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This paper presents a tunable dual-band microstrip after using step-impedance resonators (SIR) with wide stopband and low insertion loss. The dual-band Alter employs two SIR single-band Alters for the specifications of the two passbands respectively and using novel layout to make the two single-band Alter can be designed independently and achieve wide stopband. A prototype dual-band filter operated at 2.07 and 3.15 GHz is designed and fabricated. The upper stopband is extended over 10 GHz. Good agreement achieved between the numerical and measured results.