本論文使用補償電容技術，來消除九十度彎角共平面傳輸線的模轉換，共包含了九十度彎角共面波導以及九十度彎角差動傳輸線，其改良結果分述如下。
首先，為了降低九十度彎角共面波導的模轉換，我們提出一個平衡的九十度彎角共面波導。這個平衡結構可免於額外加上鎊線(Bond-wire)，進而節省PCB板的製程費用。由結果我們可知，使用平衡的九十度彎角共面波導，可以使反射損耗從DC至12 GHz維持在-11.73 dB以下，遠比使用傳統的九十度彎角共面波導-3.51 dB來得低。另外，使用平衡的九十度彎角共面波導，亦可以使時域反射的峰對峰值維持在0.020 V以下，遠比使用傳統的九十度彎角共面波導0.043 V來得小。
接著，為了降低九十度彎角差動傳輸線的模轉換，我們共探討了三種改良的架構，其分別為平行板電容之九十度彎角差動傳輸線，接地L型板之九十度彎角差動傳輸線，補償電容之九十度彎角差動傳輸線。首先，使用平行板電容之九十度彎角差動傳輸線，可以降低1-2 GHz頻率範圍內的模轉換。此外，其接收端TDT共模雜訊的振幅可以從0.089 V降低至0.075 V，但發射端TDR差模雜訊的振幅卻從0.010 V增加至0.093 V。
為了進一步降低模轉換，我們提出接地L型板之九十度彎角差動傳輸線，其可以降低DC至6 GHz頻率範圍內的模轉換至-10 dB以下。此外，其接收端TDT共模雜訊的振幅，可以下降至0.072 V，而傳送端TDR差模雜訊的振幅，可以下降至0.033 V。
為了更進一步降低模轉換，我們使用SMD電容結合一個金屬柱來實現補償電容，形成補償電容之九十度彎角差動傳輸線，其可以降低DC至6 GHz頻率範圍內的模轉換至-11.62 dB以下。此外，其接收端的TDT共模雜訊可以大幅降低至0.024 V，但傳送端的TDR差模雜訊振幅，卻增至0.094 V。

In the thesis, a compensation capacitance technique is proposed to eliminate the mode conversion induced by the bended differential transmission line using the right-angle bend, which includes the conventional coplanar waveguide using the right-angle bend and the bended differential transmission line using right-angle bend. The improvement is demonstrated as follows.
Firstly, a balanced coplanar waveguide using the right-angle bend is proposed to reduce the mode conversion of the conventional coplanar waveguide using the right-angle bend. The proposed structure does not need bond-wires, which therefore saves the PCB fabrication costs. The mode conversion of balanced coplanar waveguide using the right-angle bend is smaller than -11.73 dB from DC to 12 GHz, which is much lower than -3.51 dB of the conventional coplanar waveguide using the right-angle bend. Besides, the TDR amplitude of the balanced coplanar waveguide using the right-angle bend is 0.020 V, which is smaller than 0.043 V of the conventional coplanar waveguide using the right-angle bend.
Secondly, in order to reduce the mode conversion of bended differential transmission line using the right-angle bend, three structures are discussed, which includes the bended differential transmission line using the parallel plate capacitor, the bended differential transmission line using the L-shaped pad, and the bended differential transmission line using the SMD capacitor. First of all, the bended differential transmission line using the parallel plate capacitor can reduce the mode conversion in the frequency range from 1 to 2 GHz. Also, the amplitude of TDT common-mode noise at the receiving end is reduced from 0.089 V to 0.075 V whereas the amplitude of TDR differential-mode noise at the sending end is increased from 0.01 V to 0.093 V.
In order to further reduced the mode conversion, the bended differential transmission line using the L-shaped pad is proposed. It has been shown that the mode conversion is below -10 dB from DC to 6 GHz. Besides, the amplitude of TDT common-mode noise at the receiving end is reduced 0.072 V and the amplitude of TDR differential-mode noise at the sending end is reduced to 0.033 V.
Furthermore, in order to reduce the mode conversion, the bended differential transmission line using the SMD capacitor is used. The mode conversion is below -11.62 dB DC to 6 GHz. Besides, the amplitude of TDT common-mode noise at the receiving end is greatly reduced to 0.024 V whereas the amplitude of TDR differential-mode noise at the sending end is increased to 0.094 V.

[1] C. P. Wen, “Coplanar waveguide: a surface strip transmission line suitable for nonreciprocal gyromagnetic device applications,” IEEE Transactions on Microwave Theory and Techniques, vol. 17, no. 12, pp. 1087–1090, Dec. 1969.
[2] R. N. Simons, Coplanar Waveguide circuits, Components, and Systems, John Wiley＆Sons Inc., 2001.
[3] M. D. Wu, S. M. Deng, R. B. Wu, and P. Hsu, “Full-wave characterization of the mode conversion in a coplanar waveguide right-angled bend,” IEEE Transactions on Microwave Theory and Techniques, vol. 43, pp. 2532–2538, Nov. 1995.
[4] T. Hirota, Y. Tarusawa, and H. Ogawa, “Uniplanar MMIC hybrids—A proposed new MMIC structure,” IEEE Transactions on Microwave Theory and Techniques, vol. 35, no. 6, pp. 576–581, Jun. 1987.
[5] N. H. L. Koster, S. Koblowski, R. Bertenburg, S. A. H. S. Heinen, and I. A. W. I. Wolff, “Investigations on air bridges used for MMICs in CPW technique,” in Proc. 19th European Microwave Conference., pp. 666–671, 1989.
[6] D. Jaisson, “Coplanar waveguide bend with radial compensation,” in Proc. Inst. Elect. Eng.—Microwaves, Antennas and Propagation, vol. 143, no. 5, pp. 447–450, Oct. 1996.
[7] P. M. Watson and K. C. Gupta, “Design and optimization of CPW circuits using EM-ANN models for CPW components,” IEEE Transactions on Microwave Theory and Techniques, vol. 45, no. 12, pp. 2515–2523, Dec. 1997.
[8] T. M. Weller, R. M. Henderson, K. J. Herrick, S. V. Robertson, R. T. Kihm, and L. P. B. Katehi, “Three-dimensional high-frequency distribution networks. I. Optimization of CPW discontinuities,” IEEE Transactions on Microwave Theory and Techniques, vol. 48, no. 10, pp. 1635–1642, Oct. 2000.
[9] R. N. Simons and G. E. Ponchak, “Modeling of some coplanar waveguide discontinuities,” IEEE Transactions on Microwave Theory and Techniques, vol. 36, no. 12, pp. 1796–1803, Dec. 1988.
[10] J. Y. Park, J. H. Sim, J. K. Shin, and J. H. Lee, “Fabrication of thick silicon dioxide air-bridge for RF application using micromachining technology,” in Int. Microprocesses and Nanotechnology Conference, 2001, pp. 202–203.
[11] S. H. Hall, G. W. Hall, and J. A. McCall, High-Speed Digital System Design.
New York: Wiley, pp. 140–141, 2000.
[12] P. E. Fornberg, M. Kanda, P. M. Melinda, and H. H. Stephen, “The impact of a nonideal return path on differential signal integrity,” IEEE Transactions on Electromagnetic Compatibility., vol. 44, pp. 671–676, Feb. 2002.
[13] G. H. Shiue and R. B. Wu, “Reduction in reflections and ground bounce for signal line through a split power by using differential coupled microstrip lines,” IEEE 12th Topical Meeting on Electrical Performance of Electronic Packaging, pp.107–110, Princeton, New Jersey, USA, Oct. 2003.
[14] Y. Massoud, J. Kawa, D. MacMillen, and J. White, “Modeling and analysis of differential signaling for minimizing inductive crosstalk,” Proc. Design Automation Conference, pp. 804–809, 2001.
[15] E. P. Li, H. F. Jin, W. L. Yuan, and L. W. Li, “Parallelized computational technique for signal propagation analysis at very high speed differential transmission lines,” in Proc. IEEE Int. Symp. Electromagnetic Compatibility, pp. 850–854, 2003.
[16] W. D. Guo, G. H. Shiue, C. M. Lin, and R. B. Wu, “Comparisons between serpentine and flat spiral delay lines on transient reflection/transmission waveforms and eye diagrams,” IEEE Transactions on Microwave Theory and Techniques, vol. 54, pp. 1379–1387, Apr. 2006.
[17] http://learn-garden.blogspot.com/2008/06/pci-e-agp-pci-e128mb-agp8x-8-agp8x-pci.html.
[18] W. T. Liu, C. H. Tsai, T. W. Han, and T. L. Wu, “An embedded common-mode suppression filter for GHz differential signals using periodic defected ground plane,” IEEE Microwave and Wireless Components Letters, vol. 18, No. 4, pp. 248–250, Apr. 2008.
[19] S. J. Wu, C. H, Tsai, T. L. Wu, and T. Itoh, “A novel wideband common-mode suppression filter for gigahertz differential signals using coupled patterned ground structure,” IEEE Transactions on Microwave Theory and Techniques, vol. 57, no.4, pp. 848–855, Apr. 2009.
[20] G. H. Shiue, W. D. Guo, C. M. Lin, and R. B. Wu, “Noise reduction using compensation capacitance for bend discontinuities of differential transmission lines,” IEEE Transactions on Advanced Packaging, vol. 29, pp. 560–569, Aug. 2006.