volume | PIER Journals

Abstract

This paper presents a miniaturized tunable bandpass filter, consisting of two coaxial dielectric resonators and a pair of parallel-coupled lines. A coaxial dielectric resonators and a microstrip line form a new step-impedance resonator (SIR), which is different from a conventional SIR. Varactor diodes are connected to SIRs to tune the center frequency. The gap between parallel-coupled lines controls the inter-stage coupling coefficient. Lumped inductors used for coupling to I/O ports can reduce design complexity. The variations of coupling coefficient and external quality factor with tuning frequency are analyzed using HFSS software. A appropriate coupling coefficient which satisfies with constant fractional bandwidth within the tuning range is available. A tunable filter has been made of dielectric ceramics with dielectric constant of 38, fabricated on dielectric substrate and measured using Networks analyzer. Center frequencies vary from 0.43 GHz to 0.78 GHz, 3 dB fractional bandwidth from 6.4% to 6.8% when bias voltages are applied from 0 V to 10 V. The measured results validate the approach and agree with the simulation.

1. Liu, B., F. Wei, Q. Y. Wu, and X. W. Shi, "A tunable bandpass filter with constant absolute bandwidth," Journal of Electromagnetic Waves and Applications, Vol. 25, No. 11–12, 1596-1604, 2011.
doi:10.1163/156939311797164819 Google Scholar

2. Huang, X.-G., Q.-Y. Feng, Q.-Y. Xiang, and D.-H. Jia, "Constant absolute bandwidth tunable filter using varactor-loaded open-loop resonators," Microwave and Optical Technology Letters, Vol. 56, No. 5, 1178-1181, 2014.
doi:10.1002/mop.28285 Google Scholar

3. Jia, D.-H., Q.-Y. Feng, X.-G. Huang, and Q.-Y. Xiang, "A two-pole tunable filter with constant fractional-bandwidth characteristics," International Journal of Electronics, Vol. 101, No. 7, 983-993, 2014.
doi:10.1080/00207217.2013.805388 Google Scholar

4. Athukorala, L. and D. Budimir, "Open-loop tunable resonators and filters with constant bandwidth," IET Microw. Antennas Propag., Vol. 6, No. 7, 800-806, 2012.
doi:10.1049/iet-map.2010.0426 Google Scholar

5. Zhang, H.-L., X. Y. Zhang, and B.-J. Hu, "Tunable bandpass filters with constant absolute bandwidth," 9th International Symposium on Antennas Propagation and EM Theory (ISAPE), 1200-1203, 2010. Google Scholar

6. Yu, F. L., Y. B. Zhang, X. Y. Zhang, B. J. Hu, and X. Y. Wang, "Tunable bandpass filters with constant absolute bandwidth and high linearity," International Conference on Microwave and Millimeter Wave Technology (ICMMT), 1-3, 2012. Google Scholar

7. Makimoto, M. and M. Sagawa, "Varactor tuned bandpass filters using microstrip-line ring resonators," IEEE MTT-S Int. Microwave Symp. Dig., 411-414, 1986. Google Scholar

8. Hunter, I. C. and J. D. Rhodes, "Electronically tunable microwave bandpass filter," IEEE Trans. Microwave Theory Tech., Vol. 30, 1354-1360, 1982.
doi:10.1109/TMTT.1982.1131260 Google Scholar

9. Wang, Y.-Y., F. Wei, B. Liu, H. Xu, and X.-W. Shi, "A tunable bandpass filter with constant absolute bandwidth based on one ring resonator," Journal of Electromagnetic Waves and Applications, Vol. 26, No. 11-12, 1587-1593, 2012.
doi:10.1080/09205071.2012.705137 Google Scholar

10. Kim, B.-W. and S.-W. Yun, "Varactor-tuned combline bandpass filter using step-impedance microstrip lines," IEEE Trans. Microwave Theory Tech., Vol. 52, No. 4, 1279-1284, 2004.
doi:10.1109/TMTT.2004.825626 Google Scholar

11. Park, S.-J. and G. M. Rebeiz, "Low-loss two-pole tunable filters with three different predefined bandwidth characteristics," IEEE Trans. Microwave Theory Tech., Vol. 56, No. 5, 1137-1148, 2008.
doi:10.1109/TMTT.2008.921638 Google Scholar

12. Zhao, Z., J. Chen, L. Yang, and K. Chen, "Three-pole tunable filters with constant bandwidth using mixed combline and split-ring resonators," IEEE Microwave and Wireless Components Letters, 1-3, 2014. Google Scholar

13. El-Tanani, M. A. and G. M. Rebeiz, "Corrugated microstrip coupled lines for constant absolute bandwidth tunable filters," IEEE Trans. Microwave Theory Tech., Vol. 58, No. 4, 956-963, 2010.
doi:10.1109/TMTT.2010.2042517 Google Scholar

14. Zhao, Z.-Y., J. Chen, L. Yang, and K.-H. Chen, "Three-pole tunable filters with constant bandwidth using mixed combline resonators," International Journal of Electronics, 1-15, 2015. Google Scholar

15. Jia, D., Q. Feng, X. Huang, and Q. Xiang, "Tunable 3-pole bandpass filter with constant absolute bandwidth and > 60 dB rejection at desired location of Stopband," Journal of Electromagnetic Waves and Applications, 1-14, 2015. Google Scholar

16. Xiang, Q., Q Feng, X. Huang, and D. Jia, "Electrical tunable microstrip LC bandpass filters with constant bandwidth," IEEE Trans. Microwave Theory Tech, Vol. 61, No. 3, 1124-1130, 2013.
doi:10.1109/TMTT.2013.2241781 Google Scholar

17. Lee, J.-H., J.-W. Choi, X.-G. Wang, and S.-W. Yun, "Design of tunable bandpass filter using PIN diode with constant absolute bandwidth," Asia-Pacific Microwave Conference Proceedings, 191-193, 2013. Google Scholar

18. Kholodnyak, D., V. Turgaliev, and A. Baskakova, "A method to design lumped-element tunable bandpass filters with constant absolute bandwidth," Proceedings of the 44th European Microwave Conference, 335-338, 2012. Google Scholar

19. Lee, J. and K. Sarabandi, "An analytic design method for microstrip tunable filters," IEEE Trans. Microwave Theory Tech., Vol. 56, No. 7, 1699-1706, 2008.
doi:10.1109/TMTT.2008.925569 Google Scholar

20. Kapii, K. B., "A vacartor-tunable filter with constant bandwidth and loss compensation," Microwave Journal, 105-110, 2007. Google Scholar

21. Chaudhary, G., Y. Jeong, and J. Lim, "Harmonic suppressed dual-band bandpass filter with tunable passbands," IEEE Trans. Microwave Theory Tech., Vol. 60, No. 7, 2115-2123, 2012.
doi:10.1109/TMTT.2012.2197020 Google Scholar

22. Chaudhary, G., Y. Jeong, and J. Lim, "Dual-band bandpass filter with independently tunable center frequencies and bandwidths," IEEE Trans. Microwave Theory Tech., Vol. 61, No. 1, 107-116, 2013.
doi:10.1109/TMTT.2012.2222910 Google Scholar

23. Makimoto, M. and S. Yamashita, Microwave Resonators and Filters for Wireless Communication: Theory, Design and Application, Springer-Verlag, Berlin Heidelberg, 2001.
doi:10.1007/978-3-662-04325-7_5

24. Hong, J.-S., Microstrip Filters for RF Microwave Applications, 3rd Edition, J. Wiley & Sons, 2011.
doi:10.1002/9780470937297

25. Matthaei, G. L., E. Young, and E. M. T. Jones, Microwave Filters, Impedance-matching Networks, Coupling Structures, Artech House, Norwood, MA, USA, 1980.

Professor Liangzu Cao

Dr. Guangwen Li

Dr. Jian Hu

Dr. Lixia Yin