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J. Electromagn. Eng. Sci > Volume 16(1); 2016 > Article
Journal of Electromagnetic Engineering and Science 2016;16(1):13-18.
DOI: https://doi.org/10.5515/JKIEES.2016.16.1.13   
High Selectivity Coupled Line Impedance Transformer with Second Harmonic Suppression
Phirun Kim, Junsik Park, Junhyung Jeong, Seungho Jeong, Girdhari Chaudhary, Yongchae Jeong
Division of Electronics and Information Engineering, IT Convergence Research Center, Chonbuk National University
Correspondence:  Yongchae Jeong,Email: ycjeong@jbnu.ac.kr
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.
Key words: Coupled Line, Impedance Transformer, Selectivity, Transmission Zeros


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