다단 루프결합구조를 갖는 광대역 엔드론치형 어댑터 해석 및 구현

Abstract

A collinear end launcher waveguide adapter is utilized to the excitation of a two-dimensional array of rectangular waveguide radiators. The end launcher consists of the excitation geometry that a center conductor of coaxial line is interconnected collinearly into the '￢'-shaped multiple-step coupling loop shorted on the waveguide broad-wall, and converts a coaxial TEM mode into a waveguide dominant mode. In this thesis, the multiple-step loop coupling model for the analysis of collinear end launcher rectangular waveguide adapter is presented. The influence of propagation mode and higher modes inside a rectangular waveguide are analyzed and design parameters of the end launcher are investigated. We present the loop coupling model to design the collinear end launcher rectangular waveguide adapter and find a more exact expression without any approximation for input impedance considered the dominant mode together with higher order modes inside a waveguide. Also, the results obtained from the input impedance expression is analyzed and compared with the previous works of end launcher adapter with single loop coupling model, and verified validity of the proposed analytical expression about input impedance by a commercial electromagnetic tool of HFSS based on a numerical method known as FEM. For optimum design of the adapter, the input impedance of end launcher adapter can be matched by properly controlling the length of loop (, ), radius () and input feeding point (). It is the ideal case that the resistive component of input impedance equals to the characteristic impedance of coaxial line, and the reactive component equals to zero. However, it is difficult practically that the reactive component is realized to zero over whole waveguide frequency band. Therefore, we have to trade-off in which the resistive component approaches to the characteristic impedance of coaxial line, and also the reactive component approaches to zero over the operating frequency band as controlling the physical parameters to design of the end launcher adapter. The design for collinear end launcher adapter is achieved as follow. A resistive component flatness of input impedance for a adapter with single-step loop coupling structure by and is tuned up. A resistive component of it by is tuned up. If resistive component is good matched, reactance component approaches to zero over the operating frequency band. In the case of tuning for collinear end launcher adapter with multiple-step loop coupling structure, the same process in the limited ranges of , , and is applied. Multiple-step collinear end launcher rectangular waveguide adapter for wide band system has been designed. The percentage bandwidth(BW) of single-step adapter with total loop length of 16.08㎜ is 4.4% in the VSWR range of maximum 1.2. The BW of double-step adapter with the same length is extended up to 30.6% in the VSWR. And also, the BW of triple-step adapter with same condition also is extended up to 37.3%. After analysis of them, we have fabricated double-step adapter with total loop length of 15.8㎜. The BW of fabricated adapter is 31.3% in the VSWR range of maximum 1.2. That is the reason for the extended bandwidth since higher modes excited by multiple-step loop current cancel their reactive components out. As the result, in broadband, reactive component approaches to zero and also resistive component approaches to the characteristic impedance of coaxial line. The results show that the numerical calculations based on this thesis for input VSWR of the end launcher adapter generally agree well with the HFSS data. Therefore, the new analytical formula has more accuracy than the previous formulas and allows the design to be put on a dependable quantitative criterion.