When a wave hits a boundary between two materials, part of it reflects and part refracts — bending toward or away from the normal depending on how the material properties change on each side.
An electromagnetic wave travels in a straight line through a uniform medium, but its behavior changes the moment it crosses into a material with different electromagnetic properties. Reflection sends part of the energy back, refraction bends the transmitted portion, and attenuation gradually removes energy from the wave as it travels — three separate mechanisms every RF link, fiber-optic system, and radar design has to account for.
Snell's Law relates the incident and refracted angles to the refractive indices of the two media: n1·sin(θ1) = n2·sin(θ2). When a wave enters a denser medium (higher refractive index), it bends toward the normal, as shown above. When it exits into a less dense medium, it bends away from the normal — and past a critical angle, no refracted ray exists at all, a condition called total internal reflection, which is the entire operating principle behind fiber-optic cable.
Even without a boundary, a wave loses power as it travels — spreading loss (power spread over an ever-larger wavefront) and absorption loss (energy converted to heat in the medium) both reduce received power with distance. This is the physical basis of an RF link budget: the transmitted power minus all the losses along the path must still exceed the receiver's minimum sensitivity for the link to work.
A wave's polarization (the orientation of its electric field oscillation) can also change on reflection or refraction, and the amount of reflected versus transmitted energy actually depends on polarization at oblique angles (governed by the Fresnel equations). This is why antenna polarization matching matters in real RF link design — a mismatched polarization between transmit and receive antennas causes real, calculable signal loss.
When a wave tries to exit into a less dense medium at a steep enough angle, no refracted ray can satisfy Snell's Law — physically, all the energy reflects back into the original medium instead of transmitting through. This is the principle that keeps light trapped inside a fiber-optic core.
Yes — when a wave enters a medium where its propagation speed is lower (correspondingly, a higher refractive index), it bends toward the normal (the incident angle is always the larger angle in that case). Entering a faster medium bends the ray away from the normal.
A transmit antenna radiates a wave with a specific electric-field orientation. If the receive antenna is oriented to detect the wrong polarization (e.g., a vertically polarized antenna receiving a horizontally polarized wave), a significant fraction of the available signal power is lost regardless of how strong the transmitted signal is.
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