Research And Design Of Leaky Coaxial Cable

With the rapid development of mobile communication,communication network coverage has been extended to every corner including underground,such as the Mass Transit, tunnels,mines,and so on.There are three methods to solve the above-mentioned space signal coverage problems.First,use of coaxial-fed passive distributed antenna.This program design is flexible, the price is relatively low and the installation is convenient,but because of the antenna gain is limited,a single antenna coverage is limited,so it is usually applicable to short tunnel.Second,active fiber-fed distributed antenna system.Such program often used to cover the tunnel with complex environment.It's benefits include: reduce the number of installed cables in the room,with fiber optic cable to reduce electromagnetic interference,flexible in complex network design,but the disadvantage is the high cost of the system.The third method,using leaky coaxial cable for signal coverage.Compared with the other two methods using leaky coaxial cable has a unique advantage.First,reduce signal shadows and occlusion.In a complex tunnel,if use distributed antennas,mobile phone and a particular antenna may be blocked,causing the poor signal coverage.Second,the fluctuation range of the signal decreases,more uniform signal coverage than the other method.In addition, leaky coaxial cable is a broadband system,it can cover a variety of signal,different wireless systems can share a leaky coaxial cable,thus avoiding set up multiple antenna system.Based on the above advantages,leaky coaxial cable play an important role in the modern mobile communications.Therafore it is tendency to further study of the leaky coaxial cable.Although the leaky coaxial cable has been widespread applications in engineering practice,the current study of the leaky coaxial cable using experimental exploration.Therefore,how to take the theoretical research into the practice,reducing the blindness of experimental study,to simplify the design process of leaky coaxial cable,has very positive significance for the research and development of leaky coaxial cable.The paper has first summarized research background and meanings , introduced the classification of leaky coaxial cable,studied the leaky coaxial cable's basic principles, analyzed the main performance parameters of leaky coaxial cable.Theoretical Study of leakage coaxial cable more complex , the object functions of coupling loss usually have the characteristics of multi-parameters,non-differentiable even discontinuities.The optimization of structural parameters function is non-linear problem.Traditional optimization techniques, such as random search and gradient descent algorithm,has strong reliability,the algorithm is very mature.However,it is difficult for traditional optimization techniques to solve the problems of objective function and constraints non-differentiable,discontinuous,highly non-linear.Genetic algorithm is an efficient,parallel and robust global search algorithm.Its research is based on probability,having advantage of no restraint of differentiable, continuities and avoiding getting stuck in local minima.Based on the advantages of genetic algorithm and the characteristics of optimizaing structural parameters, this paper uses genetic algorithm.Secondly,after detailed analysis of leaky coaxial cable 's basic theory and the genetic algorithm's basic principle,the paper useing genetic algorithm to search cable structure parameters,simplifying the design process of leaky coaxial cable.Two kinds of structural parameters of leaky coaxial cable be searched by Genetic Algorithm,while the frequency and the conductor's inside and outside diameter has been given.One is vertical slot-type specific leakly coaxial cable,the work frequency is 800MHz; another one is vertical slot-type broadband leakly coaxial cable, the work frequency is 800MHz to 2400MHz(cover all kinds of the mobile phone's work frequency).The computer simulation results show the two leakly coaxial cable have a uniform radiation field,the standing wave ratio(SWR) are less than1.3, the Lc95 (coupling loss) and the Lc50 corresponding with the theoretical results,and the Lc's design goal 55dB