CN107783092B - Near-field backward RCS (Radar Cross section) measuring system and method based on chain relational expression - Google Patents
Near-field backward RCS (Radar Cross section) measuring system and method based on chain relational expression Download PDFInfo
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Abstract
The invention discloses a near-field backward RCS measuring system and method based on a chain relational expression. The cylindrical wave is generated by a line source vertical to the ground, and the cylindrical field meets the far field condition only in the height direction. In order to reduce the interference clutter of the side wall, a conical microwave darkroom is designed. The echo level of the cylindrical field rear wall is 10dB lower than that of a compact field, so that the darkroom door can be opened on the rear wall, and the target transportation is facilitated. The invention provides a radar system for near-field RCS measurement, which comprises a target and environment part, a microwave amplitude and phase measurement part and a part for NFFFT and high-resolution imaging. Also provides an implementation method of the near-field RCS measurement, which comprises the steps of vector background cancellation of the bracket and the environment, and measurement of the near-field scattering coefficient FNScaling, NFFFT, and a second scaling during NFFFT, etc. Has the advantages that: simplifying NFFFT transformation from two dimensions to one dimension; secondly, only multiple diffraction in the horizontal direction on the target can cause errors; interference clutter generated by the ground, the roof gap and the step of the darkroom is small.
Description
Technical Field
The invention belongs to the technical field of low observable technology and radar, and particularly relates to a near-field backward radar scattering cross section (RCS) measuring system and method based on a chain relational expression.
Background
The traditional methods of static measurement of RCS are outfield and compact field. The outfield occupies a large area, the cost is high, the number of environmental interference sources is large, and the measuring efficiency is low due to the influence of weather. Compact is working indoors, overcoming the disadvantages of external fields, but the cost of compact grows cubically with dead space size, and it is currently mainly used in RCS testing of scaled models and parts.
The near-field RCS measuring system occupies small space, works indoors, has the cost far lower than that of a compact range, is suitable for measuring the ultra-large target RCS, and is concerned at home and abroad. In recent years, near-field RCS measurement systems have been brought into practical use, but these systems have many defects in technology and indexes, and improvements are urgently needed.
Near-field far-field transformation (NFFFT for short) is a core technology of a near-field RCS measurement system. The NFFFT method adopted by the current near-field RCS measurement system is based on: imaging technology of SAR or ISAR; optical Fourier transform theory; and plane wave comprehensive technology of mechanical scanning. The basis of these methods is mainly the physical concept and engineering techniques.
Chain relation theoretically establishes near-field scattering coefficient FN(theta, phi) and far field scattering coefficient F0Strict mathematical analytic expression between (theta, phi) (see formula [1 ]]). A sufficient requirement for this analytical formula to be established is that complete two-station information is required when there are multiple diffractions in the object under test (see "calculation and measurement of electromagnetic scattering", 2006, beijing university of aerospace publishers).
The chain relation of equation (1) has no parameters of the radar operating frequency, and the NFFFT is practically completely independent of the frequency sweep and those imaging techniques of SAR or ISAR. Therefore, the NFFFT based on the chain relation has no error caused by imaging resolution.
Different from near-field antenna scanning, near-field RCS measurement based on a chain relational expression does not depend on spatial mechanical scanning (plane scanning, cylindrical scanning or spherical scanning), so that the problems of truncation error and low measurement efficiency caused by mechanical scanning are solved.
In the non-convolution type chain relation, a spatial electric field distribution is used for replacing a plane wave angular spectrum (PWS) in an angular domain, and the calculation problem of the abstract PWS is solved. In addition, the division and Fourier transform are used for replacing the deconvolution operation, so that the mathematical problem of deconvolution is solved. This formula can thus be directly applied in near-field RCS measurement systems.
Current near-field RCS measurement systems use a point source near-field, with transmitter and receiver antennas producing spherical waves. The electromagnetic field irradiating the target does not satisfy the far field condition in the directions of the azimuth angle phi and the pitch angle theta. If NFFFT is performed in the two-dimensional angular domain of (theta, phi), the workload is too large; if for a "flat" target, neglecting the near field effect in the theta direction, only one-dimensional angular domain NFFFT in the phi direction is performed, there will be a transformation error.
To overcome the above problems, the present invention uses a line source near field instead of a point source near field. In the near field of the line source, the transmitter antenna generates a cylindrical wave. The electromagnetic field irradiating the target satisfies the far field condition in the pitch angle theta direction and does not satisfy the far field condition in the azimuth angle phi. Therefore, only one-dimensional angular domain NFFFT is needed in the phi direction.
In the invention, a parabolic cylinder is adopted, and a spherical wave point source is arranged on the focal line of the parabolic cylinder, so that cylindrical waves can be generated. The design of the special single-cylindrical compact range enables the utilization rate of the mouth surface to reach 150%, and the manufacturing cost is reduced.
The conventional rectangular microwave darkroom is adopted in the current near-field RCS measuring system, and the reflection of the side wall of the conventional rectangular microwave darkroom seriously affects the background level of a dead zone. To overcome this problem, a new "conical darkroom" design technique was adopted.
In a small-sized RCS measuring system, a general microwave vector network analyzer is mostly adopted as a measuring instrument. For large RCS measurement systems, the need for a universal instrument has not been met. The invention provides a special measuring instrument which comprises a high-stability transmitter, a coherent receiver, a special NFFFT and a signal processing system for high-resolution imaging diagnosis.
The external field RCS measuring system and the compact field RCS measuring system are both direct measuring systems, and the near field RCS measuring system is an indirect measuring system. For more complex near-field RCS measurement systems, the invention proposes a specific implementation method of the system.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: how to perform backward RCS measurements under indoor near-field conditions, including implemented systems and implemented methods.
The technical scheme adopted by the inventionComprises the following steps: a near-field backward RCS measuring method based on chain relational expression is characterized in that a line source is adopted to irradiate a target with the size of about 20m in a short distance of 50-200 m, and a complex scattering coefficient F of a near field is carried outNThen, the far-field RCS of the target is directly calculated according to an analytic mathematical relation (called chain relation, written in "calculation and measurement of electromagnetic scattering" by heyu, et al, beijing university of aerospace publisher, 2006).
Further, the far field scattering coefficient F0(θ, φ) is related to the far-field radar scattering cross-section of the target, σ (θ, φ), by:
σ(θ,φ)＝20log|F0(θ,φ)|
in the formula, (theta, phi) is the pitch angle and the azimuth angle of the measured target respectively.
Further, the far field scattering coefficient F0(theta, phi) and near field scattering coefficient FNThe relationship of (θ, φ) is:
in the near-field RCS measurement system, the radar is in the O' point position and is fixed. The measured object rotates around the rotation center O of the rotary table at a pitch angle theta and an azimuth angle phi. The rectangular coordinate system x, y, z has an origin O, the y coordinate is perpendicular to the ground, and the x coordinate is parallel to the ground and orthogonal to the line OO', see fig. 5.
Ei(x, y) is the electric field distribution in the x, y plane as calculated by geometric optics. 2DFFT is a two-dimensional fourier transform and 2 diffft is a two-dimensional inverse fourier transform. These transforms implement a transform between spatial (x, y) and angular (θ, φ) domains.
In a near-field RCS measurement system, the near-field far-field transformation is performed by adopting a chain relation formula, which is the core technology of the invention. The technology has high precision, does not need imaging operation and broadband measurement, and has simple and convenient transformation method.
Further, the present invention irradiates the target with a line source. A line source is a source of radiation that generates a cylindrical wave. Unlike spherical waves, rays of the spherical waves in the height direction are parallel rays, and far-field conditions are met. Diverging rays are generated in the horizontal direction. Therefore, the near-field far-field transformation (NFFFT for short) necessary for RCS measurement only needs to be performed in the horizontal direction (azimuth angle phi direction), or half of the near-field far-field transformation is completed by a physical method (parabolic cylinder) and half by a mathematical method (chain relation).
In this case, the chain relation for NFFFT is simplified to:
in the formula F0(phi) is the far field scattering coefficient, FN(phi) is the near field scattering coefficient, Ei(x) The electric field distribution in the x coordinate direction calculated according to geometric optics, the azimuth angle of a phi measured target, FFT (fast Fourier transform) and IFFT (inverse Fourier transform);
obviously, the near-far field transform of the above equation reduces from a two-dimensional transform to a one-dimensional transform.
Under the irradiation of the cylindrical surface field, the electric field distribution on the plane xy is only a function of the coordinate x and is independent of the coordinate y. The field is distributed as
Where s (x) is the distance from the point O' of the line source to the point x, and d (x) s (x) -R, see fig. 5.
Further, the present invention uses a single cylindrical compact field (single cylindrical CR) to create an equivalent line source. The single-cylinder compact field consists of a parabolic cylinder and a feed source, and converts spherical waves produced by the feed source into cylindrical waves in a short distance, as shown in figure 2. The mechanism by which the single cylindrical surface CR produces a line source is shown in figures 3 and 4. As can be seen from fig. 3, the spherical wave generated by the point source is transformed into a ray parallel to the xz plane in the height direction by the action of the parabolic cylinder (satisfying the far-field condition). As can be seen from fig. 4, the reflection action of the horizontal sectional line of the parabolic cylinder generates divergent rays in the horizontal direction and forms a line source at the "mirror point".
Through special design, the single cylindrical surface of the invention has a caliber utilization coefficient of 150%. The cost of the reflecting surface is only one fifth of the cost of the same quiet zone compact range reflecting surface.
Further, the advantages of using a single cylindrical surface CR are:
interference clutter levels such as gaps and steps on the roof and the ground of a microwave darkroom are reduced;
secondly, because the height direction meets the far field condition, the multiple diffraction in the direction does not generate transformation errors in NFFFT.
Further, a conical microwave dark room design is used, see fig. 2. The advantages of this design are:
interference clutter levels such as gaps and steps on the side wall of the microwave darkroom are reduced;
the reflection of the electromagnetic wave of the cylindrical wave irradiated to the plane of the absorption material of the back wall of the conical dark room is far less than that of the back wall of the compact range. The door for the target to enter the darkroom is opened on the back wall.
Thirdly, under the same test dead zone condition, the area of the conical darkroom of the invention is only 65 percent of that of the compact range darkroom.
Further, a system for near-field RCS measurement was devised, see fig. 7. The system consists of three parts, namely a target and environment measuring system, a microwave amplitude and phase measuring system and a signal processing system.
Further, in the case of an online source, a specific implementation method of the near-field RCS measurement is provided. The implementation method comprises the following steps:
● vector background cancellation method of stent and environment;
● near-field scattering coefficient FNA real-time calibration method of measurement;
● performing NFFFT according to the chain relation;
a second scaling technique in the NFFFT transform, etc.
Compared with the prior art, the invention has the advantages that:
(1) the NFFFT of the invention is simplified from two-dimensional transformation to one-dimensional transformation, thereby greatly improving the transformation efficiency.
(2) The invention does not cause transformation errors by multiple diffraction in the height direction on the target; only multiple diffractions in the horizontal direction cause errors.
(3) The invention has small interference clutter generated by the ground, the roof gap and the step of the darkroom.
(4) The invention designs a conical microwave darkroom, reduces the level of interference clutter of the side wall, and the echo level of the rear wall of the cylindrical field is 10dB lower than that of a compact field, so that the darkroom door can be opened on the rear wall, and the target transportation is facilitated.
Drawings
FIG. 1 is a schematic diagram of a point source near field backward RCS test system;
FIG. 2 is a schematic diagram of a test system utilized by the line source near field backward RCS measurement method;
fig. 3 is a side view of the single face CR;
fig. 4 is a top view of the single cylindrical surface CR;
FIG. 5 is a schematic of the geometric optical field of a cylindrical wave;
FIG. 6 shows a line source case, represented by FNCalculating F0A block diagram of;
fig. 7 is a block diagram of a near-field RCS test system.
Detailed Description
The invention is further described with reference to the following figures and detailed description.
FIG. 1 is a schematic diagram of a current international point source near-field backward RCS test system. The rectangular echo chamber size in the figure is about: 40m (W) x 60m (L) x 25m (H), and an area of 2400 square meters. The radar transmitting antenna transmits spherical waves, and the receiving antenna and the transmitting antenna are the same and are placed at the same point.
Typical dimensions of the measured object are: length 20m, height 5 m. When the operating frequency is 8GHz, the far field conditions in the horizontal and vertical directions are respectively as follows:
the test distance of the near-field RCS measurement system is about 50 m-200 m, and the far-field condition is difficult to satisfy in both the horizontal direction (phi direction) and the vertical direction (theta direction).
The chain relation of NFFFT is:
wherein the symbol "+" represents convolution and symbol
Representing a deconvolution. FNAnd F0As near field scattering coefficient and far field scattering coefficient, C1Is a constant term. ST(theta, phi) and SR(θ, φ) are the plane angular spectra of the transmit and receive antennas, respectively. Theta and phi are illumination angles, and theta 'and phi' are scattering angles.
The far-field scattering coefficient F is shown in formula (1)0Proportional to the near field scattering coefficient FNAnd system impulse response function [ S ]T(θ,φ)*SR(θ,φ)]Is deconvolved.
The radar scattering cross section σ is defined as:
the scattering coefficient F is defined as:
the radar cross section σ is a variable in far field meaning, which is a scalar quantity. The scattering coefficient F is related to the distance R of the radar to the target. R → ∞, far field scattering coefficient F0Otherwise, the near field scattering coefficient FN. The scattering coefficient is complex, having an amplitude and a phase. Radar scattering cross section sigma and far field scattering coefficient F0The relationship of (1) is:
in the case of backward (single station) RCS, the illumination angle is equal to the scattering angle, and ST(θ,φ)＝SR(θ, Φ) ═ S (θ, Φ). The formula (1) is simplified into the formula (5),
for a given antenna, S (θ, φ) is a known function, FN(θ, φ) is the measured near-field scattering coefficient. Obtaining far field scattering coefficient F through two-dimensional deconvolution transformation0(θ,φ)。
Measurement FN(theta, phi) the azimuth angle sampling point is m points, the pitch angle sampling point is n points, FNThe total sampling point of (1) is m × n. The sampling point is very large and the work load of NFFFT is also very large.
Theoretically, the near field of a point source can be determined by the near field scattering coefficient F through two-dimensional NFFFTNCalculating far field scattering coefficient F0. But the point source samples too much in the near field and the airplane measurement time is too long. The long-time rotation of the measured target will affect the safety of the target.
For this reason, one has to actually ignore the fact that the height direction does not satisfy the far-field condition, and only perform one-dimensional NFFFT transformation in the horizontal direction. The "point source near field" at this time is actually only an approximation of the "line source near field".
The disadvantages of the point source near field are also: firstly, the stray electric level of the roof and the ground is high; second, errors are caused by multiple diffractions in the vertical direction and multiple diffractions in the horizontal direction.
The present invention uses a single cylinder compact field to generate a linear current source whereby the electromagnetic wave illuminating the target is a cylindrical wave rather than a spherical wave.
A schematic diagram of a line source near field RCS test system is shown in figure 2. The single cylindrical surface CR (i.e., the single cylindrical compact range) in fig. 2 is formed by a parabolic cylindrical surface and a feed source.
Fig. 3 is a side view of the single cylindrical surface CR. On the yz plane, the sectional line of the parabolic cylinder is a parabola, the focal line of the parabola is A, and the focal length is F. The spherical electromagnetic wave generated by the feed source placed at the point A forms rays parallel to the z axis after being reflected by the parabola. The "mirror point" of the A point to the y plane is A1. Rays generated by a linear current source (simply a line source) passing through point a1 and parallel to the y-axis coincide with rays generated by a parabola.
FIG. 4 is a top view of a single cylinder compact. On the xz plane, the section line of the parabolic cylinder is a straight line. Spherical electromagnetic waves generated by a feed source placed at the point A form divergent rays on an xz plane after being reflected by a straight line. These diverging rays coincide with the diverging rays generated by the line source at "mirror point" a 1.
Thus, in the present invention, a single reflector compact field is used to generate a source of line current that generates a cylindrical wave.
The line source (or single cylinder CR) satisfies the far field condition in the elevation direction, and does not satisfy the far field condition in the horizontal direction, which greatly simplifies the sampling workload of measurement and the conversion complexity of NFFFT.
In fig. 2, the rotation center of the turntable is the origin of the target coordinate system, and the target is placed at a specified position through two support rods and a lifting rope. The supporting rod is fixed on the rotary table and drives the target to rotate at an azimuth angle phi. The pitch angle θ of the target can be changed by the extension and contraction of the lifting rope at the rotation axis of the turntable.
The transmitter transmits a microwave signal to irradiate the measured target. Under the condition of a given pitch angle theta, the rotary table and the supporting and hoisting system are rotated, the receiver samples a target echo with an azimuth angle phi by m points to obtain a near-field scattering signal F of the targetN(φ)|θ(near field scattering coefficient). The sampling point of the line source near field is reduced by a factor of n compared to the point source near field.
Fig. 5 is a schematic diagram of the calculation of the geometric optical field produced by the single cylinder CR. As can be seen from the figure, the drawing,
d(x)＝S(x)-R
the relationship between the amplitude and the distance S over which the electromagnetic wave propagates is:
thus, the electric field distribution on the x-axis is:
Ei(x)＝A(x)exp[-jφ(x)] (6)
equation (5) reduces to:
according to the chain relation in a non-convolution form,
the block diagram of the calculation of equation (8) is shown in fig. 6.
According to measured FN(φ)|θAnd E obtained by formula (6)i(x) Calculating the required far-field scattering coefficient F from equation (8)0(φ)|θ. The NFFFT is only one-dimensional in the azimuth phi direction, and is n times faster than the two-dimensional NFFFT in the near field of the point source.
When the measured target is not the set of isolated scatterers and multiple diffractions such as corner reflectors, cavities, creeping waves and the like exist, the NFFFT in the near-field RCS measurement has errors caused by incomplete acquired information. The cylindrical near field satisfies the far field condition in the height direction, and the error of multiple diffraction in the direction is suppressed. Only the transformation error of multiple diffraction in the horizontal direction. This is a second important advantage of the cylindrical near field.
The "disadvantage" of a cylindrical field is that a parabolic cylinder is required. But the added cost required compared to compact ranges is limited.
Line sources or throwsThe object-cylindrical surface has divergent response, so that the aperture utilization rate of the single-cylindrical surface CR is very high, namely etaa＝W2/W1＝150％(W1Is the width of the reflecting surface, W2Width of dead zone), the aperture utilization η of the compact rangeb＝W2/W150%, the two are far from each other.
Width W of reflector in compact range with the same size of dead zone13 times the cylindrical field and 4 times the area of the cylindrical field. For manufacturing reasons, the cylindrical field costs are only one fifth of the same dead space compact.
In fig. 2, the shape of the dark room is not rectangular, but is specially tapered. The design of the cone-shaped darkroom can obtain extremely low quiet zone background clutter interference level.
The cylindrical field produces parallel rays in the elevation direction, resulting in reduced clutter interference levels on the ground and roof. The line source emits scattered rays in the horizontal direction, and the rays are parallel to the side wall, so that the scattering of the side wall is greatly improved. The conical darkroom overcomes the problems existing in a point source near field, and improves the cleanliness of a dead zone.
A common advantage of compact field RCS measurement systems and near field RCS test systems is indoor measurement. The measured data has high repeatability and consistency, is not influenced by the external environment, can work all the day, and has satisfactory testing efficiency. This disadvantage of the external field is overcome. However, the indoor measurement needs to build a microwave darkroom, and the area of the darkroom is very considerable for a large-size measured target.
Under the condition of the same dead zone size, the area of the conical darkroom is 1.5 times smaller than that of a compact field darkroom and 1.5 times larger than that of a rectangular darkroom of a point source near field.
The near field backward RCS measurement system of the present invention is shown in fig. 7. The system consists of three parts: firstly, a target and environment part; a microwave amplitude and phase measuring part; and thirdly, a signal processing part.
The target and environment part comprises: single-cylinder CR, conical darkroom, measured object and bracket. The transmitting antenna generates cylindrical wave, and the receiving antenna receives the reflected signal of the measured target, the cone darkroom, the bracket and the signal directly leaked from the transmitting feed source antenna to the receiving feed source antenna. In order to eliminate various interference signals except for normal echo signals, the amplitude and phase signals of the background need to be measured before the target is erected, so that vector background cancellation can be carried out.
The frequency of the microwave amplitude and phase measurement section needs to cover the frequency band in which the radar operates. The working mode is two modes of spot frequency and frequency sweep, and the latter mainly aims at carrying out high-resolution inverse synthetic aperture imaging (identification and diagnosis). For phase measurement, a coherent receiver mode is used.
The signal processing section includes: vector background cancellation, NFFFT and microwave imaging.
The specific embodiment of the cylindrical near-field backward RCS test system shown in fig. 2 is as follows.
1, measuring complex reflected signals F of background and supportB(φ)；
2, placing the calibration body on a bracket in front of a quiet area, and measuring a plurality of reflection signals FC(φ)；
And 3, erecting the measured target to a measuring height through two support rods and a lifting rope. The turntable rotates to drive the target to rotate at an azimuth angle phi, the lifting rope is positioned at the rotating center of the turntable, and the pitch angle theta of the target can be changed by stretching and contracting the lifting rope;
4, setting the pitch angle of the target, driving the target to rotate at an azimuth angle phi by the rotary table, emitting a signal with a frequency by the radar to irradiate the target, and receiving a plurality of reflected signals F of the target by the receiverT(phi), including amplitude and phase;
5, scaling the near-field echo signals,
in the formula FCRadar scattering cross section sigma of calibrated bodyCThe corresponding reflected signal.
6, to FNPerforming difference operation, and performing 2DFFT to obtain ENThe appropriate difference will be such that ENThe equal spacing distribution in the x and y planes;
7, E of formula (5)iAnd ENThe calculation is carried out by using the formula (4),
the method for determining the scaling coefficient C of NFFFT in the formula:
measuring near-field scattering coefficient F of calibration sphere under near-field conditionN(φ)；
Second, the block diagram of FIG. 7 is used to calculate the far field coefficient F of the calibration sphere0(φ)；
③ changing the coefficient C when F0(φ)＝FNWhen (phi), C converges.
8, from E02DIFFT and interpolation are carried out to obtain a far field scattering coefficient F0(phi) |, which are equally spaced apart in the angular domain phi.
9, calculating the RCS of the received signals,
σ(φ)|θ＝20logF0(φ)|θ|。
Claims (5)
1. a near-field backward RCS measuring method based on a chain relational expression is characterized in that: irradiating a target of about 20m in size with a line source at a short distance of 50-200 m to obtain a complex scattering coefficient F of the near fieldNThen, the far-field RCS of the target is directly calculated according to the chain relation; far field scattering coefficient F0(theta, phi) and near field scattering coefficient FNThe relationship of (θ, φ) is:
in the formula, (theta, phi) is a pitch angle and an azimuth angle of the measured target respectively;
in a near-field RCS measuring system, a radar is positioned at an O 'point position and is fixed, a measured target rotates around a rotating center O of a turntable at a pitch angle theta and an azimuth angle phi, a rectangular coordinate system is x, y, the origin of z is O, the y coordinate is vertical to the ground, the x coordinate is parallel to the ground and is orthogonal to a straight line OO';
Ei(x, y) is the electric field distribution in the x, y plane calculated as geometric optics, 2DFFT is the two-dimensional Fourier transform, and 2DIFFT is the two-dimensional inverse Fourier transform, which implement the transform between the spatial (x, y) and angular (θ, φ) domains.
2. The near-field backward RCS measurement method based on the chain relation formula as claimed in claim 1, wherein: far field scattering coefficient F0(θ, φ) is related to the far-field radar scattering cross-section of the target, σ (θ, φ), by:
σ(θ,φ)＝20log|F0(θ,φ)|
in the formula, (theta, phi) is the pitch angle and the azimuth angle of the measured target respectively.
3. The near-field backward RCS measurement method based on the chain relation formula as claimed in claim 1, wherein: the method is characterized in that a line source is adopted to irradiate a target, the line source is a kind of emission source which generates cylindrical wave, different from spherical wave, the ray of the line source in the height direction is parallel ray, far field condition is satisfied, and divergent ray is generated in the horizontal direction, therefore, the necessary near-field far-field transformation (NFFFT for short) of RCS measurement only needs to be carried out in the horizontal direction, namely the azimuth angle phi direction, or half of the near-field far-field transformation is completed by adopting a physical method, namely a parabolic cylinder method, and half is completed by adopting a mathematical chain relation;
in this case, the chain relation for NFFFT is simplified to:
in the formula F0(phi) is the far field scattering coefficient, FN(phi) is the near field scattering coefficient, Ei(x) The electric field distribution in the x coordinate direction calculated according to geometric optics, the azimuth angle of a phi measured target, FFT (fast Fourier transform) and IFFT (inverse Fourier transform);
obviously, the near-far field transformation of the above formula is simplified from two-dimensional transformation to one-dimensional transformation;
under the irradiation of a cylindrical surface field, the electric field distribution on a plane xy is only a function of a coordinate x and is independent of the coordinate y, and the field distribution is as follows:
where s (x) is the distance from the point O' of the line source to the point x, d (x) s (x) -R, and R is the distance from the radar to the target.
4. The near-field backward RCS measurement method based on the chain relation formula as claimed in claim 1, wherein: the single cylindrical compact field is composed of a parabolic cylinder and a feed source, spherical waves generated by the feed source are converted into cylindrical waves in a short distance, the cylindrical waves are converted into rays parallel to an xz plane in the height direction under the action of the parabolic cylinder, divergent rays are generated in the horizontal direction under the reflection action of a horizontal sectional line of the parabolic cylinder, and a line source is formed at a mirror image point.
5. The utility model provides a RCS measurement system behind near field based on chain relational expression which characterized in that: the system consists of three parts, namely a target and environment, a microwave amplitude and phase measurement system and a signal processing system, wherein the target is placed in a conical microwave darkroom, rotation on a horizontal plane is realized through support and a turntable, spherical waves are emitted by an emitting antenna, and the spherical waves are reflected into cylindrical waves through a parabolic cylinder and irradiate the target; receiving scattered electromagnetic waves of a target by a receiving antenna, and carrying out amplitude-phase measurement by down-converting the scattered electromagnetic waves to an intermediate frequency; and after being filtered by the matched filter, the amplitude-phase information is transmitted to a signal processing system for signal processing, and the RCS information of the target is obtained through NFFFT conversion.
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| CN112764001B (en) * | 2020-12-25 | 2024-01-30 | 中国航空工业集团公司沈阳飞机设计研究所 | External field RCS test field |
| CN112731301B (en) * | 2020-12-29 | 2023-06-09 | 北京环境特性研究所 | Interference suppression method and device for disc-shaped clutter simulation measurement |
| CN112859072A (en) * | 2021-01-20 | 2021-05-28 | 北京环境特性研究所 | Radar system based on planar MIMO array and three-dimensional imaging method |
| CN112859028B (en) * | 2021-01-20 | 2024-01-30 | 西安电子科技大学 | Method and system for collecting and spectrum analyzing scattering time domain echo of external field object |
| CN113589051A (en) * | 2021-08-04 | 2021-11-02 | 西安电子科技大学 | Clutter suppression field electromagnetic measurement device and method |
| CN117805754B (en) * | 2024-02-29 | 2024-06-04 | 西安瀚博电子科技有限公司 | Efficient near-field RCS test method and system based on amplitude and phase electric control technology |
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