Research Of Near-Field Antenna Measurements And Measurements Of Far-Field Patterns At A Quasi-Far-Field Distance

Antenna measurements is a crucial aspect of antenna performance measurements.Due to the fast advancement of wireless technology,more demanding criteria for antenna performance and higher standards for antenna measurements accuracy have been established.The development of traditional antenna measurement algorithms is relatively mature,but the development of high-efficiency and high-precision measurement algorithms is still relatively slow,which restricts the testing efficiency and accuracy of the existing anechoic chamber.In this thesis,the planar near-field antenna measurements algorithm based on the planar wave spectrum expansion is firstly studied.In order to further improve the efficiency of measurements,the cylindrical near-field measurements algorithm based on the planar wave spectrum expansion,the far-field antenna measurements algorithm of two-dimensional antenna array at quasi-far-field distance based on the separable excitation coefficient variable,and the far-field undersampling pattern recovery algorithm based on Fourier interpolation are further studied.The specific research content of this thesis includes the follows:1.The algorithm of the planar near-field antenna measurements is studied.First,the basic theory and parameters of near-field antenna measurements are presented.Second,the relationship between the plane-wave spectral function and the antenna’s far-field pattern is deduced using the theory of plane-wave spectrum expansion.Then,the relationship between the plane-wave spectral function and the measured value of the plane near field is deduced,and the near and far field transformation method without considering the probe compensation is obtained.Finally,the method of determining the far-field pattern from the near-field measurements data of the plane with considering the influence of the probe is obtained by means the Lorentz reciprocity theorem.The accuracy of the algorithm is proved by plane near-field measurements of horn antenna.2.The algorithm of the cylindrical near-field antenna measurements is studied.In order to improve the efficiency of data processing for cylindrical near-field measurements,based on the antenna coupling equation in the planar near-field measurements theory,the antenna coupling formula for cylindrical near-field measurements is derived in this study.Second,by expanding the electromagnetic field generated by the antenna into the sum of finite Fourier series,the method of determining the probe compensation coefficient from the farfield pattern of the probe is derived.Then the method of determining the antenna far-field pattern from the cylindrical near-field measurements data considering the probe compensation is obtained.The algorithm effectively simplifies the data analysis process and ensures the accuracy of measurements,so as to improve the efficiency of cylindrical nearfield measurement algorithm.Finally,the accuracy of the algorithm is verified by the actual cylindrical near-field measurements of slot coupled array antenna.3.The far-field antenna measurements algorithm of two-dimensional antenna array at quasifar-field distance based on the separable excitation coefficient variable is studied.In order to solve the problems that the conventional anechoic chamber environment is difficult to meet the requirements of large-aperture antenna,the near-field measurements equipment is expensive,the measurements system is complex,the transformation theory is complicated and the measurements efficiency is low,a far-field antenna measurements algorithm of twodimensional antenna array at quasi-far-field distance based on the separable excitation coefficient variable is proposed in this thesis.Firstly,the far-field antenna measurements algorithm of one-dimensional antenna array at quasi-far-field distance based on cylindrical wave expansion is described.Secondly,based on the pattern multiplication,the far-field antenna measurements algorithm of two-dimensional antenna array at quasi-far-field distance based on the separable excitation coefficient variable is deduced,and the gain correction method is also given.Finally,in order to verify the proposed method,the symmetrical dipole antenna array is simulated,and the results show that the calculated results are consistent with the theoretical analysis.This algorithm can be applied to the farfield antenna measurements of two-dimensional antenna array at a quasi-far-field distance,which increases the universality of the calculation at quasi far field method and improves the measurements efficiency.4.The algorithm for recovering far-field undersampled pattern of antenna based on Fourier Interpolation is studied.In order to obtain specific information about the pattern during actual far-field antenna measurements,the angular sampling interval must be less than 1/10 of the half-power lobe width of the antenna.Otherwise,the antenna radiation parameters will be affected.For the high-gain narrow-beam antenna,the sampling interval is very small in the far-field measurement,resulting in many sampling points,long measurement time and low measurement efficiency.If the number of sampling points is insufficient in the measurement process,the radiation characteristic parameters of the antenna(such as halfpower beamwidth and sidelobe electric equality)will cause errors.In this thesis,the antenna far field based on Fourier interpolation undersampling pattern recovery algorithm was presented,sampling interval can be added to the antenna under test half power beam width of magnitude,and can accurately reconstruct any small angle interval of radiation pattern,significantly improving measurements efficiency,especially in multi-channel measurements,sweep frequency measurements and multi-beam measurements.Finally,the practicability and reliability of the algorithm is verified by numerical simulation and antenna measurements.