A compact dual-band bandpass filter with adjustable second passband using S-shaped stepped impedance resonator embedded by open stubs

A dual-band bandpass filter (BPF) is discussed in this paper. To obtain adjustable second passband, two same open stubs are embedded on S-Shaped stepped impedance resonator. By changing the length of two same stubs, the second resonant frequency can be adjusted significantly, In addition, filter with only one stub embedded has also been discussed, the differences between them has been analysed. Based on the proposed topology, a prototype was fabricated to achieve dual-band applications around 2.4 and 3.5 GHz. Experiment results demonstrate the newly designed filter available.