An improved fractal tree log-periodic dipole antenna

Abstract

This paper presents a fractal log-periodic dipole antenna (LPDA) based on the fractal tree described by Qiu in [1]. In many situations, the lateral size of the LPDA has to be reduced to fit the antenna installation space. In Qiu’s work, the fractal tree structure is adopted as the radiation element of the LPDA, which is proved to be an effective way to foreshorten the lateral size of the antenna, and 39 percent size-reduction is claimed there. However, due to the too much reduction of the longest element, the gain is too small (2dB) to be acceptable at the low frequency. To improve the antenna’s performance of the original structure and increase the gain at the lowest frequency, a modified structure is discussed here. The improved radiation element has a lower resonant frequency, so under the condition of the same lateral length of the antenna, a better gain could be obtained.