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Near-Far Field - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


maxwell
 Post subject: Near-Far Field
Posted: Mon Oct 10, 2005 12:25 pm 
 
Captain
User avatar

Joined: Mon Sep 01, 2003 6:59 pm
Posts: 13
Location: Boston
Hey there is a great article linked from the RF Cafe home page on near-field vs. far-field. Definitely worth reading. Good find Kurt.

... :smt023 Maxwell


 
   
 
UWB_antenna_guy
 Post subject: Re: Near-Far Field
Posted: Mon Oct 10, 2005 5:20 pm 
 
Colonel
User avatar

Joined: Tue Aug 09, 2005 1:07 pm
Posts: 28
maxwell wrote:
Hey there is a great article linked from the RF Cafe home page on near-field vs. far-field. Definitely worth reading. Good find Kurt.

... :smt023 Maxwell


a link would be nice. Couldn't find the article on the main page


 
   
 
Kirt Blattenberger
 Post subject:
Posted: Mon Oct 10, 2005 9:28 pm 
 
Site Admin
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Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Greetings UWB_antenna_guy:

The article is titled, "The World of the Near Fied," and the link to it is in the Recent Additions list in the right column. The link is replicated here so you don't have to go back to the homepage to get to it. I will be adding a calculator page for obtaining the three near field boundary distances given in the article.

http://www.evaluationengineering.com/ar ... _world.asp

.

_________________
- Kirt Blattenberger :smt024
RF Cafe Progenitor & Webmaster


 
   
 
Graham
 Post subject:
Posted: Tue Oct 11, 2005 6:44 am 
 
Colonel
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Joined: Fri Sep 02, 2005 7:25 pm
Posts: 34
Location: Hampshire UK
Excellent article. For me, its a setback. I always knew to get the probes more than a couple of wavelengths away from the antenna, or more than about 4 antenna dimensions away, whichever was the larger.

That is such a gross rule of thumb, especially in the face of all the graphs this author uses.

The concept explanations originally taught to me about how the energy storage near fields were different in nature to the one that radiates at the speed of light, left a bit to be desired. Here is where I just had to put my faith in the formulae out of the books, without *really* understanding.


 
   
 
sag
 Post subject: near field for parabolic antennas
Posted: Mon Oct 24, 2005 10:23 am 
Hay all,
If we are on the subject of near field, how would you define the
near field of a parabolic dish? I mean if you take a 10ft dish operating
at 5GHz you'll get a very large near field area by using the standard rules.
So do you use the dish size to evaluate the far field or you use
the feed size and thus get that the dish is actualy at the far
field of the feed?




Posted  11/12/2012

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