The time independent Maxwell curl equations with a positive time convention (ej ω t )

BPM - Equation 1

and the divergence equations are

BPM - Equation 2

The factor j does not suit the current purpose, so make the substitution

BPM - Equation 3

where n0 BPM - Equation b is the free space impedance, so that h and E have the same

units. Then

BPM - Equation 4

where BPM - Equation a. Eliminating the h gives the electric wave equation

BPM - Equation 5