Research On Fractal Microstrip Antenna With PBG Structure

Fractal antenna made a rapid development in the aspect of antenna's multi-frequency ability for its self-comparability and the ability of filling in space. PBG structure was applied more and more in passive parts and antennas for its special band-stop character. In the development trend of multi-frequency broadband and small antennas, the combination of these two technologies will show great potential, and the goal of this paper is to research the fractal microstrip antenna based on PBG structure. Therefore, this article first makes a detailed theoretical analysis and simulation study on Sierpinski fractal antenna and 2-D medium PBG structure, and grasps the characteristics and the law of these technologies. Then makes study on triangle Sierpinski microstrip antenna and triangular lattice hole PBG structure by CST Microwave Studio and Ansoft HFSS, and presents results. On this basis, the author makes preliminary ideas of the combination of the two structure and do some simulation experiments. The final is a high-gain, dual frequency microstrip antenna.In aspect of fractal antenna, Sierpinski fractal structure is applied in ordinary microstrip antenna. The simulation results show that the triangular microstrip antennas have not the regular multi-frequency characteristic compared to monopole antenna. Through the analysis of multi-frequency characteristics of triangular microstrip antennas, the author put forward the concept of air patch and the calculation formulas of equilateral triangular Sierpinski fractal antenna's working frequency. In the inspection of the triangular microstrip antenna's directivity, it shows that the antenna's directivity has a certain similarity in its working frequency.In aspect of medium PBG structure, the author observes PBG structure's stopband through the simulation of the S parameters of the microstrip transmission line, in which the PBG structure is embedded. First the author does a comparison between 1-D and 2-D PBG structure and finds that the stopband characteristics of 2-D PBG can be obtained by the simulation of 1-D PBG, which simplifies the simulation model. Then the author does simulation and comparison to PBG structures with different dielectric constants, lattice constants, fill rates, medium thickness and the cell cycle number separately and obtains general law of hole-medium PBG structure's stopband characteristics changing with each parameters, which provides a basis for the design of medium PBG structure.In the combination of the two, on the basis of the model in fractal antenna's study, according to the obtained PBG structure's law in which the stopband characteristic changing with each parameter, a match PBG structure is designed. Then embeds the structure in the fractal antenna, and makes comparison to the antennas with and without PBG structure. Simulation result shows that antenna's gain increases at the corresponding frequencies with PBG structure, sidelobe and back-radiation have a certain degree of lowing.