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