Re: [Phys-l] spherical waves

[brian whatcott <betwys1@sbcglobal.net>]

On 6/23/2011 12:10 PM, Bernard Cleyet wrote:
> On 2011, Jun 23, , at 09:30, John Denker wrote:
>
> >   By "far field" I mean r large compared to the wavelength.
> Fine for a single dipole radiator, but I wonder about an array antenna of many dipoles.  Would not the far field be r>>  diameter or diagonal of the system?
>
> Wikipedia (a very quick read) also doesn't mention this, but does discuss this on the receiving end with the difference between Fraunhofer and Fresnel diffraction.
>
> http://en.wikipedia.org/wiki/Near_and_far_field
>
>
>
> bc  thinks one must be somewhat further than the dimensions of the oven's leaky door gasket instead of just the one foot wavelength.  (giant restaurant ones, of course.)
>
>
> p.s. The field from such an array starts out as a plane wave, no?  and the field at the mouth of a horn antenna?
I think that the thrust of your comparison of spherical waves and beams 
from directional devices
 is that their respective  intensities and amplitudes vary differently 
with distance.
Who would argue with that?

Brian W