antenna-theory.com

[antenna9071]

Me and my friend had some discussion about the distance for far field region for patch antennas.

One formula that is used for far field region is R>2D^2/lambda and by balanis D>lambda,

But for many patch antennas d<lambda, if I understand what means with D.

Which formula are used for far field region for example patch antennas there d<lambda?

/Thomas

[Schubert]

See equations 1,2,3 here:
http://www.antenna-theory.com/basics/fieldRegions.php

You need all 3 to be satisfied to be in the far-field (plane wave propagation). No one equation is sufficient.

[antenna9071]

My question was: Which formula are used for far field region for example patch antennas there d>lambda?

If the conditions is not satisfied. Have the antenna no far field then?

[Schubert]

All 3 conditions need satisfied, always.

There is always a far field.

You didn't put much thought into that post.

[antenna9071]

I know there always is a far field but balanis says that the formula 2D^2/lamda can be used if D>lambda but in my case D<lambda so I cant use this formula so my question is: Which formula should I use or have I missunderstanding something? Have balanis wrong?

[Schubert]

Just figure out which R is the largest for the 3 equations:

R >> lambda ( this means R > 10*lambda )
R > 2*D*D/lambda
R >> D (or R > 10*D)

Whichever equation gives you the largest value for R, that equation will dictate the far field region.

I'm not sure what Balanis is talking about, but for sure all 3 equations need to be true.