地下电短天线的输入特性分析

地下电短天线的输入导纳是其几何尺寸、工作频率及地下和近地表物质(围岩及土层)电磁参数的函数.通过分析其变化规律得到下列结论:(1)短天线的输入导纳随频率的变化比较复杂.当频率较低时,短天线的输入电导随地下物质电磁参数的变化不明显,而输入电纳基本上随着频率的增高呈线性变化.(2)在频率比较低时,介电常数的变化对短天线的输入电导影响不明显,存在有一个电导曲线重合频段.对于低阻物质,这个重合频段的上限比较低;对于高阻物质,重合频段的上限升高.对于输入电纳,当电阻率和频率两者都较高时,其对介电常数的变化比较敏感.(3)输入导纳对低阻物质反应敏感,而对具有中等以上电阻率的物质基本上退化成为一条相同的频率变化曲线.(4)短天线的输入导纳值随其几何尺度的增加而增加.

Analysis of the input characteristics of electrically short antenna in the subsurface

The input admittance of electrically short antenna located in the subsurface is a function of its geometrical size, the operating frequency, and the electrical parameters of the geological materials near and under the surface. By analyzing the function numerically, it is found that (1) the input admittance of electrically short antenna is a complicated function of the operating frequency. When the frequency is relative low, the driven point conductance does not change significantly with the change of the dielectric constant, while the driven point susceptance changes linearly with the frequency. (2) For low frequencies, the dielectric constant has no significant influence on the driven point susceptance, and there exists a frequency band in that different dielectric constants give the same driven point susceptance. (3) The driven point admittance is sensitive to the change of frequency in the region with low resistivity. For media with middle and high resistivities, the driven point admittance has the same value independent of the frequency. (4) The driven point admittance of electrically short antenna increases when the antenna has a larger radius and length.