[理工] [電磁]傳輸線與波導

[big1p (biglp)]

1. Consider a transmission line with Zo = 50Ω terminated with an unknown load


                                 1-jStanβl
impedance ZL, show that ZL = Zo ------------, where l is the length from the
                                 S-jtanβl


load to the first voltage minimun, S is the standing wave ratio, and β is


phase constant.



2. In our system, two coaxial cables of the same size but different insulating


dielectric materials between their inner and outer conductors are in series.


The characteristic impedances of these two cables are different and thereby


reflected signals are seen at the spatially perfectly matched junction of


these two cables. From basic electromagnetism, please clearly explain the


current in cable 1 "pushed backward" when it is moving across cable 2 though


no extra electromagnetic force is applied along the direction of these cables.




第一題感覺那個到最小值距離 l 是關鍵，但是想不太到


第二題才5分，考觀念，也是想不到



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→ gleen7902:第一題 叢集小值的地方往負載看的阻抗是Zo/S
→ gleen7902:然後再等於 阻抗轉換公式 就是答案了
→ gleen7902:1 = L
→ big1p:爲什麼從極小值看進去是那樣 ?
→ gn01216674:幫答...阻抗最小時，反射係數tau=-|tau|，所以此時阻抗
→ gn01216674:Z(min)=V/I= VL(1-|tau|)/IL(1+|tau|) =VL/IL/S = ZL/S
→ gn01216674:前提是T.L.=lossless (反之，阻抗最大時是Z(max)=ZL*S)
→ gn01216674:阿...打錯  是Zo