Cavity induced modulation of Ka-band radar signals

Anechoic chamber measurements were made of sniper rifles and surrogates from 25.0 GHz to 40.0 GHz at 5 MHz steps utilizing a stepped-frequency, horizontally linearly polarized (HH) bistatic radar. It was found that a modulation was induced on the reradiated signal when illuminating the rifles near on-boresight. Further analysis of the data led to the development of a model comprised of a linear decomposition of the targets into 3 coherently summable reradiators: a long cylinder, a perforated disk, and a resonant cavity. The cavity induced modulation (CIM) which was found in the measurements can be used to locate and detect sniper rifles and other cavities. Additional measurements were made in a clutter environment at an Air Force test range at ranges up to 100 meters which confirmed the existence and detectability of the CIM.