矩形隧道中电磁波传播模式理论的研究大部分仅针对基模或部分波模,对环境的改变缺乏共性.笔者推导出不同尺寸隧道可激励的波模个数公式,认为波模个数与电磁波频率的平方和隧道横截面面积成正比.据此进一步分析得出,随着发射频率的提高,介质波导传输损耗趋于一个收敛值,其大小取决于隧道尺寸,而收敛的趋势则取决于激励的波模数.对不同尺寸隧道的仿真表明,当激励的波模数目达200左右时,传输损耗均近似等于收敛值,对应的频率即为收敛阈值频率.%Most theoretical studies of electromagnetic (EM) wave propagation modes in a rectangular tunnel are focused on the fundamental modes or some partial modes.But these studies are lake of analysis of common properties of the change of enviroment.In this paper,we introduced a formula about the number of the excited modes in different size tunnels,in which the number of a modes is proportional to the square of the EM wave frequency and the area of tunnel cross section.Based on this point,it was concluded that the propagation loss of the dielectric waveguide is going to converge by increasing its frequency,and the convergency value depends on the size of tunnel.Forthermore,the simulation results of different size of tunnels indicate that the propagation loss is approaching to a convergency value when the number of modes is close to 200.The corresponding frequency at this number point is called the convergent threshold frequency.
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