Design of a Compact Ultra-Wide Band Bow-Tie Slot Antenna System for the Evaluation of Structural Changes in Civil Engineering Works

Abstract—A compact UWB bowtie-slot antenna (36× 23 cm2) fed by a CPW transition is proposed for an improved ground-coupling radar. The antenna has an operating frequency band in the range [0.46; 4] GHz. Full-wave modeling using the FDTD approach has allowed to study in details the antenna radiation characteristics in air and in the presence of a soil. Afterwards, a radar system made of a pair of independent shielded bowtie antennas has been considered to probe the sub-surface very close to the air-soil interface. The polarization diversity in the E and H-planes is an important aspect which has been studied in order to further detect the orientation of damages (cracks, delaminations . . . ) in civil engineering structures. Measurements in a dry and wet sand in different system configurations have allowed to first characterize the GPR system and to draw comparisons with numerical results. The ability of the radar to detect small buried objects has been investigated.