| Summary: | 碩士 === 長庚大學 === 電子工程學研究所 === 97 === In modern communication systems, the miniaturization of circuits is an important issue especially dual-band operation in about the same size of communication components. For this reason, how to enable single circuit operated in dual-band is a popular research topic. In this research, we propose the new circuit structure of compact dual-band branch-line couplers. According to the aforementioned, this thesis is divided into three parts: (1) T-shaped dual-band branch-line coupler: Open stub tapped branch lines are used to replace the traditional quarter-wave branch lines to obtain dual-band operation. (2) Dual-band stepped-impedance-stub branch-line coupler: The proposed stepped-impedance-stub branch line can have dual-band performance and is smaller than that of the T-shaped branch line for about 21.7% because of its increased non-uniform impedances. The synthesis method is developed and it is found that there has two degrees of freedom which can be exploited to miniaturize circuit size and/or replace impractical impedances with more realizable ones. The advantage of wide range of realizable frequency ratio of dual bands is also observed. (3) Two-section dual band branch-line coupler: In this part, we cascade two dual-band stepped-impedance-stub branch-line couplers to increase wide bandwidths. The measured results validate good dual-band performance at 2.4/5.8 GHz with enhanced bandwidth of up to 21% and 12%, respectively.
Totally 4 couplers are fabricated and measured with Arlon 25N boards, which show good performance as expected.
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