Cut off in its prime: the influence of waveguides on microwave technology

A paper by Lord Rayleigh, published in February 1897, was seminal in establishing the waveguide as a possible transmission medium which was `out of the ordinary´ for the time and, in the event, some years ahead of its practical application. The waveguide is now well established as an engineering tool, especially where there is a requirement for high power along with high sensitivity and low loss. The behaviour of waveguides in the below cut-off region, where the attenuation does not become infinite but reaches an asymptotic value dependent on the guide dimensions, is now the basis of a primary standard of attenuation used in standards laboratories throughout the world. Despite the high attenuation, `propagation´ in a waveguide in the cut-off mode has attracted interest recently through claims that the group velocity may be of the order of four times the velocity of light