平面近場轉遠場與適用於無線區域網路的倒F天線

Abstract

本論文分為兩部分，第一部份探討平面近場電場轉換遠場場型，第二部份為設計適用於無限區域網路的平面倒F天線。 第一部份利用等效磁流法的方法。過程中利用到等效原理及映像法理論，將天線等效成磁流源，使其分佈於等效磁流面上，所得到的等效磁流就可以用來決定遠場場型。經由適當的推導，利用動差法 ( Method of Moment ) 將電場積分公式轉成矩陣形式，最後用共軛梯度法 ( CGFFT )來解矩陣，就可以得到等效磁流解，遠場場型也就可以獲得。最後，我們選取極短電偶極陣列天線來測試此過程的準確度及可行性。結果顯示在一定的範圍內，遠場準確度能到 。 第二部份利用Ansoft HFSS軟體設計一個適用於無限區域網路的天線。此天線為立體的倒F天線，因為無限區域網路限制其高度要在3mm附近，因此我們用一個簡單的方法來增加頻寬，即多加一個寄生銅片。結果顯示多加一個寄生銅片能使頻寬符合所求。

This thesis included two topics . In the first part , we discussed the planar near electric field to far field transformation . In the second part , we designed planar inverted-F antenna ( PIFA ) suitable for Wireless LAN . The first part is fulfilled by using equivalent magnetic current approach . In the process , utilizing equivalence principle and image theory could replace antenna with equivalent magnetic currents , and the equivalent magnetic current plane has to encompass the antenna under test . From certain derivations , the equivalent magnetic currents could be obtained by method of moment ( MOM ) and conjugate gradient method with fast Fourier transformation ( CGFFT ) . Then , the equivalent magnetic currents could determine the far field patterns . In the second part , we utilized a simulation software , named Ansoft HFSS , to design a planar inverted-F antenna suitable for Wireless LAN in ISM band . Due to the limit of the specification , the height of antenna has to be below 3 mm . Therefore , we used a simple way to promote the bandwidth of the antenna , adding a parasitic element ( PE ) to the antenna . At last , the results reveal that adding a PE certainly increased the bandwidth of the antenna .