| Summary: | 碩士 === 國立高雄第一科技大學 === 電子工程研究所 === 103 === This paper presents the design of dual band branch-line couplers. In the proposed design, all asymmetric spur lines and conventional branch lines are only a quarter-wavelength long(λ).Both of them equal to each other.Asymmetric spur lines structure used asymmetric coupled lines to improve and conventional circuit consisted of a branch line merging parallel open stub. In theory, it can be acquire actual size from simulation. However, symmetric spur lines were derived by asymmetric spur lines in appropriate condition. To support implement circuit from impedance relationship between the two. According to the proposed design methods, realizing the purpose of dual-band, etc.
In this paper, select the common frequency specifications on dual band branch-line circuit. Asymmetric spur branch-line coupler divided into dual band frequency. The first circuit operating at f2/f1=2GHz/0.9GHz, the result of the measurement in lower band is S11=-19.134dB、S21=-3.745dB、S31=-20.051dB、S41=-3.764dB,the phase difference of∠S21-∠S41=94.781°, bandwidth of 60MHz, in upper band is S11=-19.379 dB、S21=-4.557dB、S31=-16.998dB、S41=-4.507dB﹐the phase difference of ∠S21-∠S41=85.752°﹐bandwidth of 63MHz, asymmetric spur branch-line coupler as practical as conventional. The second circuit operating at f2/f1=2.4GHz/1.8GHz, the result of the measurement in lower band is S11=-22.638dB、S21=-3.778dB、S31=-17.675dB、S41=-3.7834dB, the phase difference of∠S21-∠S41=87.071°, bandwidth of 190MHz, in upper band is S11=-15.409dB、S21=-4.88dB、S31=-15.01 dB、S41=-4.9dB, the phase difference of∠S21-∠S41=84.248°,bandwidth of 60MHz. The second circuit as practical as conventional and to reduce the ratio of both upper and lower band. The spur lines improved conventional circuit that two frequency too close, causing the Open-circuit stub impedance is too large. And it can further study to pursuit low cost, easy fabrication in the future.
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