A shielded loop array antenna for a directional borehole radar

A borehole radar measures the distance of a reflecting object from a receiver. However, conventional omnidirectional borehole radars cannot determine the direction of the object. Some earlier attempts have been made to achieve a directional borehole radar. A cross-loop antenna (Mundry et al. 1983) and a dipole array antenna (Olsson et al. 1989, Sato 1990) have been used for the purpose. These antennas have resonance, which increases the maximum detectable range of the radar. However, the antenna resonance also tends to broaden the received signal, with a reduction in the resolution. This paper introduces a new type of array antenna for a directional borehole radar. The new antenna measures the current induced on the conducting sonde surface by an incoming electromagnetic wave. The antenna is broadband and has good potential for direction finding.