圓極化單極天線與小型化洩漏波天線

Abstract

本論文主要包含三大部分：具圓極化輻射之單極天線、擁有抑制旁波功能之小型化洩漏波天線與漸進式洩漏波天線及利用共平面波導饋入之晶片型天線。第一部份提出兩種圓極化單極天線的設計與成果。第一支天線架構主要是在接地面上加入一倒L型的槽孔，使其能產生水平方向的電流分佈，進而與垂直分佈的單極天線激發出雙頻圓極化輻射波。第二支天線的設計目的是要提升第一支天線的阻抗頻寬與圓極化頻寬，設計方法是在接地面上加上一矩形金屬線與在天線主體嵌入一矩形槽孔，此方法不僅不會影響較低頻的圓極化波，同時能有效的增加阻抗頻寬與較高頻的圓極化頻寬。 第二部份描述可抑制旁波功能之小型化洩漏波天線與漸進式洩漏波天線。就抑制旁波功能之小型化洩漏波天線之設計而言，我們將洩漏波天線之接地面嵌入一些矩形槽孔，這些槽孔的大小會影響到洩漏波天線的相位係數與衰減係數，使洩漏波天線能達到小型化的設計。但是，由於此方法造成阻抗不匹配的情況，因此我們利用漸進式洩漏波天線架構之寬頻優點取代矩形的洩漏波天線。最後，我們嵌入兩個矩形槽孔來抑制洩漏波天線產生的旁波，使得這支天線不僅可以縮小洩漏波天線20% 的寬度，也能有寬頻的阻抗頻寬及有效抑制旁波。另外，就抑制旁波功能之漸進式洩漏波天線之設計而言，主要是由於漸進式洩漏波天線雖然可以激發出極寬頻的頻寬，但是卻會有非常嚴重的旁波的問題，故我們利用兩個槽孔與一接地針改善漸進式洩漏波天線的電流分佈進而解決此類問題。就量測結果，我們提出的方法雖然阻抗頻寬沒有傳統漸進式洩漏波天線那樣的寬頻，但是卻可以維持洩漏波天線有不錯的輻射特性。 第三部份在於研製適用於無線個人區域網路系統之晶片型天線。設計理念是將傳統往Broadside方向輻射的單極天線改變成往End-Fire方向輻射。由於在做整合時，天線與前端電路將會被設計在同一晶片上，因此傳統的單極天線所產生的輻射波容易干擾後方的電路，故此天線設計目的主要是為了減少天線與主動電路做整合時所產生的電磁干擾之問題。另外，就模擬的輻射場形結果，我們提出的天線不僅能有效的降低天線輻射對前端電路，而且可以多方向的接收或發射訊號。

This thesis consists of three parts: Monopole antennas with dual-band circular polarization, study of compacting size of leaky-wave antenna and suppressing side lobe of tapered leaky-wave antenna, and on-chip antenna for wireless personal area network (WPAN) application. In the first part, novel designs of dual-band circular polarization (CP) monopole antenna are presented. The proposed antenna comprised of a ground plane embedded with an inverted-L slit, which is capable of generating a resonant mode for broadband impedance-bandwidth, and excites left-hand circular polarization (LHCP) at 2.5 GHz and right-hand circular polarization (RHCP) at 3.4 GHz. Furthermore, embedding an I-shaped slit in the rectangular radiator and adding an I-shaped stub in the ground plane, the impedance-bandwidth can be increased to 6.30 GHz, and the 3-dB AR-bandwidth at 3.4 GHz is greatly enhanced from 230 MHz to 900 MHz. In this design, we use a simple method to achieve the dual-band CP radiation and broad impedance bandwidth. In the second part, a compact wideband leaky-wave antenna (LWA) with etched slot elements and suppressing side lobe of tapered leaky-wave antenna are studied. In compact wideband LWA case, by etching slot elements on the ground plane, the current distribution of LWA can be influenced to compact the width of conventional LWA. In order to achieve the impedance matching, this multi-section tapered short leaky-wave antenna is embedded with two rectangular slots. This technique not only improves the impedance matching but also suppresses the back lobe. In suppressing side lobe of tapered LWA case, the proposed LWA contains a tapered microstrip radiator with a shorting pin and two rectangular slots. This design of two slots and a shorting pin can interfere with the current distribution of tapered LWA to suppress the radiation of side lobe. In order to achieve the impedance matching, a matching stub is added along the feeding line. The propose LWAs not only successfully reduces the width of a conventional LWA by more than 20 %, but also suppresses the side lobe. In the third part, an end-fired radiated on-chip monopole antenna for wireless personal area network (WPAN) application is designed. In general, if the on-chip antenna is integrated into RF front-end circuit, the effects electromagnetic interference (EMI) will be considered. Therefore, the proposed antenna can reduce the electromagnetic power to affect the circuit. The architecture of this antenna inherits rectangular monopole antenna except for its asymmetric-fed, slit, and shorting path approaches. The asymmetric-fed provides dual-band around 60 GHz and end-fire radiation. Besides, by embedding a slit on the monopole antenna and shorting pin on the ground plane, this antenna can achieve wide impedance bandwidth. According the simulated results, the proposed antenna can reduce the radiated power at the feed line to affect the front-end circuit, and the impedance bandwidth can be achieved about 30% with respect to the center frequency at 5.38 GHz.