| Summary: | 碩士 === 國立交通大學 === 電信工程研究所 === 107 === This thesis proposes an improved cross-polarization of two-port quadri-polarization diversity antenna design with three main layers. The upper layer is the antenna radiation layer. The antenna can be freely switched to the left or right handed circular polarization with PIN diodes and is arranged to a sequential rotation array. The advantage is that the sequential rotation array formed by the circularly polarized antenna can not only increase the bandwidth can also achieve low axial ratio of circular polarization and higher gain. The middle layer is a monopole antenna with an air layer to couple energy into the radiation antenna. Compared with the probe feed, the method can enhance the antenna bandwidth. We use the single-pole double-throw switch, a composite right/left handed transmission line phase shifter and microwave components to design a novel switchable feeding network in the lower layer. The single-pole double-throw switch is used to select energy paths to control the radiation state of antenna, and synthesize four different polarizations, which are two orthogonal linear polarizations, the right hand and the left hand circularly polarization. The biggest advantage of this architecture is to cancel out the cross polarization of the four antennas in the far field by using the symmetry of the antenna array. In the ideal case, the cross-polarization of the dual circular polarization in broadside direction can reach -40 dB level, and the cross-polarization of the dual linear polarization can be offset to only -50 dB. Compared with the traditional sequential rotation method, the feeding network proposed in this thesis can make the radiation pattern better and maintain excellent performance.
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