BANDPASS FILTER OF FORKED STEP IMPEDANCE RESONATOR WITH HARMONIC SUPPRESSION IN DIPLEXER APPLICATIONS

摘要

A novel two-stage forked stepped-impedance-resonator (FSIR) bandpass filter design is presented. The FSIR originated from an SIR has its both open ends split as a fork structure. A tunable zero from the coupled lines is created to suppress the second harmonic of the resonator. Two additional zeros obtained from using the asymmetric tapped-line feed are used to improve the filter's frequency selectivity. A diplexer design based on the FSIR structure is presented. Experiments are conducted to verify the circuit design. Good agreements between the measurements and the simulations are observed.