondary range relies on the sky of the echo after compensating with fuzzy distance district fast beat of data when secondary range relies on the sky of the echo after compensating wherein, ⊙ then represents Hadamard product;

Step 4, respectively to unambiguous distance district fast beat of data when secondary range relies on the sky of the echo after compensating with fuzzy distance district fast beat of data when secondary range relies on the sky of the echo after compensating carry out space-time adaptive process.

2. Air-borne Forward-looking frequency diversity array radar range ambiguity clutter suppression method as claimed in claim 1, is characterized in that, in step 1, and fast beat of data x when the echo of Air-borne Forward-looking frequency diversity array radar is empty _cfor:

Wherein, M represents the range unit number of Air-borne Forward-looking frequency diversity array radar, m=1,2...M; N _arepresent the scattering point number in each range unit, i=1,2 ..., N _a; γ ^{{ i, m}}represent the complex scattering coefficients of i-th scattering point in m range unit, represent Kronecker product, ⊙ then represents Hadamard product; f _t ^{{ i, m}}represent the normalization Doppler frequency of i-th scattering point in m range unit, s _t(f _t ^{{ i, m}}) represent the time domain steering vector that in m range unit, i-th scattering point is corresponding; f _r ^{{ m}}represent the normalized cumulant frequency of each scattering point in m range unit, s _r(f _r ^{{ m}}) represent the distance steering vector that in m range unit, each scattering point is corresponding; f _a ^{{ i, m}}represent the normalization direction frequency of i-th scattering point in m range unit, s _a(f _a ^{{ i, m}}) represent the direction steering vector that in m range unit, i-th scattering point is corresponding; f _s ^{{ i, m}}represent the normalization spatial frequency of i-th scattering point in m range unit, s _s(f _s ^{{ i, m}}) represent the full spatial domain steering vector that in m range unit, i-th scattering point is corresponding.

3. Air-borne Forward-looking frequency diversity array radar range ambiguity clutter suppression method as claimed in claim 1, is characterized in that, in step 2, for:

$h_{\mathrm{SRDC}}^{\left\{\mathrm{\α}\right\}}\left(f_c\right)={[1,e^{-j2\mathrm{\π}{f}_c},...,e^{-j2\mathrm{\π}{f}_c(N-1)}]}^T$

Wherein, the device of subscript T representing matrix or vector, Δ f represents the frequency increment of described frequency diversity array, and c represents the light velocity; When α=1, R _c=R ₁, R ₁for setpoint distance value; When α=2, R _c=R ₂=R ₁+ R _u, R _u=c/2f _r, f _rrepresent the pulse repetition rate that Air-borne Forward-looking frequency diversity array radar transmits.

4. the Air-borne Forward-looking frequency diversity array radar range ambiguity clutter suppression method as described in any one of claims 1 to 3, is characterized in that, the array element distance d of described frequency diversity array meets

$d\≤\frac{{\mathrm{\λ}}_0}{4}$

Wherein, λ ₀represent the carrier wavelength that the reference array element in frequency diversity array transmits.