CN111983575A - Active and passive fusion calibration method and device - Google Patents

Active and passive fusion calibration method and device Download PDF

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CN111983575A
CN111983575A CN202010824553.4A CN202010824553A CN111983575A CN 111983575 A CN111983575 A CN 111983575A CN 202010824553 A CN202010824553 A CN 202010824553A CN 111983575 A CN111983575 A CN 111983575A
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polarization
calibration
error
scattering matrix
signal
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刘芳
白杨
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Beijing Institute of Environmental Features
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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
    • G01S7/40—Means for monitoring or calibrating
    • G01S7/4052—Means for monitoring or calibrating by simulation of echoes
    • 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
    • G01S7/024—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using polarisation effects
    • 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
    • G01S7/40—Means for monitoring or calibrating
    • G01S7/4052—Means for monitoring or calibrating by simulation of echoes
    • G01S7/406—Means for monitoring or calibrating by simulation of echoes using internally generated reference signals, e.g. via delay line, via RF or IF signal injection or via integrated reference reflector or transponder
    • G01S7/4069—Means for monitoring or calibrating by simulation of echoes using internally generated reference signals, e.g. via delay line, via RF or IF signal injection or via integrated reference reflector or transponder involving a RF signal injection

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Abstract

The invention relates to an active and passive fusion calibration method and a device, wherein the method comprises the following steps: setting parameters and setting a transmitting signal under the condition that the radar completes internal calibration; adding multiplicative error of a transmitting channel and time delay caused by forward propagation to the transmitting signal to obtain a full polarization signal transmitted by an antenna; simulating a theoretical polarization scattering matrix by using a digital active calibrator according to the full polarization signal to obtain a backscattering signal of the moving target; adding multiplicative errors of a receiving channel to the received back scattering signals, performing down-conversion to zero frequency, and completing sampling storage to obtain a polarization scattering matrix; according to the obtained polarization scattering matrix, motion compensation and time delay compensation are carried out; and carrying out passive polarization calibration on the compensated polarization scattering matrix, correcting the residual error to obtain a calibrated target polarization scattering matrix, and finishing calibration. The invention combines the advantages of active and passive polarization calibration and can improve the precision of the polarization calibration of the moving target.

Description

Active and passive fusion calibration method and device
Technical Field
The invention relates to the technical field of target detection, in particular to an active and passive fusion calibration method and device.
Background
After the radar works normally for a period of time, some parameters may change, and generally, accurate target information can be extracted from the radar image only through calibration processing. Aiming at the detection and identification requirements of aerial/aerospace targets, it is very necessary to develop the full-polarization measurement error calibration research of moving targets. Before actual use, the influence of non-system factors and system non-ideal factors on the polarization measurement precision of the full-polarization radar is generally analyzed, and the measurement precision of the moving target is improved through calibration.
In the traditional polarization calibration, the given calibration method is relatively single, and for the research of radar moving targets, the problems of large polarization calibration error and poor calibration precision often exist.
Disclosure of Invention
The invention aims to provide a combined polarization calibration method aiming at least part of defects, so that the polarization calibration precision of a moving target is improved, and the polarization calibration error of a radar moving target is reduced.
In order to achieve the above object, the present invention provides an active and passive fusion scaling method, comprising the steps of:
s1, setting parameters and transmitting signals under the condition that the radar completes internal calibration; the transmitting signal is generated by a signal source and comprises two paths of orthogonal radio frequency signals;
s2, adding multiplicative error of a transmitting channel and time delay caused by forward propagation to the transmitting signal to obtain a full polarization signal transmitted by an antenna;
s3, simulating a theoretical polarization scattering matrix by using a digital active calibrator according to the full polarization signal to obtain a backscattering signal of the moving target;
s4, adding multiplicative errors of a receiving channel to the received back scattering signals, performing down-conversion to zero frequency, and completing sampling storage to obtain a polarization scattering matrix;
s5, performing motion compensation and time delay compensation according to the obtained polarization scattering matrix;
and S6, carrying out passive polarization calibration on the compensated polarization scattering matrix, correcting residual errors to obtain a calibrated target polarization scattering matrix, and finishing calibration.
Preferably, in step S1, the expression of the transmission signal is:
e(t)＝[eth(t)，etv(t)]T
wherein e isth(t) and etvAnd (t) respectively represents radio frequency signals transmitted by an H-polarization transmission channel and a V-polarization transmission channel.
Preferably, in step S2, the expression of the fully polarized signal is:
Figure BDA0002635701540000021
wherein alpha ish、αvH, V showing the amplitude gain of the polarized transmit channel, respectively; tau ish、τvTime delay generated after passing through H, V polarization transmitting channels respectively; thetah、θvRespectively representing H, V phase shifts of the polarized transmitting channel to the signals;
H. the actual gain of a V-polarized transmit antenna is described by the Jones vector as:
Figure BDA0002635701540000022
Figure BDA0002635701540000023
βh(ζ，η)、βv(ζ, η) represents main polarization gain values of H, V polarization transmitting antenna in azimuth angle ζ and pitch angle η, respectively; rhoh(ζ，η)、ρv(ζ, η) represents the ratio of the cross-polarization component to the main polarization component of H, V polarization transmit antenna gain at azimuth angle ζ and pitch angle η, respectively.
Preferably, in step S3, the expression of the backscatter signal of the moving object is obtained as follows:
Figure BDA0002635701540000024
wherein,
Figure BDA0002635701540000025
representing a polarization scattering matrix，(τd，fd) Representing the response function of the system taking into account time delay and Doppler shift, et(t) denotes the emission signal, τdRepresenting the time delay, f, due to distance and radial velocitydIndicating the Doppler shift caused by distance and radial velocity, esh(t) represents the scattered echo signal in the transmit H polarization, esv(t) represents the scattered echo signal in transmit V polarization;
the expression of the multiplicative error matrix T of the transmit channel is:
Figure BDA0002635701540000031
doppler frequency fdThe expression of (a) is:
Figure BDA0002635701540000032
ftfor radar transmit signal frequencies, "+" represents that the target is approaching radar motion and "-" represents that the target is moving away from radar.
Preferably, in step S4, when the multiplicative error of the receiving channel is added to the received backscatter signal, the expression of the multiplicative error matrix R of the receiving channel is:
R＝T′
for the polarization scattering matrix, the relationship between the measured value S' and the true value S is:
S’＝RST+I＝RCRASTATC+I
wherein I represents an additive error, RA、TAAntenna error matrix, R, produced by cross-components of polarized antennas during transmission and reception, respectivelyA＝TA T，TAThe expression of (a) is:
Figure BDA0002635701540000033
RC、TCin the receiving and sending processes, polarization channel error matrixes caused by inconsistency of two polarization receiving and sending channels except for the antenna respectively have the following expressions:
Figure BDA0002635701540000034
wherein alpha ish′、αv′、θh′、θv' means respectively ah、αv、θh、θvThe conjugate transpose of (c).
Preferably, in step S5, the performing motion compensation and time delay compensation further includes:
drawing high-resolution one-dimensional range profiles of the four polarization channels; calculating time delay according to the deviation distances of the four polarization channels; calculating the frequency shift by using a Doppler frequency shift solving formula; and carrying out calibration in the echo of the received signal to finish compensation.
Preferably, in the step S6, in the passive polarization calibration, a single calibration body or three calibration bodies are used for calibration.
Preferably, in the step S6, the scaling with the single scaling body further includes the following steps:
s61, establishing a system error model according to the polarized scattering matrix measurement error source analysis, wherein the expression is as follows:
Sm＝RScT+I
wherein S ismA scattering matrix measured for the target; i is an additive error; t is multiplicative error of a transmitting path; r is multiplicative error of a receiving path; scA scattering matrix that is the true of the target;
s62, obtaining the polarization scattering matrix after the additive error is removed according to the system error model, wherein the expression is as follows:
M＝Sm-I
Figure BDA0002635701540000041
order to
Figure BDA0002635701540000042
v＝Rhv/Rhh，h＝Rvh/RvvAnd considering the case of a single station, Tvh/Thh＝Rhv/Rhh＝v，Thv/Tvv＝Rvh/Rvv＝hThen, the elements of the polarization scattering matrix after the additive error is removed are:
Figure BDA0002635701540000043
Figure BDA0002635701540000044
Figure BDA0002635701540000045
Figure BDA0002635701540000046
wherein,handvthe cross polarization component is normalized and represents the cross polarization error when the target is irradiated;
the matrix form is obtained as:
Figure BDA0002635701540000051
wherein,
Figure BDA0002635701540000052
and
Figure BDA0002635701540000053
normalized emission errors respectively representing polarization characteristics of target illuminationThe difference matrix and the receiving error matrix are transposed when the single station is used;
s63, using the rhombus dihedral angle as the calibration body to carry out calibration, then:
Figure BDA0002635701540000054
Figure BDA0002635701540000055
Figure BDA0002635701540000056
Figure BDA0002635701540000057
Figure BDA0002635701540000058
Figure BDA0002635701540000059
wherein,
Figure BDA00026357015400000510
and
Figure BDA00026357015400000511
polarization scattering matrix S respectively representing the calculated rhombus dihedral anglesdihAnd polarization scattering matrix M of rhombus dihedral angle obtained by measurementdihAn element of (1);
roll angle beta of rhombus dihedral anglecThe value range is less than 15 degrees and less than betac< 75 °; with MtarRepresenting the measured polarization scattering matrix of the target to be measured, and then calibrating the target polarization scattering matrix ScThe expression is as follows:
Figure BDA00026357015400000512
preferably, the method further comprises:
and S7, inverting the calibrated target polarization scattering matrix, comparing the target polarization scattering matrix with the original set value, and calculating an error.
The invention also provides an active and passive fusion scaling device, comprising:
the radio frequency module is used for setting parameters and setting transmitting signals under the condition that the radar completes internal calibration; the transmitting signal is generated by a signal source and comprises two paths of orthogonal radio frequency signals;
the full polarization module is used for adding multiplicative error of a transmitting channel and time delay caused by forward propagation to the transmitting signal to obtain a full polarization signal transmitted by an antenna;
the active simulation module is used for simulating a theoretical polarization scattering matrix by using a digital active calibrator according to the full polarization signal to obtain a backscattering signal of the moving target;
the sampling module is used for adding multiplicative errors of a receiving channel to the received back scattering signals, performing down-conversion to zero frequency, completing sampling storage and obtaining a polarization scattering matrix;
the compensation module is used for performing motion compensation and time delay compensation according to the obtained polarization scattering matrix;
and the passive correction module is used for carrying out passive polarization calibration on the compensated polarization scattering matrix, correcting residual errors, obtaining a calibrated target polarization scattering matrix and finishing calibration.
The technical scheme of the invention has the following advantages: the invention provides a calibration method and a calibration device combining an active mode and a passive mode.
Drawings
FIG. 1 is a schematic diagram of the steps of an active and passive fusion scaling method in an embodiment of the present invention;
FIG. 2 illustrates the effect of point object motion on a high resolution one-dimensional range profile in an embodiment of the invention;
FIG. 3 shows a high-resolution one-dimensional range profile after correcting for velocity errors in the motion of a point target in an embodiment of the invention;
FIG. 4 shows the effect of point object motion error on RCS images in an embodiment of the present invention;
FIG. 5 illustrates the effect of exemplary ball target motion velocity on high resolution one-dimensional range profile in an embodiment of the present invention;
FIG. 6 illustrates the effect of motion velocity of a representative ball target motion modification target on a high resolution one-dimensional range profile in an embodiment of the present invention;
FIG. 7 illustrates the effect of an exemplary ball target motion error on an RCS image in an embodiment of the present invention;
fig. 8 is a schematic structural diagram illustrating an active and passive fusion scaling apparatus according to an embodiment of the present invention.
In the figure: 100: a radio frequency module; 200: a fully-polarized module; 300: an active analog module; 400: a sampling module; 500: a compensation module; 600: and a passive correction module.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
As shown in fig. 1, an active and passive fusion scaling method provided by the embodiment of the present invention includes the following steps:
s1, setting parameters and transmitting signals under the condition that the radar completes internal calibration, wherein the transmitting signals are generated by a signal source and comprise two paths of orthogonal radio frequency signals, and the two paths of orthogonal radio frequency signals are transmitted from two transmitting channels of the antenna in an orthogonal polarization mode.
Preferably, the signal emission form generated by the signal source can be given by:
with a frequency stepped signal, the transmit signal can be represented in the time domain as follows:
e(t)＝[eth(t)，etv(t)]T
wherein e isth(t) and etvAnd (t) respectively representing two paths of orthogonal radio frequency signals generated by the signal source, namely radio frequency signals transmitted by an H polarization transmitting channel and a V polarization transmitting channel.
And S2, adding multiplicative error of a transmitting channel and time delay caused by forward propagation to the transmitting signal, namely the influence of the target motion speed, and obtaining the full polarization signal transmitted by the antenna.
Generally, two polarization transmitting channels of the polarization radar are not consistent, and after considering the inconsistency caused by amplitude, phase and time delay, the transmitting signal can be preferably expressed as follows:
Figure BDA0002635701540000081
wherein alpha ish、αvH, V showing the amplitude gain of the polarized transmit channel, respectively; tau ish、τvTime delay generated after passing through H, V polarization transmitting channels respectively; thetah、θvRespectively representing H, V phase shifts imparted to the signal by the polarized transmit path.
Further, for a certain channel of the dual-polarization antenna, there is a cross-polarization component in the gain in addition to the main polarization component, which causes the polarization of the transmitted signal to be impure, and after considering the influence of the cross-polarization component, the actual gain of H, V polarization transmitting antenna can be described by Jones vector, and the actual gain of H, V polarization transmitting antenna is respectively expressed as:
Figure BDA0002635701540000082
Figure BDA0002635701540000083
wherein, betah(ζ，η)、βv(ζ, η) represents main polarization gain values of H, V polarization transmitting antenna in azimuth angle ζ and pitch angle η, respectively; rhoh(ζ，η)、ρv(ζ, η) represents the ratio of the cross-polarization component to the main polarization component of H, V polarization transmit antenna gain at azimuth angle ζ and pitch angle η, respectively.
Further, taking multiplicative error of the transmitting channel into consideration, the obtained form of the fully polarized signal transmitted by the antenna should be:
Figure BDA0002635701540000084
and S3, simulating a theoretical polarization scattering matrix by using a digital active calibrator according to the full polarization signal transmitted by the antenna to obtain a backscattering signal of the moving target.
The step S3 is to use the digital active calibrator to simulate the theoretical polarization scattering matrix, control the delay and phase, and realize the simulation of moving targets with different distances and different speeds.
Preferably, let us say the azimuth ζ at which the moving object is located0Angle of pitch η0The time delay and Doppler shift due to distance and radial velocity is τdAnd fdThe backscattering of the target can therefore be written as:
Figure BDA0002635701540000091
wherein,
Figure BDA0002635701540000092
represents a polarization scattering matrix (tau)d，fd) Representing the response function of the system taking into account time delay and Doppler shift, et(t) denotes the emission signal, τdRepresenting the time delay, f, due to distance and radial velocitydIndicating the Doppler shift caused by distance and radial velocity, esh(t) represents the scattered echo signal in the transmit H polarization, esv(t) represents the scattered echo signal in transmit V polarization;
the expression of the multiplicative error matrix T of the transmit channel is:
Figure BDA0002635701540000093
doppler frequency fdIs expressed in the form of:
Figure BDA0002635701540000094
ftfor radar transmit signal frequencies, "+" represents that the target is approaching radar motion and "-" represents that the target is moving away from radar.
And S4, adding multiplicative errors of a receiving channel to the received back scattering signals, performing down-conversion to zero frequency, completing sampling storage, and obtaining a polarization scattering matrix.
The transmitted signal is first affected by the error matrix of the transmission channel and then by the gain error of the antenna, both of which are collectively referred to as T, which is a multiplicative error matrix introduced during the signal transmission. Upon reaching the target, the signal is acted upon by the varying polarization effect (polarization scattering matrix S) of the target. Similarly, there is a similar but opposite effect on the return of the signal, which is also a multiplicative error matrix, denoted as R, introduced during the reception of the signal. Time delay and Doppler shift are generated in the whole transmission and reception process of the signals. The specific expression of the multiplicative error matrix R for the receive channel is as follows:
Figure BDA0002635701540000095
by analyzing the signal transceiving process, it can be derived that for the polarization scattering matrix, the relationship between the measured value S' and the real value S can be expressed as follows:
S’＝RST+I＝RCRASTATC+I
where I denotes additive error, caused by noise or interference from the surrounding environment, can be done experimentally by subtracting the background of the measurement. RA、TAIn order to obtain a multiplicative error matrix generated by the cross component of the polarized antenna in the transmitting and receiving processes, called an antenna error matrix, because the same antenna is adopted for transmitting and receiving, R can be easily obtained according to the reciprocity of the antennaA＝TA TThus giving only TAThe specific form of (1):
Figure BDA0002635701540000101
RC、TCthe multiplicative error matrix caused by the inconsistency of two polarization receiving and transmitting channels except the antenna in the receiving and transmitting processes is called as a polarization channel error matrix, and the expressions are respectively as follows:
Figure BDA0002635701540000102
αh′、αv′、θh′、θv' representing the conjugate transpose of the corresponding parameter for each entry in the Tc matrix, i.e. alphah′、αv′、θh′、θv' means respectively ah、αv、θh、θvThe conjugate transpose of (c).
And S5, performing motion compensation and time delay compensation according to the obtained polarization scattering matrix.
Preferably, the motion compensation and the time delay compensation are performed, and specifically, the method includes the following steps:
high resolution one-dimensional range images (HRRP) of four polarization channels were plotted. Four polarization channels, i.e., HH channel, VH channel, HV channel, and VV channel.
And calculating time delay according to the deviation distances of the four polarization channels. If the images of the four channels are not aligned due to the movement of the target, the time delay can be calculated according to the distance of the deviation.
And calculating the frequency shift by using a Doppler frequency shift solving formula. Solving formula of Doppler frequency shift
Figure BDA0002635701540000103
And carrying out calibration in the signal receiving echo to finish compensation.
And S6, carrying out passive polarization calibration on the compensated polarization scattering matrix, correcting residual errors to obtain a calibrated target polarization scattering matrix, and finishing calibration.
Preferably, passive polarization scaling is performed, and there are generally two scaling methods, i.e., a single scaling body and three scaling bodies. Further, a single calibration method is adopted, and the specific steps are as follows:
and S61, establishing a system error model according to the polarized scattering matrix measurement error source analysis.
Preferably, the expression of the systematic error model is:
Sm＝RScT+I
wherein S ismA scattering matrix measured for the target; i is additive error (matrix) including feed source coupling, target support reflection, microwave darkroom residual reflection and the like; t is the multiplicative error (matrix) of the transmit path, which contains the frequency response error and cross-polarization coupling error,
Figure BDA0002635701540000111
r is the multiplicative error (matrix) of the receive path, which contains the frequency response error and cross-polarization coupling error,
Figure BDA0002635701540000112
Scis the scattering matrix of the true of the object,
Figure BDA0002635701540000113
these matrices are all 2X2 order matrices.
And S62, obtaining the polarization scattering matrix after the additive error is removed according to the system error model.
And (3) moving the additive error matrix in the system error model to the left of the equal sign, and obtaining a polarization scattering matrix expression after removing the additive error, wherein the expression is as follows:
M＝Sm-I
Figure BDA0002635701540000114
order to
Figure BDA0002635701540000115
v＝Rhv/Rhh，h＝Rvh/RvvAnd considering the case of a single station, Tvh/Thh＝Rhv/Rhh＝v，Thv/Tvv＝Rvh/Rvv＝hThen, the elements of the polarization scattering matrix after removing the additive error can be written as:
Figure BDA0002635701540000116
Figure BDA0002635701540000121
Figure BDA0002635701540000122
Figure BDA0002635701540000123
wherein,handvto normalize the cross-polarization components, cross-polarization errors upon target illumination are represented.
Written in matrix form as:
Figure BDA0002635701540000124
in the formula,
Figure BDA0002635701540000125
and
Figure BDA0002635701540000126
the normalized transmitting error matrix and the normalized receiving error matrix respectively represent the target irradiation polarization characteristics, and the single stations are transposed mutually; a. theij(i, j-h or v) are 4 independent parameters describing the frequency response effect of the measurement channel, which contains the influence of the signal path and possibly the non-reciprocal microwave circuit. Due to reciprocity, the number of calibration parameters is reduced from 8 to 6.
And S63, taking the rhombus dihedral angle as a calibration body to carry out calibration.
The calibration body adopts a rhombic dihedral angle, which can provide stronger co-polarized echo and stronger cross-polarized echo.
The specific calibration can be summarized as follows:
Figure BDA0002635701540000127
Figure BDA0002635701540000128
Figure BDA0002635701540000129
Figure BDA00026357015400001210
Figure BDA00026357015400001211
Figure BDA0002635701540000131
wherein,
Figure BDA0002635701540000132
polarization scattering matrix S representing calculated rhombus dihedral anglesdihThe elements of (a) and (b),
Figure BDA0002635701540000133
polarization scattering matrix M representing measured rhombus dihedral anglesdihOf (2) is used. Roll angle beta of rhombus dihedral anglecTypically 15 DEG < betac< 75 deg. If using MtarThe polarization scattering matrix of the target to be measured is obtained by the above formulacComprises the following steps:
Figure BDA0002635701540000134
this calibration method is suitable for any single-station and quasi-single-station radar system.
And S7, inverting the calibrated target polarization scattering matrix, comparing the target polarization scattering matrix with the original set value, and calculating an error.
And (4) comparing the value obtained by inverting the target polarization scattering matrix in the step (S6) with the original set value, and calculating the error. Here the error for each channel and the total error for four channels are calculated separately.
The error calculation formula for each polarization channel is:
Figure BDA0002635701540000135
wherein s ismn，
Figure BDA0002635701540000137
Respectively representing the scattering value and the originally set value of each polarization channel of the measurement inversion. mn represents the subscripts of the four channels, i.e., corresponding to HH, HV, VH, VV channels.
The total error e of the four channels is then calculatedc：
Figure BDA0002635701540000136
From the error per channel and the total error of the four channels, it can be determined whether the method has sufficient accuracy for scaling.
The active and passive fusion calibration method provided by the invention utilizes the technical characteristics that active calibration can simulate target dynamic parameters and passive calibration can carry out quantitative and accurate calibration, integrates two technical advantages, and develops the research of realizing the comprehensive calibration and dynamic compensation algorithm of the polarization radar under the limited static condition. How to improve the polarization calibration accuracy is crucial to subsequent signal processing.
The invention also combines the concrete implementation mode and the simulation result to test the performance of the technical scheme provided by the invention.
In a specific embodiment, the present invention simulates a point target, and the simulation parameter settings are shown in table 1 below:
TABLE 1 Point target simulation parameter settings
Parameter(s) PRT Duty cycle SNR Δγ R0
10e-6 0.1 25 -0.0087 1000
The polarization scattering matrix set is: s1 ═ 1, 3-j; 3-j, -1-j ].
Referring to fig. 2, fig. 2(a), 2(b), 2(c) and 2(d) show high-resolution one-dimensional distance images of HH, VH, HV and VV polarization channels, respectively, in consideration of the influence of the target motion velocity (v 100 m/s). Wherein the abscissa is distance and the ordinate is amplitude.
Referring to fig. 3, fig. 3 shows a high-resolution one-dimensional distance image after correcting a speed error, fig. 3(a), fig. 3(b), fig. 3(c), and fig. 3(d) show high-resolution one-dimensional distance images of HH, VH, HV, VV polarization channels after correction, respectively, fig. 3(e) shows a comparison result of HH and VV polarization channels, and fig. 3(f) shows a comparison result of VH and HV polarization channels, wherein the abscissa is distance and the ordinate is amplitude.
Considering the influence of all errors including v (100 m/s) and R, T, I, the RCS graph obtained without calibration error is shown in fig. 4(a), and the RCS graph obtained after correcting the influence of v and R, T, I is shown in fig. 4(b), where the abscissa is distance and the ordinate is amplitude.
When considering the influence of all the factors of the v and R, T, I matrices, the calibration errors of the four channels are obtained as follows (the result of the normalization of the scattering matrix):
at 0 ° rotation (v 100m/s), the HH channel scattering matrix total average error is 0; the total average error of the scattering matrix of the VH channel is 0.051; the total average error of the HV channel scattering matrix is 0.058; the total average error of the VV channel scattering matrix is 0.045; the total error is 0.08. The results show that the calibration effect is good after the calibration by the method of the invention is adopted.
In another specific embodiment, the present invention analyzes the results of an experiment on a representative ball target. When v is 500m/s, the HRRP results are shown in fig. 5, and fig. 5(a), 5(b), 5(c), and 5(d) show high-resolution one-dimensional distance images of HH, VH, HV, and VV polarization channels, respectively. Wherein, the abscissa and the ordinate are respectively distance and amplitude.
The effect of correcting the time delay caused by the velocity on the high-resolution one-dimensional range profile is shown in fig. 6, where fig. 6(a) shows HH and VV polarization channel HRRP results before correction, and fig. 6(b) shows HH and VV polarization channel HRRP results after correction, where the abscissa and ordinate are the distance and amplitude, respectively.
Considering the influence of all errors including v (100 m/s) and R, T, I, the RCS graph obtained without calibration error is shown in fig. 7(a), and the RCS graph obtained after correcting the influence of v and R, T, I is shown in fig. 7(b), where the abscissa is distance and the ordinate is amplitude.
When considering the influence of all the factors of the v and R, T, I matrices, the calibration errors of the four channels are obtained as follows (the result of the normalization of the scattering matrix):
at 0 ° rotation (v 100m/s), the overall average error of the HH channel scattering matrix is 0, and the overall average error of the VH channel scattering matrix is 5.46 × 10-17Total average error of HV channel scattering matrix 1.12X 10-16Total average error of scattering matrix of VV channel is 1.22 × 10-15Total error of 5.6X 10-15。
As can be seen from the analysis of the simulation and experiment results, the inversion effect of the scattering matrix is good, the precision is high, and the polarization calibration effect can be effectively improved.
In conclusion, the invention discloses a calibration method combining broadband active calibration and passive calibration, which solves the problem of polarization calibration error of a radar moving target under a limited static condition. The invention firstly realizes the analog dynamic calibration of the radar system by utilizing the active calibration technology, then adopts a passive calibration method to carry out calibration, and carries out cross check on the calibration precision to form compensation. Under the condition that the radar completes internal calibration, a transmitter and a receiver of the radar can keep higher amplitude-phase stability, and at the moment, the scattering characteristic information of fixed PSM targets with various long motion speeds can be simulated by using a digital active calibrator under the conditions of limited distance and static field, so that the radar is subjected to active calibration by using the information through a dynamic compensation method. And secondly, secondarily calibrating the radar by using the passive calibration body, correcting measurement reciprocity errors, calibration body attitude positioning errors and additive errors caused by radar channel leakage, and achieving the purpose of improving target test precision through active/passive fusion calibration. The simulation and experiment results further verify the effectiveness of the method.
As shown in fig. 8, the present invention also provides an active and passive fusion scaling apparatus, comprising: the system comprises a radio frequency module 100, a full polarization module 200, an active analog module 300, a sampling module 400, a compensation module 500 and a passive modification module 600.
The radio frequency module 100 is configured to perform parameter setting and set a transmission signal under the condition that the radar completes internal calibration; the transmission signal is generated by a signal source and comprises two paths of orthogonal radio frequency signals, and the two paths of orthogonal radio frequency signals are transmitted from two transmission channels of the antenna in an orthogonal polarization mode.
The full polarization module 200 is configured to add multiplicative error of a transmission channel and time delay caused by forward propagation to the transmission signal to obtain a full polarization signal transmitted by an antenna.
The active simulation module 300 is configured to simulate a theoretical polarization scattering matrix by using a digital active calibrator according to the fully polarized signal, so as to obtain a backscattering signal of the moving target.
The sampling module 400 is configured to add multiplicative error of a receiving channel to the received backscatter signal, down-convert the backscatter signal to zero frequency, complete sampling and storage, and obtain a polarization scattering matrix.
The compensation module 500 is configured to perform motion compensation and delay compensation according to the obtained polarization scattering matrix.
The passive correction module 600 is configured to perform passive polarization calibration on the compensated polarization scattering matrix, correct the residual error, obtain a calibrated target polarization scattering matrix, and complete calibration.
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims (10)

1. An active and passive fusion scaling method is characterized by comprising the following steps:
s1, setting parameters and transmitting signals under the condition that the radar completes internal calibration; the transmitting signal is generated by a signal source and comprises two paths of orthogonal radio frequency signals;
s2, adding multiplicative error of a transmitting channel and time delay caused by forward propagation to the transmitting signal to obtain a full polarization signal transmitted by an antenna;
s3, simulating a theoretical polarization scattering matrix by using a digital active calibrator according to the full polarization signal to obtain a backscattering signal of the moving target;
s4, adding multiplicative errors of a receiving channel to the received back scattering signals, performing down-conversion to zero frequency, and completing sampling storage to obtain a polarization scattering matrix;
s5, performing motion compensation and time delay compensation according to the obtained polarization scattering matrix;
and S6, carrying out passive polarization calibration on the compensated polarization scattering matrix, correcting residual errors to obtain a calibrated target polarization scattering matrix, and finishing calibration.
2. The method according to claim 1, wherein in step S1, the expression of the transmission signal is:
e(t)＝[eth(t)，etv(t)]T
wherein e isth(t) and etvAnd (t) respectively represents radio frequency signals transmitted by an H-polarization transmission channel and a V-polarization transmission channel.
3. The method according to claim 2, wherein in step S2, the expression of the fully polarized signal is:
Figure FDA0002635701530000011
wherein alpha ish、αvH, V showing the amplitude gain of the polarized transmit channel, respectively; tau ish、τvTime delay generated after passing through H, V polarization transmitting channels respectively; thetah、θvRespectively representing H, V phase shifts of the polarized transmitting channel to the signals;
H. the actual gain of a V-polarized transmit antenna is described by the Jones vector as:
Figure FDA0002635701530000021
Figure FDA0002635701530000022
βh(ζ，η)、βv(ζ, η) represents main polarization gain values of H, V polarization transmitting antenna in azimuth angle ζ and pitch angle η, respectively; rhoh(ζ，η)、ρv(ζ, η) represents the ratio of the cross-polarization component to the main polarization component of H, V polarization transmit antenna gain at azimuth angle ζ and pitch angle η, respectively.
4. The method according to claim 3, wherein in step S3, the backscattering signal expression of the moving object is obtained as:
Figure FDA0002635701530000023
wherein,
Figure FDA0002635701530000024
represents a polarization scattering matrix (tau)d，fd) Representing the response function of the system taking into account time delay and Doppler shift, et(t) denotes the emission signal, τdRepresenting the time delay, f, due to distance and radial velocitydIndicating the Doppler shift caused by distance and radial velocity, esh(t) represents the scattered echo signal in the transmit H polarization, esv(t) represents the scattered echo signal in transmit V polarization;
the expression of the multiplicative error matrix T of the transmit channel is:
Figure FDA0002635701530000025
doppler frequency fdThe expression of (a) is:
Figure FDA0002635701530000026
ftfor radar transmit signal frequencies, "+" represents that the target is approaching radar motion and "-" represents that the target is moving away from radar.
5. The method according to claim 4, wherein in step S4, when adding the multiplicative error of the receiving channel to the received backscatter signal, the multiplicative error matrix R of the receiving channel has the expression:
R＝T′
for the polarization scattering matrix, the relationship between the measured value S' and the true value S is:
S’＝RST+I＝RCRASTATC+I
wherein I represents an additive error, RA、TAAntenna error matrix, R, produced by cross-components of polarized antennas during transmission and reception, respectivelyA＝TA T，TAThe expression of (a) is:
Figure FDA0002635701530000031
RC、TCin the receiving and sending processes, polarization channel error matrixes caused by inconsistency of two polarization receiving and sending channels except for the antenna respectively have the following expressions:
Figure FDA0002635701530000032
wherein alpha ish′、αv′、θh′、θv' means respectively ah、αv、θh、θvThe conjugate transpose of (c).
6. The method according to claim 5, wherein the performing motion compensation and delay compensation in step S5 further comprises:
drawing high-resolution one-dimensional range profiles of the four polarization channels; calculating time delay according to the deviation distances of the four polarization channels; calculating the frequency shift by using a Doppler frequency shift solving formula; and carrying out calibration in the echo of the received signal to finish compensation.
7. The method according to claim 6, wherein in the step S6, passive polarization calibration is performed by using a single calibration body or three calibration bodies.
8. The method according to claim 7, wherein in the step S6, the calibration with the single calibration body further comprises the following steps:
s61, establishing a system error model according to the polarized scattering matrix measurement error source analysis, wherein the expression is as follows:
Sm＝RScT+I
wherein S ismA scattering matrix measured for the target; i is an additive error; t is multiplicative error of a transmitting path; r is multiplicative error of a receiving path; scA scattering matrix that is the true of the target;
s62, obtaining the polarization scattering matrix after the additive error is removed according to the system error model, wherein the expression is as follows:
M＝Sm-I
Figure FDA0002635701530000041
order to
Figure FDA0002635701530000042
v＝Rhv/Rhh，h＝Rvh/RvvAnd considering the case of a single station, Tvh/Thh＝Rhv/Rhh＝v，Thv/Tvv＝Rvh/Rvv＝hThen, the elements of the polarization scattering matrix after the additive error is removed are:
Figure FDA0002635701530000043
Figure FDA0002635701530000044
Figure FDA0002635701530000045
Figure FDA0002635701530000046
wherein,handvthe cross polarization component is normalized and represents the cross polarization error when the target is irradiated;
the matrix form is obtained as:
Figure FDA0002635701530000047
wherein,
Figure FDA0002635701530000048
and
Figure FDA0002635701530000049
the normalized transmitting error matrix and the normalized receiving error matrix respectively represent the target irradiation polarization characteristics, and the single stations are transposed mutually;
s63, using the rhombus dihedral angle as the calibration body to carry out calibration, then:
Figure FDA00026357015300000410
Figure FDA00026357015300000411
Figure FDA00026357015300000412
Figure FDA0002635701530000051
Figure FDA0002635701530000052
Figure FDA0002635701530000053
wherein,
Figure FDA0002635701530000054
and
Figure FDA0002635701530000055
polarization scattering matrix S respectively representing the calculated rhombus dihedral anglesdihAnd polarization scattering matrix M of rhombus dihedral angle obtained by measurementdihAn element of (1);
roll angle beta of rhombus dihedral anglecThe value range is less than 15 degrees and less than betac< 75 °; with MtarRepresenting the measured polarization scattering matrix of the target to be measured, and then calibrating the target polarization scattering matrix ScThe expression is as follows:
Figure FDA0002635701530000056
9. the method of claim 8, further comprising:
and S7, inverting the calibrated target polarization scattering matrix, comparing the target polarization scattering matrix with the original set value, and calculating an error.
10. An active and passive fusion scaling apparatus comprising:
the radio frequency module is used for setting parameters and setting transmitting signals under the condition that the radar completes internal calibration; the transmitting signal is generated by a signal source and comprises two paths of orthogonal radio frequency signals;
the full polarization module is used for adding multiplicative error of a transmitting channel and time delay caused by forward propagation to the transmitting signal to obtain a full polarization signal transmitted by an antenna;
the active simulation module is used for simulating a theoretical polarization scattering matrix by using a digital active calibrator according to the full polarization signal to obtain a backscattering signal of the moving target;
the sampling module is used for adding multiplicative errors of a receiving channel to the received back scattering signals, performing down-conversion to zero frequency, completing sampling storage and obtaining a polarization scattering matrix;
the compensation module is used for performing motion compensation and time delay compensation according to the obtained polarization scattering matrix;
and the passive correction module is used for carrying out passive polarization calibration on the compensated polarization scattering matrix, correcting residual errors, obtaining a calibrated target polarization scattering matrix and finishing calibration.
CN202010824553.4A 2020-08-17 2020-08-17 Active and passive fusion calibration method and device Pending CN111983575A (en)

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