Slot-line resonator (SLR) with parallel line (PL) microstrip feeding structure is proposed to design a compact ultra-wideband bandpass filter (UWBBPF) with extended upper stopband. Simulation results are validated by fabrication. Measurements show that, maximum insertion loss is 1.2 dB within the ultra-wide passband, minimum return loss is better than 10 dB and maximum passband group delay variation is 0.43 nS. Upper stopband is extended at least up to 20 GHz while the implementing area is only 0.26 lambda(g) x 0.28 lambda(g), lambda(g) being the guided wavelength at 6.85 GHz.