Journal of the Institute of Electronics Engineers of Korea TC (대한전자공학회논문지TC)

The Institute of Electronics and Information Engineers (대한전자공학회)
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Doherty Amplifier Design Using a Compact Slow-Wave Microstrip Branch-Line coupler for Linearity Improvement

Compact Slow-Wave Microstrip Branch-Line Coupler를 이용한 도허티 증폭기의 선형성 개선

  • Kim, Tae-Hyung (Information and Telecommunication Engineering, Soongsil University) ;
  • Seo, Chul-Hun (Information and Telecommunication Engineering, Soongsil University)
  • 김태형 (숭실대학교 정보통신전자공학부) ;
  • 서철헌 (숭실대학교 정보통신전자공학부)
  • Published : 2008.09.25
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Abstract

In this paper, the linearity of Doherty amplifier has been improved by applying a compact slow-wave microstrip branch-line coupler on the output of Doherty amplifier. The proposed branch coupler has four microstrip high-low impedance resonant cells periodically placed inside the branch-line coupler to result in high slow-wave effect. The new coupler not only effectively reduces the occupied area to 30% of the conventional branch-line coupler at 1.8GHz, but also has high second harmonic suppression performance. We obtained the 3rd-order intermodulation distortion ($IMD_3$) of -31.16 dBc for CDMA applications with that of maintaining the constant power added efficiency (PAE). The IMD3 performance is improved as much as -7 dBc compared with a Doherty amplifier.

본 논문에서는 도허티 전력증폭기의 입력과 출력 단에 PBG와 같은 특성을 보이는 새로운 구조의 커플러를 적용하여 높은 효율을 유지하면서 선형성을 개선하도록 하였다. 제안된 새로운 구조의 커플러는 일반적인 커플러 구조에 2차 고조파 성분을 저지하도록 내부에 주기적인 격자 셀을 삽입함으로써 큰 전파 상수 값을 가진다. 주기적인 격자 셀은 일반적인 대역저지 필터의 LC공진회로와 같은 성질을 나타내고, 높은 등가 커패시턴스 때문에, 커플러의 크기를 줄일 수 있다. 이러한 구조의 커플러는 일반적인 커플러에 비해 면적이 30% 정도 효과적으로 줄일 수 있을 뿐만 아니라 높은 2차 고조파 성분을 저지하는 특성을 나타낸다. 새로운 커플러 구조를 적용한 도허티 전력증폭기의 3차 혼변조 왜곡 ($IMD_3$)은 CDMA 응용에서 -31.16 dBc이다. 제안된 커플러 구조가 없는 도허티 전력증폭기와 비교했을 때, PAE는 유지하면서 $IMD_3$은 -6 dBc 개선되었다.

Keywords

References

  1. W. H. Doherty, "A new high efficiency power amplifier for modulated waves," Proc. IRE, vol. 24, no. 9, pp. 1163-1182, Sep. 1936. https://doi.org/10.1109/JRPROC.1936.228468
  2. Yu Zhao, Andre G. Metzger, Peter J. Zampardi, Masaya Iwamoto, and Peter M. Asbeck, " Linearity Improvement of HBT-Based Doherty Power Amplifiers Based on a Simple Analytical Model", IEEE Transactions on Microwave Theory and Techniques, VOL. 54, NO. 12, December 2006.
  3. Y. Yang, J. Yi, Y. Y. Woo, and B. Kim, "Optimum Design for Linearity and Efficiency of Microwave Doherty Amplifier Using a New Load Matching Technique," Microwave Journal, vol. 44, no. 12, pp. 20-36, Dec. 2001
  4. Taesun Kim and Chulhun Seo, "A Novel Photonic Bandgap Structure for Low-Pass Filter of Wide Stopband," IEEE Microwave and Guided Wave Letters, vol. 10, no. 1, pp. 13-15, January 2000. https://doi.org/10.1109/75.842072
  5. Q. Xue, K. M. Shun, and C. H. Chan, "Novel 1-D Microstrip PBG Cells," IEEE Microwave Guided Wave Lett., October, 2000.
  6. S. S. Liao, P. T. Sun, N. C. Chin, and J. T. Peng, "A novel compact-sized branch-line coupler," IEEE Microw. Wireless Compon. Lett., vol. 15, no. 9, pp. 588-590, Sep. 2005. https://doi.org/10.1109/LMWC.2005.855378
  7. Jianpeng Wang, Bing-Zhong Wang, Yong-Xin Guo, L. C. Ong, Shaoqiu Xiao, "A Compact Slow-Wave Microstrip Branch-Line Coupler With High Performance," IEEE Microw. Wireless Compon. Lett., vol. 17, no. 7, pp. 501-503, JULY, 2007. https://doi.org/10.1109/LMWC.2007.899307
  8. K. O. Sun, S. J. Ho, C. C. Yen, and D. V. D. Weide, "A compact branch-line coupler using discontinuous microstrip lines," IEEE Microw. Wireless Compon. Lett., vol. 15, no. 8, pp. 519-520, Aug. 2005.(763) https://doi.org/10.1109/LMWC.2005.852789