Forward diffraction pattern by cylindrical cavity in lossy medium

The diffraction pattern of the total field scattered by a cylindrical cavit y excited by the electric line source in a lossy medium is analyzed in the forward region for a wavelength comparable to the radius of the cavity. It is shown hat double nulls and strong double dips, which may be useful in id entifying the underground cavity, exist in the forward diffraction pattern, and their dependences on the position of the source and the field points a nd the medium parameters are analyzed by using the forward scattering width normalized by the measurement distance. (C) 1999 John Wiley & Sons, Inc.