Millimetre wave imaging for concealed target detection

Concealed weapon detection (CWD) has been a hot topic as the concern about public safety increases. A variety of approaches for the detection of concealed objects on the human body based on earth magnetic field distortion, inductive magnetic field, acoustic and ultrasonic, electromagnetic resonance, MMW (millimetre wave), THz, Infrared, x-ray technologies have been suggested and developed. Among all of them, MMW holographic imaging is considered as a promising approach due to the relatively high penetration and high resolution that it can offer. Typical concealed target detection methods are classified into 2 categories, the first one is a resonance based target identification technique, and the second one is an imaging based system. For the former, the complex natural resonance (CNR) frequencies associated with a certain target are extracted and used for identification, but this technique has an issue of high false alarm rate. The microwave/millimetre wave imaging systems can be categorized into two types: passive systems and active systems. For the active microwave/millimetre wave imaging systems, the microwave holographic imaging approach was adopted in this thesis. Such a system can operate at either a single frequency or multiple frequencies (wide band). An active, coherent, single frequency operation millimetre wave imaging system based on the theory of microwave holography was developed. Based on literature surveys and first hand experimental results, this thesis aims to provide system level parameter determination to aid the development of a target detection imager. The goal is approached step by step in 7 chapters, with topics and issues addressed ranging from reviewing the past work, finding out the best candidate technology, i.e. the MMW holographic imaging combined with the resonance based target recog-

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