Sensing characteristics of an object includes transmitting a
stepped-frequency radar through an object and detecting, with multiple
receiving structures, deflected portions of the radar signal. The
detected portions are processed to generate processed data including
information associated with amplitudes and phases of the deflected
portions, and with the locations of the receiving structures at which the
deflected portions were detected. The processed data is analyzed to
determine information corresponding to dielectric properties particular
positions within the object.