CN104977571A - Distance blur clutter suppression method based on pitch frequency diversity STAP - Google Patents

Abstract

The invention discloses a method for suppressing range ambiguity clutter based on pitch frequency diversity STAP. The main realization idea is: after sequentially performing down-conversion and matched filter processing on the detected received signals, the pitch- The azimuth-time three-dimensional clutter snapshot model, the pitch frequency expression of each range gate and the corresponding clutter compensation term; then use the appropriate clutter compensation term to separate the range ambiguity clutter of different range rings; due to the different distance The pitch frequencies of the ambiguous clutter are separated from each other, so that the range ambiguous clutter of each range ring needs to be filtered by the filter with the corresponding coefficient, and then all the range ambiguous clutter can be suppressed, and then the range ambiguous problem can be solved; finally, in After separating the pitch distance fuzzy clutter, the distribution of the pitch spectrum and the periodicity of the digital frequency can be used to obtain the selection criteria of the frequency increment, and the present invention does not increase the degree of freedom of the system and the complexity of the calculation.

Description

Range ambiguity clutter suppression method based on pitch frequency diversity STAP

technical field

The invention belongs to the technical field of clutter suppression of radar signals, in particular to a range ambiguity clutter suppression method based on pitch frequency diversity STAP, that is, based on pitch frequency diversity space-time adaptive processing (Space-Time Adaptive Processing, STAP) range ambiguity The clutter suppression method is mainly applicable to the separation and suppression of range-ambiguous clutter in actual engineering.

Background technique

In recent years, Ground Moving Target Indication (GMTI) of airborne/spaceborne radar system has attracted extensive attention in urban traffic control and target tracking and detection; Application background, especially in the background of background noise and interference, scholars at home and abroad have proposed the space-time adaptive processing (STAP) algorithm and its corresponding improved algorithm. The starting point of these algorithms is based on two points: first, in the strong The moving target can be detected in the ground clutter; second, the parameters of the target, such as velocity and precise position, can be estimated. Therefore, the space-time adaptive processing (STAP) algorithm and its corresponding improved algorithm can achieve the target from clutter and interference in the joint domain of space domain and time domain by studying and combining multi-channel and multi-pulse signal processing methods. recognized.

In the automatic detection of radar, it is often necessary to estimate the covariance matrix of the unknown clutter background. In practice, the auxiliary data adjacent to the measured unit in the unknown clutter that does not contain the target is generally used to calculate the clutter covariance matrix of the position. It is estimated that the clutter covariance matrix is an indispensable condition for realizing adaptive weights, and the clutter covariance matrix is usually generated by the secondary training data of the test unit, and several adjacent units of the test unit in the clutter Exclude, which prevents self-cancellation of the target.

The traditional space-time adaptive processing (STAP) algorithm generally uses the method of adding fixed weights to the pitch dimension to synthesize the surface array into a linear array, and then adaptively processes in the azimuth and time domain dimensions to suppress clutter, that is, the space-time two-dimensional Adaptive signal processing (2D-STAP); however, when there is an element error, the direction patterns synthesized by each column sub-array in the pitch dimension are different, if only fixed weights are added in the pitch direction, it will cause the clutter spectrum to diffuse , and it is difficult to completely remove clutter with a large amount of distance blur.

On high-speed moving platforms such as airborne/spaceborne radars, in order to avoid severe Doppler ambiguity caused by Doppler frequency propagation, the actual space-time adaptive processing (STAP) algorithm usually uses a high pulse repetition frequency (High Pulse Repetition Frequency, HPRF), high pulse repetition frequency (HPRF) is severely blurred in distance, not blurred in speed, and has good detection performance for high-speed targets, which will make it more difficult to obtain the secondary data of the test unit; seriously, except for the side-looking radar In addition, the array radar will have the problem of distance dependence, and cannot satisfy the independent and identically distributed (IID) condition of clutter, unless the corresponding preprocessing is carried out in advance, otherwise it will not be able to perform adaptive processing. Also, the range ambiguity usually introduced by high pulse repetition frequency (HPRF) can make the clutter increasingly non-uniform; The most important is sea level, so that clutter with different statistical values will be superimposed over the distance, this complication will lead to errors in estimating the clutter covariance matrix, and cause serious degradation of the performance of the space-time adaptive processing (STAP) algorithm. Therefore, it is particularly important to solve the serious range ambiguity problem caused by high pulse repetition frequency (HPRF) in space-time adaptive processing (STAP) algorithm.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned deficiencies in the prior art, propose a kind of range ambiguity clutter suppression method based on pitch frequency diversity space-time adaptive processing (Space-Time Adaptive Processing, STAP).

The realization idea of the present invention is: when assuming that high pulse repetition frequency (HPRF) is used to alleviate the range ambiguity clutter processing in the pitching frequency diversity array (Frequency Diverse Array, FDA) radar system, the pitching channel of the radar system has also gone through beamforming processing; firstly, the detected received signal is down-converted and matched filter processed in turn, and then the pitch-azimuth-time three-dimensional clutter snapshot model of each range gate, the pitch frequency expression of each range gate and the corresponding The clutter compensation term, and then use the appropriate clutter compensation term to separate the ambiguous clutter at different ranges of the frequency diversity array (Frequency Diverse Array, FDA) radar; since the pitch frequencies of the ambiguous clutter at different ranges are separated from each other, each distance The fuzzy ring clutter needs to be filtered by a specific filter to complete the suppression of each range fuzzy ring clutter, and then solve the range ambiguity problem; finally, after separating the pitch range fuzzy clutter, the pitch spectrum can be used The distribution and the periodicity of the digital frequency obtain the selection standard of the frequency increment, and the present invention does not increase the degree of freedom of the system and the complexity of the operation.

In order to achieve the above-mentioned technical purpose, the present invention adopts the following technical solutions to achieve.

A range ambiguity clutter suppression method based on pitch frequency diversity STAP, is characterized in that, comprises the following steps:

Step 1. Establish an airborne forward-looking array radar system. The airborne forward-looking array radar system is a pitching frequency diversity array radar. The pitching frequency diversity array radar has a structure of M rows and N columns, that is, there are M transmitting channels and N receiving channels. aisle.

Step 2, assuming that each row of the pitch frequency diversity array radar emits an orthogonal signal, and the equivalent phase center of the quadrature signal is the midpoint of the corresponding row; in all receiving channels of the pitch frequency diversity array radar, the detected After the received signal is down-converted and matched filtering in turn, the echo signal r _m,n,k of the kth pulse of the pitch frequency diversity array radar transmitting signal from the mth transmitting channel and received by the nth receiving channel is obtained , where m∈{1,2,…,M}, n∈{1,2,…,N}, M represents the total number of transmitting channels, N represents the total number of receiving channels, and M, N are both positive Integer, pulse number k∈{1,2,...,K}, K represents the total number of transmitted pulses during each coherent processing interval (CPI).

Step 3, according to the echo signal obtained in step 2 Obtain the pitch-azimuth-time three-dimensional clutter snapshot model c _l of the l-th range gate, and from this three-dimensional clutter snapshot model c _l , in the case of range ambiguity in the pitch frequency diversity array radar, the l-th The pitch frequency expression of the range gate and the corresponding clutter compensation term h _c (R _l ), according to the clutter compensation term h _c (R _l ), the pitch-azimuth-time three-dimensional clutter snapshot model of each range gate After c _l is compensated, the expression of the clutter data after compensation of the mth transmitting channel is obtained in sequence The compensated clutter data expression The corresponding normalized pitch frequency Among them, K represents the total number of transmitted pulses during the coherent processing interval (CPI), k∈{1,2,…,K}, M represents the total number of transmitted channels, m∈{1,2,…,M}, N represents the total number of receiving channels, n∈{1,2,...,N}, and each transmit pulse has L range gates, l∈{1,2,...,L}.

Step 4, according to the normalized pitch frequency corresponding to the mth transmit channel The design factor is The pre-STAP filter, and use the pre-STAP filter to normalize the pitch frequency The range ambiguity clutter is separated, and then the output of the pre-STAP filter is beamformed to obtain the beamforming expression, and the beamforming expression is removed from the range ambiguity clutter to complete the range ambiguity in the range ring Clutter suppression; where, the number of pre-STAP filters is equal to the number of range ambiguity rings, that is, the number of pre-STAP filters p∈{1,2,...,N _a }, N _a means that each clutter block contains The number of distance loops, N _a also represents the number of pre-STAP filters.

The beneficial effects of the present invention are: (1) by studying the characteristics of the pitch frequency diversity array (FDA) radar signal in the pitch frequency domain, the range ambiguity clutter corresponding to the range ring can be separated; (2) the pitch frequency is After compensation, the clutter compensation can be used in the absence of mutual interference between the range ambiguous clutters, thereby improving the target detection performance and obtaining fuzzy parameter estimation; (3) because the present invention can separate the range ambiguous clutters, the present invention The invention can also suppress non-uniform clutter; (4) the present invention is not only applicable to the forward-looking array geometry in the case, but also to any array geometry; (5) the pitch frequency diversity array (FDA) proposed by the present invention ) The space-time adaptive processing (STAP) method of the radar is different from the traditional space-time adaptive processing (STAP). The present invention focuses on the characteristics of the pitch frequency diversity array (FDA) radar and then separates and suppresses the range ambiguity clutter.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is a flow chart of the steps of space-time adaptive processing (STAP) processing for pitch frequency diversity array (FDA) radar; wherein, p is the number of filters;

Fig. 2 (a) is the selected airborne radar forward-looking array geometry model figure for the present invention,

Fig. 2 (b) is the array structure schematic diagram of the selected elevation frequency diversity array (FDA) radar of the present invention;

Among them, in the three-dimensional coordinate system xyz, the pitch frequency diversity array (FDA) radar array has M rows and N columns, that is, the radar array has M transmitting channels and N receiving channels, the array element spacing is d, and the platform height is H, The motion velocity is V, and a total of K pulses are transmitted during each coherent processing interval (CPI). The pulse repetition frequency is defined as f _r =1/T _r . Each transmitted pulse has L range gates, and each range gate has It is composed of N _a statistically independent clutter blocks; the same row element uses the same carrier frequency, and the transmitting carrier frequency changes along the row, and the carrier frequencies are f ₁ , f ₂ ,..., f _M , 1, 2,... ., M represent the number of transmitting channels, T _r represents the pulse repetition period, R ₀ represents the distance from the first array element to the qth clutter block in the frequency diversity array (FDA) radar array, q∈{1 ,2,…,N _c }, θ represents the azimuth angle of the platform, Indicates the pitch angle of the platform;

Fig. 3 is the flow chart of the beamforming of the nth row of received signals in the elevation frequency diversity array (FDA) radar;

Fig. 4 is the pitch frequency distribution graph of pitch frequency diversity array (FDA) radar;

Fig. 5 (a) is the initial value distribution curve of the pitch frequency of the pitch frequency diversity array (FDA) radar;

Fig. 5(b) is a normalized value distribution curve of the pitch frequency of the pitch frequency diversity array (FDA) radar;

Fig. 6 is the corresponding normalized pitch frequency distribution graph of the clutter data expression after compensation of the present invention;

Fig. 7 is a schematic diagram of the clutter spectrum and the distance fuzzy curve when the distances are respectively 6200m, 7000m and 10000m using the present invention;

Figure 8(a) is a schematic diagram of the space-time domain clutter spectrum of a single range gate using the present invention;

Figure 8(b) is a schematic diagram of the space-time domain clutter spectra of all range gates utilizing the present invention;

Fig. 9 is a schematic diagram of the clutter spectrum of a traditional phased array radar in the pitch-distance domain;

Fig. 10(a) is a schematic diagram of the pitch-distance domain clutter spectrum of the pitch frequency diversity array (FDA) radar of the present invention after pitch frequency compensation;

Fig. 10(b) is a schematic diagram of pitch-distance domain clutter spectrum after normalized pitch frequency compensation of the pitch frequency diversity array (FDA) radar of the present invention, wherein, the abscissa is the slope distance, the unit is km, and the ordinate is the mth The normalized pitch frequency of each transmit channel;

Fig. 11(a) is a schematic diagram of the range ambiguity clutter spectrum separated by the first range ring of the elevation frequency diversity array (FDA) radar of the present invention;

Fig. 11(b) is a schematic diagram of the range ambiguity clutter spectrum separated by the second range ring of the elevation frequency diversity array (FDA) radar of the present invention;

Fig. 11(c) is a schematic diagram of the range ambiguity clutter spectrum separated by the third range ring of the elevation frequency diversity array (FDA) radar of the present invention;

Fig. 11(d) is a schematic diagram of the range ambiguity clutter spectrum separated by the fourth range ring of the elevation frequency diversity array (FDA) radar of the present invention;

Fig. 12 is a schematic diagram of the clutter spectrum after the clutter compensation of the first range ring including range ambiguity clutter is performed by the present invention.

detailed description

With reference to Fig. 1, it is the flow chart of the step that pitch frequency diversity array (FDA) radar of the present invention carries out space-time adaptive processing (STAP) processing, this based on pitch frequency diversity space-time adaptive processing (Space-Time Adaptive Processing, STAP) The distance fuzzy clutter suppression method comprises the following steps:

Step 1. Establish an airborne forward-looking array radar system. The airborne forward-looking array radar system is a pitching frequency diversity array radar. The pitching frequency diversity array radar has a structure of M rows and N columns, that is, there are M transmitting channels and N receiving channels. aisle.

Specifically, referring to Fig. 2, in the three-dimensional coordinate system xyz, the pitch frequency diversity array (FDA) radar array has M rows and N columns, that is, the radar array has M transmitting channels and N receiving channels, and the array element spacing is d , the platform height is H, the moving speed is V, a total of K pulses are transmitted during each coherent processing interval (CPI), the pulse repetition frequency is defined as f _r =1/T _r , and each transmitted pulse has L range gates , each range gate is composed of N _a statistically independent clutter blocks; T _r represents the pulse repetition period, and R ₀ represents the first array element to the qth clutter in the elevation frequency diversity array (FDA) radar array Block distance, q∈{1,2,…,N _c }, θ represents platform azimuth angle, Indicates the pitch angle of the platform; the same row of transmitting elements uses the same carrier frequency, and the transmitting carrier frequency changes along the row, and the carrier frequencies are f ₁ , f ₂ ,…,f _m ,…,f _M , m∈{1,2,… ,M}, f _m represents the carrier frequency of the mth transmission channel, and its calculation formula is as follows:

f _m =f ₀ +(m-1)△f,m=1,2,...,M (1)

Wherein, f ₀ represents the reference carrier frequency, set f ₁ =f ₀ , Δf represents the frequency increment of the pitch frequency diversity array radar, and Δf<<f ₀ .

Step 2, assuming that each row of the pitch frequency diversity array radar emits an orthogonal signal, and the equivalent phase center of the quadrature signal is the midpoint of the corresponding row; in all receiving channels of the pitch frequency diversity array radar, the detected After the received signal is down-converted and matched filtering in turn, the echo signal r _m,n,k of the kth pulse of the pitch frequency diversity array radar transmitting signal from the mth transmitting channel and received by the nth receiving channel is obtained ; Among them, m∈{1,2,…,M}, n∈{1,2,…,N}, M represents the total number of transmitting channels, N represents the total number of receiving channels, and M, N are both positive Integer, the number of pulses k∈{1,2,…,K}, K represents the total number of transmitted pulses during each coherent processing interval (CPI);

Specifically, as shown in Figure 3, beamforming processing is performed on the received signal of the nth column in the pitch frequency diversity array (FDA) radar, so that the transmission gain can reach the level of the traditional phased array radar, and the beam can also be moved for reception; In other words, it can be regarded as that there are N equivalent phase centers respectively located at the midpoints of the columns of the N receiving channels. Therefore, the pitch frequency diversity array (FDA) radar structure can be regarded as having M transmitting channels and N receiving channels.

Then, use the pitching frequency diversity array (FDA) radar to transmit and receive signals; when the pitching frequency diversity array (FDA) radar transmits signals, the array elements in the same row use the same carrier frequency, and the transmitting carrier frequencies are f ₁ , f ₂ ,… ,f _m ,...,f _M are calculated according to f _m =f ₀ +(m-1)△f respectively, m∈{1,2,...,M}, f ₀ represents the reference carrier frequency; set f ₁ = f ₀ , the variable m represents the m-th row of transmitting channels, Δf represents the frequency increment of the frequency diversity array radar, and Δf<<f ₀ .

The present invention assumes that the elevation frequency diversity array (FDA) radar transmits narrow-band signals, and the transmitted signals of any two rows of array elements are orthogonal to each other, and selects the upper left array element in the elevation frequency diversity array (FDA) radar as the reference array element ; Since the ground clutter of each range gate in the received signal of pitching Frequency Diversity Array (FDA) radar is formed by the sum of the clutter of multiple scattered centers in the range gate, the signal is transmitted by the mth transmission channel and the nth The echo signal r _m,n,k of the kth pulse received by the receiving channel can be expressed as:

${\mathrm{<span\; class="notranslate">\; r</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}\underset{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; \}</span>}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&pi;f</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; T</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&tau;</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&pi;f</span>}}_{\mathrm{<span\; class="notranslate">\; d</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; T</span>}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Among them, each transmit pulse has L range gates, and each range gate is composed of N _c statistically independent clutter blocks, N _a represents the number of range rings contained in each clutter block, and p∈{1, 2,...,N _a }, q∈{1,2,...,N _c }, N _a , N _c are all positive integers, K represents the total number of transmitted pulses during the coherent processing interval (CPI), k∈{ 1,2,…,K}, ξ ^{p,q} represents the radar scattering coefficient, Indicates the Doppler frequency of the mth transmit channel, and has V represents the moving speed of the frequency diversity array (FDA) radar, c represents the speed of light, θ represents the azimuth angle of the frequency diversity array (FDA) radar, Indicates the elevation angle of frequency diversity array (FDA) radar, f _m represents the carrier frequency of the mth transmission channel, m∈{1,2,...,M}, M represents the total number of transmission channels and is a positive integer; Indicates the launch delay, Indicates the receiving delay, and the expressions are expressed as follows:

Among them, d represents the distance between array elements, and R ₀ represents the distance from the first array element to the qth clutter block in the elevation frequency diversity array (FDA) radar.

Considering that the frequency diversity array (FDA) radar transmission signal is only a narrowband signal, the superscript {p,q} can be ignored, and after substituting Equation (3) into Equation (2), we get:

It should be noted that the scattering coefficient in formula (4) and formula (3) is the exponential term in formula (2), and formula (3) and formula (4) contain a common exponential term j2π(m-1 ).

Among them, f _e represents the normalized elevation frequency, f _a represents the normalized azimuth frequency, f _t represents the normalized Doppler frequency, and the expressions are respectively △f _e represents the additional elevation frequency, △f _a the additional azimuth frequency, and △f _t represents the additional Doppler frequency, and their expressions are respectively and Each of the three additional pitch frequency, additional azimuth frequency and additional Doppler frequency is caused by the step frequency △f; It depends on the distance R ₀ from the first array element to the qth clutter block in the frequency diversity array radar and the frequency increment Δf of the frequency diversity array radar, so f _R is also called the distance frequency.

Since the frequency increment is much smaller than the reference carrier frequency of the transmitted signal, that is, △f<<f ₀ , the terms △f _a and △f _t corresponding to equation (4) are simplified to obtain:

$\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;\; f</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 1</span>}$

$\frac{{\mathrm{<span\; class="notranslate">\; \&Delta;\; f</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; <</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Since △f<<f ₀ , the coupling term can be ignored, so the simplified form of formula (4) can be expressed as:

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; r</span>}}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; k</span>}}<span\; class="notranslate">\; \&ap;</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}\underset{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}\mathrm{<span\; class="notranslate">\; \&xi;</span>}\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&pi;\&Delta;f</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \}</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&pi;f</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; \&pi;f</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Among them, each transmit pulse has L range gates, and each range gate is composed of N _c statistically independent clutter blocks, N _a represents the number of range rings contained in each clutter block, and p∈{1, 2,...,N _a }, q∈{1,2,...,N _c }, N _a , N _c are all positive integers, K represents the total number of transmitted pulses during the coherent processing interval, k∈{1,2 ,…,K}, ξ denotes the radar scattering coefficient, f _e denotes the normalized elevation frequency, f _a denotes the normalized azimuth frequency, f _t denotes the normalized Doppler frequency, △f _e denotes the additional pitch frequency, It depends on the distance R ₀ from the first array element to the qth clutter block in the frequency diversity array radar and the frequency increment Δf of the frequency diversity array radar, so f _R is also called the distance frequency.

In this way, after simplification, the echo signal of the kth pulse of the pitch frequency diversity array (FDA) radar is transmitted by the mth transmit channel and received by the nth receive channel

Step 3, according to the echo signal of the kth pulse of the pitch frequency diversity array radar that transmits the signal from the mth transmit channel and receives the signal from the nth receive channel Obtain the pitch-azimuth-time three-dimensional clutter snapshot model c _l of the l-th range gate, and from this three-dimensional clutter snapshot model c _l , in the case of range ambiguity in the pitch frequency diversity array radar, the l The pitch frequency expression of the range gate and the corresponding clutter compensation item h _c (R _l ), according to the clutter compensation item h _c (R _l ), the pitch-azimuth-time three-dimensional clutter snapshot model of each range gate After c _l is compensated, the compensated clutter data expression corresponding to the mth transmitting channel is sequentially obtained The compensated clutter data expression The corresponding normalized pitch frequency Among them, K represents the total number of transmission pulses during the coherent processing interval, k∈{1,2,…,K}, M represents the total number of transmission channels, m∈{1,2,…,M}, N represents the reception The total number of channels, n∈{1,2,…,N}, each transmit pulse has L range gates, l∈{1,2,…,L};

The specific implementation process of step 3 is:

According to the echo signal of the kth pulse of the pitching frequency diversity array radar, the mth transmitting channel transmits the signal and the nth receiving channel receives the signal Obtain the pitch-azimuth-time 3D clutter snapshot model c _l of the lth range gate:

${\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}\underset{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; \&xi;s</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

Among them, the subscript l represents the l-th range gate, and each range gate is composed of N _c statistically independent clutter blocks, N _a represents the number of range rings contained in each clutter block, and each transmit pulse has L Range gate, l∈{1,2,…,L}, p∈{1,2,…,N _a }, q∈{1,2,…,N _c }, N _a , N _c are all positive integers , represents the Kronecker product, ξ represents the radar scattering coefficient, s _t represents the relative time steering vector, s _a represents the relative azimuth steering vector, s _e represents the relative pitch steering vector, the expressions of these three vectors are as follows:

s _t ＝[1,exp{j2πf _t },…,exp{j2πf _t (K-1)}] ^T (8.a)

s _a =[1,exp{j2πf _a },…,exp{j2πf _a (N-1)}] ^T (8.b)

s _e ＝[1,exp{j2π(f _R +f _e )},…,exp{j2π(f _R +f _e )(M-1)}] ^T ⊙[1,exp{j2π△f _e }, …,exp{j2π△f _e (M-1) ² }] ^T (8.c)

Among them, the number of pulses k∈{1,2,…,K}, K represents the total number of transmitted pulses during the coherent processing interval (CPI), m∈{1,2,…,M}, M represents the total number of transmitted pulses number, n∈{1,2,…,N}, N represents the total number of receiving channels, M, N are both positive integers, f _e represents the normalized elevation frequency, f _a represents the normalized azimuth frequency, f _t Indicates the normalized Doppler frequency, △f _e indicates the additional elevation frequency, f _R indicates the range frequency, and ⊙ indicates the Hadamard product.

Due to the carrier frequency difference in the frequency diversity array (FDA) radar receiving channel, the snapshot data model in formula (7) is slightly different from the snapshot data model generated by traditional 2D-STAP. This difference can be used to reduce the distance Additional noise for fuzzy clutter.

Compared with the pitch spectrum of the traditional phased array, the pitch spectrum of the frequency diversity array (FDA) radar has a wider distribution range in the pitch frequency domain, so it can separate its clutter from different range rings, and the pitch angle range is 0° ~90°; while for traditional phased array radar, the pitch frequency f _e-PA only depends on the pitch angle Right now

Among them, λ ₀ =c/f ₀ represents the reference wavelength, c represents the speed of light, f ₀ represents the reference carrier frequency, H represents the height of the platform, because Therefore, 0<f _e-PA <0.5; since the normalized pitch frequency usually takes a value of [-0.5,0.5], it can be seen that the traditional phased array radar only occupies the positive semi-axis of the digital frequency.

Figure 4 is the pitch frequency distribution curve of the pitch frequency diversity array (FDA) radar. Observing Fig. 4, it can be seen that the pitch frequency increases monotonically with the increase of the range gate, but it is a sine function about the pitch angle, so the pitch frequency increases with the distance The degree of change is very slow; in the long-distance area, the value of the pitch frequency is very small and changes slowly; once the difference in the pitch frequency becomes small, it will not be possible to separate the interference clutter that affects the distance blur in the pitch frequency area. The present invention can separate the range fuzzy clutter by using the processing in the background of the frequency diversity array radar.

As shown in Equation (8.c), the pitch steering vector s _e consists of two items: the first item can be regarded as a narrowband signal plus an array of equivalent pitch frequencies, that is, the sum of f _e and f _R , and the first term The binomial adopts the form of linear frequency modulation signal, and the modulation frequency is △f _e (m-1), so the pitch frequency f _e-FDA (m) of the mth transmitting channel can be written as:

f _e-FDA (m)＝f _R +f _e +△f _e (m-1) (10)

Among them, f _e represents the normalized frequency, and △f _e represents the additional pitch frequency; and because the frequency increment is much smaller than the reference frequency, the expression of the additional pitch frequency △f _e in the third item of equation (10) can be expressed as follows:

Since the value of the additional pitch frequency △f _e is usually very small, the ratio of the frequency increment △f to the reference carrier frequency f ₀ can take a value between 10 ^-3 and 10 ^-6 , and the third item in formula (10) can be ignored Neglected, so the simplified approximate expression of the pitch frequency of the mth transmit channel Can be:

From formula (12), it can be seen that the pitch frequency approximate expression The difference from traditional phased array radars is that there is an additional range-dependent term, the range-frequency Considering the range ambiguity, the pitch frequency of the p-th range ring in the m-th transmission channel and the l-th range gate Can be expressed as:

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}}_{\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; D.</span>}\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; pR</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}\frac{\mathrm{<span\; class="notranslate">\; h</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}\frac{\mathrm{<span\; class="notranslate">\; h</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 13</span>}<span\; class="notranslate">\; )</span>$

Among them, let R ₀ =R _l +(p-1)R _u , R _l represents the unfuzzy distance of the l-th range gate, R _u represents the fuzzy distance of the l-th range gate, and R _u =c/2f _r , Δf represents the frequency increment, λ ₀ represents the reference wavelength, c represents the speed of light, H represents the height of the platform, d represents the array element spacing, f _r represents the pulse repetition frequency, N _a represents the number of range rings for each clutter block, and each Each transmit pulse has L range gates, l∈{1,2,…,L}, p={1,2,…,N _a }; the range frequency f _R can be decomposed into two terms: one is the distance-dependent term , while the other depends on the number of distance rings.

Fig. 5 is a schematic diagram of pitch frequency distribution of frequency diversity array (FDA) radar described by equation (13). Fig. 5(a) is a distribution curve of initial value of pitch frequency of frequency diversity array (FDA) radar. Fig. 5(b) is pitch The pitch frequency normalized value distribution curve of frequency diversity array (FDA) radar, it is not difficult to see that the pitch frequency of frequency diversity array (FDA) radar will change greatly with the linear increase of range frequency f _R.

Since the unambiguous distance R _l and frequency increment Δf of the l-th range gate in the frequency diversity array (FDA) radar echo signal can be obtained exactly, the m-th transmitting channel and the l-th range gate in the radar echo signal The clutter compensation term h _c (R _l ) can be expressed as the following form:

${\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; ...</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; \}</span><span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; ...</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; exp</span>}<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; j</span>}\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; \&rsqb;</span>}^{\mathrm{<span\; class="notranslate">\; T</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

After the pitch-azimuth-time three-dimensional snapshot model c _l of each range gate in the frequency diversity array (FDA) radar pulse is compensated by the clutter compensation term h _c (R _l ), the compensated clutter data expression is obtained Mode

${\stackrel{<span\; class="notranslate">\; ~</span>}{\mathrm{<span\; class="notranslate">\; c</span>}}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; K</span>}}<span\; class="notranslate">\; \&CircleTimes;</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}\underset{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; \&xi;s</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; \&CircleTimes;</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 15</span>}<span\; class="notranslate">\; )</span>$

Among them, c _l represents the pitch-azimuth-time three-dimensional snapshot model of each range gate, each transmission pulse has L range gates, l∈{1,2,…,L}, each range gate is composed of N It consists of _c statistically independent clutter blocks, N _a represents the number of range rings contained in each clutter block, p∈{1,2,…,N _a }, q∈{1,2,…,N _c }, _{Na and N c are} both positive integers, st _t represents the relative time steering vector, s _a represents the relative azimuth steering vector, s _e represents the relative elevation steering vector, ξ represents the radar scattering coefficient, denotes the Kronecker product, h _c (R _l ) denotes the clutter compensation item of the mth transmit channel and the lth range gate, diag{} denotes the diagonal element of the extraction matrix, and I _NK denotes the N×K dimensional identity matrix.

So the compensated clutter data expression can be obtained The corresponding normalized pitch frequency

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}}_{\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; D.</span>}\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&ap;</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{\mathrm{<span\; class="notranslate">\; c</span>}}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}\frac{\mathrm{<span\; class="notranslate">\; h</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}\frac{\mathrm{<span\; class="notranslate">\; h</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 16</span>}<span\; class="notranslate">\; )</span>$

From formula (16), it can be seen that the final normalized pitch frequency is the sum of two terms, the first term is the purpose function of the range ring number, and the second term is the pitch frequency function of the traditional phased array radar; among them, let R ₀ =R _l +(p-1)R _u , R _l represents the unambiguous distance of the l-th range gate in the radar echo signal, R _u represents the fuzzy distance of the l-th range gate in the radar echo signal, and R _u =c/ _2fr , △f represents the frequency increment, c represents the speed of light, H represents the height of the platform, d represents the array element spacing, f _r represents the pulse repetition frequency, each range gate is composed of N _c statistically independent clutter blocks, and _Na represents the number of clutter blocks contained in each clutter block Number of range rings, p∈{1,2,…,N _a }, q∈{1,2,…,N _c }, N _a , N _c are all positive integers, R ₀ means frequency diversity array (FDA) radar In , the distance from the first array element to the qth clutter block, λ ₀ represents the reference wavelength, and f _R represents the distance frequency.

The normalized pitch frequency distribution curve corresponding to the compensated clutter data expression is shown in Fig. 6. Due to the distance ambiguity, the normalized pitch frequency distribution corresponding to the compensated clutter data expression can be regarded as A modification of the traditional pitch frequency f _e-FDA (m); and the pitch frequency of the traditional phased array radar is limited by the bandwidth and is on the positive semi-axis of the normalized frequency, that is, f _e-FDA (m)∈(0, 0.5), but the pitch frequency of frequency diversity array (FDA) radar is distributed over the entire normalized digital frequency domain. It is not difficult to see from Fig. 6 that the distances between the pitch frequencies of different distance rings are relatively large, which is due to the small change in the pitch frequencies of the long-distance areas, such as the second to fourth rings in Fig. 6, the pitch The frequency is approximately constant in the entire range ring; since the pitch frequency can be transformed to the negative half axis of the normalized frequency, ie -0.5<f<0, the range ambiguity clutter in the pitch frequency domain can be separated.

Further, in order to prevent the frequency direction of the pitch frequency domain from being ambiguous and unable to separate the range ambiguous clutter, the ratio of the frequency increment to the pulse repetition frequency (PRF) can be used according to the distribution of the pitch spectrum and the periodicity of the digital frequency. z is the integer part, and υ is the fractional part. Usually, the integer part z is selected as a parameter to obtain the selection criterion of the frequency increment, and the selection criterion of the parameter z is given.

In step 3, the compensated clutter data expression The corresponding normalized pitch frequency It can be regarded as a deformation of the traditional pitch frequency f _e-PA . Due to the periodicity of the digital frequency, the pitch frequency in equation (16) may be blurred and can be transformed into a normalized vector. The pitch frequencies of the waves may overlap, that is, in equation (16) The result will lead to the inability to separate the range ambiguity clutter.

Assuming that the ratio of the frequency increment △f to the pulse repetition frequency (PRF) consists of two parts, namely a non-negative integer part and a fractional part, the expression can be expressed as:

$\frac{\mathrm{<span\; class="notranslate">\; \&Delta;</span>}\mathrm{<span\; class="notranslate">\; f</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&upsi;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 17</span>}<span\; class="notranslate">\; )</span>$

Among them, z is the integer part, and υ is the fractional part.

Therefore, the simplified expression of the normalized pitch frequency corresponding to the mth transmit channel can be transformed into the normalized pitch frequency approximation formula corresponding to the mth transmit channel

${\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}}_{\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; D.</span>}\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; N</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}\frac{\mathrm{<span\; class="notranslate">\; h</span>}}{{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&upsi;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&upsi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; ,</span><span\; class="notranslate">\; ...</span><span\; class="notranslate">\; ,</span>{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 18</span>}<span\; class="notranslate">\; )</span>$

Among them, order And the first item z(p-1) is always an integer, p represents the number of distance rings, d represents the array element spacing, H represents the height of the platform, and R ₀ represents the first element to the qth of the frequency diversity array (FDA) radar clutter block distance, λ ₀ represents the reference wavelength.

In the traditional phased array radar, the first range ambiguity ring of the range gate in the radar echo signal will occupy most of the positive semi-axis of the pitch frequency domain, while the pitch frequencies of the other range ambiguity rings are all close to 0, and have been It is known that the pitch frequency of the first range ring of the range gate in the radar echo signal cannot be transformed in the pitch frequency domain; therefore, in order to separate the clutter on the range fuzzy ring, the frequency diversity array (FDA) radar pulse signal can be The other pitch frequencies other than the pitch frequency of the first range ambiguity ring of the range gate satisfy the following inequality

$\mathrm{<span\; class="notranslate">\; 0.5</span>}<span\; class="notranslate">\; \&le;</span>{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}}_{\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; D.</span>}\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; \&lsqb;</span>{\stackrel{<span\; class="notranslate">\; \&OverBar;</span>}{\mathrm{<span\; class="notranslate">\; f</span>}}}_{\mathrm{<span\; class="notranslate">\; e</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; f</span>}\mathrm{<span\; class="notranslate">\; D.</span>}\mathrm{<span\; class="notranslate">\; A</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 19</span>}<span\; class="notranslate">\; )</span>$

Among them, [·] represents rounding operation, Indicates the normalized pitch frequency.

And because the digital frequency is periodic, that is, the interval (0.5,1) is equivalent to the interval (-0.5,0), and α is approximately 0, so the expression (20) can be expressed as:

0.5≤υ(p-1)-[υ(p-1)]<1,p=2,3,...,N _a (20)

Available

0.5≤υ<1,p=2

0.5≤2υ-[2υ]<1, p=3

0.5≤3υ-[3υ]<1, p=4 (21)

.

.

.

0.5≤(N _a -1)υ-[(N _a -1)υ]<1,p=N _a

The final fractional part υ can be written as:

$\frac{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1.5</span>}}{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; \&le;</span>\mathrm{<span\; class="notranslate">\; \&upsi;</span>}<span\; class="notranslate">\; <</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; two</span>}<span\; class="notranslate">\; )</span>$

Combining formula (17) to formula (22), we can get

△f＝(z+υ)f _r (23)

From formula (23), it can be seen that the step frequency can be obtained by a given pulse repetition frequency (PRF); in general, the integer part z can choose any non-negative integer, but in order to ensure the independence of the ground clutter carrier frequency, the pulse repetition The frequency should be much smaller than the reference carrier frequency. Therefore, unless there are special circumstances, the value of z should be 0.

Step 4, according to the normalized pitch frequency corresponding to the mth transmit channel The design factor is The pre-STAP filter, and use the pre-STAP filter to normalize the pitch frequency The range ambiguity clutter is separated, and then the output of the pre-STAP filter is beamformed to obtain the beamforming expression, and the beamforming expression is removed from the range ambiguity clutter to complete the range ambiguity in the range ring Clutter suppression; where, the number of pre-STAP filters is equal to the number of range ambiguity rings, that is, the number of pre-STAP filters p∈{1,2,...,N _a }, N _a means that each clutter block contains The number of distance loops, N _a also represents the number of pre-STAP filters.

The specific implementation process is: in order to be able to separate the normalized pitch frequency corresponding to the mth transmit channel in the pitch frequency domain For the range ambiguity clutter, it is necessary to design a set of pre-STAP filters in the pitch direction. Since the number of range ambiguity rings is the same as the number of filters, the pitch coefficient of the pre-STAP filter is Therefore, according to the N _a filter pitch coefficients, the compensated clutter data can be expressed as Transform into NK-dimensional space-time snapshots, and get the output expression of the pre-STAP filter of the mth transmit channel

${\stackrel{<span\; class="notranslate">\; ^</span>}{\mathrm{<span\; class="notranslate">\; c</span>}}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; K</span>}}<span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; K</span>}}<span\; class="notranslate">\; \&CircleTimes;</span>\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span><span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; c</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}\underset{\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{{\mathrm{<span\; class="notranslate">\; N</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}{<span\; class="notranslate">\; \&Sigma;</span>}}{\mathrm{<span\; class="notranslate">\; \&xi;</span>}}^{<span\; class="notranslate">\; \{</span>\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; q</span>}<span\; class="notranslate">\; \}</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; g</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; h</span>}}\mathrm{<span\; class="notranslate">\; d</span>}\mathrm{<span\; class="notranslate">\; i</span>}\mathrm{<span\; class="notranslate">\; a</span>}\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; \{</span>{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \}</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; \&CircleTimes;</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; twenty\; four</span>}<span\; class="notranslate">\; )</span>$

Among them, I _NK represents the identity matrix, N _a represents the number of range ambiguity rings contained in each clutter block, N _a also represents the number of pre-STAP filters, and each range gate is composed of N _c statistically independent clutter block composition, p∈{1,2,…,N _a }, q∈{1,2,…,N _c }, N _a , N _c are positive integers, st _t represents the relevant time-oriented vector, s _a represents relative azimuth steering vector, s _e represents relative pitch steering vector, () ^H represents conjugate transpose, represents the Kronecker product, ξ ^{p,q} represents the radar scattering coefficient, h _c (R _l ) represents the compensation item of the l-th range gate, and diag{} represents the diagonal element of the extraction matrix.

Then the output expression for the set of pre-STAP filters Perform beamforming to get the beamforming expression At this time, the range ambiguity clutter in the pth range ring can be removed, p∈{1,2,...,N _a }, so that the clutter compensation will not be affected by the range ambiguity ring. The pre-STAP processing proposed by the present invention can be used to separate the range-ambiguous clutter, and then complete the clutter compensation according to the characteristics of the range-dependent clutter; it should be noted here that the non-stationarity of the range-dependent clutter has nothing to do with the pitch frequency, But the range dependence problem will be more serious in the close range area, which is also similar to the characteristics of the pitch frequency.

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

(1) Simulation conditions

The simulation experiment parameters are given in Table 1.

Simulation experiment parameter table

(2) Simulation content

Simulation experiment 1: The forward-looking geometry of the traditional phased array radar is selected here. Its clutter spectrum is symmetrical in the space-time zone and depends on distance. Figure 7 shows the clutter spectrum and ambiguity when the detection slant distance is 6200m, 7000m, and 10000m respectively. Distance curve; due to the distance dependence, the independent and identical distribution (IID) condition is not satisfied, so that when the frequency diversity array (FDA) radar does not have range ambiguity, the clutter can be compensated; for the frequency diversity array with range ambiguity clutter (FDA) radar, the clutter with different distribution characteristics will be superimposed, making the traditional clutter compensation invalid; it can be seen from Figure 7 that the distance dependence of the first range ring is very serious, and the situation of the other range rings is slightly better. Moreover, the clutter compensation of the first range ring will be affected by the clutter of the remaining range rings.

Fig. 8 (a) is a schematic diagram of the space-time domain clutter spectrum utilizing the present invention in a single range gate, and Fig. 8 (b) is a schematic diagram of the space-time domain clutter spectrum utilizing the present invention in all range gates;

It can be seen from Fig. 8(a) that the clutter spectrum of a single range ring is clearly separated from the clutter spectra of other range rings, and the clutter of the 2nd, 3rd, and 4th range rings approximately overlap; Fig. 8(b) shows the space-time domain clutter spectrum distribution, range ambiguity clutter almost occupies the entire right half of the normalized Doppler frequency-horizontal spatial frequency domain, and the target detection performance declines sharply; in the case of fast platform movement, the range ambiguity of clutter Doppler ambiguity and Doppler ambiguity will conflict with each other, so the range ambiguity of clutter must be considered in the high pulse repetition frequency radar system.

Simulation experiment 2: Figure 9 is a schematic diagram of the clutter spectrum in the pitch-distance domain of a traditional phased array radar, and Figure 10(a) is the pitch-distance domain clutter spectrum of the pitch frequency diversity array (FDA) radar of the present invention after pitch frequency compensation Schematic diagram; FIG. 10(b) is a schematic diagram of the pitch-distance domain clutter spectrum of the pitch frequency diversity array (FDA) radar of the present invention after normalized pitch frequency compensation.

For traditional phased array radars, the pitch frequency domain of clutter only accounts for the positive half of the digital frequency principal value interval, and in the first ambiguous distance region, the pitch angle changes rapidly with the slope distance, therefore, the pitch of the first ambiguous distance region The frequency changes quickly, and the pitch frequencies in the second, third, and fourth ambiguous distance areas change slowly; in addition, the pitch angles and pitch frequencies of the second, third, and fourth ambiguous distance areas are all close to 0°; The pitch frequencies of the areas (especially the second, third, and fourth ambiguous range areas) are too close to each other, so it is difficult for the traditional phased array radar to separate the range ambiguous clutter through beamforming in the vertical direction; the selected carrier The height of the aircraft is 6000m, so when the detection slant distance is less than 6000m, there is no clutter in the first fuzzy distance area.

In frequency diversity array (FDA) radar, however, the pitch clutter spectrum distribution varies greatly, which is caused by the frequency diversity, e.g., from the pitch frequency approximate expression It can be seen from Fig. 10(a) that the pitch frequencies of all detection slant ranges change significantly, and the pitch frequency is related to the slant range; it can be seen from Fig. 10(a) that the pitch frequencies of the second, third, and fourth range rings increase with the detection slant Approximate linear growth; in the present invention, range ambiguity clutter can be separated according to the set range unit, but this also requires a large number of pitch filters, once the parameters change, the filter needs to be redesigned, Figure 10(b) shows , the pitch frequency spectra of the 2nd, 3rd, and 4th range rings after pitch compensation vary little with the detection slant distance, and the only difference between the clutter distributions in Fig. 9 and Fig. 10(b) is that the range ambiguity ring The frequency change caused by the number, so the use of filters in the pitch region can separate the clutter, for example, 4 band-pass filters can separate the related distance ambiguity clutter.

Fig. 11 (a) is the distance fuzzy clutter spectrum schematic diagram of the separation of the 1st range ring of pitching frequency diversity array (FDA) radar of the present invention; Fig. 11 (b) is the 2nd distance of pitching frequency diversity array (FDA) radar of the present invention The range ambiguous clutter spectrum schematic diagram of ring separation; Fig. 11 (c) is the pitch frequency diversity array (FDA) radar of the present invention the 3rd range ambiguity clutter spectrum schematic diagram of ring separation; Fig. 11 (d) is the pitch frequency diversity array of the present invention (FDA) Schematic diagram of the range ambiguity clutter spectrum separated by the fourth range ring of the radar;

From Figure 11(a) to Figure 11(d), it can be seen that the clutter of each range ring has been successfully separated, and the clutter of the first range ring has serious distance dependence and does not satisfy the independent and identical distribution (IID) condition; while the 2nd, 3rd, and 4th distance rings respectively approximately satisfy the independent and identically distributed (IID) condition, so space-time adaptive processing (STAP) can be performed directly.

Fig. 12 is a schematic diagram of the clutter spectrum after the clutter compensation of the first range ring containing range ambiguous clutter is performed by using the present invention. In Fig. 12, the clutter is performed on the first range ring containing range ambiguous clutter After compensation, the space-time domain clutter can be separated after clutter compensation. Therefore, target detection can be performed on each range ring from which the range ambiguity clutter is separated, and the unambiguous parameters of the target can be estimated.

In summary, the simulation experiment has verified the correctness, effectiveness and reliability of the present invention.

Obviously, those skilled in the art can carry out various modifications and variations to the present invention without departing from the spirit and scope of the present invention; Like this, if these modifications and variations of the present invention belong to the scope of the claims of the present invention and equivalent technologies thereof, It is intended that the present invention also encompasses such changes and modifications.

Claims (5)

1., based on a range ambiguity clutter suppression method of pitching frequency diversity STAP, it is characterized in that, comprise the following steps:

Step 1, sets up Air-borne Forward-looking battle array radar system, and this Air-borne Forward-looking battle array radar system is pitching frequency diversity array radar, and this pitching frequency diversity array radar is the array structure of the capable N row of M, namely has M transmission channel, N number of receiving cable;

Step 2, suppose that every a line array element of pitching frequency diversity array radar launches orthogonal signal, the equivalent phase center of its orthogonal signal is the mid point of corresponding row; In all receiving cables of pitching frequency diversity array radar, after down coversion, matched filtering process are carried out successively to the Received signal strength detected, obtain pitching frequency diversity array radar m transmission channel and transmit and the echoed signal r of a kth pulse by the n-th receiving cable Received signal strength _{m, n, k}; Wherein, m ∈ 1,2 ..., M}, n ∈ 1,2 ..., N}, M represent the total number of transmission channel, and N represents the total number of receiving cable, and M, N are positive integer, umber of pulse k ∈ 1,2 ..., K}, K represent the total number of each coherent processing interim transponder pulse;

Step 3, transmits according to pitching frequency diversity array radar m transmission channel and the echoed signal of a kth pulse by the n-th receiving cable Received signal strength obtain pitching-orientation-time three-dimensional clutter snap model c of l range gate _l, and three-dimensional clutter snap model c thus _lobtain, when there is range ambiguity in pitching frequency diversity array radar, the pitching frequency expression of l range gate and corresponding clutter compensation term h _c(R _l), according to this clutter compensation term h _c(R _l) to the pitching-orientation of each range gate-time three-dimensional clutter snap model c _lafter compensating, obtain the clutter data expression formula after compensation corresponding to m transmission channel successively clutter data expression formula after this compensation corresponding normalization pitching frequency wherein, K represents the total number of coherent processing interim transponder pulse, k ∈ 1,2 ..., K}, M represent the total number of transmission channel, m ∈ 1,2 ..., M}, N represent the total number of receiving cable, n ∈ { 1,2,, N}, each transponder pulse has L range gate, l ∈ 1,2 ..., L};

Step 4, the normalization pitching frequency corresponding according to m transmission channel design ratio is pre--STAP wave filter, and utilize this pre--STAP wave filter to normalization pitching frequency in range ambiguity clutter be separated, then Wave beam forming is carried out to the output of pre--STAP wave filter, obtains Wave beam forming expression formula, and the removal of range ambiguity clutter is carried out to this Wave beam forming expression formula, complete the range ambiguity clutter recognition in rang ring; Wherein, pre--STAP number of filter is equal with range ambiguity number of rings order, namely in advance-STAP number of filter p ∈ 1,2 ..., N _a, N _arepresent the rang ring number that each clutter block contains, N _aalso pre--STAP number of filter is represented.

2. the range ambiguity clutter suppression method based on pitching frequency diversity STAP according to claim 1, it is characterized in that, in described step 2, pitching frequency diversity array radar m transmission channel transmits and the echoed signal r of a kth pulse by the n-th receiving cable Received signal strength _{m, n, k}adopt its reduced form

${\hat{r}}_{m,n,k}\&ap;\underset{p=1}{\overset{N_a}{\mathrm{\&Sigma;}}}\underset{q=1}{\overset{N_c}{\mathrm{\&Sigma;}}}\mathrm{\&xi;}\exp \left\{j2\mathrm{\&pi;}(f_R+f_e)(m-1)\right\}\exp \left\{j2{\mathrm{\&pi;\&Delta;f}}_e{(m-1)}^2\right\}\exp \left\{j2{\mathrm{\&pi;\&Delta;f}}_a(n-1)\right\}\exp \left\{j2{\mathrm{\&pi;\&Delta;f}}_t(k-1)\right\}$

Wherein, each transponder pulse has L range gate, and each range gate is by N _cthe clutter block composition of individual statistical iteration, N _arepresent the rang ring number that each clutter block comprises, and p ∈ 1,2 ..., N _a, q ∈ 1,2 ..., N _c, N _a, N _cbe positive integer, K represents the total number of coherent processing interim transponder pulse, k ∈ 1,2 ..., K}, ξ represent radar scattering coefficient, f _erepresent normalization pitching frequency, f _arepresent normalization orientation frequency, f _trepresent normalization Doppler frequency, △ f _erepresent additional pitching frequency, to depend in frequency diversity array radar the distance R of first array element to q clutter block ₀with the frequency increment △ f of frequency diversity array radar, c represents the light velocity, f _rfor frequency of distance.

3. the range ambiguity clutter suppression method based on pitching frequency diversity STAP according to claim 1, is characterized in that, in described step 3, and the normalization pitching frequency simplified expression that m transmission channel is corresponding for

${\hat{f}}_{e-FDA}\left(m\right)\&ap;\frac{\mathrm{\&Delta;}f}{c}2(p-1)R_u+\frac{d}{L_0}\frac{H}{R_0}=\frac{\mathrm{\&Delta;}f}{f_r}(p-1)+\frac{d}{{\mathrm{\&lambda;}}_0}\frac{H}{R_0}$

Wherein, R is made ₀=R _l+ (p-1) R _u, R _lrepresent the non-fuzzy distance of l range gate, R _urepresent the fuzzy distance of l range gate, and R _u=c/2f _r, △ f represents frequency increment, λ ₀represent reference wavelength, c represents the light velocity, and H represents podium level, and d represents array element distance, f _rindicating impulse repetition frequency, N _arepresent the rang ring number of each clutter block, each transponder pulse has L range gate, l ∈ 1,2 ..., L}, p={1,2 ..., N _a.

4. the range ambiguity clutter suppression method based on pitching frequency diversity STAP according to claim 3, is characterized in that, described frequency increment △ f and pulse repetition rate f _rin pass be: z is integer portion, and v is fractional part, and the value of z is 0.

5. the range ambiguity clutter suppression method based on pitching frequency diversity STAP according to claim 1, is characterized in that, in described step 4, and the output expression formula of the pre--STAP wave filter of m transmission channel

${\hat{c}}_l\left(m\right)\&ap;{(I_{NK}\&CircleTimes;g_p)}^H(I_{NK}\&CircleTimes;diag\{h_c\left(R_l\right)\left\}\right)c_l\underset{p=1}{\overset{N_a}{\mathrm{\&Sigma;}}}\underset{q=1}{\overset{N_c}{\mathrm{\&Sigma;}}}{\mathrm{\&xi;}}^{\{p,q\}}\left(g_p^{H}diag\right\{h_c\left(R_l\right)\left\}{s}_e\right)(s_t\&CircleTimes;s_s)$

Wherein, I _nKrepresentation unit matrix, N _arepresent the range ambiguity number of rings that each clutter block contains, N _aalso represent pre--STAP number of filter, each range gate is by N _cthe clutter block composition of individual statistical iteration, p ∈ 1,2 ..., N _a, q ∈ 1,2 ..., N _c, N _a, N _cbe positive integer, s _trepresent steering vector correlation time, s _arepresent relative orientations arc steering vector, s _erepresent relevant pitching steering vector, () ^hrepresent conjugate transpose, represent that Kronecker amasss, ξ ^{{ p, q}}represent radar scattering coefficient, h _c(R _l) represent that the compensation term of l range gate, diag{} represent and extract matrix diagonals element.