A signal representation used in distributed circuits and transmission lines. In such a circuit or network, the voltage and current vary spatially, therefore the indicated impedance also varies with the location of the measurement. To allow an understanding and analysis of the signal flow in the circuit, the signals are represented by power waves, which describe the incident and reflected signals in the transmission line. Given a simple transmission line circuit (see diagram) of characteristic impedance Z₀, with V_i and V_r as the incident and reflected voltages at the load,

incident power P_i = |V_i|²/Z₀

reflected power P_r = |V_r|²/Z₀

power delivered to load P_L = (|V_i|² – |V_r|²)/Z₀

load reflection coefficient Γ = (Z_L – Z₀)/(Z_L + Z₀)

If this circuit is viewed in terms of power flow, then if the power available from the source is given by

and the power delivered to the load is

then |b|² can be thought of as the power that is reflected, or scattered by the load. It then follows that

are the incident and reflected power waves, respectively. They have dimensions of √(power). See also scattering parameters.

Power waves: transmission line connecting load to source