A COMPACT DUAL-MODE DUAL-BAND BANDPASS FILTER USING STEPPED-IMPEDANCE OPEN-LOOP RESONATORS AND CENTER-LOADED RESONATORS

In this article, a compact dual-mode dual-band bandpass filter is proposed by using two modified stepped-impedance open-loop resonators and center-loaded bars. The dual-mode resonators are created by loading two center-loaded bars, and this process is investigated through dual-mode filter analysis. The external quality factor and the coupling coefficient is introduced and analyzed to optimize the proposed filter. A low insertion loss and high return loss dual-mode dual-band filter is designed and fabricated with a compact structure. Three transmission zeros are created near the passband, leading to a high selectivity. Two passbands are centered at 3.88 and 5.35 GHz with an insertion loss of -0.38 and -1.03 dB, respectively, and 3-dB fractional bandwidths of 12.4 and 8.6% are obtained. The measured return loss is higher than -24.28 and -19.33 dB at the two resonant frequencies, respectively. The simulated and measured results are in good agreement, which verifies the design methodology. (c) 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:3000-3005, 2013