Millimeter-Wave 3-D Imaging Using Leaky-Wave Antennas and an Extended Rytov Approximation in a Frequency-Diverse MIMO System

A millimeter-wave (mmW) 3-D imaging system using high scanning-rate leaky-wave antennas in a frequency-diverse multiple-input–multiple-output (MIMO) antenna configuration is proposed. A novelty of the approach is the use of high scanning-rate leaky-wave antennas combined with MIMO to obtain both frequency and spatial diversities. Furthermore, an extended Rytov approximation (xRA), recently shown to provide accurate reconstructions for high permittivity and electrically large-sized low-loss objects, is also included in the approach. Compared with frequency-diversity-only and spatial-diversity-only imaging systems, the proposed system can provide enhanced imaging performance by leveraging both spatial and frequency diversities simultaneously. In addition, the imaging time and hardware cost can be significantly reduced, resulting in a low-cost mmW imaging system. The formulation for the 3-D imaging system is simplified to a scalar form by leveraging the polarization of the leaky-wave antennas and the polarization dominance of the scattered wave components, allowing xRA to be formulated. Sensing capacity and correlation coefficient evaluation methods are used to estimate the performance of the high scanning-rate leaky-wave MIMO imaging system. The scalar formulation also allows us to straightforwardly compare MIMO microwave imaging with MIMO radar to highlight the commonality between them. Numerical and experimental examples demonstrate that the proposed system with xRA can accurately estimate the contrast function amplitude and the positions of dielectric scatterers in a 3-D imaging region using two transmit and 11 receive leaky-wave antennas and 49 frequency samples within the 37.2–42-GHz frequency range.