Quasi-optical Analysis Of Millimeter Antenna Feed System And Nearfield Measurements Research

With the development of techniques, engineers have showed increasing interest in millimeter and submillimeter systems for their high resolution, large transmission capacity and good penetration properties in atmospheric window etc. The design of millimeter and submillimeter systems involved in algorithm design, processing techniques and measurements. The high frequency, multi-polarization, multi-beam systems with large electrical length are now the key problem which should pay more attention.The expansion of corrugated horn aperture field with quasi-optical Gaussian beams was discussed, and its transmission property was used to get the near and far field. The polarization characteristic of wire grids was then analyzed and some cautions in using wire grids as a polarizer was given. The asymmetry of offset feed parabolic was modeled with modes coupling effects, and under some conditions, a simple formula could be derived. Simulations were then conducted and compared to PO and measurements. The results demonstrated that the Gaussian coupling method can effectively modeled the properties of offset antenna feeding system with reasonable accuracy.This thesis addressed at length the 18 category errors of nearfield measurements, and then introduces a new method to solve the nearfield to farfield transforms-conjugated gradients iteration. The non-equispaced fast fourier transforms algorithm was incorporated into the iteration to hasten the solving process, which takes the same time complexity as FFT. By the data of nearfield measurements, four position offset models were then simulated and the improvements were given for cases the conjugated gradient method converged at a low rate.In a word, the research of millimeter and sub millimeter antenna feeding system using quasi-optical techniques and non-uniform nearfield to farfield transforms, should offered great advantage in this field.