In order to meet the requirements for the suppression of mirror frequencies in the 5G RF front end, this paper proposes a novel miniaturized image rejection bandpass filter by loading Stepped-Impedance Resonators (SIR). By analyzing the relationship between the impedance ratio of a half-wavelength SIR and its electrical length, we have designed an improved second-order bandpass filter, which reduces the size by 34.3% compared to traditional five-order hairpin filters. In order to further enhance the performance of the filter, the use of a radial stub, as opposed to the traditional rectangular open stub, allows for the generation of a wider band transmission zero, which can be analyzed using lumped equivalent circuits. This integration improves the stopband rejection of the filter. The results show that the passband range is 5.35 GHz-6.64 GHz; the rejection in the stopband range 8.10 GHz-11.98 GHz is over 45 dB; and the size is only 0.385λg×0.295λg.
2. Sankaran, S. G. and S. R. Gulasekaran, Wi-Fi6: Protocol and Network, Artech House, 2021.
3. Naik, G., J.-M. Park, J. Ashdown, and W. Lehr, "Next generation Wi-Fi and 5G NR-U in the 6 GHz bands: Opportunities and challenges," IEEE Access, Vol. 8, 153027-153056, 2020.
4. Sun, J. X., et al., "Design of image-reject hairpin filter applied for Ku-band LNB," Proceedings of the 9th International Symposium on Antennas, Propagation and EM Theory, 1161-1164, Guangzhou, 2010.
5. Yang, L., et al., "A novel wideband bandpass filter based on CSRR-loaded substrate integrated folded waveguide," International Journal of RF and Microwave Computer-aided Engineering, Vol. 30, No. 6, e22181.1-e22181.9, 2020.
6. Vetury, R., A. S. Kochhar, and J. B. Shealy, "XBAW, an enabling technology for next generation resonators and filter solutions for 5G and Wi-Fi6/6E/7 applications (Invited)," 2022 International Electron Devices Meeting (IEDM), 6.1.1-16.1.4, 2022.
7. Tag, A., et al., "Next generation of BAW: The new benchmark for RF acoustic technologies," 2022 IEEE International Ultrasonics Symposium (IUS), 1-4, 2022.
8. Luo, Z., et al., "Aluminum nitride thin film based reconfigurable integrated photonic devices," IEEE Journal of Selected Topics in Quantum Electronics, Vol. 29, No. 3, 1-19, 2023.
9. Qamar, A. and M. Rais-Zadeh, "Coupled BAW/SAW resonators using AlN/Mo/Si and AlN/Mo/GaN layered structures," IEEE Electron Device Letters, Vol. 40, No. 2, 321-324, 2019.
10. Marin, S., et al., "Microstrip filters with enhanced stopband based on lumped bisected pi-sections with parasitics," IEEE Microwave and Wireless Components Letters, Vol. 27, No. 1, 19-21, 2017.
11. Xiang, K. R. and F. C. Chen, "Compact microstrip bandpass filter with multispurious suppression using quarter-wavelength and half-wavelength uniform impedance resonators," IEEE Access, Vol. 6, 20364-20370, 2018.
12. Ali, N. O., et al., "A compact second-order Chebyshev bandpass filter using U-shaped resonator and defected ground structure," Radioengineering, Vol. 29, No. 2, 321-327, 2020.
13. Liu, L. Q., et al., "A miniaturized wideband bandpass filter using quarter-wavelength stepped-impedance resonators," Electronics, Vol. 8, No. 12, 1540, 2019.
14. Saleh, S., et al., "5G hairpin bandpass filter," Jordanian Journal of Computers and Information Technology (JJCIT), Vol. 7, No. 1, 1-12, 2021.
15. Wan, F., et al., "Analysis of interconnect line coupled with a radial-stub terminated negative group delay circuit," IEEE Transactions on Electromagnetic Compatibility, Vol. 62, No. 5, 1813-1821, 2020.