CPW寬頻圓極化天線設計及單層基板雙頻PIFA設計

Abstract

本篇論文由兩個主題性的探討所組成：一是探討CPW結構非對稱的接地面對圓極化天線特性的影響，另一主題探討兩種天線類型所設計出的PIFA其特性上的差異，並擇優者完成設計。 針對第一個主題，我們選擇CPW結構的圓極化天線由於其擁有較寬頻軸比的優勢，先利用連接於接地面上L形狀的寄生金屬元件和直線的天線主體耦合，使整體電流於遠場等效出兩個相位差90度、大小相同且互相垂直的電場向量，產生圓極化的雛型，再藉由不對稱地截掉方形接地面的截角，有效的將軸比頻寬加大，使其包括了兩個GPS應用頻帶(L1和L3)，90%以上的天線輻射效率使得天線於兩使用頻帶中，正 z 軸右手圓極化增益可達4 dB以上，本論文將會利用全波模擬軟體(HFSS)呈現不同類型的非對稱接地面對於此天線圓極化軸比的影響，並將天線研究結果實作並且量測其特性。 另一個主題是探討針對設計一個單層微小化雙頻帶PIFA較佳的天線類型。我們以沒有多餘空間增加空氣介質為前提，分別利用patch天線和monopole天線為雛型設計一個PIFA，比較其尺寸、匹配頻寬、輻射效率、天線增益。由於monopole雛形的PIFA擁有高達88%的輻射效率因此較適合用於設計此限制前提的PIFA。本論文將會利用全波模擬軟體分別模擬出兩個類型的天線設計特性並進行比較，此外我們實作出以monopole為雛形的PIFA並量測其特性。

This paper composed by two research topics. One is the effects of asymmetrical ground on CPW-fed wideband circularly polarized antenna for application of the GPS band and another is the effects of different antenna type on the design of single layer miniaturized dual-band planar inverted-F antenna For the first topic, we choose the CPW-fed for the structure of the circularly polarized antenna due to the advantage that having wider axial ratio bandwidth than microstrip-fed. We generate the circularly polarized feature which means that there are two orthogonal resonant modes with equal amplitude and 90° phase difference by using an L-shape strip connecting on the ground of CPW structure coupling to the striate main radiator. By truncating two angles on the opposite position of the ground the axial ratio bandwidth can be broaden obviously so that the application of the proposed antenna can include two bands (L1 and L3) of the GPS application. The high radiation efficiency above 90 % both for two operating band makes the RHCP gain on the +z axial higher than 4 dB. In this paper we will illustrate the different axial ratio feature caused by different kind of asymmetrical ground by using the 3D full wave simulator (HFSS) and the measured research result will also be shown. In another topic, we will discuss and investigate a better antenna type for designing a single layer miniaturized dual-band PIFA. We use a patch antenna and a monopole antenna for the two PIFA designing bases with a restriction that we don’t have additional space for an air layer. After comprehensive comparing the monopole based PIFA is chosen due to its high radiation efficiency above 88 %. We will show and compare the two simulated antenna design by the HFSS, furthermore the monopole based PIFA will be fabricated and measured.