THEORY AND SENSING APPLICATIONS OF A LONG ANTENNA ON LAYERED MEDIA

We solved a Sommerfeld-type boundary value problem of an infinitely lo ng antenna lying over multilayered media. Rigorous integral representa tion was obtained for the current on the antenna when excited by a del ta function voltage. Comprehensive analyses of the singularities of th e integral representation were performed for the most general case of antenna lying over multilayered media. The analyses indicate that the total current on this open waveguide structure consists of, generally, infinite number of discrete modes (contributions from poles) and cont inuous modes (contributions from the integrals along the branch cuts). Detailed expressions were given for the discrete and continuous spect ral representations of the total current. Numerical results were obtai ned for the input impedance spectra of an infinite antenna lying over various layered media. Experiments were also conducted with a long ant enna connected to a time-domain reflectometer and placed horizontally over tap water. Both the numerical and experimental results suggest th at a single long antenna could be used as a sensing tool to detect the profile of a layered medium.