CN106529440B - Coincidence frequency diversity battle array radar segmented matched filter method - Google Patents
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Abstract
The present invention proposes a kind of coincidence frequency diversity battle array radar segmented matched filter method, mainly solves the problems, such as that existing radar system is difficult to realize the distance under wide area coverage condition-angle two dimension matched filtering.Implementation step is: 1. obtain coincidence frequency diversity array received end echo-signal, and thus construct the expression formula of corresponding transmitting pattern；2. according to corresponding transmitting pattern, the irradiation time section of beam main lobe when obtaining pointing space special angle designs the time width of matching subpulse；3. the transmitting burst length is evenly dividing according to the time width of adaptation function subpulse, construct the corresponding angle-time 2-D segmented matched filter function of each matching subpulse.The present invention has given full play to the total space covering power of coincidence frequency diversity array, can be used for low distance side lobe and Sidelobe direction of the launch G- Design.
Description
Technical Field
The invention belongs to the technical field of signal processing, and particularly relates to a coherent frequency diversity array radar segmented matching filtering method which can be used for designing low-distance side lobe and low-side lobe emission directional diagrams.
Background
The phased array realizes the functions of beam scanning, self-adaptive beam zero setting, multi-beam and the like by changing the phase of the antenna unit, and is an important milestone for the development of the radar. However, the transmission pattern of the phased array antenna is only related to the spatial angle and is not related to the distance, so that the distance-angle two-dimensional matched filtering is difficult to realize under the phased array system.
To address this problem, the prior art employs frequency diversity arrays. The frequency diversity array obtains extra distance dimension controllable freedom degree by introducing the frequency difference among array elements, forms a distance-angle dependent transmitting directional diagram and has more flexible beam control and signal processing capability. Frequency diversity arrays can be divided into orthogonal frequency diversity arrays and coherent frequency diversity arrays.
The coherent frequency diversity array refers to a frequency diversity array in which array elements transmit coherent signals. Under a coherent frequency diversity array radar wide pulse system, a transmitting directional diagram has a distance-time-angle three-dimensional dependence characteristic, distance-angle two-dimensional matching filtering processing can be carried out at a receiving end, and meanwhile equivalent transmitting beam forming is achieved.
Under the coherent frequency diversity array radar system, the matched filter function of the receiving end is actually determined by the baseband signal and the transmitting directional diagram together. In order to realize matched reception of any point in space, a matched filter function needs to be designed for each space angle. However, for a given angle, the matched filtering function at the receiving end is modulated by the transmission directional diagram, so that the effective matching time, that is, the time in which the transmission directional diagram is the main lobe, is only a part of the duration of the whole pulse, and the effective bandwidth of the matched filtering function is only the frequency bandwidth corresponding to the main lobe of the transmission directional diagram, and the distance-angle two-dimensional quasi-stationary matched filtering under the wide-area coverage condition cannot be completed.
Disclosure of Invention
Aiming at the existing problems, the invention provides a coherent frequency diversity array radar segmentation matched filtering method, which is used for restraining the time width corresponding to a matched filtering function and realizing distance-angle two-dimensional quasi-steady-state matched filtering under a wide area coverage condition.
The technical idea of the invention is as follows: according to the principle that the transmitting pulse time of a coherent frequency diversity array can be equivalently distributed in different spatial directions, a wide pulse corresponding to a received echo signal is uniformly divided into a plurality of narrow sub-pulses, the quasi-steady-state characteristic of a transmitting directional diagram is analyzed in each sub-pulse, and the echo signal is subjected to segmented matching receiving processing through a distance-angle two-dimensional matching filtering function modulated by the transmitting directional diagram. The method comprises the following implementation steps:
(1) obtaining coherent frequency diversity array receiving end echo signals:
(1a) obtaining the n antenna to receive the echo signal r transmitted by all the array elementsn(θ, t- τ), where n is 1,2, …, M is the number of array elements, θ is the antenna scanning angle,the time delay of an echo signal under the narrow-band transmitting condition is shown, R is a signal propagation distance, c is a light speed, and t is a signal propagation time;
(1b) according to the echo signal r received by the nth antennan(θ, t- τ) obtaining a vector form of the receiving end echo signal:
wherein, the symbol [ · [ ]]TIn order to perform the transposition operation,as a function of the pulse, TpIn order to be the pulse width of the pulse,for baseband waveforms, j denotes an imaginary number, f0For reference operating frequency, gT(θ, t- τ) is the corresponding emission pattern, a (θ) is the angle-dependent receive steering vector only;
(2) obtaining a receive beamformed signal y (θ, R, t):
(2a) construction of receiver-side ordinary beamsWeight vector w (θ)0)：
Where d is the spacing of each array element, θ0In order to be the beam pointing direction,is a reference wavelength;
(2b) according to the receiving end common beam weight vector w (theta)0) And an echo signal x (θ, R, t), obtaining a reception beam-formed signal y (θ, R, t):
wherein, the symbol [ · [ ]]HFor conjugate transpose operation, gR(θ) is a reception direction graph;
(3) constructing a piecewise matched filter function:
(3a) defining beam pointing direction as theta0Time-of-flight emission pattern matching function
Wherein Δ f is the frequency increment of the coherent frequency diversity array;
(3b) matching functions according to emission patternObtaining a beam main lobe illumination time period:
(3c) according to the beam main lobe illumination time period, selecting the time width of the matched sub-pulse as follows:
(3d) according to the sub-pulse time width TsObtaining the time period t of the kth matched sub-pulse{k}：
Wherein k is 1,2, …, M,is the central time of the kth sub-pulse, and
(3e) according to the central time of the k-th sub-pulseObtaining an angle-time two-dimensional matched filter function h corresponding to the kth sub-pulse{k}(θ0,t)：
Wherein,for the baseband waveform corresponding to the k-th sub-pulse,for the pulse function corresponding to the k-th sub-pulse,and matching the function for the emission pattern corresponding to the kth sub-pulse.
Compared with the prior art, the invention has the following advantages:
first, the present invention makes the emission pattern have angle-time-distance dependency by introducing frequency step quantity in the array, so the matched filter function of the echo signal is also two-dimensional angle-time function.
Secondly, the invention divides the pulse time corresponding to the echo signal into a plurality of narrow sub-pulses, and carries out the segmented matching receiving processing by utilizing the distance-angle two-dimensional matching filtering function modulated by the emission directional diagram in each sub-pulse, thereby replacing the space coverage by utilizing the pulse time resource.
Simulation results show that distance-angle two-dimensional quasi-steady-state matched filtering under a wide-area coverage condition can be realized by restricting the time width corresponding to the matched filtering function, and the emission directional diagram with low distance side lobes and low side lobes can be obtained.
Drawings
FIG. 1 is a flow chart of an implementation of the present invention;
fig. 2 is a block diagram of a receiver in the present invention;
FIG. 3 is a simulation diagram of an angle-time two-dimensional blur function corresponding to the kth sub-pulse in the present invention;
FIG. 4 is an angular dimension one-dimensional slice of the blur function in the present invention;
FIG. 5 is a distance-dimensional one-dimensional slice of the blur function of the present invention.
Detailed Description
The embodiments and effects of the present invention will be described in further detail below with reference to the accompanying drawings.
The use scenario of the invention is coherent frequency diversity array: assuming that there are M array elements, the distance between each array element is d, and the signal frequency of the M-th array element is:
fm＝f0+(m-1)Δf,m＝1,2,…,M
wherein f is0For reference to the operating frequency, Δ f is the frequency increment of the frequency diversity array.
Referring to fig. 1, the implementation steps of the invention are as follows:
step 1, obtaining echo signals of a receiving end of a coherent frequency diversity array.
(1a) Obtaining the nth array element to receive the signal s transmitted by the mth array elementm,n(t-τ)：
Wherein n is 1,2, …, M,as a function of the pulse, TpIn order to be the pulse width of the pulse,is the time delay of echo signal under the condition of narrow-band transmission, R is the signal propagation distance, c is the speed of light, t is the signal propagation time,is a baseband waveform, j represents an imaginary number;
(1b) receiving a signal s transmitted by an m-th array element according to an n-th array element in (1a)m,n(t-tau) obtaining that the nth antenna receives echo signals r emitted by all array elementsn(θ,t-τ)：
Wherein theta is an antenna scanning angle;
(1c) echo signal r received by nth antenna in (1b)n(θ, t- τ) obtaining a vector form of the receiving end echo signal:
wherein, the symbol [ · [ ]]TFor transposition operations, gT(θ, t- τ) is the corresponding emission pattern, and a (θ) is the angle-dependent receive steering vector, which is expressed by the following equations:
(1d) constructing a receiving end common beam weight vector:
wherein, theta0Pointing the beam;
(1e) from the echo signals x (θ, R, t) and reception in (1c)W (theta) in the end normal beam weight vector (1d)0) Obtaining a signal y (θ, R, t) after receiving beam forming:
wherein, the symbol [ · [ ]]HFor conjugate transpose operation, gR(θ) is a reception direction diagram, and its formula is expressed as:
step 2, pointing the wave beam to theta0The time required to match the function is designed.
(2a) Defining beam pointing direction as theta0Time-of-flight emission pattern matching function
(2b) Matching functions according to the emission pattern in (2a)Order toSolving t to obtain By t1Represents the start of the time period, t2Representing the end of a time periodThus, a beam main lobe illumination period [ t ] is obtained1,t2]；
(2c) According to the beam main lobe irradiation period [ t ] in (2b)1,t2]The time width of the obtained matched sub-pulse is as follows:
and 3, constructing a piecewise matching filter function.
Referring to fig. 2, the specific implementation of this step is as follows:
(3a) time of transmission pulse by T in (2c)sFor the interval, equally dividing the pulse into M matched sub-pulses to obtain the central moment of the kth sub-pulse:
wherein k is 1,2, …, M;
(3b) according to the central time of the k-th sub-pulse in (3a)The matching sub-pulse time width T in (2a) and (2b)sObtained byAs a starting point, the method comprises the following steps of,time period t of the k-th matched sub-pulse as an end point{k}：
Wherein,
(3c) the pulse function in (1a)Baseband waveformAnd the emission pattern g in (1c)TTau in (theta, t-tau)Alternatively, the pulse function in (1a)T in (1)pBy TsReplacing to obtain the baseband waveform corresponding to the kth sub-pulsePulse function corresponding to k-th sub-pulseAnd a transmission directional diagram matching function corresponding to the k sub-pulse
(3d) In the time period t of the k-th matching sub-pulse{k}According to the central time of the k-th sub-pulse in (3a)And in (3c)Andobtain the kth subThe angle-time two-dimensional matched filter function corresponding to the pulse is as follows:
the effect of the present invention is further explained by simulation experiments.
1. Simulation parameters:
assuming that the receiving angle is 0 degrees, i.e. the normal direction, the rest simulation parameters are as shown in table 1:
table 1 simulation parameters
2. Simulation content:
simulation 1, under the simulation parameters, the method of the invention is adopted to simulate the angle-time two-dimensional fuzzy function corresponding to the kth sub-pulse of the coherent frequency diversity array, and the result is shown in fig. 3.
As can be seen from fig. 3, the process of the segmented matched filtering of the coherent frequency diversity array of the present invention actually completes both the conventional time-domain matched filtering and the transmit beam forming in the spatial domain, and thus, the segmented matched filtering of the coherent frequency diversity array is a space-time two-dimensional filtering.
And 2, simulating an angle dimension one-dimensional slice of the angle-time two-dimensional fuzzy function by adopting the method under the simulation parameters, wherein the result is shown in fig. 4.
As can be seen from fig. 4, in the angular dimension, since the matched filter function is constructed by only using the sub-pulse time corresponding to the main lobe irradiation, the pulse time corresponding to the neglected side lobe is less than-19 dB in the ratio of the main lobe to the side lobe after the equivalent transmit beam is formed.
And 3, under the simulation parameters, simulating a distance dimension one-dimensional slice diagram of the angle-time two-dimensional fuzzy function by adopting the method, wherein the result is shown in fig. 5.
As can be seen from fig. 5, in the distance dimension, for the ambiguity function corresponding to the sub-pulse, the main lobe of the match function is slightly wider and the first side lobe level is around-36 dB due to the loss of match time.
The above simulation verifies the correctness, validity and reliability of the invention.
Claims (4)
1. A coherent frequency diversity array radar segmentation matching filtering method comprises the following steps:
(1) obtaining coherent frequency diversity array receiving end echo signals:
(1a) obtaining the n antenna to receive the echo signal r transmitted by all the array elementsn(θ, t- τ), where n is 1,2, …, M is the number of array elements, θ is the antenna scanning angle,for echo signals in narrow-band transmission conditionsDelay, R is signal propagation distance, c is light speed, and t is signal propagation time;
(1b) according to the echo signal r received by the nth antennan(θ, t- τ) obtaining a vector form of the receiving end echo signal:
wherein, the symbol [ · [ ]]TIn order to perform the transposition operation,as a function of the pulse, TpIn order to be the pulse width of the pulse,for baseband waveforms, j denotes an imaginary number, f0For reference operating frequency, gT(θ, t- τ) is the corresponding emission pattern, a (θ) is the angle-dependent receive steering vector only;
(2) obtaining a receive beamformed signal y (θ, R, t):
(2a) constructing a receiving end common beam weight vector w (theta)0)：
Where d is the spacing of each array element, θ0In order to be the beam pointing direction,is a reference wavelength;
(2b) according to the receiving end common beam weight vector w (theta)0) And an echo signal x (θ, R, t), obtaining a reception beam-formed signal y (θ, R, t):
wherein, the symbol [ · [ ]]HFor conjugate transpose operation, gR(θ) is a reception direction graph;
(3) constructing a piecewise matched filter function:
(3a) defining beam pointing direction as theta0Time-of-flight emission pattern matching function
Wherein Δ f is the frequency increment of the coherent frequency diversity array;
(3b) matching functions according to emission patternObtaining a beam main lobe illumination time period:
(3c) according to the beam main lobe illumination time period, selecting the time width of the matched sub-pulse as follows:
(3d) according to the sub-pulse time width TsObtaining the time period t of the kth matched sub-pulse{k}：
Wherein k is 1,2, …, M,is the central time of the kth sub-pulse, and
(3e) according to the central time of the k-th sub-pulseObtaining an angle-time two-dimensional matched filter function h corresponding to the kth sub-pulse{k}(θ0,t)：
Wherein,for the baseband waveform corresponding to the k-th sub-pulse,for the pulse function corresponding to the k-th sub-pulse,and matching the function for the emission pattern corresponding to the kth sub-pulse.
2. The method of claim 1, wherein the echo signal r in step (1a)n(θ, t- τ) according to the following formula:
wherein,receiving the signal transmitted by the M-th array element for the n-th array element, M being 1,2, …, M, fm＝f0+ (m-1) Δ f is the operating frequency of the mth array element, f0For reference operating frequency, Δ f is the coherence frequencyFrequency increment of the rate diversity array.
3. The method of claim 1, wherein the transmission pattern g in step (1b)T(θ, t- τ) and a receive steering vector a (θ), which are respectively expressed as:
4. the method of claim 1, wherein the reception pattern g in step (2b)R(θ), which is expressed as:
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