天線特性跟雜訊溫度noise temperature的關係

想請教一下 
1. 雜訊溫度的公式？ 
2. IF有公式能否把他代到 EM Tools (HFSS, CST ...... )裡做？ 請問有人做過這件事嗎？還是這個是無法考慮進去的？ 
 
 
 
以下是我從 Google 中找到的文件： 
RF電路設計講座（1）射頻、微波天線技術探微 
http://web.pcbinfo.net/mycode/artishow.asp？artid=13&ID=111149 
天線在無線電系統裏的功能是什麼呢？答案是，它是一個「門」、一個介面，透過它，射頻能量可以從發射機輻射到外面世界；或從外面世界到達接收機。底下將討論各種天線系統的技術。  
天線特性 
.........  
接收系統的效益指數（G/T）：G是天線的增益，T是雜訊溫度（noise temperature）。天線的接收靈敏度和G/T值大小有關，若G/T愈高，表示天線對微弱訊號愈敏感，接收效果也愈好。「雜訊溫度」是很抽象的觀念，它的定義應該用數學公式表示。但若要以純文本描述的話，可以這麼說：在一個通訊系統或被測元件裏，當頻率不變時，被動元件系統的溫度會使每單位帶寬的雜訊功率（noise power）ρ增加，當被動元件系統的ρ值等於此通訊系統的ρ值時，所得到的溫度就是「雜訊溫度」。請注意，被動元件是包含在此通訊系統或被測元件裏面，有時此被測元件也被稱作「網路的真正終端裝置（actual terminals of a network）」。例如：一個單純電阻的「雜訊溫度」就是此電阻的真正溫度；但是，一顆二極體的「雜訊溫度」可能是此二極體（真正的終端裝置）的真正溫度（接腳測量到的溫度）之數倍之多。雜訊溫度是以絕對溫度（-273oC）為零度，單位是K（Kelvin ）。  
 
Dish Noise Temperature  
Satellite dishes not only detect the desired satellite broadcast but also noise from natural and man-made sources. Noise from the surrounding environment and electronic equipment works in the opposite direction to gain and must be avoided if at all possible. A portion of this noise enters via the dish side lobes; a smaller amount, predominantly that from outer space, enters via the main lobe. Dish noise temperature is a measure of how much noise is detected from the surrounding environment. The warm ground emits microwave radiation so noise temperature increases as a dish is pointed at increasingly lower elevation angles. Thus the reception from a satellite located closer to either horizon would be poorer than one from one located higher in the arc. Noise also decreases as dish size increases, since larger dishes have smaller side lobes and a more narrow main lobe.  
 
 

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