Unconventional connection of ferroelectric capacitors to resonators in tunable filters





tunable filter, ferroelectric capacitor, microstrip resonator, unloaded quality factor, frequency response


Unconventional connection of ferroelectric capacitors to resonators of tunable filters is proposed. It has increased the required minimum of capacitance value and the frequency range from ku-band to K-band. The proposed method of connection is illustrated by an example of microstrip filter, which is tunable within the frequency range 18–20 GHz. The minimum capacitance of the ferroelectric capacitor, that was obtained, was Cmin = 0.22 pF, the maximum value — Cmax = 0.31 pF. In traditional connection scheme, capacitance value is Cmin = 0.11 pF, and it is not possible to implement ferroelectric capacitors in this case. Simulation results of the frequency responses of the filter are presented.


J.-S. Hong, Microstrip Filters for RF/Microwave Application, 2nd ed. N. Y. John Wiley and Sons, Inc., 2011.

P. W. Wong and I. Hunter, “Electronically tunable filters,” IEEE Microwave Mag., vol. 10, no. 6, p. 46-54, Oct. 2009. DOI: http://doi.org/10.1109/MMM.2009.933593.

B. Kapilevich, “A varactor-tuned filter with constant bandwidth and loss compensation,” Microwave Journal, vol. 50, no. 4, pp. 106-114, 2007.

A. V. Zakharov and M. E. Il’chenko. “A new approach to designing varicap-tuned filters,” J. Commun. Technol. Electron., Vol. 55, No. 12, pp. 1424-1431, 2010. DOI: http://doi.org/10.1134/S1064226910120156.


G. M. Rebeiz, K. Entesari, I. C. Reines, S.-J. Park, M. A. El-tanani, A. Grichener, and A. R. Brown, “Tuning in to RF MEMS,” IEEE Microwave Mag., vol. 10, no. 6, pp. 55-72, Oct. 2009. DOI: http://doi.org/10.1109/MMM.2009.933592.

I. Vendik, O. Vendik, V. Pleskachev, and M. Nikol’ski, “Tunable filters based on ferroelectrics,” Integrated Ferroelectrics, Vol. 49, pp. 83-92, Jan. 2002. DOI: http://doi.org/10.1080/10584580215469.

A. V. Zakharov, M. E. Il’chenko, V. Ya. Karnaukh, and L. S. Pinchuk, “Q-factors of ferroelectric capacitors used in tunable microwave filters,” J. Commun. Technol. Electron., Vol. 56, No. 8, pp. 1020-1025, 2011. DOI: http://doi.org/10.1134/S1064226911050147.

J. Sigman, C. D. Nordquist, P. G. Clem, G. M. Kraus, P. S. Finnegan, “Voltage-controlled Ku-band and X-band tunable combline filters using barium-strontium-titanate,” IEEE Microwave Wireless Compon. Lett., Vol. 18, no. 9, pp. 593-595, 2008. DOI: http://doi.org/10.1109/LMWC.2008.2002453.

J. Nath, D. Ghosh, J.-P. Maria, A. I. Kingon, W. Fathelbab, P. D. Franzon, M. B. Steer, “An electronically tunable microstrip bandpass filter using thin-film Barium-Strontium-Titanate (BST) varactors,” IEEE Trans. Microwave. Theory Tech., Vol. 53, No. 9, pp. 2707-2712, Sept. 2005. DOI: http://doi.org/10.1109/TMTT.2005.854196.


A. V. Zakharov, M. E. Il’chenko, V. N. Korpach, “Features of coupling coefficiens of planar stepped-impedance resonators at higher resonance frequencies and application of such resonators for suppression of spurious passbands,” J. Commun. Technol. Electron., Vol. 59, No. 6, pp. 550-556, 2014. DOI: http://doi.org/10.1134/S1064226914060217.

A. V. Zakharov, M. Ye. Ilchenko, V. Ya. Karnaukh, and L. S. Pinchuk, “Stripline bandpass filters with step-impedance resonators,” Radioelectron. Commun. Syst., Vol. 54, No. 3, pp. 163-169, 2011. DOI: http://doi.org/10.3103/S0735272711030071.

A. V. Zakharov, M. Ye. Ilchenko, L. S. Pinchuk, “Coupling coefficient of stepped-impedance resonators in stripline bandpass filters of array type,” Radioelectron. Commun. Syst., Vol. 57, No. 5, pp. 217-223, 2014. DOI: http://doi.org/10.3103/S0735272714050045.

A. L. Feldshtein (ed), Handbook on Elements of the Stripline Devices [in Russian]. Moscow: Svyaz’, 1979.