來波方位測定之天線系統設計

Abstract

本論文之主旨在於研究來波方位測定之天線系統設計，首先，將設計一個可在水平片上做360度方位角度掃描之天線，其半功率波束寬度較寬可涵蓋較大角度的掃瞄範圍，作為尋找來波方位的初步判別，其次，將設計一個分時多工單脈衝天線系統，其在相對較小的角度範圍內可做較精準之來波方位測定。其中，全方位角度波束掃描天線之設計，是採用適當設計之頻率選擇表面，藉由二極體開關的切換，讓電磁波可以通過或者不通過此頻率選擇表面，因此，可以經由二極體開關的切換，來達成波束掃描的功能。此波束掃描天線之結構可區分為由頻率選擇表面所構成之六面空心柱狀體，與一個置放於中心位置作為激發源使用的偶極天線，由實驗結果顯示，其半功率波束寬度約為80°，天線增益約可達到5dBi。此外，將設計一個適用於數位廣播接收之分時多工單脈衝天線系統，作為精準來波方位測定之實施例，此系統包含了模式切換電路與堆疊式圓形極化天線陣列。其中之模式切換電路包含了一個一分四路之威爾金森功率分配器以及四個路線切換形式之相移器來提供每個路徑上0°/180°相位之變化。而堆疊式圓形極化天線是由四個邊緣饋入的貼片天線置放在底層，再將四個寄生的貼片天線置放在上層的基板上所構成，此寄生天線可以增加操作頻寬與圓形極化軸比的特點。經由此模式切換電路與堆疊式圓形極化天線陣列之組合，即可形成一個在水平與垂直兩個維度上可形成合波束與差波束的單脈衝天線系統。經由實驗數據分析，在2.185GHz的頻率上，其在水平與垂直平面上的差波束中心零點深度可達到-34.2dB與-33.2dB。

This study involved two kinds of antenna system designs for direction finding. First, a reconfigurable beam-switching antenna is designed and fabricated to sweep its radiation pattern along the entire azimuth plane. The geometry of this antenna is designed as a hexagonal cylinder and composed of two major parts. One is the dipole antenna at the center of the structure as an excitation source and the other part is the active frequency selective surfaces (FSS). The FSS can be controlled as transparent or reflection one for the incident electromagnetic wave by PIN diodes. According to the measured results, the radiation pattern can be swept in six steps along the entire azimuth plane with moderate gain of 5 dB and half power beam-width of 80°. Second, a time-division multiplexing (TDM) mono-pulse antenna system for angle estimation of the DVB-SH signal operated in S-band is designed. Such a system consists of a mode-former circuit and a stacked circularly polarized antenna array, which was implemented using planar-printed circuit technology. In the mode-former circuit, a four-way power splitter comprising Wilkinson power dividers and four switched-line phase shifters were employed to provide 0°/180° phase angles at each output port. The sum-and-difference angle discriminators were implemented along vertical and horizontal planes for detecting the incident elevation and azimuth angles. The stacked circularly polarized antenna array composed of four edge-fed patches on the bottom layer and four corresponding parasitic patches were exploited on the top layer to increase the axial ratio bandwidth. The experimental results revealed that, at 2.185 GHz, the null depth of the difference patterns were -34.2 dB and -33.2 dB along the two principal planes.