雙線性極化印刷式雙偶極天線陣列及其極化雷達系統應用

Abstract

本論文提出一款印刷式雙偶極天線架構，可設計應用於無線通訊系統，亦可設計成雙線性極化印刷式偶極天線陣列以應用於雷達系統中。論文一開始先介紹偶極天線的基本原理及其相關的重要參數，接著針對印刷式雙偶極天線的輻射原理進行探討，並且改善前人研究的天線饋入架構，提出新的T型饋入架構，藉此可降低交叉極化的位準，使得該天線作為雙極化天線陣列之輻射單元後，可降低不同極化之間的耦合量。首先，透過適當地設計印刷式偶極天線的長度和間距，以及T型饋入結構的長度及寬度，即可設計出符合IEEE 802.11無線區域網路系列標準的相關頻寬及頻帶。為了驗證所設計出來的天線是否滿足標準要求，模擬和實驗是必須的。模擬的部分使用全波模擬軟體建立了天線的模型，而為了滿足商用的目的，實作時採用市售便宜的板材當作基板，藉此達到適用於無線區域網路且具成本效益的天線，並比較了相關文獻的成果與本篇的差異。接著，本論文進一步以此設計完成可應用於極化雷達系統之雙極化天線陣列，該陣列的天線單元亦為印刷式雙偶極天線，兩種極化方向的天線單元及天線單元間的間距亦需仔細設計，而雷達陣列的饋入網路採用三維的方式走線，其中採用了水平及垂直饋入網路，並巧妙地使用卡榫的技巧，一方面利於饋入網路的組裝及定位，另一方面利於焊接，模擬與實驗的結果大致都吻合，表示這種三維的饋入網路是可用於實際的應用上。最後將設計好的雙極化雷達陣列天線應用於雷達目標物辨識上，透過前人研究所提出的極化熵的演算法及模擬環境，也得到不錯的結果，並且相較於前人的研究，本篇所提之雙極化雷達陣列天線可適用的頻率範圍更廣，在實際應用上能夠有更多的彈性。

In this thesis, we proposed a printed dual dipole antenna along with a new feeding network that can be applied to wireless communication systems and can also be designed as a dual-linearly-polarized printed dual dipole array for use in polarimetric radar systems. This thesis begins with the basics of dipole antennas and some important parameters and then discusses the radiation principle of printed dual dipole antennas. Based on the feeding structure proposed in [12], we proposed a new T-shaped feeding structure that can reduce the cross-polarization level. Thus, the coupling between adjacent antenna elements with orthogonal polarizations in the array design can be reduced. By properly designing the length and spacing of the printed dual dipole antenna as well as the length and width of the T-shaped feeding structure, the desired bandwidths and frequency bands for the IEEE 802.11 wireless local area network standard can be achieved. For verification, simulated and measured results of the fabricated prototype are given and compared. The simulations are conducted using full-wave simulation software. For practical consideration, commercially available inexpensive boards are used as the substrate to achieve a cost-effective antenna for wireless local area network applications. A comparison between the recently published works and our design is given as well. Moreover, a dual-linearly-polarized array antenna for polarimetric radar system is designed based on the printed dual dipole antenna. The orthogonally polarized printed dual dipole elements and the spacing between adjacent elements need to be designed carefully. A three-dimensional feeding network is proposed for the array design, including horizontal and vertical parts. The concept of mortise and tenon is used in this design, making it compatible to PCB-process and easy for assembly, welding, and positioning of the vertical and horizontal parts of the feeding network. The results of the simulation and experiment agree well, meaning that the proposed three-dimensional feeding network is feasible for practical applications. Finally, the designed dual-linearly-polarized radar array antenna is used for radar target identification. Based on the polarization-entropy-based method previously proposed by our lab, decent identification performance can be obtained. Compared with the dual-linearly-polarized square patch antenna used in our previous work, the dual- linearly-polarized radar array antenna proposed in this thesis demonstrates a wider frequency bandwidth and greater flexibility for practical applications.