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