Terahertz FMCW Radar Imaging with a Staggered 12-Sensor Linear Array

We report the development of a terahertz frequency-modulated continuous-wave radar imaging system based on a linear array of twelve coherent radar transceivers. Each sensing unit is coupled to a dedicated PTFE quasi-optical component designed to control the emitted and received beam, improve spatial confinement, and enhance coupling efficiency. The array is implemented as two staggered rows of six radar modules, resulting in a quincunx sampling geometry. This arrangement increases the effective transverse sampling density while maintaining a compact, mechanically stable, and scalable architecture.

The sensing head has a total length of 45 cm and can be operated according to two acquisition strategies. In a first configuration, two-dimensional images are acquired during a single linear translation of the array. In this mode, the sampling pitch along the transverse direction is determined by the inter-element spacing and the staggered arrangement of the sensors, enabling rapid inspection of extended surfaces. In a second configuration, the system performs a local two-dimensional scan, typically over 3 cm along the short axis and 50 cm along the long axis. This acquisition mode provides increased spatial sampling density and enables improved reconstruction of localized features and buried discontinuities.

By combining FMCW depth-resolved measurements with parallel multi-channel acquisition, the proposed approach addresses a key limitation of terahertz imaging systems: the compromise between imaging speed, inspected area, and spatial sampling density. The architecture is particularly relevant for non-destructive evaluation in civil engineering, including the inspection of concrete, coatings, multilayer assemblies, and subsurface defects. It also provides a promising platform for security-oriented stand-off imaging of concealed dielectric objects. These results demonstrate the potential of staggered terahertz radar arrays for scalable, high-throughput inspection.