Microwave imaging of a walking person using vertical linear arrays

Active microwave and millimeter-wave imaging is commonly used for security screening at airport checkpoints and other protected facilities. This paper explores an imaging system concept that may improve screening convenience, reduce cost, and enable alternative operational concepts by allowing a person to walk naturally through the system. Millimeter-wave imaging systems require data to be acquired over a 2D spatial aperture to form a high-resolution image. This requirement is usually met using mechanical scanners or large antenna arrays that provide a 2D aperture and provide strict control over the position of the array in relation to a motionless target. The new concept explored in this paper replaces the mechanical scan with motion of the passenger. The complex motion of the passenger is expected to be optically tracked as he or she passes by stationary linear vertical millimeter-wave arrays and can be modeled using skeletal animation. Multiple linear arrays illuminate the passenger from a wide variety of angles to provide full coverage of the body. The radar data are then correlated with the skeletal animation model by employing generalized synthetic aperture focusing or back-projection techniques. These methods accurately reconstruct the image by integrating the measured response multiplied by the conjugate of the expected response from a point scatterer anywhere within a 3D image volume. This process yields an optimally focused image and can be applied to situations involving complex target motion. This paper describes this concept in detail and provides numerous simulation-based imaging results to explore the effectiveness of the proposed methods.