應用於超寬頻系統之橫向電磁波號角天線

Abstract

在此篇論文中，我們使用了二種工具，其一為基於有限元素分析法之Ansoft HFSSTM來做嚴謹之全波模擬分析，另一則為根據孔徑上電場分佈之經驗公式所使用之等效原則來設計並完成應用於超寬頻系統中之橫電磁波號角電線。此天線結構是由兩片三角形且相距高度並非均勻之金屬板所組成。由於此結構可視為在長度及寬度方向皆漸層變化之平行板傳輸線，因此傳輸線模型可用來算出阻抗特性之起始值。除此之外，由於全波模擬所耗費過多的時間，因此我們僅在觀察其寬頻特性時使用它。然而，輻射場形則根據其孔徑上電場分佈之經驗公式，再藉由等效原理來算出。為了描繪這此種天線之輻射特性，我們改變了一些結構上的參數例如天線長度以及展開角來觀察其影響。一般來說，3-dB波束寬會隨著孔徑大小的增加而減小。除此之外，如同所觀察到的，平緩的漸層轉換結構可改善高頻之轉入損耗。由於此天線具有易於製造，不錯之輻射及頻寬的特性，因此可預期將來可廣泛用於無線寬頻系統中最後一哩的應用。

In this thesis, we have employed the rigorous full-wave analysis Ansoft HFSSTM, based on the finite element method, and the equivalent principle, on the basis of empirical formula for the aperture field distribution, to design and implement the TEM horn antenna for ultra wideband applications. The structure under consideration is made up of two metallic triangular plates separated by a non-uniform distance. Since the structure can be considered as a parallel-plate waveguide with taper transition along its length and width directions both, the transmission line model could be utilized to figure out the impedance characteristics in the initial design. Besides, due to the excessive time consuming for the full-wave simulation, it is only used for examining its wideband characteristics, however, the radiation pattern is calculated by mean of equivalent principle with respect to its aperture field based on empirical formula. To characterize the radiation behavior of such a kind of antenna, we have changed some structural parameters, such as the length and the flare angle between the two metal plates. In general, the 3-dB beam-width decreases as the increase in the aperture size. Moreover, the smooth taper transition could improve the return loss in the high frequency range, as being confirmed by intuition. Since this antenna is simple in its fabrication and fairly good performance in its radiation and band width characteristics, it promises to be widespread employed in last mile applications for wireless communication systems.