CN113376599B - FDA distance fuzzy clutter suppression method based on mainlobe correction - Google Patents
FDA distance fuzzy clutter suppression method based on mainlobe correction Download PDFInfo
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract
The invention discloses an FDA distance fuzzy clutter suppression method based on mainlobe correction, which comprises the following steps: establishing a signal model, and obtaining a radar echo signal according to the signal model; constructing a distance phase compensation guide vector, and performing first compensation processing on the radar echo signal according to the distance phase compensation guide vector to obtain a first echo processing signal; constructing a correction restoration compensation vector corresponding to the main lobe correction weight, and carrying out restoration compensation processing on the first echo processing signal according to the correction restoration compensation vector to obtain a compensation restoration signal; and selecting any one of the transmitting array element data in the compensation and restoration signals to obtain a dimension reduction compensation signal, and performing second compensation processing on the dimension reduction compensation signal to realize the suppression of radar distance fuzzy clutter. According to the invention, the main lobe motion correction is carried out at the radar transmitter for recovery compensation, and the signals in different distance fuzzy areas can be distinguished by utilizing the distance coupling characteristic of the FDA signal echo, so that the distance fuzzy clutter is restrained through compensation.
Description
Technical Field
The invention belongs to the technical field of radar signal processing, and particularly relates to an FDA distance fuzzy clutter suppression method based on main lobe correction.
Background
The airborne phased array radar takes an airplane flying at high altitude as a carrier, and has the advantages of wide monitoring range, long early warning time for low-altitude targets and the like. The modern attack targets are often hit by military through maneuvering flight, which forms a serious threat to the national defense system, and how to effectively detect and early warn maneuvering targets in time is a great challenge for future radar monitoring systems.
The forward-looking array is used as a common array structure of the airborne radar, clutter distribution has distance dependence, and the number of independent co-distributed training samples is usually limited, so that the radar target detection performance is affected. Ground clutter suppression is one of the key problems of ground target detection when the airborne radar works in a downward-looking mode. The traditional Space-time adaptive signal processing method (Space-Time Adaptive Processing, STAP for short) utilizes the Space information of array element antennas and the time information between coherent pulses, and combines Space-time two-dimension to carry out adaptive suppression on clutter to detect a target with low signal to noise ratio, and in a positive side view array, clutter with different distances has the same distribution characteristic in a power spectrum, and the STAP technology can effectively detect a radar target.
However, in the case of forward looking array, the radar clutter has distance dependence, that is, clutter distribution characteristics are different according to different distances, so that the fuzzy inhomogeneous clutter is an important problem faced by the airborne forward looking array radar, and clutter echoes in different distance fuzzy areas are overlapped when the radar enters steady state operation under a high-repetition frequency pulse system. The clutter of the airborne forward-looking array radar system has distance dependency, the clutter of different areas have different distribution characteristics, the distance blurred clutter are overlapped with each other, and the observable area of the radar can be seriously polluted, so that the detection performance of the radar is difficult to improve by using the STAP method.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides an FDA distance fuzzy clutter suppression method based on main lobe correction.
One embodiment of the invention provides an FDA distance blur clutter suppression method based on mainlobe correction, which comprises the following steps:
the method comprises the following steps:
step 1, a signal model is established, and a radar echo signal is obtained according to the signal model;
step 2, constructing a distance phase compensation guide vector, and performing first compensation processing on the radar echo signal according to the distance phase compensation guide vector to obtain a first echo processing signal;
step 3, constructing a correction restoration compensation vector corresponding to the main lobe correction weight, and carrying out restoration compensation processing on the first echo processing signal according to the correction restoration compensation vector to obtain a compensation restoration signal;
and step 4, selecting any one of the transmitting array element data in the compensation and restoration signals to obtain a dimension reduction compensation signal, and performing second compensation processing on the dimension reduction compensation signal to obtain the final suppression of the radar distance fuzzy clutter.
In one embodiment of the present invention, the radar echo signal obtained by the signal model established in step 1 is expressed as:
wherein p represents the p-th distance fuzzy area in the power range, the number of the distance fuzzy areas is U, q represents clutter blocks positioned at a certain angle in the same distance fuzzy area, and the total number of the clutter blocks is N c ，s pq Represents the clutter signal corresponding to the qth clutter block of the p-th distance blurring area,representing noise->Representing main lobe correction weight vector, gamma 0p ＝Υ 0 ＝exp{-j2πf 0 R ∑ /c}，f 0 Represents the reference frequency, R ∑ Represents the pitch, c represents the speed of light, ρ pq Representing the product of the scattering coefficient of the irradiation radar target and the signal propagation gain in the qth clutter block in the p-th distance blur area, s d Representing Doppler steering vector, f pqd0 Normalized Doppler frequency, s, representing the qth clutter block in the p-th range ambiguity region r Representing a received spatial steering vector, f qr Represents the angular frequency of the received signal corresponding to the q-th clutter block, s ct Representing emissionsSpace steering vector, f pqct The angular frequency s of the composite transmission signal representing the qth clutter block in the p-th distance blur area R Representing distance-coupled phase components, f R Representing distance ambiguous region coupling term, ">Δf represents the frequency increment, f pR Representing the distance coupling phase angular frequency, s, in the p-th distance ambiguity region t Representing the transmit spatial steering vector, f qt Represents the spatial angular frequency of the transmission corresponding to the qth clutter block,/, and>indicates the Cronecker product, and the ". Iy indicates the Ha Mada product.
In one embodiment of the present invention, the signal s of the clutter signal clutter block corresponding to the qth clutter block of the p-th distance blur area in step 1 pq Expressed as:
wherein y is 0 ＝exp{-j2πf 0 R ∑ /c}，f 0 Represents the reference frequency, R ∑ Represents the slant distance, c represents the speed of light, ρ represents the product of the scattering coefficient of the illuminating radar target and the signal propagation gain,representing a main lobe correction weight vector, s d Representing Doppler steering vector, f d0 Represents normalized Doppler frequency, d r Representing the spacing, ψ, between array elements in a receive array r Representing the spatial cone angle of the target and receive array, s ct Representing the transmit spatial steering vector, f ct Representing the spatial angular frequency of the composite emission s R Representing the distance-coupled phase component>Δf representsFrequency increment, s r Representing a received spatial steering vector, f r Representing the angular frequency of the receiving space s t Representing the transmit spatial steering vector, f t Representing the angular frequency of the emission space, +.>Indicates noise, ++ Ha Mada product, ++>Representing the kronecker product.
In one embodiment of the present invention, the range phase compensation steering vector constructed in step 2 is expressed as:
wherein q R Representing a distance phase compensation steering vector, f R0 ＝Δf2R 0 /c，R 0 Represents no-ambiguity distance, c represents light velocity, Δf represents frequency increment, M represents number of transmitting array elements, [] T Is a transposed operator.
In one embodiment of the present invention, the correction restoration compensation vector corresponding to the main lobe correction weight constructed in step 3 is expressed as:
wherein,represents a correction-reduction compensation vector, h K1 ＝[0,1,...,K-1] T K represents the number of coherent processing pulses, d r (f PRF )＝[0,j2πΔf/f PRF ,...,j2π(M-1)Δf/f PRF ] T ，f PRF Representing pulse repetition frequency, +.>Representing an N x 1-dimensional all-one matrix, N representing the number of array elements of the receive array.
In one embodiment of the present invention, the compensation restoration signal obtained by the restoration compensation processing in step 3 is expressed as:
wherein,representing a corrected restoring compensation vector e R Representing distance compensation items>Representing a K x 1-dimensional all-matrix, < >>Represents an N x 1-dimensional all-matrix, q R [f R0 (R 0 )]Representing a distance phase compensation steering vector, b c Representing a correction weight vector representing the main lobe, +.>Representing the main lobe correction compensation vector b C Corresponding frequency, ++>Representing a correction-reduction compensation vector +.>Corresponding frequency term, f R Representing the frequency corresponding to the coupling term of the distance blur area, < ->f PRF Representing the pulse repetition frequency.
In one embodiment of the present invention, step 4 comprises:
selecting any one of the emission array element data in the compensation and restoration signals to enable the compensation and restoration signals of NMK dimension to be reduced to dimension-reducing compensation signals of MK dimension;
and performing second compensation processing on the dimension reduction compensation signal by using a DW technology to realize the suppression of radar distance fuzzy clutter.
Compared with the prior art, the invention has the beneficial effects that:
according to the FDA distance blur clutter suppression method based on main lobe correction, main lobe motion correction phase weighting is carried out at a radar transmitter, main lobe irradiation areas of different pulses are unified, recovery compensation is carried out at a receiving end, signals in different distance blur areas can be distinguished by utilizing distance coupling characteristics of FDA signal echoes, through compensation, signals from an observation area are identical to traditional MIMO signals, and distance blur signals in a non-observation area show low-gain discrete distribution in a power spectrum, so that the distance blur clutter is suppressed.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
Fig. 1 is a schematic flow chart of an FDA distance blur clutter suppression method based on main lobe correction according to an embodiment of the present invention;
fig. 2 is a schematic diagram of a geometric configuration of an airborne forward-looking array FDA-MIMO radar according to an embodiment of the present invention;
FIG. 3 is an illustration of FDA radar pulses and main lobe trend provided by an embodiment of the present invention;
FIG. 4 is an illustration of the FDA radar pulse time domain direction provided by an embodiment of the present invention;
FIG. 5 is an illustration of FDA radar pulses and main lobe trend after main lobe ambulation correction provided by an embodiment of the present invention;
FIG. 6 is an illustration of FDA radar pulse time domain direction after main lobe ambulation correction provided by an embodiment of the present invention;
FIG. 7 is a schematic diagram of processing a received signal in a method for performing distance-fuzzy clutter suppression and dimension reduction search on an onboard FDA-MIMO bistatic radar according to an embodiment of the present invention;
FIG. 8 is a schematic diagram of transmitting and receiving pulses at different distances provided by an embodiment of the present invention;
fig. 9 (a) to 9 (b) are diagrams illustrating equivalent transmission directions of FDA-MIMO radars before and after main lobe correction and compensation provided by the embodiment of the present invention;
fig. 10 (a) to 10 (b) are graphs of the power of the CAPON in doppler and angular dimensions of the FDA after correction and compensation of the conventional MIMO and main lobe provided by an embodiment of the present invention;
fig. 11 (a) to 11 (b) are schematic IF curves corresponding to the conventional MIMO method in the method of the present invention when the spatial angular frequency of the clutter spectrum provided by the embodiment of the present invention is 0.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but embodiments of the present invention are not limited thereto.
Example 1
Referring to fig. 1, fig. 1 is a schematic structural diagram of an FDA distance blur clutter suppression method based on mainlobe correction according to an embodiment of the present invention. The embodiment provides an FDA distance fuzzy clutter suppression method based on mainlobe correction, which comprises the following steps:
and 1, establishing a signal model, and obtaining a radar echo signal according to the signal model.
Specifically, referring to fig. 2, in the schematic geometric configuration of the airborne forward-looking array FDA-MIMO radar provided in the embodiment of the present invention in fig. 2, coordinate axes xyz are perpendicular to each other to form a space coordinate system, a motion speed direction of a platform is consistent with a y-axis direction of the coordinate system, a height is H, a radar antenna is a front-looking one-dimensional equidistant linear array, an array is parallel to an x-axis, an azimuth angle formed by a clutter block P and the antenna array is set as θ, and a pitch angle formed by the clutter block P and the antenna array is set as θThe number of transmitting array elements is M, the number of receiving array elements is N, the distances between the transmitting array elements and the receiving array elements are the same, d and the number of coherent processing pulses is K. In FDA-MIMO radar, the carrier frequency f of the transmitted signal 0 For the reference frequency of the radar, the frequency of each array element is differentThe transmission frequency of M array elements can be expressed as:
f m ＝f 0 +(m-1)Δf m＝1,2,...,M (1)
wherein Δf represents the frequency increment, and Δf is required in formula (1) 0 . Similar to a conventional phased array radar, the narrowband signal transmitted by the mth channel of the FDA-MIMO radar can be expressed as:
wherein rect (·) is a rectangular window function representing the signal pulse, T p Representing pulse width s m (t) is an orthogonal waveform corresponding to the mth channel, and when the ideal orthogonal condition is satisfied, there are:
the narrowband signal corresponding to the kth pulse transmitted by the mth array element of far-field reception is expressed as:
wherein τ r =2r/c represents the common two-way propagation delay of each array element of the radar to the far-field target P, τ sm = (m-1) dcos ψ/c represents the delay difference of the mth transmitting element to the target with respect to the reference element, R represents the slant distance between the reference element to the far field target, c represents the speed of light, and ψ represents the spatial cone angle between the target and the reference element. As can be seen from the view of figure 2, representing f generated by platform motion m Corresponding Doppler frequency->v represents the platform movement speed, +.>Representing white gaussian noise, since the signal is a narrowband signal, there is a simplification s m (t-τ r /2-τ sm )≈s m (t-τ r 2), rect [ (t- τ) r /2-τ sm )/T p ]≈rect[(t-τ r /2)/T p ]。
Referring to fig. 3, fig. 3 is an illustration of FDA radar pulses and main lobe trend provided by an embodiment of the present invention, as shown in fig. 3, the phase accumulation amount between different pulses due to Δf at the corresponding time T of PRIDifferent initial phases of transmission exist among pulses, and the FDA radar transmission directional diagram has distance (time) -angle coupling, so that the main lobe pointing angle of the equivalent transmission directional diagram of the receiving end corresponding to different pulses can walk. Referring to fig. 4, fig. 4 is a schematic diagram of a time domain direction of an FDA radar pulse provided by an embodiment of the present invention, and fig. 4 shows a walking situation of three pulse main lobes of the FDA radar transmission direction diagram in an angle and distance two-dimensional domain, wherein the pulse width is 4.76e-05 seconds, the corresponding distance is 14.2km, the pri is 6.6e-04 seconds, the corresponding distance is 200km, and Δf=1/2 f PRF It can be seen from fig. 4 that the first pulse and the second pulse coincide with each other in the main lobe directions of 60km and 20km by 30 degrees to 0 degrees and the second pulse travels in the main lobe direction of-20 to-90 degrees. Therefore, the echoes between pulses are echoes at different positions, and have no coherence, and thus no noise cancellation or space-time two-dimensional processing can be performed. Therefore, the main lobe correction weight vector of the present embodiment is specific by constructing the main lobe correction weight of the transmission pattern, which compensates the main lobe phase of each pulse so that the main lobes of different pulses are irradiated at the same angle>Expressed as:
d(Δf/f PRF )＝[0,-j2πΔf/f PRF ,...,-j2π(M-1)Δf/f PRF ] T (5)
h K1 ＝[0,1,2,...,K-1] T (6)
wherein [ (S)] T Representing transpose operation symbols, f PRF Indicating the pulse repetition frequency at which the pulse is repeated,representing the kronetime multiplicable product,and->And forming a main lobe correction weight vector.
Referring to fig. 5, fig. 5 is an illustration diagram of FDA radar pulse and main lobe trend after main lobe walk correction provided by the embodiment of the present invention, in fig. 5, a main lobe correction weight vector b is added through a transmitting end C A phase negative delay is applied between different transmitted pulses to cancel the phase component associated with T shown in the figure, so that different pulse normal patterns are all illuminated at the same angle. Referring to fig. 6, fig. 6 is an illustration of a direction diagram of a time domain of an FDA radar pulse after main lobe walk correction provided by an embodiment of the present invention, and fig. 6 is a schematic diagram of three pulse main lobe positions of a direction diagram after main lobe walk correction, where after main lobe walk correction is performed on the radar by formula (7), formula (4) is rewritten as follows:
the signal echo after far field reflection is received, and the kth pulse signal received by the nth receiving array element can be expressed as:
where ρ represents the product of the reflection coefficient of the radar target and the signal propagation gain, the far-field reflected signal echo is received, and the signal echo is processed by MIMO quadrature waveform filtering.
Referring to fig. 7, fig. 7 is a schematic diagram of processing a received signal in a method for performing distance-fuzzy clutter suppression and dimension reduction search on an onboard FDA-MIMO bistatic radar according to an embodiment of the present invention, where x is shown in fig. 7 n Representing the echo signal received by the nth receive channel,representing the conjugate transpose of the orthogonal waveform corresponding to the mth transmit channel, then the mth transmit channel of the FDA-MIMO radar transmits the echo signal of the kth pulse received in the coherent processing time received by the nth receive channel through s m (t-τ r )exp(j2πf m t) write after matched filtering and pulse compression:
where ρ represents the product of the reflection coefficient of the irradiation radar target and the signal propagation gain, f dm For frequencyThe corresponding normalized Doppler frequency, denoted +.>The term for distance coupling phase in equation (10)>Have common item->Equation (10) is re-expressed as:
since Deltaf (m-1) < f 0 Then simplify f m ＝(f 0 +Δf m )≈f 0 And f dm ＝2v(f 0 +Δf m )cosψ/(cf PRF )≈2vf 0 cosψ/(cf PRF )＝f d0 Thus, equation (11) is re-expressed as:
the snapshot array stream signal model of the received signal of this embodiment is represented as:
wherein y is 0 ＝exp{-j2πf 0 R ∑ /c}，f 0 Represents the reference frequency, R ∑ Represents the slant distance, c represents the speed of light, ρ represents the product of the scattering coefficient of the illuminating radar target and the signal propagation gain,representing a main lobe correction weight vector, s d Representing Doppler steering vector, f d0 Represents normalized Doppler frequency, d r Representing the spacing, ψ, between array elements in a receive array r Representing the spatial cone angle of the target and receive array, s ct Representing the transmit spatial steering vector, f ct Representing the spatial angular frequency of the composite emission s R Representing the distance-coupled phase component>Δf represents the frequency increment, s r Representing a received spatial steering vector, f r Representing the angular frequency of the receiving space s t Representing a spatial director of emissionQuantity f t Representing the angular frequency of the emission space, +.>Indicates noise, ++ Ha Mada product, ++>Representing Cronecker product, metropolyl>Is MNK x 1-dimensional vector. The transmit spatial steering vector is expressed as:
s ct (f ct )＝s R (f R )⊙s t (f t ) (14)
wherein distance-coupled phase components due to frequency diversityExpressed as:
wherein,emission angle frequency guide vector->Expressed as:
wherein,receiving space vector>Expressed as:
wherein,doppler guidance vector->Can be expressed as:
s d (f d0 )＝[1,exp{j2πf d0 },...,exp{j2π(K-1)f d0 }] T (18)
wherein f d0 ＝2vf 0 cosψ/(cf prf )。b C Representing the phase term present due to the emission main lobe correction compensation amount, according to equation (7), its vector form is expressed as:
wherein l K1 ＝[1,exp{1},exp{2},...,exp{(K-1)}] T ，Is an N x 1-dimensional all-one matrix.
In this embodiment, only the echoes of all the transmitting array elements received by one receiving channel are focused, and the first receiving channel is taken as an example, and the signal s of the clutter signal clutter block corresponding to the qth clutter block in the p-th distance blurring region is received pq Expressed as:
referring to fig. 8, fig. 8 is a schematic diagram of transmitting and receiving pulses at different distances according to an embodiment of the present invention, wherein the number of coherent pulses is set to k=5, and fig. 8 is a schematic diagram of primary blurred region clutter and no blurDistance R 0 Time domain pulse echo schematic diagram of region clutter, rectangle represents signal and clutter echo of no-blurring region, and semicircle represents primary blurring distance R 1 The echo of the region, the echo number and the number of the transmitted pulse correspond. As can be seen from fig. 8, the range-blurred clutter in different areas of the receiving end overlap, which reduces the detection performance of the radar. The embodiment receives a radar echo signal expressed as:
wherein p represents the p-th distance fuzzy area in the power range, the number of the distance fuzzy areas is U, q represents clutter blocks positioned at a certain angle in the same distance fuzzy area, and the total number of the clutter blocks is N c ，s pq Represents the clutter signal corresponding to the qth clutter block of the p-th distance blurring area,representing noise->Representing main lobe correction weight vector, gamma 0p ＝Υ 0 ＝exp{-j2πf 0 R ∑ /c}，f 0 Represents the reference frequency, R ∑ Represents the pitch, c represents the speed of light, ρ pq Representing the product of the scattering coefficient of the irradiation radar target and the signal propagation gain in the qth clutter block in the p-th distance blur area, s d Representing Doppler steering vector, f pqd0 Normalized Doppler frequency, s, representing the qth clutter block in the p-th range ambiguity region r Representing a received spatial steering vector, f qr Represents the angular frequency of the received signal corresponding to the q-th clutter block, s ct Representing the transmit spatial steering vector, f pqct The angular frequency s of the composite transmission signal representing the qth clutter block in the p-th distance blur area R Representing distance-coupled phase components, f R Representing distance ambiguous region coupling term, ">Δf represents the frequency increment, f pR Representing the distance coupling phase angular frequency, s, in the p-th distance ambiguity region t Representing the transmit spatial steering vector, f qt Represents the spatial angular frequency of the transmission corresponding to the qth clutter block,/, and>indicates the Cronecker product, and the ". Iy indicates the Ha Mada product.
And 2, constructing a distance phase compensation guide vector, and performing first compensation processing on the radar echo signal according to the distance phase compensation guide vector to obtain a first echo processing signal.
Specifically, for different blurred or non-blurred regions, the embodiment specifically constructs a distance phase compensation guiding vector by using a secondary distance compensation method, and performs a first compensation process on a radar echo signal corresponding to a transmitting space guiding vector according to the constructed distance phase compensation guiding vector to obtain a first echo processing signal. The distance phase compensation steering vector constructed in this embodiment:
wherein q R Representing a distance phase compensation steering vector, f R0 ＝Δf2R 0 /c，R 0 Represents no-ambiguity distance, c represents light velocity, Δf represents frequency increment, M represents number of transmitting array elements, [] T Is a transposed operator. After the formula (22) and the formula (23) are substituted into the formula (21) for compensation, the echo transmitting space steering vector of the non-fuzzy area is consistent with the traditional MIMO, and the fuzzy area still has a distance coupling phase term and is distinguished. Taking the echo signal of the kth pulse of the mth transmitting array element and the nth receiving array element as an example, there is noThe blurred region echo signal is expressed as:
the primary range ambiguity region echo signal is expressed as:
wherein R is 1 ＝R u +R 0 。
And 3, constructing a correction restoration compensation vector corresponding to the main lobe correction weight, and carrying out restoration compensation processing on the first echo processing signal according to the correction restoration compensation vector to obtain a compensation restoration signal.
Specifically, after the total echo signal in the embodiment is subjected to the first compensation processing in the step 2, the signals of the non-blurred region and the primary distance blurred region still contain the main lobe correction compensation term of the equivalent transmission direction diagram. And constructing a correction restoration compensation vector corresponding to the main lobe correction weight, and carrying out restoration compensation on the first echo processing signal to obtain a compensation restoration signal. The specifically constructed correction restoration compensation vector corresponding to the main lobe correction weight is expressed as:
d r (f PRF )＝[0,j2πΔf/f PRF ,...,j2π(M-1)Δf/f PRF ] T (26)
h K1 ＝[0,1,...,K-1] T (27)
the formulas (26), (27) and (28) are respectively brought into formulas (24) and (25) to compensate, and the echo signals of the non-fuzzy area are re-expressed as:
the primary range ambiguity region echo signal is re-represented as:
through two compensations, namely the first compensation treatment of the step 2 and the restoring compensation treatment of the step 3, due toThe primary range ambiguity region echo of this embodiment can be further expressed as:
where α=mod 5 |(k-1)+4|-(k-1)+1＝mod 5 The I k+3I-k+2 can be seen that after two times of compensation, the echo of the non-distance fuzzy area signal is not different from the MIMO radar, and can be written as
(i.e., when k is 1,2,3,4,5, respectively, α is 0, 0), the primary range-blur clutter region is written as
(when k is 1,2,3,4,5, respectively, the corresponding α is 5,0,0,0,0).
Combining the formula (21) and the formula (28), the first echo processing signal after the receiving end compensation in this embodiment is expressed as:
wherein,representation schoolPositive restoring compensation vector e R Representing distance compensation items>Representing a K x 1-dimensional all-matrix, < >>Represents an N x 1-dimensional all-matrix, q R [f R0 (R 0 )]Representing a distance phase compensation steering vector, b C Representing a correction weight vector representing the main lobe, +.>Representing the main lobe correction compensation vector b C Corresponding frequency, ++>Representing a correction-reduction compensation vector +.>Corresponding frequency term, f R Representing the frequency corresponding to the coupling term of the distance blur area, < ->f PRF Representing the pulse repetition frequency. Distance compensation term e of the present embodiment R (f R0 ) By adding the Hamond product plus and the transmission guiding vector distance coupling phase term, the transmission guiding vector distance coupling and the frequency plus are carried out>Term coupled to the number of distance blur areas and then to the main lobe correction compensation vector b C Corresponding frequency term->And correcting the restoration compensation vector b RC Frequency term of->Adding to obtain alpha p A coupled phase term that is related to the number of ambiguous regions. />
And step 4, selecting any one of the transmitting array element data in the compensation and restoration signals to obtain a dimension reduction compensation signal, and performing second compensation processing on the dimension reduction compensation signal to realize the suppression of radar distance fuzzy clutter.
Specifically, any one of the transmission array element data in the compensation and restoration signals is selected to enable the compensation and restoration signals in NMK dimension to be reduced to the dimension reduction compensation signals in MK dimension, the original NMK dimension data is reduced to obtain MK dimension data, and then clutter data dependence compensation, namely second compensation processing, is carried out on the dimension reduction compensation signals by using Doppler shift technology (DW) and the like, so that the suppression of the range-blurred clutter of the forward-looking array radar is realized.
In order to verify the effectiveness of the FDA distance blur clutter suppression method based on mainlobe correction proposed in this embodiment, the following simulation experiment is further proved.
The traditional FDA radar and the method provided by the invention are compared in different pulse emission patterns in the distance and angle fields, and the change of the equivalent emission pattern after the main lobe correction and compensation is analyzed. The simulation parameters in the simulation process of this example are shown in table 1.
Table 1 list of simulation parameters
| Parameter name | Parameter value |
| Linear array element number (M/N) | 20 |
| Carrier frequency f 0 | 1.2GHz |
| Array element spacingd | 0.0625m |
| Platform speed | 150m/s |
| Maximum distance without ambiguity | 50km |
| Noise ratio of the impurity | 30dB |
| Signal to noise ratio | 40dB |
| Platform height | 6km |
| Desired target distance | 20km |
| Desired target angle | 30° |
| Pulse repetition frequency PRF | 3000Hz |
| Number of coherent pulses K | 5 |
Simulation 1:
referring to fig. 9 (a) to 9 (b), fig. 9 (a) to 9 (b) are diagrams illustrating equivalent transmission directions of FDA-MIMO radar before and after main lobe correction compensation provided by the embodiment of the present invention, fig. 9 (a) shows an equivalent transmission direction diagram of FDA-MIMO radar before main lobe correction compensation, fig. 9 (b) shows an equivalent transmission direction diagram of FDA-MIMO radar after main lobe correction compensation, fig. 9 (a) has coupling of a distance angle, so that main lobes present S-shape in an angular distance two-dimensional region, fig. 9 (a) has a desired signal position of 0 degree, shows a direction diagram main lobe distribution condition of three continuous pulse periods, a pulse width of 4.76e-05S, a corresponding distance of 14.29km, a pulse repetition interval of 6.67e-04S, a corresponding distance of 200km, as can be seen from a review of fig. 9 (a), the high gain angle of the main lobe of the first pulse period directional diagram is between 0 and 30 degrees, since the carrier frequencies between different array elements of the FDA-MIMO radar are different, after accumulation of one pulse repetition interval, the initial phases of the array elements are different when the second pulse is transmitted (as shown in fig. 9, the accumulation initial phase of the m-th array element is 2pi m deltaft), and the FDA-MIMO directional diagram has S-type distance angle coupling distribution characteristics, so that the high gain angle of the main lobe of the directional diagram is between-23 and-110 degrees during the second pulse period, and due to the angle periodicity, in the diagram [ -90, -110] is displayed at the [70,90] position, in the simulation deltaf=1/(2T), so that during the third pulse period, the m-th element accumulation initial phase is 2pi m.DELTA.f2T=2pi.m, and each element initial phase is the same, so that the condition is the same as the first pulse period. Fig. 9 (b) is an equivalent transmission pattern of the FDA-MIMO radar after main lobe correction compensation, and as can be seen from equation (7), the first pulse period initial phase compensation is 0, so that the same as fig. 9 (a), the m-th array element compensation amount of the second pulse period is 2pi m Δt, and the same as the Δf accumulation initial phase, so that the pattern is the same as the first pulse period, and the third pulse period after compensation is the same as the first pulse period.
Simulation 2:
referring to fig. 10 (a) to fig. 10 (b), fig. 10 (a) to fig. 10 (b) are the power spectrums of the CAPON scanning of the FDA in the doppler and angle dimensions after the conventional MIMO and main lobe correction compensation provided by the embodiment of the present invention, the embodiment simulates ground clutter in different distances, simulates the echo of a front view array airborne platform, and draws the clutter power spectrums, specifically fig. 10 (a) is the power spectrums of the CAPON scanning of the conventional MIMO in the doppler and angle dimensions, and fig. 10 (b) is the power spectrums of the CAPON scanning of the FDA in the doppler and angle dimensions after the main lobe compensation provided by the embodiment of the present invention. Because of the single base platform, the receiving angles of the transmitting angle fields are consistent, and the graphThe middle abscissa is the Doppler domain, the ordinate is the transmitting angle domain, and clutter echoes exist in the simulation at the positions of the non-fuzzy region R=20 km and the first distance fuzzy region R=70 km. As the front view array is adopted, the clutter is distributed in a positive ellipse, and as can be seen from FIG. 10 (a), the clutter has distance dependence, the clutter echoes with different distances have different shapes, and the clutter at two distances are overlapped together at 0 degree f d The presence of a notch due to the different clutter shapes in the different blur areas can be seen around =0.4. It can be seen from FIG. 10 (b) that only the no-blur region R0 exhibits clutter, while clutter in the first blur region R1 is suppressed, comparing FIG. 10 (a) with FIG. 10 (b), at f d Around 0.4, up and down the clutter loop, the gain at this position becomes high due to the discrete distribution of the distance blurred clutter, changing from-80 dB to between-60 dB and-70 dB.
Simulation 3:
referring to fig. 11 (a) to 11 (b), fig. 11 (a) to 11 (b) are schematic IF curves corresponding to the conventional MIMO method when the spatial angular frequency of the clutter spectrum provided by the embodiment of the present invention is 0, in this embodiment, the clutter suppression effect of the present invention is compared with an evaluation of an Improved Factor (IF) index, and the IF curve is an index for evaluating the effectiveness of the radar, which is defined as the ratio of signal to noise ratio of output to input:
wherein,representing the output signal power,/-, and>representing input signal power,/-, etc>Representing output noise power, < >>Representing input noise power, s representing signal vector, w representing receiving-side steering vector, Q representing noise covariance matrix, tr (·) representing trace of matrix, (·) * Representing the conjugate.
Due to the presence of the distance-blurred clutter, clutter ridge is severely widened in the Doppler and angular domains, resulting in reduced target detection performance. Fig. 11 (b) is an enlarged view of fig. 11 (a), and the observation results show that the clutter suppression effect can be greatly improved by the method proposed by the present invention. Due to the clutter echoes of the distance ambiguity region and the first distance ambiguity region, the conventional MIMO radar intermediate frequency curve of fig. 11 (b) has two notches at 0.88 and 0.93, the notch at 0.88 is caused by the clutter of the distance ambiguity region, the notch at 0.93 is caused by the clutter of the first distance ambiguity region, and in the presence of the distance ambiguity clutter, the performance of the conventional MIMO radar is significantly reduced in the region between the clutter notch position and the clutter notch, so that the larger the clutter notch, the wider the radar detection pollution range, and the performance reduction is more obvious. The method provided by the invention can effectively inhibit the distance fuzzy clutter outside the non-fuzzy area, the IF curve of the main lobe correction FAD of the figure 11 (b) has only one notch at 0.88, which is caused by the clutter in the non-fuzzy area, and the formed notch width is smaller than that of the traditional MIMO method, which shows that the method can obviously reduce the clutter expansion in the power spectrum, therefore, the method provided by the invention inhibits the distance fuzzy clutter, reduces the area of radar performance loss and improves the detection performance.
In summary, according to the FDA range ambiguity clutter suppression method based on main lobe correction provided in this embodiment, main lobe motion correction phase weighting is performed at the radar transmitter, main lobe irradiation areas of different pulses are unified, recovery compensation is performed at the receiving end, signals in different range ambiguity regions can be distinguished by using the range coupling characteristics of FDA signal echoes, signals from an observation region are the same as conventional MIMO signals through compensation, and range ambiguity signals in a non-observation region show low gain discrete distribution in a power spectrum, so that range ambiguity clutter is suppressed.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (4)
1. The FDA distance fuzzy clutter suppression method based on main lobe correction is characterized by comprising the following steps of:
step 1, a signal model is established, and a radar echo signal is obtained according to the signal model; the radar echo signal corresponding to the established signal model is expressed as:
wherein p represents the p-th distance fuzzy area in the power range, the number of the distance fuzzy areas is U, q represents clutter blocks positioned at a certain angle in the same distance fuzzy area, and the total number of the clutter blocks is N c ，s pq Represents the clutter signal corresponding to the qth clutter block of the p-th distance blurring area,representing noise->Representing the main lobe correction weight vector, gamma 0p ＝Υ 0 ＝exp{-j2πf 0 R ∑ /c}，f 0 Represents the reference frequency, R ∑ Represents the pitch, c represents the speed of light, ρ pq Representing the product of the scattering coefficient of the irradiation radar target and the signal propagation gain in the qth clutter block in the p-th distance blur area, s d Representing Doppler steering vector, f pqd0 Normalized Doppler frequency, s, representing the qth clutter block in the p-th range ambiguity region r Representing a received spatial steering vector, f qr Represents the angular frequency of the received signal corresponding to the q-th clutter block, s ct Representing the transmit spatial steering vector, f pqct The angular frequency s of the composite transmission signal representing the qth clutter block in the p-th distance blur area R Representing distance-coupled phase components, f R Representing distance ambiguous region coupling term, ">Δf represents the frequency increment, f pR Representing the distance coupling phase angular frequency, s, in the p-th distance ambiguity region t Representing the transmit spatial steering vector, f qt Represents the spatial angular frequency of the transmission corresponding to the qth clutter block,/, and>indicates the Cronecker product, and the addition indicates the Ha Mada product; signal s of clutter signal clutter block corresponding to the (th) clutter block of the (p) th distance blurring area pq Expressed as:
wherein y is 0 ＝exp{-j2πf 0 R ∑ /c}，f 0 Represents the reference frequency, R ∑ Represents the slant distance, c represents the speed of light, ρ represents the product of the scattering coefficient of the illuminating radar target and the signal propagation gain,representing a main lobe correction weight vector, s d Representing Doppler steering vector, f d0 Represents normalized Doppler frequency, d r Representing the spacing, ψ, between array elements in a receive array r Representing the spatial cone angle of the target and receive array, s ct Representing the transmit spatial steering vector, f ct Representing the spatial angular frequency of the composite emission s R Representing the distance-coupled phase component>Δf represents frequencyRate increment, s r Representing a received spatial steering vector, f r Representing the angular frequency of the receiving space s t Representing the transmit spatial steering vector, f t Representing the angular frequency of the emission space, +.>Indicates noise, ++ Ha Mada product, ++>Represents the kronecker product;
step 2, constructing a distance phase compensation guide vector, and performing first compensation processing on the radar echo signal according to the distance phase compensation guide vector to obtain a first echo processing signal; the constructed distance phase compensation steering vector is expressed as:
wherein q R Representing a distance phase compensation steering vector, f R0 ＝Δf2R 0 /c，R 0 Represents no-ambiguity distance, c represents light velocity, Δf represents frequency increment, M represents number of transmitting array elements, [] T Is a transposed operator;
step 3, constructing a correction restoration compensation vector corresponding to the main lobe correction weight, and carrying out restoration compensation processing on the first echo processing signal according to the correction restoration compensation vector to obtain a compensation restoration signal;
and step 4, selecting any one of the transmitting array element data in the compensation and restoration signals to obtain a dimension reduction compensation signal, and performing second compensation processing on the dimension reduction compensation signal to obtain the final suppression of the radar distance fuzzy clutter.
2. The FDA distance blur clutter suppression method based on mainlobe correction according to claim 1, wherein the correction restoration compensation vector corresponding to the mainlobe correction weight constructed in step 3 is expressed as:
wherein,represents a correction-reduction compensation vector, h K1 ＝[0,1,...,K-1] T K represents the number of coherent processing pulses, d r (f PRF )＝[0,j2πΔf/f PRF ,...,j2π(M-1)Δf/f PRF ] T ，f PRF Representing pulse repetition frequency, +.>Representing an N x 1-dimensional all-one matrix, N representing the number of array elements of the receive array.
3. The FDA distance blur clutter suppression method based on mainlobe correction according to claim 2, wherein the compensation restoration signal obtained by the restoration compensation processing in step 3 is represented as:
wherein,representing a corrected restoring compensation vector e R Representing distance compensation items> Representing a K x 1-dimensional all-matrix, < >>Represents an N x 1-dimensional all-matrix, q R [f R0 (R 0 )]Representing a distance phase compensation steering vector, b c Representing a correction weight vector representing the main lobe, +.>Representing the main lobe correction compensation vector b C Corresponding frequency, ++>Representing a correction-reduction compensation vector +.>Corresponding frequency term, f R Representing the frequency corresponding to the coupling term of the distance blur area, < ->f PRF Representing the pulse repetition frequency.
4. The FDA distance blur clutter suppression method based on mainlobe correction according to claim 3, wherein step 4 comprises:
selecting any one of the emission array element data in the compensation and restoration signals to enable the compensation and restoration signals of NMK dimension to be reduced to dimension-reducing compensation signals of MK dimension;
and performing second compensation processing on the dimension reduction compensation signal by using a DW technology to finally realize the suppression of radar distance fuzzy clutter.
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