Miniaturized microstrip crosscoupled bandpass filter using novel stepped impedance resonators with a desirable upper stopband

A miniaturized microstrip cross-coupling bandpass filter using new stepped impedance resonators (SIRs) with simultaneous suppression of the 2nd harmonic passband response is presented. Four improved and miniaturized SIRs constitute the Compact filter, which exhibits a sharp transition band due to two transmission Zeros at both sides of the passband. Two quarter-wavelength open-ended stub resonators are applied to provide extra transmission zeros for suppressing the 2nd harmonic passband. A bandpass filter with a center frequency at 2.5 GHz was designed and fabricated, of which experimental results validated the proposed filter design. (C) 2008 Wiley Periodicals, Inc.