Microstrip Dual-Band Branch-Line Balun With Arbitrary Complex Frequency-Dependent Input and Load Impedances in Bands
DOI:
https://doi.org/10.64915/RADAP.2026.104.5-14Keywords:
balun, dual-band operating, method of even-odd mode analysis, frequency-dependent input and termination impedances, complex impedance transformingAbstract
This article proposes a planar microstrip circuit configuration for designing a compact dual-band balun, whose two output signals have equal amplitudes and opposite phases in two operating frequency bands. At the same time, such circuit provides the transformation of complex load impedances different in these bands into the complex source input impedances, which also differ in these bands. The proposed balun circuit is based on a symmetric four-port branch line-based planar structure with one open port, formed by single-line segments with three reactive elements and an isolation scheme. To implement these reactive elements with different values across the frequency bands, transmission-line stubs are used. By applying even-odd mode analysis to the symmetrical four-port network, expressions were obtained for calculating the electrical parameters of the dual-band balun circuit elements. To remove restrictions on the transformable complex impedance values (both load and input), additional line segments are also introduced into this circuit, the parameters of which are set arbitrarily. The choice of the values of these parameters allows to provide as a result of calculations the electrical parameters of the line segments suitable for technical implementation. To verify the proposed circuit and calculation method, a prototype dual-band balun operating at 2.4 and 5.2 GHz was implemented and measured. To manufacture a balun based on microstrip transmission lines, a dielectric substrate with a dielectric constant of 2.6 and a thickness of 1.45 mm was used. Measurements showed that for amplitude and 180°-phase difference mismatches below 0.6 dB and 5°, respectively, the bandwidth of the dual-band balun is 290 MHz in both bands. Simulated and measured results agree well, proving the design concept.
References
1. Gorur, A. K. (2020). A Dual-Band Balun BPF Using Codirectional Split Ring Resonators. IEEE Microwave and Wireless Components Letters, Vol. 30, Iss. 10, pp. 949–952. DOI: 10.1109/LMWC.2020.3016622.
2. Ge, J., Jiang, W., and Wang, G. (2021). A Dual-Band Balun BPF Using Double-Sided Parallel-Strip Line. 2021 IEEE MTT-S International Microwave Symposium (IMS), 07-25 June 2021, Atlanta, GA, USA, pp.251-253. DOI: 10.1109/IMS19712.2021.9574948.
3. Xiao, J.-K., Wu, R.-T., and Li, X.-F. (2024). Self-Packaged Wideband Filtering Baluns Based on Suspended Coplanar Waveguide-Microstrip Hybrid. IEEE Transactions on Components, Packaging and Manufacturing Technology, Vol. 14, Iss. 3, pp. 489-500. DOI: 10.1109/TCPMT.2024.3366612.
4. Li, E. S., Lin, C.-T., Jin, H., and Chin, K.-S. (2019). A systematic design method for a dual-band balun with impedance transformation and high isolation. IEEE Access, Vol. 7, pp. 143805-143813. DOI: 10.1109/ACCESS.2019.2945049.
5. Gupta, R., Hashmi, M. S., and Chaudhary, M. A. (2020). Flexible design scheme for a simple dual-band ultra-high impedance transformer and its application in a balun. IEEE Access, Vol. 8, pp. 125745-125754. DOI: 10.1109/ACCESS.2020.3008046.
6. Gupta, R., Kairatova, S., Hashmi, M., and Nauryzbayev, G. (2021). A dual-band balun architecture with unequal port-terminations. 50th European Microwave Conference (EuMC) (IEEE, 2021), 12–14 Jan. 2021, Utrecht, Netherlands, pp. 848–851. DOI: 10.23919/EuMC48046.2021.9337973.
7. Maktoomi, M. H., Ren, H., Marbell, M. N., Klein, V., Wilson, R., and Arigong, B. (2020). A wideband isolated real-to-complex impedance transforming uniplanar microstrip line balun for push–pull power amplifier. IEEE Trans. Microw. Theory Tech., Vol. 68, No. 11, pp. 4560-4569. DOI: 10.1109/TMTT.2020.3019003.
8. Oborzhytskyy, V. I., Storozh, V. H., and Fabirovskyy, S. Ye. (2023). Dual-band Microstrip Balun with Different Complex Load Impedances in Frequency Bands. Radioelectronics and Communications Systems, Vol. 66, No. 1, pp. 1–14. DOI: 10.3103/S0735272723030044.
9. Oborzhytskyy, V., Fabirovskyy, S., and Sidelnyk, I. (2024). Design method of a dual-band balun, loaded with frequency-dependent complex impedances. 17th International Conference on Advanced Trends in Radioelectronics, Telecommunications and Computer Engineering (TCSET), Lviv-Slavsko, Ukraine, 09-12 Octob., pp. 1-4. DOI: 10.1109/TCSET64720.2024.10755514.
10. Li, E. S., Lin, C.-T., Jin, H., and Chin, K.-S. (2019). A Broadband Balun With Complex Impedance Transformation and High Isolation. IEEE Access, Vol. 7, pp. 112295-112303. DOI: 10.1109/ACCESS.2019.2934506.
11. Tang, D., Luo, X. (2021). Compact Filtering Balun With Wide Stopband and Low Radiation Loss Using Hybrid Microstrip and Substrate-Integrated Defected Ground Structure. IEEE Microwave and Wireless Components Letters, Vol. 31, No. 6, pp. 549-552. DOI:10.1109/lmwc.2021.3065416.
12. Deb, P. K., Moyra, T., and Bhattacharyya, B. K. (2021). Miniaturized and enhanced bandwidth Marchand balun using CSRR. IET Microw. Antennas Propag., Vol. 15, Iss. 7, pp. 788–796. DOI: 10.1049/mia2.12086.
13. Steele, J., Psychogiou, D. (2024). Wideband Broadside-Coupled Line Baluns Enabled by Multimaterial Additive Manufacturing. IEEE Trans. Microw. Theory Tech., Vol. 72, No. 10, 2024, pp. 5904-5916. DOI: 10.1109/TMTT.2024.3392434.
14. Ke, Y.-H., Yang, L.-L., and Chen, J.-X. (2021). Design of Switchable Dual-Balun Feeding Structure for Pattern-Reconfigurable Endfire Antenna. IEEE Antennas and Wireless Propagation Letters, Vol. 20, Iss. 7, pp. 1463-1467. DOI:10.1109/LAWP.2021.3087479.
15. Yu, Y.-Q., Jiang, W., Qin, L., Shao, H.-Y., and Gong, S.-X. (2020). Design of a Planar Transmission Line Balun Based on Novel Phase Inverter. IEEE Access, Vol. 8, pp. 18915 – 18924. DOI:10.1109/ACCESS.2020.2968341.
16. Zhang, W., Wu, Y., Liu, Y., Yu, C., and Chen, W. (2015). Compact coupled-line balun with complex impedances transformation and high isolation. IET Microwaves, Antennas Propag., Vol. 9, Iss. 14, pp. 1587-1594. DOI: 10.1049/iet-map.2014.0775.
17. Zhang, W., Wu, Y., Wang, W., and Shen, X. (2017). Planar compact dual-band coupled-line balun with high isolation. China Commun., Vol. 14, No. 2, pp. 40-48. DOI: 10.1109/CC.2017.7868173.
18. Gupta, R., Hashmi, M. (2018). High impedance transforming simplified Balun architecture in microstrip technology. Microw. Optical Technol. Lett., Vol. 60, Iss. 12, pp. 3019-3023. DOI: 10.1002/mop.31450.
19. Wu, Y., Yao, L., Zhang, W., Wang, W., and Liu, Y. (2016). A planar dual-band coupled-line balun with impedance transformation and high isolation. IEEE Access, Vol. 4, pp. 9689-9701. DOI: 10.1109/ACCESS.2016.2640187.
20. Oborzhytskyy, V., Protasevych, V., Storozh, V., and Khiblin, O. (2024). Microstrip dual-band transformer of complex load impedances into complex input impedances with different values in frequency bands. 17th International Conference on Advanced Trends in Radioelectronics, Telecommunications and Computer Engineering (TCSET), Lviv-Slavsko, Ukraine, 09-12 Octob., pp. 574-577. DOI: 10.1109/TCSET64720.2024.10755665.
21. Prudyus, I., Oborzhytskyy, V. (2017). Dual-band devices based on coupled striplines for different power distribution in the frequency bands. Radioelectronics and Communications Systems, Vol. 60, No. 12, pp. 545–554. DOI: 10.3103/S0735272717120044.
Downloads
Published
Issue
Section
License
Copyright (c) 2026 В. І. Оборжицький, С. Є. Фабіровський, В. Г. Сторож, Ю. М. Матієшин, Т. Є. Банщикова
This work is licensed under a Creative Commons Attribution 4.0 International License.
Authors who publish with this journal agree to the following terms:
- Authors retain copyright and grant the journal right of first publication with the work simultaneously licensed under a Creative Commons Attribution License that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal.
- Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal's published version of the work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgement of its initial publication in this journal.
- Authors are permitted and encouraged to post their work online (e.g., in institutional repositories or on their website) prior to and during the submission process, as it can lead to productive exchanges, as well as earlier and greater citation of published work (See The Effect of Open Access).
