Microstrip BPFs with increased selectivity and asymmetric frequency responses





bandpass filter, BPF, mixed coupling, cross coupling, transmission zero, TZ, frequency response


Two symmetrical third-order microstrip bandpass filters (BPF) with all mixed coupling coefficients are proposed and analyzed. The first filter is a combline filter with stepped impedance resonators (SIR) closely spaced to each other. This leads to mixed couplings between adjacent resonators. The cross coupling of the end resonators is also mixed K13 = Km13 + Ke13 (MCC). Its magnetic component Km13 is due to a parasitic magnetic coupling between these resonators. To form the electric coupling component Ke13 a thin microstrip line segment was used that connects the resonators through the capacitive gaps. It was found that such a filter has two adjustable transmission zeros (TZ), which can be located both to the right and left of the central frequency f0 of the bandwidth. The second BPF differs from the first in that its central SIR is replaced by a half-wave through-type resonator, which is included in the filter as a two-port circuit. The used half-wave resonator has a U-shape and it works as the admittance inverter, in addition to the resonance phenomenon. This feature leads to a change in the frequency response of the filter. This filter has two adjustable TZs, which are located on both sides of the center frequency f0 of the bandwidth asymmetrically. The direct and inverse problems for the third-order BPF with all mixed couplings are also solved. The solution is based on the conductance matrix [Ỹ] and its minor M31. The direct problem solution makes it possible to determine the TZs of the filter using the given coupling coefficients. In the inverse problem, the filter’s coupling coefficients are determined by the specified TZs. The samples of two experimental filters and measuring frequency responses are presented.


A. V. Zakharov, S. A. Rozenko, “Duplexer designed on the basis of microstrip filters using high dielectric constant substrates,” J. Commun. Technol. Electron., vol. 57, no. 6, pp. 649–655, 2012, doi: https://doi.org/10.1134/S1064226912030187.

J.-S. Hong, M. J. Lancaster, “Microstrip cross-coupled trisection bandpass filters with asymmetric frequency characteristics,” IEE Proc. - Microwaves, Antennas Propag., vol. 146, no. 1, p. 84, 1999, doi: https://doi.org/10.1049/ip-map:19990146.

R. M. Kurzrok, “General three-resonator filters in waveguide,” IEEE Trans. Microw. Theory Tech., vol. 14, no. 1, pp. 46–47, 1966, doi: https://doi.org/10.1109/TMTT.1966.1126154.

R. Hershtig, R. Levy, K. Zaki, “Synthesis and design of cascaded trisection (ct) dielectric resonator filters,” in 27th European Microwave Conference, 1997, 1997, vol. 2, pp. 784–791, doi: https://doi.org/10.1109/EUMA.1997.337890.

C.-C. Yang, C.-Y. Chang, “Microstrip cascade trisection filter,” IEEE Microw. Guid. Wave Lett., vol. 9, no. 7, pp. 271–273, 1999, doi: https://doi.org/10.1109/75.774144.

R. M. Kurzrok, “General four-resonator filters at microwave frequencies,” IEEE Trans. Microw. Theory Tech., vol. MTT-14, no. 6, pp. 295–296, 1966, doi: https://doi.org/10.1109/TMTT.1966.1126254.

R. J. Cameron, C. M. Kudsia, R. R. Mansour, Microwave Filters for Communication Systems. Hoboken, NJ: John Wiley & Sons, Inc., 2018, doi: https://doi.org/10.1002/9781119292371.

K. Ma, J.-G. Ma, K. S. Yeo, M. A. Do, “A compact size coupling controllable filter with separate electric and magnetic coupling paths,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 3, pp. 1113–1119, 2006, doi: https://doi.org/10.1109/TMTT.2005.864118.

A. Zakharov, S. Rozenko, S. Litvintsev, M. Ilchenko, “Trisection bandpass filter with mixed cross-coupling and different paths for signal propagation,” IEEE Microw. Wirel. Components Lett., vol. 30, no. 1, pp. 12–15, 2020, doi: https://doi.org/10.1109/LMWC.2019.2957207.

A. V. Zakharov, S. N. Litvintsev, M. Ilchenko, “Trisection bandpass filters with all mixed couplings,” IEEE Microw. Wirel. Components Lett., vol. 29, no. 9, pp. 592–594, 2019, doi: https://doi.org/10.1109/LMWC.2019.2929650.

S. Tamiazzo, G. Macchiarella, “Synthesis of cross-coupled filters with frequency-dependent couplings,” IEEE Trans. Microw. Theory Tech., vol. 65, no. 3, pp. 775–782, 2017, doi: https://doi.org/10.1109/TMTT.2016.2633258.

P. Zhao, K. Wu, “Cascading fundamental building blocks with frequency-dependent couplings in microwave filters,” IEEE Trans. Microw. Theory Tech., vol. 67, no. 4, pp. 1432–1440, 2019, doi: https://doi.org/10.1109/TMTT.2019.2895532.

L. Szydlowski, A. Lamecki, M. Mrozowski, “Coupled-resonator filters with frequency-dependent couplings: coupling matrix synthesis,” IEEE Microw. Wirel. Components Lett., vol. 22, no. 6, pp. 312–314, 2012, doi: https://doi.org/10.1109/LMWC.2012.2197386.

L. Szydlowski, N. Leszczynska, A. Lamecki, M. Mrozowski, “A substrate integrated waveguide (siw) bandpass filter in a box configuration with frequency-dependent coupling,” IEEE Microw. Wirel. Components Lett., vol. 22, no. 11, pp. 556–558, 2012, doi: https://doi.org/10.1109/LMWC.2012.2221690.

P. Chu et al., “A planar bandpass filter implemented with a hybrid structure of substrate integrated waveguide and coplanar waveguide,” IEEE Trans. Microw. Theory Tech., vol. 62, no. 2, pp. 266–274, 2014, doi: https://doi.org/10.1109/TMTT.2013.2294861.

W. Shen, L.-S. Wu, X.-W. Sun, W.-Y. Yin, J.-F. Mao, “Novel substrate integrated waveguide filters with mixed cross coupling (mcc),” IEEE Microw. Wirel. Components Lett., vol. 19, no. 11, pp. 701–703, 2009, doi: https://doi.org/10.1109/LMWC.2009.2032007.

M. Hoft, T. Shimamura, “Design of symmetric trisection filters for compact low-temperature co-fired ceramic realization,” IEEE Trans. Microw. Theory Tech., vol. 58, no. 1, pp. 165–175, 2010, doi: https://doi.org/10.1109/TMTT.2009.2035870.

R. Levy, “New cascaded trisections with resonant cross-couplings (ctr sections) applied to the design of optimal filters,” in IEEE MTT-S International Microwave Symposium Digest, 2004, vol. 2, pp. 447–450, doi: https://doi.org/10.1109/mwsym.2004.1336007.

A. V. Zakharov, M. Y. Ilchenko, L. S. Pinchuk, “Coupling coefficient of quarter-wave resonators as a function of parameters of comb stripline filters,” Radioelectron. Commun. Syst., vol. 58, no. 6, pp. 284–289, 2015, doi: https://doi.org/10.3103/S0735272715060060.

A. V. Zakharov, M. E. Il’chenko, “Pseudocombline bandpass filters based on half-wave resonators manufactured from sections of balanced striplines,” J. Commun. Technol. Electron., vol. 60, no. 7, pp. 801–807, 2015, doi: https://doi.org/10.1134/S1064226915060182.

C.-L. Hsu, C.-H. Yu, J.-T. Kuo, “Microstrip trisection filters with quasi-elliptic and flat group delay responses,” in 2012 4th International High Speed Intelligent Communication Forum, 2012, pp. 1–2, doi: https://doi.org/10.1109/HSIC.2012.6212988.

B.-W. Kim, S.-W. Yun, “Varactor-tuned combline bandpass filter using step-impedance microstrip lines,” IEEE Trans. Microw. Theory Tech., vol. 52, no. 4, pp. 1279–1283, 2004, doi: https://doi.org/10.1109/TMTT.2004.825626.

A. V. Zakharov, 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: https://doi.org/10.1134/S1064226910120156.

F. Zhu, W. Hong, J.-X. Chen, K. Wu, “Quarter-wavelength stepped-impedance resonator filter with mixed electric and magnetic coupling,” IEEE Microw. Wirel. Components Lett., vol. 24, no. 2, pp. 90–92, 2014, doi: https://doi.org/10.1109/LMWC.2013.2290225.

G. L. Matthaei, L. Young, E. M. T. Jones, Microwave Filters, Impedance-Matching Networks, and Coupling Structures. New York: Artech House Books, 1980.

S. B. Cohn, “Direct-coupled-resonator filters,” Proc. IRE, vol. 45, no. 2, pp. 187–196, 1957, doi: https://doi.org/10.1109/JRPROC.1957.278389.

G. L. Matthaei, “Direct-coupled bandpass-filters with lo/4 resonators,” in 1958 IRE National Convention Record, New York: IRE, 1958, pp. 98–111.

J.-S. Hong, Microstrip Filters for RF/Microwave Applications, 2nd ed. New Jersey: Wiley, 2011, uri: https://www.amazon.com/Microstrip-Filters-Microwave-Applications-Engineering-ebook/dp/B005CD1DTC.

H. Wang, Q.-X. Chu, “An inline coaxial quasi-elliptic filter with controllable mixed electric and magnetic coupling,” IEEE Trans. Microw. Theory Tech., vol. 57, no. 3, pp. 667–673, 2009, doi: https://doi.org/10.1109/TMTT.2009.2013290.

Q.-X. Chu, H. Wang, “A compact open-loop filter with mixed electric and magnetic coupling,” IEEE Trans. Microw. Theory Tech., vol. 56, no. 2, pp. 431–439, 2008, doi: https://doi.org/10.1109/TMTT.2007.914642.

A. V. Zakharov, M. E. Il’сhenko, V. N. Korpach, “Features of the coupling coefficients 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: https://doi.org/10.1134/S1064226914060217.

A. V. Zakharov, M. Y. Ilchenko, L. S. Pinchuk, “Coupling coefficients of step-impedance resonators in stripeline band-pass filters of array type,” Radioelectron. Commun. Syst., vol. 57, no. 5, pp. 217–223, 2014, doi: https://doi.org/10.3103/S0735272714050045.





Research Articles