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The dielectric constant of traditional FR4 substrate (epsivr =4.4) is not big enough. So, it is not suitable for making the miniature microwave filter. In order to reduce the size, the Al2O3 ceramic with higher dielectric constant (epsivr = 9.4) can be used as the substrate to design the microwave filters. In this paper, the novel 2.4/5.2 GHz dual-band bandpass filters are proposed for WLAN (IEEE-802.Ha/b/g) applications. The filters are based on rectangle-patch resonators, square notches and two T-type input/output transmission lines. It is found that the length of patch and the size of notch will influence the insertion loss (S21) and the resonant frequencies of the proposed bandpass filter. Because of the higher dielectric constant substrate and modify structure, the filters with optimized parameters exhibit good dual-band filtering performances and small size.