An artificial impedance surface for rotating a surface wave on the artificial surface about a point along a circumferential path relative to said point in a phase preserving manner along said circumferential path. A method of guiding a transverse electric or transverse magnetic surface wave bound to an artificial impedance surface along a non-linear path comprising: smoothly rotating a principal axis of a surface tensor impedance matrix of the artificial impedance surface as a function of space, so the a propagation wavevector of the transverse electric or transverse magnetic surface wave rotates along with it, remaining aligned with the direction of the principal axis; and tailoring a surface wavenumber in a propagation direction of the non-linear path in such a way as to maintain a constant-phase for a wavefront of the transverse electric or transverse magnetic surface wave.