Realization of perfectly anisotropic impedance boundary

The perfectly anisotropic boundary (PAB) is defined as one possessing no isotropic component in its surface impedance dyadic. It can be realized in terms of a slab of material called guiding-wave medium. PAB can serve as a polarization transformer transforming a linearly polarized field to a field with given elliptic polarization and handedness or conversely. Also, unlike an isotropic impedance boundary, PAB can simultaneously support two surface waves with orthogonal polarizations propagating within a certain sector along the boundary.