Influence of Ferrite Loading on Feeding Lines Near a Loop Array Antenna in a Borehole

This paper shows that loading ferrite beads on feeding lines causes significant errors in direction estimation in a loop array antenna in a borehole radar. This contradicts the conventional wisdom that ferrite bead loading avoids undesirable scattering. The numerical simulation of a plane wave incidence on the loop array found that the ferrite loading worsened the DOA estimation by about 30°. We conducted a field experiment of cross-hole measurement in soil. The azimuth angle estimation error of the loop array without the ferrite loading was less than 25 °, while that with the ferrite loading ranged between 30° and 120°.