Broadband Designs of Circular Polarization and Polarization Reconfigurable Antennas

• Main Authors: Jhih-Ming Chen, 陳志銘
• Other Authors: 羅鈞壎
• Format: Others
• Language: zh-TW
• Online Access: http://ndltd.ncl.edu.tw/handle/57502221833950262579

碩士 === 國立彰化師範大學 === 電機工程學系 === 103 === A design for wideband circularly-polarized (CP) antennas with unidirectional radiation is first described in the thesis. The antenna structure is mainly composed of a rectangular slotted patch and a metallic reflector. An optimum CP design for the stand-alone slotted patch antenna is investigated, and a 3dB-axial-ratio bandwidth of 53 % is obtained. Then, the metallic reflector is placed at the rear of the slotted patch for generating unidirectional radiation, and the effects of various reflector sizes on CP performances are studied. Measured results show that the slotted-patch antenna with a reflector has almost the same CP bandwidth as the stand-alone slotted patch antenna, and it has good impedance matching as well as stable radiation patterns across the CP operating frequencies. Then, the CP slotted-patch antenna fed with a microstrip-to-slotline balun is studied. The balun serves as a differential feeding scheme for the CP slotted-patch antenna. Both simulated and measured results demonstrate that the proposed antenna can offer more symmetrical radiation patterns and lower cross polarization as compared to a same-size patch antenna with an unbalanced feed. Based on the differential-feed CP antenna, a design for polarization reconfigurable antennas is developed. Four PIN diodes and one control voltage are involved in the reconfigurable design that can give dual orthogonal circular polarization radiations within a 3dB-axial-ratio bandwidth of 18.4 %. The detailed process of designing the polarization reconfigurable antenna is shown. Experimental results of the completed prototype are also exhibited.