A triband bandpass filter with low loss and high band selectivity using the split-end asymmetric stepped impedance resonators

In this article, a triband bandpass filter for the applications of global system for mobile communications at 1.8 GHz, WiMAX at 3.5 GHz, and WLAN at 5.2 GHz with low insertion loss and high selectivity is presented. First, the triband passband responses are designed by tuning the length ratio (u) and impedance ratio (R) of asymmetric stepped impedance resonators (SIRs). Second, the band performances are improved by carefully arranging the coupling structure of the SIR. In this design, the split-end asymmetric SIRs are used to provide desired triband performances. Due to the four transmission zeros near the passband edge, the band selectivity of the proposed filter is much improved. The filter was fabricated and the measured results have a good agreement with the full-wave simulated results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1427-1430, 2014