摘要


本篇論文利用位於中壢與高雄地區的Ka 頻段地面通訊實驗系統進行地對地的通訊實驗，並分別利用在2004 年和2005 年間所接收之觀測訊號進行資料分析，目的是要來探討Ka 頻段無線電波在雨中傳播的特性，也對系統進行溫度補償的分析，且針對Ka 頻段無線電波受大氣及雨衰減的程度，做進一步的了解，其2004年分析的結論為：ａ為0.0699，ｂ為1.0984（其中ａ和ｂ是與電波頻率、雨滴粒徑分布及雨溫度有關的函數，已有一些學者求出ａ和ｂ的經驗值），與Laws-Parsons的理論數據較為接近，意即在台灣必須要有非常足夠的功率餘裕來克服大降雨率所造成訊號的嚴重衰減，如此才有可靠穩定的通訊品質。
同時為了研究Ka 頻段無線電波在地表傳播時受水汽吸收和散射整體衰減的特性情形，第一：利用二維雨滴譜儀配合進行觀測，經過一連串的數值分析找出適合在中壢地區雨滴粒徑分佈模型再進一步估算出水汽的總衰減係數，目的是希望得到適合中壢地區Ka 頻段衰減係數的整體模型，其中降水粒子的粒徑和下降速度的關係是符合冪次定律(Power－Law)的關係V(D)=ADＢ，而雨滴粒徑分佈是屬於伽瑪(Gamma) 分佈函數形式 N(D)=N0Dμexp(-δD)；第二：為因應高雄地區發射至接收端觀測距離較長（2066 m），有別於中壢地區（158 m），所以光學雨量計所測得的單點降雨率並無法滿足整體系統的總路徑降雨率的情形，故利用觀測雨衰減的情形估算出一個屬於高雄地區的降雨率因子，而目前高雄地區正在觀測當中，初步的資料還不足以做分析的結論，但數據可以作為爾後分析的參考之用。

Abstract


The objective of this thesis is propagating in rainy condition to investigate the characteristic of the EM wave at ka-band to try to establish a suitable rain attenuation model over Taiwan area.
The rain attenuation experiment conclusion is conducted at Chung-Li in 2004 show that the magnitudes of a and b in the expression A=aRb are, respectively, a=0.0699 and b=1.0984, ( where a and b is function of radio frequency, drop size distribution and rain temperature ), A is specific rain attenuation and R is rain rate. The drop size distribution of Laws-Parsons type can be used to fit the relation between A and R, which provides a useful tool to apply to the communication service.
In addition to the rain attenuation, the property of the drop size distribution is also investigated in this thesis. We find that Gamma distribution can be perfectly fitted to the observed drop size distribution obtained from 2-dimensional distrometer, which in term can be applied to estimating attenuation coefficient.
In this thesis, we also present the a number of examples of the rain attenuations obtained by the same system carried out at Kao-hsiung area. Because of the short data amount, the behavior of the rain attenuation in Kao-hsiung is still in investigating. We hope that this work can be complete after sufficient amount of the data are collected and analyzed.

目錄

第一章 前言----------------------------------------------1

第二章 基礎理論
2-1 Ka 頻段電磁波傳播特性-----------------------------4
2-2 自由空間衰減--------------------------------------9
2-3 系統基本特性理論推導-----------------------------12
2-4 ka 頻段在雨滴中的衰減----------------------------16

第三章 實驗儀器說明與系統架構
3-1 光學雨量計(Optical Rain Gauge) -------------------23
3-2 二維雨滴譜儀 (Distrometer) ------------------------24
3-3 自動氣象觀測儀-----------------------------------26
3-4 Ka 頻段雙圓形極化反射面天線系統（桃園中壢地區）----27

第四章 實驗觀測結果分析與雨衰減模型的建立
4-1 Ka 頻段降雨衰減模型建立（桃園中壢地區）------------32
4-2 Ka 頻段接收功率與溫度之補償分析（桃園中壢地區）----34
4-3 Ka 頻段水汽與大氣衰減分析與統計-----------------36
4-4 雨滴粒徑分佈的建立及特性分析---------------------37
4-5 利用雨滴粒徑分佈估算中壢地區衰減係數模型---------40
4-6 高雄海邊地區Ka 頻段實驗初步結果------------------42
第五章 討論---------------------------------------45

第六章 結論與未來展望
6-1 結論---------------------------------------48
6-2 未來展望------------------------------------51

參考文獻------------------------------------------------52

圖表一覽----------------------------------------------57∼106

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