| In the millimeter wave,submillimeter wave and terahertz bands,quasi-optical system is widely used in atmospheric remote sensing,radio astronomy,terahertz communication,security imaging and other fields,with the advanteges of wide working bandwidth,low transmission loss,multi-frequency and multi-polarization processing capabilities.From the perspective of domestic and foreign development,the research and application of the quasi-optical system tend to be more complex in system structure and higher frequency in operation,which puts forward higher requirements for the design,simulation,processing and testing of the quasi-optical system.In this research background,the author has carried out a series of work around the research and application of electromagnetic simulation method of the quasi-optical reflector system,including the electromagnetic simulation of three-dimensional quasi-optical reflector systems,the rapid design method of three-dimensional quasi-optical reflector systems with low cross-polarization,and the design method of high-performance reflector-based Compact Antenna Test Range for quasi-optical band antenna test.The main innovations include:For the first time,a three-dimensional Gaussian beam mode analysis is proposed,which effectively extends the analysis method only applicable to two-dimensional multi-reflector systems to three-dimensional conditions.Based on the three-dimensional Gaussian beam mode analysis and the Particle Swarm Optimization algorithm,a design method of three-dimensional multi-reflector quasi-optical systems with low cross-polarization is presented.The theory of offset single parabolic reflector Compact Antenna Test Range is deduced,and 100%aperture utilization can be achieved by analysis of Geometric Optics.A new design method for high performance tri-reflector Compact Antenna Test Range based on B-spline curve is presented,which improves the aperture utilization from 70%to nearly 90%.The above research and application of electromagnetic simulation algorithm for quasi-optical reflector systems will improve the ability of electromagnetic simulation in quasi-optical band in China,and lay a solid foundation for solving the blockade of foreign techniques and softwares,and realizing the localization of electromagnetic simulation software for quasi-optical systems.Specifically,the main research contents are as follows:First,a three-dimensional Gaussian beam mode analysis was developed and verified.Specifically,the two-dimensional Gaussian beam mode analysis proposed by J.A.Murphy et al.has been improved to realize the complete calculation of the amplitude and phase of the co-and cross-polarization.On this basis,an improved Gaussian beam mode analysis for three-dimensional multi-reflector quasi-optical systems was realized through rigorous mathematical derivation.In order to further optimize this method,a vector summation method was adopted,which eliminates redundant Gaussian beam modes and improves calculation efficiency.Several three-dimensional multi-reflector quasi-optical systems were modelled and simulated.The simulation results and the calculation time of the commercial electromagnetic simulation software GRASP based on physical optics,and the quasi-optical system simulation software SiMatrix based on the diffraction Gaussian beam analysis were compared.It is verified that this method can provide similar calculation accuracy as the simulation softwares,and the calculation efficiency is improved by nearly 30 times.Finally,two sets of quasi-optical systems were designed,processed and tested.By comparing the measurement results with the simulation results,it is further verified that the calculation accuracy of the three-dimensional Gaussian beam mode analysis.The research of the three-dimensional Gaussian beam mode analysis provides a theoretical guarantee for the rapid and accurate analysis of three-dimensional quasi-optical systems in the future.Secondly,based on the research of the three-dimensional Gaussian beam mode analysis,a fast design method of three-dimensional quasi-optical systems with low cross-polarization was further proposed.Specifically,the advantages and disadvantages of the traditional three-dimensional quasi-optical system design method were elaborated first,and the parameters needed to design a three-dimensional system were discussed.Then,combined with the proposed three-dimensional Gaussian beam mode analysis,the influence of the system design parameters on the cross-polarization level was discussed,and a fast analysis method for the cross-polarization of the three-dimensional quasi-optical system was developed.By comparing with the calculation results and time of GRASP and time,it is proved that this fast analysis method can accurately calculate the cross-polarization level of the system,and the calculation efficiency is improved more than 300 times.Finally,based on the above discussion of the system design parameters and the cross-polarization level,the Particle Swarm Optimization algorithm was applied.By searching the system design parameters within a certain range,the fast design method of the low cross-polarization three-dimensional system was realized.Three sets of three-dimensional quasi-optical systems were designed and simulated.The calculation results and time were compared with GRASP,the calculation accuracy,efficiency and stability of the fast design method are verified.This fast design method of the low cross-polarization quasi-optical system based on Gaussian beam mode analysis meets the rapid design requirements of three-dimensional system with the specific performance and volume,which provides a reference for the design of three-dimensional quasi-optical system with more complex and compact structure in the future.Finally,to solve the problem of quasi-optical band antenna measurement,the theory of the reflector-based Compact Antenna Test Range was studied and the design method of the high-performance Compact Antenna Test Range was developed.Specifically,the performance index of Compact Antenna Test Range was introduced first.Subsequently,the single-reflector Compact Antenna Test Range was studied.Based on the theory of the forward-fed single parabolic reflector Compact Antenna Test Range,an ideal feed form suitable for Compact Antenna Test Range with an offset single parabolic reflector was derived.The quiet zone utilization can reach 100%analyzing by Geometrical Optics.Based on this,an offset-fed single parabolic reflector Compact Antenna Test Range was designed and simulated in GRASP,which verify the correctness of the proposed theory.Then,in view of the advantages and shortcomings of the tri-reflector Compact Antenna Test Range design method based on dynamic ray tracking,a new high-performance tri-reflector Compact Antenna Test Range design method was proposed,which uses B-spline curve to to design the surfaces,and can generate more accurate and smoother shaped sub-reflectors.So that the quiet zone utilization is increased from 70%to nearly 90%.At the same time,fewer reflection points are required and the design efficiency is higher.Finally,the tri-reflector Compact Antenna Test Range design method based on B-spline curve was adopted to design a high-performance tri-reflector Compact Antenna Test Range with a parabolic reflector as the main reflector.And the simulation results in GRASP verify its comprehensive high-performance such as high aperture utilization,high cross-polarization isolation,and wide working bandwidth.The proposal of the design method of the high-performance reflector-based Compact Antenna Test Range provides technical support for the precise and rapid measurement of the large-aperture antennas in the millimeter wave,submillimeter wave and terahertz bands in the future. |
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