Formulae for the Impedance and Transmission Factor of an Electrically Small Half-Sheath Dipole Antenna Immersed in Seawater

To develop optimal antennas for underwater radio frequency communication, we formulate the impedance and the transmission factor of an electrically small half-sheath dipole antenna immersed in seawater and validate the results by comparing them with full-wave electromagnetic simulations. The derived formulas are quite practical because they express the impedance and the transmission factor only in terms of the antenna dimensions and the physical properties of the medium. Furthermore, they reveal that the transmission factor increases with decreasing impedance, thus providing important insight into designing underwater antennas.