Numerical And Experimental Verification Of 3D Quasi-Optical Network System

Quasi-Optical Network(QON) system, which can transmit electromagnetic signals in free space with very low loss. Signals are separate into various frequency bands and polarization channels. QON system therefore has been widely utillized in the field of deep space exploration and microwave remote sensing. Recently, the operating frequencies of deep space exploration and microwave remote sensing systems have marched into to millimeter, sum-millimeter and terahertz band, posing a stringent demand on the QON system. Firstly, the increasing frequency brings in challenge on the numerical simulation of the QON system; secondly, with more and more channels in the QON system, miniaturization is required in the system design; lastly, electrical performance measurement of the system at such high frequency becomes an urgent problem to be addressed properly.In this regard, this project focus on the numerical and experimental verification of 3D QON system, targeting the quick design and simulation, testing of the miniaturized QON system in millimeter, submillimeter and terahertz band. The major points of this dissertation include the realization of a modular 3D diffracted Gaussian Beam(GB) analysis method, the design, facbrication and testing of a 3D QON system, and numerical analysis of a terahertz tri-reflector Compact Antenna Test Range(CATR) system using this 3D method. The main contributions of this paper are as follows:Firtly, a modular 3D diffracted GB analysis method, consisting of frame-based Gabor transformation,3D GB reflection and diffraction techniques is proposed and implemented. Full plane sub-GB expansion and a novel 3D GB diffraction solution are utillized in this work to analyze the whole reflector and therefore the method is capable of analyzing a 3D QON system, overcoming the shortcomings of the 2D diffracted GB analysis method original proposed by Query Mary University of London. The analysis procedures are:a) the field on the input plane is expanded as a superposition of vector sub-GBs via frame-based Gabor transform; b) these sub-GBs are then traced into the reflector where a bi-paraboloid surface are modeled at the intersection points so as to derive an analytical expressions for the reflected and diffracted field; c) the output filed can be computed by superimposing the reflected and diffracted field; d) the analysis procedure ceases if the underlying reflector is the last one. Otherwise, frame-based Gabor transform is employed to expand the output field into sub-GBs, initializing another cycle of analyzing the next reflector. The key contribution of the proposed method is that a novel 3D GB diffraction technique is developed to treat the scattering from the reflector edge, which gracefully extends Zogbi’s solution into more practical scenarios and enables one analyze the beam diffraction from offset reflector edge. In addition, the proposed GB analysis method has been integrated into a in-house software SiMatrix, making it possible to simulate the 3D QON systems.Secondly, in order to numerically verify the accuracy of the proposed modular 3D GB analysis method, a 3D dual-channel QON system is designed, fabricated and measured. The QON system employs a two-layer structure, with the two channel operating at the 183GHz and 325GHz, which are water vapor absorption lines. The whole system includes two corrugated horns, three elliptical reflectors and one Frequency Selective Surface(FSS). The FSS is used to separate the dual frequency bands, transmitting the 325GHz signal on the top layer while redirects the 183GHz signal into the bottom layer. The proposed modular GB analysis method in this work is utillized to analyze the 3D QON system. Compared to the measured results, good agreements down below-30dB within the main beam of the far field pattern can be achieved for both channels. In contrast to the traditional 2D system where optical centers of the components are all in one plane, the 3D structure is more size-economical and compact, showing further potential of miniaturization of the QON system.Thirdly, I pacitipated part work for the national project, focusing on simulation work of the system. The proposed GB anaylsis method is utillized to evaluate the CATR performance. The amplitude distribution deviation between the simulated and measured results whithin the quiet zone is less than 1.1 dB. Compared with the simulation results of the comercial software GRASP (based on Physical optics), the agreement of amplitude distribution is less than 1dB within the quiet zone; however, the computational efficiency is five times than that of the PO method above 325 GHz, demonstrating ultra high efficiency of the GB method in analysis of electrically large reflector systems. The proposed GB method can provide a mean of quick design and simulation verification for terahertz reflector-based CATR systemwith higher frequency and larger aperture in the future.