A broadband directional corner reflector antenna for borehole applications

A promising technique being developed for probing coal seams (3 m thick) ahead of the cutting face is to drill a horizontal borehole midway through the seam in which a ground-penetrating FM radar probe can be inserted to measure the seam thickness and to detect the presence of faults. For this application, the radar antennas (bistatic system) must be broadband and directional, operate in the VHF/UHF bands, and fit within a borehole diameter of approximately 4 inches (10.2 cm). A 90 degrees corner reflector antenna was developed to meet the design requirements. The required bandwidth, front-to-back ratio, and low feedover were achieved by using triangular flat-blade dipole elements (resistively terminated) and by filling the antennas with titanium dioxide (TiO/sub 2/) powder. Performance results are presented and discussed.<>