Dual-band bandpass filter using quarter-wavelength resonator with controllable bandwidths and good selectivity

A compact microstrip dual-band bandpass filter (BPF) using quarter-wavelength resonator is proposed in this paper. By tuning the length and width of quarter-wavelength line, two center frequencies can be easily adjusted to the desired value. Furthermore, new structure of couple-line is introduced to produce five transmission zeroes (TZ) at the adjacent two passbands. Thus, the bandwidths of this filter are controllable and good selectivity. Two passbands are designed to operate at 2.4 GHz and 3.5 GHz, respectively. A prototype of dual-band bandpass filter is designed and fabricated for demonstration, good agreement is observed between the simulation and experiments.