CN110988499A - Antenna radiation characteristic obtaining method based on phase-free near field measurement - Google Patents

Abstract

The invention discloses an antenna radiation characteristic acquisition method based on phase-free near-field measurement. First, in the near-field area not far from the antenna to be measured, the electric field amplitude information of all sampling points on the closed curved surface is acquired, and then, through the spherical surface Wave expansion theory establishes two nonlinear relationships between the electric field distribution on a sphere in the near field and the amplitude data on the measurement surface; finally, the genetic algorithm is used to "guess" the electric field distribution on the target sphere in the near field; when the algorithm stops During iterative optimization, the tangential electric field distribution on the spherical surface to be guessed will be basically close to the ideal result. At this time, the weighting coefficient on the spherical surface to be optimized is calculated by using the spherical wave mode expansion theory, and the far field is obtained through the spherical near-far field transformation; the present invention An antenna measurement technique suitable for various specifications is provided.

Description

An antenna radiation characteristic acquisition method based on phase-free near-field measurement

technical field

The invention belongs to the technical field of microwave measurement, in particular to a test method for reconstructing far-field radiation characteristics by using near-field phase-free data.

Background technique

λ是波长，D是天线的最大尺寸；随着天线尺寸的增大，直接测量远场已经变得不现实，尤其是当测试尺寸增大且频率升高时，测量远场将变得十分困难，由此发展了天线近场测量技术。该技术具有全天候、测试精度高、保密性好等优点，因而得到广泛关注；近场测量技术是一种间接测量法，一般是在暗室中放置待测天线，然后在距离待测天线3到10个波长的包围面上用一个已知特性的小探头进行扫描，一次来获取被测天线的近场电场信息，然后，通过严格的近远场变换得到天线的远场辐射特性，如果能够合理设计机械控制软件而且妥善处理各种误差，近场测量的精度将会优于直接远场的情况。Antenna measurement technology mainly includes three methods: far-field measurement, near-field measurement, and tight-field measurement. The far-field measurement method is a direct measurement method, which obtains the far-field radiation characteristics of the antenna through certain mechanical control. The far-field test distance R of the antenna satisfies

λ is the wavelength and D is the maximum size of the antenna; as the size of the antenna increases, it has become unrealistic to measure the far field directly, especially when the test size increases and the frequency increases, it will become very difficult to measure the far field , which developed the antenna near-field measurement technology. This technology has the advantages of all-weather, high test accuracy, good confidentiality, etc., so it has received widespread attention; near-field measurement technology is an indirect measurement method. Generally, the antenna to be tested is placed in a dark room, and then the antenna to be tested is placed at a distance of 3 to 10. A small probe with known characteristics is used to scan the surrounding surface of each wavelength to obtain the near-field electric field information of the antenna under test. Then, the far-field radiation characteristics of the antenna are obtained through strict near-far field transformation. With mechanical control software and proper handling of various errors, the accuracy of the near-field measurements will be better than the direct far-field case.

Near-field measurement technology is roughly divided into plane, cylindrical and spherical near-field measurement according to different shapes. The three measurement technologies are all based on Maxwell's equations and are derived from the equivalence theorem. However, from the perspective of programming, the spherical near-field measurement technology is more complicated, while the plane and cylindrical near-field measurements are relatively simple; from the perspective of measurement difficulty and probe compensation, the plane and cylinder are relatively easy to control mechanically. , and the measurement cost is low, however, there are problems such as truncation error when calculating the far-field radiation characteristics of the plane and cylindrical near-field measurements;

Since the development of near-field measurement technology, it has become a very mature and widely used method, which requires the amplitude and phase information of the electric field to be obtained in the near-field region, both of which are indispensable; however, with the increase of antenna frequency, It is very difficult to obtain very fine and accurate phase information, especially in the sub-millimeter wave to millimeter waveband, the error of the probe antenna position, the temperature fluctuation of the device during the measurement process, the noise of the test system, the antenna probe to be tested and its The coupling effect between the two and various human factors, etc., make it very difficult for people to measure accurate phase information in the near-field area. Even if more reliable phase data can be obtained, it will pay a very high price. It requires very precise and expensive instruments, and ordinary laboratories cannot achieve high-precision phase measurement. Therefore, people began to imagine that very accurate far-field radiation characteristics can still be obtained even if the phase signal is ignored. This is the near-field technology of phaseless antennas, which is gradually heating up.

At present, there is a relatively common phase-free near-field measurement technology, which is the phase recovery technology. Generally, one or more sets of amplitude data in the near-field region are used to recover the phase data, and then strict mathematical transformation is used to calculate the distance. Field, such as the Chinese patent application No. 201710676154.6, according to the spherical tangential electric field amplitude data at two different radii in the near-field region, the far-field radiation characteristics are accurately calculated. Field measurement technology, and the amplitude data on the two measurement surfaces must be measured; in addition, this method puts forward high requirements for the quality of the initial phase. The Chinese patent with application number 201610614730.X provides a near-field antenna measurement method for arbitrary curved surfaces, however, both amplitude and phase data must be obtained at discrete grid points, and this method will pay extra when the frequency increases to obtain phase information, which will increase the measurement cost.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a phase-free near-field measurement method for arbitrary curved surface scanning, which can be applied to a near-field measurement method for arbitrary closed curved surface scanning, which aims to reconstruct the electric field distribution of an unknown source domain, and then calculates the far field.

The technical scheme adopted in the present invention is: a method for obtaining antenna radiation characteristics based on phase-free near-field measurement, which is characterized in that: the antenna to be measured is placed on a turntable, and a movable probe is used in a microwave anechoic chamber to measure an antenna for one of the antennas. The near-field electric field information on the closed surface is measured, and the electric field amplitude data on the regular closed surfaces #1 and #2 composed of two circular planes and one cylindrical surface, and an irregular surface Irregular are obtained respectively;

方向的电场分量振幅数据；Among them, for closed surfaces #1 and #2, uniform sampling is used to discretize the grid; the obtained electric field information of grid points includes: in the cylindrical coordinate system, along the

The amplitude data of the electric field component in the direction;

方向的电场分量振幅数据；For the irregular surface Irregular, non-uniform sampling is used to discretize the grid; the obtained electric field information of grid points includes: in the cylindrical coordinate system, along the

The amplitude data of the electric field component in the direction;

Then the electric field amplitude information obtained at each sampling point includes:

分别表示柱坐标系下电场的三个极化分量，均为矢量；

分别表示柱坐标系下三个极化分量的幅度大小，均为标量。in,

respectively represent the three polarization components of the electric field in the cylindrical coordinate system, all of which are vectors;

respectively represent the amplitudes of the three polarization components in the cylindrical coordinate system, all of which are scalars.

Compared with the prior art, the beneficial effects of the present invention are:

First: Generally speaking, in the near-field measurement, it is necessary to measure the amplitude and phase information of any point on the scanning surface in the near-field area. In the present invention, the phase signal can be ignored, and the Accurate far-field radiation characteristics; for near-field measurements under phase-free conditions, there are few domestic literatures;

Second: In the existing phase-free near-field measurement, the amplitude data acquisition is performed on a plane or a cylinder. However, whether it is a cylinder or a plane near-field measurement, a truncation error will inevitably occur. And plane and cylindrical near-field measurements are only applicable to some antennas. The present invention is applicable to any antenna; in addition, the present invention combines the plane and the cylindrical surface to form a closed surface, which will avoid truncation errors;

Third: In the existing phase-free near-field measurement technology, it is generally necessary to collect the amplitude data of the measurement surfaces two or more away from the antenna to be measured. These measurement surfaces often must be regular sampling surfaces, such as planes and cylinders. , spherical. The measurement surface required by the present invention can be any irregular curved surface, and the number of measurement surfaces can be one or more, which can greatly reduce the measurement cost and also expand the application scope of the present invention;

Fourth: In the existing phase-free near-field measurement technologies, local optimization algorithms are often used for iterative reduction. Such methods often require obtaining a reasonable initial iterative estimate, and the quality of the initial iterative estimate will directly determine the reconstruction distance. Field accuracy, but in the present invention, there is no requirement for the value of the initial iterative estimation, which can be any set of random data;

Fifth: the present invention uses the spherical wave expansion theory to guess the tangential electric field distribution on a certain spherical surface surrounding the antenna under test at the near field; It saves time, and the program writing is relatively simple, which improves the implementation efficiency of the present invention.

Description of drawings

1 is a schematic diagram of an example of the present invention;

Fig. 2 is the genetic algorithm optimization flow chart that the example of the present invention provides;

3 is a schematic structural diagram of a microstrip antenna;

Fig. 4 provides the shape schematic diagram of regular surface #1, #2 for the example of the present invention;

Fig. 5 provides the shape schematic diagram of irregular surface Irregular for the example of the present invention;

Fig. 6 is the fitness trend graph of previous iterations respectively;

Figures 7 and 8 are the RMSE trend diagrams of the two components of the far field, respectively;

Figures 9 and 10 are the far-field patterns of the H and E planes of the microstrip antenna, respectively.

Detailed ways

In order to facilitate the understanding and implementation of the present invention by those of ordinary skill in the art, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are only used to illustrate and explain the present invention, but not to limit it. this invention.

Referring to Fig. 1, a method for obtaining antenna radiation characteristics based on phase-free near-field measurement provided by the present invention is characterized in that: the antenna to be measured is placed on a turntable, and a movable probe is used in a microwave anechoic chamber to measure one of the antennas. The near-field electric field information on the closed surface is measured, and the electric field amplitude data on the regular closed surfaces #1 and #2 composed of two circular planes and one cylindrical surface, and an irregular surface Irregular are obtained respectively; it is worth mentioning that, For the present invention, by using the amplitude information on a closed surface (regular closed surface #1 or #2, or an irregular closed surface Irregular), the present invention can already obtain relatively accurate far-field radiation characteristics, while The method shown in the general patent requires two or more regular measurement surfaces. In order to better verify the effectiveness of the present invention, three test conditions will be set, namely one regular closed surface #1 and two regular closed surfaces. Surface #1+#2, an irregular closed surface Irregular; the present invention will carry out all the tests for the above three tests;

方向的电场分量振幅数据；Among them, for closed surfaces #1 and #2, uniform sampling is used to discretize the grid; the obtained electric field information of grid points includes: in the cylindrical coordinate system, along the

The amplitude data of the electric field component in the direction;

方向的电场分量振幅数据；For the irregular surface Irregular, non-uniform sampling is used to discretize the grid; the obtained electric field information of grid points includes: in the cylindrical coordinate system, along the

The amplitude data of the electric field component in the direction;

Then the electric field amplitude information obtained at each sampling point includes:

别表示柱坐标系下电场的三个极化分量，均为矢量；

分别表示柱坐标系下三个极化分量的幅度大小，均为标量。in,

respectively represent the three polarization components of the electric field in the cylindrical coordinate system, all of which are vectors;

respectively represent the amplitudes of the three polarization components in the cylindrical coordinate system, all of which are scalars.

In this embodiment, as shown in FIG. ₁ , on two circular planes #1-1 and #1-3 with a radius R ₁ and a height H ₁ , respectively, a cylinder with a radius R 1 and a height H ₁ Face #1-2; measured on two circular planes #2-1, #2-3 with radius R ₂ and height H ₂ apart, and cylindrical face #2-2 with radius R ₂ and height H ₂ Amplitude data, for the convenience of expression, the closed surface #1 is regarded as the combination of #1-1, #1-3 and #1-2, and the closed surface #2 is regarded as #2-1, #2-3 and Combination of #2-2. In order to better illustrate the superiority of this method, an irregular closed surface is added, named Irregular for the time being.

The specific steps of data collection are as follows:

处，首先，探头沿着平行于Z轴的一条直线运动得到一个柱面上的电场幅度数据，每隔

度测量一次圆平面上三个柱极化电场的幅度数据；在圆柱面上采样时，必须满足

在这里R_cylinder表示圆柱面的半径。(1) Place the antenna under test (AUT) on the turntable, and the probe is in

At first, the probe moves along a straight line parallel to the Z axis to obtain the electric field amplitude data on a cylinder.

Measure the amplitude data of the three cylindrical polarized electric fields on a circular plane once; when sampling on the cylindrical surface, it must meet the

Here R _cylinder represents the radius of the cylindrical surface.

度测量一次圆平面上三个柱极化电场的幅度数据；在圆平面上采样时，必须满足

在这里R_planar表示圆平面的半径。(2) The probe is parallel to the XOY plane, at a certain height from XOY, every other

The amplitude data of the three cylindrical polarized electric fields on the circular plane are measured once; when sampling on the circular plane, it must meet the

Here R _planar represents the radius of the circular plane.

(3) Repeat (1) and (2) to complete the collection of amplitude information on one or two regular closed surfaces; and for measurements on irregular closed surfaces, depending on the specific situation, it should meet the requirements of Quest as far as possible. Sampling Theorem.

(4) After completing the amplitude data acquisition, save the measurement data in the format of Table 1 below.

Table 1

方向的坐标，后三行分别为柱极化下三个分量的幅度数据。The first, second, and third rows of Table 1 are the arbitrary sampling points along the

The coordinates of the direction, the last three lines are the amplitude data of the three components under the column polarization.

During the entire data collection process for regular closed surfaces (#1 and #2), the Nyquist theorem must be satisfied, that is, the distance between any adjacent measurement points must be less than λ/2; for irregular surfaces (Irregular) The acquisition situation needs to be dealt with according to the specific situation, and try to satisfy the Nyquist sampling theorem.

和

的初始大小在[0,1]之间，通过随机生成，表示待优化球面上θ和

方向上的幅度；

和

的初始大小在[-180,180]之间，通过随机生成，表示待优化球面上沿着θ和

方向上的相位；

表示在球坐标系下源点处的坐标；

表示在球坐标系下场点处的坐标；In this embodiment, let the radius of the spherical surface surrounding the antenna to be tested be R _min , and R _min is the minimum spherical radius surrounding the antenna to be tested; select a spherical surface #0 surrounding the antenna to be tested in the near field area, and the radius is R ₀ (R ₀ ≥R _min ), the tangential electric field on the spherical surface #0 is used as the target electric field to be optimized, and the target electric field consists of four sets of data:

and

The initial size of is between [0, 1], which is randomly generated to represent θ and θ on the sphere to be optimized.

magnitude in direction;

and

The initial size of is between [-180, 180], which is randomly generated, indicating that the spherical surface to be optimized is along θ and

phase in the direction;

Represents the coordinates of the source point in the spherical coordinate system;

Represents the coordinates of the field point in the spherical coordinate system;

The purpose of the present invention is to guess the tangential electric field value of the spherical surface to be optimized by using the amplitude on the measuring surface in the near field area:

Among them, the electric field of the spherical θ component to be optimized is:

分量的电场为：Sphere to be optimized

The electric field of the component is:

方向上的步长满足

k是波数，π是圆周率。where: j is the base unit of the imaginary number; θ and

The step size in the direction satisfies

k is the wave number and pi is the pi.

和

与三个极化幅度数据|E_ρ|、

|E_z|的两种非线性关系：In this embodiment, the target electric field to be guessed is established by the spherical wave theory

and

and the three polarization amplitude data |E _ρ |,

Two nonlinear relationships for |E _z |:

|E_z|分别为E_i,ρ、

E_i,z，是利用

和

计算得到的#1或#2、Irregular上的电场；M表示测量面上的总采样点数，i表示#1或#2、Irregular上第i个采样点的索引；M_i,ρ、

M_i,z表示测量面上#1或#2、Irregular上任意一点的幅度信息，表示在柱坐标系下，沿着

方向的电场分量振幅数据；

和

表示利用

和

计算包围待测天线半径为R ₀的球面上#0的切向电场，

为球面#0上任意源点的坐标信息；

为球面#0上任意场点的坐标信息；where |E _ρ |,

|E _z | are E _i,ρ ,

E _i,z , is the use of

and

Calculated electric field on #1 or #2, Irregular; M represents the total number of sampling points on the measurement surface, i represents the index of the ith sampling point on #1 or #2, Irregular; M _i,ρ ,

M _i,z represents the amplitude information of any point on #1 or #2, Irregular on the measurement surface, and represents in the cylindrical coordinate system, along the

The amplitude data of the electric field component in the direction;

and

indicate use

and

Calculate the tangential electric field on #0 on a spherical surface with radius R ₀ surrounding the antenna under test,

is the coordinate information of any source point on spherical #0;

is the coordinate information of any field point on spherical #0;

Set the number of points to be optimized on the sphere as M ₀ , and combine f ₁ and f ₂ to obtain the algebraic relationship between the tangential electric field to be optimized and the measured amplitude data, which is expressed by the root mean square error RMSE, that is, for

和

猜测地越准确；当算法停止迭代优化时，将得到准确地，半径为R₀上的球面切向电场分布。Iteratively optimize and reduce the mean root error RMSE, the size of the RMSE will reach an acceptable range, and the smaller the RMSE value, the more

and

The more accurate the guess is; when the algorithm stops iterative optimization, an accurate, spherical tangential electric field distribution on radius _R0 will be obtained.

In this embodiment, the electric field of the grid point is calculated by using the electromagnetic field equivalent theorem and the relevant theory of spherical wave expansion, and the specific implementation process is as follows:

和

表示为：The vector spherical wave function can be used for any simple harmonic electromagnetic field in the known passive region

and

Expressed as:

表示球坐标系下任意一场点的坐标；N越大，则加权系数的阶数越大，计算效率大幅度降低，因此，在实施本发明的过程中时，应尽可能减小N的数值大小，具体地讲，要尽可能将天线的几何中心与坐标系的原点吻合。Among them, n and m are a variable, N represents the order of the highest-order mode in the antenna field expansion, which is represented by a positive integer; a _mn and b _mn are the mode expansion coefficients, also called weighting coefficients;

Represents the coordinates of any field point in the spherical coordinate system; the larger N is, the larger the order of the weighting coefficient is, and the calculation efficiency is greatly reduced. Therefore, in the process of implementing the present invention, the value of N should be reduced as much as possible Size, specifically, to fit the geometric center of the antenna with the origin of the coordinate system as much as possible.

表示第二类球汉克尔函数；in,

represents the spherical Hankel function of the second kind;

表示连带勒让德函数，k是波数；

S′_mn(θ)是S_mn(θ)的导数，j是虚数的基本单位，

表示在球坐标系下场点处的坐标，r表示场点和坐标系原点的径向距离，θ表示沿着俯仰角的角度大小，

表示沿着方位角的角度大小；in,

represents the associated Legendre function, and k is the wave number;

S' _mn (θ) is the derivative of S _mn (θ), j is the base unit of imaginary numbers,

Represents the coordinates of the field point in the spherical coordinate system, r represents the radial distance between the field point and the origin of the coordinate system, θ represents the angle along the pitch angle,

Represents the angular size along the azimuth;

Therefore, in the spherical coordinate system, outside the smallest spherical surface surrounding the antenna to be measured, the electric field at any point in space is expressed as:

Then the electric field in the spherical coordinate system is converted into the electric field expression in the cylindrical coordinate system as:

Among them, N represents the expansion coefficient of the highest order mode of the antenna, which is proportional to the minimum spherical radius surrounding the antenna under test and the operating frequency of the antenna.

和

复数场将越接近准确值；在经过一定次数的迭代后，算法将收敛，将最后一次迭代的解利用球面波理论计算得到准确的加权系数，进而求得远场。Referring to Fig. 2, this embodiment optimizes the initial data of the sphere to be guessed by using the fitness function of the genetic algorithm. In each iteration, the value of f will become smaller and smaller.

and

The complex field will be closer to the exact value; after a certain number of iterations, the algorithm will converge, and the solution of the last iteration will be calculated using spherical wave theory to obtain accurate weighting coefficients, and then the far field will be obtained.

Genetic algorithm is a search algorithm used to solve optimization in computational mathematics, and it belongs to a kind of global algorithm. The algorithm was originally developed by drawing on some phenomena in evolutionary biology, including heredity, mutation, natural selection, and hybridization. It simulates the survival law of nature, "survival of the fittest", and is widely used in electromagnetic and other interdisciplinary fields.

Each chromosome in the genetic algorithm corresponds to a solution of the genetic algorithm, and the fitness function is generally used to measure the pros and cons of the solution. So, the fitness from a genome to its solution forms a map. The process of genetic algorithm can be regarded as a process of finding the optimal solution in a multivariate function. It can be imagined that there are countless "mountains" in this multi-dimensional surface, and these peaks correspond to the local optimal solution. And there will also be a "mountain" with the highest altitude, then this is the global optimal solution. The task of the genetic algorithm is to try to climb to the highest peak, instead of falling into some small peaks. In addition, it is worth noting that the genetic algorithm does not necessarily need to find the "highest mountain". If the fitness evaluation of the problem is as small as possible, then the global optimal solution is the minimum value of the function. Correspondingly, the genetic algorithm is looking for It is "the deepest valley". Generally speaking, the longer the chromosome length, the more parameters (genes) to be optimized, the lower the possibility of the genetic algorithm to search for the global optimal value, and the optimization scale and time consumption increase greatly.

The core of the genetic algorithm is the fitness function, which establishes the algebraic relationship between the decision variables (chromosomes) to be optimized and the known data. In the present invention, the smaller the fitness, the better, because the smaller the fitness, the better. The optimized spherical tangential electric field is closer to the real value; in the optimization process of the genetic algorithm, it is mainly completed by three operators: selection, crossover and mutation. Each iteration, the solution space that the algorithm seeks is closer to the real value When the algorithm converges, it means that the solution space found is basically stable.

Referring to Figure 2, in this embodiment, the genetic algorithm is used to iteratively optimize and reduce the root mean error RMSE, and the specific implementation process includes the following sub-steps:

和

计算一个封闭面或两个封闭面上任意一点的幅度信息，将该幅度信息和测量得到的幅度数据

和

进行相减；接着，利用

和

计算待猜测球面本身的切向电场

和

将

和

进行绝对值运算得到

和

然后利用这两个变量与

和

的绝对值进行相减；Step 1: Utilize

and

Calculate the amplitude information of any point on a closed surface or two closed surfaces, and combine the amplitude information with the measured amplitude data

and

perform subtraction; then, use

and

Calculate the tangential electric field of the sphere itself to be guessed

and

Will

and

Perform the absolute value operation to get

and

Then use these two variables with

and

Subtract the absolute value of ;

Step 2: Use the selection operator of the genetic algorithm to evaluate the root mean square error f, and calculate the root mean square error of the far field for the optimal solution in the genetic algorithm population. Note: The so-called optimal solution here is the smallest f For that group of data, the population number is set to 24 in the present invention;

执行相关的代数运算，将

变换一次；每变换一次，以上四项将更加接近我们想要的数值一次；Step 3: Using the Genetic Algorithm's Crossover and Mutation Operator Pairs

perform the relevant algebraic operations,

Transform once; for each transformation, the above four items will be closer to the value we want once;

Step 4: Repeat the above steps 1-3 until the genetic algorithm converges. The present invention sets the maximum number of iterations of the genetic algorithm as the termination condition.

The present invention does not have any requirements on the shape and number of measurement surfaces (one or more), which can be any regular or irregular surface, as long as the measurement surface can surround the antenna to be measured, and the coordinates of any discrete point on it are in the near field In addition, when sampling, it is not necessary to satisfy the Nyquist sampling theorem.

In order to better illustrate the effectiveness of the method in this paper, in each iteration, the algorithm will calculate the fitness value and the root mean square error RMSE of the far field, so as to better observe the convergence characteristics of the algorithm and the degree of agreement with the target far field. , and a specific measurement example is given below.

As shown in Figure 3, the working frequency of the microstrip antenna is f=10.0GHz, and the wavelength λ=30mm.

The sampling range, step size and specific parameters of the regular closed surfaces #1 and #2 are shown in Figure 4 and Table 2. The field amplitude information of 5063 and 6527 points is collected respectively.

Table 2 Sampling range and step size settings for #1 and #2

The sampling range, step size and specific parameters of the irregular closed surface Irregular are shown in Figure 5. The field amplitude information of 7391 points is collected respectively. It can be seen from the figure that the sampling interval of some points is greater than λ/2, and some points are more than λ/2. The sampling interval between them is less than λ/2.

The optimization flow chart of the genetic algorithm is shown in Figure 2; in the calculation example of the present invention, the crossover probability Pc=0.95, the mutation probability Pm=0.001, and the population size PS=24; for the regular closed surface, the maximum number of iterations is set is 91650, and the calculation example of the irregular surface is set to 231720;

The electric field to be optimized is selected from a spherical surface with a coordinate radius of R ₀ =1.5λ, and the step sizes in theta and phi directions are both 6°, and a total of 31×61×4 parameters need to be optimized.

It can be seen from Figures 6, 7, and 8 that the algorithm basically converges after 30,000 iterations. As the iteration progresses, both the fitness value and the root mean square error of the far field become smaller and smaller.

In order to have a comparison with the invention in this paper, the electromagnetic simulation software FEKO is used to measure the far-field radiation characteristics. It can be seen from Figures 9 and 10 that whether it is one or two regular closed surfaces or an irregular measurement surface, its near and far The results of the field transformation are in good agreement with the far-field results obtained by the probe test (see the example reference). As a result, the three are in good agreement, thus confirming the effectiveness of the present invention.

It should be understood that the parts not described in detail in this specification belong to the prior art; the above description of the preferred embodiments is relatively detailed, and therefore should not be considered as a limitation on the protection scope of the patent of the present invention. Under the inspiration of the present invention, without departing from the scope of protection of the claims of the present invention, substitutions or modifications can also be made, which all fall within the scope of protection of the present invention. Requirements shall prevail.

Claims (4)

1. an antenna radiation characteristic acquisition method based on phase-free near-field measurement, is characterized in that: the antenna to be measured is placed on the turntable, in the anechoic chamber, by movable probe, to the near-field electric field on a closed curved surface of the antenna The information is measured, and the electric field amplitude data on the regular closed surfaces #1 and #2 composed of two circular planes and one cylindrical surface, and an irregular surface Irregular are obtained respectively; Among them, for closed surfaces #1 and #2, uniform sampling is used to discretize the grid; the obtained electric field information of grid points includes: in the cylindrical coordinate system, along the

The amplitude data of the electric field component in the direction; For the irregular surface Irregular, non-uniform sampling is used to discretize the grid; the electric field information of the obtained grid points is included in the cylindrical coordinate system, along the

The amplitude data of the electric field component in the direction; then the electric field amplitude information obtained at each sampling point includes:

in,

respectively represent the three polarization components of the electric field in the cylindrical coordinate system, all of which are vectors;

respectively represent the amplitudes of the three polarization components in the cylindrical coordinate system, all of which are scalars. 2. the antenna radiation characteristic acquisition method based on phase-free near-field measurement according to claim 1, is characterized in that: suppose that the spherical radius surrounding the antenna to be measured is R _min , and R _min is the minimum spherical radius surrounding the antenna to be tested; A spherical surface #0 surrounding the antenna to be tested in the near-field area, with a radius of R ₀ , R ₀ ≥ R _min ; the tangential electric field on spherical surface #0 is used as the target electric field to be optimized, and the target electric field consists of four sets of data:

in,

and

The initial size of is between [0, 1], which is randomly generated to represent θ and θ on the sphere to be optimized.

magnitude in direction;

and

The initial size of is between [-180, 180], which is randomly generated to represent the θ and θ on the sphere to be optimized.

phase in the direction;

Represents the coordinates of the source point in the spherical coordinate system;

Represents the coordinates of the field point in the spherical coordinate system; Then, the electric field of the spherical θ component to be optimized is:

Sphere to be optimized

The electric field of the component is:

where j is the base unit of imaginary numbers; θ and The step size in the direction satisfies

k is the wave number, pi is the pi; The target electric field to be guessed is established by spherical wave theory

and

and the three polarization amplitude data |E _ρ |,

|E _z |, and the two nonlinear relationships of the electric field of the sphere itself to be guessed:

where |E _ρ |,

|E _z | are E _i,ρ ,

E _i,z , is the use of

and

Calculated electric field on #1, #2, Irregular, M represents the total number of sampling points on the measurement surface, i represents the index of the ith sampling point on closed surfaces #1, #2, Irregular; M _i,ρ ,

M _i,z represents the amplitude information of any point on the closed surface #1, #2, and Irregular, and represents in the cylindrical coordinate system, along the

The amplitude data of the electric field component in the direction;

and

indicate use

and

Calculate the tangential electric field distribution on spherical surface #0 with radius R ₀ surrounding the antenna under test,

is the coordinate of any point on the sphere #0; Set the number of points to be optimized on the sphere as M ₀ , and combine f ₁ and f ₂ to obtain the algebraic relationship between the tangential electric field to be optimized and the measured amplitude data, which is expressed by the root mean square error RMSE, that is, for

Iteratively optimize and reduce the mean root error RMSE, the size of the RMSE will reach an acceptable range, and the smaller the RMSE value, the more

and

The more accurate the guess is; when the algorithm stops iterative optimization, the exact tangential electric field distribution on a sphere of radius R ₀ will be obtained. 3. the antenna radiation characteristic acquisition method based on phase-free near-field measurement according to claim 2, is characterized in that: described utilizing electromagnetic field equivalent theorem and spherical wave expansion correlation theory to calculate the electric field at grid point, concrete realization process Yes: The vector spherical wave function can be used for any simple harmonic electromagnetic field in the known passive region

and

Expressed as:

Among them, n and m are a variable, N represents the order of the highest-order mode in the antenna field expansion, which is represented by a positive integer; a _mn and b _mn are the mode expansion coefficients, also called weighting coefficients;

Represents the coordinates of any field point in the spherical coordinate system;

in,

represents the spherical Hankel function of the second kind;

in,

represents the associated Legendre function, and k is the wave number;

S' _mn (θ) is the derivative of S _mn (θ), j is the base unit of imaginary numbers,

Represents the coordinates of the field point in the spherical coordinate system, r represents the radial distance between the field point and the origin of the coordinate system, θ represents the angle of the pitch angle,

Indicates the angular size of the azimuth; Therefore, in the spherical coordinate system, outside the smallest spherical surface surrounding the antenna to be measured, the electric field at any point in space is expressed as:

Then the electric field in the spherical coordinate system is converted into the electric field expression in the cylindrical coordinate system as:

Among them, N represents the expansion coefficient of the highest order mode of the antenna, which is proportional to the minimum spherical radius surrounding the antenna under test and the operating frequency of the antenna. 4. the antenna radiation characteristic acquisition method based on phase-free near-field measurement according to claim 2, is characterized in that: the described iterative optimization reduction is carried out to the root mean error RMSE, and the concrete realization process comprises the following substeps: Step 1: Utilize

and

Calculate the amplitude information of any point on a closed surface or two closed surfaces, and combine the amplitude information with the measured amplitude data

and

perform subtraction; then, use

and

Calculate the tangential electric field distribution of the sphere itself to be guessed

and

Finally, will

and

Perform the absolute value operation to get

and

Then use these two variables with

and

Subtract the absolute value of ; Step 2: Use the selection operator of the genetic algorithm to evaluate the root mean square error f, and calculate the root mean square error of the far field for the optimal solution in the genetic algorithm population; Step 3: Using the Genetic Algorithm's Crossover and Mutation Operator Pairs

perform the relevant algebraic operations,

transform once; Step 4: Repeat steps 1-3 above until the genetic algorithm converges.

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