Hf Omnidirectional Monopole Antenna Of Broadband Miniaturization And Realization

Monopole antennas have been used in many applications, especially in HF antennas, due to their inherent advantage like simple structure, easy to machine and mount, and omnidirectional radiation pattern. However, in HF band, the band of the antennas is narrow, and the input impedance of monopole antenna with limited height undergoes rapid variation with frequency. In order to overcome the shortcomings of the monopole antennas, a methods of quasi-fractal is used, which decrease the resonant frequency. Then, lump loading is used to enhance the valid height of the antennas, as a result the input impedance of the monopole antenna undergoes gently variation with frequency, and consequently it is easy to match by wideband matching network.In this thesis, MoM, FIT and GA are used to design and simulate the quasi-fractal loaded HF monopole antenna, and some antenna models were measured. Some design methods of miniaturization and broadband are studied, and the main work includes:1. Quasi-fractal monopole antenna is introduced, and the relationship between the design parameters of quasi-fractal antenna and their corresponding radiation characteristics is studied by the method of MoM.2. Based on the relationship between the design parameters of quasi-fractal antenna and their corresponding radiation characteristics, a quasi-fractal loaded monopole antenna whose height is 7m was designed by the methods of MoM, FIT and GA. A 1/10-scale model quasi-fractal RCL-loaded monopole antenna was fabricated and measured, which has a bandwidth ratio of about 10:1, with VSWR less than 3.0, calculated system gain greater than -9.4dB and the efficiency above 14%. The agreement in measured and computed data of the antenna is good.In this thesis, a novel quasi-fractal monopole antenna was introduced. The quasi-fractal is valid to decrease the resonant of the monopole antenna. A broadband miniature HF loaded quasi-fractal antenna was fabricated and measured.