Newsgroups: sci.physics.electromag
Subject: Re: anyone (experimental researchers in this area included) know EM radiation formula?
Date: 3 Aug 1998 10:09:30 GMT
Organization: GEC-Marconi Research Centre
In article , Rune Landen (r*u*n*e@dircon.co.uk*fix*to*email) wrote:
> I am interested in understanding EM, electricity, magnetics, etc, but so
> far I havent found any real equations that describe the radiation given
> off by an antenna. (I use antenna loosely). Eg, just the ones which are
> experimental, not theoretical, and most of the time doent have any theory
> behind it.
There's a theory behind *all* of it. The equations describing
electromagnetism are quite simple. It's just that in many real-world
situations the boundary conditions are too complicated to allow for
a simple closed-form solution.
>I think you will know the kind I am talking about. So does
> anyone have some kind of formula for this?
Jackson's Classical Electrodynamics, 2nd edition, page 392,
equations 9.3 to 9.5. Gaussian units, for reasons best understood
by JDJ himself.
A(x) = 1/c integral J(x') exp(ik|x-x'|) / |x-x'| d3 x'
B = curl A
E = i/k curl B
J is the current distribution, k the wavenumber (2 pi/wavelength)
c the speed of light. J, A, B and E are vector fields.
In short, *if* you know the current at each part of the antenna, you
can calculate the vector potential A from it, summing over each
element of the antenna. From A you can easily find E and B.
The catch? In general there's no simple way to determine the
current distribution.
richard.herring@gecm.com