NEC-LIST: cfa near field and far field

Chuck W1HIS wrote:

>In free space, the near field is usually regarded as extending to a
>radius of roughly lambda over two pi, but bear in mind that there is
>no sharp cutoff. The strength of the reactive component of the total
>E or H field decreases as the inverse cube of the radius as the radius
>goes to infinity, whereas the radiation field strength decreases as
>the inverse first power of the radius.

Of course the nearfield/farfield transition point depends on how much
accuracy one needs from the farfield model. At lambda over two pi the
farfield term only contributes 30% of the overall field (for a
dipole). The standard of farfield transition is given by three
criteria which all must be met. Given a radiating structure of size
D, a wavelength of L, and a distance from the structure of R. Here
are the three criteria.

R>>L
R>>D
R>2DD/L

For the CFA the R>>L is the criteria to meet.

Alexander
Received on Thu May 27 1999 - 05:46:21 EDT