Compact microstrip bandpass filters using triple-mode resonator with lumped elements

Compact microstrip bandpass filters using triple-mode resonator are investigated in this paper. At the center frequency of 2.45 GHz, a half-wavelength microstrip open-circuited resonator is loaded with a chip capacitor and a chip inductor to realize the triple-mode resonator. By adjusting the resonator's parameters, the first three resonant mode frequencies could be tuned for bandpass filters with various fractional bandwidths. Three bandpass filters with different measured bandwidths (13.8%, 55.5%, 98.6%) are designed, fabricated, and tested to validate the design concept.