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Description
When a charged point particle moves parallel to the axis of a two-layer cylindrical metal-dielectric waveguide with a sufficiently small thickness of the internal dielectric coating, its radiation field has a single-mode character, i.e., the frequency distributions of both the longitudinal and transverse impedances of the waveguide contain a single, clearly expressed narrow-band resonance. However, at frequencies significantly exceeding the main resonant frequency, a sequence of low-amplitude secondary resonances is detected, which, nevertheless, due to their low amplitude, do not violate the single-resonance character of the radiation as a whole. The article examines the patterns of occurrence of the mentioned side resonances, in particular, their geometric nature is revealed: the location of their resonant frequencies is completely determined by the thickness of the dielectric coating and the value of its dielectric constant and does not depend on either the radius of the waveguide or the ordinal number of the multipole component of the expansion of the radiation field. It is shown that the "geometric" resonance frequencies generated by particle radiation in a two-layer cylindrical metal-dielectric waveguide in the case of a perfectly conducting outer wall coated from the inside with a dispersion-free dielectric layer correspond to singularities in the dispersion relations of the eigenmodes of the same waveguide, which determine the discontinuous nature of their solutions at resonance frequencies. Replacing the perfectly conducting wall with a wall with a highly conducting metal leads to the elimination of singularities in the dispersion relations and to the occurrence of perturbations on the dispersion curves at the same frequencies.
