Inductive-coupling scheme for microstrip bandpass filters with quarter-wavelength stepped-impedance resonators is proposed. This is realized by a short-end stub which behaves as a K-inverter. It is investigated that the coupling coefficient of the resonators can be easily controlled by the length of the short-end stub. The filter has a compact size and good stopband rejection by employing the quarter-wavelength stepped-impedance resonators. The design procedure of this kind of filter is provided. Two filters working at 2.4 GHz are designed and fabricated to demonstrate the proposed method.
1. Lee, J.-R., J.-H. Cho, and S.-W. Yun, "New compact bandpass filter using microstrip λ\4 resonators with open stub inverter," IEEE Microw. Wireless Compon. Lett., Vol. 10, No. 12, 526-527, 2000.
2. Wang, C.-H., Y.-S. Lin, and C. H. Chen, "Novel inductance-incorporated microstrip coupled-line bandpass filters with two attenuation poles ," IEEE MTT-S Int. Microw. Symp. Dig., 1979-1982, 2004.
3. Athukorala, L. and D. Budimir, "Design of open-loop dual-mode microstrip filters," Progress In Electromagnetics Research Letters, Vol. 19, 179-185, 2010.
4. Hong, J.-S., H. Shaman, and Y.-H. Chun, "Dual-mode microstrip open-loop resonators and filters," IEEE Trans. on Microwave Theory and Tech., Vol. 55, No. 8, 1764-1770, 2007. doi:10.1109/TMTT.2007.901592
5. Kuo, Y.-T. and C.-Y. Chang, "Analytical design of two-mode dual-band filters using E-shaped resonators," IEEE Trans. on Microwave Theory and Tech., Vol. 60, No. 2, 250-260, 2012. doi:10.1109/TMTT.2011.2176506
6. Makimoto, M. and S. Yamashita, Microwave Resonators and Filters for Wireless Communication: Theory, Design and Application, , Springer, Berlin, 1997.
7. Liang, C. H. and C. Y. Chang, "Compact wideband bandpass filters using stepped-impedance resonators and interdigital coupling structures," IEEE Microw. Wireless Compon. Lett., Vol. 19, No. 9, 551-553, 2009. doi:10.1109/LMWC.2009.2027060
8. Hong, J.-S. and M. J. Lancaster, "Microstrip Filters for RF/Microwave Applications," Wiley, 2001.
9. Kuo, T.-N., S.-C. Lin, C.-H. Wang, and C.-H. Chen, "Compact bandpass filters based on microstrip and coplanar waveguide resonators ," 2006 Asia-Paci¯c Microwave conference Proceedings, 1431-1434, 2006.