# High Selectivity Coupled Line Impedance Transformer with Second Harmonic Suppression

• Kim, Phirun (Division of Electronics and Information Engineering, IT Convergence Research Center, Chonbuk National University) ;
• Park, Junsik (Division of Electronics and Information Engineering, IT Convergence Research Center, Chonbuk National University) ;
• Jeong, Junhyung (Division of Electronics and Information Engineering, IT Convergence Research Center, Chonbuk National University) ;
• Jeong, Seungho (Division of Electronics and Information Engineering, IT Convergence Research Center, Chonbuk National University) ;
• Chaudhary, Girdhari (Division of Electronics and Information Engineering, IT Convergence Research Center, Chonbuk National University) ;
• Jeong, Yongchae (Division of Electronics and Information Engineering, IT Convergence Research Center, Chonbuk National University)
• Accepted : 2015.11.24
• Published : 2016.01.31
• 86 22

#### Abstract

This paper presents a design of an impedance transformer (IT) with high frequency selectivity characteristics. The frequency selectivity can be controlled by even- and odd-mode impedance of a shunt coupled transmission line (TL). For experimental validation, a 50- to $20-{\Omega}$ IT was implemented at a center frequency ($f_0$) of 2.6 GHz for the long-term evolution signal. The measured results were in good agreement with the simulations, showing a return loss higher than 19 dB over a passband bandwidth of 0.63 GHz (2.28-2.91 GHz) and good sharp frequency selectivity characteristic near to the passband. The series coupled TL provides a transmission zero at 5.75 GHz, whereas the shunt coupled TL provides three transmission zeros located at 2 GHz, 3.1 GHz, and 7.14 GHz.

#### Keywords

Coupled Line;Impedance Transformer;Selectivity;Transmission Zeros

#### References

1. K. Jang, S. Kahng, J. Jeon, and Q. Wu, "Compact dual-band three-way metamaterial power-divider with a hybrid CRLH phase-shift line," Journal of Electromagnetic Engineering and Science, vol. 14, no. 1, pp. 15-24, Mar. 2014. https://doi.org/10.5515/JKIEES.2014.14.1.15
2. W. Lee and H. Hwang, "Size and harmonic reduced Wilkinson balun using parallel coupled line with open stub," Journal of Electromagnetic Engineering and Science, vol. 14, no. 4, pp. 387-392, Dec. 2014. https://doi.org/10.5515/JKIEES.2014.14.4.387
3. P. Kim, G. Chaudhary, and Y. Jeong, "Analysis and design of a branch-line balun with high-isolation wideband characteristics," Microwave and Optical Technology Letters, vol. 57, no. 5, pp. 1228-1234, May 2015. https://doi.org/10.1002/mop.29065
4. S. Ta and I. Park, "Wideband double dipole quasi-Yagi antenna using a microstrip-to-slotline transition feed," Journal of Electromagnetic Engineering and Science, vol. 13, no. 1, pp. 22-27, Mar. 2013. https://doi.org/10.5515/JKIEES.2013.13.1.22
5. H. R. Ahn and T. Itoh, "Impedance-transforming symmetric and asymmetric DC blocks," IEEE Transactions on Microwave Theory and Techniques, vol. 58, no. 9, pp. 2463-2474, Sep. 2010. https://doi.org/10.1109/TMTT.2010.2058936
6. H. T. Nguyen, K. S. Ang, and G. I. Ng, "Design of coupled three-line impedance transformers," IEEE Microwave and Wireless Components Letters, vol. 24, no. 2, pp. 84-86, Feb. 2014. https://doi.org/10.1109/LMWC.2013.2290215
7. H. R. Ahn and B. Kim, "Left-handed lumped transmission lines and left-handed small impedance transformers," Microwave and Optical Technology Letters, vol. 50, no. 9, pp. 2269-2271, Sep. 2008. https://doi.org/10.1002/mop.23676
8. P. Kim, G. Chaudhary, and Y. Jeong, "Enhancement impedance transforming ratios of coupled line impedance transformer with wide out-of-band suppression characterristics," Microwave and Optical Technology Letters, vol. 57, no. 7, pp. 1600-1603, Jul. 2015. https://doi.org/10.1002/mop.29144
9. P. Kim, G. Chaudhary, and Y. Jeong, "Wideband impedance transformer with out-of-band suppression characteristics," Microwave and Optical Technology Letters, vol. 56, no. 11, pp. 2612-2616, Nov. 2014. https://doi.org/10.1002/mop.28664
10. P. Kim, G. Chaudhary, and Y. Jeong, "Ultra-high transforming ratio coupled line impedance transformer with bandpass response," IEEE Microwave and Wireless Components Letters, vol. 25, no. 7, pp. 445-447, Jul. 2015. https://doi.org/10.1109/LMWC.2015.2429075
11. P. Kim, G. Chaudhary, J. Park, Y. Jeong, and J. Lim, "High frequency-selectivity impedance transformer," in Proceedings of 2015 IEEERadio and Wireless Symposium (RWS), San Diego, CA, 2015, pp. 135-137.
12. L. Zhu, S. Sun, and R. Li, Microwave Bandpass Filters for Wideband Communications. New York, NY: John Wiley & Sons, 2012.

#### Cited by

1. A Coupled Line Impedance Transformer for High Termination Impedance with a Bandpass Filtering Response vol.18, pp.1, 2018, https://doi.org/10.26866/jees.2018.18.1.41