Transient interactions of an EM pulse with a dielectric spherical shell

The authors study the scattering interaction of short electromagnetic pulses with a spherical target. The target is assumed penetrable and they model it as an air-filled dielectric shell. The radar cross-section (RCS) of such a target is obtained and its resonance features are analyzed. A dielectric composition makes the resonance features become very prominent compared with the case of a perfectly conducting sphere. When the interrogating waveform is a pulse of short duration, the resonance features of the RCS can be extracted within the frequency band of the spectrum of the incident pulse. To verify their theoretical predictions they illuminate spherical targets with short, broadband pulses using an impulse radar system. The actual shape of the pulse that is incident on the targets is theoretically modeled using a digital filter design technique together with pulse returns from a reference target. They verify that the shape of the predicted, backscattered pulse that results from their design method agrees well with the experimental findings using three additional targets of different sizes and materials. They investigate in the combined time-frequency domain the development in time of the various frequency features of the spectra of backscattered pulses using time-windowed Fourier transforms. The methodology developed can handle broadband pulses of any sufficiently smooth spectrum, interacting with (lossy or lossless) dielectric scatterers, and can extract resonance features within the frequency band of the spectrum of the transmitted pulse. Accordingly, this method could be also used for assessing the performance of high-power impulse radar systems