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The broadband band-pass filter(BPF) is an important component in mobile and satellite system Etc. Many design techniques have been researched to obtain broadband characteristics. In the same way, several literatures reported about the BPF using open stub filters. On the other hand, since the D. C. Chang and C. W. Hsue reported the development of wideband filters in the Z-domain using cascade shunt transmission line(T.L). However, in this paper, broadband BPFs are developed from a conventional open configured half-wavelength stub BPFs with 50 % bandwidth and achieved more broad bandwidth about 95%. Broad BPFs were important not only the response characteristic but also the decreasing size. The way to decrease is to use the high dielectric substrate(Teflon). But substrate has high cost. Therefore, we used lower dielectric substrate. And we designed the stub BPF that was decreased the T.L length to half using mismatching. In this filter had two-dimensional (2D) structure that help to MMIC (monolithic microwave integrated circuits).