Open Access Open Access  Restricted Access Subscription Access
Filter without screen containing units with varicaps

Varicap-tuned narrowband filters with extended rejection band based on U-shaped microstrip resonators

Alexander V. Zakharov, Mykhailo Ye. Ilchenko


A resonance equation for the first unwanted resonant frequency of tunable microwave U-shaped loop-type resonator with variable capacitance has been derived. This frequency does not depend on the variable capacitance value; it is invariable and proportional to λ-type oscillations. The ascertained feature makes it possible to determine the ratio of the first unwanted resonant frequency to the frequency of the main resonance and control the rejection bandwidth of tunable filters with U-shaped resonators. A narrowband (2%) varicap-tuned filter with extended rejection band has been built and its experimental data are presented. The experimental four-resonator filter could be tuned in the frequency range 225–400 MHz. The filter rejection band in terms of the attenuation level of –40 dB was located in the frequency range 420–1290 MHz, i.e., fmax/fmin = 3.07. Varicap-tuned filters with microstrip U-shaped resonators are shown to have a good potential for their practical use.


tunable filter; U-shaped resonator; varicap; tuning range; rejection band

Full Text:



WONG, P.W.; HUNTER, I. Electronically tunable filters. IEEE Microwave Mag., v,10, n.6, p.46-54, 2009. DOI:

HONG, J.-S. Reconfigurable planar filters. IEEE Microwave Mag., v.10, n.6, p.73-83, 2009. DOI:

BROWN, A.R.; REBEIZ, G.M. A varactor-tuned RF filter. IEEE Trans. Microwave Theory Tech., v.48, n.7, p.1157-1160, 2000. DOI:

KAPILEVICH, B. A varactor-tuned filter with constant bandwidth and loss compensation. Microwave J., n.4, p.106-114, 2007. URI:

ZAKHAROV, A.V.; ILCHENKO, M.E. A new approach to designing varicap-tuned filters. J. Commun. Technol. Electron., v.55, n.12, p.1424-1431, 2010. DOI:

SIGMAN, J.; NORDQUIST, C.D.; CLEM, P.G.; KRAUS, G.M.; FINNEGAN, P.S. Voltage-controlled Ku-band and X-band tunable combline filters using barium-strontium-titanate. IEEE Microwave Wireless Compon. Lett., v.18, n.9, p.593-595, 2008. DOI:

NATH, J.; GHOSH, D.; MARIA, J.-P.; KINGON, A.I.; FATHELBAB, W.; FRANZON, P.D.; STEER, M.B. An electronically tunable microstrip bandpass filter using thin-film Barium-Strontium-Titanate (BST) varactors. IEEE Trans. Microwave Theory Tech., v.53, n.9, p.2707-2712, 2005. DOI:

ZAKHAROV, A.V.; ILCHENKO, M.E.; KARNAUKH, V.Y.; PINCHUK, L.S. Tunable microstrip resonators with ferroelectric capacitors. Radioelectron. Commun. Syst., v.53, n.8, p.418-423, (2010). DOI:

ZAKHAROV, A.V.; ILCHENKO, M.E.; KARNAUKH, V.Y.; PINCHUK, L.S. Quality of ferroelectric capacitors used in tunable microwave filters. J. Commun. Technol. Electron., v.56, n.8, p.1020, 2011. DOI:

CHAN, K.Y.; FOULADI, S.; RAMER, R.; MANSOUR, R.R. RF MEMS switchable interdigital bandpass filter. IEEE Microwave Wireless Compon. Lett., v.22, n.1, p.44-46, 2012. DOI:

LIU, X.; KATEHI, L.P.B.; CHAPPELL, W.J.; PEROULIS, D. Power handling of electrostatic MEMS evanescent-mode (EVA) tunable bandpass filters. IEEE Trans. Microwave Theory Tech., v.60, n.2, p.270-283, 2012. DOI:

HUANG, F.; FOULADI, S.; MANSOUR, R.R. High-Q tunable dielectric resonator filters using MEMS technology. IEEE Trans. Microwave Theory Tech., v.59, n.12, p.3401-3409, 2011. DOI:

SEKAR, V.; ARMENDARIZ, M.; ENTESARI, K. A 1.2-1.6-GHz substrate-integrated-waveguide RF MEMS tunable filter. IEEE Trans. Microwave Theory Tech., v.59, n.4, p.866-876, 2011. DOI:

MAKIMOTO, M.; YAMASHITA, S. Microwave Resonators and Filters for Wireless Communication. Springer, 2001. DOI:

HONG, J.-S. Microstrip Filters for RF/Microwave Application, 2nd ed. New York: Wiley, 2011.

GUILLEMIN, E.A. Synthesis of Passive Networks. Wiley, 1957.

MATTHAEI, G.; JONES, E.M.T.; YOUNG, L. Microwave Filters, Impedance-Matching Networks, and Coupling Structures, Vol. 2. Artech Microwave Library, 1980.

ZAKHAROV, A.V.; ILCHENKO, M.E.; PINCHUK, L.S. Microstrip U-shaped resonators. Radioelectron. Commun. Syst., v.55, n.8, p.368-374, 2012. DOI:

ZAKHAROV, A.V. Quality of tunable transmission line resonators with capacitor. J. Commun. Technol. Electron., v.56, n.5, p.603-610, 2011. DOI:

ZAKHAROV, A.V.; ROZENKO, S.A. Duplexer designed on the basis of microstrip filters using high dielectric constant substrates. J. Commun. Technol. Electron., v.57, n.6, p.649-655, 2012. DOI:



  • There are currently no refbacks.

© Radioelectronics and Communications Systems, 2004–2018
When you copy an active link to the material is required
ISSN 1934-8061 (Online), ISSN 0735-2727 (Print)
tel./fax +38044 204-82-31, 204-90-41