Miniaturized Wide Stopband Microwave Integrated Filters

This paper introduces a new technique based on exact synthesis to design integrated microwave filters. It is applicable to miniature filters with wide stopband, and high selectivity in low part of microwave frequency domain. As they are realized on microwave printed circuit, it is convenient to integrate a system. The main contents are presented here:1. The network's extract method of filter, which has finite attenuation poles in S-plane and Z-plane, are presented in detail. The filters are exceedingly small devices with wide stopband as a result of using transmission line elements which are a quarter-wavelength well above the frequency of the passband. In order to meet filter's high selectivity, each filter corresponds to a bandpass S-plane prototype which is derived using exact synthesis procedures from a specification of transmission zero locations.2. The design formulae of the frequency and network transformation in exact synthesis theory are presented in detail. With the help of microwave software, it is easy to make network transform and the results of it are perfect.3. Five ways are introduced to meet arbitrary passband and stopband widths. And the first four structures have synthesized in Z-plane. Correspond to it four programs have been written in Matlab language to prove the mathematical truth of the theory.4. Considering to the department's practical requirement, some structures have been selected to design and construct four bandpass filters in microstrip line, their frequency domain are as follows: 0 .8GH₂ - 2GH₂, 1 .8GH₂ - 2GH₂,1 .45GH₂ - 1.65GH₂, 2 .25GH₂ - 2.35GH₂. It proves the realization of the theory.5. Lumped planar capacitor in microwave frequency domain, which is designed and produced independently, has been proved to be realizable in microstrip lines to achieve the function of series-wound capacitor.