Richard Harrison wrote:
If a phasor represents an alternating current:
I = Io cos omega t,
then the sum of the two phasors representing forward and reflected
sinusoidal components is another sinusoid of the same frequency.

Point is the components are amenable to phasor representation. All the
old authors do it. This amenability is proof the standing wave is a
sinusoid too.

The absence of harmonic frequencies generated by the antenna
is also proof that the standing wave is a sinusoid. All
nonsinusoidal waveforms contain harmonics.
--
73, Cecil http://www.qsl.net/w5dxp