Linear FM radar operating in the Tera-Hertz regime for concealed objects detection

Abstract

Sub-millimeter and Terahertz waves maintain reasonable penetration depth in certain common materials, such as cloth, plastic, wood, sand and soil. Therefore, THz radiation can detect concealed weapons since many non-metallic, non-polar materials are transparent to this type of radiation (and are not transparent to visible radiation). Target compounds such as explosives and illicit drugs have characteristic THz spectra that can be used to identify these compounds. Investigation, design and development of a sub-millimeter wave remote sensing RADAR system for homeland security applications are presented. The RADAR, operating at 330GHz is based on transmission of a frequency modulated continuous wave (FMCW) and aimed at detection of concealed objects for ranges up to 20m. The system consists of 2 horn-lens antennas integrated with a homodyne transceiver. The synthesized linear FM signal with a frequency span of 200MHz at X-band is multiplied by a factor of 32 to generate the transmitted Tera-Hertz wave. Using a splitter, the signal is fed to an antenna and to a local oscillator port of a second harmonic balanced mixer. As a result, an intermediate frequency signal is obtained, containing the information on the target. Distance measurements were made by performing data acquisition and signal processing commercial programs, resulting in a range resolution better than 1cm. Preliminary Tera-Hertz imaging was also carried out to perform a three-dimensional image of the object.