Perfectly anisotropic impedance boundary

The concept of a perfectly anisotropic boundary (PAB) is defined in terms of a surface impedance dyadic without an isotropic component. Realisation of PAB in terms of a slab of anisotropic metamaterial is suggested. It is shown that PAB can serve as a simple rotatable polarisation transformer, transforming a linearly polarised field to a field with given elliptic polarisation and handedness, or conversely. It is also shown that, unlike at a regular impedance boundary, a PAB can simultaneously support two orthogonally polarised surface waves propagating in certain directions along the boundary