Unidirectional evanescent-wave coupling from circularly polarized dipole sources is one of the most striking evidences of spin-orbit interactions of light and an inherent property of circularly polarized dipoles. Polarization handedness self-determines propagation direction of guided modes. In this paper, we compare two different approaches currently used to describe this phenomenon, the first requires the evaluation of the coupling amplitude between dipole and waveguide's modes, while the second is based on the calculation of the angular spectrum of the dipole. We present a novel analytical expression of the angular spectrum of dipole radiation, unifying the description for both electric and magnetic dipoles. The symmetries unraveled by the implemented formalism show the existence of specific terms in the dipole spectrum which can be recognized as directly responsible for directional evanescent-wave coupling. This provides a versatile tool for both a comprehensive understanding of the phenomenon and a fully controllable engineering of directionality of guided modes.
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