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https://tkuir.lib.tku.edu.tw/dspace/handle/987654321/35830
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| Title: | 適用於Ku頻帶圓極化相位陣列天線之設計及最佳化之初步研究 |
| Other Titles: | Design of the satellite Ku-band CP array antennas and its initial study of optimization |
| Authors: | 段龍輝;Tuen, Fai-lung |
| Contributors: | 淡江大學電機工程學系碩士班
李慶烈;Li, Ching-lieh |
| Keywords: | 陣列天線;威爾金森;遺傳演算法;Ku頻帶衛星頻帶;Circular polarization array antenna;Genetic Algorithm;Ku-band satellite |
| Date: | 2009 |
| Issue Date: | 2010-01-11 07:12:44 (UTC+8) |
| Abstract: | 本論文的目的是在設計一使用於Ku頻帶衛星的圓極化陣列天線，微波頻段的Ku頻帶範圍是12GHz~18GHz，本論文主要探討的是用於固定式衛星服務及衛星廣播服務11.45~12.75GHz之頻率範圍的圓極化陣列天線，首先設計出一符合圓極化Ku頻帶衛星頻帶要求之單一天線元件，此單一元件達到寬頻、圓極化的特性外，更要有高增益(高指向性)、低旁瓣及隔離度的基本要求。
本論文提出的衛星圓極化陣列天線結構為以簡單的槽孔耦合patch天線(Aperture Coupling Patch Antenna)為基礎，此天線具有三層金屬結構，上層為方形patch輻射體之所在，中層為接地面(Ground Plane) 金屬，也是耦合槽孔之所在，下層金屬為50Ω饋入線之所在，當槽孔1和槽孔2的饋入線的相位相差90度即可產生圓極化輻射，另外，為了減少背向輻射又加上另一金屬接地面形成四層金屬的結構。
我們發現令激發槽孔位在patch的角會比位在patch的邊有更好的隔離度，並於後續結構中採用。另外，針對饋入網路，考慮頻寬的因素，吾人選用威爾金森(Wilkinson)功率分配器來做為訊號功率饋入的分配元件。為了考慮饋入網路走線之間彼此的耦合效應，它的激發路徑也是必須要經過精密的調整。我們探討了2X1及2X2陣列的模擬特性，並實作了2X2陣列的原型，模擬和量測結果非常一致。
接著，本論文進一步將遺傳演算法應用於圓極化陣列天線（Antenna Arrays）的最佳化，目標在調控激發相位使得圓極化陣列天線可在空間座標中進行波束掃描，為了在掃描主波束的過程中維持圓極化的特性，並達到較低的旁瓣位準(SLL)，必須將其鄰近元件的耦合效應納入。為此，吾人得事先計算取得整個天線陣列環境（至少包含鄰近元件）中的單一天線元件在單阜（不是雙阜）饋入下的輻射特性，吾人利用全波模擬軟體來模擬2X2陣列天線在某一單阜獨自激發的情況下的輻射遠場rE，包括各角度的數據之收集，以作為GA演算程式做進行個別阜的激發相位調整時的輻射遠場更新之用。最後，針對2X2陣列天線的激發相位進行優化設計，但得先選擇適當的條件式與權重：由於是圓極化的陣列天線，故在波束掃描過程中，高增益（高指向性）、低旁瓣位準(SLL)以及低軸比等特性的維持都被納入搜尋條件。再藉由遺傳演算法來搜尋最佳解，以計算出掃瞄各角度所需的激發值相位列表，並將GA最佳化的結果與模擬軟體的數據進行的比對，結果顯示兩者之間的準確度及一致性極高，兩者誤差比約在1%以內。
The purpose of this thesis is to design a Ku-band circular polarization array for satellite application. Ku-band microwave frequency ranges from 12GHz to 18GHz in general. The objective of this thesis is to explore the circular polarization array antenna for fixed satellite services and satellite broadcasting services covering 11.45 ~ 12.75GHz frequency range. At first, one need to design a single antenna element with circular polarization that meet Ku-band satellite bandwidth requirements. The single antenna element need to achieve broadband characteristics of circular polarization, but also have high isolation.
This thesis presents an array of circular polarization satellite antenna, of which the structure is based on a simple slot-coupled patch antenna. The patch antenna has three matellic layers, of which the upper layer is where a square patch radiator resides. Meanwhile, the middle layer is the metallic ground plane, where the coupling slots are etched, and the lower layer is intended for the 50Ω feed line and/or feeding network. When the feed line for slot 1 and slot 2, respectively, exhibits 90-degree phase difference the circular polarization of radiation can be generated. In addition, in order to reduce the backscattered radiation another metal surface is added to form a four-layer metallic structure.
We found that putting the excitation slot at the corner of the patch can improve the isolation as compared with putting the excitation slot at the edge of the patch. Thus the structure with excitation slot being at the corner of the patch is adopted for the successive investigation. In addition, for the feeding network the Wilkinson power splitter is used to feed input signal power regarding the frequency bandwidth. Taking into account of the coupling effect between the feed lines of near paths, careful adjustment for the path length is necessary. We have examined the simulated characteristics of the 2X1 and 2X2 arrays, and the prototype of the 2X2 array is fabricated and measured. The simulation and measurement results are found in very good agreement.
Then, in this thesis the genetic algorithm is applied to further optimize the design for the circular polarization array antenna. The objective is to scan the main beam by suitable adjustments of the phase of the excitation current. During the course of scanning the characteristics of circular polarization must be maintained, meanwhile, the sidelobe level (SLL) is kept low, for which the coupling effect between the antenna elements must be took into account. To accomplish this, we have to calculate in advance the radiated E fields of the entire antenna array (at least including the neighboring components) with only a single antenna element being excited. The full-wave simulation software is employed to simulate the the 2X2 array antenna as mentioned. The far zone E fields rE of all the angles (up to one degree resolution) are obtained and saved for successive optimization using GA algorithm. In GA, the far zone E fields must be updated for different phase adjustments of the excitation current.
Finally, for the optimal excitation phase searching for the 2X2 phase array, one must first select the appropriate optimization conditions and weights: as a circular polarization array antenna is considered, the conditions of high-gain, low sidelobe level (SLL) and low axial ratio are included into the searching fitness criteria. Then through the genetic algorithm the optimal solution to achieve the required scanning angle can be obtained, and the list of the excitation phases of the current is calculated and saved for practical usage. The results of GA optimization are compared with the simulation results by software, and the results show very good accuracy and consistency with error less than 1% |
| Appears in Collections: | [電機工程學系暨研究所] 學位論文
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