The use of impulse response in electromagnetic scattering problems

It is customary to develop approximate solutions to electromagnetic scattering problems by assuming monochromatic sources and imposing further conditions on the ratio of physical dimensions to wavelength. If the ratio of physical dimension to wavelength is large, the solution is obtained as a perturbation of the geometrical or physical optics solution. If the ratio is small, the solution differs little from that predicted by Rayleigh scattering. It is not usually possible to obtain a single approximate solution which yields the correct result for the limiting cases of zero and infinite source frequencies. This paper presents a method of approximating the exact solution to electromagnetic scattering problems for any source frequency by an approximation to the impulsive response of the scatterer. This approximation is chosen so as to yield the correct solution for the limiting cases of zero and infinite source frequency. The relation between this approach and the physical optics approximation as well as the quasi-static approximation is discussed. The application of this technique is illustrated for several types of scatterers, and the results are compared with those obtained by standard methods.