Abstract: A dual bandpass filter (BPF) with two center frequencies tuned asynchronously and independently is presented. The proposed filter consists of a stepped-impedance resonator (SIR) with two-terminal shorted stubs and a dual-mode open-loop resonator. To generate additional transmission zeros and improve frequency selectivity, the common input and output coupling lines are used for these two structures. Using the odd-even mode analysis method, resonant frequencies of odd-even mode are electrically tuned due to the loaded varactors at the end of transmission line. The measured performance shows that
the first passband can be tuned in a frequency range of 1.93~2.20 GHz, whereas the second passband varies from 2.78 to 3.10 GHz. Comparisons of simulated and measured results show effectiveness of the method.

Key words: bandpass filter (BPF), dual-band, electronically tuned, odd-even mode