倒F型天线

应用于数位增强无线电话系统中的一个倒F型天线
倒F型天线（inverted-F antenna）是用于无线通讯的一种天线，主要运作于特高频和微波频率。构造包含导电的Ground plane以及一个与之平行的Monopole antenna。相对于简易版的单极天线，此设计有两个好处：第一，这种天线的长度较短且体积更加小巧，可被安装在行动装置中。第二，这种天线无需其他元件即可透过设计与馈电电路达成阻抗匹配，提高效率。
与倒F型天线有关的构想最早出现在1950年代，当时构想的是一个立体的弯折天线。然而，如今倒F型天线最为广泛的应用形式是平面倒F型天线（planar inverted-F antenna，PIFA）。其接地平面和天线平行于一平面上，大幅节省了立体空间，小巧的尺寸使其能够融入于行动通讯装置中。PIFA能被以微带线形式印刷在电路板上。
PIFA是一种Patch antenna。许多的贴片天线（包含PIFA）都可实现宽频和多频功能，实现方式包含使用耦合谐振器（coupled resonator）或是在天线上打洞。

**发展与历史**
倒F型天线是由广受使用的四分之一波长（quarter-wave）Monopole antenna演变而来，其构造包含一个接地平面以及一个直立于平面上的杆状天线，天线由底部接受馈电。最早具有F状造型的天线于1940年代被发明，这个天线从位于中间位置的分支接受馈电，而其底部则连接到接地平面。从馈电线一直到接地平面这个区段的天线具有短截线的作用。只要调整这个区段的长度，就能够改变天线的输入阻抗，因此设计者可以透过改变馈电点位置来达成阻抗匹配。

**注脚**

**参考书目**
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