# Antenna matching to housing ??

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

1. ### BokiGuest

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. ### ArtGuest

???? Kinda vauge are we??? Explain what you are attempting so we have a
viable chance to underestand what answer you are expecting.

3. ### martin griffithGuest

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. ### BokiGuest

Art å¯«é?“ï¼š

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 KolstadGuest

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. ### BokiGuest

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 KolstadGuest

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. ### BokiGuest

Sounds great, cheers !

Best regards,
Boki.

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