臺灣博碩士論文加值系統

衛星通信在近年蓬勃發展，在國內或國外通信都身為很重要的腳色，也對許多國家帶來龐大的收入。衛星通信具有許多優點：架設方便、通信涵蓋的範圍廣、並能克服各種地理上的障礙。目前許多通信衛星使用C和Ku頻段，但隨著對衛星的需求增加，我們便需要更高頻、頻帶更寬的Ka頻段。本論文就是針對Ka頻段來做討論。
本論文在Ka頻段設計雙頻極化器，低頻位於17.7~20.2 GHz，高頻位於27.5~30 GHz，設計了16級iris隔板極化器，iris隔板極化器結構緊湊，參數含有極化器邊長、隔板高度、隔板厚度、隔板間隔，可改變的參數較多，相較於其他種類的極化器能達到更好的模擬結果。本論文利用iris隔板使兩個互相垂直的線極化波，產生90度的相位差，形成圓極化。
設計方形波導iris隔板極化器，利用全波模擬系統(HFSS)進行最佳化，將設計的極化器結合昇達科技股份有限公司提供之五端口正交轉換(OMT)器進行模擬，本論文不對OMT參數進行調整，目標規格return loss < -18 dB、insertion loss > -0.5/-0.4 dB(低頻/高頻)、axial ratio < 1.2/1 dB、port isolation < -90 dB、group delay < 0.8 ns。模擬結果，單討論極化器皆有符合規格，但發現在高頻帶外產生尖點，與OMT結合後return loss產生些微偏差。axial ratio有部分頻段超出規格，但仍保持在3 dB以下。
最後本論文設計了圓形波導iris隔板極化器，希望能改善高頻帶外尖點問題，模擬結果單討論極化器，確實可以改善高頻帶外尖點問題，但Axial Ratio模擬結果頻寬較窄，部分頻段超出規格。結合OMT後部分結果較不理想。極化器與OMT結構皆複雜，本論文只針對極化器進行參數調整，也造成最佳化上的限制，部分結果無法達到規格。

Satellite communication has flourished in recent years and played a very important role nationwide and abroad, bringing huge revenue in many countries. Satellite communications have many advantages, namely, ease of erection, wide coverage of communications, and the ability to overcome various geographic barriers. At present, many communication satellites mostly use the C and Ku bands, but as the demand for satellites increases, we need the higher frequency wider bandwidth Ka-bands.
In this paper, a dual-frequency polarizer was designed in the Ka-band, the low-frequency is located at 17.7~20.2GHz, and the high-frequency is located at 27.5~30GHz. The dual-frequency polarizer in the form of a 16-stage square waveguide iris polarizer (SWIP) was designed. The polarizer in the form of iris is compact. There are many parameters that can be tuned and better simulation results can be achieved compared to other types of polarizers. In this paper, a phase difference of 90 degrees were generated by the iris polarizer on two orthogonally linearly polarized waves to form a circular polarization.
The optimized SWIP was accomplished by using the full wave simulation software HFSS. The polarizer was then combined with a five-port ortho-mode transducer (OMT) provided by Universal Microwave Technology, Inc. In the current work, the OMT parameters were fixed and cannot be altered. The target specifications are calling for a return loss < -18dB, insertion loss > -0.5 /-0.4dB (low frequency/high frequency), axial ratio (AR) < 1.2/1dB, port isolation < -90dB, and the group delay < 0.8ns. Our simulation results show that the polarizers met the specifications within the dual frequency bands. For the present design, sharp points are visible beyond the high frequency band. Nevertheless, when combined with the OMT, some small deviations were observed for the return loss and AR. The deviation on return loss is minimal. The AR for both low and high frequency bands are about 1.3 dB, which exceeded the specification but is within the well accepted 3 dB for circular polarized waves.
Finally, attempts have been made to eliminate the high frequency sharp points by designing a circular waveguide iris polarizer(CWIP). The simulation results showed that CWIP can indeed alleviate the sharp points problem. However, other shortcomings such as a narrower bandwidth for the AR. to be less than 1.2/1dB. An integration with the five port OMT revealed more problems as the results were not better than the SWIP. At this point, we suspected that in order to fully meet the specifications, the OMT parameters may need to be tuned together with that of the polarizer.

摘要-I
Abstract-II
圖次-IV
表次-V
第一章 緒論-1
1.1 極化器簡介-1
1.2 iris隔板極化器簡介-1
1.3 研究目的與動機-2
1.4 論文架構-2
第二章 方形波導iris隔板極化器與五端口OMT-3
2.1 設計規格與流程-3
2.2 iris隔板極化器初始參數設計-4
2.3 隔板高度與相位差關係-4
2.4 極化器全波電路模擬(Ansoft HFSS)-7
2.5 正交轉換器-12
2.6 方形波導iris極化器結合五端口OMT全波電路模擬-12
第三章 實作與測量-19
3.1 實作模型-19
3.2 實測結果-22
第四章 圓形波導iris隔板極化器-27
4.1 設計目的-27
4.2 全波電路模擬-28
第五章 結論與未來展望-39
5.1 結論-39
5.2 未來展望-39
參考文獻-40

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