[[alternative]]Reconfigurable Circularly-Polarized Microstrip Antennas

碩士電機工程學系[[abstract]]本論文將研究並設計具有重置特性的圓極化天線。天線結構採用槽孔耦合微帶天線，分別提出極化切換、頻率切換以及結合極化與頻率切換的三種設計方式，也針對影響圓極化特性的重要參數作詳細分析。為了能透過電力來控制極化的變換，所提出的設計使用3伏特鋰電池控制二極體的狀態以重置天線特性。對於極化切換設計是利用改變微帶饋入線上電流流動路徑的方式達成；而頻率切換及結合極化與頻率切換的設計則是利用改變輻射金屬片結構的方式完成。從實驗結果得知，本論文所提出的可重置圓極化天線，在每個圓極化模態皆有良好的阻抗匹配以及軸比，利用這些重置特性有助於通訊傳輸品質的提升。[[abstract]]This thesis presents the designs for reconfigurable microstrip antenna. Three types of the reconfigurable antenna are studied. The first one is a circularly-polarized (CP) microstrip antenna capable of switching polarisation sense. The microstrip antenna is excited by an open-loop microstrip line through the coupling of a ring slot in the ground plane. The polarisation diversity is achieved by using a pair of pin diodes to reconfigure the flowing path of the current on the open-loop microstrip feed line. The measured results show the 3dB-axial-ratio bandwidth of more than 10 % can be obtained at the two polarisation senses. The second one is a CP reconfigurable microstrip antenna with dual-frequency operation. The antenna has a square radiating patch, and each side of the square patch is connected a shorting wall via a diode. By switching the four diodes, the CP operating frequency of the antenna can be varied. Several prototypes of the reconfigurable dual-frequency antennas with different frequency ratios were fabricated. The last one is a CP reconfigurable microstrip antenna with polarization and frequency diversities. The antenna is excited through the coupling of a cross slot with unequal lengths. Two diodes are used to reconfigure the radiating patch, and by controlling the states of the diodes, the polarization sense of the antenna can be switched between left-hand and right-hand CP. Moreover, the two CP modes are operated at different frequencies. An antenna prototype was also implemented and the obtained results are shown