Fields of a horizontal loop antenna over a layered half-space

Abstract

We obtain an exact solution for a circular wire loop, carrying a non-uniform current, located above a layered half-space The method, while straight-forward, allows for both T.E. and T.M. electromagnetic fields. The T.M. fields would not be present if the current distribution was uniform. As a consequence of the nonuniformity, vertically polarized radio ground waves may be excited and such could be a source of unwanted interference. Such loop sources are employed in geophysical probing schemes and it is suggested that the most desirable configuration would be if the vertical magnetic field is measured at the center of the horizontal loop. The contributions of the higher spatial harmonics of the current in the loop vanishes in this case. On the other hand one may wish to employ such a source loop, lying on the earth's surface, to provide a useable radio ground wave for point-to-point communication over poorly conducting terrain such as in polar regions.