印刷式對數週期天線與超寬頻饋入網路之雙圓極化整合設計

Abstract

本論文主旨為整合印刷式對數週期天線與超寬頻饋入電路來實現超寬頻雙圓極化天線。本論文之設計原理是將超寬頻線性極化天線擺放成圓極化序列旋轉陣列的形式，並且透過超寬頻饋入網路來產生圓極化的序列相位差。我們選用線性極化之對數週期天線的主要原因有二：一是阻抗匹配頻寬較寬，二是相位中心比較穩定 (不隨頻率改變)。而饋入網路的部分我們整合了超寬頻的180度平衡器與90度耦合器，除了將能量均分之外，組合後的輸出埠可以產生0o、90o、180o、270o的相位差。本論文第二章至第四章分別會介紹平衡器、耦合器與對數週期天線；第五章則是將天線與平衡器、耦合器整合成一平面超寬頻雙圓極化序列旋轉陣列天線。

This thesis presents the integrated design of printed log periodic antennas and the feeding balun and coupler circuits for the ultra-wideband dual-sense circularly polarized operations. The design concept is to employ two ultra-wideband linearly polarized antenna with a 90o rotation fed by a ultra-wideband network providing 90o phase difference. There are two reasons we choose log-periodic antennas as the antenna elements. One is the very wide bandwidth in terms of the impedance and gain, and the other is the fixed phase center as the frequency varies. The feeding network consists of two ultra-wideband 180o-balun and a 90o-coupler, providing the equal power but sequential phase of 0o, 90o, 180o, and 270o to the four antenna input ports. We carefully investigated the performance of the balun, the coupler, and the log-periodic antennas individually. The final integrated antenna module performs an ultra-wideband dual-sense circularly polarized operation (RHCP and LHCP) with a bandwidth ratio better than 4:1.