可變輻射場型圓極化天線之研製與雷達應用

Abstract

在無線通訊應用上，圓極化天線可降低多重路徑產生的干擾以及極化不匹配造成接收訊號時的損耗。基於這些優點，本篇論文以一寬頻圓極化天線為基礎並加以改良，藉著180°分波器產生輸入訊號相位差的效果進而控制輻射場型，設計一可變場型圓極化天線，並應用於追蹤雷達上。量測結果在合場型的情況下可達到5.6 % 之3dB軸比頻寬以及12.6 % 之6dB軸比頻寬，天線正上方增益約為2dBi；在差場型的情形下，輻射場型十分對稱，並且在天線正上方產生極小值。最後在天線背面設計電磁能隙結構，以此結構作為天線的反射體達到單向輻射的效果，量測結果在合場型的情況下可達到6.9 % 之3dB軸比頻寬，天線正上方增益則約3 dBi；在差場型的情形下，輻射場型十分對稱，並且在天線正上方產生極小值。

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.