Compact tri-band bandpass filter using stub-loaded resonator and quarter-wavelength resonator

摘要

A novel compact microstrip tri-band bandpass filter (BPF) using stub-loaded resonator and 1/4 resonator are proposed in this paper. Three passbands are designed to operate at 1.8/2.4/3 GHz, respectively. The stub-loaded resonators are used to generate the first and third passbands, while the 1/4 resonator is used to generate the second passband. The center frequencies of three passband for the tri-band BPF can be conveniently tuned to desired values. One set of resonators are embedded inside the other and thus causing compact size for the filter. A prototype of tri-band bandpass filter is designed and fabricated for demonstration, indicating good agreement with the theoretical expectation.