Radiation characteristic of eight-shaped slot leaky coaxial cable and the restraint of high-order mode

摘要

In finite spaces such as tunnels and mines, mobile communication is mostly implemented by using leak coaxial cable. Starting from the basic electromagnetic theory, the radiation characteristics of eight-slot leaky coaxial cable is studied, the existing condition of radiation mode is given, and the frequency bandwidth of the single-mode radiation is discussed. In this paper, the authors point out that the cable does not have radiation waves of even mode but only has waves of odd mode such as -1, -3, -5 and so on. A series of new slots can be opened at the outer conductor of the cable where the distance between the new slot and old ones is P/2n where n must be an odd number and it should be equal to or less than -3. Consequently, the corresponding high-order mode is restrained and the frequency bandwidth of the single-mode radiation is extended. The conclusions have all important meaning to the design and use of eight-slot leaky coaxial cable.