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A novel compact microstrip triband bandpass filter (BPF) with controllable bandwidths is proposed in this article. Two sets of short-stub loaded dual-mode resonators, which are designed for the second and third passband (1.8 GHz/3.5 GHz for GSM/WiMAX), respectively, and asymmetric λ/4 resonator pairs for the first passband (5.8 GHz for WLAN). The three passband frequencies and bandwidths could be independently controlled. To achieve high-selectivity, a nonuniform coupled-line with two U-folded shapes on one line is then proposed to introduce an additional weak I/O cross coupling, thereby bringing one pair of transmission zeros at each side of all the triple passbands. Simulated and measured results are in good agreement indicating that the proposed BPF has respective fractional bandwidths of 6.0, 3.9, and 2.7% and a stopband region with 31 dB attenuation up to 9.7 GHz. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2906–2908, 2015 |
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