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Field Experiments to Investigate Cross-polarization Characteristics of a Dipole Array Antenna in a Water-filled Borehole
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 10th International Workshop on Advanced Ground Penetrating Radar, Sep 2019, Volume 2019, p.1 - 7
Abstract
We investigated cross-polarization characteristics of a dipole array antenna in a water-filled borehole. We theoretically determined the electromagnetic fields when a plane wave is incident to multiple cylindrical layers. According to our analysis, the dipole array antenna may be characterized by a spatial frequency spectrum of the dipole array signals. If a cross-polarized wave is incident on the antenna, the absolute value of the spectrum is maximized to the first order. Furthermore, there is a phase difference of 90 deg. between the co-polarization and cross-polarization incidence angles at the first order spatial frequency. Numerical simulations confirmed that the cross-polarization characteristics in the spatial frequency spectrum may be observed as suggested in the theoretical analysis. Field experiments in soil were carried out at a test site. Data equivalent to signals of a dipole array in a borehole were obtained using a transmitting loop in another borehole. In the experimental data, cross-polarization characteristics were observed similar to those deduced from the theoretical and numerical analyses.