Study Of Near-Field Measurement Method For Determining RCS Of Targets Based On ISAR Imaging And Cylindrical Scanning Respectively

As an important parameter for describing the scattering characteristics of various military targets such as aircraft and ships,Radar Cross Section(RCS)has always been a research hotspot at home and abroad.Near-field measurement is one of the main methods to study the target radar cross section of targets.Compared with the traditional far-field measurement and compact range measurement,the near-field measurement has the advantages of small measurement space,more information content obtained high measurement accuracy,strong confidentiality,and less outside interference.Although near-field scattering measurement technology has been researched and developed for decades,there are still many problems to be solved in some subdivision fields.Based on this,the monostatic near-field scattering measurement method of targets based on Inverse Synthetic Aperture Radar(ISAR)imaging and the bistatic near-field scattering measurement method of targets based on cylindrical scanning are studied in this thesis.The main research contents are as follows.Firstly,the monostatic near-field scattering measurement method of targets based on ISAR imaging is studied.Combined with the turntable imaging system model,the basic principle of the ISAR imaging algorithm is analyzed,the ISAR near-field 2D imaging and 3D imaging algorithms are deduced,and the RCS extrapolation method based on ISAR imaging is proposed.The two-dimensional and three-dimensional continuous targets are selected as the algorithm verification objects,and the two-dimensional double-conductor flat plate and the ideal conductor cylinder are taken as examples to calculate the scattered echo of the targets under the illumination of the broadband signal,and substitute it into the ISAR near-field two-dimensional imaging algorithm to obtain the imaging results,then the far-field RCS value is obtained by the imaging extrapolation algorithm and compared with the theoretical RCS value of the targets.In the turntable model,the height resolution is added to the 3D imaging algorithm,so it is necessary to increase the height scan based on the original sampling.Based on the ideal conductor cylinder,the near-field echo data under 3D imaging is simulated by FEKO,with which ISAR near-field 3D imaging and extrapolation are performed,Then the extrapolated RCS value is compared with the theoretical RCS value of the ideal conductor cylinder.Compared with the 2D imaging extrapolation results,the 3D imaging extrapolation results are more accurate.Secondly,the bistatic near-field scattering measurement method based of targets on cylindrical scanning is studied,and the 3D cylindrical wave expansion theory for cylindrical near-field scattering measurement is deduced in detail.According to the three-dimensional cylindrical wave expansion formula,the three-dimensional cylindrical near-field to far-field transformation formulas are deduced.With the ideal conductor ball and the ideal conductor cylinder as simulation models,the near-field data on the cylindrical scan surface are obtained through strict analytical solution and FEKO software simulation.The two groups of data are compared to verify the reliability of the experimental data.The near-field data is substituted into the 3D cylindrical near-field to far-field transformation algorithm to obtain the far-field RCS value of the target and compare with the theoretical value to verify the accuracy of the three-dimensional cylindrical near-field to far-field transformation algorithm.In addition,the influencing factors in the cylindrical near-field scattering measurement are analyzed,and the effect cylindrical scanning height and the measurement distance on the results of the near-field to far-field transformation are analyzed.Finally,the main errors and compensation methods in bistatic cylindrical near-field scattering measurement are studied,and the effects of position error and truncation error on the near-far field transformation results are analyzed with the ideal conductor sphere as the target under test.The cosine window function is used to compensate for the truncation error that has a major influence,and the near-field and far-field transformation is performed after processing the near-field data,with the cosine window function,the results of computer simulation show that the truncation error can be effectively reduced by this method.The window parameters of the cosine window function are further optimized by the exhaustive method,and the optimal optimization parameters and optimization results are obtained.The exhaustive method takes a long time.For this reason,the genetic algorithm is used to optimize the window parameters,and the optimal window parameters that are basically consistent with the exhaustive method are obtained quickly and accurately.