可抑制旁波瓣與改善增益之半模基板合成波導洩漏波天線設計

Abstract

使洩漏波天線縮小化並仍能維持應用所需之輻射場型和可以接受增益 是個近年來很具挑戰性的天線設計難題。由於洩漏波天線本身是行波天線， 所以於洩漏波天線上，我們會希望只有正向的行進波於天線結構中存在． 於天線結構任何地方引起的反射波都會對於輻射場型有相當程度的干擾； 但是就算反射波可能可以被完全壓抑，由於洩漏波天線也可被視為是一種 孔徑天線，當一個孔徑天線上近場分布是均勻時，我們仍可以理論上預測 有旁波瓣的存在．這幾點對於洩漏波天線的輻射場型是需要接受改進之處． 基於以上現象，本論文提出一個轉接設計和兩個設計方法以助於改善半模 基板合成波導洩漏波天線的輻射場型和增益． 我們首先提出一個轉接設計以提升饋入洩漏波天線並激發洩漏波模態 的效率．此設計可以較為有效率的激發洩漏波的模態以壓抑於洩漏波天線 端口引起的反射，進而可以避免反射波的激發．此設計對接下來兩個設計 方法具有相當程度的幫助． 接下來是提出一個調整半模基板合成波導寬度的方法以達到對旁波瓣 的壓抑．由於這個調整方法能夠改變於洩漏波天線孔徑上的近場分布使其 等效磁流源分佈容易滿足Taylor’s Rules，故旁波瓣可以因而被壓抑． 最後是提出一個回授網路的設計來把洩漏波天線尚未輻射之殘餘能量 導引回洩漏波天線饋入端．如此可以利用其剩餘能量來達到增益的提升． 由於以上設計簡易方便，且容易於所需的頻率點做設計改良，故其在 應用上有很大的潛力．

This thesis gives a study on two techniques to suppress the side lobes and enhance the gain of a half mode substrate integrated waveguide leak wave antenna, respectively.

In this thesis, we are aware of two phenomenon that may spoil the performance of a leaky wave antenna: 1. Due to the traveling wave nature of the leaky wave antennas, the remaining power at the end of the leaky wave antenna should always be carefully guided and terminated or the reflected wave will be excited with the corresponding back lobes that may spoil the radiation pattern. 2. Even if one can guide the wave in the leaky wave antenna to avoid reflections, an ideal leaky wave line source may still introduce side lobes due to the effect of the finite uniform illumination of the aperture antennas. We would here give a study on two methods accompanied with a proposed transition dedicated for a half mode substrate integrate waveguide leaky wave antenna to handle the problems mentioned above.

First, a transition to efficiently convert the input power to construct the leaky mode of the leaky wave antenna is proposed to enhance the efficiency of the leaky wave antenna and avoid possible reflections at the terminal of the leaky wave antenna. This transition can be considered as a stepping stone to facilitate the later analysis and design of the leaky wave antenna.

Secondly, a cosine-shaped tapering profile is proposed to taper the waveguide width of the half mode substrate integrated waveguide. Since one can thus shape the aperture field of the leaky wave antenna to satisfy the Taylor’s rules, the side lobes of the radiation pattern can having a better chance to be suppressed.

Finally, a feed-back network is proposed to guide the non-radiated power back to the feed of the leaky wave antenna. The gain is expected to be enhanced with the aid of the non-radiated power. These two methods accompanied with the proposed transition can improve the performance of the leaky wave antenna at an arbitrary frequency range easily and thus has great potential in many applications.