STUDY OF VLF ANTENNAS IMMERSED IN SEA-WATER - THEORETICAL, NUMERICAL,AND EXPERIMENTAL RESULTS

The problem of receiving VLF electromagnetic fields with an underwater electric antenna is of great interest, especially for military-applic ation purposes. In this study, a simple and closed-form expression for the E field in sea water is derived from two physical models, which a gree but are different: the surface-wave theory and the Fresnel formul as. Three configurations of immersed receiving antennas are investigat ed by means of computer simulations. The scattered electric field and expected measured voltage are computed, using an EFIE [electric-field integral equation], and the Method of Moments (MoM). Then, an equivale nt-circuit model of the underwater antenna is investigated, with a foc us on two dominant antenna parameters: the impedance and the voltage m easured between the wire terminals. Calculations and computed results are compared with off-shore measurements.