In this paper a dual taper loaded resonator (DTLR) is presented and modeled (LC model). The proposed equation between the insertion loss and LC parameters of the resonator, enables designers to calculate the proper amount of these parameters for a considered response, through the mathematical equations and then two microstrip lowpass filters (LPFs) are designed using this resonator. One of them has a sharp roll-off and an ultra wide stopband (LPF1). The cutoff frequency of this filter is 1.71 GHz and its transition band is 0.17 GHz. This filter has an ultra wide stopband that is expanded from 1.86 to 40 GHz with more than −16 dB attenuation level. The second filter (LPF2) is designed to improve the suppressing level of the LPF1 with a lower cutoff frequency. These filters have been designed, fabricated and measured
