Novel microstrip single-band and dual-band bandpass filters (BPFs) are presented in this paper. Firstly, a pair of open-ended stubs of less than λ/4 in length is connected to a uniform impedance resonator (UIR) at two symmetrical positions with respect to its centre, and at the same time other two open-circuited stubs with different lengths are loaded in the middle of the resonator. By virtue of parallel-coupling structure at I/O ports, a single-band BPF is constructed centered at 2.2 GHz with 10.6% 3-dB bandwidth, and two transmission zeros are implemented at the right side of the passband. Next, the L-shaped I/O coupled lines are applied to suppress the inherent spurious response of the stubs-loaded resonator. As a result, a dual-band BPF with two passbands at 2.2 GHz and 5.2 GHz, which is self-contained with three transmission zeros between the two passbands, is constituted. Finally, the proposed bandpass filters are designed and fabricated to provide an experimental validation for the predicted performances.
2. Kurzrok, R. M., "General three-resonator filters in waveguide," IEEE Trans. Microw. Theory Techn., Vol. 14, No. 1, 46-47, 1966.
3. Cameron, R. J. and J. D. Rhodes, "Asymmetric realizations for dual-mode bandpass filters," IEEE Trans. Microw. Theory Techn., Vol. 29, No. 1, 51-58, 1981.
4. Levy, R., "Direct synthesis of cascaded quadruplet (CQ) filters," IEEE Trans. Microw. Theory Tech., Vol. 43, No. 8, 2940-2945, 1995.
5. Franti, L. F. and G. M. Paganuzzi, "Odd-degree pseudoelliptical phase-equalized filter with asymmetric band-pass behaviour," IEEE European Microwave Conference, 111-116, 1981.
6. Hong, J. S. and M. J. Lancaster, "Microstrip triangular patch resonator filters," IEEE MTT-S International Microwave Symposium Digest, 331-334, 2000.
7. Bell, H. C., "Canonical lowpass prototype network for symmetric coupled-resonator bandpass filters," Electronics Letters, Vol. 10, No. 13, 265-266, 1974.
8. Bell, H. C., "Canonical asymetric coupled-resonator filters," IEEE Trans. Microw. Theory Tech., Vol. 30, No. 9, 1335-1340, 1982.
9. Zhang, M., M. Li, P.-J. Zhang, K. Duan, B. Jin, L. Huang, and Y. Song, "A novel miniaturized bandpass filter basing on stepped-impedance resonator," Progress In Electromagnetics Research Letters, Vol. 97, 77-85, 2021.
10. Ieu, W., et al., "Compact dual-mode dual-band HMSIW bandpass filters using source-load coupling with multiple transmission zeros," Electronics Letters, Vol. 55, No. 4, 210-222, 2019.
11. 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., Vol. 3, 1979-1982, 2004.
12. Wang, L. T., Y. Xiong, W.-J. Wang, L. Gong, Z. Li, X. Q. Li, and Z.-L. Liang, "Design of compact transversal wideband bandpass filter with wide upper stopband," Progress In Electromagnetics Research M, Vol. 96, 79-87, 2020.
13. Wattikornsirikul, N. and M. Kumngern, "Dual-mode dual-band bandpass filter with asymmetrical transmission zeros," Progress In Electromagnetics Research M, Vol. 86, 193-202, 2019.
14. Sami, A. and M. Rahman, "A very compact quintuple band bandpass filter using multimode stub loaded resonator," Progress In Electromagnetics Research C, Vol. 93, 211-222, 2019.
15. Konpang, J. and N. Wattikornsirikul, "Dual-mode dual-band bandpass filter with high cutoff rejection by using asymmetrical transmission zeros technique," Progress In Electromagnetics Research M, Vol. 100, 225-236, 2021.
16. Wang, Y. X., Y. L. Chen, W. H. Zou, W. C. Yang, and J. Zen, "Dual-band bandpass filter design using stub-loaded hairpin resonator and meandering uniform impedance resonator," Progress In Electromagnetics Research Letters, Vol. 95, 147-153, 2021.
17. Hong, J.-S. and M. J. Lancaster, Microstrip Filter for RF/Microwave Application, Wiley, New York, 2001.
18. Rahman, M. and J.-D. Park, "A compact tri-band bandpass filter using two stub-loaded dual mode resonators," Progress In Electromagnetics Research M, Vol. 64, 201-209, 2018.
19. Rahman, M. U., D.-S. Ko, and J. D. Park, "A compact tri-band bandpass filter utilizing double mode resonator with 6 transmission zeros," Microwave and Optical Technology Letters, Vol. 60, No. 7, 1767-1771, 2018.
20. Basit, A., M. Irfan Khattak, J. Nebhen, A. Jan, and G. Ahmad, "Investigation of external quality factor and coupling coefficient for a novel SIR based microstrip tri-band bandpass filter," PLoS ONE, Vol. 16, No. 10, e0258386, 2021.