In this letter, a novel compact dual-band microstrip bandpass filter (BPF) with multiple transmission zeros is proposed using the third-order interdigital structure and dual-mode short stub center-loaded resonator (DSLR) for wideband and WLAN applications. The high impedance feedline for the filter with the folded DSLR can function as the quarter-wavelength resonator (QWR) for the third-order interdigital filter. Meanwhile, the folded DSLR can be adopted without an evident increase of the size of the compact interdigital filter. Three transmission zeros between two passbands and in the lower- and upper-stopbands can be created due to the cross coupling between two high impedance feedlines as well as between the input and output, and the intrinsic characteristic of the DSLR. Further, two inverse QWR coupling short stubs with different size loaded in the 50 Ω feedlines can generate four transmission zeros to improve the isolation and deepen the stopband. Finally, a compact dual-band BPF prototype is designed, and good agreement can be obtained between measured and simulated results.
2. Deng, H. W., Y. J. Zhao, L. Zhang, X. S. Zhang, and W. Zhao, "Dual-band BPF with DSIR and TSIR," Electron. Lett., Vol. 46, No. 17, 1205-1206, Aug. 2010.
doi:10.1049/el.2010.0995
3. Liu, A.-S., T.-Y. Huang, and R.-B. Wu, "A dual wideband filter design using frequency mapping and stepped-impedance resonators," IEEE Trans. Microw. Theory Tech., Vol. 56, No. 12, 2921-2929, Dec. 2008.
doi:10.1109/TMTT.2008.2007357
4. Qshima, S., K. Wada, R. Murata, and Y. Shimakata, "Multilayer dual-band bandpass filter in low-temperature co-fired ceramic substrate for ultra-wideband applications," IEEE Trans. Microw. Theory Tech., Vol. 58, No. 3, 614-623, Mar. 2010.
doi:10.1109/TMTT.2010.2040337
5. Xin, J., W.Wu, and C. Miao, "Compact and sharp skirts microstrip dual-mode dual-band bandpass filter using a single quadruple-mode resonator (QMR)," IEEE Trans. Microw. Theory Tech., Vol. 61, No. 3, 1104-1113, Mar. 2013.
doi:10.1109/TMTT.2013.2238949
6. Zhang, R. Q. and L. Zhu, "Synthesis and design of wideband dual-band bandpass filters with controllable in-band ripple factor and dual-band isolation," IEEE Trans. Microw. Theory Tech., Vol. 61, No. 5, 1820-1828, May 2013.
doi:10.1109/TMTT.2013.2256145
7. Deng, H. W., Y. J. Zhao, Y. Fu, X. J. Zhou, and Y. Y. Liu, "Compact and high selectivity dual-band microstrip BPF with QWR and SLR," Microwave and Optical Tech. Lett., Vol. 54, No. 12, 2702-2705, Dec. 2012.
doi:10.1002/mop.27211
8. Hsu, K.-W., C.-H. Chien, and W.-H. Tu, "Compact dual-wideband bandpass filter using asymmetrical resonator," Electron. Lett., Vol. 49, No. 2, 123-124, Jan. 2013.
doi:10.1049/el.2012.3633
9. Xu, J., Y.-X. Ji, C. Miao, and W. Wu, "Compact single-/dual-wideband BPF using stubs loaded SIR (SsLSIR)," IEEE Microw. Wireless Compon. Lett., Vol. 23, No. 7, 338-340, Jul. 2013.
doi:10.1109/LMWC.2013.2263220
10. Matthaei, G. L., "Interdigital band-pass filters," IEEE Trans. Microw. Theory Tech., Vol. 10, No. 6, 479-461, Feb. 1962.
doi:10.1109/TMTT.1962.1125556
11. Deng, H. W., Y. J. Zhao, Y. Fu, J. Ding, and X. J. Zhao, "Compact and high isolation microstrip diplexer for broadband and WLAN application," Progress in Electromagnetics Research, Vol. 133, 133-555, 2013.
Submit
