Band pass filters for ultra wideband systems

In this work, a new type of planar band pass filters with application in ultra wideband systems is proposed. The devices consist on microstrip lines with complementary split ring resonators (CSRR) etched on the ground plane, and shunt connected stubs. Coupling between adjacent resonators is achieved by means of λ/4 lines, acting as impedance inverters. To illustrate the potentiality of the proposed approach a 3-stage prototype band pass filter with 90% fractional bandwidth has been designed. By cascading two additional CSRR to the filter in order to reject the first and second spurious bands, it is found that the filter exhibits very good out-of-band performance with 30dB suppression up to three times the central filter frequency.