Guided radiation by coaxial cable for train wireless systems in tunnels

In railway radio systems and vehicular communications, a very important problem is that of maintaining stable communications at all locations, especially in tunnels and in spaces between buildings. A leaky coaxial cable having a new type of slot as a radiating element combining longitudinal slots with circumferential slots is described, and the desired radiation power or coupling loss can be easily designed by varying the dimensions of the slots and by selecting an appropriate pitch length. The results of the experimental studies at a frequency of 450 MHz are expected to give a satisfactory solution to this problem.