A compact narrow badnpass filter using meandered lines shunted with microstrip open-ended stepped impedance resonators

A novel and compact bandpass filter (BPF) using meandered microstrip/coplanar waveguide (CPW) hybrid structures paralleled with a pair of open-ended stepped impedance resonators (SIRs) is proposed. The distinct filtering characteristics of this new classification of transmission line filter are investigated theoretically and experimentally. At the bottom of substrate material, the two identical CPW short-circuited resonators and an open-circuited resonator are broadside-coupled to the top microstrip main transmission line, respectively. To reduce the area of the filter, the folded microstrip/CPW composite structures and the microstrip open-circuited SIRs have been applied to layout. A demonstrator with approximately 4.6 % fractional bandwidth (FBW) at the center frequency 6.45 GHz is designed. The developed filter is successfully realized in theory and verified by the full-wave electromagnetic (EM) simulation and the experiment. The obtained frequency responses demonstrated the filter with an excellent band-pass property. Measured results are in good agreement with the electromagnetic simulation results.