Study On Electromagnetic Band-Gap Structure And Its Application In Spiral Antenna

Electromagnetic Band-Gap (EBG) is a kind of artificial periodic structure. Because of its band-gap characteristics and in-phase reflection characteristics, it is widely used in the design of antenna and microwave field and a lot of achievements have been made in the aspects of theory and practice. Due to the EBG structure can suppress the surface wave, it can be used as a reflector,loaded onto the bidirectional radiation antennas,and turn bidirectional radiation into unidirectional radiation. It can not only improve the gain of the antenna, but also effectively reduce the profile of the antenna. However, the traditional EBG structure has large size, single frequency and narrow band defects, thus its application in the field of ultra wideband antenna is limited. Therefore, it is important to study the structure of broadband EBG. In such a background, based on the characteristics of EBG structure, the broadband EBG structure and and its application in the field of the spiral antenna are studied in this project.The research content of this paper consists of the following two parts:In the first part, using the simulation software HFSS, the band gap characteristics and the in-phase reflection characteristics of the traditional mushroom type EBG structure are studied. The results show that the larger the size of the EBG structure, the smaller the working frequency, the narrower the bandwidth. In order to extend the bandwidth of EBG structure,a Koch fractal EBG structure is designed,and its shortcomings are pointed out after analyzing its characteristics.Then,a progressive EBG structure is proposed,and its feasibility is analyzed.In the second part, an equiangular spiral antenna and exponential tapered balun, which work in 4-9GHz, are designed. In order to verify the effect of broadband EBG structure,EBG structure is assigned onto the spiral antenna. After studying the influence of parameters of progressive EBG structure on the antenna, the parameters of the EBG structure are optimized according to the results of the simulation, and finally, the antenna with good radiation performance is obtained. The simulation results show that the radiation gain of the antenna with the progressive EBG structure increased by 2.24dB compared with the original antenna. The axial ratio is less than 3dB,and profiles of antenna and EBG structure is only 9.3mm, which means the requirement of low profile is implemented. Compared with the existing research,the proposed progressive EBG structure has a certain innovation and a good application prospect in terms of the good performance, smaller area and smaller thickness.