在本論文中利用在步階式阻抗共振器(Stepped-impedance resonator, SIR)末端加上二極體負載製作成可開關式的帶通濾波器。此負載的二極體可改變步階式阻抗共振器共振條件。由於散佈式耦合的饋入技術的低負載效應，因此不需要複雜的匹配網路來設計多頻帶的電路。
本論文之四頻帶通濾波器電路架構包含二分之一波長步階式阻抗共振器、四分之一波長步階式阻抗共振器。每個通帶皆由一對共振器控制可增加設計自由度，並且使用散佈式耦合技術減少頻帶間的負載效應，即可將四個帶通濾波器整合在一起。其中，使用開路殘段與在饋入線末端加上電容元件皆為了增加傳輸零點以提升通帶之選擇度。將二極體負載接在共振器末端以設計可獨立開關四個頻帶的可調式裝置。
利用散佈式耦合的饋入架構、非對稱式四分之一波長共振器、並聯開路殘段與負載二極體可設計出具有帶通特性之單刀四擲切換器(Single-pole-quadruple-throw, SPQT)及可開關式四工器，其皆具有高隔離度及寬止帶的特性。在隔離度的部分可以達到35 dB 以上，20-dB止帶可達到13倍的最低操作中心頻率。最後，在本論文中利用實作之電路驗證設計的方法是有效的。

Stepped-impedance resonators with diodes loaded at one end are used to develop switchable bandpass filters in this thesis. The loaded diodes are used to switch the resonance conditions of the stepped-impedance resonators. Due to the low loading effect from distributed coupling technique, the proposed circuits can obtain many channels without the need of complicated matching network.
The switchable quad-band bandpass filter consisting of half-wavelength/quarter- wavelength resonator. Each passband is controlled by a respective pair of resonators to increase design freedom, and the four BPFs are combined by utilizing distributed coupling technique to reduce channel-to-channel loading effect. The loaded open stubs and the source-load coupling capacitor are used to introduce transmission zeros to improve in-band selectivity. The p-i-n diodes are loaded at the end of the resonators as the switching devices to independently control the four passbands.
The bandpass SPQT switch and the switchable quadruplexer consisting of distributed coupling technique feeding line, asymmetrical quarter-wavelength resonators, shunt open stubs, and p-i-n diodes features compactness, high isolation and wide stopband. The isolation is better than 35 dB and the 20-dB stopband extends up to 13the lowest operation center frequency. Finally, to validate the design concept, theory as well as experiment are presented and compared in this article.

[1]P. Mondal and M. K. Mandal, “Design of dual-band bandpass filters using stub-loaded open-loop resonators,” IEEE Trans. Microw. Theory Tech., vol. 56, no. 1, pp. 150–155, Jan. 2008.
[2]X.-Y. Zhang, J.-X. Chen, Q. Xue, and S.-M. Li, “Dual-band bandpass filters using stub-loaded resonators,” IEEE Microw. Wireless Compon. Lett., vol. 17, no. 8, pp. 583–585, Aug. 2007.
[3]J.-T. Kuo and H.-P. Lin, “Dual-band bandpass filter with improved performance in extended upper rejection band,” IEEE Trans. Microw. Theory Tech., vol. 57, no. 4, pp. 824–829, Apr. 2009.
[4]Y.-C. Chiou, C.-Y. Wu, and J.-T. Kuo, “New miniaturized dual-mode dual-band ring resonator bandpass filter with microwave C -Sections,” IEEE Microw. Wireless Compon. Lett., vol. 20, no. 2, pp.67–69, Feb. 2010.
[5]S. Sun, “A dual-band bandpass filter using a single dual-mode ring resonator,” IEEE Microw. Wireless Compon. Lett., vol. 21, no. 6, pp. 298–300, Jun. 2011.
[6]S.-F. Chang, Y.-H. Jeng, and J.-L. Chen, “Dual-band step-impedance bandpass filter for multimode wireless LANs,” Electron. Lett., vol. 40, no. 1, pp. 38–39, Jan. 2004.
[7]C.-Y Chen, C.-Y. Hsu, and H.-R. Chuang, “Design of miniature planar dual-band filter using dual-feeding structures and embedded resonators, ” IEEE Microw. Wireless Compon. Lett., vol. 16, no. 12, pp. 669–671, Dec. 2006.
[8]H.-W. Wu, Y.-F. Chen, and Y.-W. Chen, “Multi-layered dual-band bandpass filter using stub-loaded stepped impedance and uniform impedance resonators,” IEEE Microw. Wireless Compon. Lett., vol. 22, no. 3, pp. 114–116, Mar. 2012.
[9]A. Djaiz, T. A. Denidni, and M. Nedil, “Dual-band filter using multilayer structures and embedded resonators,” Electron. Lett., vol. 43, no. 9, pp. 527–528, Apr. 2007.
[10]C.-F. Chen, T.-Y. Huang, and R.-B. Wu, “Design of dual- and triple-passband filters using alternately cascaded multiband resonators,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 9, pp. 3550–3558, Sep. 2006.
[11]Q.-X. Chu and X.-M. Lin, “Advanced triple-band bandpass filter using tri- section SIR, ” Electron. Lett., vol. 44, no. 4, pp. 295–296, Feb. 2008.
[12]C.-I G. Hsu, C.-H. Lee, and Y.-H. Hsieh, “Tri-band bandpass filter with sharp passband skirts designed using tri-section SIRs,” IEEE Microw. Wireless Compon. Lett., vol. 18, no. 1, pp. 19–21, Jan. 2008.
[13]X. Lai, C.-H. Liang, H. Di, and B. Wu, “Design of tri-band filter based on stub loaded resonator and DGS resonator,” IEEE Microw. Wireless Compon. Lett., vol. 20, no. 5, pp. 265–267, May 2010.
[14]H.-W. Wu and R.-Y. Yang, “A new quad-band bandpass filter using asymmetric stepped impedance resonators,” IEEE Microw. Wireless Compon. Lett., vol. 21, no. 4, pp. 203–205, Apr. 2011.
[15]S.-C. Lin, “Microstrip dual/quad-band filters with coupled lines and quasi-lumped impedance inverters based on parallel-path transmission,” IEEE Trans. Microw. Theory Tech., vol. 59, no. 8, pp. 1937–1946, Aug. 2011.
[16]K.-W. Hsu and W.-H. Tu, “Design of a novel four-band microstrip bandpass filter using double-layered substrate,” in IEEE MTT-S Int. Microw. Symp. Dig., Boston, MA, Jun. 2009, pp. 1041–1044.
[17]J.-C. Liu, J.-W. Wang, B.-H. Zeng, and D.-C. Chang, “CPW-fed dual-mode double-square-ring resonators for quad-band filters, ” IEEE Microw. Wireless Compon. Lett., vol. 20, no. 3, pp. 142–144, Mar. 2010.
[18]J.-Y. Wu and W.-H. Tu, “Design of quad-band bandpass filter with multiple transmission zeros,” Electron. Lett., vol. 47, no. 8, pp. 502–503, Apr. 2011.
[19]J. Xu, C. Miao, L. Cui, Y.-X. Ji, and W. Wu, “Compact high isolation quad-band bandpass filter using quad-mode resonator,” Electron. Lett., vol. 48, no. 1, pp. 28–30, Jan. 2012.
[20]Y.-S. Lin, P.-Y. Chang, and Y.-S. Hsieh, “Compact electronically switchable parallel-coupled microstrip bandpass filter with wide stopband,” IEEE Microw. Wireless Compon. Lett., vol. 18, no. 4, pp. 254–256, Apr. 2008.
[21]W.-H. Tu, “Switchable microstrip bandpass filters with reconfigurable frequency responses,” in IEEE MTT-S Int. Microw. Symp. Dig., Anaheim, CA, May 2010, pp. 1488–1491.
[22]W.-H. Tu, “Switchable microstrip bandpass filters with reconfigurable on-state frequency responses,” IEEE Microw. Wireless Compon. Lett., vol. 20, no. 5, pp. 259–261, May 2010.
[23]W.-H. Tu, “Design of switchable dual-band bandpass filters with four states,” IET Microw. Antennas Propag., vol. 4, no. 12, pp. 2234–2239, Dec. 2010.
[24]C.-H. Kim and K. Chang, “Independently controllable dual-band bandpass filters using asymmetric stepped-impedance resonators,” IEEE Trans. Microw. Theory Tech., vol. 59, no. 12, pp. 3037–3047, Dec. 2011.
[25]P.-H. Deng and J.-H. Jheng, “A switched reconfigurable high-isolation dual-band bandpass filter,” IEEE Microw. Wireless Compon. Lett., vol. 21, no. 2, pp. 71–73, Feb. 2011.
[26]S.-F. Chao, C.-H. Wu, Z.-M. Tsai, H. Wang, and C. H. Chen, “Electronically switchable bandpass filters using loaded stepped-impedance resonators,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 12, pp. 4193–4201, Dec. 2006.
[27]S.-C. Lin, P.-H. Deng, Y.-S. Lin, C.-H. Wang, and C. H. Chen, “Wide-stopband microstrip bandpass filters using dissimilar quarter-wavelength stepped- impedance resonators,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 3, pp. 1011–1018, Mar. 2006.
[28]Y.-S. Lin, P.-C. Wang, C.-W. You, and P.-Y. Chang, “New designs of bandpass diplexer and switchplexer based on parallel-coupled bandpass filters,” IEEE Trans. Microw. Theory Tech., vol. 58, no. 12, pp. 3417–3426, Dec. 2010.
[29]S.-C. Lin and T.-L. Jong, “Microstrip bandpass filters with various resonators using connected- and edge-coupling mechanisms and their applications to dual-band filters and diplexers,” IEEE Trans. Microw. Theory Tech., vol. 60, no. 4, pp. 975–988, Apr. 2012.
[30]C.-F. Chen, T.-Y. Huang, C.-P. Chou, and R.-B. Wu, “Microstrip diplexers design with common resonator sections for compact size, but high isolation,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 5, pp. 1945–1952, May 2006.
[31]T. Yang, P.-L. Chi, and T. Itoh, “Compact quarter-wave resonator and its applications to miniaturized diplexer and triplexer,” IEEE Trans. Microw. Theory Tech., vol. 59, no. 2, pp. 260–269, Feb. 2011.
[32]P.-H. Deng, M.-I. Lai, S.-K. Jeng, and C. H. Chen, “Design of matching circuits for microstrip triplexers based on stepped-impedance resonators,” IEEE Trans. Microw. Theory Tech., vol. 54, no. 12, pp. 4185–4192, Dec. 2006.
[33]C.-F. Chen, T.-M. Shen, T.-Y. Huang, and R.-B. Wu, “Design of multimode net-type resonators and their applications to filters and multiplexers,” IEEE Trans. Microw. Theory Tech., vol. 59, no. 4, pp. 848–856, Apr. 2011.
[34]J.-Y. Wu, K.-W. Hsu, Y.-H. Tseng, and W.-H. Tu, “High-isolation microstrip triplexer using multiple-mode resonators,” IEEE Microw. Wireless Compon. Lett., vol. 22, no. 4, pp. 173–175, Apr. 2012.
[35]S.-J. Zeng, J.-Y. Wu, and W.-H. Tu, “Compact and high-isolation quadruplexer using distributed coupling technique,” IEEE Microw. Wireless Compon. Lett., vol.21, no.4, pp.197–199, Apr. 2011.
[36]C.-F. Chen, T.-M. Shen, T.-Y. Huang, and R.-B. Wu, “Design of compact quadruplexer based on the tri-mode net-type resonators,” IEEE Microw. Wireless Compon. Lett., vol.21, no.10, pp.534–536, Oct. 2011.
[37]M. Zewani and I. C. Hunter, “Design of ring-manifold microwave multiplexers,” in IEEE MTT-S Int. Microw. Symp. Dig., San Francisco, CA, Jun. 2006, pp. 689–692.
[38]M. Sagawa, M. Makimoto, and S. Yamashita, “Geometrical structures and fundamental characteristics of microwave stepped-impedance resonators,” IEEE Trans. Microw. Theory Tech., vol. 45, no. 7, pp. 1078–1085, Jul. 1997.
[39]J. S. Hong and M. J. Lancaster, Microstrip Filters for RF/Microwave Application, New York: Wiley, 2001.
[40]W.-H. Tu, H. Li, K. A. Michalski, and K. Chang, “Microstrip open-loop ring bandpass filter using open stubs for harmonic suppression,” in IEEE MTT-S Int. Microw. Symp. Dig., San Francisco, CA, Jun. 2006, pp. 357–360.