Analytical Modeling of Conventional and Miniaturization Three-Section Branch-Line Couplers

  • You, Kok Yeow (Dept. of Communication Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia) ;
  • AL-AREQI, Nadera (Dept. of Communication Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia) ;
  • Chong, Jaw Chung (Dept. of Communication Engineering, Faculty of Electrical Engineering, Universiti Teknologi Malaysia) ;
  • Lee, Kim Yee (Dept. of Electrical and Electronic Engineering. Lee Kong Chian Faculty of Engineering and Science, Universiti Tunku Abdul Rahman) ;
  • Cheng, Ee Meng (School of Mechatronic Engineering, Universiti Malaysia Perlis) ;
  • Lee, Yeng Seng (Dept. of Electronic Engineering Technology, Faculty of Engineering Technology, Universiti Malaysia Perlis)
  • Received : 2017.04.07
  • Accepted : 2017.09.26
  • Published : 2018.03.01


Analytical modeling equations are proposed for the conventional and modified three-section branch-line couplers. The analytical equations are explicit and capable of determining the characteristic impedance of each branch line for the coupler at desired coupling level as well as the suitability of broadband S-parameters analysis. In addition, a bandwidth extension and miniaturization of three-section branch-line coupler using slow-wave and meandering line structures were designed. The modified coupler, which is able to operate within frequencies from 1.5 to 3.32 GHz has been fabricated, tested and compared. A bandwidth extension of 600 MHz and 53% reduced size of the modified coupler have been achieved compared to a conventional coupler. The modified coupler has roughly insertion loss and coupling of -4 dB and -3.2 dB, while the isolation and return loss, respectively less than -14 dB with fractional bandwidth of 77 %, as well as phase imbalances less than $2^{\circ}$ over the operating bandwidth. Overall, the derived analytical model, simulation and measurement results demonstrated a good agreement.


Three-section branch-line coupler;Slow-wave structure;Meandering line;Wide-band;Miniaturization;S-parameters


Supported by : Universiti Teknologi Malaysia, Ministry of Higher Education of Malaysia (MOHE)


  1. Hyunchul Kim, Byungje Lee and Myun-Joo Park, "Dual-Band Branch-Line Coupler with Port Extensions," IEEE Trans. Microw. Theory Tech., vol. 58, no. 3, pp. 651-655, Mar. 2010.
  2. Seungku Lee and Yongshik Lee, "Wideband Branch-Line Couplers with Single-Section Quarter-Wave Transformers for Arbitrary Coupling Levels," IEEE Microw. Wireless Compon. Lett., vol. 22, no. 1, pp. 19-21, Jan. 2012.
  3. Yongle Wu, Junyu Shen, and Yuanan Liu, "Comments on 'Quasi-Arbitrary Phase-Difference Hybrid Coupler'," IEEE Trans. Microw. Theory Tech., vol. 61, no. 4, pp. 1725-1727, April 2013.
  4. Leung Chiu and Quan Xue, "Investigation of a Wideband $90^{\circ}$ Hybrid Coupler with an Arbitrary Coupling Level," IEEE Trans. Microw. Theory Tech., vol. 58, no. 4, pp. 1022-1029, Aug. 2010.
  5. Young-Hoon Chun and Jia-Sheng Hong, "Compact Wide-Band Branch-Line Hybrids," IEEE Trans. Microw. Theory Tech., vol. 54, no. 2, pp. 704-709, Feb. 2006.
  6. Ching-Wen Tang, Chien-Tai Tseng, and Ko-Cheng Hsu, "Design of Wide Passband Microstrip Branch-Line Couplers with Multiple Sections," IEEE Transactions on Components, Packaging and Manufacturing Technology, vol. 4, no. 7, pp. 1222-1227, Feb. July 2014.
  7. Debapratim Ghosh and Girish Kumar, "A Four Branch Microstrip Coupler with Improved Bandwidth and Isolation," in Twenty First National Conference on Communications (NCC), Mumbai, India, 27 Feb-01 Mar 2015.
  8. M. Muraguchi, T. Yukitake, and Y. Naito, "Optimum Design of 3-dB Branch-Line Couplers Using Microstrip Lines," IEEE Trans. Microw. Theory Tech., vol. 31, no. 8, pp.674-678, Aug. 1983.
  9. P. Kurgan, J. Filipcewicz and M. Kitlinski, "Development of a Compact Microstrip Resonant Cell Aimed at Efficient Microwave Component Size Reduction," IET Microwaves, Antennas & Propagation, vol. 6, no. 12, pp. 1291-1298, Sep. 2012.
  10. Kae-Oh Sun, Sung-Jin Ho, Chih-Chuan Yen and D. van der Weide, "A Compact Branch-Line Coupler Using Discontinuous Microstrip Lines," IEEE Microw. Wireless Compon. Lett., vol. 15, no. 8, pp. 519-520, Aug. 2005.
  11. B. F. Zong, G. M. Wang, C. X. Zhang and Y. W. Wang, "Miniaturised Branch-Line Coupler with Ultra-Wide High Suppression Stopband," Electron. Lett., vol. 50, no. 19, pp. 1365-1367, Sep. 2014.
  12. A. Bekasiewicz and S. Koziel, "Miniaturised Dual-Band Branch-Line Coupler," Electron. Lett., vol. 51, no. 10, pp. 769-771, 2015.
  13. K. W. Eccleston and S. H. M. Ong, "Compact Planar Microstripline Branch-Line and Rat-Race Couplers," IEEE Trans. Microw. Theory Tech., vol. 51, no. 10, pp. 2119-2125, Oct. 2003.
  14. V. Iran-Nejad, A. A. Lotfi-Neyestanak and A. Shahzadi, "Compact broadband quadrature hybrid coupler using planar artificial transmission line," Electron. Lett., vol. 48, no. 25, pp. 1602-1603, Dec. 2012.
  15. David M. Pozar, Microwave Engineering, 4th ed: Wiley, 2012, p.147-149.
  16. W. J. Getsinger, "End-Effects in Quasi-TEM Transmission Lines," IEEE Trans. Microw. Theory Tech., vol. 41, no. 4, pp. 666 - 672, April 1993.