From Maxwell's equations, the field equation of a plane wave propagating along a waveguide can be derived, in terms of the spatial dimensions , and , and the temporal dimension , as where is the 2-dimensional cross-section of the distribution of the electromagnetic field, is the propagation constant, and is the angular frequency of the wave excitation in units of radians (with being the frequency in hertz). Technical names exist for each term in the equation: * is called the transverse term * is known as the phase term * is the harmonic term