Improvement of Stopband Property of Parallel CoupledMicrostrip Bandpass Filters by Use of Open Stubs

In this paper a novel method is presented forsuppressing spurious response of parallel coupled microstripfilters. This technique is based on introducing open stubs to thefilter. A third order filter is presented with central frequency at3GHZ. The filter insertion is less than 1 dB. The harmonicsuppression at the first and second harmonic is more than 20 dBand 25 dB, respectively. The performance of the new filter isalso compared with characteristic of a conventionally designedfilter to highlight the advantages of the proposed designed filter.