Electromagnetic propagation along contacting dielectric tubes

Experiments performed in the 50?80 GHz band show that single-mode propagation is possible near the contact line of two thin-wall dielectric tubes. The group delay c/vg, is found to be almost a constant(3·3)from 55 to 75 GHz. Pulsespreading is therefore very low for that structure (< 1·6 ns/km?). These experimental results are in good agreement with a semiclassical theory of propagation.