Miniaturized microstrip bandpass filter with interdigitated fingers

In this paper, a compact microstrip bandpass filter with improved selectivity and spurious harmonic suppression is presented. The proposed filter design makes use of a resonator with interdigitated fingers to achieve compactness as well as high-selectivity by introducing two transmission zeros, with just two resonators. Miniaturization of about 48% and 20% is achieved in comparison to filters realized using open-loop resonators and stepped-impedance resonators, respectively. In addition, the filter design is modified to suppress the spurious resonances without significant increase in the filter size. Spurious resonances are suppressed to frequencies more than 5 times the fundamental resonance frequency. Good agreement between simulated and measured results is obtained.