寬邊耦合傳輸線之高階特性與設計

Abstract

本論文的目的包含有兩個層次：第一、詳細地描述這種被大量應用的寬邊耦合傳輸線之高階洩漏模；第二、這種洩漏模在天線方面的實際應用。一種具代表性的寬邊耦合傳輸線結構，可以闡明多層、立體之微波與毫米波電路的高階洩漏效應。雙層的案例以一種物理層面的透視而被詳加分析，並發現第一高階洩漏模的個數會等於微帶線的總數。 通過三至五層寬邊耦合微帶線的案例討論，存在於廣義多層寬邊耦合傳輸線中的高階洩漏效應被徹底地調查研究。數個深具意義的結論可以從存在於這種多層寬邊耦合微帶線的高階洩漏模，它們的色散特性與模電流分布來得知。藉著本論文所提出結果輔助，讀者可以精巧地控制這種耦合洩漏模，以避免負面效應，或者將這些模應用在高增益天線方面。 在所發現存在於雙層案例中的兩個第一高階洩漏模，其中一個是屬於弱衰減性。在此同時，另一個則是強衰減性。本文設計並量測了一種僅僅使用前述弱衰減性洩漏模的高增益、低輻射夾角的天線，做為這種寬邊耦合結構的應用。這種天線展現出顯著的輻射夾角縮小，幅度達到60%。這種天線是第一支應用微帶線高階洩漏模的似八木式陣列天線，其中三個基本元素（驅動單元、反射單元及導向單元）是在天線的寬邊方向上堆疊而成。藉由調整導向單元的微帶線寬度，衰減率可以進一步被調降。使用雙層寬邊耦合微帶線的洩漏模天線，其半功率輻射夾角在34 GHz，從寬邊量起25.2o處的測量值是2.1o。 一維的洩漏模天線被成功地設計並測量。這種陣列天線只需要較簡單的饋入網路，就可以實現近寬邊的筆狀波束輻射，並且具有高的效率及表現。

The aim of this work is two fold, 1) detailed description of the higher-order leaky modes of the much used broadside-coupled microstrips and 2) practical application of such leaky modes as an antenna. A representative broadside-coupled transmission line structure is examined to elucidate the detail of leakage effects at higher-order of multilayered, 3-D microwave and millimeter-wave circuits. Two-layered cases are analyzed from a physical perspective and the total number of first higher-order leaky modes is found to be equal to that of microstrips. The higher-order leakage effects of general multilayered broadside-coupled transmission lines are thoroughly investigated via the studies of the cases of three to five-layered broadside-coupled microstrips. Several significant conclusions can be derived from the details of the dispersion characteristics and modal current distributions of the higher-order leaky modes exist in the broadside-coupled microstrips. With the aim of the results found in this thesis, one can sophisticatedly control the coupled leaky modes to avoid adverse effects, or apply these modes in high-gain antenna application. One of the two first higher-order leaky modes obtained in the two-layered case is weakly attenuated, while the other is strongly attenuated. A high-gain, narrow-beam leaky-mode antenna using only the weakly attenuated leaky mode is designed and measured as an application of this broadside-coupled structure, exhibiting a marked beam-width reduction of 60%. This antenna is the first Yagi-Uda-like array antenna that utilizes the higher-order leaky modes of the microstrip, for which the three basic elements - driver, reflector and director - are stacked in the broadside direction. The attenuation rate can be further reduced by adjusting the strip width of the director. The half-power beam-width of the leaky-mode antenna applying two-layered broadside-coupled microstrips with wider top microstrip is measured to be 2.1o at 25.2o from the broadside at 34 GHz. A one-dimensional leaky-mode antenna is successfully designed and measured. This antenna array needs simpler feeding network to realize a nearly-broadside pencil beam radiation and shows high efficiency and performance.