Research On The Radiation Characteristics Of Leaky Coaxial Cable With Periodic Slots

Nowadays, wireless communication networks are increasing fast, the requirements of system design are mainly: try to expand coverage, improve communication quality and increase system capacity. Leaky coaxial cable (LCX) has been widely used in tunnels and buildings in order to provide reliable mobile communications coverage.LCX is transmission line in the usage of the radiation field, part of the energy along the cable launched out uniformly in the form of radiation waves along the line during transmission, the emission direction of the radiation wave is perpendicular to the propagation direction. Most of the energy still transmitted along the cable. The LCX can both transmit and emit signals, so it can resolve the problem in the region where radio can't transmit information.The resonance points of LCX interfere communication quality strongly, by adding slots on the outer conductor of LCX can, to some extent, solve the problem. By simulating and analyzing, when the new slots are at different places, they can restrain different resonance points. through this method, we can extend the frequency band and supply theoretic foundation to improve communication quality. Some scholars have already by increasing slots regularly on the surface of LCX to extend frequency band, but as the number of the slots increases in each period, the interaction between slots will become stronger which is reflected on the increasing of the reflectance. If we can reduce the reflectance to allowable communication range, we can restrain the interference and extend the communication frequency band consequently and the communication quality can be improved largely. Based on the Reference 28,the article derive from the theory to expand bandwidth by adding periodic slots, use MATLAB program and plot the VSWR curves when increased slots in different positions of the LCX. We use formula in the part 5 of chapter 2 program and draw curves of VSWR, in the forth chapter, through establishing different models and simulating the models, we can also see VSWR curve changes with the increased slots in different positions of the LCX. The methods of research on the radiation field of LCX are almost theoretical operations, which almost assumed their radiation fields have the ideal opening boundary. This has disparity with the environment actually. The article using the HFSS software of the Ansoft company to simulate the radiation field of the models which is builded based on the different structure of radiation style and coupling style LCX and analyze their graphics which consist to the theoretic and the actual measurement results, proves the feasibility of the HFSS software in designing and analyzing the LCX. On this basis, the radiation field of the LCX in the rectangular tunnel of concrete material and general brick wall are simulated; the results showed that the electromagnetic fields inside LCX decline with the increase of real part of relative complex permittivity. Next, through establishing different models to simulate and analyze, we found that the VSWR curve changes with the increase of the periodic slots and suppress the resonant points, expand bandwidth, this is consistent with the results of the previous theoretical analysis. Through simulating and analyzing the radiation field characteristics of the LCX with periodical slots, we can clearly see that with the slots increasing the radiation directivity gradually enhanced and electric field intensity increased. These conclusions illustrate that use the HFSS software can obtain some characteristics indicators of LCX, provide convenience in engineering application. The results of the article apply the foundation for the application of HFSS software in the field prediction and construction of the LCX.