Re: NEC-LIST: Near field

John Belrose wrote:
>
> Curious!!
>
> NEC-2 and NEC-4 accurately calculate the near fields out to distances
> where only the radiation field is found. There is a smooth
> transition from near to far fields.
>
> But, for ground wave you cannot go too far, in terms of wavelengths
> for low radio frequencies, since the ground beneath the antenna is
> assumed to be flat.

My comments were based on the following example.

CM
CE
GW1,41,0,-7.5,1.0,0,7.5,1.0,0.002
GE1
GN2,0,0,0,14.0,0.0001
FR0,1,0,0,10.0,0
EX0,1,21,01,1.0,0
NE0,90,1,1,5.0,0,1.0,0.5,0,0
EN

This is an input file of a half wave horizontal dipole placed 1 meter
above imperfect ground. The NE card specifies computation of the near
field E 1 meter above ground and at distances of 5 through to 50
meters in the direction perpendicular to the dipole. The plot of
20log10(|E| X^2) versus distance X suddenly changes its behavior from
oscillations with the amplitude of about 3.5dB to a straight
horizontal line. It happens at a distance of one wavelength from the
dipole independently on frequency. Of course it is a very special
case, but it still worth thinking about.

    Stan Tarnavskii
Received on Thu Jun 22 2000 - 07:21:07 EDT