Influence of a Horizontally Polarized Wave Incidence on DOA Estimation by a Dipole Array Antenna in a Borehole

In this article, we claim that a vertical dipole array antenna in a vertical borehole may sense a horizontally polarized plane wave incoming from outside the borehole, which worsens the antenna’s directivity. This is caused by cylindrical inhomogeneity around the antenna. According to the problem formulation and numerical simulation, the spatial spectrum of the electromagnetic field from an incident plane wave depends on the wave polarization because of scattering excitation in a medium inside a borehole. Unique field experiments in which a dipole antenna is moved on a plane perpendicular to the axis of a borehole confirmed this phenomenon. The numerical simulation predicted that the estimation of an inclined conducting cylinder direction has an error due to the horizontally polarized wave’s scattering. Single-hole measurements were performed to estimate the direction of an inclined conducting cylinder in soil to a dipole array. We found that the estimated direction of the reflected wave had an error of several degrees in the azimuth angle, as numerically expected.