Ultra wideband (UWB) radar systems are a promising technology for surveillance systems. Many of the existing imaging algorithms are based on large-scale antenna arrays that are not necessarily practical because of their complexity and high cost. To resolve this difficulty, we had previously proposed an UWB radar imaging algorithm that estimates unknown 2-dimensional target shapes and motions using only three antennas. In this paper, we extend this method so that 3-dimensional target shapes and motions can be estimated. Some numerical simulations establish that the proposed method can accurately estimate the target shape even under extreme conditions.