Research On The Transmission Characteristics Of Leaky Coaxial Cables

With the booming development of telecommunication industry in our country, customers’ requirements for the quality of communication, especially coverage nowadays are more and more urgent. People can not be satisfied only with the wireless connection on the ground, but also in some special areas, such as parking lots, subways, tunnels, coal mines, offices, etc., can also contact with others. So urgent solutions are required for the signal transmitting problem in these enclosed regions. However, in these situations, due to the severe multi-path effects, huge transmission loss, great expense of setting and maintaining and so on, ordinary discrete base station antennas fail to meet these requirements. As a type of leaky-wave guide, the leaky coaxial cables (LCX) are able to radiate signals by the periodical slots while the waves are propagating along the cables, which can avoid complicated feeding problems of distributed antennas. At the same time, as the LCX is flexible to the terrain, easy to set and maintain, well-proportioned in the field coverage strength, and reliable of communication quality, it is broadly used in the daily life of people. Nowadays, the production progress of LCX with some parameters in the factory is still imperfect. The main process is usually first manufacturing sample, testing, and then modification by experience. A complete numerical simulation method has not been established. In view of this point, an equivalent circuit model approach is presented in this paper, which can greatly simplify the design of transmission parameters.In this paper the transmission characteristics of LCX are studied as following:1. In the paper, the LCX is divided into a number of periodic segments with slots. The unit segment with slot is simulated by HFSS. The equivalent circuit model of the single slot unit circuit model is established by comparing the admittance Y matrix of single slot and the existing circuit model.2. Based on the single slot unit circuit model, the effect of mutual coupling among slots on the circuit model and parameters in the mono-frequency band is studied, and the reason is analyzed in theory. The formulas for calculating the transmission matrix and S parameter of multi-slot LCX are derived. The S parameters of LCX are obtained by equivalent circuit model and simulation, respectively, under the condition of identical number of slots. The agreement of the results verifies the correctness of the equivalent circuit method. 3. The influences of inclined angle and flare angle on the LCX circuit model are studied and analyzed. After summarizing, the reason of this parameter trend is analyzed in theory.4. By using the variation trends of circuit model parameters, two approaches for compensating the transmission loss with coupling loss are proposed. With the help of principle of equivalence, the far-field strength of the slot segment with different inclined angles and different flare angles are calculated, and hence the feasibility and correctness of the two presented methods are verified.