The more feeds, the better the axial ratio bandwidth is. Starting from the mechanism of circular polarization obtaining from multiple-feed method, the multiple-feed can improve the axial ratio bandwidth of a microstrip antenna effectively than the single-feed microstrip antenna is demonstrated by theoretical analysis and simulation. When using multiple-feed for one patch, the sequential rotation technology ( Hall et al., 1989) can be adopted. We adopt theoretical analysis and simulation by CST Microwave Studio to give out the method of improving the axial ratio bandwidth of the circularly polarized microstrip antenna.įirst, we briefly introduce the basic methods which can form the circular polarization for a microstrip antenna, including the single-feed and the multiple-feed. Kishk has done a lot of research work on the circularly polarized microtrip antenna recently ( Yang et al., 2008) ( Yang et al., 2007) ( Yang et al., 2006) ( Chair et al., 2006) ( Kishk et al., 2006). The previous reference books discussed the axial ratio bandwidth less, always said that the axial ratio bandwidth of a circularly polarized microstrip antenna was limited, and it was less than the impedance bandwidth of a linearly polarized microstrip antenna ( Lin & Nie, 2002). In this chapter, we focus on the axial ratio bandwidth of a circularly polarized microstrip antenna.

Also there are some methods to enhance the impedance bandwidth of the miniaturized microstrip antenna ( Liu et al., 2002) ( Wang & Gao, 2003). And some technologies can achieve the miniaturization of the microstrip antenna ( Xue and Zhong, 2002). Microstrip antenna can adopt many methods to obtain circular polarization ( Xue and Zhong, 2002). Microstrip antenna has been widely used due to its many advantages, such as, small volume, light weight, easy to get various polarization and easy to be integrated ( Dang & Liu, 1999).

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