An important concept in microwave engineering is that of circular polarisation. The two possibilities correspond to two equal vectors in space quadrature with one or the other advanced or retarded in time quadrature. Counter-rotating magnetic fields occur naturally on either side of the symmetry plane of an ordinary rectangular waveguide propagating the dominant TE mode; and at the interface and everywhere outside two different dielectric regions. Furthermore, in each instance, the hand of rotation is interchanged if the direction of propagation is reversed. Situations in which the rotation of these waves are different in the two directions of propagation are, of course, of special interest.