臺灣博碩士論文加值系統

本論文主要以空氣層厚度在一反射陣列天線特性影響之研究，利用變化每個環狀元素旋轉角度去組成陣列。這個結構已經在一些文獻中被研究並且也有蠻高的效率，然而，這些研究主要還是以昂貴的板材做成。在這論文中，利用了較不昂貴的FR4板材被做成並且加入空氣層也同樣能夠產生高效率的圓形極化效果。
空氣層的影響是以一平面波入射所產生的雷達截面去驗證，利用變化空氣層厚度去展現出雷達截面在一最佳化厚度中有一最高能量而導致在反射陣列中有一最高之增益。
在實作中可到達x-band 的35.23%的效率。而陣列被製作在一0.8mm的FR4 板材上而空氣層厚度控制在3mm，整個面積為324 cm2 並且有137個元素，最大增益為25.85dBi，而其中的缺點是sidelobe的大小會在4dB左右 。

This thesis studies thickness effect of an air layer on the performance of a reflectarray. The array is composed of ring elements having variable rotation angle. This configuration has been studied in the literature to show its suitability as a high efficiency circularly polarized reflectarray. However, most of the work was made on an expensive substrate. In this thesis, samples were made on a less expensive FR4 substrate. It is show that high efficiency can still be achieved by adding an air layer on the FR4 substrate.
The effect of an air layer is checked by studying the radar cross section incident by a plane wave. It is shown that radar cross section can be tuned by varying the thickness of the air layer and there exists an optimum thickness which can result in the highest gain of the reflectarray.
Experiment has shown that an efficiency of 35.23% can be achieved at x-band. The array was built on a 0.8mm thickness FR4 substrate along with an air layer of 3.0mm. There are 137 elements on an area of 324 cm2. The maximum gain is 25.85dBi. One disadvantage is that the sidelobe level is around 4db. The future study should be focused on reduction of the sidelobe level.

ENGLISH ABSTRACT...........................................................i
CHINESE ABSTRACT...........................................................ii
ACKNOWLEDGEMENTS...........................................................iii
TABLE OF CONTENTS..........................................................iv
LIST OF FIGURES............................................................vi
LIST OF TABLES.............................................................x
CHAPTER
I Introduction..........................................................1
II The Geometry and Principle Microstrip Reflectarray....................6
2.1 Radiation Analysis of the Microstrip Reflectarray.....................6
2.2 Taper and Spillover Efficiency Analysis...............................15
III Design and Simulation................................................18
3.1 The dimension of antenna and feed antenna.............................18
3.2 Single element design.................................................19
3.3 Element phase delay and effective dielectric constant evaluation.......20
3.4 RCS Simulation........................................................24
3.5 Axial Ratio Simulation................................................27
3.6 The Pattern Simulation of Different Air Layer Thickness...............28
3.7 Phase Simulation......................................................35
IV Measurement Results...................................................36
4.1 Antenna Structure Introduction........................................37
4.2 Effect and Measurement of Air Layer...................................41
4.3 Effect and Measurement of Gain and Efficiency.........................47
4.4 Measurement of Axial Ratio............................................56
4.5 The Left-Hand Circular Polarization Structure and Property............57
4.5.1 The Ground Plane as Reflection Surface Measurement...................59
4.5.2 The FR4 Substrate as Reflection Surface Measurement..................61
4.5.3 Effect and Measurement of Air Layer..................................63
4.5.4 The Gain and efficiency Versus Frequency Measurement.................69
4.5.5 Measurement of Axial Ratio...........................................78
V Conclusions............................................................79
REFERENCES.................................................................80

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