Rigorous Representations of Antenna Fields in Cylindrically Stratified Unbounded Gyrotropic Media

We consider electromagnetic fields excited by spatially bounded, arbitrary given sources in the presence of a cylindrical guiding structure immersed in an infinitely extended homogeneous gyrotropic medium whose permittivity and permeability are both describable by tensors with nonzero off-diagonal elements. The axis of symmetry of the considered cylindrical structure is assumed to coincide with the gyrotropic axis. The total field is sought in terms of the vector modal solutions of source-free Maxwell´s equations. By demanding completeness of the modal spectrum and using a continuity argument, we determine the content of the modal spectrum and obtain an eigenfunction expansion of the antenna-excited field in terms of discrete- and continuous-spectrum modes.