含人工材料之四波束號角天線設計

Abstract

在本論文中，我們設計了一個含人工材料之四波束號角天線，它是結合週期結構的特殊折射現象與號角天線的設計原理而成。人工材料經過三種分析方式設計其金屬柱的尺寸及晶格間的距離，合成擁有等效折射係數趨近於0的二維晶格人工材料。因此，一旦電磁波由放置於週期結構中的同軸線激發，折射波傳遞的方向會幾乎與介質和空氣的交界面垂直。根據這樣的物理現象，我們製作了一個四路的功率分歧器，使其把能量平均的分往四個方向，再導引各路的能量進入E-plane號角天線中，使其擁有四個錐狀波束的輻射場型。不僅在理論上計算出其色散與相位關係，並經過軟體的模擬及實際的量測其反射係數與輻射場型，最後可得9.20dBi的輻射增益，以及200MHz的頻寬。由於此結構允許擁有較大的機械製作誤差、極低的介質能量損耗以及廉價的製作費，所以必定會在未來點對點的通訊系統上擁有極大的發展。

In this thesis, we reported a four-beam E-plane horn antenna incorporating a wire-based metamaterial. Such a metamaterial is made up of metallic cylinders organized in a two-dimensional square lattice. After properly designing the lattice constant and unit cell pattern, we synthesized a medium having the effective refractive index smaller than unity. Therefore, once waves within the metamaterial were excited, the refractive wave tends to be perpendicular to that of the interface between metamaterial and uniform medium. Based on this concept, a 4-way power divider was design to equally distribute the input power into four different directions. We then guide each of the power into individual E-plane flared opening to radiate a directional beam pattern in each sector. In addition to the theoretical calculation regarding the dispersion- and phase- relation of the two-dimensionally periodic medium, we fabricated this antenna and measured its radiation characteristics including the return loss and far-field pattern. The excellent agreement between the measured and simulated results was obtained. Due to the properties of robust, low-loss, and low-cost, this antenna may have promising application in a point-to-multiple-point radio link system.