嵌入式設(shè)計天線的選擇

　　對于嵌入式開發(fā)者來說，廣泛的RF協(xié)議選擇使得已經(jīng)復(fù)雜的天線選擇變得更加困難。增益、方向性和帶寬都代表了決定天線選擇的嚴重權(quán)衡——偶極子、單極、貼片、扁棒、中心饋電、端饋。選擇似乎永無止境。所謂的智能天線使選擇變得更加復(fù)雜，正如你的PCB布局幾乎保證你選擇的天線不能像廣告那樣工作一樣。

　　本文將研究基本的天線設(shè)計參數(shù)，并推薦哪種類型的天線對最流行的嵌入式無線應(yīng)用最有意義。它也將解決一些設(shè)計上的考慮，這些因素可以對你的天線在實際工作中產(chǎn)生怎樣的影響。你不需要知道如何設(shè)計天線，以便知道如何與它們一起設(shè)計。

　　Theoretically speaking

　　An antenna is a device that converts electric currents into electromagnetic waves to transmit information and the reverse to receive it. You can think of an antenna as a complex RLC network. If the antenna is too long， it will display a predominantly inductive reactance. If it is too short， it will present to the PA as a primarily capacitive reactance; at resonance， these reactances will cancel each other out and the impedance will be purely resistive （see Figure 1）.