Selective observation of resonances via their ringing in transient radar scattering, as illustrated for conducting and coated spheres

Radar scattering amplitudes contain pole singularities whose importance was recognized in the context of the singularity expansion method. The scattering of impulsive signals, studied previously, was shown to involve a large number of such poles, whose residues combine to form creeping-wave pulses. It is shown here that the use of sinusoidal pulses of long but finite duration, with the carrier frequency tuned to a pole frequency, may selectively probe one pole at a time. The ringing of any such selected resonance may be viewed as a coherent superposition of a succession of long creeping-wave pulses. Illustrative numerical calculations are carried out for the example of conducting spheres with or without dielectric coating