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Antenna matching to housing ??

Discussion in 'Electronic Design' started by Boki, Jul 25, 2006.

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  1. Boki

    Boki Guest

    Hi All,

    Heard something just now:

    Antenna will matching to housing... ?

    I think it will only matching to PCB, the housing is only to avoid ESD.

    am I right?

    Best regards,
    Boki.
     
  2. Art

    Art Guest

    ???? Kinda vauge are we??? Explain what you are attempting so we have a
    viable chance to underestand what answer you are expecting.
     
  3. It's the weekly Team Boki challenge. Boki seems to go through about 5
    management organised disasters a month, have pity on him

    PS dont top post please.


    martin
     
  4. Boki

    Boki Guest

    Art 寫�:

    What I didn't understand is that why plastic housing will effect the
    antenna characteristic?

    My co-worker told me that is possible to effect about 200MHz in a
    2.4GHz system.

    Please comment.

    Thanks.
    Best regards,
    Boki.
     
  5. Joel Kolstad

    Joel Kolstad Guest

    Boki,

    "What I didn't understand is that why plastic housing will effect the
    antenna characteristic?"

    The plastic housing can affect the antenna's characteristics because plastic
    has a relative permittivity that's often significantly different than 1.
    (Vacuum *is* 1, and air is very close to 1.)

    Think of it this way: The speed of light in a substance is 3*10^8/sqrt(k) m/s,
    where k is the relative permittivity. And of course, a wavelength (lambda)=c
    (the speed of light in the material)/f (the frequency of operation). Hence,
    to calculate dimensions to build something like "a quarter-wavelength dipole,"
    you need to know the relative permittivity of the material surrounding that
    dipole so that you can correctly compute c. When you have a plastic housing,
    you have a mixed environment that's mostly air and somewhat plastic, so the
    *effective* dielectric constant is "something" greater than 1 and your
    dimensions need to be changed accordingly or the antenna's resonance will
    occur at a lower frequency.

    --

    This is all first-quarter undergraduate electromagnetics material, so you
    might want to take a look at the books targeted towards such students.
    Popular tomes include Cheng's "Field and Wave Electromagnetics," which assumes
    you have a solid grasp on undergraduate calculus. If you're a little skay
    there, I'd suggest something like "Introduction to Electrodynamics" by
    Griffiths or "Electromagnetics" by Kraus (which is a truly excellent book -- I
    think it's a fair statement that many people who received A's in traditional
    EM courses couldn't solve many of Kraus's problems, even though he uses far
    less fancy math than most... Kraus was all about real world applications...
    and searching for E.T. in his spare time :)... his death a few years ago was
    a great loss). If you want to avoid the textbook approach, something like
    "Electromagnetics Explained" by Schmitt is good for the working engineer.

    In many cases, the more "colorful" the cover, the less mathematically involved
    the text will be. :) Something like "Classical Electrodynamics" is good if
    you ever need to let a little wind out of your sails...

    ---Joel
     
  6. Boki

    Boki Guest

    The plastic housing can affect the antenna's characteristics because plastic
    Great introduction, I can recall the formula now, but I am not good on
    this course.

    Cheng's book is our textbook, but too many courses, only study enough
    to pass... sad.

    However, it is a very good a new start point by your introducion!

    Thanks a lot! Great!

    Best regards,
    Boki.
     
  7. Joel Kolstad

    Joel Kolstad Guest

    Hi Boki,

    Well, you're certainly not alone... electromagnetics is often one of the least
    favorite courses in EE curriculums, given the heavy math involved and the
    (initial) difficulty in seeing the real world applicability.

    I was always intrigued with antennas and had one of those rare professors who
    had done Real Commercial Development in the area (he now works for TDK, still
    designing antennas); it certainly helped.

    ---Joel
     
  8. Boki

    Boki Guest

    Sounds great, cheers !

    Best regards,
    Boki.
     
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