本篇論文的研究目的為製作出將輸入的矩形TE10模式通過H-plane型功率分配器轉換成圓形TM11模式的模式轉換器。利用側邊激發作為理論基礎，藉由高頻結構模擬軟體HFSS- High Frequency Structure Simulator，先設計出兩個輸出端相差180度相位的H-plane型功率分配器，此功率分配器雖然結構簡單，但卻對精細度非常敏感。藉由控制模式轉換器上的矩形結構大小，來降低反射損耗與抑制其他模式的產生。最後將功率分配器與模式轉換器結合，完成此設計。
再利用背對背對接方式來測量其穿透係數與反射係數來驗證模擬結果。此外，也分析了機械加工所造成的誤差與表面粗糙度對轉換效率的影響。

This work proposes an approach to convert rectangular TE10 mode to circular TM11 mode by using H-plane power divider around 94 GHz. The reciprocity theorem and current source are taken into designing the coupling strength. 180 degree phase difference excitation at input rectangular ports is important. To generate 180 degree phase difference excitation, we design a width difference H-plane power divider let the wave velocity change. This power divider are structurally simple, but sensitive to the structure size. Also, adding two symmetry slots at the converter and controlling the size of these slots can improve the mode conversion efficiency. Finally, back-to-back transmission measurements is used to confirm the quality and show great agreement to the results of simulation by high frequency structure simulator (HFSS) under the consideration of the conductor loss.

[1] K. R. Chu, "The electron cyclotron maser," Reviews of Modern Physics, vol. 76, no. 2, pp. 489-540, 05/04/ 2004.
[2] H. H. Song et al., "Theory and experiment of a 94 GHz gyrotron traveling-wave amplifier," Physics of Plasmas, Conference Paper vol. 11, no. 5 PART 2, pp. 2935-2941, 2004.
[3] N. C. Chen, C. F. Yu, and T. H. Chang, "A TE21 second-harmonic gyrotron backward-wave oscillator with slotted structure," Physics of Plasmas, vol. 14, no. 12, 2007.
[4] N. C. Chen, C. F. Yu, C. P. Yuan, and T. H. Chang, "A mode-selective circuit for TE01 gyrotron backward-wave oscillator with wide-tuning range," Applied Physics Letters, vol. 94, no. 10, 2009.
[5] N.-C. Chen, T.-H. Chang, C.-P. Yuan, T. Idehara, and I. Ogawa, "Theoretical investigation of a high efficiency and broadband subterahertz gyrotron," Applied Physics Letters, vol. 96, no. 16, 2010.
[6] G. S. Nusinovich, M. K. A. Thumm, and M. I. Petelin, "The Gyrotron at 50: Historical Overview," Journal of Infrared, Millimeter, and Terahertz Waves, vol. 35, no. 4, pp. 325-381, 2014.
[7] T. H. Chang, W. C. Huang, and W. C. Chen, "Feasibility study of TM modes for electron cyclotron maser," in IRMMW-THz 2015 - 40th International Conference on Infrared, Millimeter, and Terahertz Waves, 2015.
[8] T. H. Chang and B. Y. Su, "Linear and nonlinear analysis of TM modes for gyrotron operation," in International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, 2016, vol. 2016-November.
[9] T. H. Chang, W. C. Huang, H. Y. Yao, C. L. Hung, W. C. Chen, and B. Y. Su, "Asymmetric linear efficiency and bunching mechanisms of TM modes for electron cyclotron maser," Physics of Plasmas, Article vol. 24, no. 2, 2017.
[10] T. H. Chang, H. Y. Yao, B. Y. Su, W. C. Huang, and B. Y. Wei, "Nonlinear oscillations of TM-mode gyrotrons," Physics of Plasmas, Article vol. 24, no. 12, 2017.
[11] T. H. Chang and K. J. Xu, "Gain and bandwidth of the TM-mode gyrotron amplifiers," Physics of Plasmas, Article vol. 25, no. 11, 2018.
[12] T. H. Chang, "TM-mode gyrotrons," in International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, 2019, vol. 2019-September.
[13] H. Y. Yao, C. C. Chen, and T. H. Chang, "Starting behaviors of the TM-mode gyrotrons," Physics of Plasmas, Article vol. 27, no. 2, 2020.
[14] C. F. Yu and T. H. Chang, "High-performance circular TE 01-mode converter," IEEE Transactions on Microwave Theory and Techniques, Article vol. 53, no. 12, pp. 3794-3798, 2005.
[15] C. F. Yu and T. H. Chang, "High-performance circular TE21 TE01and TE41 mode converters," in IRMMW-THz 2006 - 31st International Conference on Infrared and Millimeter Waves and 14th International Conference on Terahertz Electronics, 2006, p. 84.
[16] T. H. Chang, C. H. Li, C. N. Wu, and C. F. Yu, "Excitation of a pure TEmn mode at low terahertz region," in 33rd International Conference on Infrared and Millimeter Waves and the 16th International Conference on Terahertz Electronics, 2008, IRMMW-THz 2008, 2008.
[17] T. H. Chang, C. H. Li, C. N. Wu, and C. F. Yu, "Exciting circular TEmn modes at low terahertz region," Applied Physics Letters, Article vol. 93, no. 11, 2008.
[18] T. H. Chang, C. H. Li, C. N. Wu, and C. F. Yu, "Generating pure circular TEmn Modes," in IRMMW-THz 2010 - 35th International Conference on Infrared, Millimeter, and Terahertz Waves, Conference Guide, 2010.
[19] N.-C. Chen, T.-H. Chang, and C.-Y. Yang, "Broadband conversion of TE01 mode for the coaxial gyrotron at low terahertz," Physics of Plasmas, vol. 19, no. 3, 2012.
[20] J. Y. Jiang, B. Y. Shew, Y. S. Cheng, and T. H. Chang, "Design, fabrication, and measurement of terahertz mode converter," in IRMMW-THz 2015 - 40th International Conference on Infrared, Millimeter, and Terahertz Waves, 2015.
[21] G. Liu, R. Yan, Y. Luo, and S. Wang, "A TE13 Mode Converter for High-Order Mode Gyrotron-Traveling-Wave Tubes," IEEE Transactions on Electron Devices, vol. 63, no. 1, pp. 486-490, 2016.
[22] Y. Yao, J. Wang, H. Li, G. Liu, and Y. Luo, "Broadband rectangular TEn0 mode exciter with H-plane power dividers for 100 GHz confocal gyro-devices," Rev Sci Instrum, vol. 88, no. 7, p. 074701, Jul 2017.
[23] J. Wang, Y. Yao, Q. Tian, H. Li, G. Liu, and Y. Luo, "Broadband High-Efficiency Input Coupler With Mode Selectivity for a W-Band Confocal Gyro-TWA," IEEE Transactions on Microwave Theory and Techniques, vol. 66, no. 4, pp. 1895-1901, 2018.
[24] D. B. McDermott et al., "94 GHz heavily loaded TE01 gyro-TWT," in IEEE International Conference on Plasma Science, 2001.
[25] D. B. McDermott et al., "Design of a W-band TE01 gyro-TWT with high power and broadband capabilities," in IEEE International Conference on Plasma Science, 2002, p. 184.
[26] C. H. Du et al., "Design of a W-band gyro-TWT amplifier with a lossy ceramic-loaded circuit," IEEE Transactions on Electron Devices, Article vol. 60, no. 7, pp. 2388-2394, 2013.
[27] C. H. Du et al., "Design of a W-band TE01 mode gyro-TWT amplifier with a lossy ceramic-loaded circuit," in International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, 2013.
[28] S. H. Chen, T. H. Chang, F. H. Cheng, C. S. Kou, and K. R. Chu, "Experimental study of an injection locked gyro-BWO," IEEE International Conference on Plasma Science, Article p. 173, 2000.
[29] C. H. Tsai, T. H. Chang, and Y. Tatematsu, "Frequency-Tunable Reflective Gyro-BWO," in International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz, 2019, vol. 2019-September.
[30] T. H. Chang and B. R. Yu, "High-power millimeter-wave rotary joint for radar applications," in 34th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2009, 2009.
[31] T. H. Chang and B. R. Yu, "High-power millimeter-wave rotary joint," Review of Scientific Instruments, Article vol. 80, no. 3, 2009.
[32] T. Chang, L. Barnett, K. Chu, F. Tai, and C. Hsu, "Dual-function circular polarization converter for microwave/plasma processing systems," Review of scientific instruments, vol. 70, no. 2, pp. 1530-1534, 1999.
[33] J. R. Montejo-Garai, I. O. Saracho-Pantoja, J. A. Ruiz-Cruz, and J. M. Rebollar, "High-performance 16-way Ku-band radial power combiner based on the TE01-circular waveguide mode," Rev Sci Instrum, vol. 89, no. 3, p. 034703, Mar 2018.
[34] J. R. Montejo-Garai, J. A. Ruiz-Cruz, and J. M. Rebollar, "Design of a Ku-Band High-Purity Transducer for the TM01 Circular Waveguide Mode by Means of T-Type Junctions," IEEE Access, vol. 7, pp. 450-456, 2019.
[35] S. P. Morgan Jr, "Effect of surface roughness on eddy current losses at microwave frequencies," Journal of Applied Physics, Article vol. 20, no. 4, pp. 352-362, 1949.
[36] M. Yi et al., "Surface Roughness Modeling of Substrate Integrated Waveguide in D-Band," IEEE Transactions on Microwave Theory and Techniques, Article vol. 64, no. 4, pp. 1209-1216, 2016.
[37] B. Huang and Q. Jia, "Accurate modeling of conductor rough surfaces in waveguide devices," Electronics (Switzerland), Article vol. 8, no. 3, 2019.