Abstract-The detection and identification of metal items and, in particular weapons, of linear size ≥ 10 cm, concealed upon the human body, is demonstrated as being entirely feasible by using a phased array of suitably ultra wide band transceivers. The complex natural resonances and especially the fundamental resonance, are excited by ultra wide band, stepped frequency continuous wave illumination of the target, using a phased array of antennae to focus the radiation. Broadband illumination of the target with microwave radiation of suitable frequency range (Typically 0.3-3 GHz for handgun sized objects) excites low order complex natural resonances and the late time response of the concealed item can be spatially located using phased array imaging techniques. Further processing of the late time response enables classification of the concealed object, based on the complex natural resonant frequencies of the object, so that threat items such as handguns and knives can be differentiated from benign items such as mobile phone handsets and cameras.

The authors discuss and demonstrate the feasibility of using ultra wide band microwave radar to detect and identify small arms fire. Detection and tracking is by standard radar techniques, but identification is carried out by exciting the projectiles Complex Natural Resonances and using this aspect independent information to assign a caliber to the incoming projectiles. The typical sizes of small arms projectiles (calibers 5.56 mm through to 13 mm) imply that ultra wide band illumination in the microwave region of the spectrum between 1.5-5.5 GHz is required to excite these object's fundamental resonances. The authors give a discussion of the effects of motion on the quality of the complex natural resonance data obtainable and present both simulated and laboratory data for the radar cross section of three different caliber projectiles (5.56 mm, 7.62 mm and 13 mm).