On the accuracy of the UTD for the scattering by a cylinder

The UTD formulation for the scattering by a cylinder is valid for antennas that are removed from the cylinder surface. The usual guideline is that reliable results can be obtained for antennas that are about λ/4 or more away from the surface. By exploring a few cases, we show that λ/4 is unnecessarily large for the lit region and sometimes too small for the shadow region. In addition, we find that with a simple heuristic modification to the UTD, heights as small as λ/20 can be accommodated, with an accuracy that is sufficient for most engineering applications