  Due to the growing number of publications and applications based on the
exploitation of Bloch surface waves and the gross errors and approximations
that are regularly used to evaluate the properties of this type of wave, we
judge seriously important for successful interpretation and understanding of
experiments to implement adapted formalism allowing to extract the relevant
information. Through a comprehensive calculation supported by an analytical
development, we establish a generalized formula for the propagation length
which is different from what is usually employed in the literature. We also
demonstrate that the Goos-H\"anchen shift becomes an extrinsic property that
depends on the beam dimension with an asymptotic behavior limiting its value to
that of the propagation length. The proposed theoretical scheme allows
predicting some new and unforeseen results such as the effect due to a slight
deviation of the angle of incidence or of the beam-waist position with respect
to the structure. This formalism can be used to describe any
polarization-dependent resonant structure illuminated by a polarized Gaussian
beam.
