Fields and Waves Lesson 5 5 Wave Reflection

Fields and Waves Lesson 5. 5 Wave Reflection and Transmission Lale T. Ergene

Normal incident MEDIUM 1 η 1 MEDIUM 2 η 2 incident plane wave transmitted plane wave reflected plane wave • wave is normally incident on an infinite interface separating two different media • impedance discontinuity • similar to the transmission lines • EM waves represented with rays or wavefronts

Lossless media • two lossless, homogenous, dielectric media MEDIUM 1 MEDIUM 2 ε 1, μ 1 . . z=0 Incident wave ε 2, μ 2

Lossless media transmitted wave reflected wave

Boundary conditions Tangential component of the electric field should be continuous across the boundary Tangential component of magnetic field should be continuous (no current source) At the boundary (z=0): or or

reflection and transmission coefficients Normal incident Γ and τ are real for lossless dielectric media Normal incident For nonmagnetic media

transmission line analogy • One to one correspondence between the transmission line parameters and plane wave parameters • incident and reflected waves create a standing wave pattern Standing wave ratio § if η 1= η 2 Γ=0 S=1 § η 2= 0 (perfect conductor) Γ=-1 • Smith chart can be used S= ∞ • the max and min locations of the electric field intensity from the boundary are defined by the same expressions for the voltage max and min locations

Power flow in lossless media The average power density flowing in medium 1 The average power density flowing in medium 2 For lossless media

Boundary between lossy media • two lossy media MEDIUM 1 MEDIUM 2 ε 1, μ 1, σ1 . . z=0 Medium 1 ε 2, μ 2, σ2

Boundary between lossy media Medium 2 . Γ and τ are real for lossless dielectric media