Novel compact multiband microstrip transversal bandpass filters (BPF) using short-circuited or open-circuited stub-loaded half-wavelength resonators (SLR) are presented. The dual-band BPF consists of two SLRs and two T-shaped feedlines, and the tri-band BPF can be implemented by a simple reconfiguration of adding one resonator above the original circuit of the dual-band BPF. Multiple transmission zeroes are created to improve the selectivity of the filters. Furthermore, the high degree of design freedom is obtained for every passband of dual- or triple-band BPF is achieved by independent resonators and independent signal paths. To verify the proposed concept, two dual-band bandpass filters (filter I and II) and one tri-band bandpass filter (filter III) are designed and fabricated. Both theoretical and measured results are presented, with good agreements.
2. Liu, Y., Y. J. Zhao, Y. G. Zhou, and Z. Y. Niu, "Integrated dual-band BPF and single-band BSF for tri-band filter design," Journal of Electromagnetic Waves and Applications, Vol. 25, No. 17-18, 2420-2428, 2011.
3. Mokhtaari, , M., J. Bornemann, K. Rambabu, S. Amari, "Coupling-matrix design of dual and triple passband filters ," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 11, Nov. 2006.
4. Sun, S. and L. Zhu, "Compact dual-band microstrip bandpass filter without external feed," IEEE Microw. Wireless Comp. Lett., Vol. 15, No. 10, 644-646, 2005.
5. Chen, F. C. and Q. X. Chu, "Design of compact tri-band bandpass filters using assembled resonators," IEEE Trans. Microw. Theory Tech., Vol. 57, 165-171, 2009.
6. Wu, , H.-W. and 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.
7. Zhang, Y. and M. Sun, "Dual-band microstrip bandpass filter using stepped-impedance resonators with new coupling schemes," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 10, 3779-3785, Oct. 2006.
8. Sung, Y., "Dual-mode dual-band filter with band notch structures," IEEE Microw. Wireless Compon. Lett., Vol. 20, No. 2, 73-75, Feb. 2010.
9. 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, May 2011.
10. 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, 2029-203, 2010.
11. Chen, C. F., T. Y. Huang, and R. B. Wu, "Design of dual-and triple-passband filters using alternately cascaded multiband resonators," IEEE Trans. Microw. Theory Tech., Vol. 54, 3550-3558, 2006.
12. Zhou, M. Q., X. H. Tang, and F. Xiao, "Compact dual band transversal bandpass filter with multiple transmission zeros and controllable bandwidths," IEEE Microw. Wireless Compon. Lett., Vol. 19, No. 6, Jun. 2009.
13. Rosenberg, U. and S. Amari, "Novel coupling schemes for microwave resonator filters," IEEE Trans. Microw. Theory Tech., Vol. 50, No. 12, 2896-2902, Dec. 2002.
14. Liao, C.-K., P.-L Chi, and C.-Y Chang, "Microstip realization of generalized Chebyshev filters with box-like coupling schemes," IEEE Trans. Microw. Theory Tech., Vol. 55, No. 1, 147-153, 2007.