We designed stepped impedance resonator bandstop filter (SIR-BSF) with improved hairpin coupling structures. The SIR-BSF is compact in size and great advantage having an excellent bandstop property. The center frequency of SIR-BSF is 9.1GHz which is the harmonic of the 4.55GHz band. The 3dB bandwidth of the designed filter is 1.65GHz with the insertion loss (S21) of 42dB. The application is made for domestic UWB and microwave relay station, and international fixed and mobile satellite communication. The overall size is 10mm ´ 20mm.

filter, SIR, microstrip, bandstop, resonator.