隨建即連行動網路小型化高隔離度寬頻之分集天線

Abstract

本篇論文設計一支具有非對稱共平面帶線結構(asymmetric coplanar strip；ACS)的平面式微小化高隔離度之寬頻-極化分集 (wideband-polarization Diversity) 天線，此設計可運用在數位戰士之隨建即連行動網路 (mobile ad hoc network；MANET)off-body通訊，利用天線的分集效應解決在MANET的off-body中因多重路徑衰落(multi-path fading)。為能有效減少分集天線的面積，本論文分集天線應用極化分集搭配ACS結構所具有之「偏向輻射特性」，即可有效降低天線單元間的耦合效應，且不同於以往的ACS饋入分集天線著重於ACS結構的小型化效果，需另外在接地面加入分支結構使隔離度增加，此種方法不須隔離結構，即可達到面積小型化降低成本的實際需求。再利用寄生貼片(parasitic patch)做為耦合匹配電路增加天線的頻寬並改變低頻耦合路徑提升隔離度，解決ACS饋入天線不易達到寬頻匹配以及低頻耦合較強的問題。最後，再搭配在實體場域中的分集效應量測，驗證ACS饋入分集天線在實體場域中擁有良好的分集增益(diversity gain)。

本論文分集天線整合後大小為0.178𝜆2，比起過去的文獻縮小約20%的面積，操作頻段為1.3 GHz -4.7 GHz，使用FR4基板，為單面結構，製作容易且成本低。本論文天線不僅擁有寬頻段(約 114%)，在超寬頻段的相互耦合大小均在-15 dB之下、單元天線之間相關度係數均在-20 dB之下，使其具備良好的通道差異，分集增益因環境不同約為4 dB~13 dB，達到微小化之寬頻–極化分集天線具備隔離度之最佳化。

In this thesis, we design a planar miniaturized wideband-polarization diversity antenna system (two elements) with asymmetric coplanar strip (ACS) fed structure, used for digital soldiers mobile ad hoc network off-body communication, for solving the problem of connection failed caused by multi-path fading in the application of MANET off-body communication. For reducing the size of diversity antenna, the polarization diversity structure is designed with the asymmetric radiation characteristic of ACS-fed structure to lower the coupling effect between two antenna elements. Different to the ACS-fed diversity antenna in the past studies focused on the miniaturized characteristic of ACS structure and needed to design stubs as isolators on the ground, the proposal antenna could achieve the demand of high isolation, miniaturization design and low cost without isolators. In order to improve the problem of impedance mismatch caused by ACS structure and mutual coupling at low-band frequency, we add a parasitic patch as the coupled matching circuit and change the path of mutual coupling at low-band frequency. The parasitic patch could also enhance the isolation at lower-band frequency. Finally, we measured the diversity effect in the real field, to prove that it could achieve high diversity gain in the real field applications. The proposed antenna has been fabricated on a FR4 substrate with a single plane for verifying the design concepts, and the overall size of this antenna is 0.178𝜆2, reducing about 20% size than the past literatures. The antenna operates frequency range which is 1.3-4.7GHz. The result show that the proposal antenna has not only wide band-width (about 114% for port 1 and port 2), but also good isolation above 15 dB and the correlation coefficient below -20 dB over the entire frequency band. The miniaturized wideband-polarization diversity antenna could be achieve optimization of isolation with the value of diversity gain is about 4dB-13dB in different environments.