Related Algorithms And Technologies Of Near-field To Far-field Transformation On Antennas

With the rapid development of antenna design and measurement technology in the field of satellite and radar, we introduce the new method of near-field to far-field transformation in this dissertation. It is based on the basic theory of the electromagnetic field and the finite difference time domain method which combines the characteristics of time domain and frequency domain. Through the near field measurement and far field extrapolation, the direction of the far field or the radar cross section of a scatter is obtained, so we can achieve the purpose of describing the radiating or scattering characteristics of the antenna accurately.In this dissertation, we first introduce the calculation methods of the far-field radiation pattern for the antennas in the simple system, which include time domain transformation, frequency domain transform and numerical transform. These algorithms have their own characteristics, but they cannot solve the corresponding problem in large-scale antenna arrays, because they cannot meet the requirements of the uncomplicated calculation, little computing time and error. Based on this, we give the corresponding analysis of the far-field pattern or radar cross section in the planar, cylindrical and spherical near-field to far-field transformation from the point of view that the near field scanning surface can be divided into three kinds and the whole processing should satisfy the basic theorem in the electromagnetic field.To face the application of the fifth generation of mobile communication system and to solve the test problems in active array antennas of the single cell, our project team participated in the sub topic of the 5G National 863 project, the project is called communication technology evaluation and test verification technology research, and the topic is massive MMO planar near field scanning and far field extrapolation technology research. In order to reduce the computational complexity and memory, the near field transform algorithm for large scale antenna arrays is introduced in this dissertation. The main work of this dissertation is as follows:1) In the planar near-field to far-field transformation, an equivalent electric and magnetic current algorithm is combined, and when the point of the equivalent electromagnetic current is less than the number of sample points, an equivalent magnetic couple matrix method is used to reduce the computational time and complexity.In addition to comparing the far field pattern with the plane wave expansion obtaining and theoretical values, we also verify the consistency between the 3D pattern and the pattern of E and H orientations, we also give the relationship between the additional computation time, the storage capacity and the scanning frequency points.2) In the cylindrical transformation, we introduce the focusing factor and calibration error based on the image algorithms, it can repair the asymmetric scattering radar cross section.Experimental results indicate that the radar scattering cross section can be described more precisely through the two-dimensional shadow. What’s more, we can also get the relationship between the scattering cross section and the scanning radius.3) In the spherical transformation, we can get the restructuring of the far-field pattern precisely based on the modal coefficients, under the condition that characteristics of the whole electromagnetic field and antenna parameters do not need to be acquired.For different antennas and cutting angles, experimental result is compared with the FDTD algorithm, and the relationship between the reconstructed far-field and the scanning distance is analyzed.