A dual-band bandpass filter synthesized by using frequency transformation and circuit conversion technique

In this paper, a novel synthesis method is proposed to design dual-band bandpass filters (BPFs) from a prototype lowpass filter. By implementing two successive frequency transformations and circuit conversions, a new filter topology that consists of only admittance inverters and series resonators is obtained, and is thereby easy to be realized by using conventional distributed elements. A dual-band BPF with central frequencies of 2.4GHz and 3.5GHz is designed and fabricated using microstrip lines and stubs. The measured results show a good agreement with simulated results and validate thereby the proposed theory.