| Summary: | 碩士 === 臺灣大學 === 電信工程學研究所 === 95 === For wireless communication applications, circularly polarized antenna may reduce the interference from multi-path and the loss from polarization mismatching. Because of these advantages, we aim at designing a circularly polarized antenna with reconfigurable patterns for tracking RADAR applications. In this thesis, we design a broadband circularly polarized antenna, and we use a rat race circuitry to feed the antenna with an in-phase or out-of-phase signal for switched radiation patterns. In the case of sum pattern, the proposed antenna radiates the maximum gain around 2 dBi at the zenith with a 3-dB axial ratio bandwidth about 5.6%. In the case of difference pattern, we get symmetric pattern with a null in the zenith. In addition, we design an EGB (electromagnetic band gap) structure on the back side of PCB antenna for unidirectional radiation. In the symmetric difference pattern, the proposed antenna is measured with a bandwidth about 6.9 % for 3dB axial ratio and gain about 3 dBi at the zenith.
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