| The coupling effect of antenna on lightning electromagnetic pulse(LEMP)and the theory and technology of LEMP protection of antenna are emphases when studying the protection of lightning electromagnetic pulse in electronic and communicational facilities.And the mobile communication base station is the basic facility of the electronic communication operation network,which has been threatened by lightning frequently and seriously.Therefore,it is of great significance to study the electromagnetic coupling characteristics and LEMP protection of the mobile communication base station antenna.What's more,compared to the far-zone electromagnetic field of lightning,the distribution of the near-zone electromagnetic field is much more complicated,so the focus of this paper on the research of lightning electromagnetic field is in the near field.Based on the antenna theory model of lightning and the lightning current model of double exponential function,firstly,the calculation model of lightning channelcommunication tower and 900 MHz dipole antenna was established by the electromagnetic simulation software of CST Studio Suite(CST)in this paper.And when the lightning rod of mobile communication base station tower was attacked by lightning,the coupling characteristics of 900 MHz dipole antenna near the lightning channel was discussed in terms of the heights of tower,the heights of antenna,the horizontal distances of antenna from the tower and the polarization directions of antenna.Secondly,a new 900 MHz microstrip antenna of communication base station was designed in this paper.And the 900 MHz microstrip antenna's coupling effect near the lightning channel was simulated by CST in the basis of the calculation model of lightning channel-communication tower and 900 MHz microstrip antenna when lightning attacked the lightning rod of communication tower.Finally,based on the working polarization mode of the base station microstrip antenna,a new intelligent and active concept of LEMP protection by using horizontal polarization mode of microstrip antenna was proposed.From the analysis above,we obtained the following results:(1)The induced voltage of antenna in horizontal polarization or antenna's horizontally polarized part is so small that the signal can be basically regarded as noise,while the induced voltage of antenna in vertical polarization or antenna's vertically polarized part is much greater and the peak voltage can reach to 200 V or even higher,which is enough to do serious damage to the back-end low-voltage equipment,interfaces,etc.(2)The further the antenna is from the base station tower top,the smaller the induced voltage of antenna is.When the communication tower is at the common heights(30,25,20 and 15 meters),within the range of 5 meters below the tower top,the antenna induced voltage increases rapidly as the antenna approaching the tower top.While outside the range,the induced voltage decreases slightly with the reducing of antenna's height until it is almost unchanged.Therefore,when the tower is at the common heights above,it is relatively dangerous for the back-end electronic equipment within the range of 5 meters below the tower top due to the hazard/damage caused by lightning when the lightning rod of tower is attacked.(3)For the antenna installed within the range of 5 meters below the top of communication tower(tower is at the common heights of 30,25,20 and 15 meters),the closer the antenna is to the tower,the greater the change rate of antenna induced voltage is.For the antenna installed outside the range,the effect of horizontal distance between antenna and tower on the induced voltage is not obvious.(4)The antenna induced voltage peak is almost linearly decreased with the increase of antenna's polarization rotation angle ? which is defined in this paper.Moreover,no matter how high the antenna is from the ground,the induced peak voltages all tend to be 0V as the antenna changes from the working state of vertical polarization to the working state of horizontal polarization(it also means that the polarization rotation angle ? of antenna increases to from 0). |
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