An experimental study of a cylindrical antenna in two half-spaces

Conducting structures residing partially within air and partially within a lossy half-space are investigated experimentally. The conducting structures are modeled by monopole antennas, and the lossy half-space is modeled by the water within a nonmetallic tank. A sleeve monopole antenna is oriented normal to the water surface with driving point near the bottom of the tank and source gap (aperture) in air. Gap height above the water surface, antenna radius and monopole length are varied. Electromagnetic properties of the water are changed by variation of its common salt (NaCl) content. Reflection coefficient at the driving point is measured for the 0.5-1.0 GHz octave by means of swept-frequency network analysis with automated data collection. Measured data are compared to results obtained from a numerical solution of an integral equation. Good agreement is obtained in all cases between the aperture admittance determined experimentally and that determined theoretically from knowledge of the current distribution on the structure. The water surface is shown to act as a good reflector with aperture admittance differing only slightly from that measured for the same antenna above an aluminum ground plane. The electromagnetic constitutive properties of the tank water are measured by guided wave techniques.