平面式陣列漏波天線回波器設計

Abstract

本論文探討一個由漏波天線建構而成具有二維回波效果的回波反射器的設計，由於平面性的結構，使得回波器具備了輕薄、低成本的優勢，依循著反射器之寬掃描仰角對於入射源的高回波量特性，我們設計的回波器非常合適於智慧型運輸系統的應用。使用漏波天線建構回波器的優點是，可以避免以往傳統二維效果反射器連接佈線網路之複雜性。本論文中設計了由八個漏波天線所組合而成的陣列回波器，並且針對設計及量測皆有詳盡的探討，亦採用了一個近似的方法來分析我們設計的回波器之再輻射與散射效應；針對X頻段的分析可以幫助了解回波器的運作，來自回波器的總反射量分成兩個主要部分；其一為來自漏波天線的再輻射場，另一為來自金屬接地平板的散射場，再輻射場是以導波管模組和映射定理來計算，金屬接地平板的散射場則是以物理光學的方法來分析，實驗結果顯示了在電場與磁場切平面中，回波陣列相對於金屬接地平板的反射量在10分貝內有著高回波場量；於電場切平面有著230度、磁場切平面有著110度的高寬度反射仰角。

A two-dimensional Van Atta retrodirective reflector based on the microstrip leaky-wave antennas was designed in this thesis. Planar structure makes this reflector low cost and low profile. Along with the reflector’s property of being able to reflect high fields toward the source point over a wide range of incident angles makes it very suitable for applications in intelligent vehicle highway systems (IVHS). Using the leaky-wave antenna as the basic constructing unit has the advantage of avoiding complex routing of the connecting network commonly encountered in two-dimensional retrodirective array. An eight-element leaky-wave retrodirective array was designed and measured in this thesis. An approximate method associated with the re-radiated and scattered principles of the reflector is presented at X band for the purpose of understanding and designing the reflector. The total reflected field from the reflector is separated into two primary parts, the re-radiated field from the leaky-wave antennas and the scattered field from the metal ground plane. The re-radiated field is calculated by using waveguide model together with the image theory; the scattered field from ground plane is analyzed by the physical optics (PO) method. The experimental results show that both in the E-plane and H-plane the array has a high reflected field within 10dB down from that of a flat metal plate over a range of more than 230 degrees in the E-plane and 110 degrees in the H-plane.