Research Of Filter Based On Microshield Transmisson Line

MEMS microshield transmission line is a structure supported by dielectric membrane, and the substrate under the membrane is etched to form a cavity filled with air. Microshield transmission line can realize the TEM mode propagation of signal in a wide frequency range, and it is still characterized by low loss and small dispersion under the condition of high frequency compared to traditional transmission line structures such as CPW and microstrip. By change the structure parameters of microshield line, it also can realize a large range of variable impedance. Filters can filter out noise and unwanted signals for the communication system, and is an important part of it. And study of filter based on microshield transmission line can improve the performance of circuits working under high frequency. This thesis mainly pays attention to the design of filters composed of microshield transmission line, and on the basis of analyzing the characteristic of microshield transmission line, designs low-pass filter with 140 GHz cutoff frequency、band-pass filter and band-stop filter with 140 GHz center frequency, and study a new kind of miniature filter.This thesis mainly includes the following:1. Analyze the characteristic of microshield line. Introduce the microshield structure with sloped sidewall, and calculate the capacitance per unit by conformal mapping method. By the calculation of the capacitance, analyze the characteristic impedance and effective relative permittivity and the imfluence of the angle of sidewall. Simulating and study the characteristic of microshield line by HFSS compared to traditional transmission line, and analyze the effect different structure parameter has on its characteristic.2. Study the characteristic of discontinuities in microshield line and the transition to CPW. Study the transmission characteristic of usual transmission structures such as open-end stub、short-end stub、right angle bend, which lay the foundation for filter design. Design several kinds of transition from microshield line to CPW, and analyze the match between them. Design the transition from microshield line to rectangular waveguide and study the fabrication process.3. Design filter based on microshield transmission line. On the basis of study of characteristic of microshield line, design a low-pass filter with 140 GHz cutoff frequency by stepped impedance method. Then design a band-pass filter with 45 GHz center frequency by series open-end stubs method and coupled transmission line method respectively. There is also a simple band-stop filter composed of short-end stubs and the center frequency is 140 GHz. Aimed at decreasing the length of the filter, analyze the method of folding the center conductor of stubs to reduce the size. In the end, introduce the fabrication process of the filters.