使用雙層介質合成波導於圓極化槽孔陣列天線

Abstract

本論文以波導耦合之概念將能量由主波導(Main-line)的槽孔以共振的方式饋入支波導(Brach-line)，再經由可產生圓極化之四槽孔元件組成陣列輻射能量，產生一高增益的主波束在邊射方向(Broadside)，其邊緣波束等級(side lobe level)可經由良好的設計大幅降低。我們使用介質合成波導(Substrate integrated waveguide, SIW)來實現此天線，因此導波波長會小於空氣中的波長，當設計的元件間距約為一倍的導波波長時，就可以避免光柵波瓣(Grating lobe)的產生。 圓極化之元件設計，為兩對接近垂直角度的矩形槽孔構成，其中旋轉角度為正的一對矩形槽孔為激發電場 ，令一對旋轉為負角度的矩形槽孔則激發相位差 的電場。再藉由控制矩形槽孔的長度以達到設計元件時所需要的激發量，也因此各輻射元件會稍微偏離共振長度。各元件本身因為幾何條件的不同，造成激發時相位的變化，為了使每個元件可以達到等相位激發，我們可以利用元件間距作相位補償。 最後設計出圓極化的陣列天線於12GHz的頻段，此天線之優點有高增益、高指向性、製作較傳統的波導更為輕巧，未來可將其應用在衛星天線上。

The thesis based on the concept of the waveguide coupling employs resonant slots to couple power from the main waveguide to crossed branch waveguides. An antenna array which is composed of the circularly polarized (CP) four-slots radiated elements can result in a high gain at the broadside direction. The side lobe level (SLL) can be greatly reduced by appropriate design. In the substrate integrated waveguide (SIW), the guided wavelength is less than the wavelength in air. When the array spacing is around a guided wavelength, the grating lobe can be avoided. The circularly polarized element consists of two orthogonal rectangular slots pair. One rotated with positive angle excites zero phase of electric field and the other one with negative angle excites the ninety degrees phase of electric field. In order to achieve the varies excitations for our design, we control the length of rectangular slot. Therefore every element must be slightly off-resonance. The varies slots geometries cause the varies phase excitations. We can choose array spacing to do phase compensation to get equiphase excitations of the array element. Finally, we design the circularly polarized array antenna at the 12GHz frequency band which can be applied to the satellite antenna. It has better performance than traditional waveguide, especially high gain, high directivity and more compact size.