In this paper, a novel synthesis procedure is presented to achieve optimum solution for UWB filter parameters. It is found that the narrowband approximation is not valid for any arbitrary powered rational type filtering function. For wider bandwidths, the frequency dependent terms have significant effects on the frequency response. Hence, extracted filtering function cannot be mapped to generalize Chebyshev polynomials. This paper will provide an exact synthesis procedure for step impedance resonators (SIR's) type UWB bandpass filters. To validate the synthesis procedure prototypes are designed and fabricated. Simulated and measured results show good agreement with proposed theory.