CN107783092A - To rcs measurement system and method behind near field based on Chain relation - Google Patents
To rcs measurement system and method behind near field based on Chain relation Download PDFInfo
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- CN107783092A CN107783092A CN201710856834.6A CN201710856834A CN107783092A CN 107783092 A CN107783092 A CN 107783092A CN 201710856834 A CN201710856834 A CN 201710856834A CN 107783092 A CN107783092 A CN 107783092A
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- G—PHYSICS
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- 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 behind a kind of near field based on Chain relation to rcs measurement system and method.Cylindrical wave is produced using line source perpendicular to the ground, cylinder field only meets far field condition in short transverse.To reduce side wall interference noise, the microwave dark room of a kind of " taper " is devised.The echo level of wall is smaller 10dB than Compact Range behind cylinder field, is advantageous to darkroom gate being opened in rear wall, facilitates target to transport.The present invention proposes a kind of radar system near field RCS measurement, including target and environment division, microwave amplitude and phase measurement part and the part for carrying out NFFFT and high-resolution imaging.The implementation of near field RCS measurement is also proposed, including the background vector of support and environment offsets, measures near-field scattering coefficient FNCalibration, NFFFT and second during NFFFT calibration etc..Have the advantage that：1. NFFFT conversion is one-dimensional from Simplified two-dimension；2. the multiple diffraction for there was only horizontal direction in target can cause error；3. darkroom ground, roof gap and interference noise caused by step are small.
Description
Technical field
The invention belongs to low considerable survey technology and Radar Technology field, more particularly to a kind of near field based on Chain relation
Backward RCS (RCS) measuring system and method.
Background technology
The conventional method of RCS static measurements is outfield and Compact Range.Outfield is taken up an area greatly, and cost is high, and sources of environmental interference is more, by
Climatic effect measurement efficiency is low.Compact Range works indoors, the shortcomings that overcoming outfield, but Compact Range cost with dead zone size into
Cube and increase, at present it also mainly the RCS of scale model and part test in be applied.
The occupation of land of near field RCS measuring system is small, works indoors, its cost is far below Compact Range, is suitable for ultra-large type target
RCS is measured, therefore by concern both domestic and external.In recent years, near field RCS measuring system has stepped into realistic application conditions, but these
There are many shortcomings in system, it would be highly desirable to be improved and improve in terms of technology and index.
Near field Far-Zone Field Transformation (abbreviation NFFFT) is the core technology of near field RCS measuring system.Current near field RCS measurement system
The NFFFT methods that system uses are based on：1. SAR or ISAR imaging technique；2. optical Fourier transform is theoretical；3. mechanical scanning
Plane-Wave Synthesis technology.The basis of these methods is mainly physical concept and engineering technology.
Chain relation establishes near-field scattering coefficient F in theoryN(θ, φ) and Far Field Scattering coefficient F0Between (θ, φ)
Strict analytic equation (see formula [1]).The analytic expression set up sufficient and necessary condition be, when in measured target exist repeatedly around
, it is necessary to which completely (referring to " calculating and measurement of electromagnetic scattering ", 2006, BJ University of Aeronautics ＆ Astronautics went out dual station information when penetrating
Version society).
There is no the parameter of radar operating frequency in the Chain relation of formula (1), actually NFFFT is completely independent of frequency sweep
And these of SAR or ISAR imaging technique.Therefore the mistake that imaging resolution is brought is not present in the NFFFT based on Chain relation
Difference.
Different near field antenna scanning, the near field RCS based on Chain relation measures the mechanical scanning independent of space
(flat scanning, cylinder scanning or spherical scanning), therefore avoid truncated error that mechanical scanning brings and measurement efficiency is low
The problem of.
In non-convolution form Chain relation, the plane wave angular spectrum (PWS) in angular domain is replaced with spatial domain Electric Field Distribution, is solved
Determine abstract PWS computational problem.In addition, replacing de-convolution operation with division and Fourier transformation, solves deconvolution
Difficult math question.Thus the formula can directly obtain application near field RCS measuring system.
Current near field RCS measuring system uses point source near field, and transmitter and receiver antenna produces spherical wave.Irradiate target
Electromagnetic field be unsatisfactory for far field condition in azimuth φ and pitching angle theta direction.If carried out in the two-dimentional angular domain of (θ, φ)
NFFFT, then workload is excessive；If to " flat " target, ignore the near-field effect in θ directions, only carry out the one-dimensional angle in φ directions
Domain NFFFT, there will be mapping fault.
To overcome above mentioned problem, the present invention uses line source near field, instead of point source near field.In line source near field, transmitter antenna
Produce cylindrical wave.The electromagnetic field of irradiation target meets far field condition in pitching angle theta direction, and far field bar is unsatisfactory in azimuth φ
Part.So when only need to be one-dimensional angular domain NFFFT in φ directions.
In the present invention, using parabolic cylinder, spherical wave point source is placed on its focal line, cylindrical wave can be produced.Special list
The design of cylinder Compact Range makes Qi Kou faces utilization rate reach 150%, reduces manufacturing cost.
Current near field RCS measuring system is using conventional rectangle microwave darkroom, and the reflection of its side wall is to dead zone ambient level
Influence serious.In order to overcome this problem, new " taper darkroom " designing technique is employed.
It is more using instrument of the general microwave vector network analyzer as measurement in small-sized rcs measurement system.For
Large-scale rcs measurement system, all purpose instrument can not meet needs.The present invention proposes a kind of special measuring instrumentss,
The signal processing system of emitter, coherent receiver including high stable, special NFFFT and high-resolution imaging diagnosis.
Outfield and Compact Range rcs measurement system are direct measurement system, and near field RCS measuring system is for measurement indirectly
System.To using more complicated near field RCS measuring system, the present invention proposes the specific implementation method of system.
The content of the invention
The technical problem to be solved in the present invention is：How indoors under Near Field, backward rcs measurement, including reality are carried out
Existing system and the method realized.
The technical solution adopted by the present invention is：To rcs measurement method behind a kind of near field based on Chain relation, 50~
The 200m closely interior target that size 20m or so is irradiated using line source, carry out the plural scattering coefficient F near fieldNMeasurement,
Then directly (claim Chain relation according to the relationship of a parsing, " the calculating of electromagnetic scattering is write referring to He Guoyu etc.
And measurement ", publishing house of BJ University of Aeronautics ＆ Astronautics, 2006) calculate the far-field RCS of target.
Further, Far Field Scattering coefficient F0The far field RCS σ (θ, φ) of (θ, φ) and target relation is：
σ (θ, φ)=20log | F0(θ,φ)|
(θ, φ) is respectively the angle of pitch and the azimuth of measured target in formula.
Further, Far Field Scattering coefficient F0(θ, φ) and near-field scattering coefficient FNThe relation of (θ, φ) is：
In near field RCS measuring system, radar is in O ' points position, fixed.Measured target is in turntable rotation
Heart O carries out pitching angle theta and azimuth φ rotates.Rectangular coordinate system is x, and y, z origin are O, and y-coordinate is perpendicular to the ground, and x is sat
Mark parallel to the ground and orthogonal with straight line OO ', see Fig. 5.
Ei(x, y) is the x calculated according to geometric optics, the Electric Field Distribution on y plane.2DFFT is two-dimensional Fourier transform,
2DIFFT is two-dimentional inverse Fourier transform.The conversion between spatial domain (x, y) and angular domain (θ, φ) is realized in these conversion.
In near field RCS measuring system, the core technology that near field Far-Zone Field Transformation is the present invention is carried out using Chain relation.
The technology acuracy is high, and without carrying out being imaged computing and wide-band width measurement, transform method is simply, conveniently.
Further, the present invention is using line source irradiation target.Line source is a kind of emission source for producing cylindrical wave.With spherical wave
Difference, it is infinite ray in the ray of short transverse, meets far field condition.The ray of diverging is produced in the horizontal direction.Therefore
RCS, which measures necessary near field Far-Zone Field Transformation (referred to as NFFFT), only needs (azimuth φ direction) progress in the horizontal direction, or
Person says that Near-far fields transfer half uses physical method (parabolic cylinder), and half is completed using mathematical method (Chain relation).
In this case, the Chain relation for carrying out NFFFT is reduced to：
F in formula0(φ) is Far Field Scattering coefficient, FN(φ) is near-field scattering coefficient, Ei(x) it is to be calculated according to geometric optics
X coordinate direction Electric Field Distribution, the azimuth of φ measured targets, FFT is Fourier transform, and IFFT is inverse Fourier transform；
Obviously, the Near-far fields transfer of above formula is reduced to one-dimensional transform from two-dimensional transform.
Under being irradiated in cylinder field, the Electric Field Distribution on plane xy is coordinate x function, unrelated with coordinate y.The field distribution
For
S (x) is the distance that line source O ' points arrive x points in formula, d (x)=S (x)-R, sees Fig. 5.
Further, the present invention produces equivalent line source using single-column face Compact Range (single-column face CR).Single-column face Compact Range
It is made up of parabolic cylinder and feed, it is transformed to cylindrical wave in the closely interior spherical wave by feed production, sees Fig. 2.Single-column face
The mechanism that CR produces line source is shown in Fig. 3 and Fig. 4.As seen from Figure 3, acted on through parabolic cylinder, spherical wave is in height side caused by point source
To being transformed to the ray parallel with xz planes (meeting far field condition).From fig. 4, it can be seen that the reflection through the horizontal transversal of parabolic cylinder is made
With producing the ray of diverging in the horizontal direction, and line source is formed at " mirror point ".
By particular design, single-column face of the invention has 150% bore usage factor.The cost of the reflecting surface only has
/ 5th of same dead zone Compact Range reflecting surface cost.
Further, also had using the advantages of single-column face CR：
1. reduce the interference noise level such as gap and step on microwave dark room roof and ground；
2. because short transverse meets far field condition, mapping fault is not produced in NFFFT in the multiple diffraction of the direction.
Further, designed using the microwave dark room of taper, see Fig. 2.The advantages of this design, has：
1. reduce the interference noise level such as gap and step on microwave dark room side wall；
2. the reflection that cylindrical wave is irradiated to the electromagnetic wave of wall absorbing material plane behind taper darkroom is much smaller than wall after Compact Range
Reflection.The gate for being advantageous to enter target darkroom is opened on rear wall.
3. under the conditions of same test dead zone, taper darkroom area of the invention only has the area 65% in Compact Range darkroom.
Further, the system for devising near field RCS measurement, is shown in Fig. 7.The system by target and environment, microwave amplitude and
Three parts of phase measuring system and signal processing system form.
Further, in the case of line source, the specific implementation method of near field RCS measurement is given.The implementation includes：
● the background vector of support and environment offsets method；
● near-field scattering coefficient FNThe real-time calibration method of measurement；
● the method that NFFFT is carried out according to Chain relation；
Second of calibration technology in NFFFT conversion etc..
The present invention compared with prior art the advantages of be：
(1) NFFFT of the present invention is reduced to one-dimensional transform from two-dimensional transform, substantially increases conversion efficiency.
(2) present invention multiple diffraction of short transverse in target will not cause mapping fault；Only horizontal direction is more
Secondary diffraction can cause error.
(3) darkroom ground of the present invention, roof gap and interference noise caused by step are small.
(4) present invention have devised a kind of microwave dark room of " taper ", reduce side wall interference noise level, behind cylinder field
The echo level of wall is smaller 10dB than Compact Range, and this result is advantageous to darkroom gate being opened in rear wall, facilitates target to transport.
Brief description of the drawings
Fig. 1 is to RCS test system schematic diagrames behind point source near field；
Fig. 2 is the test system schematic diagram that is utilized to rcs measurement method behind line source near field；
Fig. 3 is single-column face CR side view；
Fig. 4 is single-column face CR top view；
Fig. 5 is the schematic diagram of the geometrical optics field of cylindrical wave；
Fig. 6 be line source in the case of, by FNCalculate F0Block diagram；
Fig. 7 is the block diagram of near field RCS test system.
Embodiment
Below in conjunction with the accompanying drawings and embodiment further illustrates the present invention.
Fig. 1 is to the schematic diagram of RCS test systems behind current point source near field in the world.Rectangle echo chamber size is about in figure：
40m (W) × 60m (L) × 25m (H), the square meter of area 2400.Transmitting radar antenna launches spherical wave, reception antenna and transmitting antenna
It is identical, and it is placed on same point.
The typical sizes of measured target are：Length 20m, height 5m.When working frequency is 8GHz, horizontal and vertical direction
Far field condition be respectively：
The measuring distance of near field RCS measuring system about 50m~200m, no matter horizontal direction (φ directions) is also vertically oriented
(θ directions), all it is difficult to meet above-mentioned far field condition.
NFFFT Chain relation is：
Symbol " * " represents convolution, symbol in formulaRepresent deconvolution.FNAnd F0For near-field scattering coefficient and Far Field Scattering
Coefficient, C1For constant term.ST(θ, φ) and SR(θ, φ) is respectively the plane wave angular spectrum of transmitting antenna and reception antenna.θ and φ are
Illumination angle, θ ' and φ ' are angle of scattering.
Formula (1) shows, Far Field Scattering coefficient F0It is proportional to near-field scattering coefficient FNWith system shock receptance function [ST(θ,
φ)*SR(θ, φ)] deconvolution.
RCS σ definition is：
Scattering coefficient F definition is：
RCS σ is the variable of a far field meaning, and it is a scalar.Scattering coefficient F and radar to target
Distance R it is relevant.R → ∞, it is Far Field Scattering coefficient F0, it is otherwise near-field scattering coefficient FN.Scattering coefficient is plural number, there is amplitude
And phase.RCS σ and Far Field Scattering coefficient F0Relation be：
Rear in the case of (single stand) RCS, illumination angle is equal to angle of scattering, and ST(θ, φ)=SR(θ, φ)=S (θ, φ).
Formula (1) is reduced to formula (5),
To giving antenna, S (θ, φ) is known function, FN(θ, φ) is the near-field scattering coefficient of measurement.By two dimension
Warp product transformation obtains Far Field Scattering coefficient F0(θ,φ)。
Measure FNWhen (θ, φ), azimuth sampled point is m points, and angle of pitch sampled point is n points, FNTotal sampled point be m × n.
Sampled point is very big, and NFFFT workload is also very big.
In theory, point source near field, can be according to near-field scattering coefficient F by bidimensional NFFFTNCalculate Far Field Scattering coefficient F0。
But sampled too much during point source near field, aircraft time of measuring is long.The long-time of measured target, which rotates, to influence whether target
Security.
For this, people actually have to ignore the fact that short transverse is unsatisfactory for far field condition, only carry out horizontal direction
One-dimensional NFFFT conversion." point source near field " now is that the one kind in " line source near field " is approximate in fact.
The shortcomings that point source near field, also has：1. the spurious level on roof and ground is high；2. the multiple diffraction and water of vertical direction
Square it can cause error to multiple diffraction.
The present invention produces electric line source using single-column face Compact Range, and the electromagnetic wave for thus irradiating target is cylindrical wave, without
It is spherical wave.
The schematic diagram of line source near field RCS test system is shown in Fig. 2.Single-column face CR (i.e. single-column face Compact Range) is by one in Fig. 2
Parabolic cylinder and feed are formed.
Fig. 3 is single-column face CR side view.In yz planes, the transversal of parabolic cylinder is parabola, parabolical focal line
For A, focal length F.It is placed on spherical electromagnetic wave caused by the feed of A points and parallel with z-axis penetrate is formed after parabolic reflective
Line.A points are A1 to " mirror point " of y plane.By A1 points, and caused by the straight line current source parallel with y-axis (abbreviation line source)
Ray overlaps with ray caused by parabola.
Fig. 4 is the top view of single-column face Compact Range.In xz planes, the transversal of parabolic cylinder is straight line.It is placed on the feedback of A points
Spherical electromagnetic wave caused by source forms the ray of diverging after " straight line " reflection in xz planes.These diverging rays with
The ray of diverging is consistent caused by line source on " mirror point " A1.
Therefore, in the present invention, an electric line source is produced using single reflection face Compact Range, the line source produces cylindrical wave.
Line source (single-column face CR in other words) meets far field condition in height direction, and it is big to be unsatisfactory for far field condition in the horizontal direction
Simplify the sampling work amount of measurement and NFFFT conversion complexity greatly.
In Fig. 2, turntable pivot is the origin of target-based coordinate system, is laid target by two poles and a lifting rope
To formulation position.Pole is fixed on turntable, and band moving-target produces azimuth φ and rotated.Pass through hanging positioned at turntable rotation axis
Rope stretches, thus it is possible to vary the pitching angle theta of target.
Emitter transmitting microwave signal irradiation measured target.Turntable and branch crane system in the case of a given pitching angle theta,
Rotate turntable, receiver azimuthal φ target echo does m point samplings, obtains the near-field scattering signal F of targetN(φ)|θ
(near-field scattering coefficient).Compared with point source near field, the sampled point in line source near field reduces n times.
Fig. 5 is the schematic diagram for calculating geometrical optics field caused by single-column face CR.As seen from the figure,
D (x)=S (x)-R
The distance S of amplitude and Electromagnetic Wave Propagation relation is：
Thus, the Electric Field Distribution in x-axis is：
Ei(x)=A (x) exp [- j φ (x)] (6)
Formula (5) is reduced to：
According to the Chain relation of non-convolution form,
The computing block diagram of formula (8) is shown in Fig. 6.
According to tested FN(φ)|θThe E obtained with formula (6)i(x) the Far Field Scattering coefficient F of requirement, is calculated by formula (8)0
(φ)|θ.This NFFFT is that one-dimensional conversion is carried out in azimuth φ direction, than the two-dimentional NFFFT in point source near field speed
It is fast n times.
When measured target is not the set of isolated scattering object, when the multiple diffractions such as corner reflector, cavity, Creeping Wave be present,
Near field RCS measurement in NFFFT will appear from due to collection information it is imperfect caused by error.Cylinder near field is in the height direction
Meet far field condition, the error of multiple diffraction in this direction is inhibited.The only conversion of the multiple diffraction of horizontal direction
Error.This is second important advantage in cylinder near field.
" shortcoming " of cylinder field is to need a parabolic cylinder.But compared with Compact Range, required increased cost is limited
's.
There is diverging to respond for line source or parabolic cylinder, make single-column face CR bore utilization rate very high, i.e. ηa=W2/W1=
150% (W1For reflecting surface width, W2For dead band width), the bore utilization rate η of Compact Rangeb=W2/W1=50%, both differ very
Far.
When dead zone size is identical, Compact Range reflecting surface width W1For 3 times of cylinder field, area is 4 times of cylinder field.Consider
To manufacture factor, cylinder field cost only has 1/5th of same dead zone Compact Range.
In Fig. 2, the shape in darkroom is not rectangle, but special taper.The design in taper darkroom can obtain extremely low
Dead zone background clutter interference level.
Cylinder field is producing infinite ray in short transverse, reduces the noise jamming level on ground and roof.Line source exists
For horizontal direction into diverging ray, these rays are parallel with side wall, side wall scattering is greatly improved.The taper darkroom of the present invention
The problem of point source near field is present is overcome, is improved the cleanliness in dead zone.
The Common advantages of Compact Range rcs measurement system and near field RCS test system are indoor measurements.The data of measurement have
Very high repeatability, uniformity, it is free from the influence of the external environment, there can be satisfied testing efficiency with all weather operations.Overcome
This shortcoming in outfield.But indoor measurement needs to build microwave dark room, and it is non-to large scale measured target, darkroom area
Chang Keguan.
Under identical dead zone dimensional conditions, the area in the taper darkroom of the present invention is smaller than Compact Range darkroom 1.5 times, compares point source
The rectangle darkroom near field is big 1.5 times.
See Fig. 7 to rcs measurement system behind the near field of the present invention.The system is made up of three parts：1. target and environment division；
2. microwave amplitude and phase measurement part；3. signal processing.
Target includes with environment division：Single-column face CR, taper darkroom, measured target and support.Transmitting antenna produces cylinder
Ripple, reception antenna remove receive measured target reflected signal outside, also to receive taper darkroom, support and from transmitting feed antenna
It is directly leaked to receive the signal of feed antenna.In order to eliminate the various interference signals outside normal echo-signal, it is necessary in frame
If before target, the amplitude and phase signal of background are measured, to carry out the background cancel of vector.
The frequency of microwave amplitude and phase measurement part needs to cover the frequency range of radar work.Mode of operation a little frequently and is swept
Frequently two kinds, the latter's main purpose is to carry out high-resolution inverse synthetic aperture imaging (identification and diagnosis).In order to carry out phase measurement,
Using coherent receiver pattern.
Signal processing includes：Background vector offsets, NFFFT and microwave imaging.
It is as follows to the embodiment of RCS test systems after cylinder near field shown in Fig. 2.
1, measure the complex reflection signal F of background and supportB(φ)；
2, calibration body is placed on the support before dead zone, measurement complex reflection signal FC(φ)；
3, measured target is set up to measurement height by two poles and a lifting rope.Turntable rotational band moving-target is in orientation
Angle φ is rotated, and lifting rope is in the pivot of turntable, the flexible pitching angle theta that can change target of lifting rope；
4, to the angle of pitch to set the goal, turntable band moving-target carries out azimuth φ rotation, the letter of one frequency of radar emission
Number irradiation target, receiver receive target complex reflection signal FT(φ), including amplitude and phase；
5, near field echoes signal is calibrated,
F in formulaCFor the RCS σ of calibration bodyCCorresponding reflected signal.
6, to FNDifference operation is carried out, 2DFFT is then, obtains EN, suitable difference will make ENIn x, y plane is at equal intervals
Distribution；
7, by the E of formula (5)iAnd EN, calculated using formula (4),
NFFFT calibration coefficient C determination method in formula：
1. the near-field scattering coefficient F of calibration sphere is measured under Near FieldN(φ)；
2. calculate the far field coefficient F of calibration sphere using Fig. 7 block diagram0(φ)；
3. changing coefficient C, work as F0(φ)=FNWhen (φ), C convergences.
8, by E02DIFFT and interpolation are, obtains Far Field Scattering coefficient F0(φ) |, it is spacedly distributed in angular domain φ.
9, RCS is calculated,
σ(φ)|θ=20logF0(φ)|θ|。
Claims (6)
1. to rcs measurement method behind a kind of near field based on Chain relation, it is characterised in that：In the closely interior of 50~200m
Size 20m or so target is irradiated using line source, carries out the plural scattering coefficient F near fieldNMeasurement, then directly according to chain
Relational expression calculates the far-field RCS of target.
2. to rcs measurement method behind a kind of near field based on Chain relation according to claim 1, it is characterised in that：
Far Field Scattering coefficient F0The far field RCS σ (θ, φ) of (θ, φ) and target relation is：
σ (θ, φ)=20log | F0(θ,φ)|
(θ, φ) is respectively the angle of pitch and the azimuth of measured target in formula.
3. to rcs measurement method behind a kind of near field based on Chain relation according to claim 1, it is characterised in that：
Far Field Scattering coefficient F0(θ, φ) and near-field scattering coefficient FNThe relation of (θ, φ) is：
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(θ, φ) is respectively the angle of pitch and the azimuth of measured target in formula；
In near field RCS measuring system, radar is in O ' points position, and fixed, measured target enters around turntable pivot O
Row pitching angle theta and azimuth φ rotate, and rectangular coordinate system x, y, z origin are O, and y-coordinate is perpendicular to the ground, x coordinate and ground
Face is parallel, and orthogonal with straight line OO '；
Ei(x, y) is the x calculated according to geometric optics, and the Electric Field Distribution on y plane, 2DFFT is two-dimensional Fourier transform,
2DIFFT is two-dimentional inverse Fourier transform, and the conversion between spatial domain (x, y) and angular domain (θ, φ) is realized in these conversion.
4. to rcs measurement method behind a kind of near field based on Chain relation according to claim 1, it is characterised in that：
Target is irradiated using line source, line source is a kind of emission source for producing cylindrical wave, different from spherical wave, its ray in short transverse
For infinite ray, meet far field condition, produce the ray of diverging in the horizontal direction, therefore the necessary near field far field of rcs measurement becomes
Changing (referred to as NFFFT) only needs in the horizontal direction i.e. azimuth φ direction progress, and Near-far fields transfer half uses thing in other words
Reason method is parabolic cylinder method, and half is completed using mathematical method Chain relation；
In this case, the Chain relation for carrying out NFFFT is reduced to：
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</mrow>
F in formula0(φ) is Far Field Scattering coefficient, FN(φ) is near-field scattering coefficient, Ei(x) it is that the x calculated according to geometric optics is sat
The Electric Field Distribution in direction is marked, the azimuth of φ measured targets, FFT is Fourier transform, and IFFT is inverse Fourier transform；
Obviously, the Near-far fields transfer of above formula is reduced to one-dimensional transform from two-dimensional transform；
Under being irradiated in cylinder field, the Electric Field Distribution on plane xy is coordinate x function, unrelated with coordinate y, and the field distribution is：
<mrow>
<msup>
<mi>E</mi>
<mi>i</mi>
</msup>
<mrow>
<mo>(</mo>
<mi>x</mi>
<mo>)</mo>
</mrow>
<mo>=</mo>
<mfrac>
<mn>1</mn>
<msqrt>
<mrow>
<mi>S</mi>
<mrow>
<mo>(</mo>
<mi>x</mi>
<mo>)</mo>
</mrow>
</mrow>
</msqrt>
</mfrac>
<mi>exp</mi>
<mo>&lsqb;</mo>
<mo>-</mo>
<mi>j</mi>
<mi>k</mi>
<mi>d</mi>
<mrow>
<mo>(</mo>
<mi>x</mi>
<mo>)</mo>
</mrow>
<mo>&rsqb;</mo>
</mrow>
S (x) is that line source O ' puts the distance for arriving x points, d (x)=S (x)-R in formula.
5. to rcs measurement method behind a kind of near field based on Chain relation according to claim 1, it is characterised in that：
Equivalent line source is produced using single-column face Compact Range, single-column face Compact Range is made up of parabolic cylinder and feed, and it is closely interior
The spherical wave that feed produces is transformed to cylindrical wave, acted on through parabolic cylinder, spherical wave caused by point source converts in short transverse
For the ray parallel with xz planes, the reflex through the horizontal transversal of parabolic cylinder, the ray of diverging is produced in the horizontal direction, and
Line source is formed at " mirror point ".
6. to rcs measurement system behind a kind of near field based on Chain relation, it is characterised in that：The system by target and environment,
Microwave amplitude and phase measuring system and three parts of signal processing system form, wherein, target is placed on the micro- of " taper "
In ripple darkroom, supported by support and the rotation on horizontal plane, transmitting antenna transmitting spherical wave, by throwing are realized by turntable
Thing cylindrical surface for reflection is cylindrical wave and irradiates target；Reception antenna receives the scattering electromagnetic wave of target, downconverts to intermediate frequency and carries out width
Mutually measure；After width phase information is filtered by matched filter, it is transmitted to signal processing system and carries out signal transacting, become by NFFFT
Change, obtain the RCS information of target.
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