This paper proposes a novel miniaturized interdigital capacitor loaded interdigital filter, which is applied in C-band (3.2 GHz~4.2 GHz). By loading an interdigital capacitor on the open end of the resonator of the interdigital filter, the length of the resonator is shortened by 28%. The resonant frequency offset caused by tap introduction is adjusted by using the method of impedance compensation at the open end of resonator 1 and resonator 5, which further reduces the size of the filter. The miniaturized filter is fabricated on a 0.254 mm-thickness alumina substrate with relative dielectric constant of 9.8 by thin film process. Measured results are as follows: the passband of the filter is 3.2 GHz~4.2 GHz; the insertion at center frequency is -1 dB; the return loss is less than -18.3 dB. The size of the filter is 4.98 mm*6.45 mm (0.15λg*0.20λg), which is 37.8% smaller than that of the traditional interdigital filter.
2. Haddi, S. B., A. Zugari, A. Zakriti, and S. Achraou, "A compact microstrip T-shaped resonator band pass filter for 5G applications," 2020 International Conference on Intelligent Systems and Computer Vision (ISCV), 1-5, 2020.
3. Luo, L., H. Tie, Q. Ma, and B. Zhou, "Compact LTCC filter with 7th-order harmonics suppression for 5G N77 band applications," Progress In Electromagnetics Research Letters, Vol. 98, 69-74, 2021.
4. Wang, P., K. Duan, M. Li, M. Zhang, and B. Jin, "A novel miniaturized L-band filter with great stopband characteristics using interdigitated coupled lines CRLH-TL structure," Progress In Electromagnetics Research C, Vol. 114, 57-67, 2021.
5. Cheng, T., W. Yang, and Y. Ze, "Development of C-band embedded layout filter based on LTCC," Electronic Design Engineering, Vol. 28, No. 19, 107-112, 2020.
6. Peng, Y., et al., "Design of C-band double-layer MEMS filter," Journal of Microwave, No. S1, 223-226, 2016.
7. 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.
8. Tang, L., X. Jiang, H. Wei, and W. Liu, "A novel miniaturized C-band bandpass filter," Progress In Electromagnetics Research M, Vol. 106, 167-177, 2021.
9. Bharathi, R. D., J. E. Yamini, A. Evangeline, and D. B. Narayanan, "Design and analysis of interdigital microstrip bandpass filter for center frequency 2.4 GHz," 2017 Third International Conference on Science Technology Engineering & Management (ICONSTEM), 930-933, 2017.
10. Li, H., "Design and realization of a microminiaturized filter based on broadside-coupled interdigital structure," 2012 International Conference on Microwave and Millimeter Wave Technology (ICMMT), 1-3, IEEE, 2012.
11. Zhang, X., Q. Zhai, Z. Li, W. Ou, and Y. Ou, "Design of a K-band two-layer microstrip interdigital filter exploiting aggressive space mapping," Journal of Electromagnetic Waves and Applications, Vol. 32, No. 17, 2281-2291, 2018.
12. Min, T., et al., "Design of C-band interdigital filter and compact C-band hairpin bandpass film filter on thin lm substrate,", Springer International Publishing, 2017.
13. Wen, S. W., G. Yang, and X. X. Qian, "Initial design flow of tapped microstrip interdigital filter," High Power Laser and Particle Beams, Vol. 26, No. 9, 2262-2269, 2018.
14. Hong, J. S., Microstrip Filters for RF/Microwave Applications, John Wiley & Sons, USA, 2004.
15. Qiao, D. and Y. Dai, "Research on LTCC bandpass filter loaded with high performance capacitor," Electronic Components and Materials, Vol. 34, No. 12, 68-71, 2015.
16. Huang, X., et al., "A capacitive loaded broadband waveguide filter," Radar and Countermeasure, Vol. 41, No. 1, 62-64, 2021.
17. Fang, J., Z. Zhuang, and Y. Dai, "Miniaturized ultra-wideband high-pass filter based on LTCC," Research and Progress of Solid-state Electronics, Vol. 39, No. 4, 269-272+296, 2019.
18. Xu, H. and W. Sheng, "The X-band microstrip filter design," 2017 7th IEEE International Symposium on Microwave, Antenna, Propagation, and EMC Technologies (MAPE), 351-355, 2017.
19. Duan, K., P. Zhang, D. Cheng, Y. Song, L. Huang, and M. Li, "Design of new miniaturized broadband bandpass filter based on SIR," 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall), 1640-1644, Xiamen, China, Dec. 17-20, 2019.