A wideband bandpass filter with multiple transmission zeros using a shorted stub-loaded stepped-impedance ring resonator is proposed. The resonant characteristics are investigated by even- and odd-mode analysis. In order to obtain a wideband response, the even resonant frequencies can be lowered by the shorted stub and the stepped-impedance ring. The transmission line theory is used to analyze the transmission zeros. Besides the parameters of the shorted stub and stepped-impedance ring, the transmission zeros can also be adjusted by the port separation angle. To verify the proposed design concept, a filter with 132% 3 dB fractional bandwidth and five transmission zeros in the upper stopband is designed, simulated, and fabricated. Good agreement is observed between the simulated and measured results.
2. Shaman, H. and J. S. Hong, "An optimum ultra-wideband (UWB) band pass filter with spurious response suppression," Wireless and Microw. Tech. Conf. (WAMICON), 1-5, Dec. 2006.
3. Zhu, H. and Q. X. Chu, "Compact ultra-wideband (UWB) bandpass filter using a dual-stub-loaded resonator (DSLR)," IEEE Microw. Wireless Compon. Lett., Vol. 23, No. 10, 527-529, Oct. 2013.
4. Chu, Q. X., X. H. Wu, and X. K. Tian, "Novel UWB bandpass filter using stub-loaded multiple-mode resonator," IEEE Microw. Wireless Compon. Lett., Vol. 21, No. 8, 403-405, Aug. 2011.
5. Tand, C. W. and M. G. Chen, "A microstrip ultra-wideband bandpass filter with cascaded broadband bandpass and bandstop filters," IEEE Trans. Microw. Theory Tech., Vol. 55, No. 11, 2412-2418, Nov. 2007.
6. Zhu, L., S. Sun, and W. Menzel, "Ultra-wideband (UWB) bandpass filters using multiple-mode resonator," IEEE Microw. Wireless Compon. Lett., Vol. 15, No. 11, 796-798, Nov. 2005.
7. Fan, J., D. Z. Zhan, C. J. Jin, and J. R. Luo, "Wideband microstrip bandpass filter based on quadruple mode ring resonator," IEEE Microw. Wireless Compon. Lett., Vol. 22, No. 7, 348-350, Jul. 2012.
8. Qian, S. L. and J. S. Hong, "Miniature quasi-lumped-element wideband bandpass filter at 0.5–2GHz band using multilayer liquid crystal polymer technology," IEEE Trans. Microw. Theory Tech., Vol. 60, No. 9, 2799-2807, Sep. 2012.
9. Awai, I. and T. Yamashita, "Theory on rotated excitation of a circular dual-mode resonator and filter," IEEE MTT-S Int. Dig., Vol. 2, 781-784, Jun. 1997.
10. Kuo, J.-T., S.-C. Tang, and S.-H. Lin, "Quasi-elliptic function bandpass filter with upper stopband extension and high rejection level using cross-coupled stepped-impedance resonators," Progress In Electromagnetics Research, Vol. 114, 395-405, 2011.
11. Gao, M.-J., L.-S. Wu, and J.-F. Mao, "Compact notched ultra-wideband bandpass filter with improved out-of-band performance using quasi electromagnetic bandgap structure," Progress In Electromagnetics Research, Vol. 125, 137-150, 2012.
12. Chiou, Y.-C., P.-S. Yang, J.-T. Kuo, and C.-Y. Wu, "Transmission zero design graph for dual-mode dual-band filter with periodic stepped-impedance ring resonator," Progress In Electromagnetics Research, Vol. 108, 23-36, 2010.
13. Xue, S., W. Feng, H. Zhu, and W. Che, "Microstrip wideband bandpass filter with six transmission zeros using transversal signal-interaction concepts," Progress In Electromagnetics Research C, Vol. 34, 1-12, 2013.