antenna-theory.com

[pascualhr]

It is known that the conditions needed to be in the far-field region are:

d > 2D^2/lambda

d > 5D

d > 1.6*lambda

Being D = the largest physical linear dimension of the antenna.

If in my case I am working with a planar array of elements, my question is: D would be the length of my element or the length of the whole array?

Many thanks in advance ,
Pascual

[admin]

If you use the size of each element (D), then at that distance you would be in the far field for each element individually. WHat I mean is, if you are at a point x, where the minimum distance to the nearest element is larger than d (as defined by the equations below), then you would technically be in the far field at point x, for all antennas, assuming you evaluated your functions d with the individual element size D.

However, if you are making a phased array and applying array factor equations, then you will need to use the total size of the array. This ensures the rays from each antenna are approximately parallel.

[pascualhr]

[pascualhr]

Hi,

I am calculating the field regions and for that purpose I need D (the maximum distance of my antenna). In my case I have this array:



My question is: D should be d1 or d2?

Many thanks in advance!

[helix]

Nothing "magic" happens suddenly when you cross d^2/lambda. Look up how it's derived... It has to do with phase front curvature (deviation from plane wave) from an aperture (which you don't have) being a certain (arbitrary) amount. Whether you use d1 or d2 in your calc is going to be insignificant as far as any practical antenna application is concerned.