Borehole radar measurement with a dipole array and a loop antenna

This paper proposes a signal processing method suitable for a dipole array and a loop antenna in a borehole (DALAB) that enables estimation of the polarization states of a wave incident on the DALAB in directional borehole radar. In the processing, we pick complex amplitudes of both a dipole signal and a loop signal in the time domain, and calculate a ratio of the two amplitudes. The polarization state is estimated by comparing the theoretical and experimental ratios. We then applied the signal processing method to field experimental data. This experiment consists of a vertical conducting cylinder and inhomogeneity caused by an interface. We found an almost vertical and linearly polarized wave from the vertical conducting cylinder are estimated by the DALAB, whereas a rather elliptical and horizontally polarized wave are estimated from the inhomogeneity.