[2] If the source has a plasma coating of the spherical or cylindrical shape [Bichoutskaia and Makarov, 1999; Novikov and Soloviev, 1996], it may lead to a considerable intensification of the radiation field (by 1-2 orders of magnitude) at resonance frequencies depending on the coating shape and plasma properties. The presence of a depleted ion layer around the source in the plasma [Ratcliffe, 1972; Whale, 1964] is able to enhance this intensification by several times [Bichoutskaia and Makarov, 2002, 2005; Messiaen and Vandenplas, 1967]. In this paper we study the influence on the radiation field of a ground-based source with the plasma coating of a more complicated spheroidal form, and also the value of the field for a changing form of the spheroid from a strongly prolate to a uniformly spherical and further to a compressed up to a strongly oblate spheroid form.
[3] The problem on the field of a ground-based source covered by a plasma semispheroid is considered in the presence of a flat boundary with the well-conducting Earth semispace. Such problem is reduced to the equivalent problem for the given source and its image in an ideally conducting plane (created using usual rules) located in the vacuum and surrounded by a plasma semispheroid and its reflection on the same plane. A vertical electric dipole and slot gap in a metal semispheroid are considered as the sources. In the equivalent problem the current at the antenna clamps or the voltage applied to the gap are doubled for these sources. We will consider these problems in a sequence and will call the resonance taking place in both cases as a resonance in current in the problem with a dipole and as a resonance in voltage in the problem with the slot antenna.
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