A novel mixed and cross-coupled bandpass filter based on Stepped-Impedance-Resonator

An improved stepped impedance resonator (SIR) is proposed in this paper. Due to this improved resonator, mixed coupling is obtained in filter design. Additional transmission zero is achieved base on new added coupling path. The proposed resonator was adopted to instead one resonator in conventional fourth-order cross-coupled filter. Base on proposed filter topology, a four-pole bandpass filter both with mixed-coupling and cross-coupled have been fabricated and measured. Advantages of this filter not only its sharp rejection, but also its spurious suppression with multi-zeros.