Compact microstrip dual-band bandpass filter using short-stub loaded half-wavelength resonator

A compact microstrip dual-band bandpass filter (BPF) using short-stub loaded half-wavelength resonator is proposed in this paper. By tuning the length and width of short-stub and half-wavelength line, two center frequencies can be easily adjusted to the desired value. Furthermore, new structure of couple-line is introduced to satisfy desired external coupling degree for each band. In this way, the bandwidths of this filter are controllable, while taking good selectivity and improved upper-stopband performance. 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 measured and the theoretical expectation.