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A novel compact ultra-wideband (UWB) bandpass filter is developed by using microstrip stub-loaded dual-mode resonator doublets. The proposed doublet consists of two parallel but oppositely arranged stub-loaded resonators, and has a significantly widened passband. A UWB filter is designed by cascading three doublets, and eight transmission poles are obtained in its passband. The filter has a passband covering 3.3-10.4 GHz, and exhibits sharp attenuations near its passband. The measured frequency response of the filter has a good agreement with the designed one, and the FCCpsilas indoor limit is satisfied quite well. The minimum strip and gap widths of the filter are larger than 0.1 mm. Therefore, critical fabrication precision requirement or complicated backside-aperture-fabrication process is avoided.