3-D Radiometric Aperture Synthesis Imaging

The aperture synthesis technique, historically used for imaging in radio astronomy, is generalized to three dimensions as a means to generating 3-D images in the near-field. The technique uses a multi-channel electronic cross-correlator and an array of radio receivers to generate a 3-D visibility function. This is transformed by a 3-D inverse Fourier transform into a 3-D image of space. The basic equations, experimentation, and simulation indicate the Abbe microscope half-wavelength spatial resolution is achievable in three dimensions when a subject is surrounded by receivers. At longer ranges, further from the array, the resolution perpendicular to the range is proportional to the ratio of the range to aperture size (corresponding to the Fraunhofer diffraction limit) while the resolution in range is proportional to the square of this ratio (a passive ranging capability). Experimental data from a 10-channel 94-GHz and a 32-channel 22-GHz receiver array and a digital cross-correlator demonstrate the imaging capability. The technique enables arbitrarily large volumes to be imaged using multiple inverse 3-D Fourier transforms for adjacent regions of space, when suitable phase corrections are applied to cross-correlations. The technique is mainly directed at the millimeter-wave band for the application of personnel security screening.