In this study, a varactor-loaded slotted ground structure is investigated and utilized to construct a new tunable common-mode (CM) suppression filter for differential signals. A four-port distributed equivalent circuit model is developed for interpreting the working mechanism of CM signal suppression. It is found that the proposed simple structure is capable of tunable CM suppression with a wide frequency tuning range. The parameter selection and design principle are also given. Finally, the design theory is well vindicated by a common-mode filter using three periodic varactorloaded slots. Simulated and measured results, showing good agreement, exhibit a tuning range from 0.80 to 2.10 GHz, corresponding to the fractional tuning range of 89.7% and more than 30 dB CM rejection level.
2. Wu, S. J. and C. H. Tsai, "A novel wideband common-mode suppression filter for gigahertz differential signals using coupled patterned ground structure," IEEE Trans. Microw. Theory Tech., Vol. 57, No. 4, 848-855, 2009.
3. Zhao, X. L. and L. Gao, "Tunable balanced bandpass filter with high common-mode suppression," IET Electron Lett., Vol. 51, No. 24, 2021-2023, 2015.
4. Zhou, L. H. and Y. L. Ma, "Differential dual-band bandpass filter with tunable lower band using embedded DGS unit for common-mode suppression," IEEE Trans. Microw. Theory Tech., Vol. 64, No. 12, 4183-4191, 2016.
5. Safwat, A. M. E. and F. Podevin, "Tunable bandstop defected ground structure resonator using reconfigurable dumbbell-shaped coplanar waveguide," IEEE Trans. Microw. Theory Tech., Vol. 54, No. 9, 3559-3564, 2006.
6. Chen, J. X. and W. J. Zhou, "Wideband tunable common-mode suppression filter based on varactor-loaded slot-ring resonator for high-speed differential signals," IET Micro. Anten. & Propa., Vol. 11, No. 2, 151-157, 2017.
7. Mao, J. R., W. Q. Che, and Y. L. Ma, "Tunable differential-mode bandpass filters with wide tuning range and high common-mode suppression," IET Micro. Anten. & Propa., Vol. 8, No. 6, 437-444, 2014.
8. Zhang, S. X., Z. H. Chen, and Q. X. Chu, "Compact tunable balanced bandpass filter with novel multi-mode resonator," IEEE Micro. Wireless Compon. Lett., Vol. 27, No. 1, 43-45, 2017.
9. Qin, W., "Wideband tunable bandpass filter using optimized varactor-loaded SIRs," IEEE Micro. Wireless Compon. Lett., Vol. 27, No. 9, 812-815, 2017.
10. Zhu, H. and A. M. Abbosh, "Tunable balanced bandpass filter with wide tuning range of center frequency and bandwidth using compact coupled-line resonator," IEEE Micro. Wireless Compon. Lett., Vol. 26, No. 1, 7-9, 2016.
11. Sun, S. H. and B. Z. Wang, "Parameter optimization based on GA and HFSS," Journal of Electro. Scien. Tech. of China, Vol. 3, No. 1, 45-47, 2005.