Design of second-order capacitive-coupled resonator-based bandpass filter with controllable multiple transmission zeros

This study proposes synthetic design for a compact LTCC bandpass filter with high rejection over a wide stopband operating in the 3.4-3.6 GHz WIMAX band. The presented design derives formulas for synthesizing a filter to meet the specification requirement in the passband insertion and return losses as well as the stopband attenuation. The presented bandpass filter has feedback paths for a grounding inductor and a coupled capacitor to provide controllable multiple transmission zeros at stopband, which enhances the desired stopband rejection.