A modified open-stub-loaded three sections stepped impedance resonator (OSL-TSIR) is analysed in this paper. Based on the even- and odd-mode analysis technique, it can be easily achieved that the proposed OSL-TSIR have the advantage of improving spurious resonant mode frequencies. Besides, more degrees of freedom are provided to control the location of harmonics. A third order Chebyshev dual-wideband bandpass filter composed of cascade parallel sandwich coupled three-lines sections of types SC/CS and OSL-TSIR which act as multi-mode resonator was developed and the design procedure is described. To demonstrate the efficiency of the design process, DB-BPF operating at 5.15/12.58 GHz (2.45 ) and FBW of 19/5.7% for 5G Wi-Fi/Ku-band Applications is designed and simulated. Three transmission zeros are created, resulting in the excellent band-in-band isolation and high selectivity. The filter has a miniaturized size of 27 mm 18 mm.
