Influence of Mode Conversion at Borehole on Direction Finding with Dipole Array Antenna

We investigate influence on DOA estimation with the circular dipole array antenna in a borehole (CAB), when the TE plane wave incident on the CAB. According to calculation of electromagnetic fields of the TE plane wave, vertical component of the electric field is excited by the cylindrical layers around the antenna, and these phenomena are called mode conversion in this paper. This increases error of DOA estimation, if we assume that the TM wave is incident on the CAB like in [4] during the array signal processing. We introduce the index α(t) in order to represent quantity of component excited by the mode conversion. According to the experiment in air and field experiments, we confirmed that the mode conversion occurs, and this would influence DOA estimation with the CAB.