A COMPACT DUAL-BAND BANDPASS FILTER USING STUB-LOADED TWOMODE RESONATORS AND DIRECT SOURCE-LOAD COUPLING TO OBTAIN IMPROVED STOPBAND CHARACTERISTICS

摘要

In this article, a dual-band bandpass filter is designed by using microstrip stub-loaded two-mode resonators. Because the resonant frequencies of the odd-mode and even-mode of the stub-loaded resonator can be varied individually, the midband frequencies of the dualbands of filter can be controlled separately. Direct coupling between the source and load of the filter is introduced, and four transmission zeros in the stopband of the filter are produced. As a consequence, excellent performance of the filter with sharp passband skirts and wide stopbands is realized. For example, dual-band filter has midband frequencies of 2.4 GHz and 3.6 GHz, respectively, with fractional bandwidths of 11.35% and 5.21%, correspondingly. The measured frequency response of the filter agrees excellently with the predicted result.