CN116502524A - RCS reduction method for metal structure under broadband scanning - Google Patents

Abstract

The invention discloses a method for reducing the RCS of a metal structure under broadband scanning, comprising the following steps: S1. Given a working frequency band, incident plane wave parameters and a geometric model of the metal structure; S2. Selecting discrete frequency points under the frequency band to establish a metal structure Impedance matrices are combined, and the radiation basis vector and singular value under the structure broadband are obtained by using singular value decomposition; S3. Based on the size of the singular value, determine the position of the main radiation of the structure under the broadband and set it as the loading position; S4. Use impedance loading to carry out For current regulation, the impedance loading value on the surface of the metal structure is determined by the method of moments and GA genetic algorithm. The invention uses SVD decomposition to obtain the radiation characteristics of the structure under broadband, finds the best loading position, regulates the singular value through impedance loading, and optimizes the loading resistance through a genetic algorithm, and finally physically realizes the required singular value , thereby regulating the current and effectively improving the efficiency of the RCS reduction design.

Description

A RCS Reduction Method for Metal Structures under Broadband Scanning

technical field

The invention relates to RCS reduction and reduction of metal structures, in particular to a method for RCS reduction and reduction of metal structures under broadband scanning.

Background technique

For aircraft, improving the stealth capability is to reduce the radar cross section (Radar Cross Section, RCS). RCS is the main parameter to measure the scattering intensity of an object and describe the stealth performance of an object. The smaller the RCS of an object, the better its stealth performance in an electromagnetic environment.

One of the difficulties in realizing the RCS reduction of the aircraft is to realize the RCS reduction of the antenna installed on the aircraft. First of all, with the development of military science and technology and communication technology, various antennas are installed on the aircraft, which makes the number of antennas on the aircraft large, so it becomes difficult to realize the stealth of the antennas on the aircraft. Secondly, due to the particularity of the antenna, the antenna cannot realize its own invisibility by coating the outer shell with stealth materials such as electromagnetic wave absorbing materials like other non-signal transmitting and receiving devices such as the upper shell of the aircraft. Moreover, the antenna must be exposed to work outside the metal casing. It is also impossible to change the shape of the fuselage to achieve the stealth of the antenna, because changing the shape of the antenna will definitely bring about changes in the performance of the antenna.

Therefore, it becomes more difficult to realize the stealth of the antenna on the aircraft. In addition, there are many types of radars and their operating frequencies are widely distributed. Therefore, for aircraft antennas, it is also necessary to consider the RCS reduction under broadband scanning rather than the design under a single frequency point.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a method for RCS reduction of metal structures under broadband scanning, which can physically realize the ideal singular value of the broadband impedance matrix to change the surface current of the metal structure, thereby effectively improving the efficiency of RCS reduction design .

The purpose of the present invention is achieved by the following technical solutions: a method for reducing the RCS of a metal structure under broadband scanning, comprising the following steps:

S1. Given the working frequency band, the incident plane wave parameters and the geometric model of the metal structure:

The working frequency band includes a frequency band starting frequency and a cutoff frequency, and incident plane wave parameters include an incident angle and an electric field polarization angle;

S2. Select discrete frequency points under the frequency band to establish the impedance matrix of the metal structure and combine them, and use Singular Value Decomposition (SVD) to obtain the radiation basis vector and singular value under the wide band of the structure;

S201. First, use triangular surface elements to subdivide the surface of the metal structure. The subdivision provides N triangular units, and the surface current of each triangular unit is represented by a basis function, wherein the RWG basis function corresponding to the nth triangular unit is f _n (x);

The current distribution on the surface of the metal structure is expressed by the weighted sum of the RWG basis functions as

where α _n is the weighting coefficient of the RWG basis function f _n (x);

Sampling the working frequency band to obtain f ₁ , f ₂ ,...,f _m frequency points in total, and establishing an electric field integral equation for the metal structure at each frequency point and discretizing it to obtain the impedance matrix

The electric field integral equation is Where E ^s is the scattering field, G is the Green's function; dS' is the vector surface element on the surface of the metal structure; ω is the operating angular frequency, μ is the free space magnetic permeability, which is a constant;

According to the electric field boundary condition on the metal surface, where E ⁱ is the incident field of the plane wave;

Substituting the current distribution in the form of a weighted sum of basis functions into Obtain the matrix equation under m frequency points by the method of moments;

...

in, is the N-dimensional impedance matrix of the structure at f _i frequency point, /> is the N-dimensional current coefficient vector at f _i frequency point, /> is the N-dimensional excitation vector at the f _i frequency point, i=1,2,...,m;

S202. Assemble the matrix equations under m frequency points, and use the orthogonal relationship under different frequency points to obtain a matrix equation containing frequency band information:

Denote the assembled impedance matrix as [Z] _f and perform singular value decomposition to obtain the radiation information matrix U, Σ and V of the metal structure with respect to frequency,

U＝[u ₁ ,u ₂ ,...,u _mN ], Σ＝diag(σ ₁ ,σ ₂ ,...,σ _N ), V＝[v ₁ ,v ₂ ,...,v _N ]

U and V are unitary matrices, Σ is a diagonal matrix, and the diagonal elements are the singular values of [Z] _f .

S3. Determine the position of the main radiation of the structure under the broadband based on the size of the singular value and set it as the loading position;

The relationship between the current and the excitation vector under broadband scanning can be obtained by SVD decomposition,

The current under broadband can be realized by adjusting the singular value, thereby adjusting the size of the overall RCS of the structure;

The diagonal elements of Σ are sorted according to the size of the singular value, and its position coordinates correspond to the number of the basis function one by one. The size of the singular value represents the contribution of the basis function to radiation. Generally speaking, only a few finite singular values satisfy Radiation conditions, where the basis functions corresponding to the first p (first 5%) largest singular values are selected as the loading position for current regulation, and the loading position is recorded as l ₁ , l ₂ ,...,l _p ;

S302. Using resistance loading to realize current regulation on the surface of the straight-rod metal structure;

The surface current of the metal structure is discretized into N basis functions, and the loading position obtained by SVD decomposition is loaded with resistance, and the loading matrix is expressed as [R _L ]=diag(R ₁ ,R ₂ ,...,R _p ,0, ...,0); resistive loading can achieve a regulation effect, that is, changing the current distribution on the surface of the metal structure.

S4. Use impedance loading to regulate current, and determine the impedance loading value on the surface of the metal structure through the method of moments and GA genetic algorithm;

According to the moment equation, the impedance matrix in S202 will be regulated after the impedance is loaded; the loaded matrix can be decomposed by SVD, and the loaded singular value matrix can be obtained. The ultimate purpose of loading is to reduce the broadband impedance matrix [Z] The singular value of _f , thereby reducing the radiation of the current;

Determine the optimized objective function, that is, F _obj =Σ=SVD([Z _f +R _L ]), the optimized variable is [R _L ], in order to reduce the singular value, the optimized variable [R _L ] needs to make the objective function The two-norm ||F _obj || ₂ is small enough, ideally ||F _obj || ₂ is close to 0, and the GA genetic algorithm will automatically converge to the objective function F _obj ＝Σ＝SVD([Z _f +R _L ]) The local minimum value of the two-norm ||F _obj || ₂ , at this time, it is considered that the optimization is completed, and the optimized variable at this time [R _L ] is output;

On the metal structure, the resistance loading is carried out according to [ _RL ] to realize the singular value characteristics of the broadband impedance matrix close to the ideal state, thereby realizing RCS reduction.

The beneficial effect of the present invention is: the present invention uses SVD decomposition to obtain the radiation characteristics of the structure under broadband, finds the best loading position, regulates the singular value through impedance loading, and optimizes the loading resistance through genetic algorithm, finally Physically realize the required singular value, thereby regulating the current and effectively improving the efficiency of the RCS reduction design.

Description of drawings

Fig. 1 is method flowchart of the present invention;

Detailed ways

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following description.

As shown in Figure 1, an RCS reduction method for metal structures under broadband scanning includes the following steps:

S1. Given the working frequency band, the incident plane wave parameters and the geometric model of the metal structure:

In the embodiment of the present application, the scanning frequency band is 300 MHz-3 GHz, and the incident angle of the incident plane wave is θ=150°. The metal structure is a straight bar metal with a length of 4m, and 480 line segments can be obtained by dissecting it, and there are 479 unknowns of discrete surface currents in total.

S2. Select discrete frequency points under the frequency band to establish the impedance matrix of the metal structure and combine them, and use Singular Value Decomposition (SVD) to obtain the radiation basis vector and singular value under the wide band of the structure;

A total _{of 20} frequency points _{f 1} , f ₂ , . Establish a 479-order impedance matrix at each frequency point A matrix [Z] _f containing spectrum information can be obtained by assembling, and the matrix has 479*20 rows and 479 columns. SVD decomposition of the matrix [Z] _f can be obtained,

U＝[u ₁ ,u ₂ ,...,u _mN ], Σ＝diag(σ ₁ ,σ ₂ ,...,σ _N ), V＝[v ₁ ,v ₂ ,...,v _N ]

U is a unitary matrix of order 479*20, V is a unitary matrix of order 479, Σ is a diagonal matrix with the same dimension as [Z] _f and the diagonal elements are singular values of [Z] _f .

S3. Determine the position of the main radiation of the structure under the broadband based on the size of the singular value and set it as the loading position;

The relationship between the current and the excitation vector under broadband scanning can be obtained by SVD decomposition,

The diagonal elements of Σ are sorted according to the size of the singular value, and its position coordinates correspond to the number of the basis function one by one. The size of the singular value represents the contribution of the basis function to radiation. Here, the top 20 largest singular values σ ₁ are selected, The basis functions corresponding to σ ₂ ,...,σ... ₂₀ are used as the loading position for current regulation. The loading matrix is expressed as a 479-order square matrix [R _L ]=diag(R ₁ ,R ₂ ,...,R ₂₀ ,0,...,0); resistance loading can realize the control effect, that is, change the surface of the metal structure current distribution.

S4. Use impedance loading to regulate current, and determine the impedance loading value on the surface of the metal structure through the method of moments and GA genetic algorithm.

In the step S4, the singular value of the broadband impedance matrix [Z] _f can be changed by carrying out impedance loading on the surface of the straight-rod metal structure, and the impedance loading value is optimized by combining the method of moments and GA genetic algorithm. SVD decomposition is performed on the loaded broadband impedance matrix, and the singular value is used as the optimization variable and the norm of the first 20 singular values is used as the objective function and brought into the GA genetic algorithm, that is, F _obj ＝Σ＝SVD([Z _f +R _L ] ), the GA genetic algorithm can automatically complete the optimization process and output the optimized loading matrix [R _L ]. The optimized loading value can reduce the singular value of the broadband impedance matrix, thereby reducing the radiation influence of the surface current of the metal structure, and can achieve an excellent RCS reduction effect.

The above description shows and describes a preferred embodiment of the present invention, but as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various Various other combinations, modifications, and environments can be made within the scope of the inventive concept described herein, by the above teachings or by skill or knowledge in the relevant field. However, changes and changes made by those skilled in the art do not depart from the spirit and scope of the present invention, and should all be within the protection scope of the appended claims of the present invention.

Claims (4)

1. The RCS reduction method of the metal structure under broadband scanning is characterized by comprising the following steps of: the method comprises the following steps:

s1, giving a working frequency band, incident plane wave parameters and a metal structure geometric model:

the working frequency band comprises a frequency band starting frequency and a cut-off frequency, and the incident plane wave parameters comprise an incident angle and an electric field polarization angle;

s2, selecting discrete frequency points under a frequency band, establishing an impedance matrix of a metal structure, combining the impedance matrix, and obtaining a radiation base vector and singular values under a structural broadband by utilizing singular value decomposition;

s3, determining the position of main radiation of the structure under the broadband based on the singular value and setting the position as a loading position;

s4, current regulation and control are carried out by utilizing impedance loading, and the impedance loading value of the surface of the metal structure is determined through a moment method and a GA genetic algorithm.

2. The RCS reduction method for a metal structure under broadband scanning of claim 1, wherein: the step S2 includes:

s201, firstly, utilizing triangular surface elements to split the surface of a metal structure, and obtaining N triangular units by splitting, wherein the surface current of each triangular unit is represented by adopting a basis function, wherein the RWG basis function corresponding to the nth triangular unit is f _n (x)；

The current distribution of the metal structure surface is expressed as a weighted sum of RWG basis functions

Wherein alpha is _n As RWG basis function f _n (x) Weighting coefficients of (2);

sampling the working frequency band to obtain f ₁ ，f ₂ ，…，f _m M frequency points are used, an electric field integral equation is respectively established for the metal structure at each frequency point, and the impedance matrix is obtained by discrete

The electric field integral equation isWherein E is ^s For the fringe field, G is the Green's function; dS' is a vector bin on the surface of the metal structure; omega is working angular frequency, mu is free space magnetic permeability and is constant;

obtained from electric field boundary conditions of metal surfacesWherein E is ⁱ An incident field being a plane wave;

substituting the current distribution in the form of a weighted sum of basis functions intoObtaining a matrix equation under m frequency points by a moment method;

...

wherein,,is of the structure f _i N-dimensional impedance matrix at frequency point, +.>At f _i An N-dimensional current coefficient vector at the frequency bin,at f _i N-dimensional excitation vectors at frequency points, i=1, 2, …, m;

s202, assembling matrix equations under m frequency points, and obtaining the matrix equations containing frequency band information by utilizing orthogonal relations under different frequency points:

the impedance matrix after assembly is denoted as [ Z ]] _f Singular value decomposition is performed to obtain a radiation information matrix U, sigma and V,

U＝[u ₁ ,u ₂ ,...,u _mN ],Σ＝diag(σ ₁ ,σ ₂ ,...,σ _N ),V＝[v ₁ ,v ₂ ,...,v _N ]

u and V are unitary matrices, Σ is a diagonal matrix, and the diagonal element is [ Z ]] _f Is a singular value of (c).

3. The RCS reduction method for a metal structure under broadband scanning of claim 1, wherein: said step S3 comprises the sub-steps of:

s301, determining a loading position according to a singular value decomposition result;

the relation between the current and the excitation vector under the broadband scanning is obtained through singular value decomposition,

the current under the broadband is realized by regulating and controlling singular values, so that the size of the RCS of the whole structure is regulated and controlled;

the diagonal elements of the sigma are ordered according to the size of singular values, the position coordinates of the diagonal elements are in one-to-one correspondence with the numbers of the base functions, the size of the singular values represents the contribution of the base functions to radiation, the base functions corresponding to the first p largest singular values are selected as loading positions for current regulation, and the loading positions are marked as l ₁ ,l ₂ ,...,l _p ；

S302, current regulation and control of the surface of the straight-bar type metal structure are achieved in a resistance loading mode;

the metal structure surface current is discretized into N basis functions,resistance loading is carried out on loading positions obtained by singular value decomposition, and a loading matrix is expressed as [ R ] _L ]＝diag(R ₁ ,R ₂ ,...,R _p 0..0., 0); the resistance loading can realize the regulation and control effect, namely, the current distribution on the surface of the metal structure is changed.

4. The RCS reduction method for a metal structure under broadband scanning of claim 1, wherein: said step S4 comprises the sub-steps of:

according to the moment equation, the impedance matrix in S202 is regulated and controlled after impedance loading; singular value decomposition is carried out on the loaded matrix to obtain a loaded singular value matrix, and the final purpose of loading is to reduce a broadband impedance matrix [ Z ]] _f To reduce the radiation of current;

determining an optimised objective function, i.e. F _obj ＝Σ＝SVD([Z _f +R _L ]) The optimized variable is [ R _L ]In order to reduce the singular values, the variables R are optimized _L ]It is necessary to make the two norms of the objective function F _obj || ₂ Is small enough and is ideal in the state of F _obj || ₂ Near 0, the GA genetic algorithm will automatically converge to the objective function F _obj ＝Σ＝SVD([Z _f +R _L ]) Two norms F _obj || ₂ Is considered to be complete at this time, and outputs an optimization variable [ R ] at this time _L ]；

On the metal structure, according to [ R ] _L ]And carrying out resistance loading to realize the singular value characteristic of the broadband impedance matrix approximate to an ideal state, thereby realizing RCS reduction.