CN104635214B - Air-borne Forward-looking frequency diversity array radar range ambiguity clutter suppression method - Google Patents

Abstract

The invention belongs to radar clutter suppression technology field, particularly to Air-borne Forward-looking frequency diversity array radar range ambiguity clutter suppression method, it concretely comprises the following steps: fast beat of data x when obtaining the echo sky of Air-borne Forward-looking frequency diversity array radar_c；Determine that the secondary range in unambiguous distance district relies on the secondary range in compensation vector and fuzzy distance district and relies on the secondary range that compensation vector draws in Doppler's Combined Frequency district, spatial domain and rely on compensation vector and show that fast beat of data carries out space-time adaptive process to unambiguous distance district fast beat of data and fuzzy distance district fast beat of data when secondary range relies on the echo sky after compensating when secondary range relies on the echo sky after compensating respectively when secondary range relies on the echo sky after compensating.

Description

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

Technical Field

The invention belongs to the technical field of radar clutter suppression, and particularly relates to a method for suppressing range ambiguity clutter of an airborne forward-looking frequency diversity array radar, which is mainly used for distinguishing the clutter in a non-ambiguity range region from the clutter in a spatial frequency domain.

Background

Space-time adaptive processing (STAP) has important application value in an onboard early warning radar, and can detect a target from clutter and interference by combining time and space information. In the airborne positive side-looking array radar, the coupling relation between the spatial frequency and the Doppler frequency of clutter is not changed along with the distance. However, in some special airborne radar applications (such as forward looking array airborne radar, circular array airborne radar, etc.), the distance invariance of the clutter distribution is no longer true, and the clutter distribution has a severe distance dependency. The range dependence of clutter will lead to a severe degradation of STAP method performance. When range ambiguity occurs, the slow target needs to compete not only with the unambiguous range clutter but also with the ambiguous range clutter, and the low signal-to-noise ratio signal will be completely submerged in the clutter. Fig. 1 shows a range ambiguity diagram of an airborne radar in the prior art. Referring to fig. 1, the clutter of the unambiguous range region and the ambiguity range region are mixed together in the time domain, and it should be noted that the clutter characteristics of the two regions are very different. Therefore, the conventional STAP method is severely degraded in such severe cases.

Disclosure of Invention

The invention aims to provide a method for suppressing distance fuzzy clutter of an airborne forward-looking frequency diversity array radar, explores the controllable degree of freedom of a Frequency Diversity Array (FDA) in a distance dimension, constructs a signal model of FDA-STAP (frequency diversity array-space-time adaptive processing), and provides a method for suppressing the distance fuzzy clutter. The frequency diversity array is adopted, so that the array guide vector is a function of the distance, and therefore, the distance information provided by the array guide vector can be utilized to realize the separation of the clutter of the unambiguous distance area and the ambiguity distance area. Considering that the guide vector can generate quadratic distance dependency, the invention provides a quadratic distance dependency compensation method. The clutter of the unambiguous distance region and the clutter of the ambiguous distance region are distinguished in a space frequency domain, secondary distance dependence compensation is combined with a traditional clutter spectrum compensation method, and the problems of distance dependence and distance ambiguity are solved.

In order to achieve the technical purpose, the invention is realized by adopting the following technical scheme.

The method for suppressing the range ambiguity clutter of the airborne forward-looking frequency diversity array radar comprises the following steps:

step 1, transmitting signals by using each array element of a frequency diversity array, and receiving corresponding echo signals by using the frequency diversity array; obtaining echo space-time snapshot data x of airborne forward-looking frequency diversity array radar_c；

Step 2, determining the quadratic distance dependent compensation vector of the unambiguous distance area asAnd the quadratic distance-dependent compensation vector of the blurred distance region is represented asDeriving quadratic distance-dependent compensation vectors in the spatial domain-Doppler joint frequency region Wherein,representing the Kronecker product, α being 1 or 2; 1_KColumn vectors of N rows, 1_KAll elements in the array are 1, and N represents the array element number in the frequency diversity array;

step 3, obtaining the secondary distance of the non-fuzzy distance areaRelying on compensated echo space-time snapshot dataEcho space-time snapshot data of fuzzy distance area after secondary distance dependence compensation ⊙ represents Hadamard product;

step 4, respectively carrying out echo space-time snapshot data after secondary distance dependence compensation on unambiguous distance areasEcho space-time snapshot data of fuzzy distance area after secondary distance dependence compensationAnd performing space-time self-adaptive processing.

The invention is characterized by further improvement:

in step 1, echo space-time snapshot data x of airborne forward-looking frequency diversity array radar_cComprises the following steps:

wherein, M represents the distance unit number of the airborne forward-looking frequency diversity array radar, and M is 1,2.. M; n is a radical of_aDenotes the number of scattering points in each distance unit, i 1,2_a；γ^{i,m}Represents the complex scattering coefficient of the ith scattering point in the mth range unit,representing the Kronecker product, ⊙ representing the Hadamard product;represents the normalized doppler frequency of the ith scattering point in the mth range bin,representing a time domain guide vector corresponding to the ith scattering point in the mth distance unit; f. of_R ^{m}Representing the normalized distance frequency, s, of each scattering point in the m-th range bin_R(f_R ^{m}) Representing a distance guide vector corresponding to each scattering point in the mth distance unit; f. of_a ^{i,m}Representing the normalized directional frequency, s, of the ith scattering point in the mth range bin_a(f_a ^{i,m}) Representing a direction guide vector corresponding to the ith scattering point in the mth distance unit; f. of_s ^{i,m}Representing the normalized spatial frequency, s, of the ith scattering point in the mth range bin_s(f_s ^{i,m}) And representing the full-space steering vector corresponding to the ith scattering point in the mth distance unit.

In the step 2, the process is carried out,comprises the following steps:

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

wherein the superscript T represents a matrix or vector means,Δ f denotes the frequency increment of the frequency diversity array, c denotes the speed of light, and R is the speed of light when α is equal to 1_c＝R₁，R₁For setting the distance value, when α is equal to 2, R_c＝R₂＝R₁+R_u，R_u＝c/2f_r，f_rRepresenting the pulse repetition frequency of the airborne forward looking frequency diversity array radar transmitted signal.

The array element spacing d of the frequency diversity array satisfies

$d\≤\frac{{\mathrm{\λ}}_0}{4}$

Wherein λ is₀Which represents the carrier wavelength of the reference array element transmission signal in the frequency diversity array.

The invention has the beneficial effects that: 1) the distance dependence characteristic of an airspace and the quadratic dependence relation of space-time two-dimensional clutter of the forward-looking frequency diversity array radar are analyzed and indicated; 2) a new quadratic distance dependence compensation method is provided; 3) the quadratic distance dependence compensation and the traditional clutter spectrum compensation method are combined, so that distance fuzzy clutter is effectively suppressed. 4) The forward looking frequency diversity array radar can separate the clutter in the unambiguous distance region from the clutter in the ambiguous distance region in the airspace frequency domain, so that the non-uniform clutter suppression performance can be greatly improved.

Drawings

FIG. 1 is a prior art airborne radar range ambiguity diagram;

FIG. 2 is a schematic diagram of a geometric model and an echo receiving process of the airborne forward-looking frequency diversity array radar of the present invention;

FIG. 3 is a schematic diagram of the relationship between the spatial frequency of the scattering point of the airborne forward-looking frequency diversity array radar and the distance and angle;

FIG. 4 is a schematic diagram of a clutter space Doppler coupling relationship of an airborne forward-looking frequency diversity array radar of the present invention in the presence of range ambiguity;

FIG. 5a is a schematic diagram of a clutter space Doppler coupling relationship of a space Doppler frequency coupling relationship obtained by applying quadratic dependence compensation proposed by the present invention to an unambiguous distance region;

FIG. 5b is a schematic diagram of a clutter space Doppler coupling relationship of a space Doppler frequency coupling relationship obtained by applying quadratic dependence compensation proposed by the present invention to a fuzzy distance region;

FIG. 6 is a schematic flow chart of a method for suppressing range ambiguity clutter of an airborne forward-looking frequency diversity array radar according to the present invention;

FIG. 7a is a schematic diagram of the original clutter spectrum distribution when detecting a moving target in a non-blurred distance region in a simulation experiment;

FIG. 7b is a schematic diagram of clutter spectrum distribution after secondary distance-dependent compensation obtained by the present invention when detecting a moving target in a non-ambiguous distance region in a simulation experiment;

FIG. 7c is a schematic diagram of a clutter spectrum compensated by a conventional clutter spectrum when detecting a moving target in a non-ambiguity distance region in a simulation experiment;

FIG. 8a is a schematic diagram of the original clutter spectrum distribution when detecting a moving target in a fuzzy distance region in a simulation experiment;

FIG. 8b is a schematic diagram of clutter spectrum distribution after secondary distance-dependent compensation obtained by the present invention when detecting a moving target in a fuzzy distance region in a simulation experiment;

fig. 8c is a schematic diagram of a clutter spectrum after performing conventional clutter spectrum compensation when detecting a moving target in a fuzzy distance region in a simulation experiment.

Detailed Description

The invention will be further described with reference to the accompanying drawings in which:

referring to fig. 2, a schematic diagram of a geometric model and an echo receiving process of the airborne forward looking frequency diversity array radar of the present invention is shown. The height (platform height) of the airborne frequency diversity array radar is H, the speed of the airborne frequency diversity array radar is V, the number of coherent pulses of the received signals of the airborne forward-looking frequency diversity array radar is K, and the interval of the coherent pulses of the transmitted signals of the airborne forward-looking frequency diversity array radar is T_rPulse repetition frequency f of radar transmitted signals of airborne forward-looking frequency diversity array_r＝1/T_r。

In the airborne front video frequency diversity array radar, a frequency diversity array is a uniform linear array consisting of N omnidirectional array elements, and the array element interval in the frequency diversity array is d. Carrier frequency f of nth array element transmitting signal in frequency diversity array_nComprises the following steps:

f_n＝f₀+(n-1)Δf,n＝1,2,…,N (1)

wherein f is₀Δ f is the frequency increment of the frequency diversity array for the reference frequency of the frequency diversity array. Under the premise, the method for suppressing the range ambiguity clutter of the airborne forward-looking frequency diversity array radar of the inventionThe method comprises the following steps:

step 1, transmitting signals by using each array element of a frequency diversity array, and receiving corresponding echo signals by using the frequency diversity array; obtaining echo space-time snapshot data x of airborne forward-looking frequency diversity array radar_c。

The method comprises the following specific steps:

transmitting signals by using each array element of the frequency diversity array, and receiving corresponding echo signals by using the frequency diversity array; in the embodiment of the invention, the frequency diversity array is a uniform linear array with N array elements, and the reference frequency (the carrier frequency of the 1 st array element transmitting signal of the frequency diversity array) of the frequency diversity array is f₀The frequency increment of the frequency diversity array is Δ f. The waveforms transmitted by any two array elements of the frequency diversity array are orthogonal to each other, and the signals transmitted by each array element of the frequency diversity array can be effectively separated in the received echo data. To achieve sufficient signal gain, receive beamforming is performed on each transmit waveform in the echo data as the frequency diversity array receives the signal. This step can also be described as being transmitted by a single array element and received by a full aperture array.

For any ground scattering point, the slope from the ground scattering point to the nth array element of the frequency diversity array is expressed asWhere N is 1,2, …, N, theta denotes the azimuth angle of the corresponding ground scatter point with respect to the frequency diversity array,the pitch angle of the corresponding ground scattering point relative to the frequency diversity array is shown, R represents a given reference pitch (e.g., the pitch from the ground scattering point to the nth array element), and d represents the array element spacing in the frequency diversity array.

The phase psi of the echo signal received by the frequency diversity array (full array aperture) after the transmitted signal of the nth array element of the frequency diversity array is scattered_nComprises the following steps:

wherein c represents the speed of light, f_nThe carrier frequency of the signal transmitted by the nth array element in the frequency diversity array is shown. Taking the 1 st array element in the frequency diversity array as the reference array element, the phase difference delta psi between the nth array element and the reference array element in the frequency diversity array_nComprises the following steps:

wherein f is₀Representing a reference frequency of said frequency diversity array, af representing a frequency increment of said frequency diversity array, λ₀Representing the carrier wavelength, λ, of a reference array element transmission signal in a frequency diversity array₀＝c/f₀. As can be seen from the content on the right side of the last equal sign of equation (3), the first term is a function of distance and frequency increment, the second term is the same as the conventional phased array, and the third term is a quadratic modulation term. In practice, the third term can be ignored since the carrier frequency is negligible compared to the frequency increment. It can be seen that Δ ψ in equation (3) is different from that of the conventional phased array_nBoth in relation to angle and distance.

For convenience of consideration, the invention only considers the horizontal speed of the motion platform, and then the normalized Doppler frequency f of the signal reflected by the corresponding ground scatterer from the transmission signal of the nth array element of the frequency diversity array_tComprises the following steps:

wherein V represents the speed of the carrier, f_rRepresenting the pulse repetition frequency of the airborne forward looking frequency diversity array radar transmitted signal. From equation (4), it can be seen that the frequency diversity array is notIn the same array element, the normalized doppler frequencies of the signals reflected back by the corresponding ground scatterers are slightly different, however, in general, the difference can be ignored due to the small frequency increment of the frequency diversity array. In the embodiment of the present invention, the transmitted signal of the nth array element of the frequency diversity array is scattered, and then the k pulse echo signal x is received by the frequency diversity array (full array aperture)_nkComprises the following steps:

wherein, γ_pFor complex coefficients, gamma, independent of the carrier frequency_pIs a set complex coefficient. Zeta_kIs composed of

The echo signal x of the corresponding scattering point received by the airborne forward-looking frequency diversity array radar is:

wherein,representing the Kronecker product, ⊙ representing the Hadamard product, f_tIndicating the normalized Doppler frequency, f, of the corresponding scattering point_sRepresenting the normalized spatial frequency, f, of the corresponding scattering point_RRepresenting the normalized distance frequency, f, of the corresponding scattering point_aRepresenting the normalized directional frequency of the corresponding scattering point. f. of_t、f_s、f_RAnd f_aRespectively as follows:

f_s＝f_R+f_a；

s_trepresenting a time-domain steering vector and,s_tthe column vector of the K rows represents the coherent pulse number of the received signal of the airborne forward-looking frequency diversity array radar; s_RA distance-oriented vector is represented which is,s_Ris a column vector of N rows, N representing the number of array elements of the frequency diversity array. s_aWhich represents a directional steering vector, is,s_aa column vector of N rows. s_sIs a full-airspace guide vector synthesized by a distance guide vector and a direction guide vector,s_sa column vector of N rows. s_t(f_t)、s_R(f_R)、s_a(f_a) And s_s(f_s) Respectively as follows:

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

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

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

where the superscript T represents a matrix or vector arrangement. It can be seen that s_t(f_t) The same time domain steering vector as that of the traditional phased array radar, s_a(f_a) The same as the directional steering vector of a conventional phased array radar. But s_a(f_a) Different from the full airspace guide vector of the traditional phased array radar, s_R(f_R) Depending on the ramp distance R and the frequency increment af of the frequency diversity array.

In the embodiment of the invention, the echo signal of the airborne forward-looking frequency diversity array radar is formed by scattering and superposing clutter in an equidistant ring, so that the echo space-time snapshot data x of the airborne forward-looking frequency diversity array radar_cComprises the following steps:

where M denotes the number of range units (fuzzy range number), M being 1,2.. M; n is a radical of_aDenotes the number of independent scattering points in each distance unit, i 1,2_a。γ^{i,m}Represents the complex scattering coefficient (as a known quantity) of the ith scattering point in the mth range bin,representing the Kronecker product, ⊙ representing the Hadamard product, f_t ^{i,m}Representing the normalized Doppler frequency, s, of the ith scattering point in the mth range bin_t(f_t ^{i,m}) Representing the time domain steering vector corresponding to the ith scattering point in the mth distance unit,s_t(f_t ^{i,m}) And the column vector of K rows represents the coherent pulse number of the signals received by the airborne forward-looking frequency diversity array radar. f. of_R ^{m}Representing the normalized distance frequency, s, of each scattering point in the m-th range bin_R(f_R ^{m}) Representing the range steering vector corresponding to each scattering point in the mth range bin,s_R(f_R ^{m}) Is a column vector of N rows, N representing the number of array elements of the frequency diversity array. f. of_a ^{i,m}Representing the normalized directional frequency, s, of the ith scattering point in the mth range bin_a(f_a ^{i,m}) Representing the corresponding square of the ith scattering point in the mth range unitA direction vector is guided to the direction vector,s_a(f_a ^{i,m}) A column vector of N rows. f. of_s ^{i,m}Representing the normalized spatial frequency, s, of the ith scattering point in the mth range bin_s(f_s ^{i,m}) Representing the full-space steering vector corresponding to the ith scattering point in the mth distance unit,s_s(f_s ^{i,m}) A column vector of N rows.

In the examples of the present invention, f_t ^{i,m}、f_R ^{m}、f_a ^{i,m}And f_s ^{i,m}Are respectively:

wherein V represents the speed of the carrier, f_rRepresenting the pulse repetition frequency, λ, of radar transmitted signals of an airborne forward-looking frequency diversity array₀Representing the carrier wavelength, λ, of a reference array element transmission signal in a frequency diversity array₀＝c/f₀，f₀A reference frequency representing the frequency diversity array; Δ f represents the frequency increment of the frequency diversity array, c represents the speed of light, and d represents the array element spacing in the frequency diversity array. Theta^{i,m}Represents the azimuth angle of the ith scattering point in the mth range bin relative to the frequency diversity array,represents the elevation angle of the ith scattering point in the mth range bin relative to the frequency diversity array,R^{m}a given reference slope corresponding to each scattering point in the mth range bin (e.g., the slope from any scattering point in the mth range bin to the nth array element) is indicated.

In the examples 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}) Are respectively:

where the superscript T represents a matrix or vector arrangement.

Step 2, determining the quadratic distance dependent compensation vector of the unambiguous distance area asAnd the quadratic distance-dependent compensation vector of the blurred distance region is represented asDeriving quadratic distance-dependent compensation vectors in the spatial domain-Doppler joint frequency region

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

Wherein,denotes the Kronecker product, α ═ 1, 2; 1_KColumn vectors of N rows, 1_KAll elements in (1).

The method comprises the following specific steps:

for ground scatter points, the full-space steering vector consists of two parts: a direction guide vector and a distance guide vector. For an airborne forward-looking frequency diversity array radar, the direction steering vector of the ground scattering point is the same as that of a traditional phased array radar. It should be noted that the distance guide vector is a function of distance and frequency increment, and will correspond to the normalized spatial frequency f of the ground scattering point_sRewritten as:

from equation (9), the spatial frequency depends on the distance and angle.

Referring to fig. 3, it is a schematic diagram of the relationship between the spatial frequency of the scattering point of the airborne forward-looking frequency diversity array radar and the distance and angle. As shown in FIG. 3, the solid line represents a distance R₁With the dashed line representing a distance R₂Wave front of, R₁And R₂Are given values; r₁-R₂Δ R. For a given direction, the spatial frequency of the ground scattering point of the airborne forward-looking frequency diversity array radar varies with distance.

In the embodiment of the invention, the airborne forward-looking frequency diversity array radar relates to R₁Normalization of ground scattering pointsChange the spatial frequency f_s(R₁) Is shown as

Airborne forward looking frequency diversity array radar with respect to R₂Normalized spatial frequency f of ground scattering points_s(R₂) Is shown as

Then there are:

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

equation (12) gives the spatial frequency difference in dependence on the ramp distance difference Δ R at a given direction and frequency increment. Therefore, a more problematic distance dependence problem, i.e., a secondary distance dependence problem, is encountered in the airborne forward looking frequency diversity array radar of the present invention.

When the ambiguity distance occurs, the spatial frequency difference of the unambiguous distance and the ambiguity 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 is₂＝R₁+R_u，R_u＝c/2f_r，R_uRepresenting the maximum unambiguous distance. R₁Is a given value. Although clutter in the unambiguous distance region and the ambiguous distance region cannot be separated in the time domain, the airborne forward-looking frequency diversity array radar can still utilize the spatial frequency difference Deltaf_sThey are separated. This also verifies the superiority of the frequency diversity array over conventional phased arrays.

In the airborne forward-looking frequency diversity array radar, the angle Doppler frequency relation of the clutter corresponding to the ground scattering point is expressed as

Wherein,h is the height of the carrier. Equation (14) shows the elliptical coupling relationship of the clutter distribution. Referring to fig. 4, a schematic diagram of a clutter space doppler coupling relationship of the airborne forward looking frequency diversity array radar in the presence of range ambiguity is shown. In fig. 4, the horizontal axis represents normalized doppler frequency (normalized doppler frequency) and the vertical axis represents normalized spatial frequency (normalized spatial frequency), different lines represent different distance elements, respectively, with the unit m, A, B, C representing three different scattering points, and R represents the slant range. It can be seen that when the slant distance changes, the curve of the elliptical coupling relationship (clutter space Doppler coupling relationship) also follows the space frequency f_RAnd changes accordingly. In addition, the ellipse increases with increasing slope distance.

Therefore, unlike the traditional phased array radar, the clutter distribution of the airborne forward looking frequency diversity array radar of the invention changes along with the change of the slant range in the airspace frequency domain. Therefore, the airborne forward looking frequency diversity array radar can realize the separation of the unambiguous range clutter and the ambiguous range clutter in the airspace frequency domain. It should be noted that although the Frequency Diversity Array (FDA) provides additional information in the spatial and frequency domains, it also causes quadratic distance dependence problems.

The airborne forward-looking frequency diversity array radar can provide additional information in a space frequency domain, and an effective distance fuzzy clutter suppression method is discussed in the invention. Firstly, in order to overcome the problem of secondary distance dependence, a secondary distance dependence compensation method is provided; two groups of compensation vectors are respectively constructed according to the fuzzy distance area and the fuzzy distance area, and then distance fuzzy clutter suppression is realized by combining a traditional clutter spectrum compensation method.

Specifically, in the embodiment of the present invention, for a given distance (the distance units are the same), the quadratic distance-dependent compensation vector of the unambiguous distance region is expressed asThe quadratic distance-dependent compensation vector of the blurred distance region is represented asLet α be 1,2, then there are:

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

wherein the superscript T represents a matrix or vector means, a column vector of N rows. f. of_cWhich is indicative of the frequency of the compensation,Δ f represents the frequency increment of the frequency diversity array, c represents the speed of light, R_cIs corresponding slope distance, when α is equal to 1, R_c＝R₁When α is equal to 2, R_cFor fuzzy distance, R_c＝R₂＝R₁+R_u，R_uDenotes the maximum unambiguous distance, R_u＝c/2f_r，f_rRepresenting the pulse repetition frequency of the airborne forward looking frequency diversity array radar transmitted signal.

In the embodiment of the invention, the compensation vectorThe quadratic distance dependence of clutter can be compensated. After the secondary distance dependence compensation processing, the clutter spectrum meets the independent same distribution characteristic in an airspace.

In the embodiment of the invention, quadratic distance dependence compensation vector in airspace-Doppler joint frequency regionComprises the following steps:

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

wherein,denotes the Kronecker product, α ═ 1, 2; 1_KColumn vectors of N rows, 1_KAll elements in (1).

Step 3, obtaining echo space-time snapshot data of the unambiguous distance area after secondary distance dependence compensationEcho space-time snapshot data of fuzzy distance area after secondary distance dependence compensation Wherein ⊙ represents the Hadamard product.

The method comprises the following specific steps:

in an on-board front video frequency diversity array radar, diversityRespectively carrying out secondary distance dependence compensation on the echo space-time snapshot data in the unambiguous distance region and the ambiguous distance region to obtain the echo space-time snapshot data in the unambiguous distance region after the secondary distance dependence compensationEcho space-time snapshot data of fuzzy distance area after secondary distance dependence compensation

Let α be 1,2, then:

wherein, the first and second guide rollers are arranged in a row, a column vector of N rows. f. of_cWhich is indicative of the frequency of the compensation,Δ f represents the frequency increment of the frequency diversity array, c represents the speed of light, R_cIs corresponding slope distance, when α is equal to 1, R_c＝R₁When α is equal to 2, R_cFor fuzzy distance, R_c＝R₂＝R₁+R_u，R_uDenotes the maximum unambiguous distance, R_u＝c/2f_r，f_rRepresenting the pulse repetition frequency of the airborne forward looking frequency diversity array radar transmitted signal.Is a compensated spatial domain steering vector and,

for the corresponding compensated spatial frequencies:

as is clear from the above, the angular doppler frequency relation of the clutter in equation (14) can be rewritten as follows:

when α is 1, there are:

when α is 2, there are:

referring to fig. 5a, a clutter space doppler coupling relationship schematic diagram of a space doppler frequency coupling relationship obtained after the secondary dependence compensation proposed by the present invention is applied to a non-ambiguity distance region; referring to fig. 5b, a clutter space doppler coupling relationship diagram of a space doppler frequency coupling relationship obtained after the secondary dependence compensation proposed by the present invention is applied to the fuzzy distance region; in fig. 5a and 5b, the horizontal axis represents the normalized doppler frequency (normalized doppler frequency) and the vertical axis represents the normalized spatial frequency (normalized spatial frequency), and different lines represent different distance elements, respectively. As can be seen from fig. 5a and 5b, clutter without and in the ambiguity range can be effectively resolved in the spatial frequency domain. As shown in fig. 5a, from the spatial frequency domain, the clutter distribution of the unambiguous range region of the airborne forward looking frequency diversity array radar will be aligned to the middle part, and the ambiguous range region will be aligned to both sides. In contrast, as shown in fig. 5(b), the clutter of the unambiguous range region is located on both sides, and the clutter of the ambiguous range region is located in the middle of the spatial frequency domain.

In addition, in the embodiment of the invention, in order to ensure the effective classification of the unambiguous distance clutter and the ambiguous distance clutter, the array element spacing d of the frequency diversity array of the invention should satisfy

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

Wherein λ is₀Representing the carrier wavelength, λ, of a reference array element transmission signal in a frequency diversity array₀＝c/f₀，f₀Representing a reference frequency of the frequency diversity array. Without loss of generality, the array element space d is usually a quarter of a wavelength, i.e., d is 0.25 λ₀。

Step 4, respectively carrying out echo space-time snapshot data after secondary distance dependence compensation on unambiguous distance areasEcho space-time snapshot data of fuzzy distance area after secondary distance dependence compensationPerforming space-time self-adaptive processing to obtain echo space-time snapshot data of the fuzzy distance area after the corresponding clutter suppression after the secondary distance dependence compensation and echo space-time snapshot data of the fuzzy distance area after the corresponding clutter suppression after the secondary distance dependence compensationAnd (4) data.

In step 4, the procedure of the space-time adaptive processing is well known to those skilled in the art and will not be described in detail herein.

In summary, the space-time adaptive processing (STAP) performance of conventional phased array radars may be severely degraded when range ambiguities are present. Firstly, due to the fact that clutter non-stationarity is serious due to distance ambiguity, samples required by clutter covariance matrix estimation are difficult to obtain; secondly, in a non-front side-view geometrical structure, the compensation of the unambiguous range clutter and the fuzzy range clutter is mutually restricted, so that the traditional clutter spectrum compensation method is invalid; finally, clutter freedom degree is greatly increased due to distance ambiguity, and burden of system clutter suppression is increased. In the embodiment of the invention, after secondary distance dependent compensation (clutter spectrum compensation), the airborne forward-looking frequency diversity array radar realizes the separation of distance fuzzy clutter in an airspace frequency domain, the clutter spectrum compensation of a non-fuzzy distance area and a fuzzy distance area is not mutually restricted any more, and the clutter compensation and the clutter suppression can be realized by utilizing a traditional clutter spectrum compensation method. Referring to fig. 6, a schematic flow chart of the method for suppressing the airborne forward looking frequency diversity array radar range ambiguity clutter according to the present invention is shown.

The effect of the present invention can be further illustrated by the following simulation results:

1) simulation conditions

TABLE 1 simulation parameters

In the simulation experiment, the test distance of the non-fuzzy distance area is set to be 8000m, and the test distance of the fuzzy distance area is set to be 18000 m.

2) Emulated content

Simulation experiment 1: the target is set in the unambiguous distance zone. Referring to fig. 7a, it is a schematic diagram of the original impurity spectrum distribution when detecting a moving target in a non-fuzzy distance region in a simulation experiment; fig. 7b is a schematic diagram of clutter spectrum distribution after secondary distance-dependent compensation obtained by the method when a moving target is detected in a non-fuzzy distance area in a simulation experiment; referring to fig. 7c, a clutter spectrum schematic diagram after conventional clutter spectrum compensation is performed when a moving target is detected in a non-fuzzy distance region in a simulation experiment; in fig. 7a to 7c, the horizontal axis represents the normalized doppler frequency and the vertical axis represents the normalized spatial frequency, and different gray values represent different clutter spectral amplitudes. As can be seen from fig. 7a to 7c, in the on-board front video frequency diversity array radar, the unambiguous range clutter and the ambiguous range clutter in the spatial frequency region can be discriminated. Due to quadratic distance dependence, clutter is heavily spread in the spatial frequency domain. After the quadratic distance dependent compensation and clutter compensation are carried out by using the invention, the distribution of clutter in an unambiguous region in a spatial frequency domain is [ -1/4,1/4], and the distribution of clutter in an ambiguous distance region is [ -1/2, -1/4 ]. U [1/4,1/2 ]. At this time, the clutter in the fuzzy distance region does not have much influence on the target detection in the non-fuzzy distance region.

Simulation experiment 2: the target is set to be in the fuzzy distance zone. In fact, the distance dependence of clutter varies little in ambiguous distance regions, but varies significantly in unambiguous distance regions. Referring to fig. 8a, a schematic diagram of original clutter spectrum distribution when detecting a moving target in a fuzzy distance region in a simulation experiment; referring to fig. 8b, a schematic diagram of clutter spectrum distribution after secondary distance-dependent compensation obtained by the present invention when detecting a moving target in a fuzzy distance region in a simulation experiment is shown; referring to fig. 8c, a clutter spectrum schematic diagram after performing conventional clutter spectrum compensation when detecting a moving target in a fuzzy distance region in a simulation experiment is shown; in fig. 8a to 8c, the horizontal axis represents the normalized doppler frequency and the vertical axis represents the normalized spatial frequency, and different gray values represent different clutter spectral amplitudes. As can be seen from fig. 8a to 8c, after the fuzzy distance region clutter is compensated by the present invention, the distribution of the fuzzy distance region clutter is [ -1/4,1/4], the distribution of the non-fuzzy distance region clutter is [ -1/2, -1/4], [ u ], [1/4,1/2], and the distance fuzzy clutter can also be resolved in the spatial frequency domain. It follows that the unambiguous distance clutter and the ambiguous distance clutter after quadratic distance dependence compensation are separable. And by combining the traditional clutter compensation method, the clutter suppression performance can be obviously improved.

In conclusion, the simulation experiment verifies the correctness, reliability and effectiveness of the method.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims (4)

1. The method for suppressing the range ambiguity clutter of the airborne forward-looking frequency diversity array radar is characterized by comprising the following steps of:

step 1, transmitting signals by using each array element of a frequency diversity array, and receiving corresponding echo signals by using the frequency diversity array; obtaining echo space-time snapshot data x of airborne forward-looking frequency diversity array radar_c；

Step 2, determining the quadratic distance dependent compensation vector of the unambiguous distance area asAnd the quadratic distance-dependent compensation vector of the blurred distance region is represented asDeriving quadratic distance-dependent compensation vectors in the spatial domain-Doppler joint frequency region Wherein,representing the Kronecker product, α being 1 or 2; 1_KColumn vectors of N rows, 1_KAll elements in (1), N represents the number of array elements in the frequency diversity array, f_cRepresents the compensation frequency;

step 3, obtaining echo space-time snapshot data of the unambiguous distance area after secondary distance dependence compensationEcho space-time snapshot data of fuzzy distance area after secondary distance dependence compensation Wherein ⊙ represents the Hadamard product,representing the echo space-time snapshot data after quadratic distance-dependent compensation, α is 1 or 2, when α equals 1,is a non-fuzzy distance zone twiceThe distance-dependent compensated echo space-time snapshot data is updated, when α is 2,echo space-time snapshot data of the fuzzy distance area after secondary distance dependence compensation;

step 4, respectively carrying out echo space-time snapshot data after secondary distance dependence compensation on unambiguous distance areasEcho space-time snapshot data of fuzzy distance area after secondary distance dependence compensationAnd performing space-time self-adaptive processing.

2. The method for range ambiguity suppression for an airborne forward looking frequency diversity array radar as claimed in claim 1 wherein in step 1, the echo space time snapshot data x for the airborne forward looking frequency diversity array radar is obtained_cComprises the following steps:

wherein, M represents the distance unit number of the airborne forward-looking frequency diversity array radar, and M is 1,2.. M; n is a radical of_aDenotes the number of scattering points in each distance unit, i 1,2_a；γ^{i，m}Represents the complex scattering coefficient of the ith scattering point in the mth range unit,representing the Kronecker product, ⊙ representing the Hadamard product, f_t ^{i，m}Representing the normalized Doppler frequency, s, of the ith scattering point in the mth range bin_t(f_t ^{i，m}) Representing a time domain guide vector corresponding to the ith scattering point in the mth distance unit; f. of_R ^{m}Representing the normalized distance frequency, s, of each scattering point in the m-th range bin_R(f_R ^{m}) Representing a distance guide vector corresponding to each scattering point in the mth distance unit; f. of_a ^{i，m}Representing the normalized directional frequency, s, of the ith scattering point in the mth range bin_a(f_a ^{i，m}) Representing a direction guide vector corresponding to the ith scattering point in the mth distance unit; f. of_s ^{i，m}Representing the normalized spatial frequency, s, of the ith scattering point in the mth range bin (f_s ^{i，m}) And representing the full-space steering vector corresponding to the ith scattering point in the mth distance unit.

3. The method for range ambiguity suppression for an airborne forward looking frequency diversity array radar according to claim 1, wherein in step 2,comprises the following steps:

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

wherein the superscript T represents a matrix or vector means,Δ f denotes the frequency increment of the frequency diversity array, c denotes the speed of light, and R is the speed of light when α is equal to 1_c＝R₁，R₁For setting the distance value, when α is equal to 2, R_c＝R₂＝R₁+R_u，R_u＝c/2 f_r，f_rRepresenting the pulse repetition frequency of the airborne forward looking frequency diversity array radar transmitted signal.

4. The method for range ambiguity suppression for an airborne forward looking frequency diversity array radar according to any of claims 1 to 3 wherein the array element spacing d of the frequency diversity array is such that

$d\≤\frac{{\mathrm{\λ}}_0}{4}$

Wherein λ is₀Which represents the carrier wavelength of the reference array element transmission signal in the frequency diversity array.