Abstruct-An algorithmic procedure for extrapolating near-field radar cross section (RCS) measurements to the far zone has been evolved, coded, and experimentally validated. The derivation of the extrapolation algorithm uses the optical model to estimate the surface currents induced on the scattering body by the incident field and a specially weighted version of the Fourier transform to calculate the near-field scattering amplitudes associated with such surface currents. The extrapolation algorithm entails three steps. First, near-field measurements of the scattered electric and/or magnetic field are used to infer the monostatic vector potential A,,,. Next, the inverse Fourier transform of the inferred vector potential is multiplied by a special weighting function to estimate an equivalent obliquity factor 0.. Finally, the far-field scattering pattern is estimated by taking the Fourier transform of the reweighted obliquity factor. We have validated our extrapolation procedure with anechoic chamber data taken on a right-circular aluminum cylinder 25 X high and 2.5 X in radius at near-field range of 19 percent of 2D*/X, where D is the nominal target diameter and h the radiation wavelength. In particular, we have compared the extrapolated RCS pattern for this target with an analytical estimate of its far-zone pattern and noted good amplitude and phase agreement over a 20" cone of scattering angles.

We have designed and built an ultra-wideband differential radar that images targets moving behind walls, fences, trees, and other obstacles. We have demonstrated the differential-radar concept in anechoic, indoor, and outdoor environments. The outdoor demonstration proved the radar's ability to detect people moving behind walls and illustrated its capability for suppressing high-level clutter froni the radar imagery.

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