Comparative study of multi-physics generated small dipoles in conducting media

Abstract

In this paper we present the results of a study of electronically and mechanically generated transverse magnetic (TM) and transverse electric (TE) dipoles in a lossy environment, so that antenna design guidelines may be established at the system level. At far-zone, the ratio \(|\frac{E}{H}|:= \eta _0\) is the intrinsic impedance, and they are identical for the TM and its dual TE dipoles. Nonetheless, the ratio in near-zone behaves drastically different between the TM and dual TE. We derived closed form expressions of the antenna Ohmic loss in a spherical lossy shell (SLS) for the first time, yielding precise radiation efficiency \(\eta _r\) and accurate computations. For electrically small dipole of normalized half dipole-length \(|ka|\ll 1\), analytic results show that \(\eta _r\) is proportional to \(|ka|^3\) for TM dipole, and |ka| for TE dipole, respectively. Consequently, efficiency \(\eta _r\) of TE can be better than TM in two to three orders of magnitude for under seawater communication. The time-domain energy flow velocity (EFV) patterns show that the TE dipoles are always radiation-dominating, in either lossless or lossy medium. Numerical results reveal that mechanically spinning dipole is smaller in size and weight but it requires more operation power, compared to its electromagnetic counter-partners. Finally, design, tuning and impedance matching of low-profile TE dipole antenna are outlined.