If you have a system of independently radiating electrons/point-charges, the far field distribution of the EM waves can be approximated by the Fraunhoffer diffraction integral, or simply by the Fourier transform of the charge/electron density distribution.
When taking the Fourier transform of something, there is always a zero frequency value. What does this represent in terms of the EM wave example? Is it the average of the near field? Is it the average of the entire field summed in all space (this case it should never vary)?