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High frequencies - dispersive and directional?

  1. Jul 30, 2012 #1
    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
     
  2. jcsd
  3. Jul 30, 2012 #2

    mfb

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    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.
     
  4. Jul 30, 2012 #3
    Ah, so what is dispersion, then?
     
  5. Jul 30, 2012 #4

    mfb

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    Different phase velocities for different frequencies, this can lead to different refraction for them.
    Wikipedia article
     
  6. Jul 30, 2012 #5
  7. Jul 30, 2012 #6
    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!
     
  8. Jul 31, 2012 #7
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