A dual-band bandpass filter with wide and highly attenuated stopbands is designed using parallel coupled microstrip line (PCML) and stepped-impedance-resonators (SIRs). The proposed filter is composed of a pair of highly coupled PCML-SIR structure and a central resonator using a low impedance rectangular microstrip. Initially, the wide dual-band performance is achieved by creating a transmission zero between those two bands using a tightly coupled PCML-SIR with a suitable impedance ratio. Then, a low impedance resonator is placed between the pair of PCML-SIR to generate multiple resonant frequencies for a broadband performance. The simulated and measured results of those filters agree very well. The bandwidth of the first band in the developed filters extends from 1.75 GHz to 3.75 GHz with less than 0.3 dB insertion loss at the center of the band. The second band has a bandwidth that extends from 6.95 GHz to 8.75 GHz with less than 0.5 dB insertion loss at the center of that band. The stopband separating those two passband has more than 30 dB attenuation with transmission zero at 5.85 GHz.
2. Xiao, , J.-K. and H.-F. Huang, "New dual-band bandpass filter with compact sir structure," Progress In Electromagnetics Research Letters, Vol. 18, 125-134, 2010.
3. Chen, C., "Dual-band bandpass filter using coupled resonator pairs," IEEE Microwave and Wireless Components Letters, Vol. 15, No. 4, 259-261, 2005.
4. Kuo, J., T. Yeh, and C. Yeh, "Design of microstrip bandpass filters with a dual-passband response," IEEE Trans. Microwave Theory Tech., Vol. 53, No. 4, 1331-1337, 2005.
5. Wang, J., Y. Guo, B. Wang, L. Ong, and S. Xiao, "High-selectivity dual-band stepped-impedance bandpass filter," Electronics Letters, Vol. 42, No. 9, 2006.
6. Hu, X., Q. Zhang, and S. He, "Compact dual-band rejection filter based on complementary meander line split ring resonator," Progress In Electromagnetics Research Letters, Vol. 8, 181-190, 2009.
7. Wu, G.-L., W. Mu, X.-W. Dai, and Y.-C. Jiao, "Design of novel dual-band bandpass filter with microstrip meander-loop resonator and CSRR DGS," Progress In Electromagnetics Research, Vol. 78, 17-24, 2008.
8. Mokhtaari, M., J. Bornemann, and S. Amari, "Quasi-elliptic dual-band filter design using stepped-impedance resonators and coupling topologies for narrow-to-wide-band applications," IET Microwave Antenna Propag., Vol. 2, No. 8, 863-870, 2008.
9. Djoumessi, E. and K. Wu, "Multilayer dual-mode dual-bandpass filter," IEEE Microwave and Wireless Components Letters, Vol. 19, No. 1, 21-23, 2009.
10. Zhang, X., J. Chen, J. Shi, and Q. Xue, "High-selectivity dual-band bandpass filter using asymmetric stepped-impedance resonators," Electronics Letters, Vol. 45, No. 1, 2009.
11. Shi, J. and Q. Xue, "Dual-band and wide-stopband single-band balanced bandpass filters with high selectivity and common-mode suppression," IEEE Trans. Microwave Theory Tech., Vol. 58, No. 8, 2204-2212, 2010.
12. Jiang, M., L. Chang, and A. Chin, "Design of dual-passband microstrip bandpass filters with multi-spurious suppression," IEEE Microwave and Wireless Components Letters, Vol. 20, No. 4, 199-201, 2010.
13. Velazquez-Ahumada, M. D. C., J. Martel-Villagr, F. Medina, and F. Mesa, "Application of stub loaded folded stepped impedance resonators to dual band filters," Progress In Electromagnetics Research, Vol. 102, 107-124, 2010.
14. Ma, D.-C., Z.-Y. Xiao, L.-L. Xiang, X.-H. Wu, C.-Y. Huang, and X. Kou, "Compact dual-band bandpass filter using folded SIR with two stubs for WLAN," Progress In Electromagnetics Research, Vol. 117, 357-364, 2011.
15. Kuo, J.-T., C.-Y. Fan, and S.-C. Tang, "Dual-wideband bandpass filters with extended stopband based on coupled-line and coupled three-line resonators," Progress In Electromagnetics Research, Vol. 124, 1-15, 2012.
16. Zhu, L., S. Sun, and W. Menzel, "Ultra-wideband (UWB) bandpass filters using multiple-mode resonator," IEEE Microwave and Wireless Components Letters, Vol. 15, No. 11, 2005.
17. Marimuthu, J. and M. Esa, "Three element compact broadband parallel-coupled microstrip bandpass filter of simple configuration," IEEE Proc. of Asia-Pacific Conference on Applied Electromagnetics, Melaka, Malaysia, Dec. 2007.
18. Hong, J. S. and M. J. Lancaster, Microstrip Filters for RF/Microwave Applications, Wiley, New York, 2001.
19. Zysman, G. I. and A. K. Johnson, "Coupled transmission line networks in an inhomogeneous dielectric medium," IEEE Trans. Microwave Theory Tech., Vol. 17, No. 10, 1969.
20. Marimuthu, J. and M. Esa, "Equivalent J --- Inverter network parameters analysis and cancellation of spurious response of parallel coupled microstrip line," IEEE International RF and Microwave Conf., Kuala Lumpur, Malaysia, Dec. 2006.
21. Marimuthu, J. and M. Esa, "Experimental performance of harmonic suppressed bandpass filter," IEEE Proc. of Asia-Pacific Conference on Applied Electromagnetics, Melaka, Malaysia, Dec. 2007.