<title>Target identification by means of impulse radar</title>

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The scattering interaction of short electromagnetic pulses with a spherical target is studied. The target is assumed penetrable and is modeled 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 an ideally conducting sphere. When the interrogating waveform is a pulse of short duration, the resonance features of the backscattering cross-section can be extracted within the frequency band of the incident pulse. To verify theoretical predictions, spherical targets were illuminated with short broad-band pulses using an impulse radar system. The actual shape of the pulse that is incident on the target is theoretically modeled using a digital filter design techniques, and the predicted backscattered returns of spherical targets are compared with selected echoes of the pulses transmitted by the impulse radar. The authors verify that the shape of the predicted backscattered pulse that results from the design method agrees well with the experimental findings using metal spheres of three different sizes. By means of an incident pulse of designed shape, the form-function in the backscattering radar cross-section of a dielectric target is predicted using a discrete Fourier transform (DFT) technique. It is shown that many of the resonance features of a dielectric spherical shell can be extracted from the frequency band of the incident pulse employing this method. The methodology that is developed can handle broadband pulses of any sufficiently smooth spectrum, interacting with (lossy or lossless) dielectric scatterers, and can extract the resonance features within the frequency band of the transmitted pulse. Accordingly, this methodology could also be used for assessing the performance of high-power impulse radar systems.