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標題: | 平面式高增益空腔共振天線之模型與最佳化設計 Modeling and Optimal Design of Planar High-Gain Cavity Resonant (Fabry-Pérot) Antenna |
作者: | Yi-Fong Lu 盧宜鋒 |
指導教授: | 林怡成(Yi-Cheng Lin) |
關鍵字: | 天線,高增益,空腔共振,部分反射面, antenna,high gain,cavity resonant,partially reflective surface (PRS), |
出版年 : | 2013 |
學位: | 博士 |
摘要: | 在考慮天線有限的尺寸下,本論文針對正向輻射的空腔共振天線提出了一個簡單的模型與混合式設計方法作設計,該模型能夠快速且準確地估計出天線的指向度和孔徑效率,並因而得到最佳化部分反射面參數和天線尺寸之設計。在模型中,利用洩漏波之分析和傅立葉轉換,吾人能獲取天線最大指向度和所需天線尺寸之關係。本模型亦經由電磁全波模擬,驗證了所提出之模型的正確性。此外,經由模型所產生的設計曲線,本論文亦將天線進行實作與量測。由實驗數據證實本論文提出設計方法之可行性與模型之正確性。實驗數據顯示,此原型天線之增益可達到19.7 dBi,孔徑效率為74%。模型預測之結果和全波模擬與實驗結果皆有很好的一致性。
本論文亦探討天線饋入與激發結構之研究。一般常用的微帶線天線作激發,跟偶極天線相比,易因其基板的損失和表面波的產生使得天線增益降低。因此,我們選擇偶極天線作為空腔共振天線之激發,但它不利於雙極化天線的實現。將平衡非平衡轉換器導入偶極天線饋入,能經由兩埠饋入線交錯而避開饋入線碰撞之問題,且透過阻抗轉換器,阻抗匹配亦可順利達成。實驗結果證實,能達到20 dBi的天線增益,與超過23 dB的兩埠間隔離度。 本論文之另一重點是部分反射面之研究。相較於一般的單層部分反射面,雙層部分反射面經由設計能夠有零反射相位或正相位梯度的特性。前者可用於減少空腔共振天線的空氣腔高度,它由兩個週期且正交排列的條狀結構分別在介質板的上下所組成,一個是電感性,另一個則是電容性。根據部分反射面的等效電路模型,在設計流程中發現一種新型的人工磁導體部分反射面。新穎的部分反射面是由兩層具有相同的方向排列之週期條狀所構成的,換言之,在等效電路中其具有兩個電容性導納。透過全波模擬,新穎部分反射面與過去的相比,能實現更高的天線增益。之後將天線作量測,這裡部分反射面採用的尺寸為90毫米×90毫米。對於一般和新穎的人工磁導體部分反射面,實驗結果呈現在10.5 GHz的天線增益分別達到15.1 dBi和18.3 dBi。在增進天線頻寬之研究方面,吾人利用一般的人工磁導體部分反射面,將其金屬層交換放置,且經由適當之參數設計,可獲得反射相位隨頻率增加之部分反射面。根據部分反射面的等效電路,我們提供了一個解釋相位增加的原因。最後,實驗結果證實,與傳統單層部分反射面構成之天線相比,能得到約二倍之頻寬。 We present a simple hybrid approach for the design of finite-size Fabry-Pérot antennas (FPAs), which are also called cavity resonant antennas, used for broadside radiation. The model provides an accurate estimation on the directivity and aperture efficiency, and hence may obtain the optimal configuration of the partially reflective surface (PRS) and the antenna dimensions. The overall FPA maximum directivity and the required dimensions are derived using leaky-wave analysis and the Fourier transform. The presented model was validated by conducting a full-wave simulation on a classic FPA structure. Additionally, from design curves of the presented model, a PCB-based patch-patterned FPA has been implemented and measured. The illustrated FPA prototype has a realized gain of 19.7 dBi with an aperture efficiency of 74%. The model predictions were very consistent with the full-wave simulation and measured results. After discussing the directivity and its adapted aperture area, we focus on excitation structures. A patch source is compared with a dipole source, revealing a degradation of the gain for the patch source due to the substrate loss and the surface loss. Therefore, we chose the dipole source for antenna excitation. However, it is hard to be implemented on dual-polarization excitation for FPAs. The intersecting dipoles with fed baluns are presented for dual-polarization FPAs and the impedance matching can still be achieved by an impedance transformer. The experimental results show that a gain of 20 dBi and the isolation of two ports is good enough and better than 23 dB. Unlike the classic single-layered PRS, double-layered PRSs with reflection phase zero and positive phase gradient are proposed, respectively. The former can be used to reduce the FPA’s air-cavity height. It is comprised of two orthogonal periodic strips where one is inductive and the other is capacitive, etched on both sides of a dielectric slab, respectively. According to the PRS equivalent circuit model, the design guideline is presented, exploring a novel PRS with characteristics of artificial magnetic conductor (AMC) as well. The novel PRS is constituted of two layers of strip gratings with the same permuted direction, that is, the PRS comprises two capacitive screens. Through full-wave simulations, FPAs with novel PRSs have the advantages over traditional AMC-PRSs, with respect to achieving higher gains. Accordingly, PRS dimensions of 90 mm × 90 mm are employed here to verify an agreement between the measurement and simulation. The measurement demonstrates gains at 10.5-GHz as high as 15.1 dBi and 18.3 dBi for the traditional and novel AMC-PRSs, respectively. A PRS with a positive phase increment against frequencies can be used for bandwidth enhancement. Traditional AMC-PRS metallic layers can be placed upside down and modified adaptively to form the PRS with a positive phase gradient. According to the PRS equivalent circuit, we provide an explanation for the reason why the reflection phase of the presented PRS may increase against frequencies. Subsequently, experimental results validated the bandwidth enhancement by comparing the modified PRS to the conventional FPA with a single-layered PRS. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/58766 |
全文授權: | 有償授權 |
顯示於系所單位: | 電信工程學研究所 |
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