TRANSIENT INTERACTIONS OF AN EM PULSE WITH A DIELECTRIC SPHERICAL-SHELL

We study the scattering interaction of short electromagnetic pulses wi th a spherical target. The target is assumed penetrable and we model i t as an air-filled dielectric shell. The radar cross-section (RCS) of such a target is obtained and its resonance features are analyzed. A d ielectric composition makes the resonance features become very promine nt compared with the case of a perfectly conducting sphere. When the i nterrogating waveform is a pulse of short duration, the resonance feat ures of the RCS can be extracted within the frequency band of the spec trum of the incident pulse. To verify our theoretical predictions we i lluminate spherical targets with short, broad-band pulses using an imp ulse radar system. The actual shape of the pulse that is incident on t he targets is theoretically modeled using a digital filter design tech nique together with pulse returns from a reference target. We verify t hat the shape of the predicted, backscattered pulse that results from our design method agrees well with the experimental findings using thr ee additional targets of different sizes and materials. We investigate in the combined time-frequency domain the development in time of the various frequency features of the spectra of backscattered pulses usin g time-windowed Fourier transforms. The methodology that we have devel oped can handle broad-band pulses of any sufficiently smooth spectrum, interacting with (lossy or lossless) dielectric scatterers, and can e xtract resonance features within the frequency band of the spectrum of the transmitted pulse. Accordingly, this method could be also used fo r assessing the performance of high-power impulse radar systems.