An exploration of radiation physics in electromagnetics

There would be no radiated, propagated or scattered fields were it not for radiation. Our understanding of how and why radiation occurs is relatively superficial. It is true that mathematical analysis shows radiation occurs due to charge acceleration. It is also true that we are able to solve for the near and far fields of rather complex objects subject to arbitrary excitation and can thus analyze and design EM systems. However, for example, if the problem is to determine the spatial distribution of radiation originating from the surface of a conducting body, a solution becomes less obvious. Either this particular problem has no answer, or it has eluded us. It seems undeniable that knowing where radiation originates is worth knowing. A conceptual way to think about this problem could be to ask, were our eyes sensitive to X-band frequencies and capable of resolving source distributions a few wavelengths in extent, what kind of image would such simple objects as dipoles, circular loops, conical spirals, log-periodic structures, continuous conducting surfaces, etc. present when excited as antennas or scatterers? Various kinds of measurements, analyses and computations have been made over the years that bear on this question. This presentation summarizes some relevant observations concerning radiation physics in both the time and frequency domains for a variety of observables. Even if a quantitative recipe for computing a radiation image using the source distribution obtained from a numerical model is not available, a variety of qualitative statements can be made that bear on this question.