161_1_Lecture_11

161_1_Lecture_11 - EE161 El EE161 Electromagnetic Waves...

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EE161 Electromagnetic Waves all 2010 Fall, 2010 Instructor: Dr. Shenheng Xu Electrical Engineering Dept., UCLA gg p , © Prof. Y. Ethan Wang
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ecture 1 Lecture 11 • Waveguide Loss • Optical Fiber • Transmission Line Resonator ectangular Waveguide Cavity • Rectangular Waveguide Cavity aveguide Excitation Waveguide Excitation
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Waveguide Loss In a lossy waveguide, as power decays according to the factor z e 2 efine the power dissipated per unit length in waveguide as nd the incident Define the power dissipated per unit length in waveguide as P l and the incident power as P 0 , the ratio between the power observed at the unit length away and the original incident power is 2 0 2 0 0 1 e P P e P P P l l 2 when loss is small 0 2 P P l The attenuation constant can thus be determined by In general, power dissipation in a non-ideal waveguide may be attributed to both conductor loss and dielectric loss ielectric loss attenuation constant due d c ld lc P P conductor loss dielectric loss to conductor loss attenuation constant due P 0 2 to dielectric loss
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Current Flow in Good Conductor DC current l Current flows inside the conductor uniformly. The resistance of the conductor is given by h l l R 1 1 Ohm’s law, area A = w h w igh Frequency h w A Due to the skin effect, current flows within a l High Frequency current very thin layer of conductor close to the surface. The resistance of the conductor is thus given by, s l l l R 1 1 ' 1 s R area A’ = w  s w w w A s s  f 1  f s 1 R s s Surface impedance is thus defined as,
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Surface Current Density How to find the surface current density on the waveguide walls? Boundary conditions: H J n ˆ z j x s s z e a A H cos 10 z j x e x A a j H sin 10 Side wall (x=0): Side wall (x=a): a z j z s e A y H z x 10 ˆ ˆ ˆ J 0 , 0 z x H H z j z s e A y H z x 10 ˆ ˆ ˆ J 0 , 0 z x H H Bottom wall (y=0): J s plot for TE 10 mode x z s H x H z y ) ˆ ˆ ( ˆ J op wall (y=b): z j e a x a j A z a x A x sin / ˆ cos ˆ 10 10 10 Top wall (y b): x z s H x H z y ) ˆ ˆ ( ˆ 0 J z j e a a j A z a A x sin / ˆ cos ˆ 10 10 10
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Conductor Loss general conductor loss per surface impedance
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161_1_Lecture_11 - EE161 El EE161 Electromagnetic Waves...

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