槽孔耦合之三極化天線與雙平面式倒F形三極化天線設計

Abstract

本論文前半部分提出一槽孔耦合之三極化天線設計，透過枝幹耦合器結合槽孔饋入天線，實現雙圓一線可切換式三極化電磁波特性。由於訊號在枝幹耦合器的兩輸出端埠，會隨著操作在不同的頻段而有不同的相位差與振幅比，以單埠輸入而言，當操作在枝幹耦合器中心頻以及三倍中心頻的時候，能產生振幅相等且相位差 90度以及 -90度的訊號，如此便能滿足圓極化波之形成條件。而雙埠同時輸入則能產生線性極化波。第一部分提出的結構即操作於枝幹耦合器三倍中心頻區。

本論文後半部分則提出另一種結構，使用一對平面式倒F形天線來實現極化切換特性。值得一提的是，由於倒F形天線一端開路一端短路的結構，電磁波邊界條件不同於前半部份的槽孔耦合天線，相同操作頻率下，天線共振路徑將能縮短，也就是等效電氣長度的縮小化，故整體天線面積可降低。在此，極化切換的操作同於第一部分敘述過的原理，然而本結構得以操作在枝幹耦合器中心頻以及三倍中心頻區，且皆具備三極化切換的特性。在論文的最後，引入序列旋轉法天線陣列進行實驗，以增加雙平面式倒F形天線之圓極化頻寬及波束寬。本論文將針對天線設計原理與不同極化的機制進行深入探討。

A design of aperture coupled tri-polarization antenna is presented in the first part of this thesis. By integrating an aperture coupled-fed antenna and a branch line coupler, the proposed antenna can provide a linear polarization and a pair of orthogonal circular polarizations, realizing the switchable tri-polarization characteristics. Since the phase difference and magnitude from two output ports of the branch line coupler varies by frequency, the polarization characteristic will also be changed. Since the branch line coupler provides two output signals with the same magnitude and 90° phase difference, RHCP and LHCP can therefore be generated by switching two input ports. Also, when the two input ports are fed simultaneously with equal phase, a linear polarization can be obtained. This mechanism can be applied at operation frequency and three times the operation frequency of the branch line coupler. In the second part of this thesis, another structure is presented by using a pair of Planar Inverted-F Antenna (PIFA) to achieve the switchable polarization characteristics. Due to its quarter wavelength resonant characteristic, the equivalent electrical length is reduced, therefore reduces the overall antenna size. In this part, the mechanism of polarization diversity is the same as first part, however, this structure can be operated at the operation frequency and three times the operation frequency of the branch line coupler, and both have switchable tri-polarization characteristics. In the end of the thesis, we introduce the sequential rotation method antenna array, and do some experiments in order to further improve the dual PIFAs' circular polarization bandwidth and beamwidth. The design principles and the polarization mechanisms of proposed antennas will be further discussed in our research of this thesis.