本論文主要的內容是設計並製造出在Sub GHz中可使用的寬頻且低損耗的環行器。首先探討電磁波在鐵氧體中的非互易性質以及損耗特性，其有助於我們了解鐵氧體的各項特性並且在設計產品時，可以選擇更具優勢的鐵氧體材料。除了找到縮小環行器尺寸的關鍵以外，我們也運用實驗室所設計的雙Y結理論中的運算決定中心帶線的基本形狀及尺寸，最後使用電磁波模擬軟體HFSS ( High Frequency Structure Simulator )進行結構優化。
此篇論文面臨最大的挑戰是為了因應IoT(Internet of Things)的到來，要將環行器在Sub-GHz的頻段，盡其所能的小型化，將過往的環行器大小縮小至一半的尺寸，並且設計成SMT(Surface Mount Technology)的型式。我們也克服了以往或是其他設計上需要額外增加一個介電環的結構限制。利用實驗室研發出來的雙Y結帶線結構，以及對於鐵氧體的特性操作，去設計出能符合產業界的標準Insertion loss 大於-0.35 dB的同時Reflection和Isolation 也小於-20 dB。此篇論文也將說明設計帶線上的關鍵以及如何呈現更寬的頻寬。
除了Sub-GHz的頻段以外，為了因應未來5G時代的來臨，我們也著手開始設計20-30GHz的環行器。在高頻段我們選擇將環行器設計成Microstrip 的型式，除了更簡易的結構以外，也能將尺寸縮小至10mm以下，讓原件在使用上增加了更多的自由度。

This work provides a detailed analysis and simulation to demonstrate how to broaden the operating bandwidth of a circulator. A double-Y junction circulator is designed, and the shape of the central stripline is optimized with the knowledge of a modified equation. The equation predicts two resonant conditions. The overlapping of the two resonant conditions jointly constitutes the broad bandwidth. The bias magnetic field is simulated and then used in full electromagnetic-wave simulation. The designed circulator was fabricated in the S-band for communication purpose. The overall operation range is from 925 to 960 MHz with the insertion loss less than 0.35 dB, reflection, and isolation better than 20 dB. The mechanism will be discussed.

[1] T. H. Chang, “Gyromagnetically-induced transparency for ferrites,” Am. J.Phys., vol. 84, p. 279, 2016.
[2] H.W. Chao, S.Y. Wu, T.H. Chang, “Bandwidth broadening for stripline circulator”, Rev. Sci. Instrum., vol. 88, Feb. 2017
[3] D. M. Pozar, Microwave Engineering, 3rd ed. NJ: John Wiley & Sons, 2005.
[4] Martha Pardavi-Horvath,“Microwave Applications of Soft Ferrites”, Journal of Magnetism and Magnetic Materials., vol. 215-216, pp. 171-183, 2000.
[5] 蔡育超,“一對二高功率高速射頻切換裝置研製”,碩士論文, 國立清華大學,2012.
[6] 魏克珠, 李士根, 蔣仁培,“微波鐵氧體新器件”第一版 國防工業出版社, 1995.
[7] 金重勳, 主編“磁性技術手冊”初版 中華民國磁性技術協會, 2002.
[8] J. Helszajn, M. Powesland, "Low-loss high power microstrip circulators", IEEE Trans. Microwave Theory Tech., vol. MTT-29, pp. 572-578, July 1981.
[9] 陳振瑋, “4G頻段夾心帶線型環行器研製”, 碩士論文, 國立清華大學, 2013.
[10] 吳詩嶢, “4G 頻段低損耗及寬頻之環行器研發”,碩士論文, 國立清華大學, 2016.
[11] 張潔宜, “帶線環行器極限之模擬研究”,碩士論文, 國立清華大學, 2017.
[12] 傅國欽, “磁性材料之環行傳輸介質研究”,碩士論文, 國立清華大學, 2012.
[13] H. Bosma, "A general model for junction circulators; choice of magnetization and bias field", IEEE Trans. Magn., vol. MAG-4, pp. 587-596, Sept. 1968.
[14] J. L. Young, C. M. Johnson, "A Compact Recursive Trans-Impedance Green's Function for the Inhomogeneous Ferrite Microwave Circulator", IEEE Transactions on Microwave Theory and Techniques, vol. MTT-52, no. 7, pp. 1751-1759, 2004.
[15] Y. Wang, B. Peng, W.–L. Zhang and K. Tan, “CPW circulators with barium ferrite thin film”, J. Electron. Sci. Tech., vol. 8, no. 4, pp. 351-355, Dec. 2010.
[16] A. Kuseik, W. Marynowski and J. Mazur, “Investigation of four-port circulator uti-lizing cylindrical ferrite coupled line juction”, Progress In Electromagnetics Research, vol. 134, pp. 379-395, 2013.
[17] M. Darques, J. De La Torre Medina, L. Piraux, L. Cagnon, I. Huynen, "Microwave circulator based on ferromagnetic nanowires in an alumina template", Nanotechnology, vol. 21, no. 14, 2010.
[18] T. Jensen, V. Krozer and C. Kjaergaard, “Realisation of microstrip junction circulator using LTCC technology”, Electronics Letters., vol. 47, no. 2, Jan. 2011.
[19] J. Wang, A. Yang, Y. Chen, Z. Chen, A. Geiler, S. M. Gillette, V. G. Harris and C.
Vittoria, “Self biased Y-junction circulator at Ku band”, IEEE Microw. Wirel. Compon. Lett., vol. 21, no. 6, pp. 292-294, Jun. 2011.
[20] B. Peng, H. Xu, H. Li, W. Zhang, Y. Wang and W. Zhang, “Self-Biased microstrip junction circulator based on barium ferrite thin films for monolithic microwave integrated circuits”, IEEE Trans. Magn., vol. 47, no. 6, pp. 1674-1677, Jun. 2011.
[21] A. J. B. Fuller, Ferrites at Microwave Frequencies., pp. 235-255, 1987.
[22] K. Sliwa et al., "Reconfigurable Josephson Circulator/Directional Amplifier", Phys. Rev. X, vol. 5, no. 4, Nov. 2015 V. Kelaiya, M. R. Naik, "Design and simulation of X band microstrip circulator", Proc. IEEE 10th Region Conf. (TENCON), pp. 1961-1964, Nov. 2016.
[23] A. Saib, M. Darques, L. Piraux, D. Vanhoenacker-Janvier, I. Huynen, "An unbiased integrated microstrip circulator based on magnetic nanowired substrate", IEEE Trans. Microw. Theory. Tech., vol. 53, no. 6, pp. 2043-2049, Jun. 2005.
[24] U. Milano, J. H. Saunders, L. Davis, "A Y-junction strip-line circulator", IRE Trans. Microwave Theory Tech., vol. MTT-8, pp. 346-351, May 1960.
[25] H. Bosma, "On stripline circulation at UHF", IEEE Trans. Microwave Theory Tech., vol. MTT-12, pp. 61-72, 1964.
[26] Y. Naito, N. Tanaka, "Broadbanding and changing operating frequency of circulators", IEEE Trans. Microwave Theory Tech., vol. MTT-19, pp. 367-372, 1971.
[27] H. How, T.-M. Fang, C. Vittoria, R. Schmidt, "Design of six-port stripline ferrite junction circulators", IEEE Trans. Microwave Theory Tech., vol. 42, pp. 1272-1275, July 1994.
[28] B. K. O'Neil, J. L. Young, "Experimental investigation of a self-biased microstrip circulator", IEEE Trans. Microw. Theory Tech., vol. 57, no. 7, pp. 1669-1674, Jul. 2009.
[29] J. W. Wang, A. L. Geiler, V. G. Harris, C. Vittoria, "Self biased Y-junction circulator at Ku band", IEEE Microw. Wireless Compon. Lett., vol. 21, pp. 292-294, 2011.