a novel ultra wideband microstrip bandpass filter using radial stub loaded resonator and interdigital coupled lines is presented in this paper. the radial stub loaded resonator and decagonal patch form a resonator named m to create tuneable multiple notches in the passband for suppression wlan interference. to realize sharp roll-off, two adjustable transmission nulls are located at the lower and upper frequencies out of the passband. even and odd-mode analysis is presented to calculate modal resonance frequencies contributing to create the ultra-wide passband. bessel function is employed to estimate the input impedance of the radial stub which is used in formulation of even and odd mode admittances. simulated and measured results show a passband from 3.4 to 12 ghz (135% bandwidth around 6.39 ghz) with a rejection notch at 4.99 ghz is achieved with return losses better than 14, 12 db in the first and second passbands, respectively. the insertion loss is lower than 0.9 db in the 90% of passband and rejection level is greater than 19 db from 12.25 to 17.45 ghz.