CN111812639B - Array radar complex terrain low elevation angle estimation method based on multipath judgment - Google Patents
Array radar complex terrain low elevation angle estimation method based on multipath judgment Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/885—Radar or analogous systems specially adapted for specific applications for ground probing
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
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Abstract
The invention discloses a multi-path judgment-based array radar complex terrain low elevation angle estimation method, which comprises the following steps: establishing a target multipath signal model according to the array radar system parameters; calculating a first multipath characteristic value according to the target multipath signal model to obtain an amplitude curve of the reflection discrimination coefficient; acquiring target echo data acquired by a radar system, and calculating a second multipath characteristic value according to the target echo data; obtaining a reflection coefficient amplitude estimation value according to the reflection coefficient amplitude discrimination curve and the second multipath characteristic value; scanning the target echo data by adopting a beam scanning algorithm to obtain the 3dB beam width of a beam scanning curve; and carrying out multipath judgment according to the reflection coefficient amplitude estimation value and the 3dB wave beam width of the wave beam scanning curve to obtain a final target elevation estimation value. The low elevation angle estimation method for the complex terrain of the array radar provided by the invention reduces the influence of complex reflection on angle measurement and improves the angle measurement precision and robustness.
Description
Technical Field
The invention belongs to the technical field of radars, and particularly relates to a low elevation estimation method of an array radar complex terrain based on multipath judgment.
Background
The radar has the main task of effectively detecting the target and simultaneously realizing angle measurement and tracking of the target. When the array radar is used for positioning a low-elevation target, the radar beam is grounded, so that direct waves of the target and multipath reflected waves reflected by the ground are overlapped in a main lobe of the antenna beam. The direct wave signal and the multipath signal are coherent, the two coherent signals are received by the radar antenna at the same time, and the existence of the multipath signal can cause lobe division and upwarp of a radar vertical plane, so that not only is the detection of the signal influenced, but also the estimation of the radar on the target elevation angle can be seriously influenced, and especially when a reflecting surface is complex, the influence of the multipath reflected signal is more complex.
Currently, for elevation estimation involving multipath signals, the prior art mainly provides the following methods: the first prior art discloses a low elevation angle estimation method of an array radar, which is an angle measurement method for measuring the real position of a target by using a synthetic guiding vector. The synthetic steering vector method uses the prior information of the reflection coefficient, uses the composite steering vector under the multipath condition to replace the conventional steering vector in the free space, and uses the maximum likelihood method to estimate the elevation direction. However, this method requires that the reflection surface must be flat, and when the reflection surface is complex, part of the target echo does not contain multipath signals, the signal model does not match with the actual situation, and the angular accuracy will be severely degraded.
The second prior art discloses a low elevation angle estimation method of a meter wave radar, which is an angle measurement method for measuring the real position of a target by using a synthesized guiding vector corrected by terrain. The traditional synthetic steering vector method through terrain correction is to correct the antenna elevation by utilizing the terrain information of the reflection area, then replace the conventional steering vector in free space by the synthetic steering vector under the multipath condition, and then estimate the elevation direction by using the maximum likelihood method. The method has the following defects: when the terrain is too complex, effective terrain information is difficult to acquire, and errors exist in reflection coefficients, so that the elevation angle measurement performance is seriously reduced.
The three-dimensional search low elevation estimation method is characterized in that the target elevation and the antenna height are searched simultaneously to estimate the target elevation, and meanwhile, the calculation amount of the two-dimensional search is reduced by using an alternate projection algorithm. The method can be equivalent to searching the phase of the reflection coefficient when searching the antenna elevation, and does not need topographic information. However, this method has the disadvantages that: neglecting the situation when some topography (especially particularly severely undulating topography) is free of multipath, the elevation performance of the method will severely degrade when the target echo is free of multipath signals.
The fourth prior art discloses an array radar elevation angle estimation method, which is an angle measurement method for measuring the real position of a target by using a conventional guiding vector. However, this method requires that the target echo does not contain multipath signals, and when the target echo contains multipath signals, the angular accuracy will be severely degraded.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a low elevation estimation method of complex terrain of an array radar based on multipath judgment. The technical problems to be solved by the invention are realized by the following technical scheme:
a low elevation estimation method of complex topography of array radar based on multipath judgment comprises the following steps:
establishing a target multipath signal model according to the array radar system parameters;
calculating a first multipath characteristic value according to the target multipath signal model to obtain an amplitude curve of the reflection discrimination coefficient;
acquiring target echo data acquired by a radar system, and calculating a second multipath characteristic value according to the target echo data;
obtaining a reflection coefficient amplitude estimation value according to the reflection coefficient amplitude discrimination curve and the second multipath characteristic value;
scanning the target echo data by adopting a beam scanning algorithm to obtain the 3dB beam width of a beam scanning curve;
and carrying out multipath judgment according to the reflection coefficient amplitude estimation value and the 3dB wave beam width of the wave beam scanning curve to obtain a final target elevation estimation value.
In one embodiment of the present invention, the target multipath signal model is:
y＝ws；
wherein y represents the echo signal received by the array element, and y is C M×1 C represents a complex set, M represents the number of antenna array elements, w represents a composite steering vector, and the expression is as follows: w=a (θ) r )+ρe -jψ a(-arcsin(sin(θ r )+2h r /R d ) And), wherein a (θ r ) Guide vector, θ, representing direct wave signal r The method comprises the steps that a true value of a target elevation angle is represented, ρ represents a reflection coefficient, ψ represents a phase difference of a direct wave signal and a multipath signal at an array reference point, and ψ=2pi delta R/lambda, delta R represents a distance difference between a direct distance and a multipath distance, and lambda represents a radar working wavelength; a (-arcsin (sin (θ) r )+2h r /R d ) Indication)Steering vector of multipath signal, h r Representing the true value of the antenna elevation, R d Representing the distance of the target from the radar antenna, s representing the complex envelope of the target direct wave signal.
In one embodiment of the present invention, calculating a first multipath characteristic value according to the target multipath signal model to obtain an amplitude curve of an authenticated reflection coefficient includes:
calculating the average value of M array element data of the multipath signals according to the target multipath signal model;
the echo amplitude of the zero frequency component is removed according to the average value of M array element data of the multipath signal;
performing FFT processing on the echo amplitude from which the zero frequency component is removed to obtain a first multipath characteristic value;
and taking a variation curve of the first multipath characteristic value along with the amplitude of the reflection coefficient as the amplitude curve of the reflection coefficient.
In one embodiment of the present invention, the expression of the first multipath characteristic value is:
F y ＝max(F(m))；
wherein F is y Representing a first multipath characteristic value, max (·) representing a maximum value taking operation, F (m) representing a spectrum of echo amplitudes from which a zero frequency component is removed, expressed asM represents the number of frequency spectrum points, Y represents the echo amplitude of the zero frequency component, and M represents the number of antenna elements.
In one embodiment of the present invention, the expression of the target echo data is:
x＝ws+n；
wherein x represents target echo data and x ε C M×1 C represents a complex set, M represents the number of antenna array elements, w represents a composite steering vector, s represents the complex envelope of the target direct wave signal, n represents zero-mean circular Gaussian white noise, and n epsilon C M×1 。
In one embodiment of the present invention, obtaining the reflection coefficient amplitude estimation value according to the reflection coefficient amplitude identifying curve and the second multipath characteristic value includes:
and finding out the value closest to the second multipath characteristic value in the reflection coefficient amplitude identifying curve, and taking the corresponding reflection coefficient amplitude as the reflection coefficient amplitude estimated value.
In one embodiment of the present invention, obtaining a final target elevation angle estimation value according to the reflection coefficient amplitude estimation value and the 3dB beam width of the beam scanning curve includes:
if the reflection coefficient amplitude estimated value is larger than a first preset value or BD is larger than or equal to T, estimating a target elevation according to an alternate projection two-dimensional search algorithm to obtain a first target elevation estimated value, and outputting the first target elevation estimated value as a final target elevation estimated value;
otherwise, estimating the target elevation according to a beam scanning algorithm to obtain a second target elevation estimation value, and outputting the second target elevation estimation value as a final target elevation estimation value;
where BD denotes the 3dB beam width of the beam sweep curve, and T denotes the 3dB width threshold of the beam sweep curve.
In one embodiment of the present invention, before estimating the target elevation according to the alternate projection two-dimensional search algorithm, the method further includes:
if the amplitude estimated value of the reflection coefficient is smaller than or equal to a second preset value and BD is larger than or equal to T, the amplitude estimated value of the reflection coefficient is made to be 0.9; otherwise, the reflection coefficient amplitude estimation value is kept unchanged.
In one embodiment of the present invention, estimating a target elevation angle according to an alternate projection two-dimensional search algorithm to obtain a first target elevation angle estimation value includes:
setting an initial estimated value of antenna elevation;
taking the initial estimated value of the antenna elevation as a true value of the antenna elevation, carrying out one-dimensional search on a target elevation, and calculating the initial estimated value of the target elevation;
taking the initial estimated value of the target elevation angle as a true value of the target elevation angle, and carrying out one-dimensional search on the antenna stand to obtain an estimated value of the antenna stand;
and repeatedly carrying out one-dimensional search on the target elevation angle and the antenna stand until the iteration result converges to obtain a first target elevation angle estimated value.
In one embodiment of the present invention, the calculation formula of the second target elevation angle estimation value is:
wherein,representing a second target elevation estimate, +.>Indicating->θ when maximum value is taken r Is a value of (2); θ r Representing the true value of the target elevation angle, T (θ r ) Representing the beam scanning cost function value.
The invention has the beneficial effects that:
1. the array radar complex terrain low elevation angle estimation method based on multipath judgment provided by the invention utilizes the characteristic value of multipath signals to estimate the amplitude of the reflection coefficient, judges the target characteristic according to the estimated value of the amplitude of the reflection coefficient and the 3dB width of a beam scanning curve to select a more proper angle measurement algorithm, thereby obtaining a final target elevation angle estimated value, weakening the influence of complex reflection on angle measurement and improving angle measurement precision and robustness;
2. when the low elevation estimation method of the complex topography of the array radar provided by the invention comprises multipath signals in target echo data, an alternate projection two-dimensional search algorithm is adopted, so that the operand of the two-dimensional search algorithm is reduced; meanwhile, the two-dimensional search algorithm can obtain the estimated value of the target elevation without the information of the antenna height and the topographic information, and the angle measurement robustness is further improved.
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 a low elevation estimation method of an array radar complex terrain based on multipath judgment, which is provided by the embodiment of the invention;
FIG. 2 is a schematic diagram of a multipath reflection model provided by an embodiment of the present invention;
FIG. 3 is a schematic flow chart of another method for estimating low elevation angle of complex terrain of array radar based on multipath judgment according to an embodiment of the present invention;
FIG. 4 is a graph comparing the variation of the root mean square error of the angle measurement with the elevation angle of the target according to the present invention, and the conventional two-dimensional search algorithm and beam scanning algorithm provided by the present invention;
fig. 5 is a graph comparing the variation curves of the conventional two-dimensional search algorithm and beam scanning algorithm and the variation curves of the angle-measuring root mean square error of the method according to the signal to noise ratio of direct wave detection.
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 flow chart of a method for estimating a low elevation angle of a complex terrain of an array radar based on multipath determination according to an embodiment of the present invention, including:
step 1: and establishing a target multipath signal model according to the array radar system parameters.
Specifically, referring to fig. 2, fig. 2 is a schematic diagram of a multipath reflection model according to an embodiment of the present invention, in which θ r Representing the true value of the elevation angle of the target, h r Representing the true value of the antenna elevation, R d Indicating the distance between the target and the radar antenna, h t Representing the true value of the target height.
Assuming that the antennas are vertical uniform equidistant linear arrays, and not considering the influence of noise, the target multipath signal model is:
y＝ws；
wherein y represents an array element connectionReceived echo signal, and y E C M×1 C represents a complex set, M represents the number of antenna array elements, w represents a composite steering vector, and the expression is as follows:
w＝a(θ r )+ρe -jψ a(-arcsin(sin(θ r )+2h r /R d ))；
wherein a (θ) r ) The method comprises the steps that a guide vector of a direct wave signal is represented, ρ represents a reflection coefficient, ψ represents a phase difference of the direct wave signal and a multipath signal at an array reference point, and ψ=2pi delta R/lambda, delta R represents a distance difference between a direct distance and a multipath distance, and lambda represents a radar working wavelength; a (-arcsin (sin (θ) r )+2h r /R d ) A) represents the steering vector of the multipath signal and s represents the complex envelope of the target direct wave signal.
Further, in the present embodiment, since the magnitude of the reflection coefficient ρ may take any value between 0 and 1, the established target multipath signal model is changed with the change of the magnitude of the reflection coefficient.
Step 2: calculating a first multipath characteristic value according to the target multipath signal model to obtain an amplitude curve of the reflection discrimination coefficient, wherein the method comprises the following steps:
2a) Calculating the average value of M array element data of the multipath signals according to the target multipath signal model;
specifically, the calculation formula of the average value z of M array element data of the multipath signal is:
wherein,representing a modulo operation.
2b) The echo amplitude of the zero frequency component is removed according to the average value of M array element data of the multipath signal;
specifically, the average value of the echo amplitudes received by M array elements is subtracted from the module value to obtain the echo amplitude Y from which the zero frequency component is removed, namely
Y＝|y|-z。
2c) Performing FFT processing on the echo amplitude from which the zero frequency component is removed to obtain a first multipath characteristic value;
specifically, the echo amplitude Y from which the zero frequency component is removed is regarded as a time series, and the FFT processing is performed on Y to obtain the frequency spectrumDefining the peak value of the frequency spectrum as a first multipath characteristic value F y The expression is:
F y ＝max(F(m))；
wherein,representing a maximum value operation, m represents a spectral point number.
2d) And taking a variation curve of the first multipath characteristic value along with the amplitude of the reflection coefficient as the amplitude curve of the reflection coefficient.
Specifically, since the amplitude of the reflection coefficient in the embodiment is changed, the change range is 0-1, so that the first multipath characteristic value will change along with the change of the amplitude of the reflection coefficient, and the change curve of the first multipath characteristic value along with the amplitude of the reflection coefficient is the reflection coefficient identification amplitude curve.
Step 3: target echo data acquired by the radar system are acquired, and a second multipath characteristic value is calculated according to the target echo data.
Specifically, the expression of the target echo data is:
x＝ws+n；
wherein x represents target echo data and x ε C M×1 C represents a complex set, M represents the number of antenna array elements, w represents a composite steering vector, s represents the complex envelope of the target direct wave signal, n represents zero-mean circular Gaussian white noise, and n epsilon C M×1 。
In the present embodiment, zero-mean circle gaussian white noise n is uncorrelated with the signal, and zero-mean circle gaussian white noise variance is Var (n) =σ 2 I, wherein sigma 2 Indicating the magnitude of its variance value, I indicating the identity matrix.
Based on target echo data xCalculating a second multipath characteristic value F x 。
In the present embodiment, due to the second multipath characteristic value F x Is calculated from the real target echo data acquired by the radar system, thus, the second multipath characteristic value F corresponding to each group of target echo data x Is unique. Second multipath eigenvalue F x And a first multipath characteristic value F y The same calculation principle as in (a) is not described in detail herein.
Step 4: and obtaining a reflection coefficient amplitude estimation value according to the reflection coefficient amplitude identifying curve and the second multipath characteristic value.
Specifically, find the second multipath characteristic value F in the amplitude curve of the reflection discrimination coefficient x The closest value and the corresponding reflection coefficient amplitude is taken as the reflection coefficient amplitude estimation value.
In the present embodiment, the amplitude curve of the reflectance is based on the first multipath characteristic value F y And the amplitude of the reflection coefficient, which covers all the cases of the target multipath signal model, so that the second multipath characteristic value F obtained according to the target echo data truly received by the radar system x In contrast, the reflection coefficient amplitude corresponding to the closest value is found and is used as the reflection coefficient amplitude estimated value and denoted as P.
Step 5: scanning the target echo data by adopting a beam scanning algorithm to obtain the 3dB beam width of a beam scanning curve, which comprises the following steps:
5a) The beam scanning cost function value is selected as follows: t (theta) r )＝w H x, H represents the conjugate transpose.
5b) Calculating elevation angle estimation value of beam scanning algorithmThe calculation formula is as follows:
wherein,indicating->θ when maximum value is taken r Is a value of (2).
5c) Order the The base 10 logarithm is shown, at the elevation value +.>Left and right sides find T respectively dB Corresponding elevation angle value theta when closest to-3 dB L And theta R The 3dB beamwidth BD of the beam sweep curve is expressed as bd=θ R -θ L 。
Step 6: multipath judgment is carried out according to the reflection coefficient amplitude estimation value and the 3dB wave beam width of the wave beam scanning curve, and a final target elevation angle estimation value is obtained, and the method comprises the following steps:
if the reflection coefficient amplitude estimation value P is larger than a first preset value or BD is larger than or equal to T, estimating a target elevation according to an alternate projection two-dimensional search algorithm to obtain a first target elevation estimation value, and outputting the first target elevation estimation value as a final target elevation estimation value;
otherwise, estimating the target elevation according to a beam scanning algorithm to obtain a second target elevation estimation value, and outputting the second target elevation estimation value as a final target elevation estimation value;
where BD denotes the 3dB beam width of the beam sweep curve, and T denotes the 3dB width threshold of the beam sweep curve.
Specifically, the first preset value in this embodiment is 0.3, and the calculation formula of the 3dB width threshold T of the beam scanning curve is:
wherein d represents the array element spacing.
When P is more than 0.3 or BD is more than or equal to T, the target echo is considered to contain multipath signals, and an alternate projection two-dimensional search algorithm is selected to estimate the target elevation angle, so that a target elevation angle estimated value of the alternate projection two-dimensional search algorithm is obtainedI.e. the first target elevation estimate, and taking this value as the final target elevation estimate +.>And outputting.
When the condition P is less than or equal to 0.3 and BD is less than T, the target echo is considered to contain no multipath signal, and a beam scanning algorithm is selected to estimate the target elevation angle, so as to obtain an elevation angle estimated value of the beam scanning algorithmI.e. the second target elevation estimate. Since the elevation estimate of the beam scanning algorithm has already been obtained in step 5 b) above +.>It can thus be used directly here as final target elevation estimate +.>And outputting. Referring to fig. 3, fig. 3 is a flowchart of another method for estimating a low elevation angle of a complex terrain of an array radar based on multipath determination according to an embodiment of the present invention.
According to the method, firstly, an amplitude curve of the reflection discrimination coefficient is established according to the characteristics of multi-path signals of the array radar, then the amplitude of the reflection coefficient of a target echo signal is estimated, whether the multi-path signals are contained in the echo is judged, if the multi-path signals are contained in the echo, the target elevation angle is estimated by using an alternate projection two-dimensional search algorithm to obtain an estimated value of the target elevation angle, and if the multi-path signals are not contained in the echo, the target elevation angle is estimated by using a beam scanning algorithm to obtain an estimated value of the target elevation angle, so that the influence of complex reflection on angle measurement is weakened, and the angle measurement precision and the robustness are improved.
Further, before calculating the final target elevation estimate according to the alternate projection two-dimensional search algorithm, the method further comprises:
if the reflection coefficient amplitude estimated value P is less than or equal to a second preset value and BD is more than or equal to T, the reflection coefficient amplitude estimated value P is made to be 0.9; otherwise, the reflection coefficient amplitude estimation value P is kept unchanged.
In this embodiment, the second preset value is 0.5. When P is less than or equal to 0.5 and BD is more than or equal to T, P=0.9, otherwise, the P value is kept unchanged.
Further, estimating the target elevation angle according to an alternate projection two-dimensional search algorithm to obtain a first target elevation angle estimated value, including:
first, an initial estimate of antenna elevation is set
Then, the initial estimated value of the antenna stand is taken as the true value of the antenna stand, one-dimensional search is carried out on the target elevation angle, and the initial estimated value of the target elevation angle is calculated.
Specifically, the true value of raising the antennaOne-dimensional search is carried out on the target elevation angle, and the initial estimated value of the target elevation angle is calculated>The method comprises the following steps:
wherein L (θ) r ) Representing a cost function value, expressed as:
P w ＝w[w H w] -1 w H h represents the conjugate transpose.
Then, the initial estimated value of the target elevation angle is used as the true value of the target elevation angle, and one-dimensional search is carried out on the antenna elevation to obtain the estimated value of the antenna elevation.
Specifically, let the true value of the target elevation angleOne-dimensional search is performed on the antenna boom to obtain an estimated value of the antenna boom>The method comprises the following steps:
repeatedly carrying out one-dimensional search on the target elevation angle and the antenna stand height until the iteration result is converged to obtain a target elevation angle estimated value of the alternate projection two-dimensional search algorithmI.e. the first target elevation estimate, and takes this as the final target elevation estimate +.>And outputting.
When the low elevation estimation method of the complex topography of the array radar provided by the invention comprises multipath signals in target echo data, an alternate projection two-dimensional search algorithm is adopted, so that the operand of the two-dimensional search algorithm is reduced; meanwhile, the two-dimensional search algorithm can obtain the estimated value of the target elevation without the information of the antenna height and the topographic information, and the angle measurement robustness is improved.
Example two
The beneficial effects of the invention are further described below by simulation experiments.
1. Simulation conditions:
the operation platform configuration of the simulation experiment of this embodiment is as follows:
CPU: intel (R) Core (TM) i7-7700 CPU@3.60GHz, 8.00GB of memory;
operating system: windows 10 family version 64-bit operating system.
Simulation software: MATLAB R (2016 a).
The simulation parameters of the simulation experiment of this embodiment are set as follows:
using vertical uniform equidistant linear array, setting array element number M=16, wavelength lambda=2m, array element distance d=1m, antenna height h r Distance R between target and radar antenna of =10m d =150 km, reflectance ρ=0.9e jπ 。
The receiving noise of each array element is assumed to be zero mean circle Gaussian white noise which is independently and uniformly distributed. The accuracy of estimation of the target elevation is defined as:
wherein,for the estimated value obtained in the first experiment, θ r For the true value of the target elevation, MC is the total number of Monte-Carlo experiments, in this simulation experiment, mc=1000, and whether the target signal contains multipath signals in each experiment is random. The smaller the RMSE, the smaller the error representing the elevation estimate.
2. Simulation content and result analysis:
simulation experiment 1: setting the elevation angle of the target as theta under the simulation condition r ∈[0.7°,8°]The signal-to-noise ratio of direct wave detection is 30dB, a target echo signal is established, and the target elevation angle is estimated by adopting the method provided by the invention, the existing two-dimensional search algorithm and the existing beam scanning algorithm.
Referring to fig. 4, fig. 4 is a graph comparing the variation curves of the root mean square error of the angle measurement along with the target elevation angle of the conventional two-dimensional search algorithm and beam scanning algorithm provided by the embodiment of the invention; the abscissa of fig. 4 represents the target elevation angle, the ordinate represents the root mean square error of the elevation angle measured value, the dotted line represents the curve of the variation of the root mean square error of the angle of measurement with the elevation angle of the existing beam scanning algorithm, the solid line represents the curve of the variation of the root mean square error of the angle of measurement with the elevation angle of the existing two-dimensional searching algorithm, and the plus solid line represents the curve of the variation of the root mean square error of the angle of measurement with the elevation angle of the present invention. As can be seen from FIG. 4, the angular accuracy of the present invention is higher than that of the existing two-dimensional search algorithm and beam scanning algorithm.
Simulation experiment 2: under the simulation condition, the target elevation angle is set to be 4 degrees, the direct wave detection signal-to-noise ratio is set to be 15-35 dB, the target echo signal is established, and the target elevation angle is estimated by the provided method, the existing two-dimensional search algorithm and the beam scanning algorithm.
Referring to fig. 5, fig. 5 is a graph comparing the variation curves of the conventional two-dimensional search algorithm and beam scanning algorithm provided by the embodiment of the present invention and the root mean square error of the angle measurement along with the signal to noise ratio of direct wave detection; the abscissa of fig. 5 represents the signal-to-noise ratio of direct wave detection, the ordinate represents the root mean square error of elevation angle measurement, the broken line represents the variation curve of the angle-measuring root mean square error of the existing beam scanning algorithm along with the signal-to-noise ratio of direct wave detection, the solid line represents the variation curve of the angle-measuring root mean square error of the existing two-dimensional searching algorithm along with the signal-to-noise ratio of direct wave detection, and the plus line represents the variation curve of the angle-measuring root mean square error along with the signal-to-noise ratio of direct wave detection. As can be seen from FIG. 5, the angular accuracy of the present invention is higher than that of the existing two-dimensional search algorithm and beam scanning algorithm.
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 (6)
1. The array radar complex terrain low elevation angle estimation method based on multipath judgment is characterized by comprising the following steps of:
establishing a target multipath signal model according to the array radar system parameters; the target multipath signal model is as follows:
y＝ws；
wherein y represents the echo signal received by the array elementNumber, and y.epsilon.C M×1 C represents a complex set, M represents the number of antenna array elements, w represents a composite steering vector, and the expression is as follows: w=a (θ) r )+ρe -jψ a(-arcsin(sin(θ r )+2h r /R d ) And), wherein a (θ r ) Guide vector, θ, representing direct wave signal r The method comprises the steps that a true value of a target elevation angle is represented, ρ represents a reflection coefficient, ψ represents a phase difference of a direct wave signal and a multipath signal at an array reference point, and ψ=2pi delta R/lambda, delta R represents a distance difference between a direct distance and a multipath distance, and lambda represents a radar working wavelength; a (-arcsin (sin (θ) r )+2h r /R d ) A) a steering vector representing a multipath signal, h r Representing the true value of the antenna elevation, R d Representing the distance between a target and a radar antenna, and s represents the complex envelope of a target direct wave signal;
calculating the average value of M array element data of the multipath signals according to the target multipath signal model;
the echo amplitude of the zero frequency component is removed according to the average value of M array element data of the multipath signal;
performing FFT processing on the echo amplitude from which the zero frequency component is removed to obtain a first multipath characteristic value; the expression of the first multipath characteristic value is:
F y ＝max(F(m))；
wherein F is y Representing a first multipath characteristic value, max (·) representing a maximum value taking operation, F (m) representing a spectrum of echo amplitudes from which a zero frequency component is removed, expressed asM represents the number of frequency spectrum points, Y represents the echo amplitude of removing zero frequency component, M represents the number of antenna array elements;
taking a variation curve of the first multipath characteristic value along with the amplitude of the reflection coefficient as the amplitude curve of the reflection coefficient;
acquiring target echo data acquired by a radar system, and calculating a second multipath characteristic value according to the target echo data; the expression of the target echo data is as follows:
x＝ws+n；
wherein x represents target echo data and x ε C M×1 C represents a complex set, M represents the number of antenna array elements, w represents a composite steering vector, s represents the complex envelope of the target direct wave signal, n represents zero-mean circular Gaussian white noise, and n epsilon C M×1 ；
Obtaining a reflection coefficient amplitude estimation value according to the reflection coefficient amplitude discrimination curve and the second multipath characteristic value;
scanning the target echo data by adopting a beam scanning algorithm to obtain the 3dB beam width of a beam scanning curve;
and carrying out multipath judgment according to the reflection coefficient amplitude estimation value and the 3dB wave beam width of the wave beam scanning curve to obtain a final target elevation estimation value.
2. The method of claim 1, wherein obtaining a reflection coefficient amplitude estimation value from the reflection coefficient amplitude curve and the second multipath eigenvalue comprises:
and finding out the value closest to the second multipath characteristic value in the reflection coefficient amplitude identifying curve, and taking the corresponding reflection coefficient amplitude as the reflection coefficient amplitude estimated value.
3. The method for estimating low elevation angle of complex terrain of array radar according to claim 1, wherein performing multipath judgment according to the reflection coefficient amplitude estimation value and the 3dB beam width of the beam scanning curve to obtain a final target elevation angle estimation value comprises:
if the reflection coefficient amplitude estimated value is larger than a first preset value or BD is larger than or equal to T, estimating a target elevation according to an alternate projection two-dimensional search algorithm to obtain a first target elevation estimated value, and outputting the first target elevation estimated value as a final target elevation estimated value;
otherwise, estimating the target elevation according to a beam scanning algorithm to obtain a second target elevation estimation value, and outputting the second target elevation estimation value as a final target elevation estimation value;
where BD denotes the 3dB beam width of the beam sweep curve, and T denotes the 3dB width threshold of the beam sweep curve.
4. A method of estimating low elevation angle of complex terrain for an array radar as claimed in claim 3, further comprising, prior to estimating the target elevation angle according to an alternate projection two-dimensional search algorithm, obtaining a first target elevation angle estimate:
if the amplitude estimated value of the reflection coefficient is smaller than or equal to a second preset value and BD is larger than or equal to T, the amplitude estimated value of the reflection coefficient is made to be 0.9; otherwise, the reflection coefficient amplitude estimation value is kept unchanged.
5. The method for estimating low elevation angle of complex terrain of array radar according to claim 3, wherein estimating the elevation angle of the target according to an alternate projection two-dimensional search algorithm to obtain a first estimated elevation angle of the target comprises:
setting an initial estimated value of antenna elevation;
taking the initial estimated value of the antenna elevation as a true value of the antenna elevation, carrying out one-dimensional search on a target elevation, and calculating the initial estimated value of the target elevation;
taking the initial estimated value of the target elevation angle as a true value of the target elevation angle, and carrying out one-dimensional search on the antenna stand to obtain an estimated value of the antenna stand;
and repeatedly carrying out one-dimensional search on the target elevation angle and the antenna stand until the iteration result converges to obtain a first target elevation angle estimated value.
6. The method for estimating low elevation angle of complex terrain of array radar according to claim 3, wherein the calculation formula of the second target elevation angle estimation value is:
wherein,representing a second target elevation estimate, +.>Represents θ when (-) is maximized r Is a value of (2); θ r Representing the true value of the target elevation angle, T (θ r ) Representing the beam scanning cost function value.
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