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嵌入式设计天线的选择
对于嵌入式开发者来说,广泛的RF协议选择使得已经复杂的天线选择变得更加困难。增益、方向性和带宽都代表了决定天线选择的严重权衡——偶极子、单极、贴片、扁棒、中心馈电、端馈。选择似乎永无止境。所谓的智能天线使选择变得更加复杂,正如你的PCB布局几乎保证你选择的天线不能像广告那样工作一样。
本文将研究基本的天线设计参数,并推荐哪种类型的天线对最流行的嵌入式无线应用最有意义。它也将解决一些设计上的考虑,这些因素可以对你的天线在实际工作中产生怎样的影响。你不需要知道如何设计天线,以便知道如何与它们一起设计。
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).