Re: NEC-LIST: Near field

Stanislav Tarnavskii <stan_at_cssip.edu.au> wrote:
>
> I have solved similar problem at 10 MHz. A plot of electric field
> versus distance had a step exactly one wavelength away from the
> dipole. It looked like imperfect match of two different
> approximations. The inaccuracy depended on ground conductivity and
> was getting essential as the dipole approached the ground. >
>
> Apparently, NEC-2 employs rigorous near field formulas within the
> radius of one wavelength only. The field outside this region is
> computed in the far field approximation. It means that the region of
> possible inaccurate computation is between one and two wavelengths
> from the dipole.

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.

Regards, Jack, VE2CV

_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
Communications Research Centre
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2779
FAX 613-998-4077
e-mail <john.belrose_at_crc.ca>
_____________________________________________
Received on Wed Jun 21 2000 - 18:37:09 EDT