介質隔板架構極化器之寬頻化研究

Abstract

在本篇論文中，首先由相關研究來說明為何使用此架構來作極化器設計，由於採用介質隔板架具有結構簡單，設計容易，校調方便，對波導管製作精密度要求較低的優點，因而以此架構作為基礎來作進一步研究。 然而由色散曲線(dispersion curve)以及利用微擾理論所作分析，可以發現波導管兩正交模態傳播常數的差，Db隨頻率變化的性質，會在通過最為平緩的極小點之後，隨頻率上升而增加。為求達到寬頻效果，吾人在波導管內增加縱向插槽，藉此能影響Db在高頻時的響應，而達到增加頻寬的目標，同時更可利用此插槽來固定隔板的位置與角度。 除了引入插槽效應來增加頻寬之外，本文另提出了兩種方式來對於所要求頻段內Db可能的大小不一致來作出修正。分別是：利用兩段不同介質隔板來平行串接；以及在隔板兩側貼上介質薄片的方式。在此研究中，前者以一實際製作於V頻段的寬頻化設計作為例子，後者則是以Ku/Ka頻段的雙頻化設計為例。最後並探討利用加入漸變結構(taper)的方式以改善反射損耗。

In this article, a circular polarizer based on dielectric septum loaded waveguide structure is chosen to be implemented because of its simple structure, good accuracy tolerance and easy tuning property. Both the perturbation theory and the 2-D full wave analysis have been used to find the waveguide propagation constant and the difference between the propagation constants of the two fundamental modes, Db. It is found that the Db curve increases with frequency rapidly after passing its minimum. To broaden the bandwidth of the polarizer, longitudinal slots were introduced in the waveguide. With these slots, the increasing trend of Db at high frequency could be reduced. The Db curve might even decrease with frequency, depended on slot depth. In addition to the slot effect, two methods are introduced to modify the probable difference of Db within the desired frequency band, which is caused by either the simulation or fabrication error on slot dimensions. One is parallel cascading two different dielectric septa. The other is attaching two dielectric slices on both faces of septum symmetrically. In this thesis, a V-band wideband design and a Ku/Ka-band dual-band design were implemented as examples for the former and latter methods, respectively.