DUAL-MODE BANDPASS FILTER USING INTERNALLY COUPLED STUB-LOADED RESONATORS

A dual-mode bandpass filter using stub-loaded resonators with internal coupled lines for high-selectivity application has been presented. Based on the odd- and even-mode equivalent circuits, the resonant characteristics of the proposed microstrip resonator are investigated. The proposed resonator is found to have the merit that the even-mode resonant frequencies can be flexibly controlled, whereas the odd-mode resonant frequencies are unaffected. It is also found that there is a finite-frequency transmission zero inherently through the stopband. Based on the proposed resonator, a compact and high-selectivity bandpass filter is demonstrated. Experimental results are presented, which confirm our idea. (C) 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:643-646, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25769