| Summary: | 碩士 === 長庚大學 === 電子工程學系 === 98 === Abstract
The purpose of this thesis is to develop the circuit structures and synthesis methods of miniaturized dual-band rat-race couplers. In modern communication systems, microstrip couplers are useful because of they can provide output signals with equal or unequal power ratios and with 90 or 180 phase differences. The rat-race couplers are popular circuits often used in communication systems. Since they require structures with uniform impedances and specific wavelengths involved, they only can be used for single band applications.
For this reason, how to enable single coupler operated in dual bands is a popular research topic recently. In this thesis, we propose the stepped-impedance-stub line to replace the traditional /4 and 3/4 lines for dual-band rat-race design. By taking the advantage of non-uniform impedance distribution, the stepped-impedance-stub line can have an equivalent 90 electrical length in dual bands. The proposed stepped-impedance-stub line can have dual-band performance and is smaller than the conventional T-shaped line because of its increased non-uniform impedances. The synthesis method is developed and found that it 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. Moreover, the novel dual-band -90° stepped-impedance-stub coupled lines are developed to replace the conventional 3/4 lines of rat-race for further size reduction.
This thesis develops several novel dual-band rat-race couplers with stepped-impedance-stub lines. In addition to the formulation and simulation, we will also fabricate and measure practical circuits to demonstrate the capability of the proposed circuit structures.
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