寬頻圓極化天線設計

Abstract

本研究主要針對寬頻圓極化天線以及應用於無線區域網路之雙頻天線作設計及探討，並分析這兩種天線的模擬與實驗的結果。 首先，提出一種平面寬頻天線設計概念，在天線上增加寄生元件以提升頻寬，為了達到激發正交能量的目的，採取非對稱饋入方式，接著為了將低頻帶之相位差拉到九十度附近，在天線的輻射器下方所對應的接地面上截出一塊槽孔，最後再配合接地面與輻射器上的開槽，不僅提升了中心頻率在5.6GHz上的阻抗頻寬達到121%，也近一步達到圓極化激發模態，並且將中心頻率在4GHz的軸比頻寬拓展為40%，順利激發左手圓極化波。 在一般的雙頻天線激發方式，常使用兩段分枝各自激發高低頻段，接著，提出一種拉近兩個頻帶的方式，在兩分枝後方加上一塊貼片，分別將高低頻段匹配在5.8GHz以及2.4GHz的無線區域網路頻段。

This thesis mainly focus on the design and discuss of wideband circularly polarized antennas and dual band antennas for wireless LAN purpose. Furthermore, the results from simulation and experimentation belong to the two kinds of antenna will be analyzed. At first, it would be proposed a concept designing planar wideband antennas in which improving bandwidth by way of adding parasitic elements. In order to achieve orthogonal energy exciting, it employs asymmetric-fed. Truncate a slot in the ground plane corresponding to radiator so as to pull the phase difference in lower band to the vicinity of 90 degrees. Finally, embedding slit both in the radiator and the ground plane of the antenna. It would be not only improved the impedance bandwidth to 121% at the center frequency of 5.6GHz, and further excited circularly polarized modes. Moreover, extending the bandwidth of axial ratio to 40% at the center frequency of 4GHz, and exciting the Left Hand circularly Polarized waves successfully. In general, the higher and lower band is exciting through two branches separately. It would be proposed that adding a patch in the rear of the two branches and the higher and lower band will be matched to the wireless LAN band in which 5.8 GHz and 2.4GHz.