Theory Analysis And Data Processing Of Spherical Near-field Measurement

Antenna measurement as an important means of antenna design,testing and improvement has received increasing attention in the industry.With the development of MIMO(Multiple Input Multiple Output)antenna technology,the shape of the antenna pattern will be unpredictable.With spherical near-field measurement technology,more accurate directional pattern measurement results can be obtained.In recent years,spherical near-field measurements have been increasingly used in the measurement of various large antennas because of their unique advantages.To make this measurement method more accurate and effective,perfect theory and general algorithms are particularly important.In this thesis,starting from the electromagnetic field in vacuum,using the antenna's scattering matrix model,the sphere near-far field transform algorithm is deduced and verified by examples.The design of the near-far field conversion algorithm requires the support of spherical near-field measurement theory.In the first step,the spherical wave expansion theory is used to derive the expression of the electric and magnetic fields in the passive region.In the second step,the scattering matrix model of the antenna is introduced,and the expression of the wave coefficient expression and transmission coefficient of the radiation field is further obtained.In the third step,the transmission of the antenna to be measured is related to the transmission of the probe by the coordinate axis rotation and translation.The fourth step is to derive the calculation method of the antenna transmission coefficient under the conditions of no probe response and probe response.In the fifth step,when near-field and infinity probe response coefficients are known,near-far field conversion algorithm is implemented in MATLAB.The accuracy and versatility of the algorithm need to have enough simulation examples to test.Firstly,in order to verify the accuracy,standard horn antennas with three bands of low,medium,high(L,Ku,and Ka)are simulated on the HFSS electromagnetic software.Near field sampling data is input into the near-far field conversion algorithm and the far field data is output.It fits well with the simulation value.Secondly,in order to verify the generality of the algorithm,an omni-directional half-wave symmetric oscillator and an eight-element array simulation example are added.The coincidence degree of the directional pattern is high,and the error occurs only at the zero point or the side lobe.Just obtaining the spherical far-field data does not reflect the performance of the pattern,and the corresponding data processing software needs to be designed.In order to visually show the gain parameters and the main parameters of the antenna at each frequency point of the antenna,the thesis finally compiles a data processing software.The programming language is C++.The actual environment adopts the MFC framework in Visual Studio.The main function is to process the data from the near field to the far field,output the pattern,and calculate the performance indicators of the antenna,such as the maximum,minimum,front-to-back ratio,roundness,3 d B beam width,and so on.The spherical near-far field transform algorithm is verified by examples and data processing is performed in this thesis.Although the simulation example of this thesis verifies the accuracy of the algorithm,only one of the reasons for the error is analyzed,and there is no deep exploration of other factors that affect the error.There are a lot of problems of data processing software in practical applications,and further research is needed.