A novel microstrip dual-mode tri-band bandpass filter is presented. The filter consists of an open stub loaded dual-mode resonator and two short stub loaded dual-mode resonators. By utilizing the odd- and even-mode resonance properties of the proposed dual-mode resonators and the introduced source-load coupling (S-L coupling), the filter is designed with two transmission zeros at both sides of each passband, which will improve the selectivity of the filter. To validate the design theory, one 100 MHz 3 dB absolute equal bandwidths dual-mode tri-band filter with three passbands located at the centre frequencies of 1.8, 2.4 and 5.0 GHz, respectively, is designed and fabricated. Both experimental results agree well with the simulations.
2. Ma, D.-C. , Z.-Y. Xiao, L.-L. Xiang, X.-H. Wu, C.-Y. Huang, and X. Kou, "Compact dual-band bandpass filter using folded sir with two stubs for WLAN," Progress In Electromagnetics Research, Vol. 117, 357-364, 2011.
3. Yin, Q. , L.-S. Wu, L. Zhou, and W.-Y. Yin, "Compact dual-band bandpass filter using asymmetrical dual stub loaded open-loops," Journal of Electromagnetic Waves and Applications, Vol. 24, No. 17-18, 2397-2406, 2010.
4. Guo , L. , Z.-Y. Yu, and L. Zhang, "Design of a dual-mode dual-band filter using stepped impedance resonators," Progress In Electromagnetics Research Letters, Vol. 14, 147-154, 2010.
5. Weng, M.-H. , C.-H. Kao, and Y.-C. Chang, "A compact dual-band bandpass filter with high band selectivity using cross-coupling," Journal of Electromagnetic Waves and Applications, Vol. 24, No. 2-3, 161-168, 2010.
6. Chu , Q.-X. and X.-M. Lin, "Advanced triple-band bandpass filter using tri-section SIR," Electron. Lett., Vol. 44, No. 4, 295-296, 2008.
7. Hsu , C.-I. G., C.-H. Lee, Y.-H. Hsieh, "Tri-band bandpass filter with sharp passband skirts designed using tri-section SIRs," IEEE Microw. Wireless Compon. Lett., Vol. 18, No. 1, 19-21, 2008.
8. Lee, C.-H., C. I. G. Hsu, and H. K. Jhuang, "Design of a new triband microstrip BPF using combined quarter-wavelength SIRs," IEEE Microw. Wireless Compon. Lett., Vol. 16, No. 11, 594-596, 2006.
9. Lin, X.-M., "Design of compact tri-band bandpass filter using λ/4 and stub-loaded resonators," Journal of Electromagnetic Waves and Applications, Vol. 24, No. 14-15, 2029-2035, 2010.
10. Chen, F. C., Q. X. Chu, and Z. H. Tu, "Tri-band bandpass filter using stub loaded resonators filter for multimode wireless LANs," Electron. Lett., Vol. 44, No. 12, 747-749, 2008.
11. Chen , F.-C. and Q.-X. Chu, "Design of compact tri-band bandpass filters using assembled resonators," IEEE Trans. Microw. Theory Tech., Vol. 57, No. 1, 165-171, 2009.
12. Ren, L.-Y., "Tri-band bandpass filters based on dual-plane microstrip/DGS Slot Structure," IEEE Microw. Wirel. Compon. Lett., Vol. 20, No. 8, 429-431, 2010.
13. Wu, H.-W. and R.-Y. Yang, "Design of a triple-passband microstrip bandpass filter with compact size," Journal of Electromagnetic Waves and Applications, Vol. 24, No. 17-18, 2333-2341, 2010.
14. Liu, Y., W.-B. Dou, and Y.-J. Zhao, "A triband bandpass filter realized using tri-mode T-shaped branches," Progress In Electromagnetics Research, Vol. 105, 425-444, 2010.
15. Luo, S., L. Zhu, and S. Sun, "Compact dual-mode triple-band bandpass filters using three pairs of degenerate modes in a ring resonator," IEEE Trans. Microw. Theory Tech., Vol. 59, No. 5, 1222-1229, 2011.
16. Chen, B.-J., T.-M. Shen, and R.-B.Wu, "Design of tri-band filters with improved band allocation," IEEE Trans. Microw. Theory Tech., Vol. 57, No. 7, 1790-1797, 2009.
17. Wei , C.-L. , B.-F. Jia, Z.-J. Zhu, and M.-C. Tang, "Design of different selecticity dual-mode filters with E-shaped resonator," Progress In Electromagnetics Research, Vol. 116, 517-532, 2011.
18. Hong , J.-S. , H. Shaman, and Y. H. Chun, "Dual-mode microstrip open-loop resonators and filters," IEEE Trans. Microw. Theory Tech., Vol. 55, No. 8, 1764-1770, 2007.
19. Rosenberg, U. and S. Amari, "Novel coupling schemes for microwave resonator filters," IEEE Trans. Microw. Theory Tech., Vol. 50, No. 12, 2896-2902, 2002.
20. Cameron, R. J., "Advanced coupling matrix synthesis techniques for microwave filters," IEEE Trans. Microw. Theory Tech., Vol. 51, No. 1, 1-10, 2003.