Design and Test of an Improved Dipole Antenna for Detecting Enclosure Structure Defects by Cross-Hole GPR

In underground engineering, the enclosure structure is a crucial part to guarantee the safety of excavation in soft ground regions. To inspect defects in the enclosure structure and assess its integrity, the cross-hole ground-penetrating radar (GPR) is considered as a promising tool. To make this technique feasible for underground structure applications, suitable antennas should be devised. In this paper, we designed an improved dipole antenna for a stepped frequency cross-hole GPR system to detect enclosure structure defects. Numerical simulations were adopted to optimize antenna design parameters including the half-cone angle θ, the feeding gap g, the cylinder radius r, and the cylinder length l. Then the optimized antenna was fabricated, and the performance of the antenna was evaluated by measuring the return loss, the voltage standing wave ratio (VSWR), the phase response, and the coupling. The results indicated that the proposed antenna operated well in the frequency range from 0.45 to 1.1 GHz and had the best performance at 0.52 GHz. Moreover, a physical model experiment was carried out and proved the antenna's feasibility for enclosure structure defects detection.