Reflection coefficient

The reflection coefficient measures how much of a wave bounces back when it hits a mismatch — the electromagnetic version of an echo. Shout into a canyon and part of your voice returns; send a signal down a cable into a load that doesn't 'fit', and part of the signal returns the same way. The coefficient, written Γ (gamma), runs from 0 (a perfect match — nothing reflects, all power delivered) up to 1 (a total mirror — everything reflects, like hitting an open or a short). A Γ of 0.1 means a tenth of the wave's amplitude comes back, wasting one percent of the power.

Γ depends on the gap between the load impedance and the line's characteristic impedance: Γ = (Z_L − Z₀)/(Z_L + Z₀). Match them perfectly and the numerator vanishes, so Γ = 0. This single ratio is the heartbeat of RF and high-speed design — it sets how much of your transmitter's precious power actually reaches the antenna, how cleanly a gigahertz edge travels down a circuit board, and what an S-parameter (S₁₁) on a network analyzer is really reporting. Engineers often quote it as 'return loss' in decibels, where bigger numbers mean a better match.