A periodically loaded ultra wideband (UWB) bandpass filter based on the electromagnetic band-gap (EBG) concept is presented. Compact wideband filters with steep transition bands can be designed easily using this novel methodology. Unit cells in the EBG circuit model are realized by capacitive and inductive parallel loading of a transmission line. These unit cells are cascaded to realize bandpass filters whose bandwidth depends on the reactive loading of unit cells. The number of unit cells determines the steepness of the band edges of the filter. The main advantage lies in the fact that the size of unit cells can be small because electrical length of transmission line segments in unit cells can be chosen arbitrarily, hence the final filter structure becomes small in size. A microstrip filter with 60% bandwidth is designed and the physical size is compared with a conventional wideband bandpass filter designed with quarter wavelength admittance inverters.