  The selective excitation of localized surface wave modes remains a challenge
in the design of both leaky-wave and bound-wave devices. In this Letter, we
show how the truncation of a metasurface can play an important role in breaking
the spatial inversion symmetry in the excitation of surface waves supported by
the structure. This is done by combining a large anisotropy in the dispersion
relation and the presence of an edge which also serves as a coupling mechanism
between the plane wave excitation and the induced surface waves. By resorting
to the exact solution of the scattering problem based on a discrete Wiener-Hopf
technique we show that by inverting the component of the impinging wavevector
parallel to the truncation, two distinct surface waves are excited.
