# Ray model for radio waves?

kent davidge
I have never seen ray model of light being considered for radio waves, or waves of larger wavelengths. I have a feeling that this model does not apply to them. Am I right?

Staff Emeritus
Do you mean as in ray tracing?

Homework Helper
I have never seen ray model of light being considered for radio waves, or waves of larger wavelengths. I have a feeling that this model does not apply to them. Am I right?
It is "just" a matter of scale. Light and radio waves are the same thing.

kent davidge
@anorlunda , @jbriggs444

Let me be more clear,
I have only seen light being described by rays (geometrical optics) when it is visible light. I did not see up until now light of large wavelength, like radio waves, being described by geometrical optics.

Staff Emeritus
Then you haven't met the physicists on this site. They describe light as waves every day.

2022 Award
A radio telescope dish? Geometric "optics" is probably pretty decent for that application (even if you then make your telescope part of a synthetic aperture telescope). But generally "rays" are useful concepts when wave-y effects like interference and diffraction are negligible - which is pretty often not the case for radio waves.

Dr_Nate, berkeman and kent davidge
Gold Member
I did not see up until now light of large wavelength, like radio waves, being described by geometrical optics

ummm really ?
you haven't looked very hard

There's no difference to their optical counterparts

ummm really ? you haven't looked very hard
To be fair, the OP doesn't claim to have looked for it at all.

Gold Member
2022 Award
It is "just" a matter of scale. Light and radio waves are the same thing.

But this scale difference is the key to the answer of the question. Ray optics is an approximation of wave optics for the case that the scale of the obstacles the wave hits is large compared to the typical wave lengths of the em. waves. This is usually not fulfilled for radio waves, which have wavelength roughly in the range of cm to some 100 m.

Dr_Nate and Ibix
Gold Member
To be fair, the OP doesn't claim to have looked for it at all.

and that is the problem, he should have

Gold Member
This is usually not fulfilled for radio waves, which have wavelength roughly in the range of cm to some 100 m
Usually not but not 'never'. Ray tracing methods for long and medium wavelength radio signals in the ionosphere are about the only way to predict propagation over very long paths. In that case, the dimensions of the propagation path are large compared with the wavelengths involved.

vanhees71 and davenn