volume | PIER Journals

Abstract

In this letter, a series of high-selectivity bandpass filters based on parallel-coupled microstrip lines are proposed. The developed filters are derived from conventional parallel-coupled microstrip line filter, with an additional pair of parallel-coupled microstrip lines being incorporated into the two open ends, one end of which is short-circuited. Accordingly, a pair of transmission zeros is introduced into the transmission coefficient of the traditional parallel-coupled microstrip line filter by this modification, thereby enhancing its selectivity. Additionally, to further enhance the selectivity of the developed filter, a pair of quarter-wavelength transmission lines are connected to each of the short-circuited ends. This additional structure introduces another pair of transmission zeros, thereby further improving the selectivity of the developed filter. For demonstration, two bandpass filters have been designed and fabricated. Specifically, measured attenuation slopes for the modified structure were 213 dB/GHz and 106 dB/GHz at the lower ND upper band edges, respectively.

1. Aidoo, Michael Wilson, Kaijun Song, and Yong Fan, "High selectivity wideband two-channel bandpass filter for 5G microwave communication systems," Microwave and Optical Technology Letters, Vol. 66, No. 10, e34289, 2024.
doi:10.1002/mop.34289 Google Scholar

2. Yan, Jun-Mei, An-Qi Tong, and Liang-Zu Cao, "Design of a compact microstrip box-like bandpass filter with high-frequency selectivity and excellent stop-band performance," Microwave and Optical Technology Letters, Vol. 67, No. 8, e70340, 2025.
doi:10.1002/mop.70340 Google Scholar

3. Pozar, David M., Microwave Engineering, 4th Ed., John Wiley & Sons, Hoboken, NJ, USA, 2012.

4. Ramkumar, S. and R. Boopathi Rani, "Compact high-selective wide-stopband coupled bandpass filter using middle-shorted hairpin-resonators," AEU --- International Journal of Electronics and Communications, Vol. 162, 154580, 2023.
doi:10.1016/j.aeue.2023.154580 Google Scholar

5. Lu, Xilong, Xueyang Fang, Guangsong Wei, Shigang Zhou, Li Sun, Xudong Bai, Bokai Weng, Yanhong Gao, and Dongbo Chen, "High selectivity wideband superconducting filter design based on feed line resonator (FLR) method," IEEE Microwave and Wireless Technology Letters, Vol. 34, No. 9, 1079-1082, Sep. 2024.
doi:10.1109/lmwt.2024.3415074 Google Scholar

6. Kanaparthi, V. Phani Kumar, Vamsi Krishna Velidi, Rengasamy Rajkumar, et al. "A compact ultra-wideband multimode bandpass filter with sharp-rejection using stepped impedance open stub and series transformers," IEEE Transactions on Circuits and Systems II: Express Briefs, Vol. 69, No. 12, 4824-4828, Dec. 2022.
doi:10.1109/tcsii.2022.3192512 Google Scholar

7. Lu, Lin-Xi, Yu-Ke Zhou, Wei Qin, Wen-Wen Yang, and Jian-Xin Chen, "A novel and compact dual-orthogonal-ridged dielectric waveguide resonator and its applications to bandpass filters," IEEE Transactions on Microwave Theory and Techniques, Vol. 73, No. 3, 1671-1679, Mar. 2025.
doi:10.1109/tmtt.2024.3447011 Google Scholar

8. Tang, Wei Sheng, Yi-Ming Zhang, Shao Yong Zheng, and Yong Mei Pan, "Low-cost compact inline single-/dual-band filters based on dual-mode dielectric resonators with highly integrated and flexible mixed couplings," IEEE Transactions on Microwave Theory and Techniques, Vol. 73, No. 9, 6589-6602, Sep. 2025.
doi:10.1109/tmtt.2025.3556090 Google Scholar

9. Shaman, Hussein and Jia-Sheng Hong, "Input and output cross-coupled wideband bandpass filter," IEEE Transactions on Microwave Theory and Techniques, Vol. 55, No. 12, 2562-2568, Dec. 2007.
doi:10.1109/tmtt.2007.910066 Google Scholar

10. Choi, Hyunjong, Minhyup Song, and Juseop Lee, "Novel transmission-line circuit configuration of cross-coupled filter with negative coupling," IEEE Transactions on Microwave Theory and Techniques, Vol. 72, No. 8, 4842-4853, Aug. 2024.
doi:10.1109/tmtt.2024.3357932 Google Scholar

11. Chu, Peng, Jialong Zhou, Wenyu Zhang, Fang Zhu, Li Cheng, Leilei Liu, and Ke Wu, "Cross coupled substrate integrated waveguide filter with quasi elliptic response and wide stopband," IEEE Transactions on Components, Packaging and Manufacturing Technology, Vol. 15, No. 8, 1726-1731, Aug. 2025.
doi:10.1109/tcpmt.2025.3581956 Google Scholar

12. Hong, Jia-Sheng and M. J. Lancaster, "Cross-coupled microstrip hairpin-resonator filters," IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 1, 118-122, Jan. 1998.
doi:10.1109/22.654931 Google Scholar

13. Liu, Huan, Long Chen, Song Wu, Minmin Mao, Harry Baxter, Bin Yang, Wenjun Li, and Kaixin Song, "A new electric coupling and its applications on millimeter-wave SIW filter with high selectivity and controllable TZs," AEU --- International Journal of Electronics and Communications, Vol. 173, 154989, 2024.
doi:10.1016/j.aeue.2023.154989 Google Scholar

14. Zhang, Xinyu, Yongle Wu, Huiting Yu, Weimin Wang, Yuhao Yang, and Jinchun Gao, "High selectivity wideband bandpass filters based on flexibly transferring the structure of a coupled-line," AEU --- International Journal of Electronics and Communications, Vol. 155, 154334, 2022.
doi:10.1016/j.aeue.2022.154334 Google Scholar

15. Lin, Wen-Jeng, Jian-Yi Li, Lih-Shan Chen, Ding-Bing Lin, and Mau-Phon Houng, "Investigation in open circuited metal lines embedded in defected ground structure and its applications to UWB filters," IEEE Microwave and Wireless Components Letters, Vol. 20, No. 3, 148-150, Mar. 2010.
doi:10.1109/lmwc.2010.2040213 Google Scholar

16. Luo, Xun, Jian-Guo Ma, and Er-Ping Li, "Hybrid microstrip/DGS cell for filter design," IEEE Microwave and Wireless Components Letters, Vol. 21, No. 10, 528-530, Oct. 2011.
doi:10.1109/lmwc.2011.2163497 Google Scholar

17. Matthaei, G. L., L. Young, and E. M. T. Jones, Microwave Filters, Impedance-matching Networks, and Coupling Structures, Artech House, Mountain View, CA, USA, 1980.

18. Gomez-Garcia, Roberto, Manuel Sanchez-Renedo, Bernard Jarry, Julien Lintignat, and Bruno Barelaud, "A class of microwave transversal signal-interference dual-passband planar filters," IEEE Microwave and Wireless Components Letters, Vol. 19, No. 3, 158-160, Mar. 2009.
doi:10.1109/lmwc.2009.2013738 Google Scholar

19. Gomez-Garcia, R. and J. I. Alonso, "Design of sharp-rejection and low-loss wide-band planar filters using signal-interference techniques," IEEE Microwave and Wireless Components Letters, Vol. 15, No. 8, 530-532, Aug. 2005.
doi:10.1109/lmwc.2005.852797 Google Scholar

20. Bahl, I. J. and D. K. Trivedi, "A designer's guide to microstrip line," Microwaves, Vol. 16, No. 5, 174-182, May 1977. Google Scholar

21. Li, Rui and Lei Zhu, "Compact UWB bandpass filter using stub-loaded multiple-mode resonator," IEEE Microwave and Wireless Components Letters, Vol. 17, No. 1, 40-42, Jan. 2007.
doi:10.1109/lmwc.2006.887251 Google Scholar

22. Ishii, Hiroyuki, Toru Kimura, Naotaka Kobayashi, Atsushi Saito, Zhewang Ma, and Shigetoshi Ohshima, "Development of UWB HTS bandpass filters with microstrip stubs-loaded three-mode resonator," IEEE Transactions on Applied Superconductivity, Vol. 23, No. 3, 1500204-1500204, Jun. 2013.
doi:10.1109/tasc.2012.2232697 Google Scholar

23. Feng, Wenjie, Xin Gao, Wenquan Che, Wanchen Yang, and Quan Xue, "LTCC wideband bandpass filters with high performance using coupled lines with open/shorted stubs," IEEE Transactions on Components, Packaging and Manufacturing Technology, Vol. 7, No. 4, 602-609, Apr. 2017.
doi:10.1109/tcpmt.2017.2662202 Google Scholar

24. Feng, Wenjie, Xin Gao, Wenquan Che, and Quan Xue, "Bandpass filter loaded with open stubs using dual-mode ring resonator," IEEE Microwave and Wireless Components Letters, Vol. 25, No. 5, 295-297, May 2015.
doi:10.1109/lmwc.2015.2410174 Google Scholar

Dr. Chuan Shao

Dr. Xin Gao

Dr. Rong Cai

Dr. Ke Wang

Dr. Xinnai Zhang

Dr. Kai Xu