A miniaturized dual-band bandpass filter with sharp roll-off rate using coupled lines and dual transmission lines

This paper presents a compact, high roll-off rate second-order dual-band bandpass filter with seven transmission zeros. The proposed filter design constructs of dual transmission lines, coupled lines, stepped impedance open stubs, and quarter-wavelength transmission lines. The proposed filter has a size of 0.31 lambda(g) x 0.24 lambda(g) and is printed on RT/duroid 5880 substrate to operate at two different frequencies (1.16 GHz and 2.71 GHz). The proposed filter is fabricated and measured, and good input matching is obtained at desired frequencies. Excellent isolation is achieved between two passbands due to the stopband effect created by the dual transmission lines. The simulated and tested frequency responses are in high agreement with each other.