Abstract :
It is shown that in the neighbourhood of cut-off in an inhomogeneous waveguide, a considerable amount of energy travels in the negative direction, i.e. in the direction opposite to that of the wavefront. It has previously been shown that in the neighbourhood of cut-off it is possible for the group velocity to be negative; under these circumstances the negative power exceeds the positive power. This question is discussed, and a new concept of waveguide Q-factor is introduced.
