CN108445303B - Near-field electromagnetic scattering characteristic simulation method - Google Patents
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Abstract
The invention relates to a near-field electromagnetic scattering characteristic simulation method, and relates to the technical field of electromagnetic scattering. Wherein, the method comprises the following steps: subdividing a target to obtain a plurality of surface elements; generating a matrix equation of each surface element under a near-field condition according to a multilayer rapid multistage sub-algorithm, and then obtaining the current on the surface element through the matrix equation; determining a polarization receiving electric field corresponding to the surface element according to the current on the surface element; and carrying out vector superposition processing on the polarized receiving electric fields corresponding to all surface elements to obtain the characterization parameters of the electromagnetic scattering characteristics of the target under the near-field condition. Through the steps, the precision and universality of the target near-field electromagnetic scattering characteristic simulation result can be improved, and the method can be widely applied to the research on the near-field electromagnetic scattering characteristic of the target under the conditions of various antenna irradiation and bullet-and-eye interaction.
Description
Technical Field
The invention relates to the technical field of electromagnetic scattering, in particular to a near-field electromagnetic scattering characteristic simulation method.
Background
Near-field electromagnetic scattering property research of targets is an important field of target scattering property research. Different from a mature far-field electromagnetic scattering theory, the target presents a body target effect under a near-field condition, and the radar echo characteristic of the target is influenced by multiple factors such as a spherical wave effect, an antenna directional diagram, local irradiation and the like.
Currently, a high-frequency approximation method (such as a physical optical method) is mostly used to calculate the near-field electromagnetic scattering property of the target. The existing method can not calculate the effect generated by electromagnetic coupling between parts of a complex target, and mostly does not consider the influence of factors such as an antenna directional diagram, local illumination and the like.
With the increase of the complexity of the environment where the target is located and the requirement of high precision of the calculation result, the research requirement on the near-field electromagnetic scattering property of the target is more urgent. Therefore, it is necessary to research a method for accurately simulating the near-field electromagnetic scattering characteristics of a complex target to improve the accuracy and universality of the near-field electromagnetic scattering characteristic calculation.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for simulating near-field electromagnetic scattering characteristics, aiming at the defects in the prior art.
In order to solve the technical problem, the invention provides a method for simulating near-field electromagnetic scattering characteristics.
The method for simulating the near-field electromagnetic scattering property provided by the invention comprises the following steps: dividing the target to obtain a plurality of surface elements; generating a matrix equation of each surface element under a near-field condition according to a multilayer rapid multistage sub-algorithm, and then obtaining the current on the surface element through the matrix equation; determining a polarization receiving electric field corresponding to the bin according to the current on the bin; and carrying out vector superposition processing on the polarized receiving electric fields corresponding to all surface elements to obtain the characterization parameters of the electromagnetic scattering characteristics of the target under the near-field condition.
Optionally, the step of generating a matrix equation of each bin under a near-field condition according to a multi-layer fast multilevel sub-algorithm includes: and calculating a near-field incident excitation item corresponding to each surface element and an impedance matrix corresponding to each surface element according to a multilayer rapid multistage sub-algorithm so as to generate a matrix equation of each surface element under the near-field condition.
Optionally, the step of calculating the near-field incident excitation item corresponding to each bin according to a multi-layer fast multilevel sub-algorithm includes: obtaining an incident electric field and an incident magnetic field of the surface element surface according to the polarized incident electric field model of the surface element; and constructing a near-field incident excitation item corresponding to the surface element according to the incident electric field and the incident magnetic field of the surface element surface.
Optionally, the polarized incident electric field model comprises: a linearly polarized incident electric field model, an elliptically polarized incident electric field model, or a circularly polarized incident electric field model.
Optionally, the step of obtaining the incident electric field and the incident magnetic field of the surface element according to the polarized incident electric field model of the surface element includes: the following influence parameters were calculated, including: the relative phase of incident electromagnetic waves on the surface element surface is increased, the distance between the surface element and the transmitting antenna is increased, and the power gain of the incident electromagnetic waves corresponding to the surface element is increased; substituting the calculation result of the influence parameter into a polarization incident electric field model of the surface element to obtain an incident electric field of the surface element surface; and obtaining the incident magnetic field of the surface element according to the right-hand spiral relation between the electric field and the magnetic field.
Optionally, the method further comprises calculating a power gain of the incident electromagnetic wave for the bin corresponding according to: under the condition that a directional diagram of the transmitting antenna is known, calculating the power gain of incident electromagnetic waves corresponding to the surface element according to the angle information of the incident waves; and under the condition that the direction diagram of the transmitting antenna is unknown but the power gain of the transmitting antenna at a plurality of discrete angles is known, obtaining the power gain of the incident electromagnetic wave corresponding to the surface element according to Lagrange one-dimensional interpolation.
Optionally, the method further comprises calculating a power gain of the incident electromagnetic wave for the bin corresponding according to: under the condition that the beam width of the transmitting antenna is known, power directivity functions of the antenna in two specified directions of incident waves are obtained according to the graphic characteristics of the sinc function, and then the power gain of the incident electromagnetic waves corresponding to the surface element is calculated according to the power directivity functions.
Optionally, the step of obtaining the current on the bin through the matrix equation includes: and iteratively solving the matrix equation according to a generalized minimum residual method to obtain the current on the surface element.
Optionally, the characterizing quantity of the electromagnetic scattering property includes: near field reflected power ratio of the target, near field RCS of the target.
Optionally, the near-field reflected power ratio of the target satisfies:
in the formula, DiDirection coefficient representing the maximum radiation direction of the transmitting antenna, DsA direction coefficient representing the maximum radiation direction of the receiving antenna, λ beingWavelength of incident electromagnetic wave, m represents mth bin of target, FimRepresenting the direction function of the m-th surface element of the object in the direction of the incident electromagnetic wave emitted by the transmitting antenna, FsmRepresenting the direction function, R, of the m-th surface element of the object in the direction of the scattered electromagnetic wave received by the receiving antennaimRepresenting the distance, R, between the m-th surface element of the target and the transmitting antennasmDenotes the distance between the m-th surface element of the object and the receiving antenna, EimRepresenting the polarized incident electric field of the m-th bin, EsmRepresenting the polarization acceptance electric field of the mth bin.
Optionally, the near-field RCS of the target satisfies:
in the formula, RiRepresenting the distance, R, between the reference point of the field point of the target and the transmitting antennasRepresenting the distance between the reference point of the field point of the object and the receiving antenna, Fi 2Normalized power direction function reference value, F, representing the main lobe of the transmitting antennas 2A normalized power direction function reference value representing a main lobe of a receiving antenna, m represents the mth surface element of the target, FimRepresenting the direction function of the m-th surface element of the target in the direction of the incident electromagnetic wave emitted by the transmitting antenna, FsmRepresenting the direction function, R, of the m-th surface element of the object in the direction of the scattered electromagnetic wave received by the receiving antennaimRepresenting the distance, R, between the mth bin of the target and the transmitting antennasmDenotes the distance between the m-th surface element of the target and the receiving antenna, EimRepresenting the polarized incident electric field of the m-th bin, EsmRepresenting the polarization acceptance electric field of the mth planar element.
The implementation of the invention has the following beneficial effects:
according to the method, a surface element is divided for a target, a matrix equation of each surface element under a near-field condition is generated according to a multilayer rapid multistage sub-algorithm, then the current on the surface element is obtained through the matrix equation, the polarization receiving electric fields corresponding to the surface elements are determined according to the current on the surface element, vector superposition processing is carried out on the polarization receiving electric fields corresponding to all the surface elements, and the like, so that the characterization parameters of the electromagnetic scattering characteristics of the target under the near-field condition can be obtained. Compared with the prior art, the method can improve the precision and universality of the target near-field electromagnetic scattering characteristic simulation result, and can be widely applied to the research of the near-field scattering characteristic of the target under the conditions of various antenna irradiation and bullet interaction.
Drawings
Fig. 1 is a schematic diagram of main steps of a near-field electromagnetic scattering property simulation method according to a first embodiment of the present invention;
fig. 2 is a schematic diagram of main steps of a near-field electromagnetic scattering characteristic simulation method according to a second embodiment of the present invention.
FIG. 3 is a schematic diagram of a target coordinate system and an antenna coordinate system;
FIG. 4 is a schematic diagram of the incidence of electromagnetic waves emitted by a transmitting antenna at different surface elements of a target;
fig. 5 is a schematic diagram of antenna beams in an antenna coordinate system.
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 derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example one
Fig. 1 is a schematic diagram of main steps of a near-field electromagnetic scattering characteristic simulation method according to a first embodiment of the present invention. As shown in fig. 1, a method for simulating near-field electromagnetic scattering characteristics according to an embodiment of the present invention includes:
step S101, subdividing the target to obtain a plurality of surface elements.
For example, the target may be split into a plurality of triangular bins.
And S102, generating a matrix equation of each surface element under the near-field condition according to a multilayer rapid multistage sub-algorithm.
The multilayer fast multipole method is based on Maxwell equation and strict electromagnetic theory derivation, can deal with various structures and scattering mechanisms, has high calculation precision, and is an efficient and accurate numerical calculation method.
Specifically, when a matrix equation under a near field condition is generated according to a multilayer fast multipole method, the influence of factors such as a spherical wave effect, an antenna directional diagram, local illumination and an electromagnetic coupling effect is considered, and the phenomena of low calculation precision and non-coincidence of a calculation curve and a measured value caused by the problems of incapability of calculating a detailed structure, incapability of calculating an electromagnetic coupling effect, difficulty in processing a complex electromagnetic scattering mechanism (such as traveling waves, peristaltic waves and the like) and the like in a high-frequency approximation method are avoided, so that the calculation precision of the near field scattering property of a complex target is greatly improved.
And step S103, obtaining the current on the surface element through the matrix equation.
Illustratively, the matrix equation is solved iteratively according to a generalized minimum residual method (GMRES) to obtain the currents on the bins.
And step S104, determining a polarization receiving electric field corresponding to the surface element according to the current on the surface element.
Wherein, the polarization receiving electric field corresponding to the surface element can be understood as: and receiving the scattered electric field from the target surface element received by the antenna.
And S105, carrying out vector superposition processing on the polarized receiving electric fields corresponding to all surface elements to obtain the characterization parameters of the electromagnetic scattering characteristics of the target under the near-field condition.
Wherein the characterizing parameters of the electromagnetic scattering property include: near field reflected power ratio of the target, near field RCS (radar scattering cross section) of the target.
In the embodiment of the invention, an accurate solving model of the near-field electromagnetic scattering property of the target is established through the steps, and the solving model can be used for calculating the near-field scattering property of the target under the conditions of various antenna irradiation and target rejection.
Example two
Fig. 2 is a schematic diagram of main steps of a near-field electromagnetic scattering characteristic simulation method according to a second embodiment of the present invention. As shown in fig. 2, the method for simulating near-field electromagnetic scattering characteristics according to the embodiment of the present invention includes:
step S201, establishing a target coordinate system and an antenna coordinate system.
Fig. 3 is a schematic diagram of a target coordinate system and an antenna coordinate system. As shown in FIG. 3, the target coordinate system may be represented by xtytztThe antenna coordinate system may be represented by xayazaAnd (4) showing. Wherein the coordinate of the antenna in the target coordinate system is (x)0,y0,z0) Three euler angles (α, γ) may be used to describe the relative rotational orientation of the two coordinate systems, where α is the precession angle, β is the nutation angle, γ is the rotation angle, and the rotation matrix at each rotational orientation may be expressed as:
further, a rotation matrix from the target coordinate system to the antenna coordinate system can be obtained as follows:
R(α,β,γ)＝Z(γ)N(β)Z(α)
furthermore, the target coordinate system can be coincided with the antenna coordinate system through position translation and rotation transformation based on three Euler angles, so that the relative position and the posture of the target and the antenna can be described, and meanwhile, the method can be used for mutual conversion of variables (such as wave vector vectors and the like) in the two coordinate systems.
Step S202, the target is subdivided to obtain a plurality of surface elements.
In this step, the target may be split into a plurality of triangular bins. Hypothesis targetThe center coordinate of the mth triangular surface element in the target coordinate system is (x)m,ym,zm)，m＝1,2,ΛN0. Wherein N is0The total number of triangular bins included for the target. Further, assume that the coordinates of the transmitting antenna in the target coordinate system are (x)0,y0,z0). Furthermore, each influence parameter corresponding to the mth surface element of the target can be conveniently calculated in the next step.
Step S203, calculating an influence parameter corresponding to each bin, including: the distance between the surface element and the emission antenna, the relative phase increase of incident electromagnetic waves on the surface element surface and the power gain of the incident electromagnetic waves corresponding to the surface element.
As shown in fig. 4, when the distance between the antenna and the target does not satisfy the far-field condition, the spherical wave has a large influence, and the parameters, such as the wave vector of the target, the relative phase increase, and the like, are related to the distance and the relative attitude between the target and the antenna. In addition, since the distances between different parts of the target and the antenna are different (cannot be approximately equal), the distance attenuation of the incident and scattered electromagnetic fields between different bins of the target and the antenna is also different. Therefore, the influence parameters need to be calculated based on bins, which specifically includes:
a) and calculating the distance between the mth surface element and the transmitting antenna.
For example, the distance between the mth bin and the transmitting antenna may be calculated according to the following formula:
in the formula,
is the distance vector between the mth bin and the transmitting antenna, RinIs the distance value between the m-th surface element and the transmitting antenna.
b) Calculate the firstUnit wave vector k of incident electromagnetic wave at m surface element centerin。
For example, the unit wave vector k of the incident electromagnetic wave at the center of the m-th surface element can be calculated according to the following formulainComprises the following steps:
for an increase in the relative phase of the incident electromagnetic wave at the center of each bin, the antenna position can be calculated as the phase null. Further, the relative phase of the incident electromagnetic wave at the center of the m-th surface element is increased by Δ φimComprises the following steps:
wherein,
is the wave number.
c) And calculating the angle of the incident wave vector of the mth surface element in the antenna coordinate system.
As shown in FIG. 5, the unit wave vector at the center of the m-th surface element in the antenna coordinate system can be expressed as kim-aThe angle of the incident wave vector of the mth bin in the antenna coordinate system can be expressed as thetaim、
For example, the angle of the incident wave vector of the mth bin in the antenna coordinate system can be calculated according to the following formula:
θim＝arcos(z(kim-a))
kim-a＝R(α,β,γ)·kim
wherein, thetaimThe incident wave vector of the m-th bin and zaThe included angle of the axes is set by the angle,
the incident wave vector of the m surface element is in xaoyaProjection of plane and xaThe angle of the axes.
d) And calculating the power gain of the incident electromagnetic wave of the mth surface element surface.
For example, the power gain of the incident electromagnetic wave on the mth surface element surface can be calculated separately in the following two cases.
In the first case: the pattern of the transmit antenna or the power gain over discrete angles is known.
1.1) in the known transmitting antenna pattern (e.g. power direction function of the antenna)
Or field strength direction function of the antenna
) In the case of (3), the power gain of the incident electromagnetic wave corresponding to the bin can be calculated according to the angle information of the incident wave, and the calculation formula is as follows:
in the formula, GimThe power gain of the incident electromagnetic wave of the mth surface element surface. Thetaim、
Is the angle of the incident wave vector of the first m-bin in the antenna coordinate system (referred to as "incident angle of the first m-bin" for short).
1.2) Pattern at unknown transmit antenna, but known transmit antenna at multiple discrete angles θj(j＝1,2,…M)、
Under the condition of the power gain, the power gain of the incident electromagnetic wave corresponding to the surface element can be obtained according to Lagrange one-dimensional interpolation, and the calculation formula is as follows:
in the formula, Pexample1(θj) At a discrete angle thetajThe gain of the power at the output of the power amplifier,
at an angle of divergence
Power gain of P (theta)im)、
For the power gain at the angle of incidence of the mth bin,
the power gain of the incident electromagnetic wave corresponding to the mth surface element,
the field intensity gain of the incident electromagnetic wave corresponding to the mth surface element.
In the second case: only the beamwidth of the transmit antenna is defined.
When the electromagnetic scattering property of a target extremely near field is researched, the electromagnetic scattering result is extremely sensitive to the width of an antenna lobe due to the fact that the local illumination effect under the extremely near field condition is particularly obvious, and therefore an antenna directional diagram is only required to meet the requirement of the set lobe width.
Specifically, in the second case, power directivity functions of the antenna in two specified directions of the incident wave can be obtained according to the pattern characteristics of the sinc function, and then the power gain of the incident electromagnetic wave corresponding to the bin is calculated according to the power directivity functions. Wherein the power directivity functions in the two specified directions are as follows:
according to the power directivity functions in the two specified directions, the power gain of the incident electromagnetic wave of the m surface element can be calculated
And the field intensity gain of the incident electromagnetic wave of the mth bin
And S204, substituting the influence parameters corresponding to the surface elements into the polarized incident electric field model of the surface elements to obtain the incident electric field of the surface elements.
Wherein the polarized incident electric field model of the bin comprises: a linearly polarized incident electric field model of a bin, an elliptically polarized incident electric field model of a bin, or a circularly polarized incident electric field model of a bin. The linearly polarized incident electric field model of the surface element can be divided into a horizontal polarization model, a vertical polarization model or a general linearly polarized model of the surface element.
For example, the horizontal polarization incident electric field model of the mth bin in the antenna coordinate system can be expressed as:
EH-a(z)＝0
EimH-a＝EH-acos(ωt+φH)
EimH＝R-1(α,β,γ)gEimH-a
in the formula,
the angle of the incident wave vector of the mth surface element in the antenna coordinate system; omega is the angular frequency of the electromagnetic wave; t is time; phi is aHIs an arbitrary constant; r-1(α, gamma) is obtained by inverting R (α, gamma) and is a rotation matrix from the antenna coordinate system to the target coordinate system, EH-a(x)、EH-a(y)、 EH-a(z) respectively representing the amplitude components of the incident electric field of the m-th surface element in the horizontal polarization unit in the antenna coordinate system on each coordinate axis; eimH-aThe horizontal polarization unit incident electric field vector of the mth surface element in the antenna coordinate system; eimHAnd (3) horizontally polarizing the unit incident electric field vector of the mth surface element in the target coordinate system.
In addition, the vertical polarization incident electric field model of the mth surface element in the antenna coordinate system can be expressed as:
EV-a(z)＝-sinθim
EimV-a＝EV-acos(ωt+φV)
EimV＝R-1(α,β,γ)gEimV-a
in the formula, thetaim、
The angle of the incident wave vector of the mth surface element in the antenna coordinate system; omega is the angular frequency of the electromagnetic wave; t is time; phi is aVIs an arbitrary constant; r-1(α,β,γ)Obtained by inverting R (α, gamma) to obtain a rotation matrix from the antenna coordinate system to the target coordinate system, EV-a(x)、EV-a(y)、 EV-a(z) respectively representing the amplitude components of the incident electric field of the vertical polarization unit of the mth surface element in the antenna coordinate system on each coordinate axis; eimV-aThe vertical polarization unit incident electric field vector of the mth surface element in the antenna coordinate system; eimVAnd (3) vertically polarizing the unit incident electric field vector of the mth surface element in the target coordinate system.
In addition, the general linearly polarized incident electric field model of the m-th surface element in the antenna coordinate system can be expressed as:
EimL＝R-1(α,β,γ)gEimL-a
in the formula, C0Is an arbitrary constant; omega is the angular frequency of the electromagnetic wave; t is time; phi is an arbitrary constant; r-1(α, gamma) is obtained by inverting R (α, gamma) and is a rotation matrix from the antenna coordinate system to the target coordinate system, EimL-aThe general polarization unit of the m surface element in the antenna coordinate system is used as an incident electric field vector; eimLThe incident electric field vector is the general polarization unit of the mth bin in the target coordinate system.
The elliptical polarization and circular polarization incident electric field model of the m-th surface element in the antenna coordinate system can be obtained by linear combination of a vertical polarization incident electric field vector and a horizontal polarization incident electric field vector after a certain initial phase is given, and is not given one by one here.
And S205, obtaining an incident magnetic field of the surface element surface according to the right-hand spiral relation between the electric field and the magnetic field.
And S206, constructing a near-field incident excitation item corresponding to the surface element and an impedance matrix corresponding to the surface element according to the multilayer rapid multi-level sub-algorithm to generate a matrix equation of the surface element under the near-field condition.
Wherein, the near-field incident excitation item corresponding to the mth surface element can be represented as CmThe method comprises the following steps:
in the formula, gmIn order to select the basis functions for use,
is the incident electric field of the mth surface element,
is the incident magnetic field of the mth surface element surface, a1For the combined field coefficient, η is the wave impedance, dS' is the bin differential of the mth bin, [ integral ] fS'dS' indicates that the integration calculation is performed in the mth bin.
Wherein, the impedance matrix corresponding to the mth bin and the nth bin can be represented as [ Z [ ]mn]The matrix reflects the electromagnetic coupling property between different edge currents of the target.
Furthermore, the matrix equation of the mth surface element under the near field condition is as follows:
in the formula, bnIs the current coefficient of the surface element edge, N1The total number of other bins having a coupling effect on the mth bin.
And step S207, iteratively solving the matrix equation according to a generalized minimum residual error method to obtain the current on the surface element.
Specifically, current J on the m-th surface elementm(r) can be expressed as:
in the formula, niRepresenting the common edge, g, corresponding to the ith edge of the mth binniAs selected basis functions, bniAre the expansion coefficients of the corresponding basis functions.
And S208, determining a polarized receiving electric field corresponding to the bin according to the current on the bin.
Specifically, the scattering electric field E 'of the mth surface element can be obtained by adopting a Stratton-Chu integral formula'sm(r) of (A). Then, considering different antenna patterns and polarized reception, can be according to E'sm(r) obtaining a polarized reception electric field E on the m-th surface elementsm(r)。
Step S209, the polarized receiving electric fields corresponding to all surface elements are subjected to vector superposition processing to obtain the characterization parameters of the electromagnetic scattering characteristics of the target under the near-field condition.
Wherein the characterizing parameters of the electromagnetic scattering property may include: near field reflection power ratio of the target, near field RCS (radar scattering cross section) of the target. Further, the near-field reflected power ratio of the target satisfies:
in the formula, DiDirection coefficient representing the maximum radiation direction of the transmitting antenna, DsA directional coefficient representing a maximum radiation direction of the receiving antenna, λ is a wavelength of the incident electromagnetic wave, m represents an mth bin of the target, and FimRepresenting the direction function of the m-th surface element of the object in the direction of the incident electromagnetic wave emitted by the transmitting antenna, FsmRepresenting the direction function, R, of the m-th surface element of the object in the direction of the scattered electromagnetic wave received by the receiving antennaimRepresenting the distance, R, between the m-th surface element of the target and the transmitting antennasmDenotes the distance between the m-th surface element of the object and the receiving antenna, EimRepresenting the polarized incident electric field of the m-th bin, EsmRepresenting the polarization acceptance electric field of the mth bin.
Further, the near-field RCS of the target satisfies:
in the formula, RiRepresenting the distance, R, between the reference point of the field point of the target and the transmitting antennasRepresenting objectsThe distance between the field point reference point and the receiving antenna, Fi 2Normalized power direction function reference value, F, representing the main lobe of the transmitting antennas 2A normalized power direction function reference value representing a main lobe of a receiving antenna, m represents the mth surface element of the target, FimRepresenting the direction function of the m-th surface element of the target in the direction of the incident electromagnetic wave emitted by the transmitting antenna, FsmRepresenting the direction function, R, of the m-th surface element of the object in the direction of the scattered electromagnetic wave received by the receiving antennaimRepresenting the distance, R, between the mth bin of the target and the transmitting antennasmDenotes the distance between the m-th surface element of the target and the receiving antenna, EimRepresenting the polarized incident electric field of the m-th bin, EsmRepresenting the polarization acceptance electric field of the mth planar element.
The method of the embodiment of the invention can at least realize one or more of the following technical effects:
1. a complex target near-field scattering characteristic simulation model is established and can be used for calculating the near-field scattering characteristics of the target under the conditions of various antenna irradiation and bullet-and-eye intersection. During specific implementation, the near-field scattering characteristic of a certain missile model under the rendezvous condition is simulated according to the target near-field scattering characteristic simulation model, the comparison result is compared with the actual measurement result, and the accuracy of the complex target near-field scattering characteristic simulation model is fully verified according to the comparison result.
2. By adopting a multilayer fast multipole algorithm and simultaneously considering the spherical wave effect, the antenna direction diagram, the local irradiation, the electromagnetic coupling effect and other influence factors, the problems of low calculation precision and the phenomenon that a calculation curve is not matched with a measured value due to the problems of incapability of calculating a detailed structure, incapability of calculating the electromagnetic coupling effect, difficulty in processing complex electromagnetic scattering mechanisms (such as traveling waves, peristaltic waves and the like) and the like in a high-frequency approximation method are avoided, and the calculation precision of the near-field scattering characteristic of a complex target is greatly improved.
3. The near-field RCS and the near-field reflection power ratio are obtained, and the near-field RCS and the near-field reflection power ratio can be used for accurately quantitatively describing the scattering characteristics of the target under the near-field condition.
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 should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may 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.
Claims (5)
1. A method for simulating near-field electromagnetic scattering characteristics, the method comprising:
subdividing a target to obtain a plurality of surface elements;
generating a matrix equation of each surface element under a near-field condition according to a multilayer rapid multistage sub-algorithm, and then obtaining the current on the surface element through the matrix equation;
determining a polarization receiving electric field corresponding to the surface element according to the current on the surface element;
carrying out vector superposition processing on the polarized receiving electric fields corresponding to all surface elements to obtain a characterization parameter of the electromagnetic scattering characteristic of the target under the near-field condition;
the step of generating a matrix equation of each bin under the near-field condition according to the multilayer fast multilevel sub-algorithm comprises the following steps:
calculating a near-field incident excitation item corresponding to each surface element and an impedance matrix corresponding to each surface element according to a multilayer rapid multistage sub-algorithm so as to generate a matrix equation of each surface element under a near-field condition; the step of calculating the near-field incident excitation item corresponding to each bin according to the multilayer fast multilevel sub-algorithm comprises the following steps:
obtaining an incident electric field and an incident magnetic field of the surface element surface according to the polarized incident electric field model of the surface element; constructing a near-field incident excitation item corresponding to the surface element according to the incident electric field and the incident magnetic field of the surface element surface;
the step of obtaining the incident electric field and the incident magnetic field of the surface element surface according to the polarized incident electric field model of the surface element comprises the following steps:
the following influence parameters were calculated, including: the relative phase of incident electromagnetic waves on the surface element surface is increased, the distance between the surface element and the transmitting antenna is increased, and the power gain of the incident electromagnetic waves corresponding to the surface element is increased; substituting the calculation result of the influence parameter into a polarization incident electric field model of the surface element to obtain an incident electric field of the surface element surface; obtaining an incident magnetic field of a surface element according to the right-hand spiral relation between the electric field and the magnetic field;
the characterizing parameters of the electromagnetic scattering property include: the near field reflected power ratio of the target, the near field RCS of the target;
the near-field reflected power ratio of the target satisfies:
in the formula, DiDirection coefficient representing the maximum radiation direction of the transmitting antenna, DsA directional coefficient representing a maximum radiation direction of the receiving antenna, λ is a wavelength of the incident electromagnetic wave, m represents an m-th surface element of the target, FimRepresenting the direction function of the m-th surface element of the target in the direction of the incident electromagnetic wave emitted by the transmitting antenna, FsmRepresenting the direction function, R, of the m-th surface element of the object in the direction of the scattered electromagnetic wave received by the receiving antennaimRepresenting the distance, R, between the m-th surface element of the target and the transmitting antennasmDenotes the distance between the m-th surface element of the object and the receiving antenna, EimRepresenting the polarized incident electric field of the m-th bin, EsmRepresenting the polarization acceptance electric field of the mth bin;
the near-field RCS of the target satisfies:
in the formula, RiRepresenting the distance, R, between the reference point of the field point of the target and the transmitting antennasRepresenting the distance between the reference point of the field point of the object and the receiving antenna, Fi 2Reference value of a normalized power direction function, F, representing the main lobe of a transmitting antennas 2Normalized work representing the main lobe of a receiving antennaReference value of the rate-direction function, m denotes the m-th surface element of the target, FimRepresenting the direction function of the m-th surface element of the target in the direction of the incident electromagnetic wave emitted by the transmitting antenna, FsmRepresenting the direction function, R, of the m-th surface element of the object in the direction of the scattered electromagnetic wave received by the receiving antennaimRepresenting the distance, R, between the m-th surface element of the target and the transmitting antennasmDenotes the distance between the m-th surface element of the object and the receiving antenna, EimRepresenting the polarized incident electric field of the m-th bin, EsmRepresenting the polarization acceptance electric field of the mth bin.
2. The method of claim 1, wherein the polarized incident electric field model comprises: a linearly polarized incident electric field model, an elliptically polarized incident electric field model, or a circularly polarized incident electric field model.
3. The method of claim 1, further comprising calculating a power gain of the binned incident electromagnetic wave according to:
under the condition that a directional diagram of the transmitting antenna is known, calculating the power gain of incident electromagnetic waves corresponding to the surface element according to the angle information of the incident waves; and under the condition that the directional diagram of the transmitting antenna is unknown but the power gain of the transmitting antenna on a plurality of discrete angles is known, obtaining the power gain of the incident electromagnetic wave corresponding to the surface element according to Lagrange one-dimensional interpolation.
4. The method of claim 1, further comprising calculating a power gain of the binned incident electromagnetic wave according to:
under the condition that the beam width of the transmitting antenna is known, power directivity functions of the antenna in two specified directions of incident waves are obtained according to the graphic characteristics of the sinc function, and then the power gain of the incident electromagnetic waves corresponding to the surface element is calculated according to the power directivity functions.
5. The method of claim 1, wherein the step of deriving the current over a bin by the matrix equation comprises:
and iteratively solving the matrix equation according to a generalized minimum residual method to obtain the current on the surface element.
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