單埠及多埠隙孔耦合微帶天線 : 設計與應用

Abstract

本論文旨在研究幾種單埠及多埠隙孔耦合微帶天線結構，使其可運用於主動天線電路、遠端識別及通訊傳輸方面。這些結構包括︰一、變更傳統的隙孔耦合微帶天線架構而形成嶄新的雙埠天線；二、將多對隙孔耦合微帶天線安排成具有廣角回波性質的天線陣列；三、以兩個隙孔天線搭配等功率分配器之架構組成新式雙圓極化天線。以上所提之三種天線的饋入方式皆採用隙孔耦合饋入法。對於這些天線，論文中將以動差法配合積分方程法來分析各個結構的電磁特性。為了簡化分析過程，文中以波導管模型來模擬微帶饋入線。 論文所提之雙埠隙孔耦合微帶天線包含一饋入埠與一耦合埠。從饋入埠輸入的能量大部分會由微帶天線輻射出去而部分的能量則會傳送至耦合埠。此結構不僅當成天線使用，同時亦可做為振盪器之回授線路。運用此雙埠天線結構，我們製作出一運作非常穩定之振盪器，其振盪頻率為9.79 GHz與模擬結果比較僅有百分之零點二的誤差。 論文所提之第二種結構為具有二維(E面與H面)廣角回波特性之平面反射板。文中分析與製作了一片操作在X頻段之反射板，此板內置六對隙孔耦合微帶天線，每一對天線皆以反射板中心作對稱分佈並藉一段微帶線來做聯結。從反射板所反射之電波主要來源有三：一是各微帶天線對的回波，二為各微帶天線的散射波，第三種則是基板接地面的散射波。藉由調整串接於每一天線對的微帶線長度，可以使反射板反射出較寬且較平坦之電波場型。經實驗測量後得知，反射波場型之量測結果與模擬結果非常地近似。 最後一種結構是利用偏移饋入之隙孔天線去取代等功率威爾金生分配器中的電阻，進而設計出一組操作在S頻段的雙圓極化天線。當此圓極化天線之駐波比小於二時，其反射損耗頻寬有百分之三十九點三，隔絕頻寬有百分之十點三。另外，此天線擁有頻寬為百分之二十八的半功率軸比。

In this thesis, we propose and analyze several slot-coupled microstrip antennas with single or multiple ports for applications in active integrated antennas, remote identification, and communications. These antenna structures consist of (a) adding a second port to the traditional slot-coupled microstrip antenna to obtain a brand-new two-port antenna, (b) arranging several slot-coupled microstrip antennas to achieve a planar retrodirective antenna array, and (c) using two slot antennas constructed with the Wilkinson power divider configuration to form a novel dual circularly polarized antenna. To analyze these antenna structures of slot coupling feed, Galerkin's method of moments together with a mixed-potential integral equation (MPIE) was used. Also, the microstrip feed line was modeled as a waveguide for simplifying the problems. The two-port slot-coupled microstrip antenna contains a feeding port and a coupling port. Most of the incident power coming from the feeding port is radiated by the microstrip patch, and part of the power enters to the coupling port. A feedback antenna oscillator was designed by applying the present structure where it served as a feedback resonator and a radiator at the same time. The oscillation was stable and with a clean spectrum at the frequency of 9.79 GHz which was only 0.2% different from the design one. An effective isotropic radiated power (EIRP) of 39 mW was achieved. The measured cross-polarized fields were at least 15 dB lower than the co-polarized ones. Next, a planar antenna array reflector with retrodirectivity in both the E-plane and the H-plane is analyzed and demonstrated at X-band. The reflector consists of six pairs of symmetrically located slot-coupled patch antennas paired by microstrip lines. The total reflected field from the reflector is separated into three primary components, that is, the reradiation field from the patch antennas (RFPA), the scattering field from the patch antennas (SFPA), and the scattering field from the ground plane (SFGP). The first two components are calculated by using the method of moments and the last one is by the physical optics (PO) method combined with the method of equivalent currents (MEC). By tuning the microstrip-line lengths, the total reflected field contributed by the three components is designed to possess a broad-beamed pattern in both the E-plane and the H-plane. The measured reflected-field patterns of the fabricated reflector show good agreement with the designed ones. Finally, an offset-fed slot antenna was used to replace the lumped resistor in the equal-split Wilkinson power divider, and a dual CP slot antenna operating at S-band was designed and fabricated experimentally. The antenna possessed a return loss bandwidth of 39.3%, an isolation bandwidth of 10.3% for VSWR < 2, and a 3-dB axial ratio bandwidth of 28%.