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倒F型天線

維基百科,自由的百科全書
應用於數位增強無線電話系統中的一個倒F型天線

倒F型天線(英語:inverted-F antenna)是用於無線通訊的一種天線,主要運作於特高頻微波頻率。構造包含導電的接地平面英語Ground plane以及一個與之平行的單極天線英語Monopole antenna。相對於簡易版的單極天線,此設計有兩個好處:第一,這種天線的長度較短且體積更加小巧,可被安裝在流動裝置中。第二,這種天線無需其他元件即可透過設計與饋電電路達成阻抗匹配,提高效率。

與倒F型天線有關的構想最早出現在1950年代,當時構想的是一個立體的彎折天線。然而,如今倒F型天線最為廣泛的應用形式是平面倒F型天線(英語:planar inverted-F antenna,PIFA)。其接地平面和天線平行於一平面上,大幅節省了立體空間,小巧的尺寸使其能夠融入於行動通訊裝置中。PIFA能被以微帶線形式印刷在電路板上。

PIFA是一種貼片天線英語Patch antenna。許多的貼片天線(包含PIFA)都可實現寬頻和多頻功能,實現方式包含使用耦合諧振器(coupled resonator)或是在天線上打洞。

發展與歷史

倒F型天線是由廣受使用的四分之一波長(quarter-wave)單極天線英語Monopole antenna演變而來,其構造包含一個接地平面以及一個直立於平面上的桿狀天線,天線由底部接受饋電。最早具有F狀造型的天線於1940年代被發明,[1]這個天線從位於中間位置的分支接受饋電,而其底部則連接到接地平面。從饋電線一直到接地平面這個區段的天線具有短截線的作用。只要調整這個區段的長度,就能夠改變天線的輸入阻抗,因此設計者可以透過改變饋電點位置來達成阻抗匹配。

註腳

  1. ^ Waterhouse & Novak, p. 19

參考書目

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