ANALYSIS OF A GUIDED-WAVE ALONG A CONDUCTING STRUCTURE IN A BOREHOLE

A guided wave along a borehole is often observed in borehole radar mea surements. These guided waves deform the antenna pattern and can cause artefacts in radar measurements. A water-filled borehole or a conduct ing logging cable can function as a waveguide for electromagnetic wave s under some conditions. We describe the theoretical characteristics o f such a guided wave in a borehole and compare them with our experimen ts. The measured signal discussed was obtained with a directional bore hole radar. This radar uses a cylindrical conformal array antenna as r eceiver and is a model of a conducting structure in a borehole. The in duced field around the borehole was compared with the theory. The most fundamental symmetrical and asymmetrical modes were TM01 and HE11, an d they were identified in the measured signals using time-frequency di stribution analysis and by observation of the azimuthal field distribu tion of the magnetic field.