In this paper, design of a novel dual-band microstrip bandstop filter is presented. The designed filter is constructed by loading two stepped impedance hairpin resonators to a simple straight transmission line, which also connects to the input and output ports. By virtue of the proposed resonator, the ratio of the first and second resonance frequencies can be obtained as approximately 4.4. Two stopbands centered at 2.34 GHz and 7.81 GHz with the fractional bandwidths of 33.2% and 7.9% can be obtained, respectively. Rejection levels inside the stopbands are obtained as better than 20 dB. Total electrical length of the proposed filter is 0.317λgx0.136λg, where λg is the guided wavelength at the lowest resonance frequency. The designed filter was also fabricated and tested for experimental verifications. The measured results are in an excellent agreement with the simulated ones.
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