This study presents a design of a compact stub-type bandpass filter with capacitively loaded stubs and a fold-back structure. This paper employed the fabrication process of low-temperature co-fired ceramic (LTCC) for filter realization of a multi-layer structure. The proposed filter structure required adding end capacitors to stubs to extend their electrical length, while achieving a length reduction of 30%. This study provided design curves to determine the dimensions of the end capacitor for reaching maximum electrical length extension. In addition, a fold-back configuration was applied to halve the filter size. An experimental filter operating at 5.8 GHz was fabricated and measured to validate the design concept, achieving a highly compact size of 14.3×8.2×0.76 mm3.
1. Hong, J.-S. and M. J. Lancaster, Microstrip Filters for RF/Microwave Application Engineering, John Wiley & Sons, New York, 2001.
2. Chang, K., I. Bahl, and V. Nair, RF and Microwave Circuit and Component Design for Wireless Systems, John Wiley & Sons, New York, 2002.
3. Matthaei, G. L., L. Young, and E. M. T. Johns, "Microwave Filters, Impedance Matching Networks, and Coupling Structures," Artech House, Norwood, MA, 1980.
4. Abdel-Rahman, A., A. K. Verma, A. Boutejdar, and A. S. Omar, "Compact stub type microstrip bandpass filter using defected ground plane," IEEE Microwave and Wireless Components Letters, Vol. 14, No. 4, 136-138, 2004. doi:10.1109/LMWC.2003.821503
5. Lin, W.-J., C.-S. Chang, J.-Y. Li, D.-B. Lin, L.-S. Chen, and M.-P. Houng, "Improved compact broadband bandpass filter using branch stubs co-via structure with wide stopband characteristic," Progress In Electromagnetics Research C, Vol. 5, 45-55, 2008.
6. Razalli, M. S., A. Ismail, M. A. Mahdi, and M. N. Bin Hamidon, "Novel compact microstrip ultra-wideband filter utilizing short-circuited stubs with less vias," Progress In Electromagnetics Research, Vol. 88, 91-104, 2008. doi:10.2528/PIER08102303
7. Zhang, L., Z.-Y. Yu, and S.-G. Mo, "Novel planar multimode bandpass filters with radial-line stubs," Progress In Electromagnetics Research, Vol. 101, 33-42, 2010. doi:10.2528/PIER09121303
8. Li, R., S. Sun, and L. Zhu, "Synthesis design of ultra-wideband bandpass filters with composite series and shunt stubs," IEEE Trans. Microwave Theory Tech., Vol. 51, 684-692, 2009.
9. Ma, Z., K. Kikuchi, Y. Kobayashi, T. Anada, and G. Hagiwara, Novel microstrip dual-band bandstop filter with controllable dual-stopband response , Proceedings of Asia-Pacific Microwave Conference, 1177-1180, 2006.
10. Tsai, C.-M., H.-M. Lee, and C.-C. Tsai, "Planar filter design with fully controllable second passband," IEEE Trans. Microwave Theory Tech., Vol. 53, 3429-3439, 2005. doi:10.1109/TMTT.2005.855739
11. Chin, K.-S. and C.-K. Lung, "Miniaturized microstrip dual-band bandstop filters using tri-section stepped-impedance resonators," Progress In Electromagnetics Research C, Vol. 10, 37-48, 2009. doi:10.2528/PIERC09080306
12. Chin, K.-S. and J.-H. Yeh, "Dual-wideband bandpass filter using short-circuited stepped-impedance resonators," IEEE Microwave and Wireless Components Letters, Vol. 19, No. 3, 155-157, 2009. doi:10.1109/LMWC.2009.2013736
13. Quendo, C., E. Rius, and C. Person, "Narrow bandpass filters using dual-behavior resonators," IEEE Trans. Microwave Theory Tech., Vol. 51, 734-743, 2003. doi:10.1109/TMTT.2003.808729
14. Zhu, L. and W. Menzel, "Compact microstrip bandpass filter with two transmission zeros using a stub-tapped half-wavelength line resonator," IEEE Microwave and Wireless Components Letters, Vol. 13, 1618, 2003.
15. 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.
16. Velázquez-Ahumada, M. D. C., J. Martel-Villagr, F. Medina, and F. Mesa, "Application of stub loaded folded stepped impedance resonators to dual band filters," Progress In Electromagnetics Research, Vol. 102, 107-124, 2010. doi:10.2528/PIER10011406
17. Liu, C.-Y., T. Jiang, and Y.-S. Li, "A novel UWB filter with notch-band characteristic using radial-UIR/SIR loaded stub resonators ," Journal of Electromagnetic Waves and Applications, Vol. 25, No. 2-3, 233-245, 2011. doi:10.1163/156939311794362902
18. 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. doi:10.1163/156939310793675718
19. Liu, H., R. H. Knoechel, and K. F. Schuenemann, "Miniaturized bandstop filter using meander spurline and capacitively loaded stubs," ETRI Journal, Vol. 29, No. 5, 2007. doi:10.4218/etrij.07.0107.0077
20. Drozd, J. M. and W. T. Joines, "A capacitively loaded half-wavelength tapped-stub resonator," IEEE Trans. Microwave Theory Tech., Vol. 45, No. 7, 1100-1104, 1997. doi:10.1109/22.598447
21. Hoa, D. T. and I. S. Kim, "Miniaturized low insertion loss multilayer capacitively loaded step-impedance interdigital bandpass filter," Proceedings of Asia Pacific Microwave Conference, 1-4, 2007. doi:10.1109/APMC.2007.4554862
22. Görür, A., C. Karpuz, and M. Akpinar, "A reduced-size dual-mode bandpass filter with capacitively loaded open-loop arms," IEEE Microwave and Wireless Components Letters, Vol. 13, No. 9, 385-387, 2003. doi:10.1109/LMWC.2003.817136
23. Stark, A. and A. F. Jacob, A broadband vertical transition for millimeter-wave applications, Proceedings of the 38th European Microwave Conference, 476-479, 2008.
24. Valois, R., et al., "High performances of shielded LTCC vertical transitions from DC up to 50 GHz," IEEE Trans. Microwave Theory Tech., Vol. 53, No. 6, 2026-2032, 2005. doi:10.1109/TMTT.2005.848832
25. Yang, T.-H., C.-F. Chen, T.-Y. Huang, C.-L. Wang, and R.-B. Wu, A 60 GHz LTCC transition between microstrip line and substrate integrated waveguide, Proceedings of Asia Pacific Microwave Conference, 3, 2005.
26. Lee, Y. C., "CPW-to-stripline vertical via transitions for 60 GHz LTCC SoP applications," Progress In Electromagnetics Research Letters, Vol. 2, 37-44, 2008. doi:10.2528/PIERL07122805