Research On Propagation Character Of Leaky Coaxial Cable In The Blind Zone

Owing to the specialty of wide coverage, Leaky Coaxial Cable (LCX) is widely used in mobile communication in confined areas such as mines, subways, tunnels and buildings, and the research on its key characteristics is becoming a hotspot increasingly.Beginning with the basic theory of LCX, the paper introduced its structure, classification and three important performance indexes including operation frequency-band, coupling loss and transmission loss. According to the slots on the outer conductor of LCX, the radiation theory was discussed; the radiation mode and the radiation direction were analyzed. By the method of cylinder fourier transform, the radiated field of LCX with different slots in free space was obtained. Because LCX is widely used in the blind zone, the paper in detail discussed the radiated field of LCX in the blind zone combined with geometrical optics and waveguide matching method, including rectangular tunnel, circular tunnel, arch tunnel and rectangular space indoor. We also compared the radiated field of spiral antenna in a tunnel and monopole antenna in space indoor with that of LCX. By comparison, LCX shows advantages in realizing moble communition in such special areas.Theoretical research on LCX mostly bases on operation frequency-band and coupling loss, so the paper emphasized the two performance indexes. The value of coupling loss of LCX with different slots in free space was calculated and the factors that affect the coupling loss were analyzed. Meanwhile the band-width of single mode of LCX was given, the method of how to extend the band-width of single mode was pointed out, and the relation between the numbers of the slots on the outer conductor of LCX and the extension of the band-width was derived, and made use of the method of FDTD to solve the radiated field of LCX in free space. In conclusion, we provided basic theories for the application of LCX in mobile communication.