161_1_Class14

# 161_1_Class14 - EE161 Electromagnetic Waves Spring 2010...

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Unformatted text preview: EE161 Electromagnetic Waves Spring, 2010 Prof. Y. Ethan Wang Electrical Engineering Dept. UCLA Lesson 14 • Waveguide Loss • Transmission Line Resonator • Rectangular Waveguide Cavity • Waveguide Excitation Current Flow in Good Conductor s δ DC current area A l area A’ w w l h High Frequency current h w l A l R ⋅ = = σ σ 1 1 Current flows inside the conductor uniformly. The resistance of the conductor is given by Ohm’s law, Due to the skin effect, current flows within a very thin layer of conductor close to the surface. The resistance of the conductor is thus given by, w l w l A l R s s σδ δ σ σ 1 1 ' 1 = ⋅ = = s R σ μ π σδ f R s s = = 1 Surface impedance is thus defined as, μσ π δ f s 1 = Waveguide Loss In general, power dissipation in a non-ideal waveguide may be attributed to both conductor loss and dielectric loss α α 2 10 2 1 − − − = ⇒ = − e P P e P P P l l 10 2 P P l = α In a lossy waveguide, as power decays according to the factor z e α 2 − Define the power dissipated per unit length in waveguide as P l and the incident power as P , the ratio between the power observed at the unit length away and the original incident power is α 2 ≈ The attenuation constant can thus be determined by when loss is small d c ld lc P P P α α α + = + = 10 2 conductor loss dielectric loss attenuation constant due to conductor loss attenuation constant due to dielectric loss Conductor Loss ∫ = C s s l dl J R P 2 2 In general, conductor loss per unit length is given by: surface impedance surface current density...
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161_1_Class14 - EE161 Electromagnetic Waves Spring 2010...

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