Study on Normal Mode Helical Antennas

用于移动的或便携式无线电通信系统的天线需要是小的和低轮廓的结构。当螺旋天线的直径小于1/10波长时，它就相当于一个磁流天线，并且这种磁流的镜像电流对于一个导电平面是同相的。为了获得大的方向性，要求天线系统采用阵列结构和顺序激励。为了获得具有上述特性的螺旋天线的基本设计，必须准确而清楚地获得天线上的电流分布，特别是相位常数。本文应用改进的电路理论，通过实验和数值分析，得到了任意直径、节距、间隔物厚度等参数下的电流分布。代替圆形螺旋天线，三角形和矩形螺旋天线也进行了研究。为了得到更低剖面的天线系统，我们研究了埋在导体平面上各个槽中的圆形、三角形和矩形螺旋天线的电流分布。

Antennas for mobile or portable radio communication systems are required to be small and low-profile structures. When the diameter of helical antenna is shorter than 1/10 times of wave length, it acts as a magnetic current antenna and an image current of this magnetic current is same phase for a conducting plane. In order to get a large directivity, the antenna systems are desirable to be array structures and sequencial excitation. To get a fundamental design of the helical antennas which have the above mentioned characteristics, the current distributions on the antennas, particularly phase constant, must be obtained exactly and clearly. In this paper, the current distributions of the arbitraly diameter pitch length thickness of spacer etc. are obtained by experiments and numerical analysis appling the Improved Circuit Theory. Instead of the circular helical antennas, triangular and rectangular helical antennas are also investigated. And in order to get more low-profile antenna system, we studied the current distributions of the circular, triangular and rectangular helical antennas which are burried in a each trough on the conducting plane.