機(jī)箱內(nèi)天線匹配：理論與原理

　　開發(fā)無線產(chǎn)品可能是一項(xiàng)艱巨的任務(wù)。在設(shè)計(jì)和開發(fā)過程中，有許多陷阱、陷阱和常見的錯(cuò)誤。將天線的實(shí)現(xiàn)保存到最后是很常見的。事實(shí)是，天線使你的產(chǎn)品無線。它是發(fā)射信號(hào)進(jìn)入太空的最關(guān)鍵部件。通常很少考慮天線位置以及附近的物體如何影響它。這不僅對(duì)產(chǎn)品的性能，而且對(duì)進(jìn)度和成本都是毀滅性的。

　　天線是其環(huán)境的函數(shù)。無論是坐在辦公桌上，在制造商的開發(fā)板上，還是在產(chǎn)品中，所有這三種情況都會(huì)導(dǎo)致不同的性能。與設(shè)計(jì)中的大多數(shù)元件不同，它可以在電路上產(chǎn)生預(yù)期的效果，天線受到周圍所有事物的影響。天線的輻射電磁場與附近的材料相互作用，可以改變其工作頻率。天線必須放置在其最終環(huán)境中，阻抗匹配，使其工作在所需頻帶內(nèi)。一個(gè)不匹配的天線可以降低你的鏈路預(yù)算10-30分貝和嚴(yán)重減少范圍。所有天線，不管是現(xiàn)成的還是實(shí)驗(yàn)室設(shè)計(jì)的，都可能需要匹配。

　　To understand why an antenna is affected by objects near it， how an antenna radiates must be reviewed. First， forget about what is happening to the antenna or what is nearby. What is important is the input impedance to the antenna. Examining the dipole in Figure 1， when a potential is applied to the antenna inputs， there is opposite charge buildup on the ends. Essentially the dipole ends can be viewed as open circuits， with a high voltage and no current. Due to the charge buildup at either end of the dipole， current begins to flow. As you move from the end of the dipole inwards towards the feed point， the voltage falls and the current rises. At the feed point， the current reaches its peak along with some now reduced voltage. The ratio between the voltage and current at the feed point is the input impedance to the antenna. This is the impedance that drives the antenna performance. Additionally， since there is current flow on the antenna， electromagnetic fields are radiating.