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Re: [Phys-l] spherical waves




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?