Research On Fractal Top-loaded Monopole Antenna

Fractal antenna can achieve multiband or wideband characteristic with small size due to its efficient space-filling and self-similarity, which is very attractive for modern wireless communications such as mobile platform and airborne platform. In this dissertation, antenna miniaturization and bandwidth enhancement have been studied by introducing fractal loading on the top of monopole. The main contributions of this dissertation are listed as follow:Based on the current distribution of scaled fractal curve, the principle of reducing the height of fractal loaded monopole antenna is given. Shorting pins are introduced at the end of fractal structure for impedance matching. Measurement shows that Hilbert and Peano fractal loaded monopole antennas achieve 15.7% and 13.7% impedance bandwidth in the height ofλ/14, respectively.Next, effects of finite ground plane are investigated. Simulations show that it is an effective method to adjust E-plane beam bearing and 3dB beamwidth by adjusting the finite ground plane size.Next, multiple shorting pins technique is introduced to further enhance the impedance bandwidth of the proposed fractal loaded monopole antennas. Measurements show that a bandwidth improvement of 25.8% and 27% is achieved for the 1st order and 2nd order Peano fractal loaded monopole antennas, respectively.In addition, a lumped network is studied as loading for reducing the antenna height and loading area. There is a trade-off between the required antenna height and loading area according to simulations. For example, with the increase of loading area, the 2nd order Peano fractal loaded monopole antenna can achieve a 50% decrease on antenna height. When the loading area remains unchanged, the monopole antenna can achieve a 26.7% decrease on antenna height.