| A hot issue in the area of lightning protection technology is the very influence of a lightning pulse on a mobile communications base station. Construction on weald or highland has advantage for requirement to transmit-receive wireless communications signal. Thus, for the base station tower, suffering a lightning stroke is common. When it happens, a serial of problems becomes the key of lightning protection ability and design of the mobile communications base station:lightning current distribution of the tower body and of the grounding network, leakage current distribution and ground potential rise of the grounding network. Affected by a lightning stroke, moreover, induced current on antenna cable shielding layer could result in error codes. Voltage between the shielding layer and the tower body, generated by potential distribution, might break down the antenna cable, and interrupt communications. In addition, as a powerful electromagnetic pulse phenomenon, lightning is of time-domain electromagnetics; and technology against it is much of project application. Inevitably, lightning protection researchers are facing many challenges.It is very difficult to instruct practical lightning project design by the means of pure theoretical research. This paper is achieved during the study of lighting protection design for China Mobile Group Guangdong Co.,Ltd. Therefore, it emphasizes the requirement of practical lightning protection project. Focusing on the movement of lightning discharge, this paper establishes a physical model which describes a lightning striking the base station tower. The above issues are discovered in account of concrete geological condition, possible lighting position and different connecting manners between the tower body and the antenna cable, as well as those simulation data to instruct lighting protection design for the mobile communications base station.Innovation of this paper lies in that a discharging loop model consisting of thundercloud, tower body, grounding network, antenna cable and the infinite far is proposed. In lightning protection project design, employing an equivalent circuit model is justified by analysis. A "Tower Body-Grounding Network" entire network system, composed by the base station tower body and grounding network, is established. Based on analyzing the current channel, when a lightning strikes the mobile communications base station tower, several models are revealed one by one-base station tower body network model, grounding network model and antenna cable model:(1) Establishing time-domain electromagnetic model of tower body steel and equivalent circuit model of tower body network, based on its real structure; Simulating and comparing influence of every factor on lighting current distribution of the tower body; Researching on interference character caused by current distribution of the tower body; Showing normalized lightning current distribution of the tower body;(2) Based on grounding network real structure, establishing its equivalent circuit model; Simulating and comparing influence of every factor on leakage current distribution and ground potential rise character caused by these leakage current; Showing normalized lightning current distribution of the grounding network;(3) Analyzing and prosing interference channel model of the lightning current influence on the mobile communications base station, and the model of interference from lightning current, suffered by the antenna cable; Based on these two models and on structure relationship between the antenna cable and tower body, establishing an equivalent circuit model of the antenna cable; Combining the antenna cable model with the "Tower Body-Grounding Network" entire network system model; Simulating and comparing influence of every factor on induced current of shielding layer and voltage between the shielding layer and the tower body; Showing pulse impedance of the base station tower, under every condition; Advising lightning protection by quantitive analysis. |
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