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near field and far field

 
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btb4198
Antenna Theory Regular


Joined: 19 May 2011
Posts: 20

PostPosted: Thu May 19, 2011 5:38 pm    Post subject: near field and far field Reply with quote

ok so the r in R<< D is the radius of what? radius of antenna ? or radius of something else ?
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Schubert
Antenna Wizard


Joined: 08 Apr 2009
Posts: 161

PostPosted: Thu May 19, 2011 6:40 pm    Post subject: Reply with quote

It is R >> D.

R is the distance from the antenna where you are measuring the fields transmitted from the antenna.

R>>D is one of the requirements to be in the "far field" of the antenna. This means that if the antenna is of size D, then to be in the far field you must be at least 10*D away from the antenna. Note that this is only one of the requirements to be in the far field, all 3 conditions must be satisfied:
http://www.antenna-theory.com/basics/fieldRegions.php
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btb4198
Antenna Theory Regular


Joined: 19 May 2011
Posts: 20

PostPosted: Fri May 20, 2011 2:50 pm    Post subject: Reply with quote

D is the length of the antenna right?
R >> D
178m >> 0.03125m is true

R >> λ
178m >> 0.125 is true

R > ( 2D^2)/λ

178m > 0.015625m is true

so my point is in the Far Field, right?
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bigSteve
Antenna Wizard


Joined: 14 Mar 2009
Posts: 265

PostPosted: Fri May 20, 2011 5:23 pm    Post subject: Reply with quote

Yes, all the requirements are met to be in the far field.
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