Plane Waves, Media and Interfaces

$E$, $H$ and the direction of travel form a right-handed set, and $E/H=\eta$ everywhere. Knowing $\eta_0=120\pi\approx377\,\Omega$ turns most numerical questions into one division.

The loss tangent $\sigma/\omega\varepsilon$ decides which approximation applies: $\ll1$ is a good dielectric, $\gg1$ a good conductor. In a good conductor the fields decay within a skin depth and $E$ leads $H$

At normal incidence the reflection coefficient has the same algebraic form as on a transmission line with $\eta$ in place of $Z$. Two special angles matter: total internal reflection above $\theta_c$, and zero reflection for parallel polarisation at $\theta_B$

Read polarisation off the two orthogonal components: equal amplitudes at $\pm90^\circ$ give circular, anything else elliptical, zero phase difference linear. Phase velocity may exceed $c$; group velocity, which carries the information, never does.