| Summary: | 博士 === 國防大學理工學院 === 國防科學研究所 === 100 === In this thesis, we propose firstly a compact-size circularly polarized (CP) square slot antenna (SSA) design. The next, we propose new procedures and concepts to enhance the axial-ratio bandwith (ARBW). The proposed antennas not only have the campact-sizes and broad ARBWs but also have the unidirectional CP patterns. The first one is a new miniaturized CP SSA fed by a halberd-shaped co-planar waveguide (CPW). The good ARs can be obtained by adjusting the lengths of vertical and horizontal strips of feedline. The characteristics of the design are that the CP operation and impedance matching can be achieved independently. The second design, we propose a newly designed compact wideband CP SSA, to ehance the ARBW of first design, in the square slot of which are a halberd-shaped feeding line and a square ring patch. By placing a specially designed reflector behind the bidirectional CP SSA, one can obtain unidirectional CP patterns with the associated 3-dB ARBW almost the same as that of the bidirectional antenna. The third design, we propose a greatly enhanced ARBW for CP SSA. We replace the halberd-shaped CPW feeding line by an asymmetrical T-shaped one to gain a 3-dB ARBW about 11%. The 3-dB ARBW can largely increase to 4 times by a stretched metal strip and an embedded rectangular metal patch in square slot. A grounded metal strip is employed to result that the CP band can be moved to lower ones to obtain the compact design and achieve the optimum impedance matching. The last design, we propose a novel procedure for broadband CP SSA. We employ the asymmetrically T-shaped CPW feedline as same as the third design to obtain the lower and higher CP band. The higher CP band can be lowered by the implanted grounded strip and the ARs improved by the grounded L-shaped strip. The unidirectional patterns can be gained and the radiating gains increased by the specially designed reflector.
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