High frequencies - dispersive and directional?

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Discussion Overview

The discussion revolves around the relationship between frequency, directionality, and dispersion in wave propagation, particularly in the context of high-frequency applications such as those involving Plasma Antennas. Participants explore the definitions and implications of dispersion and directionality, questioning how these concepts interact as frequency increases.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that higher frequencies lead to more directional waves, but caution that this is not a universal rule.
  • It is noted that dispersion and directionality are not the same, with dispersion potentially leading to divergence.
  • One participant seeks clarification on the definition of dispersion, suggesting it involves different phase velocities for different frequencies.
  • A participant references a figure illustrating dispersion, questioning how it relates to directionality.
  • There is a suggestion that the term "focus" may have been misused in a source, proposing that "collimation" might be a more accurate term in the context of reducing dispersion.
  • Another participant points to a glossary that equates directivity with dispersion, prompting further inquiry into the accuracy of this interpretation.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between frequency, directionality, and dispersion, indicating that the discussion remains unresolved with multiple competing interpretations of these concepts.

Contextual Notes

There are limitations in the definitions and assumptions surrounding dispersion and directionality, as well as the potential misuse of terminology in referenced materials. The discussion highlights the complexity of these concepts without reaching a consensus.

OJFord
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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
 
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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.
 
mfb said:
Dispersion can lead to divergence, too, but they are not the same.

Ah, so what is dispersion, then?
 
Different phase velocities for different frequencies, this can lead to different refraction for them.
Wikipedia article
 
OJFord said:
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!
 

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