Abstract: A conventional UWB band-pass filter has narrow stopband and can not suppress harmonics effectively.Based on analyzing interdigital resonator and semicircle defected ground structure and stepped-impedance shunt stub structures,a new microstrip band-pass filter is designed,which has good stopband performance and can suppress harmonics and improve sensitivity.The proposed filter tested by Agilent N5230A vector network analyzer has working frequency of 3.1～10.6GHz.The insertion loss is less than 1.5dB in pass-band and the upper-stopband with more than-10dB attenuation is up to 18GHz.The designed filter can effectively suppress harmonics.