An ultra-wide-band (UWB) multiple-input multiple-output (MIMO) radar with a sparse array is designed and manufactured for three-dimensional near-field imaging applications such as concealed weapon detection. Contrary to existing mmW imaging radars, UWB components working in the lower microwave frequencies are more cost effective and yield images with resolutions satisfactory for contraband detection while not raising concerns related to personal privacy. A UWB sparse array provides resolution values equivalent to a fully populated array with a similar aperture size albeit with much fewer antenna elements, while yielding lower sidelobe levels compared to a narrowband sparse array. Performance of the proposed system is studied using a full-wave electromagnetic simulation environment which is capable of modelling the antenna array, the environment and the target in 3D while allowing modifications in mechanical and electrical properties of the materials. For image reconstruction, Kirchhoff-migration and back-projection algorithms are used and performances of these algorithms are compared. The effects of the spatial and temporal frequency response of the antenna array as well as array calibration on the image quality are also studied. A prototype of UWB MIMO sparse antenna array in Archimedean spiral configuration with an RF switch matrix is manufactured. Measurements are performed using a stepped-frequency continuous waveform (SFCW) transceiver for various metallic and non-metallic targets. It is observed that these targets are identifiable in the images formed based on measurement data. Consequently, promising concealed weapon detection performance is demonstrated with full-wave electromagnetic simulation and experimental results.