Dual-Band Bandpass Filter With Wide Stopband Using One Stepped-Impedance Ring Resonator With Shorted Stubs

A novel stepped-impedance ring resonator (SIRR) with two pairs of shorted stubs is proposed to design a dual-band bandpass filter. The proposed resonator is a quad-mode resonator, and one resonator can realize a dual-band filter. The frequency space between two passbands and bandwidths of two passbands can be controlled by the shorted stubs. Wide out-of-band rejection can be achieved by selecting the desired impedance and length ratios and suitable feeding point to suppress some spurious resonant frequencies. A prototype filter centered at 1.395 and 1.825 GHz is designed with the first spurious response occurring at 7.84 GHz or 5.7f01 ( f01 is the center frequency of the first passband). Good agreement between the simulated and measured results can be observed.