New ultra-wideband (UWB) bandpass filters are proposed by using stepped-impendence resonators (SIRs) and stub-loaded SIRs, aiming at transmitting the signals in the whole UWB passband of 3.1GHz-10.6GHz. Each of the proposed UWB filters consists of two parallel but oppositely arranged compact SIR with tri or quad-section or stub-loaded SIR. In the design, the first two or three resonances of the proposed resonators are properly adjusted to be placed within the UWB. In order to enhance the coupling degree, pairs of quarter-wavelength parallel-coupled lines are longitudinally stretched in both the input and output sides. The UWB bandpass filters behave multiple transmission poles and good return loss of no less than 15dB. A proposed UWB filter is fabricated and measured, and the experiment demonstrates the design.