Design of dual-mode filters using stepped impedance resonators with stub loading

A new type of stepped impedance resonator (SIR) for dual-mode bandpass filter application is proposed in this paper. The characteristic of the proposed stepped impedance resonator is investigated. With the use of proposed stepped impedance resonator, this filter can generate two reflection zeros in the passband. The technique of utilizing input-output cross-coupling to generate two transmission zeros at the out-of band. A dual-mode microstrip BPF have been designed, fabricated, and measured. The measured results exhibit good agreement with the simulation results.