Design of microstrip bandpass filters using fragment-type coupling structure based on multi-objective optimization

In this paper, microstrip bandpass filters using fragment-type coupling structure based on multi-objective optimization are proposed for the first time. The fragment-type coupling structure allows the design of bandpass filters with improved characteristics. In particular, it can implement filters with desirable upper stopband performance and reduced occupation area. The design of fragment-type coupling structure can be implemented automatically by multi-objective optimization searching with several design objectives characterizing bandpass filters. For demonstration, three filters are designed based on the proposed fragment-type coupling structure. Compared with the conventional parallel coupled-line filter, the upper stopband performance is improved due to the extra transmission zeros generated by fragment-type coupling structure, and the minimum efficient circuit area is reduced by 61.4%. The measurement results show good agreement with simulation.

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