[[alternative]]Aperture-coupled Microstrip Antennas

碩士電機工程學系[[abstract]]本論文將研究並設計具有極化切換能力的槽孔耦合微帶天線。為了產生不同的極化，天線藉由耦合微帶線經由接地面上的環形槽孔以串聯方式激發二正交模態，並選擇適當殘枝長度以激發具有良好線性或圓極化輻射特性，除此之外，線極化也可以透過接地面上的開路環形槽孔激發，所有對於圓極化和線極化特性影響的重要參數皆詳細於本文探討。為了能使用電子裝置控制極化的變換，使用開關二極體來重置殘枝長度和環形槽孔，並成功完成了具有圓極化/線極化切換和垂直/水平極化切換的微帶天線。接著，利用具有線性極化切換的天線結構，並在圓形金屬片上蝕刻不等長的交叉槽孔，以完成左旋圓/右旋圓極化切換的設計，除此之外，也可以在圓形輻射金屬片45度角的方向放置一寄生金屬片，並加入開關二極體控制導通狀態，使天線可提供垂直/水平/左旋/右旋四種極化的切換能力。從實驗結果得知，本論文所提出之可切換極化的微帶天線操作在線性極化時，有低的交叉極化，當操作在圓極化時有很好的軸比特性。[[abstract]]This thesis presents the designs of an aperture-coupled microstrip antenna with switchable polarization. Two orthogonal modes of the microstrip antenna can be excited by a series microstrip-line-feed configuration through the coupling of a ring slot in the ground plane. For the ring-slot-coupled microstrip antenna, the antenna can radiate linear (LP) or circular polarization (CP) with good performances by selecting a proper length of the open stub in the feed line. In addition, the LP radiation also can be excited through the coupling of an open-ring slot instead of the ring slot. The effects of the key parameters of the proposed design on the CP and LP performances are first investigated in details. Then, by using pin diodes to reconfigure the coupling slot and the stub length, the polarizations of the microstrip antenna can be electrically switched. Different polarization switching designs have been achieved, including linear / circular polarization, dual linear polarizations, and dual circular polarizations. Finally, the aperture-coupled microstrip antenna with quad polarization switching is also designed and implemented. From the obtained results, each polarization is operated at the same frequency band and has a broadside radiation pattern with low cross polarization