Novel compact microstrip quadruple-mode stub-loaded resonator and broadband bandpass filter (BPF) are proposed in this letter. As a starting part of designing a quadruple-mode broadband BPF, the initial novel triple-mode open impedance-stepped stub loaded resonator characteristic is investigated to choose its proper dimensions. Based on these pre-determined dimensions of the triple-mode resonator, two identical short-circuited stubs are loaded against the impedance-stepped open stubs in the resonator to generate a tuned resonant mode and a transmission zero in lower stopband which leads to a high rejection skirt. A compact broadband BPF with the quadruple-mode resonator is simulated, fabricated and measured. The measured results agree well with the EM simulations.
2. Huang, X. D. and C. H. Cheng, "A novel coplanar-waveguide bandpass filter using a dual-mode square-ring resonator," IEEE Microwave and Wireless Components Lett., Vol. 16, No. 1, 13-15, Jan. 2006.
3. Kang, W., W. Hong, and J. Y. Zhou, "Performance improvement and size reduction of microstrip dual-mode bandpass filter," Electronics Letter, Vol. 44, No. 6, 421-422, Mar. 2008.
4. Hong, J.-S., H. Shaman, and Y.-H. Chun, "Dual-mode microstrip open-loop resonators and filters," IEEE Transactions on Microwave Theory and Techniques, Vol. 55, No. 8, 1764-1770, Aug. 2007.
5. Zhou, M., X. Tang, and F. Xiao, "Miniature microstrip bandpass filter using resonator-embedded dual-mode resonator based on source-load coupling," IEEE Microwave and Wireless Components Lett., Vol. 20, No. 3, 139-141, Mar. 2010.
6. Shen, W., X.-W. Sun, and W.-Y. Yin, "A novel microstrip filter using three-mode stepped impedance resonator (TSIR)," IEEE Microw. Wireless Compon. Lett., Vol. 19, No. 12, 774-776, Dec. 2009.
7. Lei, R. and L. Zhu, "Compact UWB bandpass filter using stub-loaded multiple-mode resonator," IEEE Microw. Wireless Compon. Lett., Vol. 17, No. 1, 40-42, Nov. 2007.
8. Wong, S. W. and L. Zhu, "EBG-embedded multiple-mode resonator for UWB bandpass filter with improved upper-stopband performance," IEEE Microw. Wireless Compon. Lett., Vol. 17, No. 6, 421-423, Jun. 2007.
9. Han, L., K. Wu, and X. P. Chen, "Compact ultra-wideband bandpass filter using stub-loaded resonator," Electronics Letter, Vol. 45, No. 10, May 2009.
10. Wong, S. W. and L. Zhu, "Quadruple-mode UWB bandpass filter with improved out-of-band rejection," IEEE Microw. Wireless Compon. Lett., Vol. 19, No. 3, 152-154, Mar. 2009.
11. Ma, K., K. C. B. Liang, R. M. Jayasuriya, and K. S. Yeo, "A wideband and high rejection multimode bandpass filter using stub perturbation," IEEE Microw. Wireless Compon. Lett., Vol. 19, No. 1, 24-26, Jan. 2009.