High frequencies - dispersive and directional?

[OJFord]

My understanding is that as frequency increases, the wave (or waves, rather) become more directional.

However, Plasma Antennas' site specifies operation between 1 and 100GHz, and states their product tightly focussess the beam in order to decrease dispersion.

Unless I am totally missing something (which is fairly probable - our dialogue won't have to be so long and confused if it is the case!) dispersion is the same as directionality.

i.e. something that disperses, is 'not very directional'.

I assume I have dispersion wrong, because otherwise I don't understand why that's necessary - it threw me off for a minute and I started talking about how un-directional high frequency waves were.


TIA,

~OJFord

 

[mfb]

My understanding is that as frequency increases, the wave (or waves, rather) become more directional.

You can reduce the minimal divergence with higher frequencies, if your emitter size is fixed. But there is no general rule "higher frequency => more directional" or anything similar.

Dispersion can lead to divergence, too, but they are not the same.

 

[OJFord]

Dispersion can lead to divergence, too, but they are not the same.

Ah, so what is dispersion, then?

 

[mfb]

Different phase velocities for different frequencies, this can lead to different refraction for them.
Wikipedia article

 

[OJFord]

But this figure (from the article) shows the narrow beam dispersing, or spreading out.

http://upload.wikimedia.org/wikipedia/commons/0/06/Prism_rainbow_schema.png

Perhaps it's the directionality part I don't really understand then - because to me, that looks like it's varying direction.

 

[Darwin123]

My understanding is that as frequency increases, the wave (or waves, rather) become more directional.

However, Plasma Antennas' site specifies operation between 1 and 100GHz, and states their product tightly focussess the beam in order to decrease dispersion.

Unless I am totally missing something (which is fairly probable - our dialogue won't have to be so long and confused if it is the case!) dispersion is the same as directionality.

i.e. something that disperses, is 'not very directional'.

I assume I have dispersion wrong, because otherwise I don't understand why that's necessary - it threw me off for a minute and I started talking about how un-directional high frequency waves were.TIA,

~OJFord

I think that the writers misused the word "focus" rather than dispersion. Maybe they meant, "Our product narrowly collimates the beam in order to decrease dispersion."
One doesn't focus a beam to decrease dispersion. The more tightly the beam is focused, the faster the beam disperses from the focal point.
So replace "focusing" with "collimation". I think that will work.
Words, again!

 

[OJFord]

Hmm, thanks for your responses.

This page:

http://www.neumann-kh-line.com/neum...CE5E3F7C125728C006784FC?Open&term=directivity

Though otherwise helpful, seems to also suggest that directivity = dispersion.

Any thoughts? Or am I just reading it wrong?