A Novel Notch System Having Two Stopbands Based on Duplexer for Broadband Applications

This letter presents a novel notch system having two independent stopbands to satisfy the complicated requirements of broadband applications. The undesired interaction between the spurious responses of the first stopband and the desired bands (broad passband and the second stopband), which is difficult to be handled with traditional designs, is eliminated by the isolation feature of a duplexer pair. Three extensional prototypes with corresponding topologies are proposed to expand applications of the system. To validate the proposed idea, an example in which stopbands' fractional bandwidths are 37% and 100% at 1 GHz and 4 GHz in 0.5-18 GHz application is implemented. A good agreement between the simulated and measured results demonstrates the realizability of this novel idea.