The features of whistler wave excitation in the presence of a transversely nonuniform cylindrical duct with depleted density in a homogeneous magnetoplasma are studied. An expression for the radiation resistance of a uniform ring electric current inside the duct is obtained on the basis of the rigorous solution of Maxwell's equations for the total field represented in the form of wave expansion over discrete and continuous parts of the spatial spectrum. Conditions are determined under which the presence of a density depletion duct leads to a notable increase in the radiation resistance of the ring current as compared with the case where this source is located in a homogeneous plasma with density corresponding to the duct near-axis region or the background medium. Numerical results are given which illustrate changes in the radiation characteristics of the ring current in the resonance region of the whistler frequency range as applied to conditions of model laboratory and active ionospheric experiments on the formation of density depletion ducts in a magnetoplasma.
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