A fifth-order bandpass filter with high selectivity and wide-stopband by using quarter- and half-wavelength uniform impedance resonators (UIRs) is presented in this letter. The use of a terminated coupled line provides controllable transmission zeros that can suppress the parasitic passbands. A pair of transmission zeros is generated on both sides of the passband by introducing cross-coupling. As a result, high selectivity and wide stopband can be achieved simultaneously. The method of controlling transmission zeros using a coupled line and an open/short-circuited stub is analyzed, and the method of improving passband selectivity using cross-coupling is given in detais. The concept is experimentally tested in a microstrip bandpass filter with center frequency 1 GHz. The measured attenuation is better than 24 dB up to 18 GHz.
2. Huang, C.-Y., M.-H. Weng, C.-S. Ye, and Y.-X. Xu, "A high band isolation and wide stopband diplexer using dual-mode stepped-impedance resonators," Progress In Electromagnetics Research, Vol. 100, 299-308, 2010.
doi:10.2528/PIER09112701
3. Wu, H.-W., S.-K. Liu, M.-H. Weng, and C.-H. Hung, "Compact microstrip bandpass filter with multispurious suppression," Progress In Electromagnetics Research, Vol. 107, 21-30, 2010.
doi:10.2528/PIER10061601
4. Akra, M., E. Pistono, H. Issa, A. Jrad, and P. Ferrari, "Full study of the parallel-coupled stub-loaded resonators: Synthesis method in a narrow band with an extended optimal rejection bandwidth," IEEE Trans. Microw. Theory Techn., Vol. 62, No. 12, 3380-3392, Dec. 2014.
doi:10.1109/TMTT.2014.2364599
5. Tang, C., X. Q. Lin, W. M. Liu, and Y. Fan, "Wide stopband bandpass filters based on quarter-wavelength resonators," IET Microw. Antennas Propag., Vol. 11, No. 10, 1379-1388, Aug. 2017.
doi:10.1049/iet-map.2016.0785
6. Chen, F. C., et al., "Design of wide-stopband bandpass filter and diplexer using uniform impedance resonators," IEEE Trans. Microw. Theory Techn., Vol. 64, No. 12, 4192-4203, Dec. 2016.
doi:10.1109/TMTT.2016.2613056
7. He, Z. S., Z. H. Shao, and C. J. You, "Parallel feed bandpass filter with high selectivity and wide stopband," Electron. Lett., Vol. 52, No. 10, 844-846, May 2016.
doi:10.1049/el.2015.3345
8. Weng, S.-C., K.-W. Hsu, and W.-H. Tu, "Compact and switchable dual-band bandpass filter with high selectivity and wide stopband," Electron. Lett., Vol. 49, No. 20, 1275-1277, Sep. 2017.
doi:10.1049/el.2013.2154
9. Killamsetty, V. K. and B. Mukherjee, "Miniaturised highly selective bandpass filter with very wide stopband using meander coupled lines," Electron. Lett., Vol. 53, No. 13, 889-890, Jun. 2017.
doi:10.1049/el.2017.1270
10. Thomas, J. B., "Cross-coupling in coaxial cavity filters - A tutorial overview," IEEE Trans. Microw. Theory Techn., Vol. 51, No. 4, 1368-1376, Apr. 2003.
doi:10.1109/TMTT.2003.809180
11. Cameron, R. J., C. M. Kudsia, and R. R. Mansour, Microwave Filters for Communication Systems Fundamentals Design and Applications, Wiley, New York, 2007.
Submit
