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Dipoles - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Below are all of the old forum threads, including all the responses to the original posts.

-- Amateur Radio
-- Antennas
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S4C
 Post subject: Dipoles
Posted: Fri Jan 14, 2005 11:24 am 
A basic question concerning Dipole elements. I apologize for my ignorance, and any help would be greatly appreciated.

As I understand it: A dipole element is cut to 1/2 wave length of a desired frequency.

Question: Why?

Background: Im studying Chaff and why it works as a Radar Jammer. I know that chaff is made of many strips of dipole elements cut to 1/2 of the wavelength of the target "victims" radar frequency. This allows the reflected RF to present itself on the "victims" radar scope.

Why 1/2? Why not the full wavelength? What would would happen if it was cut to the full wavelength instead of 1/2? I think the reason is that the dipole element would not reflect if cut to the full wavelength...but I dont know why.

Any help...?

God Bless,
-S4C


 
  
 
Guest
 Post subject: 1/2 wave vs Full wave Reflector.
Posted: Sat Jan 15, 2005 8:05 am 
I would suggest that you download the EZNEC demo and give it a try.


 
  
 
S4C
 Post subject:
Posted: Tue Jan 18, 2005 11:14 am 
Looked at the program mentioned....

hmmm....I am not an expert in this field...far from it. I looked at the EZNEC and im not sure what I could learn from it. Pretty obvious by the question I originally asked, I am not an expert.

I am currently studying Chaff, and needed a little more information on how it works. Specifically, why the dipole elements are cut to 1/2 the wavelength of the victims RADAR frequency...and not to the full wavelength.

I stumbled across this website while searching for information. I figured what a great place to ask the question...a forum used by "professionals" in the RF field of study.

Again, I respectfully ask for any "laymans" help on the question asked.

God Bless,
-S4C


 
  
 
Kirt Blattenberger
 Post subject: Dipole chaff
Posted: Tue Jan 18, 2005 4:16 pm 
 
Site Admin
User avatar

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
A 1/2-wavelength dipole resonates at a specific frequency, depending on its physical dimensions (primarily length if the aspect ratio is high). Therefore, it is very efficient at reflecting an incident signal at the resonant frequency of the dipole.

Integer 1/2-wavelengths probably work as well, but waste storage space and add weight. I recall reading somewhere that less than a pound of well-designed and deployed aluminum chaff can reflect a signal equivalent to a large bomber (same radar cross-section, or RCS).

There has got to be lots of information for you to reference on the web. I suggest trying a Google Search.


- Kirt Blattenberger :smt024


 
   
 
Guest
 Post subject:
Posted: Tue Jan 18, 2005 5:49 pm 
Thank you for your reply Sir!

When you say "integer 1/2 wavelengths", does this mean the same as "full wavelength" (as opposed to 1/2) ?

I have done many Google searches...in fact that is how I found this fine website and forum :)

I understand your reply to say:

When dealing with Chaff, a dipole cut to the full wavelength of a victims RADAR freq will have the same effect as a dipole cut to 1/2 the wavelength. 1/2 wavelengths are then used to save space and/or weight.

Thank you for your time and your patience...
-S4C


 
  
 
Kirt Blattenberger
 Post subject: Integer multiples
Posted: Tue Jan 18, 2005 11:49 pm 
 
Site Admin
User avatar

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Your interpretation of my comments is correct.

Integer multiples of 1/2 wavelength are as follows:

1 * 1/2-wavelength = 1/2 wavelength
2 * 1/2-wavelength = 2/2 = 1 wavelength
3 * 1/2-wavelength = 3/2 = 1-1/2 wavelengths
4 * 1/2-wavelength = 4/2 = 2 wavelengths

...and so on.


- Kirt Blattenberger :smt024


 
   
 
Guest
 Post subject:
Posted: Wed Jan 19, 2005 3:28 pm 
Thanks again for your reply. It is very helpful!

-S4C



Posted  11/12/2012

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