圓柱形洩漏波天線與寬頻平面式洩漏波天線

Abstract

本論文研究兩種形式的洩漏波天線：圓柱形介質上的洩漏波天線與平面介質上的洩漏波天線。在理論上採用全波分析法-頻域法(Spectral domain approach)來研究這兩種構造中洩漏波的傳播特性。 首先文中第一部分提出圓柱形微帶洩漏波天線。從數值計算得到的傳播常數可得知圓柱形微帶洩漏波天線與平面式微帶洩漏波天線有著相同的特性。利用孔徑耦合饋入結構，我們成功的激發了圓柱形微帶線的第一高階洩漏模，並實作出高增益與寬頻的洩漏波天線。 同時本文也探討另外兩種圓柱形結構：挖槽同軸電纜與圓柱形共平面波導。由理論計算得到不同電路尺寸參數下對此類圓柱形洩漏波天線傳播特性的影響，進一步決定操作頻率。接著也設計了兩種對應結構的天線並加以量測。 本文第二部份則是主要著重在平面式洩漏波天線的設計上。我們研究槽線第一高階洩漏模與接地介質板的表面波之間的關係。在電路製作上用微帶線至共平面波導的轉換電路，來激發槽線的第一高階洩漏模，設計出一支非常寬頻的天線。 最後本文提出一種新穎的倒Ｔ形洩漏波天線。它與單導體洩漏波天線有著相同的特性，例如超寬頻與固定的主波束角度。和單導體洩漏波天線相比，倒Ｔ形天線不需要寬頻的反相器，而且天線寬度也只有原來的一半，所以倒Ｔ形天線在實作上具有更大的方便性。

This thesis proposes two types of leaky-wave antennas. One type is on a cylindrical substrates and the other type is on a planar substrate. The well-known full-wave method, spectral domain approach, is applied to investigate the propagation characteristics of leaky modes on both configurations. First, a cylindrical microstrip leaky-wave antenna is analyzed and designed. From the numerical results of computed propagation constants, it has the same characteristics as those of the planar ones. With the similar aperture-couple feeding structures used in planar microstrip leaky-wave antennas, the first higher order leaky mode is successfully excited. In addition, a high gain and wideband leaky-wave antenna is implemented. Moreover, the first higher leaky modes on two cylindrical structures, slotted coaxial lines and cylindrical coplanar waveguides, are also studied. The effects of different parameters are shown and can be used to decide the operating frequency band of leaky-wave antennas. Two design examples are presented to show the performance of these types of leaky-wave antennas. Second, the relationship between the first higher order leaky mode of a slotline and surface wave mode on a grounded dielectric slab is presented. A slotline leaky-wave antenna fed by a wideband microstrip-to-CPW transition is demonstrated. Finally, an inverted-T leaky-wave antenna is introduced. It has the same properties as the single-conductor strip leaky-wave antennas, such as wide bandwidth and fixed mainbeams. Compared to the single-conductor strip antennas, the broadband phase inverter is not needed and the antenna width is halved. Therefore, the realization of inverted-T antennas is easier than that of single-conductor strip ones.