Suppression of multi-path couplings in scaled-down experiment for cross-borehole pulse radar

A scaled-down experiment using cross-borehole pulse radar was performed in a laboratory to extract a more precise decision rule for detecting an intrusive manmade tunnel in Korea. To minimize the total size, a scaled-down model of an air-filled tunnel in underground rock was replaced by a cylindrical ceramic rod in pure water. When the upper arm of a sleeve-dipole antenna of the scaled-down cross-borehole pulse radar was directly connected to a coaxial cable, the measured B-scan data were contaminated by unwanted striped patterns that were generated by multipath coupling. Such multipath coupling between the sleeve-antenna pair was generated by the glass-tube-guided waves. To suppress the glass-tube-guided waves, the coaxial cable was clad in ferrite cores. As the total length of the ferrite-core cladding was increased up to 150 mm, the unwanted multipath couplings were gradually suppressed, and the target signature could be more clearly recognized.