In this paper, a compact ultra-wideband bandpass filter using a back to back Coplanar Waveguide (CPW)-to-microstrip transition structure is proposed. Compared with traditional ultra-wideband bandpass filters using hybrid structures, the proposed filter has a sharper selectivity because of two transmission zeros located at the lower and upper edges of the passband, respectively, generated by a modified T-shaped stub. Moreover, to further improve its out-of-band performance open stubs are introduced to produce extra transmission zeros at high frequency. A prototype of the proposed filter is fabricated and measured. The results show that the proposed filter achieves a bandwidth of 133% from 2.4 to 11.9 GHz, and the selectivity (skirt factor) is optimized from 50% to 92% compared to a former ultra-wideband (UWB) bandpass filter (BPF) with a similar structure. Besides, the proposed filter can offer some other advantages such as good return loss, low insertion loss, stable group delay, and compact size (16×7.55mm2). This filter can be a good candidate for UWB applications.
2. Chu, Q.-X., X.-H. Wu, and X.-K. Tian, "Novel UWB bandpass filter using stub-loaded multiple-mode resonator," IEEE Microw. Wireless Compon. Lett., Vol. 21, No. 8, 403-405, 2011.
3. Deng, H. W., Y. J. Zhao, L. Zhang, X. S. Zhang, and S. P. Gao, "Compact quintuple-mode stub-loaded resonator and UWB filter," IEEE Microw. Wireless Compon. Lett., Vol. 20, No. 8, 438-440, 2010.
4. Taibi, A., M. Trabelsi, A. Slimane, M. T. Belaroussi, and J.-P. Raskin, "A novel design method for compact UWB bandpass filters," IEEE Microw. Wireless Compon. Lett., Vol. 25, No. 1, 4-6, 2015.
5. Chu, Q.-X. and X.-K. Tian, "Design of UWB bandpass filter using stepped-impedance stub-loaded resonator," IEEE Microw. Wireless Compon. Lett., Vol. 20, No. 9, 501-503, 2010.
6. Chen, L.-Y., C.-H. Lee, and C.-I. G. Hsu, "Novel UWB BPF design using modified trisection MMR," Microw. Opt. Technol. Lett., Vol. 50, 2904-2907, 2008.
7. Wang, I.-C., C.-H. Lee, and C.-I. G. Hsu, "Design of band-notched UWB BPF with very wide upper stopband using combined λ/4 TSSIR," Journal of Electromagnetic Waves and Applications, Vol. 23, No. 2-3, 183-194, 2009.
8. Hu, H. L., X. D. Huang, and C. H. Cheng, "Ultra-wideband bandpass filter using CPW-to-microstrip coupling structure," Electron. Lett., Vol. 42, No. 10, 586-587, 2006.
9. Wang, K., S. M. Wong, and Q.-X. Chu, "A compact UWB CPW bandpass filter with short-ended H-shaped resonator and controllable notched band," Microwave. Opt. Technol. Lett., Vol. 55, No. 7, 1577-1581, 2013.
10. Xia, X., Y. Liu, H. Lin, T. Yang, and H. Jin, "Novel UWB BPF with a controllable notched band using hybrid structure," IEICE Electronics Express, Vol. 14, No. 6, 1-6, 2017.
11. Ghazali, A. N., M. Sazid, and S. Pal, "A miniaturized microstrip-to-CPW transition based UWB-BPF with shaped roll-off and minimum insertion loss," Microw. Opt. Technol. Lett., Vol. 58, No. 2, 289-293, 2016.
12. Ghazali, A. N., M. Sazid, and S. Pal, "Compact broadband balun-based UWB-BPF with minimum insertion loss and sharp selectivity," Electron. Lett., Vol. 51, No. 15, 1174-1175, 2015.
13. Li, J., C. Ding, F. Wei, and X. W. Shi, "Compact UWB BPF with notch band based on SWHMSIW," Electron. Lett., Vol. 51, No. 17, 1338-1339, 2015.
14. Mirzaee, M., B. S. Virdee, and S. Noghanian, "Compact ultra-wideband bandpass filter with variable notch characteristics based on transversal signal-interaction concepts," Int. J. RF Microwave Comput-Aid Eng., Vol. 24, 549-559, 2014.
15. Feng, W. J., W. Q. Che, and T. F. Eibert, "Ultra-wideband bandpass filter based on transversal signal-interaction concepts," Electron Lett., Vol. 24, 1330-1331, 2011.
16. Fallahzadeh, S. and M. Tayarani, "A new microstrip UWB bandpass filter using defected microstrip structures," Journal of Electromagnetic Waves and Applications, Vol. 24, No. 7, 893-902, 2010.
17. Lin, H., H. Peng, X. Xia, T. Yang, and H. Jin, "A novel ultra-wideband bandpass filter using defected microstrip structures," IEICE Electron. Expr., Vol. 13, No. 7, 1-6, 2016.
18. Tang, I.-T., D.-B. Lin, C.-M. Li, and M.-Y. Chiu, "Compact pentagon ultra-wideband bandpass filter with good out-of-band performance," Journal of Electromagnetic Waves and Applications, Vol. 23, No. 13, 1695-1706, 2009.