| Different approaches to evaluating the behavior of the impedance of an electrically short dipole antenna in the ionosphere as a function of the driving frequency are discussed. The induced EMF method in quasi-static approximation is chosen for evaluating the impedance and explained in great detail. The E-region of the ionosphere is considered and the cold collisional plasma model is used.; The influence of a density gradient in plasma on the impedance is explored, and the possible current distributions on the surface of the antenna are considered, including the current distribution for the antenna with a gap. The conclusions are drawn that the density gradient, as well as the current distribution, and a small gap have little or no influence on the impedance in certain frequency regions. A closed form solution is obtained for the particular case of the exponential current distribution of the dipole parallel to the magnetic field. An anomalous behavior of the impedance is predicted for the almost collisionless cold plasma. Formulas in quadratures are obtained for the other current distributions.; Results are compared with those of Adachi, Balmain, and Bishop. The conclusions are made about the validity of different theories and which of them can be used to deal with the nonzero electron temperature of the plasma and the arbitrary dipole orientation in respect to the magnetic field. Further research topics, including the use of a kinetic model near the resonant frequencies, are discussed. |
